Content area
Full Text
A popular organic lab is the preparation of diethyltoluamide (DEET), the active ingredient in Off and Deep Woods insect repellents. Lab procedures uniformly prepare the m-toluoyl chloride intermediate by heating m-toluic acid (1) with thionyl chloride (SOCl^sub 2^) for times ranging from 15 to 45 minutes (1). Subsequent reaction of the m-toluoyl chloride (2) with diethylamine and basic workup gives DEET. However, using a similar procedure, our students consistently produced DEET as a dark brown oil which was contaminated with a by-product as seen by infrared (IR) spectroscopy, and unfortunately, they never had enough time to vacuum-distill the crude DEET.1 The students' parting comment that they'd "rather be bitten by mosquitoes" than use their product prompted a reexamination of the DEET synthesis.
The infrared (IR) spectrum of the crude DEET showed two strong bands at 1763 and 1720 cm^sup -1^, which were unrelated to DEET's structure. We suspected that the two IR bands represented the symmetrical and asymmetrical C=O stretch of the conjugated anhydride (3).
GC/MS analysis of the crude DEET confirmed the presence of the impurity at 12.5 minutes.2 The parent ion, a mle peak of 254, corresponded to the molecular weight of the expected anhydride. Also strong peaks at mle = 119 and 91 supported the anhydride H^sub 3^C-C^sub 6^H^sub 4^-C=O and C^sub 6^H^sub 4^-CH^sub 3^ fragments. A final independent synthesis of...