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The available literature on hexamethylenetetramine (hexamine) was reviewed with emphasis on its toxicology and epidemiology, its thermal decomposition and regulatory concerns related to its uses. Large quantities of hexamine are used in the foundry, tire and rubber, and phenolformaldehyde resins industries and in other diverse applications. Excessive exposure to solid hexamine or its vapor has been reported to cause dermatitis and respiratory allergies. Although hexamine produces a positive Ames test, most animal studies have shown hexamine to be of very low genetic risk even in very high doses. The effectiveness of hexamine as an antibacterial agent has been attributed to its slow hydrolysis to ammonia and formaldehyde. Concerns have developed in industries which use hexamine at high temperatures over emissions of HCN, NH3, CO, CO2, nitrogen oxides, and formaldehyde. The studies reviewed are in general agreement that hexamine thermal decomposition in the temperature range of 300-800 degrees C is characterized by an increase in HCN and a decrease in NH3 emissions with increasing temperature. At temperatures of 200-300 degrees C hexamine decomposition is reported to produce mainly ammonia and formaldehyde.

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Conversion of 2 to o--Bromobenzoic Acid. A solution of 2 was prepared as described in A and prior to quenching was added to bromine (excess in carbon tetrachloride). The acid 1 was isolated by conventional means and obtained in nearly quantitative yield. m-Benzoylbenzoic acid was prepared from m-bromobenzoic acid (0.0125 mol) by a procedure essentially identical with that described in B; the mixture was maintained at -20 to -10°(5 hr) prior to quenching with water. There was obtained (1) benzoic acid (mp 118-120°, 9.2%), (2) m-benzoylbenzoic acid [8, 69%, mp 155-158°; 63% from chloroform-petroleum ether,6 mp and mmp 161-162°(lit.8 mp 161-162°)]. The neutral fraction contained only trace quantities of products other than valerophenone (9%).p-Benzoylbenzoic acid was prepared from p-bromobenzoic acid as described for 8. The acid fraction on chromatography [silica gel, petroleum ether6-diethyl ether (70:30) as eluent] gave p-benzoylbenzoic acid [40%, mp 199-201°(lit.9 mp 197-200°)] and benzoic acid (30%).When the amount of tetrahydrofuran was increased twofold, only benzoic acid was obtained.When the procedure was carried out as described for 8 but with a mixture of tetrahydrofuran-hexane (60:40) the yield of p-benzoylbenzoic acid was 55-60% (multiple runs).

Bromine-lithium exchange in the isomeric bromobenzoic acids with n-butyllithium in tetrahydrofuran occurs selectively at -100°. The fate of these ions as a function of temperature has been examined. The dianions are stable at -75°but self-condense readily at -20°to give directly, and in good yield, o-, m-, and p-benzoylbenzoic acid, respectively. Anthraquinone is formed directly from o-bromobenzoic acid at higher temperature (0 to -20°).