Nucleophilic Substitution Reactions: Modifications and an Extension Three important features of nudeophilic substitution reactions are the structure of the substrate and the nature of the nucleophile and the leaving group. The first two factors are conveniently studied by comparing the reaction of n-butyl alwhol and t-hutyl alcohol with equimolar amounts of HCl and HBr. The primary alcohol should yield more n-butyl bromide than n-butyl chloride because of the greater nueleophilieity of bromide ion in the SN2 reaction, while the tertiary alcohol should produce t-hutyl chloride and t-butyl bromide in equal amounts if the SN1 process occurs under kinetic control. Such a n experiment was described originally by Helmkamp and Johnson1 and more recently by Pavia, Lampman, and K r k 2 Unfortunately, their procedure for the substitution of t-hutyl alcohol involves a 30-min reflux. Under these conditions the product mixture is not kinetically controlled. Furthermore, their recommended washing procedure can cause significant variation in the product ratio due t o differential hydrolysis. Needless t o say, data from this reaction can be misleading. We have been using the same experiment in our introductory organic labs for a number of years. Our procedure, however, involves two notahle modifications t o published procedures. First, we simplify the preparation of equimolar amounts of HCI and HBr hy mixing appropriate volumes of 36%HCl and 48% HBr. Second, and more importantly, we carry out the substitution of t-hutvl alcohol in a seosratorv funnel hv simolv shaking the slcohol with the acids for about 30 sec. Sufficient t-but$ halidesare formed in this time to hewprated fmm the aqueous phase. Washing isomitted: acidiare removed, without eifect on the produ
