Perfluorinated cyclic hemiketals, corresponding perfluorodiketones and process for preparing them

Abstract: Perfluorinated cyclic hemiketals of formula: where n = 1 - 6, m = 2 -3, and their corresponding perfluoridiketones. The latter are prepared by means of perfluoroalkylation reaction of diacyl fluorides with perfluoroalkyl-trialkyl silanes. The perfluorodiketones can be then reacted with H₂O in order to obtain said cyclic hemiketals.

Description: The present invention relates to perfluorinated cyclic hemiketals, to the corresponding perfluorodiketones and to a process for preparing them. Patent application EP-A-330,058 describes a process for transferring perfluoroalkyl radicals onto carbonyl substrates (aldehydes or ketones) by reacting the latter with a perfluoroalkyl-trimethyl silane, using an alkali metal fluoride as a catalyst. From such reaction, a silyl ether is obtained, which, by hydrolysis, provides the corresponding alcohol. The process is utilizable only on hydrogenated or partially fluorinated substrates. According to Journal of Fluorine Chemistry, 42 (1989), 371 - 387 (see especially pages 375 and 376) perfluorodiketones are prepared from the corresponding dialkylester precursor by an in situ lithium iodine exchange reaction allowing the intermediately formed perfluoroalkyllithium to react with the ester substrate so as to replace in the ester precursor the alkoxy groups by perfluoroalkyl groups. According to the method disclosed in US-A-3 185 734 perfluorodiketones are prepared by reacting a perfluoroalkanedioic acid fluoride, e. g. perfluoroglutaryl fluoride, with certain perfluoroalkylenes in the presence of a fluoride ion source. US-A-3 379 765 discloses the preparation of perfluorodiketones by reacting certain chlorinated aliphatic ketones with inorganic metal fluorides such as potassium fluoride. The Applicant has now surprisingly found that the perfluoroalkylation reaction with perfluoroalkyl-trialkyl silanes can be conducted on perfluoro-diacyl fluorides, with production of new perfluorodiketones, and that these diketones react with water to form surprisingly stable new cyclic hemiketals. Thus, an object of the present invention are the perfluorinated cyclic hemiketals of formula: where n is an integer from 1 to 6, m is 2 or 3. A second object of the present invention is a process for preparing the perfluorodiketones of formula: where n is an integer from 1 to 6, m is 2 or 3, which consists in reacting a perfluoro-diacyl fluoride of formula: with a perfluoroalkyl-trialkyl silane of formula: R₃Si-C n F 2n+1 (IV) where R is an alkyl having 1 to 4 carbon atoms, in the presence of an alkali metal or quaternary ammonium fluoride MF, in an anhydrous aprotic polar solvent. Still a further object of the present invention is represented by a process for preparing the cyclic hemiketals of formula (I), which consists in reacting the corresponding perfluorodiketone of formula (II) with H₂O. In formulas (I) and (II) n is preferably an integer from 1 to 4, more preferably it is 1 or 2. The diacyl fluorides of formula (III) are known products and are preparable, for example, according to what is described in J.Am.Chem.Soc., 91 , 1310 (1969) or in patent DE-3,032,471. Also the perfluoroalkyl-trialkyl silanes of formula (IV) are known in themselves and can be prepared according to the methods described in the already cited patent application EP-A-330,058 or in Tetrahedron Letters, 25 , 2195-2198 (1984). Fluoride MF is, for example, a Na, K, Cs or Rb fluoride. Preferably it is KF. As an alternative, it is possible to utilize a tetraalkyl ammonium fluoride, provided it is soluble enough in the solvent utilized as a reaction medium. An example is represented by the tetramethyl ammonium fluoride, which is preparable for example according to what is described in J.Am.Chem.Soc., 112 , 7619 (1990). As already mentioned above, the reaction is carried out in an anhydrous aprotic polar solvent. Any solvent of this type is suitable, provided that fluoride MF is at least partially soluble in it. There are utilizable, for example, the nitriles, such as acetonitrile and benzonitrile, the ethers, such as diethylether, dioxane, tetrahydrofuran, glymes (e.g. 2-methoxyethylether), or mixtures