Process for preparing nitric acid esters of 1,1,2,2-tetrahydro-perfluoro-alkanols
United States Patent Schuierer et al.  
 [ PROCESS FOR PREPARING NITRIC ACID ESTERS OF l.l.2.Z-TETRAI-IYDRO-PERFLUORO- ALKANOLS [75| Inventors: Erich Schuierer; Klaus Ulm, both of Burghausen; Siegfried Rebsdat, Altotting; Ignaz Wimmer, Unternau, Post Office Neuotting, all of Germany [731 Assignec: Hoechst Aktiengcsellschaft, Frankfurt, Main. Germany l22| Filed: Mar. 4, I974 l2l| Appl. No.: 447,984  
 I62} Division of Ser. No. l50.770. June 7 l97l Pat.  
 HUI Foreign Application Priority Data June It). 1970 German 2028459 [52] CS. Cl. 260/467 [51] Int. Cl. C07c 77/02 [5H] Field of Search 260/467 Apr. 1,1975  
 [56] References Cited OTHER PUBLICATIONS Boschan et al., Chem. Reviews, Vol. 55, pp. 485 to 489 1955 Primary E.\&#39;aminer-Leland A. Sebastian Attorney, Agent, or Firm-Connolly and Hutz i5 7] ABSTRACT Z-Perfluoroalkyl ethanols are obtained by reacting 2- perfluoro-alkyl ethyliodides with at least the two-fold molar amount of nitric acid of about 70 to 98 percent strength and hydrogenating the intermediates, which are the nitrates of the desired ethanols. The products are useful as starting materials for the production of hydrophobic and oleophobic textile finishing agents. e.g. the polymer acrylates and methacrylates of said Z-perfluoroalkyl-ethanols.  
 9 Claims, No Drawings PROCESS FOR PREPARING NITRIC ACID ESTERS OF l.l.2.Z-TETRAHYDRO-PERFLUORO-ALKANOLS This application is a division of application Ser. No. [50,770 filed June 7. 1971, now U.S. Pat. No. 3.824.296.  
  The object ofthe invention is a process for the manufacture of fluorine-containing alcohols of the general formula in which R, represents a preferably straight chain pertluoroalkyl radical having 4 to lo, in particular 4 to 10. carbon atoms. from fluorine-containing alkyl-iodides of the general formula R CH LCH L in which R, has the same meaning as given above, which comprises transforming in a first step the fluorine-containing iodides with nitric acid having a strength of about 7(1-98 percent. in a molar ratio of at least 1 2, preferably about 1 3 up to l 8, especially I 4&#39;. at temperatures in the range of about -l00C, into the corresponding nitrates of the general formula and hydrogenating them in a second step in the presence of the usual hydrogenating catalysts at temperatures of about 5()-l()()C and pressures of about 0-100 atmospheres gauge to obtain the desired alcohols.  
  l-luotine-containing alcohols of the above indicated constitution have been obtained hitherto according to the process described in German Patent 1 214 660 by reaction of the corresponding iodides of the general formula R,.CH- .CH- .l with oleum and following hydrolysis of the fluorine-alkylsulfate esters of the general formula R,-.(H- .CH. ,.O.SO;,H. This process has the disadvantage that a considerable amount of the fluoroalkyl-iodides used always passes into difficulty hydroli/able di-esters of sulfuric acid of the general formula tR,.(H:.(H. .SO and that. in addition, the monotlnoro-alkyl-sulfatc esters of the general formula R,.(H. ..CH:.O.S();,H in the case of R, zC F are saponlfied essentially slower in aqueous sulfuric acid at ltlll( than the corresponding compound having shorter iluoro-alkyl radicals.  
  According to the process described in U.S. Pat. No. .1401130. fluoro-alkyl-iodides are reacted with silverand mercury salts of nitric acid and the resulting nitrates are then converted by means of lithiumaluminium hydride or ammonium hydrogeno-sulfide into the corresponding fluorine-containing alcohols. Hovtev er. for the manufacture on an industrial scale lhis process cannot be used owing to it high expenditure of s-il\er or mercury nitrate and due to the necessit ofrecovering the silver and mercury from the metal halides formed during reaction.  
