The Methanol-Trimethoxyborane Azeotrope as a Solvent

The methanol-trimethoxyborane azeotrope is an ea.sily prepa. red solvent of strong H-bond donor and weak H-bond acceptor properties. It has a low viscosity and low boiling point, and is completely transparent in the visible and uv at wave lengths above 220 nm. It has a dieLectric constant of 9 and ion pair formation constants between 103 and 104 for simple electrolytes. The glass electrode pH-meter can be used in this solvent, with the ordinary calomel reference electrode. Indicator acidity measurements are somewhat complicated by the forma•tion of H-bonded ion pairs. The solvent is useful for measuning the relative acidity of strong acids; CH3S020H and CF3S020H are readily differentiated. It should be useful for other physico-chemical measurements and also in preparative chemistry