thereof. Preferably the reaction is effected in benzonitrile. The reaction temperature is usually maintained approximately from -45° to +45°C, preferably from -15° to +25°C, approximately. The pressure is not a critical parameter. The reaction is generally conducted at atmospheric or subatmospheric pressure, but, if necessary, pressures ranging from 1 to 10 atm. can be employed. As regards the reagents, the perfluoroalkyl-trialkyl silane/diacyl fluoride molar ratio generally ranges from 2.0:1.0 to 4.0:1.0, preferably from 2.0:1.0 to 2.6:1.0, while the fluoride MF/perfluoroalkyl-trialkyl silane molar ratio generally ranges from 1.0:1.0 to 4.0:1.0, preferably from 1.0:1.0 to 1.8:1.0 On conclusion of the reaction, the diketone can be isolated by suction by means of a vacuum pump, under slight heating of the solid obtained as a reaction product. Generally, a mild heating to a temperature in the range of from 50° to 90°C is sufficient. The resulting diketone can be reacted with H₂O in order to prepare the cyclic hemiketal. Such reaction does not require particular conditions: the diketone promptly reacts with water at temperatures around room temperature, i.e., for example, from 10° to 50°C. As an alternative, the reaction with water can be effected in situ, i.e. without separating the diketone from the reaction mixture obtained in consequence of the perfluoroalkylation. The same reaction conditions specified hereinabove are employable. The perfluorinated cyclic hemiketals of the present invention can be utilized as monomers in polycondensation reactions for the synthesis of fluorinated polymers (polyurethanes, polyesters, etc.). The perfluorodiketones are useful as solvents and as intermediates for the synthesis of the abovesaid hemiketals,as already described herein. The following examples are given for illustrative purposes and are by no way to be considered as a limitation of the scope of the present invention. EXAMPLE 1 Into a reactor consisting of a Pyrex R 250 ml flask, a magnetic stirrer, inlet and outlet connections connected with a vacuum line and a line for the inlet of liquids, there were introduced 0.77 g (13.0 mmols) of KF, which had been previously molten and ground,in a nitrogen atmosphere. The reactor was then evacuated and 3.0 ml of anhydrous benzonitrile were introduced thereinto by injection through the inlet line for liquids . From the reactor, cooled to -196°C with liquid nitrogen, the residual traces of air were sucked. Into the reactor there were transferred under vacuum and condensed 2.99 mmols of perfluoroglutaryl fluoride FOC-(CF₂)₃-COF and 6.33 mmols of (CH₃)₃Si-CF₃. The reactor was gradually heated to 0°C by immersion into a water-ice bath. Stirring was started as soon as the reaction mixture was molten (m.p. of C₆H₅CN = -13°C). The reactor was gradually brought from 0° to 20°C. After a 17-hour stirring, the volatile matters were removed by suction through the vacuum line (45 minutes at 23°C): no presence of diketone was observed in the recovered products. The reactor was then heated to about 70°C and suction was carried on for 2 hours. 2.41 mmols of CF₃CO-(CF₂)₃-COCF₃ were obtained (yield: 80.7%, based on FOC-(CF₂)₃-COF). The obtained product was characterized through the IR, ¹⁹F-NMR and mass spectra: IR : position and intensity of the main bands (m = medium, vs = very strong, w = weak) (p = 2 torr.): 1790 (sharp, m), 1249 (vs), 1194 (vs), 1013 (m), 910 (m), 842 (m), 732 (m), 642 (w) [cm⁻¹]. ¹⁹F-NMR : CF₃ A COCF₂ B CF₂ C CF₂ B COCF₃ A (CDCl₃, 20°C): A -75,1 (6F), B -118,1 (4F), C -121,8 (2F). MASS SPECTRUM : main peaks : EI : 247 (M-COCF₃)⁺, 197 (M-CF₂COCF₃)⁺, 147 (CF₃COCF₂)⁺, 100 (CF₂CF₂)⁺, 97 (CF₃CO)⁺, 69 (CF₃)⁺, 50 (CF₂)⁺; CI : 345 (MH)⁺ , 247 (MH-H-COCF₃)⁺ , 231 (MH-H-O-COCF₃)⁺ , 131 (MH-H-O-CF₂CF₂COCF₃)⁺, 100 (CF₂CF₂)⁺. The boiling point, determined according to the Sivoloboff method, was 78°C/750 mm Hg. EXAMPLE 2 Utilizing the same reactor and following the same modalities described in example 1, 0.84 g (14 mmols) of KF were introduced into the reactor. The reactor was evacuated, 2.5 ml of anhydrous benzonitrile were injected through the inlet line for liquids. After cooling to -196°C, the residual air traces were sucked. Through the vacuum line, 3.03 mmols of perfluorosuccinyl