Reaction of imines of fluorinated ketones and perfluoronitriles with carbon tetrachloride. A new route to polyfluorinated imines

Journal of Fluorine Chemistry 109 (2001) 123±128

Reaction of imines of ¯uorinated ketones and per¯uoronitriles with carbon tetrachloride. A new route to poly¯uorinated imines$ Viacheslav A. Petrov* DuPont Central Research and Development, Experimental Station, P.O. Box 80328, Wilmington, DE 19880-0328, USA Received 16 November 2000; accepted 6 February 2001

Abstract The reaction of imines of hexa¯uoroacetone and 1,3-dichlorotetra¯uoroacetone with CCl4 catalyzed by AlCl3 leads to the formation of (XCF2)2CClN=CCl2 in moderate to high yield. The treatment of these imines with alkali metal ¯uoride in a polar solvent results in high yield formation of (XCF2)2C=NCF3 along with isomeric (XCF2)2CFN=CF2. A reaction of nitriles of per¯uorinated carboxylic acids with CCl4 proceeds with the formation of a mixture of two products: RfCCl2N=CCl2 and RfCCl2N=CClRf. Imidoyl chloride C3F7CCl2N=CClC3F7 isolated in the reaction of C3F7CN/CCl4 is converted into per¯uoro-5-azanonene-4 by reaction with HF. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Imine of hexa¯uoroacetone; aluminium chloride; Poly¯uorinated imines

1. Introduction There are several methods of the preparation poly¯uorinated imines and imidoyl ¯uorides. Radical addition of CF2=N±X (X: Cl or Br) to ¯uoroole®ns [1,2] and pyrolysis of oxazetidines [3] are commonly used for the preparation of terminal azaalkanes. Reductive de¯uorination of per¯uorinated piperidines [4,5] provides access to azacyclohexenes; cleavage of per¯uorinated tertiary amines under the action of AlCl3 followed by ¯uorination [6,7], along with the reaction of per¯uorinated tertiary and secondary amines with SbF5 [8±10] gives access to per¯uorinated imidoyl ¯uorides containing internal C=N bond. Unfortunately, most of the methods are often based on exotic starting materials that limit the synthetic utility of those reactions. This paper reports a new approach to the synthesis of poly¯uorinated azaalkenes based on a catalytic reaction of poly¯uorinated imines and nitriles with carbon tetrachloride followed by ¯uorination step. Imine of hexa¯uoroacetone (1) rapidly reacts with AlCl3 in carbon tetrachloride as a solvent at ambient temperature. Slightly exothermic reaction between excess of 1 and aluminum chloride suspended in CCl4 results in formation of a clear homogeneous solution.

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Further heating of the reaction mixture for several hours at atmospheric pressure results in evolution of HCl and a high yield formation of a new material, i.e. imidoyl chloride 2 (see Table 1).

Structure 2 is assigned to the product of the reaction based on combined data of NMR and IR spectroscopy (see Table 2). 13 C NMR spectrum of 2 provides direct evidence in support of the structure, since the signal of carbon of the C=N group appears at 139.62 ppm as a singlet in the case of isomeric structure (2a), that signal is expected to have the corresponding splitting pattern due to interaction with six ¯uorines. Imine of 1,3-dichloro-tetra¯uoroacetone (3) in reaction with CCl4/AlCl3 behaves similarly to 1, producing imidoyl chloride 4 in high yield.

Interestingly, both reactions are catalytic and rapidly proceed in the presence of 5±15 mol% of AlCl3. However, when the reaction of excess of 1 and AlCl3 is carried out at

0022-1139/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 1 1 3 9 ( 0 1 ) 0 0 3 6 1 - X

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V.A. Petrov / Journal of Fluorine Chemistry 109 (2001) 123±128

Table 1 Ratio of reactants and reaction conditions Entry no.

