An influence of hypothetical products of dimethylamine ozonation on N-nitrosodimethylamine formation.

The paper concerns formation of N-nitrosodimethylamine (NDMA) upon ozonation of dimethylamine (DMA) aqueous solutions. According to current hypothesis ozonated DMA is oxidized to N-dimethylhydroxylamine (DMHA), then to N-methylhydroxylamine (MHA) and finally to hydroxylamine (HA). HA subsequently reacts with the remain part of DMA to form unsymmetrical dimethylhydrazine (UDMH). Finally UDMH undergoes oxidation with ozone to form NDMA. HA is thought to be an important by-product that increases the NDMA formation. We decided to verify the hypothesis by an ozonation of DMA aqueous solutions in the presence of DMHA, MHA and HA. We have clearly proved that ozonation of DMA in the presence of DMHA and/or MHA does not increase NDMA formation. These results do not exclude the possibility of HA formation during DMA ozonation, but unambiguously show that even if HA is formed during this reaction, it does not have any impact on NDMA formation. In authors opinion the formation of MHA and HA is however doubtful since both compounds seem to be rather products of reduction than oxidation. Therefore HA-DMA reaction cannot be responsible for the formation of NDMA when DMA aqueous solution is ozonized.