Nitro esters, detection

Bratin, K., P. T. Kissinger, R. Briner, and C. Bruntlett. Determination of nitro aromatic, nitramine, and nitrate ester explosive compounds in explosives mixtures and gunshot residue by liquid-chromatography and reductive electrochemical detection. Anal. Chim. Acta 130, 295-311 (1981). 

It has seemed desirable to try to detect the postulated acylimidazole intermediate by spectroscopic probing. Acetylimidazole has been shown31 to have an absorbance maximum at 245 nm with an extinction coefficient of 3000. This absorbance should provide a basis for detection of the intermediate. However, in practice the strong absorbances due to the aromatic ester substrate (nitrophenyl caproate) and the product (nitro-phenol(ate)), added to the light scattering from the polymer, have made the spectrophotometric observation of the acylimidazole intermediate unfeasible under the reaction conditions previously described.26... 

This product was characterized by its NMR spectrum and also by reaction with HC1 followed by BF3/methanol to yield methylcyanoacetate ester. The reaction occurs readily, and in the absence of detectable amounts of the oxidative addition product of acetonitrile with the iridium complex, [Hlr-(depe)2CH2CN]+. In contrast, neither Rh(depe)2Cl nor Rh(dmpe)2Cl (dmpe = Me2PCH2CH2PMe2) react with C02 in acetonitrile, though Rh(dmpe)2Cl does react with C02 in nitromethane to form the analogous nitro-acetate hydride complex, (57). 

Melphalan and the racemic analog have been prepared by two general routes (Scheme I). In Approach (A) the amino acid function is protected, and the nitrogen mustard moiety is prepared by conventional methods from aromatic nitro-derivatives. Thus, the ethyl ester of N-phthaloyl-phenylalanine was nitrated and reduced catalytically to amine I. Compound I was reacted with ethylene oxide to form the corresponding bis(2-hydroxyethyl)amino derivative II, which was then treated with phosphorus oxychloride or thionyl chloride. The blocking groups were removed by acidic hydrolysis. Melphalan was precipitated by addition of sodium acetate and was recrystallized from methanol. No racemization was detected [10,28—30]. The hydrochloride was obtained in pure form from the final hydrolysis mixture by partial neutralization to pH 0.5 [31]. Variants of this approach, used for the preparation of the racemic compound, followed the same route via the a-acylamino-a-p-aminobenzyl malonic ester III [10,28—30,32,33] or the hydantoin IV [12]. 

Derivative formation is essential for analysis of gibberel-lins because they only absorb radiation below 230 nm, which is an extremely nonspecific region. Benzyl esters (49) and p-nitro-benzyl esters (60) of gibberellins have successfully been synthesized prior to injection to permit their detection as they elute from HPLC columns. Unfortunately, these derivatives have added little selectivity to the analytical procedure. The derivatives are monitored at 254 or 265 nm which, as previously mentioned, is a nonspecific region. 

K. Bratin, P. T. Kissinger, R. C. Briner, and C. S. Bruntlett, Determination of Nitro Aromatic, Nitramine and Nitrate Ester Explosive Compounds in Explosive Mixtures and Gunshot Residue by Liquid Chromatography and Reductive Electrochemical Detection, Analytica Chimica Acta 130, no. 2 (1981) 295. 

Several enzyme-linked immunosorbent assays (ELISAS) have been developed for trinitrotoluene, trinitrobenzene, 2,4-dinitrotoluene, and 2,6-dinitrotoluene using polyclonal antibodies raised in New Zealand white rabbits. Nitro substituted benzoic and phenyl acetic acids were used as haptens by conversion to the correspond NHS esters followed by coupling to protein carriers.The antibodies which were developed to 1,3-dinitroaromatic haptens had the greatest specificity and sensitivity when the nitroaromatic analytes contained a 1,3-dinitro functionality. In one ELISA system a lower detection limit for various 1,3-dinitroaromatics analytes of 1 ng/mL with an I50 of 5 ng/mL was observed. No cross reactivity with mononitroaromatic compounds was observed. Antibodies developed to mononitroaromatic haptens showed high affinity for a variety of coating antigens but would not compete with nitroaromatic analytes in a normal ELISA. 

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