In arylsulfonyl halides, the half-wave potentials of the corresponding chlorides and fluorides differ by more than 1000 mV, the fluoride being more negative; the influence of para-substituents is small for the chlorides, large for the fluorides. In agreement with the half-wave potentials, arylsulfonyl chlorides are considerably more reactive chemically than the corresponding fluorides. The O-selectivity found for P(O)F compounds is not observed in arylsulfonyl fluorides. Studies of competitive ester formation using primary and secondary alcohols and various arylsulfonyl chlorides yielded no clear analogy to the half-wave potentials. The primary alcohol is always sulfonated in preference to the secondary alcohol, whether the hydroxy functions are present in different molecules or the same molecule. In the latter case, the secondary hydroxyl function is then attacked in a further step by a second, different, arylsulfonyl chloride, giving the compounds4–8. The further electroreduction of these diesters may be carried out in high yields, giving selective fission of one ester linkage only (that with the more positive potential) provided the difference in the half-wave potentials of the different ester linkages is sufficiently large. In the electroreductive fission the monosulfinic acid and the corresponding alcohol are liberated (See Table II).