3,3-Bis(trifluoromethyl)oxiranes. Synthesis and Amine Reactivity James R. Griffith* and Jacques G. O'Rear Naval Research Laboratory. Washington. D. C. 20375
Three new epoxides of the 3,3-bis(trifluoromethyl)oxirane type were synthesized via the reaction of diazo intermediates with hexafluoroacetone. Second-order rate constants were then measured for the reaction of this type of fluorinated epoxide with benzylamine and dibutylamine in order to assess the amine reactivities. The fluorinated groups consistently depressed the rate constants and a strong steric factor was also in evidence.
Fluorinated epoxy resins are the key intermediates for new types of practical organic coatings and plastics which have fluorocarbon properties and convenient processing characteristics. In order to obtain the highest levels of fluorocarbon content in such resins, it is necessary to place fluorine on the resin molecule in the near vicinity of an epoxy ring. However, this entails synthesis difficulties and is likely to affect the convenient reaction rate characteristics of the resins adversely. Epoxy resins of the 3,3bis(trifluoromethy1)oxirane variety promise materials of very high fluorocarbon content, but little has been found regarding syntheses of multifunctional compounds of this type nor how rapidly they may be expected to cure. The reactivity of epoxides which are substituted on one of the ring carbon atoms with two perhalogenated methyl groups is the subject of some interest in the literature. Simmons and Wiley (1960) reported that 2,2-bis(chlorodifluoromethy1)oxirane was heated to 225" with phosphorus pentafluoride, treated with hot ethanolic hydrochloric acid, 6 N nitric acid, concentrated sulfuric acid a t IOO", and 50% potassium hydroxide solution without effect. However, Gambaryan and Simonyan (1964) called this result "inexplicable" in view of their observation that benzylamine reacts readily with 2-carbethoxy-3,3-bis(trifluoromethy1)oxirane. Discussion We have reported previously (Reines, e t al., 1970, 1971) on the amine reactivities of a number of fluorinated epoxides of the glycidyl ether type. The same kinetic technique has now been used to determine rate constants for similar reactions of bis(trifluoromethy1)oxiranes which were synthesized uia diazo intermediates. The interesting preparative reaction (eq 1) appears to be quite versatile, CF,.
+
N,f
since we have used it to synthesize a difunctional compound (111) and one with a perfluorinated R group (IV) as 0
CzH50C
- C,H-C 0' 'CF3
II
I
CF >3C-, CF3
CH
0'
0
CH-C \
Ill 148
'-3
0' 'CF3
CF3(CFz), C H - C \
\'O
p
3
CF3
IV
Ind. Eng. Chem., Prod. Res. Develop., Vol. 13,No. 2, 1974
well. These epoxides react with amines (eq 2) to produce
It+
'' 0
CHzNHz+
QH-J -3
1
O C H I N H
(2)
/ \
OH
CF3
v amphoteric products, and this is consistent only with ring opening in the direction shown (Gambaryan and Simonyan, 1964). The reaction occurs in a solution of tert-amyl alcohol in a manner that is second order when there are equal initial concentrations of reactants. Kinetic results are summarized in Table I. There is no evidence, either kinetic or analytical, that the bulky secondary amines such as V react with a second molecule of epoxide under these conditions. Experimental Section 2-Carbethoxy-3,3-bis( trifluoromethy1)oxirane (I).This known compound was prepared from glycine ethyl ester hydrochloride via the diazo intermediate (Gambaryan, et al., 1964; Womack and Nelson, 1955). It was purified to analytical quality by fractionation on a Nester-Faust auto annular Teflon spinning-band still, bp 76" (65 mm); T I ~ O D 1.337 [lit. bp 74-75' (65 mm); TI"D 1.3371. 2-Phenyl-3,3-bis(trifluoromethyl)oxirane (11). In a flask equipped with a Dry Ice-alcohol condenser were placed 53.7 g (0.30 mol) of N-nitroso-N-benzylurea and 450 ml of tetrahydrofuran. An external cooling bath was applied to maintain the temperature a t -20", and as the suspended nitroso urea was stirred magnetically, 15.6 g (0.30 mol) of lithium ethoxide was added in small portions during 1 hr. A deep orange color developed as phenyldiazomethane formed, and when this reaction was completed, gaseous hexafluoroacetone was passed into the cold solution for 1 hr, during which the color was discharged. Enough hexafluoroacetone was introduced thereafter to maintain a slow reflux from the condenser for an additional hour. Fractional distillation of the final solution gave a 21.0 g (27.3%) yield of 11: bp 85" (50 mm); n 2 0 ~1.4062. Anal. Calcd for C1&$60: c, 46.89; H , 2.36; F, 44.50. Found: C, 47.13; H , 2.58; F, 44.55. 1,4 -Bi s [ 3,s-bis( trifluoromethyl)oxirane-2-yl]benzene (111). The method of Murray and Trozzolo (1964) was used to prepare 7.0 g of 1,4-bis(cu-diazomethyl)benzene from terephthalaldehyde ~ ~ the i a dihydrazone. This deep red compound was dissolved in 200 ml of benzene contained in a single-necked flask and cooled on an ice bath while a stream of gaseous hexafluoroacetone (200 ml/min)
Table I. Reaction Rates of Bis(trifluoromethy1)oxiranes with Amines.
Oxirane
Amine
Temp, "Ch
peak. Plots of reciprocal concentration us. time were linear, and rate constants were calculated from the slopes.
