A method is disclosed for preparing an alkoxysilane having reduced halide content. Said method involves contacting a first mixture comprising an alkoxysilane and residual halide with a second mixture comprising 1.5 to 15 moles of an alkyl alcohol per mole of residual halide, said alcohol having 1 to 4 carbon atoms and 0.1 to 5 moles of an orthoformate per mole of residual halide, to form a final mixture comprising additional alkoxysilane and lower boiling species and then separating the lower boiling species and the alkoxysilane. The remaining residual halide may be further contacted with metal alkoxides to achieve even greater halide content reduction. Alkoxysilanes produced herein are useful as catalyst modifiers to manufacture polypropylene.