A new efficient method of synthesizing tetramethoxysilane (TMOS) directly from silica (SiO2) and methanol was developed using a base catalyst and 2,2-dimethoxypropane (acetal) as an organic dehydrating reagent. Carbon dioxide significantly accelerated the reaction. TMOS was obtained in good yield from SiO2 in 24 h using stoichiometric or excess amounts of the acetal with a good material balance. The TMOS synthesis from a natural silica substrate, such as rice hull ash is described.