1624
PAUL TARRANT S N D D. A.
L~ARNER
Vol. 76
[ C O N T R I B U T I O N F R O M THE DEPARTMENT O F CHEMISTRY O F THE UNIVERSITY O F FLORIDA]
Fluoroolefins. IV.
The Addition of the Grignard Reagent to Fluoroolefins' BY PAUL TARRANT AITD D. 9. \V.~RNER RECEIVED OCTOBER24, 1953
Aliphatic and aromatic Grignard reagents have been found to react with various fluoroolefins. Addition apparently takes place across the double bond in a manner consistent with the behavior of fluoroolefins with other bases; the resulting adduct loses MgXt to give a new fluoroolefin containing a longer carbon chain. Phenylmagnesium bromide and unset.-dichlorodifluoroethylene gave a 64% yield of a-fluoro-0-dichlorostyrene; cu,&difluoro-0-chlorostyrene resulted from chlorotrifluoroethylene. The effect of structure of the Grignard reagent 011 the yields of olefins is discussed.
In the search for a simple method for introducing gent, the intermediate loses a halogen atom from the functional groups into organic compounds contain- carbon atom adjacent to that associated with the ing fluorine, attention was turned to the reaction of magnesium to give an olefin. the Grignard reagent with fluoroolefins. Since the In cases where fluoropropenes are used in the reGrignard reagent may act as a base and certain action, i t is thus possible to obtain two products debases add to fluoroolefins, it was supposed that a pending upon which adjacent halogen is eliminated. new Grignard reagent should arise from the addi- For example, phenylmagnesium bromide reacted tion of the reagent to compounds such as chlorotri- with 3-chloropentafluoropropene to give both fluoroethylene or I,l-dichlor0-2,2-difluoroethylene.C6H5CF=CFCF2C1 and C6H5CF2CF=CF2. It is The addition product, if stable, should undergo the interesting to note that the former was obtained in normal reactions of the Grignard reagent, leading to almost four times the quantity of the latter. Unacids, alcohols, ketones, etc., which contain fluorine doubtedly the basis for the formation of C6H5CF= atoms. CFCFzCl is the added stability gained from the Since I,1-dichloro-2,2-difluorobutane has been conjugation of the lateral double bond with the prepared and characterized previously,? its synthe- benzene ring. It might be expected that in the absis by the reaction of ethylmagnesium bromide with sence of this additional stabilization effect the 1 , l -dichloro-2,2-difluoroethylene was chosen to test heavier halide ion would be lost. This was found to be the case in the reaction of methylmagnesium the procedure. The expected reactions were bromide and 3-bromopentafluoropropene where a H20 CzHbMgBr CF?=CClz +CzH6CF&ClzMgBr -+ 24% conversion to CH3CF2CF=CF2 was obtained, CZH~CF~CHCLMg(0H)Br while the alternate reaction product, CH3CF= However, a butene corresponding to the formula CFCF2Br, was obtained, if a t all, in amounts too C4H5C12F was obtained instead of the saturated small for characterization. It follows from the discussion above that a well compound anticipated. This compound was assigned the structure CH3CH2CF=CC12. In a sec- defined carbanion is necessary for the initiation of ond experiment, phenylmagnesium bromide was the reaction of the Grignard reagent with the fluorotreated with chlorotrifluoroethylene and a 16.6% olefin. Thus, in general, aliphatic Grignard reayield of the known3 2-chloro-1,2-difluoro-l-phenyl-gents should be less effective than the aromatic since the resonance stability of the phenyl anion, ethylene was obtained. The formation of the styrene derivative may be for example, involves lower energy forms than are possible wlth the ethyl anion. The conversions obaccounted for by the mechanism tained using the two Grignard reagents bear out C6H5MgBr CF2=CFC1 + [CsH5CFsCFC1MgBr]+ this supposition ; by using 1,l-dichloro-2,2-difluoroCeH6CF=CFCI MgFBr ethylene, a 64YG conversion to I , l-dichloro-2The point of attack on the double bond by the fluoro-2-phenylethylene was obtained with phenylphenyl group is consistent with the behavior of al- magnesium bromide, while only a 107, conversion cohols and phenols, which in the presence of bases to 1,l-dichloro-2-fluorobutene-l resulted with ethyladd the alkoxy or phenoxy group to the carbon magnesium bromide under the same conditions. atom of the double bond of a fluoroolefin holding the There is a variation in yields of resulting fluorogreater number of fluorine atoms. I t has previ- olefins among the aliphatic Grignard reagents proously been postulated4 that base-catalyzed addi- portional to the expected degree of ionization; as tions to fluoroiilefins proceed as the electron release of the alkyl residue is increased the conversion rapidly diminishes. Thus, while RZH R Z - + CF?=CSn + [RZCF.CS?]- ---+ ethylmagnesium bromide and 1,1-dichloro-2,2RZFzCHX? + RZ- difluoroethylene gave a 10% conversion to 1 , l r n the case of the reaction with the Grignard rea- dichloro - 2 - fluorobutene - 1, isopropylmagnesium bromide and the same olefin gave evidence of reac(1) T h e material in this paper is abstracted from a portion of t h e tion only in trace amounts. On the other hand, doctoral dissertation submitted by D. A . Warner t o t h e Graduate Council of the University of Florida, February, 1953. Presented a t methylmagnesium bromide with %iodopentdfluorothe 122nd Meeting of the American Chemical Society, Atlantic City, propene gave a %7G conversion to 1,1,2,3,3-pentaN. J., September, 1952. fluorobutene-1. ( 2 ) A. I.. Henne and J. B. Hinkamp, Tms JOURNAL, 67, 1194 (1945). (3) S. G. Cohen. H. T. Wolosinski and P. J. Scheuer, ibid.,72, 3953 -1comparison of yields of products obtained when (l
