In the fine chemical and pharmaceutical industry, high value-added products currently remain manufactured in batch operations. So, the batch or fed-batch reactor functions at the heart of the transformation process. To increase yield and selectivity of a chemical reaction (i.e. reactor productivity and product quality), to reduce production of effluents to be treated and recycled (i.e. cost and environmental impact), it is necessary to improve automation of such processes. Due to the complexity of chemical synthesis and the difficulty to estimate on-line experimental reactant compositions, control of reactors remains a problem of temperature control, commonly performed indirectly via the jacket of the reactor. In this paper, an original approach of thermal control through pressure is proposed. The aim is to take advantage of the instantaneous dynamics of the pressure-temperature loop at boiling point and to act on the pressure in order to control the reactor temperature. The feasibility and interest of such a thermal control is exemplified through simulation results on an industrial pharmaceutical synthesis reaction, after optimization of the operating conditions (i.e. temperature profile) under environmental considerations (i.e, aiming to decrease the amount of solvent).