J. C. KAUERAND A. K. SCHNEIDER
852
would be no reason-except for the somewhat questionable interpretation of acidity function relationships-to believe that the mechanism of decarbonylation of formic and triphenylacetic acids are dissimilar.
[CONTRIBUTION N O . 556
FROM THE
Vol. 82
Acknowledgments.-The author wishes to thank John D. Roberts, F. A. Long, A. N. Bourns, A. J. Weinberger and Erling Grovenstein, Jr., for helpful discussions during the course of this work. OAKRIDGE,TENN.
CENTRAL RESEARCEI DEPARTMENT, EXPERIMENTAL STATION, E. I. AND CO. ]
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PONr
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Methoxydifluoromethyl Isocyanate by Thermal Cleavage of a Diazetidine BY J. C. KAUERAND A. K. SCHNEIDER RECEIVED JUNE 25, 1959 Dimethyl 3,3,4,4-tetrafluoro-1,2-diazetidine-1,2-dicarboxylate pyrolyzes with the migration of a metlioxyl group to yield incthoxydifluoromethyl isocyanate in over 70y0yield. Some of the reactions and properties of this material are described.
Rearrangements are involved in a number of well-known syntheses of isocyanates. Thus, in the Hofmann, Lossen and Curtius reactions, alkyl or aryl groups migrate from the carbon atom of a carbonyl group to an adjacent univalent nitrogen atom.' R
transition state such as I11 is a reasonable esplanation of the formation of the isocyanate. CHI10...CF*...CF2...?CH3
i I I ! : 0=ciy.*... .A-C=O 111
R
It is known that the difluoromethylene group I .. 1 adjacent to an isocyanate function is extremely 0-C-N +O=C=N sensitive to nucleophilic a t t a ~ k . ~ ,Methoxydi5 We wish to report the synthesis of a n isocyanate Auoromethyl isocyanate reacted vigorously with by a rearrangement involving the migration of a water to form inethyl carbamate. methoxyl group. Dimethyl 3,3,4,4-tetrafluoro-1,22H20 diazetidine-l,2-dicarboxylate(I) was prepared in CHaC)CF?NCO I1 -2HF 47'% yield by the thermal addition of tetrafluoroethylene to dimethyl azodicarboxylate. Methoxydifluoromethyl isocyanate (boiling point, 44') (11) was obtained in over 7ooj, yield by the passage of this ester a t 5 mm. pressure through a quartz- Methyl carbamate was also isolated from the reaction of 11 with methanol. Aniline reacted with packed tube heated to GOO'. the isocyanate I1 to form diphenylbiuret, possibly CFz-CFz through the intermediate formation of the amidine I I IV. A similar reaction has been reported for perCH300CX-NCOOCHa +2CHaOCFzSCO fluoropropyl isocyanate and ammonium hydroxide.6 I I1 Although the elemental analysis of the product excess was the same a s that of the diazetidine ester I, CHaOCFzSCO PhNHZ the molecular weight was just one-half. A strong infrared absorption a t 2270 crn.-' and the lack of absorption a t 1600-1800 cm.-' indicated that an isocyanate rather than an ester function was present in the molecule. Although the thermal cleavage of diazetidines has not previously been reported, the analogous reaction is well known in the cyclobutane series2
-
-
I11
+ PhXHZF
I-CHaF)
____f
0
I/
0
/I
PhSHCh7HCSHPh
A similar cleavage has been reported for the fluorinated c y c l o b ~ t a n e s . ~These homogeneous reactions exhibit first-order kinetics and do not appear to be radical chain reactions2 For the pyrolysis of I a concerted reaction involving a ( 1 ) C. K. Ingold. "Structure and Mechanism in Organic Chemistry." Corncll University Press, Ithaca, N. Y., 1953, 1). 497 fi ( 2 ) (a) C . T. Genaux, F. Kern and W. D. Walters, THIS JOURNAL, 7 6 , G l O G (1933); ( h ) M. PIT. Uas, V. Kern, 'r. D. Coyle and W. D. Walters, ibid.. 76, 6271 (1954). (3) (a) J. L. Anderson, U.S. Patents 2,733,278 (1056); (h) 2,773,089 (1956).
+ PhNII?
Acid cleavage of IV to form diphenylbiuret has been reported.6 (4) (a) R. L. Dannley and hI. l,ukin, J . O i g . Chem., 21, 103G ( I O X ) ; (b) R. I,. Dannley, I
