1. A trace, of an organic peroxide induces a reaction between sulfuryl chloride and organic compounds [formula omitted] By the use of this procedure, it is possible to chlorinate in the dark many types of organic compounds more rapidly and conveniently than can be done by the use of elementary chlorine and light. 2. The study of the chlorination by this method of cyclohexane, n-heptane, n-propyl chloride, n-butyl chloride, ethylene chloride, propylene chloride, sym-tetrachloroethylene, chloroform, and n-propyl bromide leads to the following generalization: (a) Substitution takes place on a secondary carbon atom in preference to a primary, (b) A second chlorine atom tends to substitute as far from the first chlorine atom as possible, (c) Substitution of a second chlorine atom upon a carbon atom already holding a halogen substituent is difficult; a third chlorine atom cannot be introduced. (d) A bromine substituent is not displaced. 3. The chlorination of side-chains of aromatic hydrocarbons proceeds readily as shown by a study of the chlorination of toluene, p-chlorotoluene, ethylbenzene, isopropylbenzene, t-butylbenzene, m-xylene, and triphenylmethane. The study of the chlorination of toluene, with an excess of sulfuryl chloride, reveals that in this case also the substitution of chlorine upon a carbon atom ceases with the introduction of the second chlorine atom. Both ethylbenzene and isopropylbenzene chlorinate chiefly in the alpha position of the side-chain. Diphenylmethane and the nitrotoluenes cannot be chlorinated by this method. 4. This method of chlorination is of particular value for the chlorination of side-chains in molecules containing reactive nuclei. Thus, m-xylene is chlorinated in the side-chain without the simultaneous formation of any nuclear-substituted products; and t-butylbenzene reacts readily to form β-chlorot-butylbenzene, a compound which cannot be prepared by the direct action of chlorine upon the hydrocarbon. 5. The characteristics of the reaction indicate that the slow decomposition of the peroxide at the reaction temperature initiates a chain reaction involving chlorine atoms. 1939, American Chemical Society. All rights reserved.