Nitro group, determination

Analytical and Test Methods. o-Nitrotoluene can be analyzed for purity and isomer content by infrared spectroscopy with an accuracy of about 1%. -Nitrotoluene content can be estimated by the decomposition of the isomeric toluene diazonium chlorides because the ortho and meta isomers decompose more readily than the para isomer. A colorimetric method for determining the content of the various isomers is based on the color which forms when the mononitrotoluenes are dissolved in sulfuric acid (45). From the absorption of the sulfuric acid solution at 436 and 305 nm, the ortho and para isomer content can be deterrnined, and the meta isomer can be obtained by difference. However, this and other colorimetric methods are subject to possible interferences from other aromatic nitro compounds. A titrimetric method, based on the reduction of the nitro group with titanium(III) sulfate or chloride, can be used to determine mononitrotoluenes (32). Chromatographic methods, eg, gas chromatography or high pressure Hquid chromatography, are well suited for the deterrnination of mononitrotoluenes as well as its individual isomers. Freezing points are used commonly as indicators of purity of the various isomers. 

The presence of three chlorine atoms is easily determined by the isotope ratios. The odd molecular weight shows the presence of nitrogen. The loss of m/z 30 and 46 from the molecular ions shows the presence of the nitro group. 

When aromatic compounds are reacted with hydrogen, the catalyst used determines which part of the molecule reacts. Thus, with the right catalyst, a nitro group can be converted to an amine without adding hydrogen to the ring. In this case the simplest aromatic amine (aniline) is produced. 

PPP calculations reproduce the nitro substituent effect and heterocyclic effect on the /,max. For example, the bathochromic shift by substitution of a nitro group is calculated (ca.20nm). It is in good agreement with the experimental value determined (A,max = 598 nm) in toluene. PPP calculation exactly predicts the bathochromic shift by benzo-annelation of the indoline and benzopyran residues (Table 2). In the neutral quinoid form, the calculated charge densities for the ground and first excited states by PPP... 

The decarboxylation of mercuric 3- and 4-nitro-l,8-naphthalene-dicarboxylates has been studied to determine substituent electronic effects [Eq. (83)] (95,96), since significant steric effects are unlikely. There is disagreement over the products. In an early study, 3- and 4-nitro-l,8-naphthalenedicarboxylates were found to undergo decarboxylation predominantly in the ring without the nitro group (95), consistent... 

A simple spectrophotmetric method for the determination of niclosamide in bulk and dosage forms was developed [44]. It was based on the reduction of the nitro group in niclosamide to the amino group by treatment with zinc powder and dilute HC1 for 15 min in 95% ethanol solution. The cold and clear filtrate reacted with p-benzoquinone, when a pink compound was obtained which absorbed at 506 nm. 

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