Acidic mixed oxide catalytic de-alkylation of tertiary-alkyl-ether-alkanols
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This invention is related to W. E. Smith&#39;s U.S. Application Ser. No. 189,190 filed Sept. 22, 1980, a continuation-in-part of U.S. Ser. No. 105,876, filed Dec. 20, 1979, now abandoned, which describes the use of an acidic zinc halide catalyst in a t-alkylether-alkanol de-alkylation process. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the use of a solid acidic mixed oxide catalyst to enhance a process which converts t-alkylether-alkanols to alkanediols in the substantial absence of undesirable cyclic ether by-products. 
     2. Description of the Prior Art 
     The de-alkylation of certain t-alkylether-alkanols such as 4-t-butylether-n-butan-1-ol to form alkanediols, such as 1,4-butanediol employing acidic catalysts, such as aqueous phosphoric acid or sulfuric acid, as well as acid ion exchange resins at temperatures of about 100° C. has been reported. 
     The dehydration of certain alkanediols such as 1,4-butanediol to form cyclic ethers, such as tetrahydrofuran employing strong acid catalysts such as phosphoric acid, acidic clays, acidic alumina at temperatures of about 120° C. has also been reported. 
     DESCRIPTION OF THE INVENTION 
     The process of this invention comprises contacting a solid acidic mixed oxide catalyst and a 4-t-alkylether-alkan-1-ol to selectively form alkan-1,4-diols in the substantial absence of cyclic ethers. 
     The t-alkylether-alkanols are defined by the formula: ##STR1## wherein R 1  and R 2  each, independently of the other, represents a C 1  to C 4  alkyl radical, and R 3  and R 4  each, independently of the other, represents a hydrogen atom or a C 1  to C 3  alkyl radical, or wherein R 1  represents a C 1  to C 4  alkyl radical, R 2  and R 3  together with the carbon atoms to which they are attached form a 5-membered or 6-membered cycloaliphatic ring, and C 4  represents a hydrogen atom or a C 1  to C 3  alkyl radical. 
     The reaction conditions of this process promote the formation (k 1 ) of alkanediols and alkenes while limiting the formation of cyclic ethers, i.e. (k 2 ). ##STR2## wherein R 1 , R 2 , R 3  and R 4  are the same as defined herein before. 
     The solid acidic mixed oxide catalysts include any solid acidic silica-alumina composition, e.g. any solid acidic oxide mixture of silica and alumina, i.e. SiO 2 .Al 2  O 3 . The oxides of silica and alumina can be present in any proportion. Illustratively, the weight percent of presently preferred SiO 2 .Al 2  O 3  mixed oxides are within the range of from about 90:10 to about 70:30. 
     Surface area parameters of the mixed oxides measured in square meters per gram (m 2  /g) are not critical to the efficacy of the process. Generally effective SiO 2 .Al 2  O 3  surface areas are within the range of from about 50 to about 400 m 2  /g. 
     Temperature parameters relative to optimum conversion of t-alkylether-alkanol to alkanediol without the formation of cyclic ethers are temperatures within the range of from about 100°-140°, preferably from about 125° to 135° C. 
     Pressure parameters are not critical to the efficacy of the process. Accordingly the process can be carried out under widely varying pressures, e.g. sub-, super- or atmospheric pressures. 
     In a presently preferred embodiment of this process where 4-t-butylether-n-butan-1-ol is de-alkylated to form 1,4-butanediol at least 60, preferably about 75-80, mole percent of 4-t-butylether-n-butan-1-ol is de-alkylated to form 1,4-butanediol while the minimum ultimate selectivity of the process provides a butanediol-tetrahydrofuran product selectivity (Sel.) of at least about 95 percent based upon the following calculation. 
    
    
     Examples I-IV illustrate the best mode of practicing this invention. 
     FIRST GENERAL PROCEDURE 
     A series of de-alkylation reactions were carried out involving the conversion of 4-t-butylether-n-butan-1-ol to 1,4butanediol using a solid acidic SiO 2 .Al 2  O 3  catalyst. 4.0 Grams 98+% of 4-t-butylether-n-butan-1-ol and 0.2 grams of SiO 2 .Al 2  O 3  blanketed with N 2  were heated in a 25 ml flask fitted with a reflux condenser and a magnetic stirrer. The evolved gas isobutylene containing some entrained THF and/or t-butanol, escaping from the reflux condenser was collected at -78° C. and quantified by standard vacuum line techniques at the conclusion of the reaction. 
     The liquid phase reaction product constituents were monitored employing standard G.P.C. techniques throughout the course of the reactions. The mass balance of liquid and gasous products of Examples I-IV was within the range of from 95-99%. A summary of the liquid phase reaction medium constitutes, e.g. tetrahydrofuran (THF), t-butanol, 1,4-di-t-butoxybutane, 4-t-butylether-n-butan-1-ol, and 1,4-butanediol correlated with elapsed reaction time period is reported in Tables I-IV. 
     
