Process for producing cyclohexyl acetate
This application is a continuation of application Ser. No. 07/709,983, filed Jun. 4, 1991, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a process for producing cyclohexyl acetate, and more particularly, to a process for producing cyclohexyl acetate by the reaction of acetic acid with cyclohexene in the presence of heteropolyacids mainly composed of oxides of tungsten. 
     2. Description of the Related Art 
     Heretofore, as processes for producing cyclohexyl acetate, there have been generally known an esterification method of acetic acid with cyclohexanol and a reaction of cyclohexanol with acetic anhydride. 
     However, both processes use cyclohexanol as a starting material, and cyclohexanol has a problem as to the method for preparation thereof and other various drawbacks. In addition, the esterification reaction is an equilibrium reaction so that it is difficult to produce the ester in high yield and moreover it is necessary for removing the water as a by-product in order for the reaction to proceed. 
     In the method of using acetic anhydride, although the yield of the ester is high, there are many various drawbacks, for example: acetic anhydride is expensive and in addition, one molecule of acetic acid is released and it is very difficult to convert the acetic acid into the anhydride. 
     For the purposes of solving these problems, some methods for producing cyclohexyl acetate by an addition reaction of cyclohexene with acetic acid have been recently proposed. For example, Japanese Patent Application Laid-open No. 254634/1989 discloses a method for producing cyclohexyl acetate by the reaction of cyclohexene with acetic acid in the presence of a strongly acidic cation exchange resin as a catalyst. 
     According to this method, the reaction should be effected at 130° C. for 5 hours. However, in general, the heat resistant temperature of such strongly acidic cation exchange resins are inherently about 100° C., and even highly heat resistant resins can not withstand a temperature higher than 160° C. Therefore, when such ion exchange resins are used, a high reaction temperature and a long reaction time are required. In addition, these ion exchange resins have also drawbacks that the mechanical strength is low and the resins are easily broken so that the stability as a catalyst is unreliable to a great extent and further the catalytic activity is low. 
     Japanese Patent Application Laid-open No. 313447/1989 discloses an addition reaction of acetic acid with cyclohexene in the presence of both ZSM-5, a high silica content-zeolite, as a catalyst and water. According to this method, the reaction temperature is 120° C. and the reaction time is 4 hours resulting in the formation of cyclohexanol in a 12.5% yield and cyclohexyl acetate at most in a 65% yield. The reaction temperature is high and the catalytic activity is low. 
     The present inventors have conduct research on efficient methods for the production of cyclohexyl acetate, and noted that the addition reaction of cyclohexene with acetic acid is an excellent method for producing cyclohexyl acetate and have considered the conventional drawbacks such as low catalytic activity, and low durability as catalyst including low mechanical strength and low heat resistance. As a result, the present invention has been completed. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a process for producing efficiently cyclohexyl acetate. 
     It is another object of the present invention to provide a catalyst useful for producing cyclohexyl acetate from cyclohexene and acetic acid. 
     It is a further object of the present invention to provide a catalyst for producing cyclohexyl acetate in high conversion and high selectivity within a short time. 
     It is still another object of the present invention to provide a catalyst for producing cyclohexyl acetate effectively at a low temperature region. 
     It is a still further object of the present invention to provide a catalyst capable of producing cyclohexyl acetate stably even at a high temperature region. According to the present invention, there is provided a process for producing cyclohexyl acetate which comprises reacting acetic acid with cyclohexene in the presence of at least one heteropolyacid mainly composed of oxides of tungsten. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the above-mentioned present invention, the heteropolyacids mainly composed of oxides of tungsten used as catalysts are preferably a heteropolyacid of the formula, 
     