Reactants (mol)

Temperature (8C)

Time (h)

Products (yield, %)

1 2 3 4 5 6 7 8 9 10

CCl4 (1), 1 (0.542), AlCl3 (0.152) CCl4 (0.622), 3 (0.076), AlCl3 (0.083) CCl4 (0.22), 1 (0.07), AlCl3 (0.02) 2 (0.09), KF (0.55), sulfolane (100 ml) 3 (0.029), CsF (0.1), sulfolane (100 ml) CCl4 (0.29), 9 (0.05), AlCl3 (0.023) CCl4 (0.215), 11 (0.03), AlCl3 (0.005) 13b (0.04), HF (0.35) CCl4 (0.67), 12 (0.1), AlCl3 (0.038) CCl4 (0.1), C6F5CN (0.05), AlCl3 (0.023)

100 100 25 25±50 25±50 120 100 100 100 120

12 12 2 6 12 7 16 16 12 12

2 (82)a 4 (76)a 5 (89)b 6a,b (92)c 7a,b (79)d 10a (60), 10b (38)e 13a (60), 13b (38)e 15 (63)f 14a (40), 14b (27)e Complex mixture; major components are C6F5CN, C6F5CCl3, C6ClF4CCl3, C6ClF4CN

a

Yield on converted imine at 90% conversion. Product is contaminated with small amount of AlCl3 (1±3%). c Mixture of isomers, ratio 6a:6b Ð 70:30. d Mixture of isomers, ratio 7a:7b Ð 75:25. e Calculated based on NMR and GC data. f After treatment of the reaction mixture with NaF. b

ambient temperature complex 5 is isolated after removal of carbon tetrachloride solvent.

Compound 5 is a white solid, stable at ambient temperature in the absence of moisture. 19 F NMR spectrum of 5 exhibits a broad signal between ±65 and 70 ppm. 13 C spectrum of 5 contains two multiplets: a quartet at 115 ppm (J ˆ 300 Hz) and a heptet around 164 ppm (J ˆ 29 Hz). The presence of a strong broad signals around 12 ppm in 1 H spectrum and two sharp bands (2987 and 3054 cm 1) in the IR spectrum of 5 (assigned to N±H group) are also supportive of the structure 5. It should also be noted that the formation of a similar complex between 1 and BF3 has been reported earlier [11]. A reaction of imidoyl chloride 2 with dry KF in a polar solvent leads to high yield formation of a mixture of isomeric azaalkenes 6a and 6b reported to exist in equilibrium [12]. Imidoyl chloride 4 in reaction with CsF is also converted into a mixture of azaalkenes 7a and 7b.

The suggested mechanism of the reaction of imines 1 and 3 with CCl4 is similar to the one proposed for the reaction of poly¯uorinated anilines with CCl4 leading to the formation

of ArfN=CCl2 [13±15] and includes reversible formation of trichloromethyl cation [16] as a ®rst step, followed by recombination of CCl3‡ with the corresponding imine, producing intermediate 8. This compound is rapidly isomerized under the action of AlCl3 into the ®nal product (Scheme 1).

Scheme 1.

Although nitriles of per¯uorinated carboxylic acid, reactive towards CCl4/AlCl3 mixture at elevated temperature, this process proceeds differently. For example, the reaction of C2F5CN (9) with excess carbon tetrachloride in the

presence of AlCl3 catalyst at 1208C gives a mixture of almost equal amount of two new compounds identi®ed as imines 10a and 10b (see Table 1).

Table 2 Yields and analytical data of new compounds b.p. (8C/mm Hg)

2 4 5 7a 7b 9a 9b 13a

112.5±113 81±82/30 ± ± ± 130±135 135±145 130±145

13b

151±153

14a

103/26

14b

a

137±138/44

Mixture of 9a and 9b 80:20. Mixture of 9a and 9b 40:60. c Mixture of 13a and 13b 70:30. d Mixture of 14a and 14b 10:90. b

Purity (%)

NMR (d, ppm; J, Hz)

IR (cm 1)

MS, found (calc.)

