Kinetic isotope effects and aliphatic diazo-compounds. Part IV. Primary isotope effects in general acid catalysis

Abstract

Data are presented for the solvent isotope effect on the decomposition of 3-diazobutan-2-one and of ethyl diazopropionate catalysed respectively by pyridinium ion and by acetic acid, together with data on the isotopic content of the products of the reactions. The agreement between the kinetic and product data shows that there is direct proton transfer from the acid to the diazo-compound, although there is probably also a small contribution from terms describing the solvation of the transition state. Four different models involving proton transfer through a solvent bridge are considered and rejected. Results for the decomposition of 3-diazobutan-2-one in basic solutions of H₂O and D₂O show that there is a direct reaction with water in which the OH^– formed in the proton-transfer step acts immediately as a nucleophile in the second step.