This invention relates to a process for converting a hydrocarbon reactant to a product comprising an oxygenate or a nitrile, the process comprising: (A) flowing a reactant composition comprising the hydrocarbon reactant, and oxygen or a source of oxygen, and optionally ammonia, through a microchannel reactor in contact with a catalyst to convert the hydrocarbon reactant to the product, the hydrocarbon reactant undergoing an exothermic reaction in the microchannel reactor; (B) transferring heat from the microchannel reactor to a heat exchanger during step (A); and (C) quenching the product from step (A).