A Simple Method for Analysis of Nitrobenzene in Aniline"

Indian Journal of Chemistry Vol. 21A, March 1982, pp. 279-281

A Simple Method for Analysis of Nitrobenzene In Aniline"

SUKUMAR MAITI- Materials Science Centre, Indian Institute of Technology, Kharagpur 721 302 and B. H. PATEL & (Miss) BHAVNA M. PANDYA Deepak Nitrite Ltd, Baroda 391 340

Received 7 June 1980; revised 19 May 1981; accepted 3 July 1981

A simple and sensitive method for the detennination of nitrobenzene in aniline and other aromatic nitro com- pounds has been developed. The method is based on the colour formation when nitrobenzene reacts with acetone- KOH reagent. The colour thus obtained obeys Lambert-Beer's law and therefore offers an elegant and simple colori- metric method for the determination of trace amount of nitrobenzene in aniline. The colour reaction is very specific; only ortho and para-positions to nitro groups are reactive. A mechanism of the reaction has been suggested.

perusal of the literature reveals that so far no volume (5-10 ml). The ether was completely removed simple and sensitive method is available for by adding acetone followed by evaporation. The A the determination of nitro benzene in com- concentrated extract was tested as usual. By this mercial samples of aniline. Acetone/potassium hy- enrichment technique nitrobenzene present in the droxide produces colour with di- and poly-nitro aro- order of 1-5 ppm has been successfully estimated. matic compounds but not with mononitro compounds (Janovsky reaction'). We have re-examined this Results and Discussion reaction in the case of mononitro aromatic com- Lambert and Beer's law is found to be obeyed pounds, particularly of nitrobenzene in aniline, in the concentration range 0-1,000 ppm of nitro- and have been able to develop a sensitive and simple benzene in aniline. Although the intensity of colour method for the estimation of even small amounts of initially increases and reaches a maximum value nitrobenzene in aniline. after 10 min, the colour is fairly stable. Afterwards the colour slowly fades and attains almost the initial Materials and Methods value. The rate of decrease in the intensity of colour All the chemicals and solvents used were of either depends on the concentration of the nitro compound AR or spectroscopic grade and were dried and/or present in the sample. The sensitivity of the test distilled before use. depends on the purity of acetone used. This test m-Dinitrobenzene2, l-nitronaphthalene", 9-nitro- may, therefore, be used indirectly to monitor the anthracene-, and mononitromesitylenes were syn- quality of acetone samples. Different alkalis such thesized following the standard procedures. as NaOH, LiOH, NH40H have also been tried and Procedure - Dry and distilled acetone (lOrn!) was it is found that the rate of reaction as manifested mixed with the aniline sample containing nitrobenzene in the rate of formation of colour increases with the or other aromatic nitro compounds. To it was added basicity of alkalis and decreases with their first ioni- solid, dry potassium hydroxide (1-2 g) and the zation energy. The sensitivity of the reagent with mixture slowly heated to boiling in a water-bath for respect to alkalis follows the order: lithium hydro- 5 min with stirring. The colour developed within xide < sodium hydroxide < potassium hydroxide 2 min and gradually deepened to reach the maximum < quarternary ammonium hydroxide. intensity within 5 to 10 min. No further warming However, the addition of a little amount of water of the reaction mixture was necessary. The intensity reduces the sensitivity of the reagent tremendously. of the colour formed was measured in a double cell A sample containing about 50 ppm nitrobenzene, colorimeter using green filter. Nitrobenzene or for example, does not form colour if the water present other mononitro aromatic compound could be esti- in the potassium hydroxide - acetone reagent is mated by the method of standard calibration curve. about 5 %. The reagent containing only I % of When the concentration of the nitro compounds water reduces the intensity of colour by 50 ~~. in the sample is very low, an enrichment technique Table I summarises the colour produced by diffe- may be used. About 100 ml of the sample were rent nitro compounds. A variety of organic com- extracted with 50-60 ml dry diethyl ether and the pounds, particularly taose containing carbonyl ether extract was carefully concentrated to a small groups Of activated methylene groups, are able to produce colour with nitrobenzene in the presence of . tThis paper, was presented in part, at the Annual Conven- a strong base (Table 2). Porters reported that dime- tion of Chemists, 1977, Jaipur, thyl formamide in the presence of tetraethylammo-