  The process of the invention is carried out in two stages which it is suitable to effect separately. In the first stage the corresponding iodide (R,.CH .CH I) is reacted with nitric acid under formation of the corresponding nitrate (R,.CH- .CH- ..O.NO and iodine (iodate or iodine pentmide. respectively, in the case of an e\ces of nitric acid): ZR CH CHJ 4 H.\&#39;(), ZR .(H- ..CH .O.NO l. 2NO +2H O In the second stage the ester (R;.CH- .CH .O.NO is reduced to the corresponding alcohol (R .CH .CH .OH) by means of hydrogen under pressure in the presence of the usual hydrogenation catalysts such as platinum, palladium, cobalt or nickel contacts on the usual carriers such as silica gel, charcoal, bariumsulfate, pummice stone or calcium carbonate, in particular, however, Raney-nickel, to yield the corresponding alcohol (R .CH .CH .OH) and ammonia.  
  Saponification with the aid of aqueous lyes is practically not realizable, because, in addition of a number of not identifiable products, the olefin (R;.CH CH corresponding to each iodide is formed.  
  The starting materials for the process ofthe invention are fluoro-alkyl-iodides having a fluoro-alkyl radical of 4-16, especially 4-10 carbon atoms. It is of advantage to use mixtures of such iodides which are obtainable, for example by telomerization of lower perfluoroolefins to perfluoroalkyl-iodides and addition of ethylene in known manner. For the reaction in the first stage, nitric acid is used in a concentration of about -98 percent, preferably about -98 percent, and the operation is carried out at temperatures of about 20100C, preferably 60-90C. In the case of compounds containing a perfluoro-alkyl radical in the range ofC F or C F temperatures in the range of between 60-80C should be maintained in view of the high volatility of the substances. The reaction sets in already at room temperature; for completing the reaction, however, it is recommended to raise the temperature at the end of the reaction to at least 6065C.  
  The molar proportion of fluorine-containing alkyliodide to nitric acid may amount to about 1 2 to l 8 and more, preferably 1 3 to l 8, and should suitably and preferably be 1 4.  
  The reaction may be carried out by two ways, either by introducing first the nitric acid and then adding, portionwise, the fluorine-containing alkyl-iodide or by first introducing the iodide in molten state and then continuously adding dropwise the nitric acid.  
  A preferred embodiment of the process of the invention is described hereinafter.  
  The total amount of fluoro-alkyl-iodide is introduced in molten state and the nitric acid is added dropwise, while stirringv The reaction starts rapidly. The nitrate formed as the reaction product is soluble in the mixture of the reaction partners. Iodine in elementary form is formed as a secondary product. The major part of it sublimates at the chosen reaction temperature and can be easily recovered after separation in a suitable cooling apparatus. After removal of the major part of iodine, water is added to the reaction mixture and the nitrate is separated from the aqueous phase. It is then dissolved in inert, low molecular weight, halogencontaining hydrocarbons, preferably in chloroform or methylene chloride. Residual fluorine-containing nitrates can also be recovered from the aqueous phase by means of chloroform of methylene chloride. The organic phase is still contaminated by low amounts of iodine and nitric acid. It is washed with water until it is free from acid and the iodine still contained therein as impurity is removed by pumping at about normal pressure or under reduced pressure. The fluorinecontaining nitrates are obtained in the form of weakly pink coloured oils or solids (see Table I). They are not decomposed by water or excess of nitric acid; with compounds having a Rf radical of C F up to C F they can be easily purified by distillation.  