                                           TABLE 1                                 
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EXAMPLE I                                                                 
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Silica-Alumina.sup.1 Catalyzed De-alkylation of 4-t-butylether-n-butan-1-o
l at 120° C.                                                       
               1,4-di-t-                                                  
                       4-t-butylether-n-                                  
Time/hr                                                                   
     THF.sup.2                                                            
         t-butanol.sup.2                                                  
               butoxybutane.sup.2                                         
                       butan-1-ol.sup.2                                   
                               1,4-butanediol.sup.2                       
                                       Av Rate.sup.3                      
                                            Selectivity.sup.4             
                                                  Conversion.sup.5        
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1    .95 1.05  5.3     63.4    29.2    39.7 --    29.2                    
2    .67 .73   5.6     52.6    40.4    27.4 --    40.4                    
3    .38 .42   4.7     46.4    48.0    21.9 --    48.0                    
4    .52 .60   3.7     36.9    58.2    19.9 --    58.2                    
5.5  .95 1.05  3.1     28.8    66.1    16.4 98.6  66.1                    
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 .sup.1 GraceDavison grade 98025 silicaalumina pellets crushed to a fine  
 powder. Typical analysis of commercial Davidson siliconalumina is set out
 hereafter in Example I  Table 1 Addendum.                                
 .sup.2 Mole percent.                                                     
 .sup.3 Av Rate = moles of 4t-butylether-n-butan-1-ol converted to        
 1,4butanediol/kg cat. × total elapsed reaction time period.        
 ##STR3##                                                                 
 *NOTE:                                                                   
 selectivity values at interim time periods are not reported since any THF
 contained in condensed isobutylene gas was only analyzed at conclusion of
 run.)                                                                    
 ##STR4##                                                                 
 -  -                                                                     
 
    
     
         Addendum                                                                  
Grace-Davison - SiO.sub.2 · Al.sub.2 O.sub.3 Typical Analysis    
Grade                    980-25                                           
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CHEMICAL PROPERTIES                                                       
                         2.5                                              
Silica, SiO.sub.2        74.5                                             
Alumina, Al.sub.2 O.sub.3                                                 
                         25.0                                             
Sodium, Na.sub.2 O       0.05                                             
Sulfate, SO.sub.4        0.30                                             
Iron, Fe                 0.03                                             
Calcium, CaO             0.05                                             
Chlorine, Cl             &lt;.01                                             
PHYSICAL                                                                  
Surface Area, m.sup.2 /gm                                                 
                         325                                              
Pore Volume, cc/gm       0.45                                             
Packed Density, gm/cc    0.73                                             
Avg. Crush Strength, lbs.                                                 
                         15(3/16&#34;)                                        
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     Examples V-XI including the Second General Procedure illustrate attempts to de-alkylate--in the presence of other acidic substances--tertiary alkylether-alkanols. These examples are not a part of this invention and are furnished for the purpose of contrasting the efficacy of the acidic materials used as catalyst candidates with the efficacy of the silicaalumina catalysts used in Examples I-IV. 
     SECOND GENERAL PROCEDURE 
     A series of de-alkylation reactions were tried involving attempts to convert 4-t-butylether-n-butan-1-ol to 1,4-butanediol using other acidic candidates, e.g. SiO 2 , Al 2  O 3 , MgO, WO 3 .Al 2  O 3 , Acidic Clay, Acid Ion Exchange Resin, and Aqueous H 3  PO 4  catalyst. 8.6 grams--except in Example IX where 6.0 grams was used--of a mixture containing, on a mole percent basis, 4-t-butylether-n-butan-1-ol and 3-t-butylether-2-methylpropan-1-ol plus 0.20 grams of a catalyst candidate were blanketed with N 2  and heated in a 25 ml flask fitted with a reflux condenser and a magnetic stirrer. The liquid phase reaction product constituents were monitored employing standard V.P.C. techniques throughout the course of the reactions. A summary of the liquid phase reaction medium constituents, e.g. tetrahydrofuran (THF), 3-t-butylether-2-methyl-propan-1-ol, 2-methyl-1,3-propanediol, 4-t-butylether-n-butan-1-ol, and 1,4-butanediol correlated with elapsed reaction time period is reported in Examples V-XI. 
     