>98 >98 >97 ± ± 80a 60b 70c

19

1660(s), 1767(w) 1677(s) 3054(m) 2987(m) 1807(m), 1724(m) 1807(m), 1724(m) 1652(s) 1689(w) 1641(s)

m/e 280.8984 (280.9000) [M‡, C4Cl3F6N‡] m/e 277.8683 (277.8721) [C4Cl4F4N‡, (M±Cl)‡] ± m/e 229.9559 (229.9607) [C4ClF7N‡, (M±Cl)‡] m/e 229.9588 (229.9607) [C4ClF7N‡, (M±Cl)‡] m/e 261.8979 (261.9016) [C4Cl3F5N‡, (M±Cl)‡] m/e 345.9199 (345.9248), [C6Cl2F10N‡, (M±Cl)‡] m/e 312 [C5Cl3F7N‡, (M±Cl)‡, for Cl35 isotop]

1682(w)

m/e 446 [C8Cl2F14N‡, (M±Cl)‡, for Cl35 isotop]

90d >95 >95

13

F: 73.72(s) C: 79.84(sept, 34) 120.00(q, 281), 139.62(s) F: 59.62(s) 13 C: 88.89(pent, 29) 128.40(t, 307), 137.29(s) 19 F: 67.11(br.s) 1 H: 11(br.s) 13 C: 115.38(q, 300), 164.46(hept, 29) 19 F: 56.82(3F,t, 12), 58.32(2F,m), 59.24(2F,t, 12) 19 F: 32.50(1F,m), 42.80(1F,m), 61 to 65(4F,m), 140.44(1F,m) 19 F: 76.06(3F,s), 118.14(2F,s) 19 F: 76.36(3F,s), 81.87(3F,s), 114.66(2F,s), 118.40(2F,s) 19 F: 81.62(3F,t), 114.02(2F,m), 120.79(2F,m), 13 C: 90.93(t, 32, ±CCl2±), 144.41(s, ±N=CCl2) 19 F: 80.81(3F,t), 81.82(3F,t), 111.94(2F, q), 114.02(2F,m), 120.79(2F,m), 125.78(2F,s), 13 C: 90.93(t, 32, ±CCl2±), 148.68(t, 33, ±N=CCl) 81.54(3F,t), 113.35(2F,m), 116.62(2F,m), 122.19(6F,m), 122.39(2F,m), 126.67(2F,m); 13 C: 91.10(t, 31, ±CCl2±), 144.12(s, ±N=CCl2) 81.47(6F,m), 110.94(2F,m), 113.33(2F,m), 116.75(2F,m), 121.28(6F,m), 121.57(2F,m), 123.30(4F,m), 122.40(6F,m), 126.72(4F,m); 13 C: 91.03(t, 31, ±CCl2±), 148.55(t, 34 ±N=CCl±) 19

1644(s) 1687(w)

V.A. Petrov / Journal of Fluorine Chemistry 109 (2001) 123±128

Compound no.

125

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V.A. Petrov / Journal of Fluorine Chemistry 109 (2001) 123±128

The reaction of nitriles 11 and 12 with CCl4/AlCl3 mixture proceeds similarly, producing a mixture of imidoyl chlorides 13a,b and 14a,b, respectively.

On the other hand, the interaction of penta¯uorobenzonitrile with CCl4 carried out under similar conditions leads to the formation of a complex mixture, in which C6F5CCl3,

C6ClF4CCl3 and C6ClF4CN are identi®ed as major components by GC/MS. Compounds 10a,b, 13a,b and 14a,b are separated by distillation, and the corresponding imidoyl chloride with a purity of 90±98% is isolated in each case (see Tables 1 and 2). IR spectra of chlorides 10a, 13a and 14a exhibit a strong band around 1640 cm 1 while the spectra of imines 10b, 13b and 14b contain a less intense band around 1680 cm 1. This is consistent with the presence of a terminal and internal C=N bond in all compounds. 13 C NMR spectra of 14a and 14b provide direct evidence in support of the proposed structures. Although rather complicated, both

Scheme 2.

