Separation and Identification of Aromatic Amines by Two

368 Z. Anal. Chem., Band 267, Heft 5 (1973) Separation and Identification Table 1. R~-Values of aromatic amines with n-heptane, of Aromatic Amines by Two-Dimensional chloroform and carbon tetraehloride Thin-Layer Chromatography S.No. Amines R~-values a (a) (b) (c) of Charge-Transfer Complexes Liquid amines Trennung und Identifizierung aromatischer Amine 1. Aniline 0.096 -- 0.37 durch zweidimensionale Dfinnschicht-Chromatographic 2. m-Toluidine 0.17 -- -- yon Charge-Transfer-Komplexen 3. o-Toluidine 0.19 -- -- 4. N-lYIethyl aniline 0.26 -- 0.73 Trenn. yon Aminen, aromatische; Chromatographic, 5. ~,N-Dimethyl aniline 0.46 ~ 0.89 Diinnsehieht; Charge-Transfer -Komplexe Solid amines J. P. Sharma and Sushma Ahuja 6. p-Aminobenzoic acid -- 0.03 -- Dept. of Chemistry, University Allahabad, India 7. Benzidine -- 0.09 -- Received March 9, 1973; revised l~ay 29, 1973 8. o-Aminobenzoie acid -- 0.12 -- 9. a-Naphthylamine -- 0.30 0.24 10. fl-Naphthylamine -- 0.30 0.17 Aromatic amines form weak association complexes 11. p-Toluidine -- 0.39 0.43 with aromatic nitro compounds and the association a--c ~ Solvents, see text. constants of the complexes formed with a given a All the Rf-values are average of three to four runs. aeceptor are usually different depending upon the donor strengths of amines. When m-dinitrobenzene inserted in the tanks which had already been saturated is impregnated in the thin-layers made of silica gel with solvent vapour for 10 rain. and the aromatic amines ehromatographed on these The plates were developed for 30--35 rain except in the layers, good separation is achieved. The Rf-values case of carbon tetrachloride where the development time of the systems have been given in few different was 75--80 rain. After the development, the solvent-front was marked and the solvent was allowed to evaporate at solvents, and the conditions for the separation of room temperature after marking the solvent front. The spots solid and liquid amines have been specified. were self-reveMing. The amines were identified with the help of reference spots having same area and having travelled the same distance. The corresponding R~-values were cMcu- Experimental lated. Solvents. a) n-heptane saturated with liquor ammonia, After standardising the procedure separately for liquid b) chloroform saturated with water, c) carbon tetrachloride and solid amines using n-heptane (saturated with ammonia) saturated with water. and chloroform (saturated with water) respectively, the Preparation o/Plates. Equal quantities of silica gel G and mixture of liquid and solid amines could be separated on the m-dinitrobenzene were intimately mixed. A slurry was same plate. ~irst the plate was developed with solvent prepared by mixing 5 g of the above mixture with 12.5 ml a) when only liquid amines moved. After evaporating the of distilled water. This slurry was sufficient for making five solvent at room temperature, the plate was again developed plates of 5 • 20 cm size. The slurry was spread on the plates in a perpendicular direction with the solvent b) when solid and thin-layers of 300 ~m thickness were prepared and dried amines separated. in air at room temperature for 1.5 ~o 2 h. Results of separations are recorded in Table 1. Procedure. About 0.25 ~l of each test solution was spotted with a micropipctte on the plates at a distance of about Dr. J. P. Sharma 1.5 cm from the top. The reference spots were applied on Dept. of Chemistry both sides of the central spot at the same distance from the University of Allahabad top. The spot was air-dried for 5--8 rain. The plates were Allahabad, India .

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