19.22: Amines to Alkenes: Hofmann Elimination
Alkenes can be obtained from amines via an E2 elimination. The amine is first converted into a good leaving group, such as a quaternary ammonium salt. This is accomplished by treating the amine with an excess of alkyl halide, which results in a halide salt. Next, the halide salt is transformed into a hydroxide salt that functions as a base to enable elimination.
Under thermal conditions, the hydroxide can abstract a proton from the β carbon; this generates an alkene with the simultaneous release of a neutral amine molecule. This elimination process is called the Hofmann elimination. For the elimination to occur, the β proton and tertiary amine group must be positioned opposite or anti-periplanar to each other. This reaction yields the less substituted alkene as the major product, also known as the Hofmann product.
