Unsymmetrical dimethylhydrazine transformation products: A review

Unsymmetrical dimethylhydrazine (UDMH) is a widely used rocket propellant, which oxidizes to different compounds. The determination of UDMH transformation products in the environment is of great importance since many of them are highly toxic. Along with well-known transformation products, researchers report new compounds, and establishing their structures is difficult and may be unreliable, and data on their properties, such as toxicity, are often not available. Moreover, the available information on the existence of various UDMH transformation products is quite scattered, many compounds are mentioned in the literature only once and/or without satisfactory confirmation of the structure, and labeled as assumed compounds. All this complicates the identification of new UDMH transformation products and obfuscates the search for already known compounds. This review aimed to summarize and systematize the UDMH oxidation pathways and its transformation products. The attention was paid to in which environmental compartment or only in the laboratory study UDMH transformation products were detected, as well as their formation under conditions of combustion and generating by engines. Schemes for the transformation of confirmed UDMH products were summarized; required conditions for the relevant chemical reactions were described. A group of assumed UDMH transformation products - those substances found in contaminated compartments, but without full structure confirmation - is shown in a separate table. Data on the UDMH and its transformation products acute toxicity are presented. Predicting the transformation products properties, including acute toxicity, cannot be the primary determination method, as the results obtained often do not reflect real values and, when dealing with unknown substances, may lead to using false results. Improved understanding of the UDMH transformation pathways in environmental compartments potentially can lead to more accurate identification of new transformation products with future use in developing approaches to reduce the toxic effects of UDMH and its transformation products.