Chemical Education Today
Letters An Improved Preparation of 2,4-Dinitrophenylhydrazine Reagent
first, then continue stirring without heating. When the solution has cooled, filter through a fritted funnel, if necessary.
In the analysis of aldehydes and ketones (both for characterizing the functional group and identifying such compounds by the melting points of their derivatives), 2,4dinitrophenylhydrazine reagent is often used. Of the several formulations of this reagent, the most popular uses sulfuric acid. The method involves making a paste of 2,4-dinitrophenylhydrazine in concentrated sulfuric acid, dispersion of the paste in ethanol, addition of water, and the filtration of the reagent (1). This improvement uses milder conditions, which may obviate the need for the final filtration. Those responsible for preparation of stock reagent solutions for classes should note that this method facilitates scaling up the preparation. To a clean, dry 125-mL Erlenmeyer flask and magnetic stir bar, add 3 grams of 2,4-dintrophenylhydrazine, 20 mL of water and 70 mL of 95% ethanol. Place the flask in an ice bath in a beaker. Stir and allow the mixture to cool. When the temperature reaches 10 °C, with continued rapid stirring, begin the slow addition of 15 mL concentrated sulfuric acid, trying to avoid boiling. If the temperature goes above 20 °C, stop addition until the temperature goes back to 10 °C. When the sulfuric acid has been added, turn off the stirrer, remove the ice-bath and place the flask on a stirrer-hotplate. Stir and warm the flask until the 2,4-dintrophenylhydrazine stops dissolving or the temperature reaches 60 °C, whichever comes
Hazards
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Journal of Chemical Education
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2,4-Dinitrophenylhydrazine [119-26-6] is a flammable solid, which must be kept moist and is harmful if swallowed, inhaled, or absorbed through the skin. Concentrated sulfuric acid [7664-93-9] is poisonous and corrosive. Its mist can cause severe burns to all body tissue. It may be fatal if swallowed or by skin contact. It is harmful if inhaled and may cause cancer. Ethanol [64-17-5] is flammable and should be kept from ignition sources. Eye and face protection, protective clothing, and gloves must be worn. Literature Cited 1. Linstromberg, W. W.; Baumgarten, H. E. Organic Experiments, 6th ed.; Houghton Mifflin: Boston, 2002; p 175. Shriner, R. L.; Hermann, C. K. F.; Morrill, T. C.; Curtin, D. Y.; Fuson, R. C. The Systematic Identification of Organic Compounds, 8th ed.; Wiley; Hoboken, NJ, 2004; pp 278–279. Ben Ruekberg* and Eric Rossoni University of Rhode Island Chemistry Department Kingston, RI 02881 *
[email protected] Vol. 82 No. 9 September 2005
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