CORESTA Meeting, Smoke/Technology, Innsbruck, 1999, ST04
The oxidation of nicotine with sodium hypochlorite. Identification of some of the products formed, and a rationalization of the pathways by which they arose
Philip Morris USA, Research Center, Richmond, VA, USA
The oxidation of nicotine with sodium hypochlorite was studied. Autoanalyzer-monitored reactions showed rapid consumption of about 8 molar equivalent of oxidant. Further oxidation was slow, incomplete, and pH-dependent. Simultaneous monitoring of pH showed a rapid increase, as hypochlorite was reduced, then a long gradual decline. Since nicotine oxidation could not be driven to complete "combustion", it was necessary to identify the products formed that resisted further oxidation. Reaction extracts were examined by GC/MS. Products and mechanistic pathways were identified or inferred using a mass-spectral library and chemical logic. Ultimate products persisted in reactions with excess oxidant. Intermediates formed early in the oxidation process were found in reactions with low proportions of oxidant, which had been exhausted before all vulnerable intermediates could be further oxidized. Nicotine could be understood to generate four principal families of products, depending upon the initial site of attack on the nicotine molecule by oxidant: C-2', C-5', N-methyl, or the pyridine-pyrrolidine bond. Minor other products (chlorinated nicotinic acids, pyridones) derived from initial chlorination or oxidation of the pyridine ring. Initial attack at C-5' affords cotinine (persistent), thence on to 3-acetylpyridine (quite persistent), 3-chloroacetylpyridine and (via the haloform reaction) to nicotinic acid and chloroform (both persistent). Oxidation of the N-methyl group leads to N'-formylnornicotine (persistent), or, if the carbon is lost during the oxidation, to myosmine (vulnerable), which via inferred chlorinated pyrroles ultimately affords 3-cyanopyridine (persistent) and 3,3-dichloroacrylic acid (vulnerable). Oxidation of C-2' leads briefly to nicotyrine, thence onward to 3,3-dichloroacrylic acid and to N-methylnicotinamide. Chlorinative cleavage of nicotine affords 3-chloropyridine (stable) and N-methylpyrrolidinone. Apparent nicotine dimers were found in reactions deficient in oxidizing power, probably artifacts from intermediates not normally surviving oxidation. Also observed were N'-nicotinoylnornicotine, 3-dichloromethylpyridine, 1-(3-pyridyl)-1,2-propanedione, and cyclopropyl 3-pyridyl ketone. The formation of a number of chlorinated byproducts argued against the use of hypochlorite to destroy nicotine commercially.