This paper discusses the use of parsimonious input parameterization for the dynamic optimization of reaction systems. This parameterization is able to represent the optimal inputs with only a few parameters. In the context of batch, semibatch, and continuous reactors, the method takes advantage of the concept of extents to allow the analytical computation of adjoint-free optimal control laws. It is shown that this computation can be performed in a systematic way for all types of arcs in the solution, thereby resulting in a finite set of plausible arc sequences. For each arc sequence, the optimal values of the input parameters are computed via numerical optimization. The results are illustrated via simulated examples of reaction systems.