Comparison of reagents for off-line thermochemolysis of natural organic matter

A range of tetramethylammonium salts with different base strengths was compared for off-line thermochemolysis of an aquatic natural organic matter sample. Tetramethylammonium acetate (TMAAc) in methanol produced a different suite of compounds to the more alkaline tetramethylammonium hydroxide (TMAH) in methanol and tetramethylammonium carbonate (TMACO3) in water. TMAAc treatment produced methyl 3-methylmercaptopropanoate, but no sulfur compounds were produced from TMAH or TMACO3. Only TMAAc in methanol produced methyl esters. A mechanism for this formation of methyl esters, involving transesterification with methoxide ion derived from the solvent, was proposed. Off-line TMAAc in methanol appears to avoid decarboxylation, provide more information than on-line TMAAc and preserve more structural information than off-line TMAH in methanol or TMACO3 in water.