279 INDIAN J. CHEM., VOL. 21A, MARCH 1982

nium hydroxide formed colour with ortho- and is present in the para- or ortho-position the reactivity para-nitroanilines, while nitrobenzene, ortho- and of the compound to Janovsky reaction decreases. para-nitro benzo icacids, meta- and para-nitroanisoles Meta-dinitrobenzene, for example, is the most re- failed to generate colour in the Janovsky reaction. active to Janovsky reagent among the isomers of Carr", on the other hand, noted that aromatic nitro dinitrobenzene. This may be explained on the compounds are capable of producing colour reactions basis that substituents which by virtue of their nature with a variety of carbonyl compounds in the pre- and position in the aromatic ring help in making sence of a base. He reported that mono nitro com- the ortho- and para-positions to the nitro-groups pounds respond to the colour test only under special electron deficient, increase the reactivity. This has conditions. also been supported by the results of Porter". The influence of substituents in the aromatic ring In conformity with the observation of Canbacks, is also important in controlling the reactivity of nitro it is suggested that the colour produced in the re- compounds. Ortho- and para-orienting groups like action of nitrobenzene is due to the formation of a hydroxyl, methyl, amino or chi oro when present in quinonoid complex (Scheme 1). In Scheme I, the meta-position to the nitro group decrease the x represents any substituent in the nitro compound; sensitivity of the compound to the colour test. But RH represents the compounds containing active when these are present in the ortho, or particularly methylene groups; and B+OH- denotes a strong in the para, position to the nitro group the reacti- base. vity increases. Meta-orienting substituents like nitro or carboxyl groups when present in the meta- position to the nitro group increase the reactivity of the nitro compound. But when the nitro group ;:::! [?N =eX:J"- 6 A TABLE1 - EFFECTOFVARIOUSNITROCoMPOUNDSIN ACETONE- POTASSIUMHydroxide Reagent- Nitro compound m.p.rb.p. Colour produced» I °C o-Nitrobenzoic acid 14&-150 Pale yellow m-Nitrobenzoic acid 142 Pale yellow o-Nitroaniline 14& Deep red p-Nitroaniline 71.5 Yellow [H:<:T·· p-Nitrotoluene 52-54 Light pale yellow o-Nitroaniline 220-223 Light pink red p-NitrochlorobeU7.ene 83-84 Light pink red Sc heme I p-N itroanisole 54 Light pink red m-Dinitrobenzene 89 Deep purple 2,4,6-Trini trometaxylene 182 Purple light yellow Acetone is found to be one of the best compounds p-Nitrophenol 114 Greenish yellow for the colour forming reaction. This is due to the I-Nitronaphthalene 56-58 Orange red ease of formation of acetonyl ion via enolization of Nitrobenzene 210 Pink red acetone (Scheme 2). p-Nitrobenzoic acid 242-243 p-Nitrosophenol 125 Light greenish yellow The formation of acetonyl ion, CH2-CO-CHa, Dinitrornesitylene depends on [OH-]. This is supported by the ex- Mononitromesitylene perimental observations. The influence due to the -Nitrobenzene concentration used 50 ppm. KOH pellets presence of small amount of water or acid can also were added at room temperature and heated for 10 min as usual. be explained on the basis of Scheme 2. Water can Readings were taken in a double cell colorimeter using green easily react with the acetonyl ion to give acetone. filter. Since acetonyl ion is nucleophilic, it would only attack the electron-deficient centre of the aromatic TABLE2 - ORGANIC CoMPOUNDS FOR CoLOUR FORMING nucleus i.e. the ortho- and para-positions to the REACTION nitro-g;oup. Any substituent which increases the nucleophilicity of these positions will enhance the Compound Colour produced reactivity of the nitro-compound. If all the ortho- and para-positions to the nitro group in the benzene Acetone Pink red Methanol Light yellow ring are substituted, i.e: if the electron-defic~ent Acetonitrile Light orange centres in the benzene rrng are absent, the nitro Dimethyl formamide Very light yellow compound will not respond to the colour test. Mono- Ethyl methyl ketone Pink red nitro-mesitylene and dinitromesitylene, therefore, Isobutyl methyl ketone Pale yellow Cyclohexanone Pale yellow do not react with the reagent (See Table 1). Dimethyl sulphoxide Light brown In conclusion, this colorimetric test is, therefore, Acetophenone Orange yellow neither a confirmative test for the presence of nitro- Ethyl acetoacetate- Turbid lemon yellow group in an aromatic compound, nor it can be used Acetyl acetone- Turbid pale yellow as a general procedure for determination of nitro- *KOH pellets dissolved and formed turbidity. groups present in a compound. It is applicable only to those nitro-aromatic compounds where at least

280 MAlT! et al, : DETERMINATION OF NITROBENZENE IN ANILINE

References ~ 9H H]C-C-CHs -===:t: H2C-C-CHs 1. JANOVSKY,J. V., Ber, dt ehem. Ges., 24 (1891), 971. 2. VOGEL,A. I., Textbook of practical organic chemistry, 4th Edn (Longmans, London), 1978, 626. 3. URBANSKI,T., Chemistry and technology 0/ explosives, Vol. 4 (pergamon Press, London), 1964, 427. 4. Organic synthesis, edited by N. Rabjohn, Vol. 4 (John Wiley, New York), 1963, 711. S. Organic synthesis, edited by A. H. Blatt, Vol. 2 (John Wiley, New York),1957, 449. 6. PORTER,C. C., Analyt, Chem., 27 (1955), 80S. Scheme 2 7. CARR,J. J., Analyt, Chem., 25 (1953),1859. 8. CANBACK,T., Farm. Rev., 46 (1947), 802; Chern. Abstr., anyone of the ortho- or para-positions to the nitro 43 (1949), 2126; Farm. Rev •• 48 (1949), 153; Chern. group is vacant for the reaction. Abstr., 43 (1949), 6175.

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