The Preparation of Benzoyl Esters of Phenols and Benzoic Anhydride by'Phase-Transfer tatalysis A. Yeadon, T. A. Turney, a n d G. Ramsay Slough College of Higher Education. Wellington Street, Slough SL1 lYG, U.K. The principles of phase-transfer catalysis have been reviewed in THIS JOURNAL (1.2). Examples of preparations, suitable for undergraduate students, have been described that involve nucleophilic substitution reactions in which the oroduct is an ether and one of the reactants is an alkvl halide (3,4). In our classes, students have used a phase-transfer technique to prepare henzoyl derivatives of a range of phenols which has included phenol, cresols, nitropbenols, chlorophenols, 2-naphthol, salicylaldehyde, and salicylic acid. The derivatives have been characterized by melting point, and IR and NMR spectroscopy. Salicylic acid yields a dihenzoyl ~ r o d u c t .T h e products can he obtained free from henzoyl Ehloride hy using an excess o i t h e phenol. Other advantages are that the Droduct is easilv isolated and that a student enercise, inclu&ng discussion &d purification can he performed in a 2-h laboratory period. Also, the procedure is sufficiently rapid to replace the Schotten-Baumann technique which is often used for the preparation of derivatives in qualitative analvsis of oreanic ~,~~~ . . ~ com~ounds. The phase-transfcr riltalymd henmylation of benzoate ions leads to the ti~rmntionof benzoic anhvdride. The latter compound has been prepared and characterized by classes of students a t undergraduate level within a 2-h lahoratorv oeriod. The preparation of benzoyl esters (5)and mixed k h y drides ( 6 )has formed the subject of student projects. ~
Experimental Details Benzoyl chloride is corrosive and lachrymatory. The pro-
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Journal of Chemical Education
cedure involving henzoyl chloride should be performed in a hood and students should he required to use safety glasses and gloves throughout the preparation. The Benzoylation of Substituted Phenols Place sodium hydroxide (1.5g, 0.0375 mol), the phenol (0.0375mol), tetrahutylammonium bromide (0.1 g, 0.3 X 10-3mol) and water (20 ml) in a 250-ml flask and stir the mixture by magnet until a clear solution is obtained. Add a solution of henzoyl chloride (3 ml, 0.025 mol) in dichloromethane (20 ml) and stir the two-phase mixture vigorously by magnetic stirring for 20 min. The odor of benzoyl chloride should not he detectable at this staee. .. Seoarate . the dichloromethane laver. . . and wash i r aurr~sa~vely w ~ r hioiwdium hydnmlde solutim r2Omh and w a k r (20 ml~.Remove surpmded water hy f h m o n through phase-separating paper and evaporate the dichloromethane using a rotary evaporator. Recrystallise the produce from aqueous ethanol. The yield of benzoyl derivative is 60-80%. Preparation of Benzoic Anhydride Benzoie acid (4.88 g, 0.04 mol) is used in place of the phenol. The method and isolation procedure is the same as that given above for the benzoate ester. The crude anhvdride is obtained as an oil which solidifies to give white crystals (4.i5g, 96%),mp 38.5-40°C). Literature Cited (11 Gokd, G. W., and Webar, W. P., J,CHBM. EDUC.,55,350,429 (1978) (2) Mdntoah, J. M., J. CHEM.EDUC., 55,235 (1978). 13) Hill. J. W., and Corredor, J.,J. CHEM. E~uc.,57,822 (19801. (41 Row.J.E.. J.CHEM. EDUC..57.162 (1980). ( 5 ) Turney.T. A,. GRSC Project, 1983. (6) Ramsay, G.,GRSC Project, 19%.
