Abstract (1) The reaction of rubber with zinc palmitate was found to liberate palmitic acid at low pressures, thus revealing that rubber is acidic. (2) The reaction of zinc oxide with palmitic acid in toluene solution was enhanced by the presence of water. (3) The small increase in the nitrogen content of rubber caused by its reaction with TMTD was equivalent to the palmitic acid liberated by the zinc palmitate reaction. (4) The use of TMTD as a reagent for organic acids has been studied and found to convert carboxyl groups into dimethylamide groups. This result suggests that the acidic nature of rubber is due to carboxyl groups in the rubber molecule, a suggestion which is compatible with the nearly complete removal of zinc from the TMTD vulcanizate by the zinc removal technique.
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Craig et al. (1951) studied this question.