Quaternary ammonium compounds (quats) are used commercially for a variety of applications. They are produced industrially by methylating tertiary amines with relatively hazardous methyl chloride or dimethyl sulfate. We have developed a green route for the methylation using dimethyl carbonate (DMC). With a 10:1 excess of DMC at 135°C (high pressure reactor required) the reaction with aliphatic amines was complete in 7-12 hours. Excess DMC and methanol solvent were successfully recovered and recycled. To test the process with aromatic amines and extend the scope of the methylation to secondary amines, the double methylation of diphenylamine was attempted. Reaction at 135°C with a 20:1 excess of DMC produced no products after 48 hours. Adding K2CO3 to remove the proton after the first methylation under the same conditions also produced no reaction. Increasing the temperature to 180°C resulted in formation of a carbamate instead of the quat. Tundo et al. indicate that with DMC carbamate formation occurs at lower temperatures than methylation, so perhaps a higher temperature is needed to form the dimethyldiphenylammonium methyl carbonate compound.