         (M.sub.1).sub.a (M.sub.2).sub.b (W).sub.c (O).sub.d (H).sub.e 
    
     where M 1  and M 2  are independently metal elements, W is tungsten, O is oxygen, H is hydrogen, a is an integer of 1 or 2, b is an integer of 0, 1 or 2, c is a positive integer of 20 or less, d is a positive integer of 100 or less, and e is a positive integer of 10 or less. 
     In the above-mentioned formula, preferably M 1  is an element selected from the group consisting of P, Si, Co, Mn, Ni, As, Ti, Fe, V and B, and M 2  is V. More preferably, the heteropolyacid is tungstophosphoric acid and/or tungstosilic acid. The most easily available heteropolyacids are, for example, dodecatungstosilicic acid (SiW 12  O 40  H 4 ), heteropolyacids produced by replacing one or more of tungsten atoms of dodecatungstosilicic acid with vanadium atom(s), dodecatungstophosphoric acid (PW 12  O 40  H 4 ), and heteropolyacids produced by replacing one or more of tungsten atoms with vanadium atom(s), and the like. However, the process of the present invention is not limited to these heteropolyacids. 
     The heteropolyacids mainly composed of oxides of tungsten may be those containing no water of crystallization and/or those containing water of crystallization in the process of the present invention. It is more preferable that the heteropolyacids mainly composed of oxides of tungsten have water of crystallization adjusted to an amount on average of 3.0 molecules or less per one molecule of the heteropolyacid 
     In addition, it is much more preferable in the process of the present invention to use a heteropolyacid mainly composed of oxides of tungsten wherein the amount of water of crystallization is an average of 3.0 molecules or less per one molecule of the heteropolyacid resulting from adjusting the amount of said water by heating a heteropolyacid mainly composed of tungsten oxide at a temperature range of from 150° C. to 500° C., or by heating a heteropolyacid mainly composed of tungsten oxide in a stream of a gas inert to the heteropolyacid. 
     When the process of the present invention is carried out in the presence of the heteropolyacid the amount of water of crystallization of which has been adjusted to 3.0 molecules or less per one molecule of the heteropolyacid, it is preferable that the amount of water other than water of crystallization of the heteropolyacid in the reaction system is 30.0 molecules or less per one molecule of the heteropolyacid 
     In the present invention, it is not particularly necessary to purify the starting materials, that is, acetic acid and cyclohexene, and commercially available acetic acid and cyclohexene of chemical reagent grade may be used as they are. It is preferable to remove water. 
     Heteropolyacids mainly composed of oxides of tungsten usually contain water of crystallization. In the present invention, &#34;water of crystallization&#34; of the heteropolyacids is a general term for water contained in heteropolyacids when they are prepared or commercially sold. 
     Concretely it is, for example, water attached to or taken in heteropolyacid crystals when heteropolyacids are prepared in a water-containing solvent and then precipitated by using a non-solvent or the like, or water taken in heteropolyacide by adsorption, deliquescence or the like. 
     For example, a commercially available dodecatungstosilicic acid can be represented by the general formula, H 4  SiW 12  O 40 .nH 2  O and a commercially available dodecatungstophosphoric acid can be represented by the general formula, H 3  PW 12  O 40 .nH 2  O. Water of crystallization is the n.H 2  O, and represents water molecules taken in or adsorbed to or contained in the crystal structure. 
     Therefore, in the process of the present invention the heteropolyacids represented by the above-mentioned general formulas indicate that they have n molecules of water of crystallization. The n is an average value so that it is not always an integer, but a real number. The n of commercially available heteropolyacids usually ranges from about 25 to about 30. The n can be more than these values due to the adsorption of water or the like. 
     Water of crystallization contained in those heteropolyacids can be easily reduced i.e. the value of n can be decreased, by a dehydration treatment such as heating and the like, and it is also possible to reduce the value of n to zero. In addition, it is also possible to increase the value of n by causing the dehydrated heteropolyacid to adsorb water. 
     According to the following methods, water of crystallization contained in heteropolyacids mainly composed of oxide of tungsten used as a catalyst for the process of the present invention may be reduced to 3 molecules or less per one molecule of the heteropolyacid. 
     Easily available heteropolyacids mainly composed of oxide of tungsten usually contain several tens of moles of water of crystallization. A method for reducing the water of crystallization to an average of 3 molecules or less per one molecule of the heteropolyacid is not particularly limited in the present invention, but as an easily operable method, there may be mentioned a dehydration treatment by heating etc. 
     As the dehydration treatment by heating, for example, heating in an ordinary electric furnace (muffle furnace) is recommended. Naturally, according to the present invention, the method is not limited to the heating by this apparatus. 
     Neither is the heating temperature particularly limited and any temperature may be used as far as water of crystallization can be reduced to an average of 3.0 molecules or less per one molecule of the heteropolyacid, but for the effective operation, it is preferable to effect the procedure at a temperature of 80° C.-500° C., more preferably, 200° C.-450° C. At a lower temperature, the dehydration is difficult while heteropolyacid anhydride is formed at 550° C. or higher. 
     The heating time is not particularly limited as long as the amount of water of crystallization is in the above-mentioned range. For example, when an ordinary electric furnace is used and the dehydration is conducted at about 300° C., the above-mentioned range of the amount of water of crystallization can be sufficiently attained in about 3 hours. When, as a catalyst, a heteropolyacid is used which is prepared by heating and dehydrating the heteropolyacid in an inert gas flow at the heat-dehydrating temperature and controlling the amount of water of crystallization to an average of 3.0 molecules or less per one molecule of the heteropolyacid, the activity of the resulting catalyst is much higher. This operation can provide a very effective catalyst. 
     The gas used in the heat-dehydration operation may be any gas as long as it is inert to the heteropolyacid mainly composed of oxide of tungsten at the heating temperature. 
     In addition, even if the gas is liquid or solid at ordinary temperature, it may be used, provided that it is in a gaseous state at the heating temperature and inert to the heteropolyacid. 
     Exemplary suitable gases include air, argon, nitrogen, helium, hydrogen, aliphatic hydrocarbons, aromatic hydrocarbons and the like, but naturally are not limited thereto. In addition, the flow rate of inert gas is not critical, but the space velocity in the apparatus in terms of gas volume at the heating temperature is preferably 0.2-20 vol/hr.vol. 
     According to the process of the present invention, even when the heteropolyacid contains 20-30 molecules of water of crystallization per one molecule of the heteropolyacid which are ordinary amounts of water of crystallization of the heteropolyacid, it exhibits a good catalytic activity. 
     However, when the amount of water is controlled to an average of 3.0 molecules or less per one molecule of the heteropolyacid by dehydration or the like, the resulting heteropolyacid exhibits a particularly high catalytic activity. In addition, since this catalyst is thermally very stable, the process of the present invention can be sufficiently stably carried out at an elevated temperature. 
     According to the process of the present invention, the reaction of acetic acid with cyclohexene to form cyclohexyl acetate proceeds as an addition reaction. The reaction may be carried out in a liquid phase homogeneous system, or in a solid phase-gas phase or a solid phase-liquid phase heterogeneous system or the like. 
