Commonly, TEOS is produced from four reaction step-reactions, consisted of SiCl4 synthesis, ethoxylation, neutralization, and filtration on a large scale, involving in toxic hydrogen chloride and its inorganic salt as a byproduct. To overcome such drawbacks, we have focused on a chlorine-free continuous process for the reaction of elemental silicon with ethanol in the presence of a sodium salt of long-chain polyethylene glycol monoalkyl ether like (2-ethoxy)ethoxy, 2-(2-ethoxyethoxy) ethoxy or butoxy). as a catalyst. This process can reduce the reaction steps so that it is possible to be very simple and high-yield route compared to traditional one. However there are the production of some minor compounds consisted of small amounts of tetraalkoxysilanes containing at least one long-chain alkoxy group. In this presentation, we will discuss the mechanistic study on the formation of minor compounds obtained from the direct synthesis of tetraethyl orthosilicate (TEOS).