Mechanism of thermal decomposition of 1-tert-butyl- and 1-ethyl-2-methoxydiazene-1-oxides

The mechanism of thermal decomposition of 1-tert-butyl-2-methoxydiazene-1-oxide and 1-ethyl-2-methoxydiazene-1-oxide was investigated by quantum chemistry methods at the CCSD/aug-cc-pVDZ level. It was shown that thermolysis of both compounds occurs by the same mechanism – hydrogen atom transfer from the CH₃ of ethyl or tert-butyl group to the N-oxide oxygen atom via a five-membered cyclic transition state in the limiting stage. More precise calculations at the DLPNO-CCSD(T)/aug-cc-pVTZ level were performed for this reaction channel. It was shown that the activation enthalpy at all calculation levels for this reaction channel and for both compounds is 150-170 kJ/mol, which corresponds to the experimental data. The experimental thermolysis products composition of the 1-tert-butyl-2-methoxydiazene-1-oxide completely coincides with the calculated one.