Mass transfer coupled to chemical reaction

Most reactions in two-phase systems occur in a liquid phase following the transfer of a reactant across an interface these are commonly known as extractive reactions. If the transfer is facilitated by a catalyst, it is known as phase-transfer catalysis [2]. Unusually, reactions may actually occur at an interface (interfacial reactions) examples include solvolysis and nucleophilic substitution reactions of aliphatic acid chlorides [3 ] and the extraction of cupric ion from aqueous solution using oxime ligands insoluble in water [4], see Section 5.2.1.3(ii). 

Extractive reactions can be usefully categorised into those which are too slow to occur within the diffusion film and those which occur largely within the film. Borderline cases will show intermediate behaviour. 

Reactions involving completely insoluble solid surfaces are common. Processes involving heterogeneous catalysis and most electrochemical processes fall into this category. 

---