Deoxygenation of Tertiary Amine Oxides with Carbon Bisulfide

Reduction of various tertiary amine oxides with carbon disulfide was examined and kinetic experiments were carried out. Trialkylamine oxides and N,N-dialkylarylamine N-oxides were readily reduced by CS2 to give the corresponding tertiary amines in good yields, while heteroaromatic amine N-oxides such as picoline N-oxide were not affected. The oxygen atom in the N-oxide was found to be transferred to CO2 upon mass spectral analysis of the gas evolved. The kinetic experiments were carried out following the UV spectra of N,N-dimethylaniline N-oxide in CH3CN containing much excess of CS2 and the rate was found to be of 2nd order in the N-oxide and CS2. Activation parameters (ΔH\eweq=55.7 kJ mol−1, ΔS\eweq=−78.2 J K−1 mol−1 at 20 °C are characteristic of a normal bimolecular reaction. The logarithms of the rate constants for para-substituted N,N-dimethylaniline N-oxides are nicely correlated with Hammett σ values and a small negative ρ value (ρ=−0.2) was obtained. The rate of reaction was faster in polar aprot...