CONSECUTIVE REACTIONS OF DIETHOXYDIMETHYLSILANE AND TRIETHOXYMETHYLSILANE WITH METHOXIDE IONS IN METHANOL SOLUTION

The consecutive reactions of (CH3)(2)Si(OC2H5)(2) and CH3Si(OC2H5)(3) with methoxide ions were investigated in methanol solutions. The rever se transesterification reactions with ethoxide ions could be neglected in both cases since the concentration of ethoxide in methanol solutio n was assumed to be low due to the fast equilibrium reaction C2H5O- CH3OH = C2H5OH + CH3O-. The progress of the reactions was followed by monitoring the formation of ethanol with a Fourier-transform infrared spectrometer. All rate constants were determined at 295 K. The reactio ns between the dialkoxydimethylsilanes and methoxide ions were assumed to consist of two consecutive steps that can be represented by the ne t reaction; (CH3)(2)Si(OC2H5)(2) + 2CH(3)O(-) --> (CH3)(2)Si(OCH3)(2) + 2C(2)H(5)O(-). The two consecutive rate constants were established a s 1.93 +/- 0.12 M(-1) s(-1) and 1.00 +/- 0.12 M(-1) s(-1), respectivel y. The consecutive rate constants for the reactions between the trialk oxymethylsilanes and methoxide ions can be written according to the to tal reaction; CH3Si(OC2H5)(3) + 3CH(3)O(-) --> CH3Si(OCH3)(3) + 3C(2)H (5)O(-). The three rate constants corresponding to each consecutive st ep were established as 1.12 +/- 0.09 M(-1) s(-1), 0.82 +/- 0.10 M(-1) s(-1), and 0.51 +/- 0.06 M(-1) s(-1), respectively. (C) 1995 John Wile y & Sons, Inc.