PURPOSE: To produce the titled substance which is a raw material of coenzyme Q10 useful as pharmaceuticals in high yield and quality, by reacting 2-bromo-3,4, 5-trimethoxytoluene with sodium methylate in nitrogen stream in a specific mixed solvent.

CONSTITUTION: A mixture of 1mol of 2-bromo-3,4,5-trimethoxytoluene and preferably 1.5W2.5mol of sodium methylate is heated and reacted at 80W88°C in the presence of a copper compound as a catalyst, in nitrogen stream in a mixture of methanol and one or more compounds selected from ethylene glycol, diethylene glycol, their ethers, and triethylene glycol, to obtain a mixture of 2-bromo- 3,4,5-trimethoxytoluene and the objective compound, from which the objective compound is separated by vacuum distillation. The ratio of methanol to the other solvent components is 1 to 0.06W0.27.