     The process of the present invention may be effected under any pressure condition such as ambient pressure, reduced pressure, and elevated pressure. When the reaction is effected at a high temperature, a liquid phase reaction may be conducted at an elevated pressure. The operation type of reaction is not particularly limited, and any of continuous system, batch system and semi-batch system may be employed. 
     It is possible to add a inert solvent or a diluent to the catalyst and the reaction agents (starting materials and the product). 
     Inert solvents or diluents may be added to the catalyst and reaction agents (the starting materials and product ). 
     Exemplary suitable inert solvents and diluents include aliphatic saturated hydrocarbons such as n-butane, n-pentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane, isomers thereof and the like; aromatic hydrocarbons such as benzene, toluene, ethylbenzene, xylene, anisole, cumene, nitrobenzene and the like; alicyclic saturated-hydrocarbons such as cyclopentane, alkyl-substituted cyclopentanes, alkoxy-substituted cyclopentanes, nitro-substituted cyclopentanes, cyclohexane, alkyl-substituted cyclohexanes, alkoxy-substituted cyclohexanes, nitro-substituted cyclohexanes, cycloheptane, alkyl-substituted cycloheptanes, alkoxy-substituted cycloheptanes, nitro-substituted cycloheptanes, cyclooctane, alkyl-substituted cyclooctanes, alkoxysubstituted cyclooctanes, nitro-substituted cyclooctanes and the like; nitrogen, air, argon, helium and the like. 
     When the reaction is carried out at an elevated pressure, it is possible to pressurize inert nitrogen, argon or the like into the reaction agents and catalyst in advance and carry the reaction in a liquid phase reaction system. 
     In the process of the present invention, the ratio of acetic acid to cyclohexene charged upon effecting the reaction are not particularly limited The molar ratio of acetic acid to cyclohexene is usually in the range of from 0.1 to 100. For example, in order to attain a high conversion of acetic acid, it is desirable to conduct the reaction at a molar ratio of acetic acid to cyclohexene of less than 1 while in order to attain a high conversion of cyclohexene, it is desirable to effect the reaction at a molar ratio of acetic acid to cyclohexene of more than 1. 
     For carrying out the process of the present invention, the amount of the catalyst to be added is not particularly critical, but it is advisable in the case of the reaction in a batch system to use the catalyst in an amount of 0.1-100% by weight, preferably 1-50% by weight based on the weight of cyclohexene fed. 
     When the amount of the catalyst is less than the above-mentioned amount, the reaction proceeds slowly while at the amount exceeding an above-mentioned amount the reaction proceeds sufficiently, but it is not preferable from an economical point of view. However, the process of the present invention naturally can be effected outside of the above-mentioned range. 
     Upon carrying out the process of the present invention, the manner in which the catalyst and reaction agents are fed is not particularly limited. The catalyst, acetic acid and cyclohexene may be simultaneously fed, and the catalyst may be dissolved or suspended in a solvent or the like and then fed to a reaction vessel. In addition, there are various methods, for example, before the reaction, acetic acid and the catalyst are mixed in advance and then cyclohexene is added, or the catalyst and cyclohexene are mixed and then acetic acid is added. 
     Upon effecting the process of the present invention, when the heteropolyacid catalyst mainly composed of oxide of tungsten contains an average of 3.0 molecules of water of crystallization or less per one molecule of the heteropolyacid, the water amount in the reaction system particularly affects the reaction. 
     In particular, in order to obtain a catalytic activity higher than that of commercially available heteropolyacid containing several tens of molecules of water of crystallization per one molecule of the heteropolyacid, it is necessary to control the amount of water other than water of crystallization contained in the heteropolyacid to 30 molecules or less per one molecule of the heteropolyacid used. 
     When the amount of water is higher than that, dehydration of water of crystallization in the heteropolyacid fails to give an effective result. 
     In such a case, the water content in the above-mentioned acetic acid and cyclohexene is at most 100 ppm so that when the amount of the catalyst added to the reaction system is on the order of percent based of the reaction system, the amount of water (excluding water of crystallization) in the reaction system does not exceed the above-mentioned value in case that commercially available acetic acid and cyclohexene are used in the process of the present invention. 
     The reaction temperature in the process of the present invention is not particularly limited, but the reaction may be effected at a wide range of temperature. It is preferably 0° C.-400° C., more preferably 30° C.-200° C. If the reaction temperature is too low, the reaction velocity is lowered. On the contrary, if the reaction temperature is too high, reaction agents such as cyclohexene and the like are liable to be thermally deteriorated and thereby such a high temperature is not economical. 
     The reaction time varies depending upon the catalyst amount or reaction temperature. When the catalyst amount is large and the temperature is high, the reaction time is very short, for example, about 0.1 sec. or less. On the contrary, when the catalyst amount is small and the temperature is low the reaction time is long, for example, about 24 hours. 
     After completion of the reaction, the end product can be recovered by an ordinary separation procedure such as distillation and the like. 
     Examples of various methods for carrying out the process of the present invention are as shown below. The methods are not critical, but the following are some examples of easily operable methods though the present invention is not limited thereto. 
     (1) In a glass flask equipped with a stirrer are placed prescribed amounts of the catalyst, acetic acid and cyclohexene, if desired, together with a diluent such as a solvent and the like and if necessary, a reflux condenser is fitted to the flask, and then the reaction is effected by heating with stirring. 
     (2) Prescribed amounts of the catalyst, acetic acid and cyclohexene are added to an autoclave, if desired, together with a medium such as nitrogen, argon and the like, and then the heating reaction is conducted with stirring. 
     (3) Into a reactor previously kept at a prescribed temperature and pressure are continuously introduced prescribed amounts of the catalyst, cyclohexene and acetic acid, if desired, together with a diluent such as a solvent and the like to carry out the reaction. 
     According to the process of the present invention, cyclohexyl acetate can be prepared very efficiently by an addition reaction of acetic acid with cyclohexene in the presence of a heteropolyacid mainly composed of oxides of tungsten, and further, drawbacks of conventional catalysts such as low catalytic activity, low heat resistance and the like can be solved, for example, the catalyst in the present invention is effective even at low temperatures and stable even at high temperatures. 
     In particular, when the amount of water of crystallization of the heteropolyacid is controlled to an average of 3 molecules or less per one molecule of the heteropolyacid, the reaction exhibits a very high reaction efficiency. Even under very mild conditions such as low temperature and within a short time, for example, about one hour, cyclohexyl acetate can be produced in high selectivity and in high conversion. 
     Moreover, even under high temperature conditions, the process can be stably and effectively carried out. 
     Cyclohexyl acetate may be used as a starting material for cyclohexanol which is useful as an intermediate of phenol, nylon and adipic acid and may be used as a cycloalkanol carboxylic acid ester useful as a special solvent. 
     The present invention is explained in the following more in detail referring to examples. 
     Legend in the following tables: 
     