105khlc
Results The data of Table I indicate a rather complex set of in5.62 fluences which affect the reactivities of epoxides of the 50.0 6.85 bis( trifluoromethy1)oxirane type. The presence of fluoro50.0 57.0 50.0 -0.2 carbon on the ring apparently strengthens the carbon60.0 0.3 oxygen bond of the carbon atom to which it is attached, and thus IV is the least reactive with benzylamine. How5All reactants and solvents were of analytical purity. ever, the influence of the adjacent carbonyl group of I ac* Bath temperature controlled to &O.0loC. In 1. mol-' sec -l. tivates the same ring carbon atom to nucleophilic attack by the amine. The factors which control the direction and rate of epoxy ring opening have been the subject of extenwas passed through the solution for 0.5 hr. Distillation of the product solution gave 6.0 g (30%) 111: bp 115-116" (20 sive study. McBee, et al. (1956),list studies which dealt with ( a ) relative electron densities at the two epoxy carmm). An analytical sample was prepared by gas chromabon atoms, (b) allylic or hyperconjugative stabilization of tographic treatment of the product: mp 95".Anal. Calcd a carbonium ion, (c) substituent inductive effects, (d) for C14H16F1202: C, 38.73;H, 1.39; F, 52.51.Found: C, complexing or solvent effects, (e) steric factors such as the 38.71;H, 1.41;F, 52.38. degree of substitution of the epoxide, (f) size of the sub2-(1 -Heptafluoropropyl)-3,3-bis(trifluoromethyl)oxirstituent on the ring, and (g) the size of the attacking ane (IV). 2,2,3,3,4,4,4-Heptafluorobutylamine was pregroup. The present data are too limited for an attempt a t pared in 65% yield by reduction of the amide (Sander, complete consistency in a theoretical delineation of the 1964). The amine, 4.0 g (0.020 mol) was diazotized and 2.42 g (0.011 mol) of 2,2.3,3,4,4,4-heptafluorodiazobutane rate control factors, and this would be beyond the present intent of seeking practical cure systems for heavily fluowas isolated by the vacuum transfer procedure of Fields rinated epoxy resins. However, the lack of reaction of I1 and Haszeldine ( 1964). Hexafluoroacetone was then with dibutylamine is probably due to steric hindrance of passed through the neat diazo compound contained in a the phenyl group to approach of the bulky secondary test tube fitted with a gas inlet tube and a Dry Ice conamine. Since I1 reacts at a moderate rate with benzylamdenser, first at -60", then at 0",and finally at room temine, and 1 is only about one-tenth as reactive with dibuperature. A total of 4 ml of condensed hexafluoroacetone tylamine as with benzylamine. the steric factor seems to was used to produce the crude IV, 4.1 g (5570, based on account for this observed difference adequately. amine). A characterization sample was obtained by gas chromatography, bp 70" (760 mm). Anal. Calcd for Literature Cited C7HF130: C, 24.15;H, 0.29;F, 70.96.Found: C, 24.31;H, Fields, R . , Hazeldine, R N . , J . Chem. Soc.. 1881 (1964). 0.29;F,70.81. Gambaryan, N. P.. Simonyan. L. A , , I z v Akad Nauk SSSR. Ser. Khim.. N - (2-Hydroxyl - 1- p h e n y l - 3,3,3 - tr if1u o r o 2- tr ifluo8, 1529 (1964) Gambaryan, N. P . , Simonyan, L. A . , Knunyants. I . L.. Dokl. Akad. Nauk romethylpropy1)benzylamine (V). A solution of 0.640 g SSSR. 155 14). 833 119641 (0.0025mol) II and 0.268 g (0.0025mol) benzylamine in 5 McBee, E T Hathaway C E , Robert, C W , J Amer Chem Soc 78, ml tert-amyl alcohol was allowed to react at 60" in a 3851 119561 Murray, k. W.: Trorzolo. J. Org Chem.. 29, 1268 (1964). closed container for 3 weeks. All volatile materials were Reines, S. A . , Griffith, J. R . . 0 Rear, J. G., J. Org. Chem.. 35, 2772 then stripped from the product solution on a rotary evapo(1970). Reines, S A , , Griffith. J. R . . O'Rear. J. G., J. Org. Chem.. 36, 1209 rator to give 0.83 g (91%) crude V which was crystallized (1971) from methanol-water to give an analytical sample, mp Sander, M . , Monatsh.. 95 (2),608 (1964). 66".Anal. Calcd for C17H1JFBNO: C, 56.20;H, 4.16; F, Simmons, H . E., Wiley. D W . , J . Amer. Chem. Soc.. 82, 2288 (1960) Womack, E. B . , Nelson. A B.. "Organic Syntheses," Collect. Vol. I l l , p 31.38;N, 3.86.Found: C, 56.06;H, 4.18;F,31.43;N, 3.76. 392, Wiley, New York, N. Y., 1955. Rate Measurements. The kinetic procedure employed Receiced for reuieu, December 17, 1973 has been described previously (Reines, et al., 1970). In Accepted M a r c h 12, 1974 brief, microliter samples were extracted from the reaction vessel through a rubber septum periodically during a reacT h i s work was reported in Vol. 32, S o . 1, pp 413-419, D i v i s i o n ot' tion and were injected into a gas chromatograph which Organic Coatings a n d Plastics Chemistry, 163rd N a t i o n a l M e e t i n g of the American Chemical Society. Boston, Mass., A p r i l 1972. was suitably prepared to isolate and measure a desired I1 I1 I I IV I1
Benzyl Benzyl Dibutyl Benzyl Benzyl Dibutyl
50.0 60.0
3.28
-
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