High pressure relief of steric inhibition in ionogenic organic reactions

Abstract

The pressure effect is examined in an ionogenic reaction, the phosphine-catalyzed cyanoalkylation of acrylic nitriles by primary alcohols. The increase of rate constants with pressure is enhanced with increasing chain length of the alcohol and depends on steric constraints imposed by the substituting methyl group in the acrylic compound. The pressure effect is in line with a considerable electrostriction depending on steric hindrance to ionization. Pressure is confirmed as a favorable determining factor in sterically hindered reactions.

High pressure in organic chemistry on the way to miniaturization

“…1 The 1,4-addition of alcohols to activated alkenes catalyzed by tri-n-butylphosphine is activated by pressure in the case of crotonic compounds with a hindered b reaction center, while the corresponding additions of alcohols to methacrylic analogs are hardly affected. 147,148 The phosphine-catalyzed nucleophilic addition of alcohols to unsaturated nitriles is also affected by pressure (3 kbar), when either the alcohol or the nitrile has bulky groups. 149 In this particular reaction, geometrical and electrostatic interactions (steric hindrance to ionization) are presented as the main reasons for the positive pressure effects.…”