Sodium Dichlorofluoroacetate

[2837-90-3]  · C2Cl2FNaO2  · Sodium Dichlorofluoroacetate  · (MW 168.91)

(reagent for generation of chlorofluorocarbene and the synthesis of chlorofluorocyclopropanes and chlorofluoroalkenes)

Solubility: sol DME, diglyme, triglyme, N-methylpyrrolidone.

Preparative Methods: prepared by careful neutralization of 80 g (0.54 mol) of dichlorofluoroacetic acid in 150 mL of Et2O with 29 g of anhydrous Na2CO3. The Et2O and water are removed under reduced pressure. The salt is then dried overnight at 50 °C at a pressure of less than 4 mmHg.1

Handling, Storage, and Precautions: is an irritant and is hygroscopic.

Wittig Reactions.

The thermal decomposition of sodium dichlorofluoroacetate in the presence of Triphenylphosphine and benzaldehyde in triglyme results in the formation of a mixture of (E)- and (Z)-chlorofluoroalkenes in 49% yield (eq 1). A ratio of triphenylphosphine:sodium salt:carbonyl of 1.5:1.5:1.0 is recommended. The choice of solvent had little effect on the ratio of alkene isomers obtained. However, in terms of overall yield, triglyme was the solvent of choice. Simple ketones generally do not react well under these conditions, the exceptions being when there are fluorine substituents on the a-carbon (eq 2).1

Substitution of Tri-n-butylphosphine for triphenylphosphine produced a less stable but more reactive ylide that was capable of reacting with cyclopentanone (eq 3). The yield in the cyclopentanone reaction was comparable to the haloform method of carbene formation and subsequent ylide generation. In general, the yields of chlorofluoroalkenes using the decarboxylation method for generating chlorofluorocarbene were superior to the haloform method.

Cyclopropanation.

The reaction of tetramethylethylene with the sodium salt in triglyme at 85 °C leads to the formation of the chlorofluorocyclopropane in 37% yield (eq 4). In the presence of triphenylphosphine, no cyclopropane was observed. Tetramethylethylene and triphenylphosphine have been shown to be comparable in reactivity toward chlorofluorocarbene generated using the haloform method. Thus it appears that the carbene may not be the precursor for the ylide in the decarboxylation method.1


1. (a) Burton, D. J.; Krutzsch, H. C. TL 1968, 71. (b) Burton, D. J.; Krutzsch, H. C. JOC 1970, 35, 2125.

Michael J. Taschner

University of Akron, OH, USA



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