Decomposition of 2‐Mercaptoethyl O ‐Ester: S N 2 Displacement or Acyl Transfer? A Theoretical Study

The mechanism for the decomposition of 2‐mercaptoethyl O ‐ester was theoretically investigated. The mechanism that 2‐mercaptoethyl O ‐ester undergoes an S N 2 displacement of the O atom by the S atom on α ‐C is much favored over the mechanism of N‐to‐S acyl transfer. The length of the alcohol moiety has large effects on the decomposition efficiency of thiol‐substituted alkyl O ‐esters. The reactivities of these esters are controlled by distortion energies. Only 2‐mercaptoethyl O ‐ester can undergo the decomposition at room temperature due to the low distortion energy to achieve the transition state geometry. If the thiol group of 2‐mercaptoethyl O ‐ester is replaced by an amino group, the N‐to‐N acyl transfer mechanism is more favored than the S N 2 displacement mechanism.