HYDROLYSIS OF OLIGODIMETHYLSILOXANE-ALPHA,OMEGA-DIOLS AND THE POSITION OF HYDROLYTIC EQUILIBRIUM

The hydrolysis of tetramethyldisiloxane-1,3-diol and hexamethyltrisiloxane-1,5-diol in aqueous solutions has been studied. The position of equilibrium of the system including these compounds, dimethylsilanediol, and water has been determined. Concentrations of these compounds in dilute aqueous solutions were determined by coupling HPLC to ICP analysis for Si and also by extraction into ethyl acetate followed by triethylsilylation and GC analysis. It was found that the siloxanediols hydrolyze to the equilibrium mixture at environmentally significant rates and that dimethylsilanediol dominates the equilibrium in dilute aqueous solution, even at concentrations orders of magnitude above that expected in the environment. The hydrolysis of tetramethyldisiloxane-1,3-diol in water was found to be first order in [H+] and in [phosphate buffer] by studying the rates at pH 3 and 6. The hydrolysis of a mixture of higher oligodimethylisiloxane-alpha,omega-diols as a suspension in water is also described. The first observation of dimethylsilanediol in an environmental sample is reported.