         ______________________________________                                    
Cy - Hex          Cyclohexene                                             
Cy - HexOAc       Cyclohexyl acetate                                      
Ar                Argon                                                   
He                Helium                                                  
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     (1) Quantitative Measurement of the Reaction Product: After conducting the reaction for a prescribed time at a prescribed temperature, the reaction liquid was cooled to room temperature and subjected to gas chromatography to measure the reaction product quantitatively. 
     (2) Quantitative Measurement of Water of Crystallization contained in the catalyst: 
     The amount of water of crystallization contained in the heteropolyacid mainly composed of oxide of tunsten was determined based on an anhydrous heteropolyacid (the amount of water of crystallization being zero) produced by heating and dehydrating the heteropolyacid at 500° C. until the weight became constant and did not decrease any more. 
    
    
     EXAMPLE 1 
     To a 70 ml three-necked flask equipped with a magnetic stirrer and a reflux condenser were added a commercially available dodecatungstophosphoric acid (H 4  PW 12  O 40  ,28H 2  O) 2.0 g, a commercially available 99.5% acetic acid (manufactured by Kokusan Kagaku K. K, special grade) 20.5 g and a commercially available 98% cyclohexene (manufactured by Tokyo Kasei K. K., special grade) 4.5 g, and the flask was placed in an oil bath and heated at 70° C. for 1.5 hours with stirring to effect the reaction. 
     After the procedure, stirring was stopped and the flask was taken out of the oil bath and cooled to room temperature, and then the reaction liquid was quantitatively analyzed. 
     The result is as shown in Table 1, that is, the yield of cyclohexyl acetate was 33.4% (selectivity being 97.3%) and conversion of cyclohexene was 34.3%. 
     COMPARISON EXAMPLE 1 
     The procedure of Example 1 was repeated under the same reaction conditions except that 2.0 g of H-ZSM5 zeolite was used as a catalyst in place of dodecatungstophosphoric acid, but cyclohexyl acetate was not formed and the starting materials, cyclohexene and acetic acid were recovered. 
     EXAMPLE 2 
     The procedure of Example 1 was repeated to produce cyclohexyl acetate from cylohexene and acetic acid under the same conditions except that the reaction time was 3 hours. As a result, the amount of the product, cyclohexyl acetate increased as the reaction time increased as shown in Table 1. 
     EXAMPLE 3 
     The procedure of Example 1 was repeated to carry out the reaction of acetic acid and cyclohexene under the same conditions including catalyst amount except that the catalyst was replaced with a commercially available dodecatungstosilicic acid (H 4  SiW 12  O 40  , 25H 2  O). The result is as shown in Table 1. 
     EXAMPLE 4 
     The procedure of Example 3 was repeated except that the reaction time was 3 hours and the reaction of acetic acid with cyclohexene was conducted. 
     EXAMPLE 5 
     In a 200 ml autoclave were placed the above-mentioned commercially available dodecatungstosilicic acid 5.0 g, the above-mentioned commercially available acetic acid 61.5 g and the above-mentioned commercially available cyclohexene 13.5 g and nitrogen gas was fed thereinto until the pressure reached 5 kg/cm 2  (gauge), and then a reaction was carried out with stirring by heating at 100° C. for 1 hour. The result is shown in Table 1, that is, cyclohexyl acetate was produced in high yield. 
     
                       TABLE 1                                                     
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       Cy - Hex   Cy - HexOAc                                             
       Conversion (%)                                                     
                  Yield (%) Selectivity (%)                               
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Example 1                                                                 
         34.3         33.4      97.3                                      
Example 2                                                                 
         50.6         50.2      99.2                                      
Example 3                                                                 
         57.2         54.8      95.8                                      
Example 4                                                                 
         71.2         71.2      100.0                                     
Example 5                                                                 
         88.1         87.6      99.4                                      
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     EXAMPLE 6 
     Preparation of dehydrated dodecatungstophosphoric acid catalysts by heating 
     As shown in Table 2 (infra), the above-mentioned commercially available dodecatungstophosphoric acid was heated and dehydrated in an electric furnace (muffle furnace) at a prescribed temperature for a prescribed time. As a result, the compositions of water of crystallization in dodecatungstophosphoric acid are as shown in Table 2 (infra). The number of molecule of water of crystallization per one molecule of the dodecatungstophosphoric acid thus dehydrated is designated as n&#39; in the table. 
     