V.A. Petrov / Journal of Fluorine Chemistry 109 (2001) 123±128

spectra contain a triplet around 90 ppm (J ˆ 31 Hz) assigned to carbon of the dichloromethyl group (±CF2± CCl2 ±N±). However, the spectrum of 14a contains a singlet at 144 ppm (±CCl2±N=CCl2 fragment) in contrast to the spectra of 14b that exhibits a triplet at 148 ppm (Jˆ34 Hz, ±CF2±CCl=N±) which has the corresponding multiplicity due to an interaction with two ¯uorines in adjacent chlorodi¯uoromethyl group. Mass-spectra of 10a,b and 13a,b exhibit in each case an intense signal for the [M±Cl]‡ fragment. Masses corresponding fragments observed in HRMS (GC/MS) for compounds 10a,b are in good agreement with the calculated values (see Table 2). Conversion of compound 13b to known imidoyl ¯uoride 15 [17] by reaction with HF followed by treatment with NaF [18] provides an additional proof for the correct assignment of the structure. Formation of compounds 10, 13 and 14 can be explained as a result of a Ritter type reaction between nitrile and CCl4. The electrophilic attack of trichloromethyl cation on nitrogen of nitrile leads to adduct 15a through the intermediate formation of the cation 15 (Scheme 2). Further reaction between AlCl3 and 15a leads to the formation of carbocation 16. It can react with a second mole of nitrile. 1,5-Migration of chlorine through six-member ring transition state 17 may result in ``retro-ene'' type reaction leading to formation of ClCN and cation 18.1 Addition of chloride anion by 18 leads to the formation of a second reaction product Ð imidoyl chloride 9b or 13b or 14b, respectively. 2. Conclusion A two-step process involving AlCl3 catalyzed reaction between carbon tetrachloride and either imines of poly¯uorinated ketones or nitriles of per¯uorinated carboxylic acids leads to formation of corresponding imidoyl chlorides in moderate to high yield. Imidoyl chlorides can be ¯uorinated either by reaction with metal ¯uoride or HF. The combination of two processes provides a simple relatively inexpensive route to per¯uorinated imines of general formula RfN=CXRf (X: F or Rf). 3. Experimental Proton, ¯uorine and carbon NMR spectra are recorded on a QE-300 (General Electric, 200 MHz) or Brucker DRX-400 (400.5524, 376.8485 and 75.47 MHz, respectively) instruments using TMS and CFCl3 as an internal standard and chloroform-d or acetone-d6 as a lock solvent. IR spectra are recorded in a liquid ®lm on a Perkin-Elmer 1600 FT spectrometer. Fluorinated nitriles (PCR), carbon tetrachloride are 1 The step of the mechanism including concerted 1.5-shift of chlorine was suggested by reviewer.

