JULY,1962
SYNTHESIS OF POLYFLUORITATED HETEROCYCLES. T'
2593
Synthesis of Polyfluorinated Heterocycles by Indirect Fluorination with Silver Fluorides. V. Fluorothiophene1I2 HENRIULRTCH, EHRENFRIED KOBER,RUDIR A T z , HANSJUERGEN SCHROEDER, AND CHRISTOPH GRUNDMANN Ohio State University Research Foundation, Columbus, Ohio Received November 21, 1961 Reaction of tetrachlorothiophene with silver difluoride gave 2,2,5,5-tetrafluoro-3,4-dichlorothiolene. Experiments were carried out to exchange halogen atoms of chlorinated and brominated 2,5-dimethylthiophenes with fluorine by means of silver fluoride. Only these halogen atoms were substituted by fluorine which were attached to methyl groups. An attempt to force the replacement of the p-bonded chlorine atoms of 2,5-bis( trifluoromethyl)-3,4-dichlorothiopheneby means of silver difluoride resulted in opening and desulfurization of the thiophene ring, thereby forming 1,1,1,2,5,6,6,6-octafluoro-3.4dichlorohexadiene-3,4.
The direct fluorination of thiophene gave only reaction was so violent that complete decomcleavage products instead of fluorinated thio- position of I occurred. Although also the reaction ~ h e n e . ~The , ~ only reported preparation of a of silver difluoride with the corresponding tetracompound with fluorine attached to t'he thiophene chloro compound I1 could not be controlled, even nucleus is t'he synthesis of 2-fluorothiophene from when carried out in an ice bath, a considerable 2-iodothiophene by means of arsenic trifluoride in amount of a fluorine-containing product was isonitromethane. The yield in t'his case, however, lated. Analytical data and molecular weight determination indicated the composition C4C12FdS. was very OW.^ As part of a comprehensive st'udy of the prepara- Based on the evaluation of the S l I R spectrum, tion of fluorinated heterocyclic c o m p o ~ n d s . ~ ~ 6this - ~ compound is believed to be 2,2,5,5-tetrafluoroour investigations were extended to thiophenes. 3,4-dichlorothiolene-3 (111). The spectrum conI n our first experiments we att'empted the fluori- sists of a single line with no fine structure indicating nation of ring halogenated thiophenes. For t,his that the fluorines are equivalent. The chemical purpose, the reaction of tetrabromothiophene (I) l o shift using the classical side band technique was and tetrachlorothiophene (11)" wit,h metal fluorides found to be T = 73.76 p.p.m., relative t o trichlorosuch as silver fluoride, silver difluoride, or mercuric fluoromethane. The observed value is consistent difluoride mas investigated. with XMR data reported for perfluoroalkylsulfur Surprisingly, I and 11 did not react with excess fluorides.'* silver fluoride or mercuric difluoride. This is in conThere are other possible chemical isomers having trast to our observations on other heterocyclic com- the empirical formula CdC12F4S,but in all cases pounds2p6-8 in which under the same conditions the fluorine atoms would not be equivalent. Apparently, I11 is formed by l,+addition of replacement of chlorine atoms by fluorine could be easily accomplished. Reaction of t'he tetrahalo- fluorine to the conjugated system besides substithiophenes could not be achieved even on heat,ing tution of the more reactive a-chlorine atoms by with silver fluoride to 220'. fluorine. Hexachlorothiolene-3 from which I11 In an at'tempt t80 use silver difluoride for t,he may have been derived by partial fluorination fluorination of the tetrabromo compound I, the was not present in the starting material (11). An(1) This article is baaed on work performed in 1956 and 1957 under Project 116B of The Ohio State University Research Foundation sponsored b y t h e Olin Mathieson Chemical Corporation, New York, N. P. (2) Preceding communication: H. Schroeder, R. RBtz, W. J. Schnabel, H. Ulrich, E. Kober, and C. Grnndmann, J . Org. Chem., 27, 2589 (1962). (3) J. Neudorfer. Compt. rend., 234, 1983 (1952): A n n . chim. (Paris), 8, 501 (1953). (4) J. Schultz and 11. Hanptschein, J . Am. Chem. Soc., 74, 848 (1952). ( 5 ) R . T. van Vleck, .I. Am. Chem. S O C . , 71, 3266 (1949); U. S. Patent 2,562,994. (6) E. Kober, H. Schroeder, R . R i b , H. Clrich, and C. Grundmann, J . Org. Chem., W , 2577 11962). (7) H. Schroeder, E. Kober, H. Ulrich, R. Ratz, H. Agahigian, and C. Grundmann, J . O w . Chem., 27, 2580 (1962). ( 8 ) H, Ulrich, E. Kober, H. Schroeder, R. Ratz, and C. Grundrnsnn, J . Org. Chem., 27, 2585 (1962). (9) E. Kober and C. Grundmann, J . Am. Chem. Soc.. 81, 3769 (1959). (10) V. hleyer and H. Kreis, Ber., 16, 2172 (1883). (11) L. Weitz, Ber.. 17, 794 (1884).
Cl-C-C-CI II II CI-c\ S,C-Cl
I1
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Cl--C---C-CI S
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