Determination of Oxidation Products of Unsymmetrical Dimethylhydrazine with Hydrogen Peroxide Using Gas Chromatography-Mass Spectrometry and Machine Learning

Abstract

For several decades, unsymmetrical dimethylhydrazine (UDMH) has been used as fuel for heavy launch vehicles in the rocket and space industry of many countries. It is known that both UDMH and especially its transformation products are extremely toxic to the environment and all living organisms. Despite the significant reduction in the use of UDMH and the active transition to alternative, less toxic fuels, issues of identifying the products it forms in natural objects, neutralizing existing spills, and restoring ecosystems damaged by such pollution remain relevant. One of common methods for neutralizing UDMH is its oxidation with hydrogen peroxide. However, it can also form potentially hazardous byproducts when detoxifying soils and waters. Establishing the structure and searching for new possible transformation products are important tasks for further evaluation of the potential toxicity of the resulting UDMH oxidation products. The composition of the reaction products of UDMH with hydrogen peroxide was studied using gas chromatography-mass spectrometry. A SHIMADZU GCMS-TQ8040 chromatograph mass spectrometer (Shimadzu Corporation, Japan) was used for analysis. For the chromatographic separation, a non-polar stationary phase (SP) based on 5% phenyl methylpolysiloxane and a polar stationary phase based on polyethylene glycol. The formation of 15 main products of UDMH transformation was established, including a particularly toxic one, N-nitrosodimethylamine. The final products of UDMH conversion have a molecular weight of no more than 100 Da. It has been established that the main oxidation products are low-molecular nitrogen-containing compounds of the CHN and CHNO classes, in particular aromatic heterocycles such as triazoles, pyrazoles, etc. When maintaining the reaction mixture containing UDMH and H₂O₂ more than 4 months, a significant increase in the concentration of N-nitrosodimethylamine and 1-methyl-1H-1,2,4-triazole and a decrease in the concentration of formamide and acetamide, as well as the formation of new products, were observed. The retention indices of all obtained substances were calculated for the two stationary phases, which allowed comparison with the retention indices from the NIST database, as well as with our own mini-N_i data set obtained earlier, which contains information for similar compounds. In the absence of retention indices in the NIST database for the putative UDMH transformation products, retention indices were predicted using modern machine learning methods.