In the fine chemical and pharma industry a number of reaction processes undergo selectivity losses since the target product (typically a low volatility compound) can further react with one of the reactants leading to by-products that must be separated from the target product itself and finally disposed as wastes. In such a situation, even performing the reaction in a standard semi-batch reactor requires a large excess of one reactant to limit the selectivity drop. However, operating the reactor with a large excess of one reactant lowers the reactor productivity. In this work, a process configuration is discussed that, limiting the target product accumulation in the reactor, allows achieving both high process selectivity and high reactor productivity. Moreover, general and easy to use boundary diagrams have been developed, through which the optimal process operating parameters can be easily estimated without solving the mathematical model of the system. Several boundary diagrams are provided for different systems together with a general procedure for their use. (C) 2012 Elsevier Ltd. All rights reserved.