                       TABLE 2                                                     
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        Heating        Heating                                            
        temperature (°C.)                                          
                       time (hr.)                                         
                                n&#39;                                        
______________________________________                                    
Catalyst 1                                                                
          350              3.0      0                                     
Catalyst 2                                                                
          400              3.0      0                                     
Catalyst 3                                                                
          300              3.0      0                                     
Catalyst 4                                                                
          250              1.0      1.4                                   
Catalyst 5                                                                
          250              0.5      3.0                                   
Catalyst 6                                                                
          200              0.25     4.8                                   
Catalyst 7                                                                
          120              1.0      8.0                                   
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     EXAMPLE 7 
     The reaction of acetic acid with cyclohexene was effected by using the same apparatus as that of Example 1 and under the same conditions as those of Example 1 except that the above-mentioned catalyst 1 was used as a heteropolyacid. As shown in Table 3, the catalytic activity was markedly improved. 
     EXAMPLE 8 
     The reaction of acetic acid with cyclohexene was conducted using the same apparatus and conditions as those of Example 7 except that the above-mentioned catalyst 2 was used as a heteropolyacid catalyst. As shown in Table 3, when the dehydration temperature for preparing the catalyst was elevated, the catalyst activity was hardly affected and it was confirmed that the catalyst activity was very high. 
     EXAMPLE 9 
     The reaction of Example 7 was repeated except that catalyst 3 was used. As shown in Table 3, the reaction result was similar to those for catalyst 1 and catalyst 2. The facts in Examples 7-9 show that the amount of water of crystallization of a heteropolyacid is more important than the dehydration temperature so as to improve remarkably the activity of the catalyst by dehydrating the heteropolyacid mainly composed of oxides of tungsten. 
     EXAMPLE 10 
     The procedure of Example 7 was repeated except that catalyst 4 was used as a catalyst. The result is shown in Table 3. 
     EXAMPLE 11 
     The procedure of Example 7 was repeated except that catalyst 5 was used as a catalyst. The result is shown in Table 3. 
     EXAMPLE 12 
     The reaction of acetic acid with cyclohexene was conducted under the same conditions as in Example 7 except that catalyst 6 was used as a catalyst. As is clear from the result shown in Table 3, an improvement in catalytic activity due to dehydration of the heteropolyacid was not observed. 
     EXAMPLE 13 
     The reaction was conducted under the same conditions as in Example 7 except that catalyst 7 was used as a catalyst. As is clear from the result shown in Table 3, the catalyst exhibited a catalytic activity similar to that of a commercially available dedecatungstophosphoric acid. 
     EXAMPLE 14 
     The reaction of acetic acid with cyclohexene was conducted under the same conditions as in Example 7 except that 0.5 g of catalyst 1 was used which was a reduced amount as compared with 2 g in Example 7. The result is shown in Table 3. 
     EXAMPLE 15 
     The reaction was conducted under the same conditions as in Example 14 except that the reaction time was 3 hours. As is clear from the result shown in Table 3, as the reaction time increased, the amount of produced cyclohexyl acetate increased and no deterioration of the catalyst occurred. 
     EXAMPLE 16 
     To a 200 ml autoclave were added 2.0 g of catalyst 1, 61.5 g of acetic acid and 13.5 g of cyclohexene, and nitrogen gas was fed to the autoclave until the pressure reached 5 kg/cm 2  (gauge), and then, the cyclohexyl acetate producing reaction was conducted at 100° C. for 1 hour. The result is shown in Table 3. 
     EXAMPLE 17 
     The procedure of Example 16 was repeated to conduct the reaction of acetic acid with cyclohexene except that the reaction temperature was 130° C. and the reaction time was 0.5 hour. The result is shown in Table 3, that is, cyclohexyl acetate was produced in high yield within a short time. 
     
                       TABLE 3                                                     
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             Cy - Hex Cy - HexOAc                                         
                   Conversion Yield Selectivity                           
Catalyst     n&#39;    (%)        (%)   (%)                                   
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Example 7                                                                 
        1        0     81.7     80.6  97.3                                
Example 8                                                                 
        2        0     80.9     80.5  99.5                                
Example 9                                                                 
        3        0     81.2     80.5  99.1                                
Example 10                                                                
        4        1.4   82.6     80.8  97.8                                
Example 11                                                                
        5        3.0   70.5     68.0  96.5                                
Example 12                                                                
        6        4.8    9.4      8.9  94.9                                
Example 13                                                                
        7        8.0   37.1     35.1  94.5                                
Example 14                                                                
        1        0     41.3     40.2  97.4                                
Example 15                                                                
        1        0     63.4     62.3  98.2                                
Example 16                                                                
        1        0     89.5     88.9  99.3                                
Example 17                                                                
        1        0     91.2     90.4  99.1                                
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     The amount of catalyst in each of the Examples other than Examples 14 and 15 was 2.0 g, and that in each of Examples 14 and 15 was 0.5 g. n&#39; denotes the number of molecules of water of crystallization contained in one molecule of the dehydrated heteropolyacid, the catalyst. 
     EXAMPLE 18 
     Preparation of dehydrated heteropolyacid catalyst 
     The above-mentioned commercially available dodecatungstosilicic acid (containing 25 molecules of water of crystallization per one molecule of the heteropolyacid) was placed in a muffle furnace and subjected to heating and dehydration at the prescribed temperature for the prescribed time as shown in Table 4. The number of molecules of water of crystallization contained in the dodecatungstosilicic acid thus dehydrated per one molecule of said heteropolyacid is designated as n&#39;, which is shown in Table 4. 
     
