Kinetics and mechanism of the sodium–ammonia reduction of 2,2,4,4-tetramethylpentan-3-one

Abstract

The kinetics of the reaction of sodium with 2,2,4,4-tetramethylpentan-3-one (TMP) in liquid ammonia was studied using the stopped-flow technique. The reactions were found to obey the fourth-order rate law –d[e_am^–]/dt= 2k[e_am^–]²[ketone][Na⁺]. The reaction rate was markedly reduced by addition of 2,2,2-cryptand. The addition of a weak acid (ethanol) had no effect on the observed rate. A mechanism involving ion-pairing with dianion formation being the rate-determining step is suggested. When TMP was initially exposed to an excess of lithium amide in liquid ammonia, the resulting mixture was found not to react with the ammoniated electron.