The synchronization of two coupled chaotic CSTRs, in which isothermal cubic autocatalytic reactions taking place, is investigated. II has been shown that the synchronization is possible through a hyperchaos-chaos transition, when the coupled system evolves on a 3D sub-manifold embedded in 6D phase space. The synchronization of chaotic nonlinear oscillators can be achieved when the number of positive Lyapunov exponents of the coupled system equals to the number of positive Lyapunov exponents of a single system. The unsynchronized periodic oscillations show an interesting symmetric phase plane (mirror image) with respect to the diagonal.