  If the reaction is carried out by introducing at first the nitric acid and then adding dropwise the fluorinecontaining iodide. the iodide separated during the by The fluorine-containing nitrates prepared according to the present intention are characterized by the following data:  
 Table l Compound Boiling Melting Refracti e point point lndex c,F,,c. H,o\o. FUJwlPC/l] mm Hg .H,().\&#39;() 72-77%) ll mm Hg ca.2ll( L327 (J-,4 .H.o.\&#39;O IUU IOSK&#39;IHI mm Hg 34.5% (&#39;.,.F ..C .H.0No 74C Comparatiw Tests C,,F, .C. .H,o.\&#39;o, +1 7:-77(. |t mm Hg CAIfZU C 1.32s (,,F, .H,O\&#39;() 49-5XCHI mm Hg -2t)( I314 drolysis passes immediately into an iodate or iodineprepared according to Example 6 from pentoxide due to oxidation by the excess of nitric acid. C F C H OH and HNO tl-) prepared according to The fluorine-containing nitrate is precipitated also in Example 7 from C,;F C- ,H OH and HNO this case by the addition of water. The aqueous phase The fluorine-containing alcohols prepared in this then contains the iodine in th f rm of i d C a id R6 manner are valuable starting materials in the manufaceovery of the iodine can be effected. if desired, in ture of oleophobic and hydrophobic agents and of surkn n manner y iHIFOdUCIiOfl 0f 2&#39; factants By the reaction with unsaturated organic When carrying out the second process step -C- th K acids. especially acrylic acid, acrylic acid and their eshydrogenation of the fluorinecontaining nitr re terforming derivatives. valuable esters are obtained Sl&#39;lOUld be taken that the latter is PTCVlOUSly&#39; washed 115 which after polymerization yield i] and wuteprepelling far as possible to become free of nitric acid; purificaagents f il i tion by distillati n is not abso utely necessary The following Examples illustrate the invention:  
  The hydrogenation is carried out with a view to pracm tical application in a pressure range of about to 100 EXAMPLE l atmospheres ga g pref ra y I0 atmospheres a. l l() g (1.71 moles) of 98 percent nitric acid were gauge- A5 Catalyst Runey&#39;nlckel is preferably used 11 added dropwise at 65C. while stirring. within 2.5 quantity of about 5-l() percent by weight. preferably hours. to 160 g (0.428 mole) of n-C F CH CH I. After 6-8 percent by weight. referred to he luor ecompletion of the dropwise addition. the whole was containing nitrate used. As reaction mediums, lower alkanols. especially methanol, are suitable. The reaction is effected advantageously in an autoclave made of stainless steel or an autoclave lined with silver. The reaction temperature is in the range of 50-l00C, preferably at 709()C. After termination of the hydrogen consumption pressure in the autoclave is then released and the reaction mixture obtained is freed from catalyst by filtration. The solvent is then removed by distillation and the fluorine-containing alkanols obtained are then purified by distillation under reduced pressure In principle. the hydrogenation with Raney-nickel in methanol also possible without excess pressure at about 60C; however. the time needed therefor is three to four times longer for about 30-40 g of fluorinecontaining nitrate.  
  The proof of the structure of the fluorine-containing nitrate prepared can be made by comparative tests and with the use of the infrared absorption spectrums. If. for example. C.;F,;;CH .CH- .OH (prepared according to German Patent 1 21-1 660 is esterified according to known methods on the one hand with 98 percent nitric acid (cf. Example 6) and on the other hand with nitrous acid (from NaNO and H 50 cf. Example 7). two different liquid products are obtained:  
 C F CH CH OH HNO 7; C..F ;;CH .CH- ONO: C,;F,;,CH .CH .OH HNO- C.;F,:,CH .CH- O.NO  
 of which the first with regard to its characteristical data (cf. Table l) and its infrared spectrum is identical with the reaction product obtained from C.;F,;,CH- .(H .l and HNO further stirred for 8 hours at C. The iodine set free during the reaction sublimated from the reaction mixture. deposited in a water-cooled finger within the gas space of the flask and was removed repeatedly and mechanically from this finger The reaction mixture was allowed to cool and then combined with 100 ml of water. The organic phase which was separating was taken up in 100 ml of chloroform; the aqueous phase was extracted several times with a small amount of chloroform and the chloroform phases were combined. in order to remove any present acid. the chloroform solutions were washed several times with small amounts of water. The organic phase was then subjected to distillation. At first chloroform and iodine which had been dragged in were removed by distillation up to a sump temperature of l20C. The remaining residue was passed over under reduced pressure. 1 19 g of reddish n-C,F,,C- .H,ONO were obtained at 5060C/l2 mm Hg were obtained. This corresponded to a yield of 90 percent (analysis: N calculated 4.5 percent for C H F,,NO and found 4.3 percent).  
  b.6124 g (0.202 mole) of n-C F .,C H ONO- together with l()() g of methanol and 6 g of Raney nickel were introduced in an autoclave of stainless steel. After having rinsed several times with N and H H was introduced at a pressure of 30 atmospheres gauge and the pressure vessel was then heated to C. When this temperature was reached. hydrogenation was effected at a H; pressure of5() atmospheres gauge (duration 2-4 hours). After cooling and release of the pressure any residues of the catalyst were removed from the reaction mixture by filtration and then the methanol was eliminated by distillation. A brownish liquid remained behind from which 48.5 g i 91 percent of the theory of n-C.F,.(&#39;- -H,OH were recovered by distillation at 3-76C/50 Torr. (Analysis: OH number calculated for C.,H -,l-},O 212&#39;. OH number-found 211).  
