The structures of three types of nicotine salts have been determined. These salts have acid to base ratios of either 1 : 1, 2 : 1, or 3 : 1. Salt formation between organic acids and nicotine is dependent upon the structure of the acids (aliphatic or aromatic) and their functionality. The 1 : 1 salts of nicotine have amino acids or benzoic-type acids bound to the N-methylpyrrolidine nitrogen of nicotine. The 2 : 1 salts are found to bind to one acid group as in the 1 : 1 salts and a second to the nitrogen of the pyridine ring. The 2 : 1 salts of nicotine are formed with formic acid, aliphatic dicarboxylic acids, and/or nitroaromatic acids. Nicotine forms 3 : 1 salts with aliphatic monocarboxylic acids starting with acetic acid. Here one acid is bound as in the 1 : 1 salts while the other two acids dimerize and bind to the nitrogen of the pyridine group. Infra-red (IR), ultra-violet (UV), proton nuclear magnetic resonance (PMR), and carbon nuclear magnetic resonance (CMR) spectroscopy as well as field desorption - mass spectroscopy (FD-MS) were used in this investigation of the structure of nicotine salts.
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