Decomposition of 2-Mercaptoethyl O-Ester: SN2 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 -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.