 EXAMPLE 2 a. 145 ml (3.38 moles) of 98 percent of nitric acid were added dropwise at 80C. while stirring, in the course of 3 hours to 400 g (0.845 mole) of n- (.,F,;,C- H l. The mixture was then further stirred for 8 hours at 85C. The elimination of the iodine was carried out as described in Example 1. The fluorinecontaining nitrate was separated from the mixture by the addition of 200 ml of water. The further working up was likewise effected as described in Example I. The liquid reddish crude product obtained after evaporation of the solvent could be purified by distillation under reduced pressure. 314 g i 91 percent of the theory of pure n-C F C H ONO were obtained at 73-77(/11 mm Hg.  
  (Analysis: N calculated for C H F NO found 3.409  
  b. 280 g (0.685 mole) of n-C F C H ONO together with 520g of methanol and g of Raney-nickel were introduced into an autoclave having a capacity of 2.5 liters. After having rinsed several times with N and hydrogen. hydrogen was introduced with a pressure of atmospheres gauge and the autoclave was heated within 2 hours to 90C. When this temperature was reached the pressure of hydrogen was increased to atmospheres gauge. The autoclave was then shaken at 90C for 6 hours. the pressure of hydrogen being maintaiiicd constant. The hydrogen consumed was replenished from a pressure bomb. The pressure vessel was then cooled and emptied. Any residues of catalyst were remoi cd from the mixture by filtration over folding filters. After removal ofthe methanol used as the solvent, the desired product was obtained at first in the form of a fluorine-containing. crude and alcohol. This alcohol could be purified by distillation under reduced pressure i boiling point 93C/35 mm). The yield was 239 g. corresponding to 96 percent of the theory, referred to the nitrate used initially. According to gas chromatographical tests. the t1uorine-containing alcohol was found to be identical with the product described in German Patent l 214 660. Example 1. (purity 99.4%).  
 EXAMPLE 3 .i. 120 ml of98 percent nitric acid (2.80 moles) were added dropwise. at 85C, while stirring, within 3 hours, to 400 g (0.697 mole) of n-C, F,;C- H l. and the mixture was then stirred for 8 hours at 90C. Working up of the reaction mixture was effected as described in Example 1 and 2. After evaporation of the solvent of reddish. solid. crude product remained behind which could be purified by distillation under reduced pressure at 10()-l05C/10 mm. Yield 340 g z 93 percent of the theory (iodine content 20.1%  
  iAnalysis: N calculated for C ,H.,F NO,, 2.7; N found 2.51&#39;)  
  h. 318 g (0.625 mole) of n-C F ;C-,H ONO together with 830 g of methanol and 21 g of Raney-nickel were filled into an autoclave having a capacity of 2.5 liters and being lined with silver. After several rinsings with and H at first H with a pressure of 30 atmospheres gauge was introduced and the whole was heated within 2 hours to 90C. When this temperature was reached the pressure of hydrogen was increased to&#39;SO atmospheres gauge and the autoclave was shaken for 6 hours at constant hydrogen pressure. Workin&#39;g&#39;up&#39; of the hydrogenation mixture was then carried out as described 5 under Example 2. 273 g 94 percent of the theory of n-CgF C H OH (boiling point 95-96C/l 1 mm) were obtained. According to gas chromatographical tests, the product was found to be identical with the product obtained according to German Patent 1 214 660, Example 2, n-C F C H OH (purity 99.9%).  
