Microwave specific effects in organic synthesis: A proposed model from the solvent-free synthesis of monoglycerylcetyldimethylammonium chloride

Abstract

Microwave specific effect in the organic synthesis was examined under homogeneous and heterogeneous conditions. Monoglycerylcetyldimethylammonium chloride was synthesized from 3-chloro-1,2-propanediol (CP) and N , N -dimethylhexadecylamine (DMHA) in 2-propanol solvent and in solvent-free conditions to examine microwave specific effects. None were evident in homogeneous 2-propanol media under temperature conditions identical to conventional heating. In contrast, heterogeneous solvent-free conditions brought out specific microwave effects as evidenced by variant product yields (130 °C; 30 min): 62% by microwave and 47% by conventional heating. This variance is attributed to thermal conduction and localized hot spots formed under microwave irradiation. The model proposed for the solvent-free synthesis considers hydrophilic 3-chloro-1,2-propanediol molecules form H-bonded domains (size, 2–20 μm) preferentially heated by the microwaves and dispersed in a sea of hydrophobic N , N -dimethylhexadecylamine molecules.