                       TABLE 4                                                     
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        Heating        Heating                                            
        temperature (°C.)                                          
                       time (hr.)                                         
                                n&#39;                                        
______________________________________                                    
Catalyst 8                                                                
          370              3.0      0                                     
Catalyst 9                                                                
          420              1.0      0                                     
Catalyst 10                                                               
          300              3.0      0                                     
Catalyst 11                                                               
          250              2.0      1.7                                   
Catalyst 12                                                               
          250              0.75     3.0                                   
Catalyst 13                                                               
          250              0.5      4.0                                   
Catalyst 14                                                               
          180              0.25     5.8                                   
Catalyst 15                                                               
          150              0.75     12.7                                  
Catalyst 16                                                               
          100              1.0      21.5                                  
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     EXAMPLE 19 
     The reaction of acetic acid with cyclohexene was conducted by repeating the procedure of Example 3 except that catalyst 8 (2.0 g fed) was used in place of the commercially available dodecatungstosilicic acid. As is clear from the result shown in Table 5, a very high catalytic activity was observed. 
     EXAMPLE 20 
     The procedure of Example 19 was repeated except that catalyst 9 was used in place of said catalyst. As is clear from the result shown in Table 5, the reaction result was hardly affected by elevating the dehydration temperature. 
     EXAMPLE 21 
     The procedure of Example 19 was repeated except that catalyst 10 was used in place of said catalyst. As is clear from the result shown in Table 5, the reaction result was hardly affected by lowering the dehydration temperature upon preparing the catalyst. 
     EXAMPLE 22 
     The reaction of acetic acid with cyclohexene was conducted under the same conditions as in Example 19 except that catalyst 11 was used. The result is shown in Table 5. 
     EXAMPLE 23 
     The procedure of Example 19 was repeated except that catalyst 12 was used. The result is shown in Table 5. 
     EXAMPLE 24 
     The cyclohexyl acetate production reaction was conducted by repeating the procedure of Example 19 except that catalyst 13 was used. The result is shown in Table 5. 
     EXAMPLE 25 
     The procedure of Example 19 was repeated except that catalyst 14 was used. As is clear from the result shown in Table 5, the reaction result was lowered in a similar manner to Example 24. 
     EXAMPLE 26 
     The procedure of Example 19 was repeated except that catalyst 15 was used. As is clear from the result shown in Table 5, any catalyst activation effect due to the dehydration of the heteropolyacid was not recognized. 
     EXAMPLE 27 
     The procedure of Example 19 was repeated except that catalyst 16 was used. As shown in Table 5, an effect due to the dehydration of the heteropolyacid was not recognized. 
     In view of the results of Examples 19-27, it is noted that when the amount of water, of crystallization contained in a heteropolyacid is 3.0 molecules or less per one molecule of the heteropolyacid, the heteropolyacid exhibits a very high catalytic activity in the cyclohexyl acetate forming reaction of acetic acid with cyclohexene. 
     EXAMPLE 28 
     The procedure of Example 19 was conducted except that 0.5 g of catalyst 8 was used. The result is shown in Table 5. 
     EXAMPLE 29 
     The procedure of Example 28 was repeated except that the reaction time was 3 hours. As is clear from the result shown in Table 5, as the reaction increases, the amount of cyclohexyl acetate produced increases, and this fact indicates that the catalyst is not deteriorated. 
     EXAMPLE 30 
     To a 200 ml autoclave were added 2.0 g of catalyst 8, 61.5 g of acetic acid, 13.5 g of cyclohexene, and nitrogen gas was fed into the autoclave until the pressure reached 5 kg/cm 2  (gauge), and then the cyclohexyl acetate production reaction was carried out at 100° C. for one hour. The result is shown in Table 5. 
     EXAMPLE 31 
     The procedure of Example 24 was repeated except that the reaction temperature was 130° C. and the reaction time was 0.5 hour. The result is shown in Table 5. It indicates that cyclohexyl acetate was produced in high yield within a short time. 
     
                       TABLE 5                                                     
______________________________________                                    
              Cy - Hex                                                    
                      Cy - HexOAc                                         
                    Conversion                                            
                              Yield Selectivity                           
Catalyst     n&#39;     (%)       (%)   (%)                                   
______________________________________                                    
Example 19                                                                
         8       0      87.2    86.2  98.9                                
Example 20                                                                
         9       0      86.8    86.0  99.1                                
Example 21                                                                
        10       0      85.9    85.3  99.3                                
Example 22                                                                
        11       1.7    87.5    85.7  97.9                                
Example 23                                                                
        12       3.0    72.8    71.6  98.3                                
Example 24                                                                
        13       4.0    14.2     9.1  64.8                                
Example 25                                                                
        14       5.8    15.6    12.1  77.6                                
Example 26                                                                
        15       12.7   56.2    51.8  92.8                                
Example 27                                                                
        16       21.5   55.8    51.0  91.4                                
Example 28                                                                
         8       0      43.7    42.5  97.3                                
Example 29                                                                
         8       0      73.8    72.9  98.9                                
Example 30                                                                
         8       0      91.6    91.1  99.5                                
Example 31                                                                
         8       0      95.2    94.4  99.2                                
______________________________________                                    
 
    
     The amount of catalyst used in each of Examples other than Examples 28 and 29 was 2.0 g while that in each of Examples 28 and 29 was 0.5 g. 
     EXAMPLE 32 
     Preparation of dodecatungstophosphoric Acid Dehydrated Catalyst (2) 
     The above-mentioned commercially available dodecatungstophosphoric acid was placed in a muffle furnace having an inner volume of 8 liters and wherein a gas or the like can be introduced into and discharged therefrom, and subjected to heating and dehydration at a prescribed temperature for a prescribed time by introducing various gases into the muffle at prescribed flow rates as shown in Table 6. The number of molecules of water of crystallization contained in the tungstophosphoric acid thus treated per one molecule of the tungstophosphoric acid is designated as n&#39; in Table 6. 
     
                       TABLE 6                                                     
______________________________________                                    
             Flow rate Temperature Time                                   
       Gas   (N1/hr.)  (°C.)                                       
                                   (hr.)                                  
                                        n&#39;                                
______________________________________                                    
Catalyst 17                                                               
         Ar      5.0       350       3    0                               
Catalyst 18                                                               
         Ar      5.0       400       1    0                               
Catalyst 19                                                               
         Ar      5.0       300       3    0                               
Catalyst 20                                                               
         Ar      5.0       250       1    1.3                             
Catalyst 21                                                               
         Ar      5.0       250       0.5  2.9                             
Catalyst 22                                                               
         Ar      35.0      350       3    0                               
Catalyst 23                                                               
         Air     35.0      350       3    0                               
Catalyst 24                                                               
         He      35.0      350       3    0                               
______________________________________                                    
 
