Spectrophotometric determination of alkylating agents with 4-picoline and o-dinitrobenzene

Abstract

An accurate, sensitive spectrophotometric method has been developed for determining alkylating agents. The method involves the alkylation of 4-picoline at 100" C in 2-methoxyethanol, with subsequent reaction of the 4-picolinium cation with a-dinitrobenzene in the presence of alkali to produce the chromogen. With 2-phenylethanol as the solvent, the method is autocatalytic a t 100" C. The variables in the procedures were studied, and the methods were compared to one another and to methods in the literature. Some preliminary studies of other possible methods for alkylating agents are discussed.ALKYLATING agents have been shown to be present in urban air, in air polluted by various sources, in automobile exhaust and in cigarette tar.l Many pesticides, chemical carcinogens and anticarcinogens are alkylating agents, as pointed out previous1y.l More recently, the carcinogenic properties of alkylating agents such as nitrogen mustards, sulphur mustards and alkanesulphonate esters,2 epoxides, ethyleneimines and lac tone^,^ y3 and nitroso compounds4 have been reviewed. The anti-fertility effects of alkanesulphonate esters have been s t ~d i e d , ~ and alkylating agents synthesised as possible an ti-carcinogens have been surveyed.6,7,8,9The spectrophotometric determination of alkylating agents has been accomplished by using a substituted-pyridine reagent such as 4-(li-nitrobenzyl)pyridine.lD This reagent reacts with alkylating agents to produce a substituted N-alkylpyridinium cation.The 4-(4-nitrobenzyl)pyridine procedure has been used in both its originaPJ1,123 and autocatalyticl forms to determine many alkylating agents. The sensitivity of the original 4-(4--nitrobenzyl)pyridine procedurelo is relatively low (molecular extinction coefficient of 7300). Several autocatalytic methods, in which various hydrazones were used, have produced high sensitivity, with molecular extinction coefficients as high as 1,500,000 for some alkylating agents.l These procedures, however, yield a poorer reproducibility than the present method, do not obey Beer's law for alkyl iodides, and require a special high-temperature (180" C) bath.In this study, an accurate, sensitive, reproducible method that obeys Beer's law and that utilises a readily available boiling-water bath has been developed. The method involves the alkylation of 4-picoline and the subsequent reaction of the 4-picolinium salt with o-dinitrobenzene. The method can also be used autocatalytically at 100" C. The non-catalytic and autocatalytic methods are compared with one another and with methods from the literature. Some preliminary experiments involving possible future methods for alkylating agents are discussed.