Acid chloride (ROCl) hydrolysis in a 1,2-dichloroethane (DCE)/water system has been investigated over a wide range of conditions using microelectrochemical measurements at expanding droplets (MEMED). Hydrolysis occurred spontaneously when DCE droplets containing either butyryl chloride, valeryl chloride, hexanoyl chloride, or decanoyl chloride were expanded into an aqueous buffer solution (pH 4-11). The reaction was monitored using a potentiometric Ag/AgCl ultramicroelectrode to measure local changes in Cl- concentration in the aqueous phase near the surface of the droplets during the reaction. For butyryl chloride and decanoyl chloride, the hydrolysis rate increased gradually with increasing pH. For valeryl chloride and hexanoyl chloride, the hydrolysis rate increased with pH in the range of 4-9 but decreased at higher pH values, due to the blocking of the liquid/liquid interface by products. A mechanism for the ROCl hydrolysis reaction, involving rapid (Langmuirian) adsorption of ROCl at the interface followed by rate-limiting interfacial hydrolysis, was found to account for the experimental observations.