                                           TABLE 2                                 
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EXAMPLE II                                                                
Silica-Alumina.sup.1 Catalyzed De-alkylation of 4-t-butylether-n-butan-1-o
l at 125° C.                                                       
               1,4-di-t-                                                  
                       4-t-butylether-n-                                  
Time/hr                                                                   
     THF.sup.2                                                            
         t-butanol.sup.2                                                  
               butoxybutane.sup.2                                         
                       butan-1-ol.sup.2                                   
                               1,4-butanediol.sup.2                       
                                       Av Rate.sup.3                      
                                             Selectivity.sup.4            
                                                   Conversion.sup.5       
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1    .52 1.6   6.3     54.9    36.6    50.1  --    36.6                   
2    .67 1.5   4.5     36.6    56.7    38.8  --    56.7                   
3    .55 1.2   4.2     31.4    62.6    28.6  --    62.6                   
4    .48 1.2   3.3     25.4    69.7    23.9  98.5.sup.6                   
                                                   69.7                   
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 Footnotes .sup.1, .sup.2, .sup.3, .sup.4 and .sup.5 = same as in Example 
  Table 1.                                                                
 .sup.6 = total THF 0.48 (lig. phase) + 0.57 (gas phase) = 1.05 mole %    
 
    
     
                                           TABLE 3                                 
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EXAMPLE III                                                               
Silica-Alumina.sup.1 Catalyzed De-alkylation of 4-t-butylether-n-butan-1-o
l at 130° C.                                                       
Time/hr                                                                   
     THR.sup.2                                                            
         1,4-di-t-butoxybutane.sup.2                                      
                    4-t-butylether-n-butan-1-ol                           
                                 1,4-butanediol                           
                                        Av Rate.sup.3                     
                                             Selectivity.sup.4            
                                                   Conversion.sup.5       
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1    1.2 5.0        40.9         53.4   73.1 --    53.4                   
2    1.7 3.1        26.9         68.3   46.7 --    68.3                   
3    2.0 1.7        19.0         77.3   35.3 --    77.3                   
4    2.4 0.7        11.8         85.1   29.1 --    85.1                   
5.5  0.5 0.6        11.4         87.5   21.7 97.2.sup.6                   
                                                   87.5                   
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 Footnotes .sup.1, .sup.2, .sup.3, .sup.4, and .sup.5 = same as Example I 
 Table 1.                                                                 
 .sup.6 = total THF 0.5 (lig. phase) + 2.0 (gas phase) = 2.5 mole %       
 
    
     
                                           TABLE 4                                 
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EXAMPLE IV                                                                
Silica-Alumina.sup.1 Catalyzed De-alkylation of 4-t-butylether-n-butan-1-o
l at 135° C.                                                       
Time/hr                                                                   
     THF.sup.2                                                            
         1,4-di-t-butoxybutane.sup.2                                      
                    4-t-butylether-n-butan-1-ol.sup.2                     
                                 1,4-butanediol.sup.2                     
                                        Av Rate.sup.3                     
                                             Selectivity.sup.4            
                                                   Conversion.sup.5       
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0.5  0.7 5.9        49.9         43.5   119.2                             
                                             --    43.5                   
1.0  0.9 4.4        39.3         60.5   82.9 --    60.5                   
1.5  2.4 3.5        27.7         66.4   60.6 --    66.4                   
2.0  2.0 2.4        22.4         73.2   50.1 --    73.2                   
3.0  2.6 1.1        12.0         84.3   38.5 95.4.sup.6                   
                                                    84.23                 
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 Footnotes .sup.1, .sup.2, .sup.3, .sup.4, and .sup.5 = same as Example I 
 Table 1.                                                                 
 .sup.6 = total THF 2.6 (lig. phase) + 2.5 (gas phase) = 4.1 mole %       
 
    
     
