A New Method for the Preparation of Derivatives of Carboxylic Acids Qualitative organic analysis is still a useful vehicle for the teaching of a number of lab techniques and for teaching efficient time management in the laboratory. However, some of the standard methods for the preparation of derivatives are quite unsatisfactory heeause of poor yields or competing reactions. One such reaction is the esterifieation of carboxvlieacids bv various reaeents.IThis reaction involves the reaction of the earboxylic acid in aqueous base with, for example,a,p-dihromoaeetophenone.A major problem is the production of by-product (sometimes the major product), often the alcohol derived from the bromide. We recently developed a technique for the derivatization of carhoxylic acids which uses potassium f l u ~ r i d e We . ~ now have imoroved u ~ o this n technique such that derivatives can he prepared in good yield within a relatively short time. Bath pnitrobenzYlbromide and ~ , ~ - d i b r o m a c e t o ~ h e n owere n e usedto prepare derivatives. The effect of fluoride on the course of the reaction reveals fluoride's ability to form strong hydrogen bonds with carhoxylic acids.3 Thus, the reaction proceeds via the scheme shown. ~
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Among the products of the reaction is bifluoride which should he treated with the same caution that solutions of hydrogen fluoride are accorded.
Procedure Anhydrous potassium fluoride (1.3 g) and a,p-dihromoacetophenone (2.75 g) (or 2.0 g p-nitroben~ylbromide)~ are added to 10 ml of dimethylfarmamide. After 1 min of stirring, 1.0 g of carhoxylie acid is added. The mixture is stirred for % h, after t filtered off on a Buchner funnel, washed with a little which time it is noured into 100 ml of distilled water. The ~ r o d u cis distilled water, and rrystallirrd from enher alcohol or nrmme. With dicarboxylir acids wr encountered very poor yields. whirh we rannot prrsrntiy rxplnin but shall be inreiticating further. Another difficulty mcnr.; with polghnlrgenated dwtlr ar~ds.whirh are derompnscd hg the reagent. Monmhl~~nucttic acid, however, gives a satisfactory derivative ~
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Shriner, R. L.. Fuson. R. C., and Curtin. D. Y.. "TheSystematic IdentificationofOrganicCompounds." 5thed.. John Wiley and Sons, New York. 1964. p. 235. 1 Miller, J. M., Brindle, I. D., Cater, S. R., So, K.-H., and Clark, J. H., Anal Chem. 52,2430 (19801. *For adiscussion on strong hydrogen bonds, see Clark, J. H., Chsm. Rev., 80,429 (1980). Both m,pdlbmmoacetophenoneand p-dlrobenzyl bmmlda are lachrymatom and skln iniianls: manlpulatlw wHh these compwnds are best carried out in a hood with rubber gloves. 5 Author to whom conespondance should be addressed.
Ian D. Brlndle5 and Susan Chassie
Brock University St. Calharines. Ontario L2S 3A1, Canada
Volume 61
Number 4
Aoril 1984
347