    
     EXAMPLE 33 
     The reaction of acetic acid with cyclohexene was conducted under the same conditions as in Example 1 except that catalyst 17 (added amount, 2.0g) was used in place of the above-mentioned commercially available dodecatungstophosphoric acid. The result is shown in Table 7. It indicates that the dodecatungstophosphoric acid was converted to a very highly active catalyst by heating and dehydrating dodecatungstophosphoric acid in an argon flow. 
     EXAMPLE 34 
     The procedure of Example 33 was repeated except that catalyst 18 was used in place of the catalyst. The result is shown in Table 7. 
     EXAMPLE 35 
     The procedure of Example 33 was repeated except that catalyst 19 was used in place of the catalyst. The result is shown in Table 7. 
     These results indicate that the dehydration temperature hardly affects the catalytic activity. 
     EXAMPLE 36 
     The procedure of Example 33 was repeated except that catalyst 20 was used in place of the catalyst. The result is shown in Table 7. 
     EXAMPLE 37 
     The procedure of Example 33 was repeated except that catalyst 21 was used in place of the catalyst The result is shown in Table 7. 
     EXAMPLE 38 
     The procedure of Example 33 was repeated except that catalyst 22 was used in place of the catalyst The result is shown in Table 7. It indicates that the flow rate of the entering gas does not affect the catalytic activity by comparing the result of Example 38 to that of Example 33. 
     EXAMPLE 39 
     The procedure of Example 33 was repeated except that catalyst 23 was used in place of the catalyst The result is shown in Table 7. 
     EXAMPLE 40 
     The procedure of Example 33 was repeated except that catalyst 24 was used in place of the catalyst. The result is shown in Table 7. The results in Example 33 - 40 indicate that heating dehydration while passing argon, helium or air is effective. 
     
                       TABLE 7                                                     
______________________________________                                    
             Cy - Hex Cy - HexOAc                                         
                   Conversion Yield Selectivity                           
Catalyst     n&#39;    (%)        (%)   (%)                                   
______________________________________                                    
Example 33                                                                
        17       0     86.7     85.4  98.5                                
Example 34                                                                
        18       0     85.9     85.3  99.3                                
Example 35                                                                
        19       0     86.2     84.6  98.1                                
Example 36                                                                
        20       1.3   87.6     85.0  97.1                                
Example 37                                                                
        21       2.9   75.8     73.3  96.7                                
Example 38                                                                
        22       0     86.9     85.4  98.3                                
Example 39                                                                
        23       0     87.5     85.3  97.5                                
Example 40                                                                
        24       0     87.2     85.8  98.4                                
______________________________________                                    
 
    
     EXAMPLE 41 
     Preparation of a catalyst by heating and dehydrating dodecatungstosilicic acid in a gas flow: 
     In the same muffle furnace as in Example 27 was placed the above-mentioned dodecatungstosilicic acid and a heating and dehydrating treatment was effected at a prescribed temperature for a prescribed time while each gas was passed through the furnace at a prescribed flow rate. 
     The catalysts thus prepared, preparation conditions, and the number of molecules of water of crystallization (n&#39;) per one molecule of the heteropolyacid catalyst thus prepared are shown in Table 8. 
     
                       TABLE 8                                                     
______________________________________                                    
             Flow rate Temperature Time                                   
       Gas   (N1/hr.)  (°C.)                                       
                                   (hr.)                                  
                                        n&#39;                                
______________________________________                                    
Catalyst 25                                                               
         Ar      5.0       370       3    0                               
Catalyst 26                                                               
         Ar      5.0       420       1    0                               
Catalyst 27                                                               
         Ar      5.0       300       3    0                               
Catalyst 28                                                               
         Ar      5.0       250       1    1.3                             
Catalyst 29                                                               
         Ar      5.0       250       0.5  2.9                             
Catalyst 30                                                               
         Ar      35.0      350       3    0                               
Catalyst 31                                                               
         Air     35.0      350       3    0                               
Catalyst 32                                                               
         He      35.0      350       3    0                               
______________________________________                                    
 
    
     EXAMPLE 42 
     The reaction of acetic acid with cyclohexene was effected under the same conditions as in Example 3 except that catalyst 25 (added 2.0 g) was used in place of the commercially avilable dodecatungstosilicic acid catalyst. As is clear from the result in Table 9, the tungstosilicic acid catalyst thus heated and dehydrated in argon gas flow has a high catalytic activity. 
     EXAMPLE 43 
     The procedure of Example 42 was repeated except that catalyst 26 was used in place of the catalyst. The result is shown in Table 9. 
     EXAMPLE 44 
     The procedure of Example 42 was repeated except that catalyst 27 was used in place of the catalyst. The result is shown in Table 9. 
     EXAMPLE 45 
     The procedure of Example 42 was repeated except that catalyst 28 was used in place of the catalyst. The result is shown in Table 9. 
     EXAMPLE 46 
     The procedure of Example 42 was repeated except that catalyst 29 was used in place of the catalyst. The result is shown in Table 9. 
     EXAMPLE 47 
     The procedure of Example 42 was repeated except that catalyst 30 was used in place of the catalyst. The result is shown in Table 9. As is clear from comparison of the result of Example 47 to that of Example 42, when the gas flow amount is changed, the catalytic activity is not affected by the change. 
     EXAMPLE 48 
     The procedure of Example 42 was repeated except that catalyst 31 was used in place of the catalyst. The result is shown in Table 9. 
     EXAMPLE 49 
     The procedure of Example 42 was repeated except that catalyst 32 was used in place of the catalyst. The result is shown in Table 9. 
     The results obtained i Examples 42 - 49 show that argon, helium or air is effective as a gas which is passed through the preparation system upon preparing the catalyst by heating and dehydrating. 
     