                                           TABLE 5                                 
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EXAMPLES V-XI                                                             
Attempted Acid Catalyzed De-alkylation of Tertiary-Alkylether-Alkanols    
                          3-t-          4-t-                              
                          butylether-   butylether-  1,4-  Con-           
Ex. Catalyst                                                              
           Temperature                                                    
                  Time/   2-methyl-                                       
                                 2-methyl-1,3-                            
                                        n-     1,4-  butanediol           
                                                           ver-           
No. Candidate                                                             
           Range  hr  THF.sup.1                                           
                          propan-1-ol.sup.1                               
                                 propanediol.sup.1                        
                                        butan-1-ol.sup.1                  
                                               butanediol.sup.1           
                                                     Selectivity.sup.2    
                                                           sion.sup.3     
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V   SiO.sub.2                                                             
           190°-192° C.                                     
                  0   --  13.8   --     81.7   --    --    --             
                  2.5 0   13.8   0      81.7   0     --    --             
VI  Al.sub.2 O.sub.3                                                      
           172°-175° C.                                     
                  0   --  13.8   --     81.7   --    --    --             
                  5.5  1.3                                                
                          13.8   trace  78.6   trace n.d..sup.4           
                                                           trace          
VII MgO    192°-195° C.                                     
                  0   0   16.2   --     74.2   --    --    --             
                  3   trace                                               
                          16.2   trace  74.2   trace n.d..sup.4           
                                                           trace          
VIII                                                                      
    WO.sub.3 . Al.sub.2 O.sub.3                                           
           171°  C.                                                
                  --  --  16.2   --     74.2   --    --    --             
                  4.5 trace                                               
                          15.3   0.92   70.6   3.60  n.d..sup.4           
                                                           trace          
IX  Acidic  95° C.                                                 
                  0   --  13.9   --     86.1   --    --    --             
    Clay          6.5  9.8                                                
                          0.15   14.2    0.9   75.1  88.5  87.2           
X   Acid Ion      0   --  13.6   --     86.4   --    --    --             
    Exchange                                                              
           95° C.                                                  
                  9   30.5                                                
                          6.4    8.2    24.1   30.8  50.2  35.7           
    Resin                                                                 
XI  Aq . H.sub.3 PO.sub.4                                                 
           145° C.                                                 
                  0   --  13.6   --     86.4   --    --    --             
                  5   12.1                                                
                          0.1    12.9    0.4   74.5  86.0  86.2           
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 .sup.1 Mole percent.                                                     
 ##STR5##                                                                 
 ##STR6##                                                                 
 *(NOTE no analysis of isobutylene effluent for trace amounts of other    
 constituents.)                                                           
 
    
     A brief description of the catalyst candidates of Examples V-X including their commercial sources, is set out in the following Table 5 Addendum: 
     
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Example                                                                   
No.               Catalyst Candidate Description - Table 5                
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                  Addendum                                                
V    SiO.sub.2    J.T. Baker Co. - Silicic Acid, 88% SiO.sub.2 . 12%      
                  H.sub.2 O                                               
VI   Al.sub.2 O.sub.3                                                     
                  Alcoa-Activated Alumina                                 
VII  MgO          Fisher-Magnesium Oxide, Certified Reagent Grade         
VIII WO.sub.3 . Al.sub.2 O.sub.3                                          
                  Harshaw Tungsten Oxide-W-0801 90% WO.sub.3 . 10%        
                  Al.sub.2 O.sub.3                                        
IX   Acidic Clay  Girdler KSF Montmorillonite Clay - a natural            
                  SiO.sub.2 . Al.sub.2 O.sub.3 clay treated with H.sub.2  
                  SO.sub.4                                                
X    Acid Ion Exchange Resin                                              
                  Dow Chemical Co. Dowex(TM) 50WX8 a strong-              
                  ly acidic sulfonated polystyrene resin                  
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     In general, the utility of this process provides for the de-alkylation of a tertiary-alkylether-alkanol of Formula (I) to form 1,4-alkanediols while at least 60, preferably 75-80, mole percent of tertiary-alkylether-alkanol is de-alkylated to form 1,4-alkanediols while the minimum ultimate selectivity of the process provides a 1,4-alkanediol/1,4-alkanediol plus cyclic ether product selectivity of at least about 95 percent. 
     The expression tertiary-alkylether-alkanol as used herein generically describes aliphatic and cycloaliphatic hydroxyethers commonly referred to as tertiary-alkoxy-alkanols, tertiary-cycloalkoxy-alkanols and tertiary-alkcycloalkoxy-alkanols. Illustratively as used herein the expressions: 
     tertiary-alkylether-alkanol also means tertiary-alkoxy-alkanol 
     4-t-butylether-n-butan-1-ol also means 4-t-butoxy-n-butan-1-ol 
     3-t-butylether-2-methyl-propan-1-ol also means 3-t-butoxy-2-methylpropan-1-ol 
     Accordingly, as will be apparent to those skilled in the art, either of the above forms of chemical nomenclature can be used interchangeably throughout the specification as well as the claims.