fluoride FOC-(CF₂)₂-COF and 6.50 mmols of (CH₃)₃Si-CF₃ were introduced into the reactor and condensed. The reactor was gradually heated to 0°C in a water-ice bath and stirring was started. The temperature was then gradually brought to 20°C (18 hours). The volatile matters were removed by means of suction (45 minutes at 23°C). No presence of diketone was observed in the recovered products. Suction was continued for 1.5 hours while heating the reactor to about 70°C. 1.60 mmols of CF₃CO-(CF₂)₂-COCF₃ were obtained. (Yield: 52.8%, based on FOC-(CF₂)₂-COF). The obtained product was characterized through the IR and ¹⁹F-NMR spectra: IR : position and intensity of the main bands (m = medium, s = strong, vs = very strong, w = weak) (p = 4 torr.): 1785 (sharp, m), 1311 (s), 1287 (vs), 1246 (vs), 1200 (vs), 1090 (m), 1050 (m), 909 (m), 842 (s), 724 (vs) [cm⁻¹]. ¹⁹F-NMR : CF₃ A COCF₂ B CF₂ B COCF₃ A (CDCl₃, 20°C): A -75,1 (6F), B -119,5 (4F). The boiling point, determined according to the Sivoloboff method, was equal to 59°-61°C/742 mm Hg. EXAMPLE 3 9 µl of H₂O (0.50 mmols) were injected into a 50 ml flask equipped with inlet and outlet connections connected with a vacuum line. The flask was cooled to -196°C with liquid nitrogen and evacuated. Through the vacuum line, 0.56 mmols of CF₃CO-(CF₂)₃-COCF₃ were condensed in the flask. The flask was allowed to heat up to room temperature. A white solid product of formula: was obtained; the yield was nearly quantitative. The obtained product was characterized through IR and 19F -NMR spectra : IR : position and intensity of the main bands (m = medium, s = strong, vs = very strong, w = weak): 3568 (m), 3252 (broad, m), 1654 (broad, w), 1637 (broad,w), 1301 (sharp, m), 1253 (s), 1234 (s), 1187 (s), 1161 (s), 1062 (s), 919 (s), 837 (m), 744 (m), 684 (m), 646 (w), 629 (w) [cm⁻¹]. ¹⁹F-NMR : CF₃ A C'OHO'CF₂ B CF₂ C CF₂ B C'OHCF₃ A (CD₃CN, 20°C): A -80.0 (6F), B -126.5;-129.8 (4F, AB patt J AB =266.6 Hz, v o d=631.8 Hz), C -119.3;-140.5 (2F, AB patt J AB =275.2 Hz, v o d=3978.6 Hz)). The melting point was equal to 61°-63°C. EXAMPLE 4 Following the same procedure described in example 3, 9 µl of H₂O (0.50 mmols) were reacted with 0.53 mmols of CF₃CO-(CF₂)₂-COCF₃. A white solid product of formula: was obtained; the yield was nearly quantitative. The obtained product was characterized through IR and ¹⁹F-NMR spectra: IR : position and intensity of the main bands (m = medium, s = strong, vs = very strong, w = weak): 3656 (m), 3578 (m), 3223 (broad, m), 1612 (broad, w ), 1326 (m), 1217 (vs), 1170 (s), 1130 (m), 1030 ( s), 943 (m), 860 (m), 763 (w), 743 (m), 710 (w) [cm⁻¹]. ¹⁹F-NMR : CF₃ A C'OHO'CF₂ B CF₂ B C'OHCF₃ A (CD₃CN, 20°C): it is a mixture of diastereoisomers. Diastereoisomer 1 (60%): A -80.3 (6F), B -120.6;-132.1 (4F, AB patt J AB =246.3 Hz). Diastereoisomer 2 (40%): A -79.9 (6F), B -126.0;-130.2 (4F, AB patt J AB =244.0 Hz).

Claims: Perfluorinated cyclic hemiketals of formula: where n is an integer ranging from 1 to 6, m is 2 or 3. A process for preparing perfluoro-diketones of formula: where n is an integer ranging from 1 to 6, m is 2 or 3, which consists in reacting a perfluoro-diacyl fluoride of formula: with a perfluoroalkyl-trialkyl silane of formula: R₃Si-C n F 2n+1 (IV) where R is an alkyl having 1 to 4 carbon atoms, in the presence of an alkali metal or quaternary ammonium fluoride MF, in an anhydrous aprotic polar solvent. The process of claim 2, wherein the reaction temperature ranges from -45° to +45°C. The process of one or more of claims 2 to 3, wherein said fluoride is KF. The process of one or more of claims 2 to 4, wherein the solvent is selected from ethers and nitriles or mixtures thereof. The process of claim 5, wherein the solvent is benzonitrile. A process for preparing the cyclic hemiketals of formula (I) defined as in claim 1 which consists in reacting the corresponding perfluoro-diketone of formula (II) defined as in Claim 2 with H₂O.

Inventors: ANDERSON JOHN D, DESMARTEAU DARRY D CLEMSON UNI, NAVARRINI WALTER, ANDERSON, JOHN D., DESMARTEAU, DARRY D., CLEMSON UNIVERSITY, NAVARRINI, WALTER
Applicants: AUSIMONT SPA, AUSIMONT S.P.A.
Application year: 1992
Main classification: C07D307
IPC codes: C07C45, C07C49, C07B61, C07D307, B01J27, C07D309