The use of phenylboronate and stannate in the separation and characterisation of polyols

Abstract

The preparation of cyclic phenylboronates by two methods has been described. Phenylboronates from polyols soluble in water were prepared by the method of Kuivila, Keough and Soboczenski. Those from polyols insoluble in water were prepared by the method of Sugihara and Bowman. A method for estimating the boron content of phenylboronates not containing any other phenyl group has been devised. This utilises the ultraviolet absorption due to the grouping. The structures of several phenylboronates have been investigated. It has been shown that galactitol forms a 1,3:4,6-bisphenylboronate and that glycerol forms a 1,2-mono-phenylboronate. The formation of 5- 6-membered rings in the phenylboronates of glycerol and galactitol has been discussed with reference to the reactions of aldehydes and ketones with polyols, and with reference to thermodynamics.The lack of reactivity of the free hydroxyl groups in some phenylboronates has been discussed and a reason for this suggested. The formation of a 'tridentate' structure, resulting in a boat-shaped conformation in the phenylboronates containing unreactive hydroxyl groups is indicated. Chromatography of polyols using a solvent containing phenylboronic acid has been carried out. Some correlation between the increase in R values of compounds in the presence of phenylboronic acid , and their structures is evident.In most cases it involves a 'tridentate' structure (and l(ax),2(eq),3(ax)-grouping of hydroxyl groups) as previously described. The use of a solution of sodium stannate (at pH 11.5) as an electrolyte for electrophoresis has been described, and it has been shown that for cyclic polyols a 1(ax),2(eq)-diol grouping is preferred, and for acyclic polyols a threo-diol grouping is preferred for complexing.