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commercially available and used without further puri®cation. Anhydrous AlCl3 (Aldrich, 99%) was stored and handled inside of glove box. Imines 2 and 4 are prepared using the method reported in [19]. Compounds 6a,b [12] are identi®ed by comparison of NMR and IR data with the reported values, and compound 15 by comparison with an authentic sample [16]. 3.1. Reaction of imines or nitriles with CCl4 (a typical experiment) A mixture of CCl4 (0.3±1 mol), a nitrogen-containing substrate (0.1±0.3 mol) and AlCl3 is heated in a closed vessel at 70±1208C for 8±16 h. The reaction mixture is diluted with cold water; the organic layer was separated, dried over MgSO4 and distilled. Reaction conditions, yields, spectroscopic and analytical data of products are given in Tables 1 and 2. 3.2. Preparation of imidoyl fluorides 6a,b and 7a,b The corresponding imidoyl chloride (0.03±0.1 mol) is added dropwise to a mixture of dry metal ¯uoride (KF or CsF, 0.1±0.55 mol) and 100 ml of dry sulfolane at 25±358C. The reaction mixture is agitated at ambient temperature for 6±12 h. The product is transferred into a cold trap under vacuum and distilled. Reaction conditions, yields, spectroscopic and analytical data of products are given in Tables 1 and 2. 3.3. Fluorination of 13b A mixture of 0.04 mol of 13b and 0.35 mol of anhydrous HF is kept in a shaker tube at 1008C for 16 h. The reaction vessel is vented and the reaction mixture is transferred into a ¯ask containing 15 g of sodium ¯uoride. After 1 h at ambient temperature the product is transferred into a cold trap under vacuum. The product (11.7 g) with a purity of 93% is isolated and identi®ed as 15. Acknowledgements Author wish to thank Dr. B.E. Smart and Dr. C.G. Krespan and Dr. V.V. Grushin for discussions, reviewer for valuable suggestions and B. Vekker for help in manuscript preparation. References [1] B.A. O'Brien, D.D. DesMarteau, J. Org. Chem. 49 (1984) 1467. [2] Y.Y. Zheng, D.D. DesMarteau, J. Org. Chem. 48 (1983) 4844. [3] I.L. Knunyants, A.F. Gontar', Soviet Sci. Rev. Sec. B. Chem. Rev. 5 (1984) 219; and references therein (a review of the literature up to 1983 on synthesis and reactions of perfluorinated imines). [4] R.E. Banks, K. Mullen, W.J. Nicholson, C. Oppenheim, A. Prakash, J. Chem. Soc., Perkin Trans. 1 1 (1972) 1098.

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[5] R.E. Banks, M.G. Barlow, M. Nickkho-Amiry, J. Fluorine Chem. 14 (1979) 383. [6] S.V. Sokolov, S.A. Mazalov, Dokl. AN USSR. 162 (1965) 1071. [7] V.S. Plashkin, L.N. Pushkina, S.V. Sokolov, Zh. Org. Khim. 10 (1973) 1215. [8] V.A. Petrov, V.K. Kunanets, K.N. Makarov, L.S. German, Izv AN SSSR. Ser. Khim. (1989) 646. [9] V.A. Petrov, V.K. Kunanets, B.A. Kvasov, M.V. Galakhov, K.N. Makarov, L.S. German, AN SSSR. Ser. Khim. (1989) 122. [10] V.A. Petrov, V.K. Grinevskaya, E.I. Mysov, M.V. Galakhov, K.N. Makarov, L.S. German, Izv. AN SSSR. Ser. Khim. (1990) 1616. [11] K. Niedenzu, K. Blick, C.D. Miller, Avail. CFSTI. US Clearinghouse Fed. Sci. Tech. Inform. AD (1969) 9.

[12] R.L. Kirchmeier, U.I. Lassoers, J.M. Shreeve, Inorg. Chem. 14 (1975) 592. [13] T.I. Savchenko, T.D. Petrova, I.V. Kolesnikova, V.E. Platonov, Izv AN SSSR. Ser. Khim. (1980) 1230. [14] T.I. Savchenko, T.D. Petrova, I.V. Kolesnikova, V.E. Platonov, J. Fluor. Chem. 22 (1983) 439. [15] T.D. Petrova, V.E. Platonov, Uspekhi Khimii 56 (1987) 1973. [16] G.A. Olah, L. Heiliger, G.K.S. Prakash, J. Am. Chem. Soc. 111 (1989) 8020. [17] V.A. Petrov, G.G. Belen'kii, L.S. German, Izv. AN SSSR. Ser. Khim. (1985) 1934. [18] A.F. Gontar, E.N. Glotov, A.A. Rybachev, I.L. Knunyants, Izv. AN SSSR. Ser. Khim. (1984) 1874. [19] W.J. Middleton, K.G. Krespan, J. Org. Chem. 30 (1965) 1398.