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Saponifica Tion of Acet Amide in a Batch Reactor

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Saponifica Tion of Acet Amide in a Batch Reactor laboratory SAPONIFICA TION OF ACET AMIDE IN A BATCH REACTOR S. W. WELLER ingly but not surprisingly, only one group of State University of New York students has ever chosen to refer, in their labora­ Buffalo, NY 14214 tory report, to the article in French. The saponification of acetamide is much slow­ JN DECEMBER 1974, Dr. E. 0. Eisen reported er than that of ethyl acetate, and it is convenient at an annual meeting of A.I.Ch.E. the results to conduct the reaction at modestly elevated of a survey he had made on the teaching of under­ temperatures, in the range of 40° to 80°C. This graduate kinetics [l]. Of those departments re­ fact helps in quenching the reaction when aliquot porting the use of a laboratory experiment il­ samples are taken for analyses at room tempera­ lustrating homogeneous kinetics, most utilized ture. The large difference in rates is illustrated either (a) the hydrolysis of acetic anhydride or by the data of Laidler and Chen: at 25°C., the 2 1 1 (b) the saponification of a carboxylic acid ester rate constant is 8.0 x 10- z mole- sec- for the hydrolysis of ethyl acetate, and 3.77 x 10-5 z mole-1 such as ethyl acetate. sec-1 for the hydrolysis of acetamide. The results We have refrained from the use of acetic an­ hydride by undergraduates because of the lacry­ of Willems and Bruylants on acetamide, obtained over the temperature range 65° to 85°C., lead to matory and vesicant action of this material. Our own experience with ethyl acetate, over a period of several years with students, is that the saponi­ 2.6 fication proceeds so rapidly, even in dilute solu­ tion at room temperature, that quenching of the reaction for subsequent titration of unreacted base is difficult to conduct reproducibly. As a re­ sult, wide variations in rate constants were re­ 2.2 ported by different undergraduate groups in our laboratory, and attempts to determine an activa­ QJ 0 0 tion energy were hopeless failures. E ......,._ The purpose of this note is to report some 2 work, apparently successful in the hands of -_1.8 students, on another reaction that can be useful ::c ' 0 in an undergraduate chemical engineering labora­ z0 tory. The reaction is the saponification of aceta­ u mide in aqueous solution : 0 0 • CHaCO NH2 + NaOH CH 3 COO Na+ NHa 1.4 (1) The reaction is effectively irreversible and is second order. Data on the second order rate constants are available in articles by Willems and Bruylants [2] and by Laidler and Chen [3]. Students are given 40 80 120 these references in the laboratory instructions, I, minute with the note that the 1951 article is more di­ FIGRUE 1. Second-order rectifying plot for the saponi­ rectly useful for elevated temperatures. Interest- fication of a cetamide at 47.5° C. 74 CHEMICAL ENGINEERING EDUCATION ·, ! --- ------------------- vacuum-dried first (m.p. = 82°C) . Alternately, the concentration may be determined by allow­ ing the alkaline hydrolysis with a known excess of NaOH to proceed to completion, with subse­ quent titration of residual alkali. • Non-reproducible technique in the use of a 2 ml. pipette. (Practice with this might be edu­ cational for the chemical engineering student who lacks prior exposure to an analytical chemistry laboratory.) • Failure to equilibrate the two initial solu­ tions at reaction temperature before mixing. One caution: NH, is slowly produced in the Sol Weller did his undergraduate work at Wayne and obtained reaction. The laboratory should be adequately his Ph.D., from the University of Chicago in 1941 , under the Nobel ventilated, therefore, especially when the reac­ Prize winner in physics, James Franck. After serving the N.D.R.C. tion is run at temperatures above 50°. and the Manhattan Project during W.W. 11 , he conducted research at the Bureau of Mines. He was head of fundamental research at ACKNOWLEDGEMENTS Houdry Process Corp., then he joined the Aeronautic Division of The experimental data shown in Fig. 1 were obtained by Ford (later Philco-Ford). He came to SUNY / Buffalo in 1965 as pro­ Guy Jamesson and Mahmood Jawaid, whom the author was fessor of chemical engineering. He has contentedly pursued research delighted to have as students. D in kinetics and catalysis in Buffalo since then, except for pleasant interludes as visiting professor at Berkeley, U.N. technical expert REFERENCES in Haifa, and Fulbright lecturer in Madrid. 1. Eisen, E. 0., Minisession on Teaching of Undergradu­ ate Reaction Kinetics, AIChE Meeting, Washington, the following expression for the rate constant: D.C., December 4, 1974. 2. Willems, M. and Bruylants, A., Bull. Soc. Chim. Belg. k 9.55 x 105 exp (-14,200/RT) (2) = 60, 191 ( 1951). This is also consistent with the 25° value of 3. Laidler, K. J. and Chen, D., Trans. Far. Soc. 54, 1026 Laidler and Chen. (1958). We have found it convenient to use a solution that is initially lM in both acetamide and sodium hydroxide, prepared by mixing equal volumes of BOOKS RECEIVED Continued from page 68. the corresponding 2M solutions. The batch re­ action is conducted in a multineck flask, im­ Wiley & Sons, New York, 359 pages. The purpose mersed in a thermostatted water bath, and of this book is to acquaint the reader with the equipped with a variable speed stirer; 0.1 N HCl increasing number of applications of statistics and NaOH are used for the determination of un­ in engineering and the applied sciences. reacted NaOH in 2 ml. aliquots, removed Patterns of Problem Solving, Moshe F. Rubin­ periodically by pipette. Some feeling for the fre­ stein. Published by Prentice-Hall, Inc., Englewood quency of sampling can be obtained by observing Cliffs, NJ, 544 pages. The material in this book that the half-time for reaction at 50°C., for an was developed while teaching a compus wide in­ initial concentration of lM for both reactants, is terdisciplinary course, "Patterns of Problem about 1.2 hr. Since the reactants are present in Solving." The book attempts to provide the read­ equimolar ratio, the rate constant is evaluated er with tools and concept which are most produc­ by any standard rectifying plot: e.g., 1/ CNa oH vs. t. tive in problem solving and are least likely to be Figure 1 shows such a plot for a run conducted eroded with the passage of time. at 47.5°C by a student group. The slope cor­ Thermoplastics - Properties and Design, Edit­ responds to a value of k = 1.10 x 10-2 l mole-1 ed by R. M. Ogorkiewicz. Published by Wiley­ 1 1 min-1, or 1.83 x 10-c1 l. mole- sec- • Interscience, New York, 248 pages. This book Some of the important sources of error are : sets out to provide an understanding of the • Preparation of the stock solution of aceta­ principles underlying the properties of plastics, mide by weighing directly from the bottle. Aceta­ and also of the design problems associated with mide is hygroscopic. If concentration is to be de­ plastics in a way that will appeal to designers and termined by weight, the material should be engineers. D SPRING 1976 75 .
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