  (Analysis: OH number calculated for C H F O 121: OH number found 120) EXAMPLE 4 a. 400 g of n-C F C Hfl (0.594 mole) were combined at 85C, while stirring, within 3 hours with 102 ml of 98 percent nitric acid (2.38 moles). The whole was then stirred for 8 hours at 85C. Working up of the reaction product was effected as described in Examples 2 and 3. After removal of the solvent, 322 g 89.2&#39;percent of the theory of crude n-C F2|C2H4&#39;ONO2. remained behind.  
  b. 322 g of the crude n-C ,F- ;,C H ONO (washed with water until free from acid) so prepared together with 950 g of methanol and 18 g of Raney-nickel were introduced into an autoclave having a capacity of 2.5 liters. After rinsing with N and H hydrogen having a pressure of 30 atmospheres gauge was introduced and the pressure vessel was heated to 90C. The hydrogen pressure was then increased to 50 atmospheres gauge.- Aftcr 4 hours the hydrogenation was completed and the reaction mixture was worked up as described in Examples 2 and 3. 284 g 95 percent of the theory of n- Hg) were obtained.  
  (Analysis: OH number, calculated for C&#39;, H -,F ,O 99.5, OH number found 100) v EXAMPLE 5 4( Example 3a was repeated in varying the concentration of the nitric acid used withini the range&#39;of 98 percent and the reaction temperature from --90C.&#39;  
 The results are compiled in the following Table 2:  
  Reaction temperature (&#34;C Concentration of HNO in /1 no reaction about 50% 9 l &#39;7! 9371 90% EXAMPLE 6 EXAMPLE 7 Comparative test (preparation of n-C F C H ONO):  
  10.0 g (0.0275 mole) of n-C..F &#39;,C- H,OH were combined. while stirring. at 4-5C at first with 2.3 g of NaNO; and then dropwise with 3.2 g of 50 percent H 50 The whole was then stirred for 5 hours at 4-5C. The nitrous acid ester was then separated with the aid of 30 ml of distilled H O. washed and distilled (boiling point 49-58C/l l mm l.  
 EXAMPLE 8 A mixture of 27.5 g (0.054 mole) of n- C FiflCHg- ONO- 75 g of pure methanol and 2 g of Raney-nickel was reacted at 60C at a pressure of l atmosphere for l4 hours with gaseous hydrogen. The yield of n-C, F, C- H OH was [9.0g i 76 percent of the theory.  
 EXAMPLE 9 Example 3b was repeated in varying the temperature during hydrogenation within the range of from 6090C (cf. Table 3). The reaction time was 6 hours.  
 Table 3 Reaction temperature 0 60 84 7() 45 Xtl ll 90 a4 EXA M PLE 10 Example 3a was repeated using a molar proportion of n-C F C Hfl to 9871 HNO of l J 3. ln contradistinction to Example 3a. the reaction mixture contains nonreacted n-C F C- Hd. at the rate of 7 percent.  
 EXAMPLE ll (all by means of 200 ml of H 0 and taken up in CH Cl The organic solution was washed until it was free from acid. dried and the solvent was removed by distillation. The fluorine-containing crude ester remaining behind was purified by distillation. The yield was 76 g 5 86 percent of the theory of n-C F C- H ONO We claim:  
  1. In a process for the preparation of an ester of the formula in which R is pertluoroalkyl of4 16 carbon atoms from an iodide of the formula in which R, is as defined above. the improvement comprising. reacting said iodide with at least the three-fold molar amount of nitric acid of about 85 to about 98 percent strength at a temperature of about to about 100C.  
  2. The process as claimed in claim I, in which iodides are reacted, the R, moiety of which is n-perfluoroalkyl of 4 to 16 carbon atoms.  
  3. The process as claimed in claim 1, in which iodides are reacted. the R; moiety of which is perfluoroalkyl of 4 to l0 carbon atoms.  
  4. The process as claimed in claim 1. in which the reaction temperature is about 60 to about 90C.  
  5. The process as claimed in claim I, in which the molar ratio of iodide to nitric acid is in the range of about 1:3 to about 1:8.  
  6. The process as claimed in claim 1, in which the molar ratio of iodide to nitric acid is in the range of about l:4.  
  7. The process as claimed in claim 1, in which the concentration of the nitric acid is about to about 98 percent.  
  8. The process as claimed in claim 1, in which the nitric acid is dropped to the liquid or molten iodide.  
  9. The process as claimed in claim 1, in which iodide is added portionwise to the reaction vessel precharged with nitric acid.