Kinetic study of the reaction of dimethyl carbonate with trialkylamines

Quaternary ammonium compounds are produced worldwide in hundreds of millions of pound volume annually for a plethora of end-uses from fabric-care formulations to asphalt emulsifiers, typically from nongreen alkylating reagents. The kinetics of a reaction employing dimethyl carbonate (DMC) as a green alkylating agent was investigated using three trialkylamines (tributylamine, trihexylamine, and trioctylamine) at several temperatures. Arrhenius and Eyring analysis of the data showed that values of Ea (79 kJ/mol), ΔH‡ (75 kJ/mol), and ΔS‡ (220 J/(mol K)) were the same for all three amine reactants, consistent with a report that E _a is independent of alkyl chain length when the chain length is greater than three carbons. Although rates are significantly slower with DMC than with other alkylating reagents, the resulting methyl carbonate anion has advantages for clean anion metathesis, which is important for some applications, especially those involving ionic liquids.