We have measured the rate constants and branching ratios for the reactions of Cl- with C2H5Br and n-C3H7Br as a function of temperature and kinetic energy. Both reactions proceed slowly. The reactions proceed mostly to form Br- at room temperature and above. Both the temperature and kinetic energy dependencies are flat in this regime. At low temperatures a new mechanism becomes important, namely, association followed by thermal dissociation to form both Cl- and Br-. This is especially important in the n-C3H7Br reaction for which the rate constant increases by a factor of 4 between room temperature and 230 K. Not only does the overall rate increase but also the channel-forming Br-.