Nitroanilines chromatographic separation

Chromatographic Separation of a Mixture of o- and p-Nitroaniline. Prepare a glass tube A (Fig. 24) in which the wider portion has a diameter of 3 cm. and a length of ca. 30 cm. the narrow portion at the base has a diameter of 5-7 mm. Wash the tube thoroughly (if necessary, with chromic acid, followed by distilled water and ethanol) and then dry. Insert a small plug of cotton-wool P as shown just within the narrow neck of the tube it is essential that this plug does not project into the wider portion of the tube. Clamp the tube in a vertical position. 

Similar displacement chromatographic separations have been obtained for other samples as well including naphthol iscmers (67), nitroaniline iscmers (67), nitrophenol iscmers (67), the cis- and trans-iscmers of 3-hexen-l-ol (68), and the enantiomers of mephobarbital (69), hexobarbital (69), dansyl leucine (69) and dansyl valine (69). Sample loadings on the 4.6 mn ID. analytical columns varied between 0.1 milligram and 60 milligram the concentration of the separated solutes in the collected fractions ranged from 0.1 nM to 10 nM. 

Enzyme methods using ascorbic acid oxidase have not been widely used but several versions of reagents based on diazotized nitroanilines have been reported (41). The reaction is complicated and the ascorbic acid molecule is partly destroyed in forming the colored product. A chromatographic separation stage must precede the color development reaction (42). The procedure is time-consuming and there is no provision for reducing any dehydroascorbic acid in the sample extract to ascorbic acid. 

In this example, the isomers had significant water solubility. Further, water has a small selectivity for p- over o-nitroaniline. Mandal et al (in preparation) also studied HFCLM separation of stereoisomers cis- and /raTis-stilbene which have very low water solubility. The solubility and the observed selectivity in the P-cyclodextrin liquid was significant (selectivity of almost two for the cis- over the /rans-isomer). Further, the separation was stable and continuous which opens a way for continuous separation of isomers as opposed to chromatographic separations. 

Chromatography on silica and alumina is unique among the liquid chromatographic methods in providing maximum selectivity for tfie separation of isomers. It is no problem to separated m- and p-dibromobenzene (a s 1.8 in pentane) (2) or the three nitroanilines (79) on silica or alumina stationary phases with dichloromethane as eluent. 

Structural Isomers. Chromatograms illustrating the separation of ortho, meta and para isomers of cresol (22) and and xylene ( O)on RP columns are shown in Figures 4 and 5. They enable a comparison of the chromatographic properties and selectivities due to <. - and -CD complexation between positional isomers of the above compounds.Similar behaviour was observed for ortho,meta and para isomers of fluoronitrobenzene, chloronitrobenzene, iodoni-trobenzene, nitrophenol, nitroaniline, dinitrobenzene (22), nitrocinnamic acid (22) some mandelic acid derivatives (19,21,34) and ethyltoluene (28). Both [Pg.225]

Ross et al (42) employed TEA for detection of dimethylnitros-amine and dipropylnitrosamine in several herbicide formulations after separation by GC or HPLC. With additional chromatographic cleanup, the identity of the compounds was confirmed by high resolution mass spectrometry. These results further indicated that formulations of amine salts can form nitrosamines on storage and nitrosamines can be formed in preparations of nitroaniline based herbicides. The results obtained for the determination of nitrosamines in seven technical herbicides are shown in Table 8. 

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