We have examined the kinetics and mechanism of the dediazoniation reaction of p-methylbenzenediazonium tetrafluoroborate in the presence and absence of CuCl 2 using a methodology developed by us that allows, simultaneously, and within the same experiment to identify, to quantify, and to obtain the rate constants for the formation of all dediazoniation products, and, indirectly, the rate constant for the diazonium salt decomposition. The methodology developed combines the use of coupling reactions, to form a stable azo dye, followed by analysis by HPLC.