Industrial photochemistry III: influence of the stirring of reactants on the kinetics and selectivity of consecutive long-chain photochemical reactions

Abstract Under industrial conditions it is chlorine which, after absorption of light, gives free atoms which generate chlorination chains. In the particular case of the photochemical chlorination of toluene where several successive chlorination reactions are involved we show that the presence of an intense exciting light flux can be responsible for a reduction in the selectivity of the reaction; indeed, under such conditions the chlorination reaction does not occur in a homogeneous manner in the liquid phase (kinetic regime) but rather in the vicinity of the chlorine bubbles entering the reactor (diffusion regime). Thus successive chlorination reactions occur in a region in which chlorine can diffuse; each bubble then constitutes a kind of plug flow reactor which is independent of the buffer medium. This phenomenon is responsible for a modification of the selectivity of the reaction.