                       TABLE 9                                                     
______________________________________                                    
             Cy - Hex Cy - HexOAc                                         
                   Conversion Yield Selectivity                           
Catalyst     n&#39;    (%)        (%)   (%)                                   
______________________________________                                    
Example 42                                                                
        25       0     92.6     90.5  97.8                                
Example 43                                                                
        26       0     91.9     90.2  98.1                                
Example 44                                                                
        27       0     90.6     90.0  99.4                                
Example 45                                                                
        28       1.3   92.2     90.7  98.4                                
Example 46                                                                
        29       2.9   77.3     74.4  96.2                                
Example 47                                                                
        30       0     91.8     90.2  97.7                                
Example 48                                                                
        31       0     93.1     90.8  97.5                                
Example 49                                                                
        32       0     91.5     90.3  98.7                                
______________________________________                                    
 
    
     EXAMPLE 50 
     The reaction was conducted by repeating the procedure of Example 33 except that, after feeding the catalyst, acetic acid and cyclohexene, pure water was added such that the water in the reaction system was 1.1 mole per 1 mole of catalyst 17 (water of crystallization being zero). The result is shown is Table 10. In Table 10, the result of Example 33 is also cited for reference. 
     EXAMPLE 51 
     The reaction was conducted by repeating the procedure of Example 28 except that pure water was added in a way similar to Example 50 such that the water in the reaction system was 4.5 moles per 1 mole of catalyst 17 (water of crystallization being zero). The result is shown in Table 10. 
     EXAMPLE 52 
     The reaction was conducted by repeating the procedure of Example 28 except that pure water was added in a way similar to Example 50 such that the water in the reaction system was 10.2 moles per 1 mole of catalyst 17 (water of crystallization being zero). The result is shown in Table 10. 
     EXAMPLE 53 
     The reaction was conducted by repeating the procedure of Example 28 except that pure water was added in a way similar to Example 50 such that the water in the reaction system was 29.2 moles per 1 mole of catalyst 17 (water of crystallization being zero). The result is shown in Table 10. 
     EXAMPLE 54 
     The reaction was conducted by repeating the procedure of Example 33 except that pure water was added in a way similar to Example 50 such that the water in the reaction system was 29.2 moles per 1 mole of catalyst 17 (water of crystallization being zero). The result is shown in Table 10. The result of Example 54 shows that an improvement in catalytic activity due to dehydrating the catalyst was not observed. 
     EXAMPLE 55 
     The reaction was carried out by repeating the procedure of Example 36 except that, after feeding the catalyst, acetic acid and cyclohexene, pure water was added such that the amount of water other than water of crystallization of catalyst 20 (n&#39;=1.3) was 10.2 moles per one mole of the catalyst in the reaction system. The result is shown in Table 10. 
     EXAMPLE 56 
     The reaction was carried out under the same conditions as in Example 55 except that catalyst 21 (n&#39;=2.9) was used in place of the catalyst. The result is shown in Table 10. 
     EXAMPLE 57 
     The reaction was conducted under the same conditions as in Example 42 except that pure water was added in a way similar to Example 50 such that the water amount per one molecule of catalyst 25 (water of crystallization being zero) was 1.1 molecule. The result is shown in Table 10. The result of Example 42 is also listed in Table 10. 
     EXAMPLE 58 
     The reaction was carried out under the same conditions as in Example 57 except that he amount of added pure water was 4.5 molecules per one molecule of catalyst 25 (water of crystallization being zero) in place of that in Example 57. The result is shown in Table 10. 
     EXAMPLE 59 
     The reaction was carried out under the same conditions as in Example 57 except that the amount of added pure water was 10.5 molecules per one molecule of the catalyst in place of that in Example 57. The result is shown in Table 10. 
     EXAMPLE 60 
     The reaction was carried out under the same conditions as in Example 57 except that the amount of added pure water was 29.2 molecules per one molecule of the catalyst in place of that in Example 57. The result is shown in Table 10. 
     EXAMPLE 61 
     The reaction was carried out under the same conditions as in Example 57 except that the amount of added pure water was 35.4 molecules per one molecule of the catalyst in place of that in Example 57. The result is shown in Table 10. This indicates that any improvement in the catalytic activity due to the preparation of the catalyst by heating and dehydration was not recognized. 
     EXAMPLE 62 
     The procedure of Example 45 was repeated except that the amount of water other than water of crystallization contained in catalyst 28 (n&#39;=1.3) was 10.2 moles per one mole of the catalyst. The result is shown in Table 10. 
     EXAMPLE 63 
     The procedure of Example 62 was repeated except that catalyst 29 was used in place of the catalyst. The result is shown in Table 10. 
     
                       TABLE 10                                                    
______________________________________                                    
               Cy - Hex                                                   
                       Cy - HexOAc                                        
             Water   Conversion                                           
                               Yield Selectivity                          
Catalyst     (a)     (%)       (%)   (%)                                  
______________________________________                                    
Example 33                                                                
        17       0.02    86.7    85.4  98.5                               
Example 50                                                                
        17       1.1     86.9    85.7  98.6                               
Example 51                                                                
        17       4.5     82.1    80.6  98.2                               
Example 52                                                                
        17       10.2    78.3    77.6  99.1                               
Example 53                                                                
        17       29.2    46.9    45.3  96.6                               
Example 54                                                                
        17       34.3    33.7    32.9  97.6                               
Example 55                                                                
        20       10.2    78.5    78.0  99.4                               
Example 56                                                                
        21       10.2    77.2    76.1  98.6                               
Example 42                                                                
        25       0.02    92.6    90.5  97.8                               
Example 57                                                                
        25       1.1     91.8    90.3  98.4                               
Example 58                                                                
        25       4.5     88.9    85.7  96.4                               
Example 59                                                                
        25       10.5    80.3    78.8  98.1                               
Example 60                                                                
        25       29.0    67.2    65.5  97.5                               
Example 61                                                                
        25       35.4    48.4    46.2  95.5                               
Example 62                                                                
        28       10.2    80.5    79.4  98.6                               
Example 63                                                                
        29       10.2    71.2    69.1  97.1                               
______________________________________                                    
 (a) : The number of molecules of water other than water of crystallizatio
 of the catalyst present in the reaction system per one molecule of the   
 catalyst.