Chemical Education Today
Letters Surfactant-Induced Osazone Formation at Room Temperature Surfactants are known to influence the kinetics and the product distribution of many reactions (1, 2) owing to their ability to form micelles above a particular concentration referred to as the critical micelle concentration (cmc). We have already reported in this Journal that by using surfactant solutions, the well-known redox reaction between oxalic acid and permanganate ion can be carried out quantitatively and conveniently at ambient temperatures (3); otherwise the reaction requires hot conditions (70 °C). Reducing monosaccharides are characterized by their ability to form osazone with phenylhydrazine reagent. This is a well-established reaction, recorded in almost all standard organic chemistry textbooks for undergraduate courses. The reaction is usually performed by mixing phenylhydrazine with the solid carbohydrate or its solution and heating it over a water bath for 20–30 minutes, when the yellow or orange solid osazone is precipitated. We have attempted the formation of glucosazone in anionic and cationic surfactant media. Sodium lauryl sulfate (NaLS) and cetyltrimethylammonium bromide (CTAB) were chosen as the representative anionic and cationic surfactant, respectively. Concentrations of surfactants (and also of other reagents) varying in order of magnitude from 10᎑5 to 10᎑2 M were investigated to find the optimum concentrations. In the absence of the surfactant, the reaction was not even initiated at room temperature. However, at optimum concentrations of the added surfactant, glucosazone was formed instantaneously at room temperature. On the basis of these results, we report here the experimental conditions required for quick identification of glucose at room temperature (25–30 °C): Appropriate higher concentrations of reagents were prepared and mixed so that the final concentrations in the reaction mix-
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ture were [phenylhydrazine] = 1.0 M; [glucose] = 0.16 M; [CH3COONa⭈3H2O] = 0.1 M; [NaLS] = 1.0 × 10᎑4 M (or [CTAB] = 1.0 × 10᎑5 M) in 10% aqueous acetic acid. The contents were shaken well and a yellow precipitate was formed instantaneously. This solid product was identified as glucosazone by matching its melting point and UV–vis spectral characteristics with those of the osazone prepared by the traditional heating procedure reported in textbooks of organic chemistry. This new procedure using surfactants is helpful in speedy and easy identification of reducing sugars. The advantages of this method over the traditional method are (i) reaction is instantaneous and (ii) no heating is required. Hazards The reagent phenylhydrazine is a skin and eye irritant. It may get absorbed into the body when the vapor is inhaled or the liquid is swallowed or comes into contact with the skin. Therefore, utmost care must be exercised when this reagent is used. Literature Cited 1. Attwood, D.; Florence, A. T. Surfactant Systems: Their Chemistry, Pharmacy, and Biology; Chapman and Hall: London, 1983. 2. Fendler, J. H.; Fendler, E. H. Catalysis in Micellar and Macromolecular Systems; Academic: New York, 1977. 3. Ponraj, D. S.; Venkataraman, R.; Raghavan, P. S. J. Chem. Educ. 1990, 67, 621. K. Nagajyothi, P. S. Raghavan,* and R. Gopalan Department of Chemistry, Madras Christian College, Tambaram, Chennai - 600 059, India
[email protected] Journal of Chemical Education • Vol. 78 No. 6 June 2001 • JChemEd.chem.wisc.edu
