Friday, November 9, 2007
Salon I A&B (Intercontinental at the Plaza)

Investigating the Thermal Stability of Tetramethylammonium Methyl Carbonate and Tributylmethylammonium Methyl Carbonate

Kyle L. Mickalowski, Augustana College, Sioux Falls, SD

Quaternary ammonium compounds, used extensively in a variety of commercial products, are produced industrially by methylation of tertiary amines typically using relatively hazardous methyl chloride and dimethylsulfate. Our lab has perfected an industrially-viable, greener synthesis using dimethyl carbonate as the methylating agent (1). A Mitsubishi patent assigned to Mori et al. (2) seems to suggest that methyl carbonate quaternaries (product from the alternate synthesis) are unstable compounds. This work investigated the thermal stability of tetramethylammonium (TMA) methyl carbonate and tributylmethylammonium (TBMA) methyl carbonate by headspace GC-MS and gravimetric analysis. Mass spec evidence for evolution of CO2 from the break down of methyl carbonate was first observed around 100C. Butene, Hoffman elimination product from TBMA, was first observed at about 130C. TMA was stable at all temperatures investigated. Mass loss for TMA and TBMA methyl carbonates was insignificant below 140C. The coupling of decomposition of TBMA and methyl carbonate is not surprising. Methyl carbonate, a weak base, is converted to methoxide, a strong base, upon loss of CO2. The strong base at elevated temperatures then initiates Hoffman elimination.