PURPOSE: To prepare the subject compound in two steps using an inexpensive material, by brominating 4-tert-butyltoluene to obtain a mixture of monobromides and dibromides, which is then hydrolyzed by adding water in the presence of a Sommelet reagent.

CONSTITUTION: In the absence of a solvent, 4-tert-butyltoluene is brominated to obtain a mixture of 4-tert-butylbenzyl bromide and 4-tert-butylbenzal bromide. Subsequently, this mixture is hydrolyzed in the presence of water and a Sommelet reagent and optionally a co-solvent to obtain 4-tert-butylbenzaldehyde in high purity in a high yield. The two steps in the reaction are preferably carried out continuously in a same vessel. The brimination is carried out at from 183 to 190°C, and the Sommelet raction is carried out at from 90 to 105°C. The co-solvent is preferably ethanol. 4-tert-butylbenzaldehyde is used in the preparation of agrochemical substances or aromatic substances.