THE CATALYTIC PREPARATION OF ACETONE FROM ACETIC ACID*
Squibb' found that a good yield of acetone is obtained when acetic acid vapors are passed over barium carbonate or calcium carbonate a t a temperature of about 500°C. His heating unit consisted of an iron pipe enclosed by an earthenware drainpipe which served as a furnace. Heat was obtained by Bunsen burners admitted through holes in the bottom of the drainpipe. It was found, however, that equable heating, under the conditions of this process, was impossible. Therefore, a rotary still was devised and substituted for the stationary still. A form of apparatus very similar to Squibb's stationary still is described by Cumming, Hopper, and Wbeeler.2 The only difference is that a combustion tube is used instead of an iron tube, and a cylindrical air bath made of tin or light sheet iron, heated by a combustion furnace, is used. The heating unit proposed herein has been found to be a marked and worth-while improvement on the above methods for laboratory purposes. The most noteworthy improvement is in the method of heating, this being accomplished by means of a simple, efficient, and easily regulated electric furnace, which the student can construct easily. Other wortb-while features of the equipment are the construction and use of a thermocouple instead of a thermometer, and the preparation of a catalyst mixture. The method consists in passing acetic acid vapor through a combustion tube charged with a calcium carbonate-asbestos-pumice mixture, and heated to approximately 500°C. The accompanying diagram illustrates the arrangement of the apparatus.
Apparatus Since the arrangement of the apparatus is apparent from the diagram, only the construction of the heating unit and the thermocouple will be described. It was found that a temperature of approximately 500°C. could be most easily obtained and maintained by using an electrically heated combustion tube. Three strips of thin asbestos, about 1 cm. wide, are placed along a combustion tube SO cm. X 2.2 cm.,and around these strips are wound about 600 cm.of Chrome1 " A wire, B &S 24. The whole is insulated by three or four folds of heavy asbestos which is then moistened
* Extracted from the thesis presented by Charles D. Kochakian to the Graduate School of Boston University in partial fulfilment of the requirements for the degree of Master of Arts. SQUIBB,"Improvement in the Manufacture of Acetone," J. Am. Ckem. Sac., 17, 187-201 (Mar., 1895). C~MING HOPPER, , AND WFIEELER.''Systematic Organic Chemistry. Part 11. The Linking of Carbon to Carbon," 2nd edition. Constable & Co., Ltd., London, England, 1931, p. 94. 1649
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and molded to a compact mass. The asbestos is allowed to dry--drying may be hastened by passing a small current through the coil. This heating unit is capable of raising the temperature of the tube and contents to about 700°C. which is, however, higher than necessary. Therefore, a rheostat of approximately 16 ohms is placed in series with the heating unit. The temperature is regulated by varying the resistance (R) and is measured by a chromel-cope1 thermocouple ( T ) connected to a good millivoltmeter (M) which is accurate enough for the experiment. Two lengths (80 cm. each) of chrome1 "X," B & S 22, are fused to the ends of a length (80 cm.) of copel "X," B & S 22. The ends of the wires are twisted together, dipped into borax, which acts as a flux, and fused in a gas-oxygen flame. A
A. Distilling flask-500 cc. E. Water bottle B. Air condenser F. Heating unit C. Water condenser M. Millivoltmeter D. Erlenmeyer flask-25.0 cc. R. Rheostat T . Thermocouple APPARAT~S aoR THE CATALYTIC PREPARATION OP ACETONE PROM ACETIC ACID C
little practice is required before a good fusion, which is absolutely necessary, is obtained.* Preparation of the Catalyst The catalyst consists of calcium carbonate dispersed in asbestos fibers and mixed with small pieces of pumice to give a maximum surface. Fifteen to twenty grams of pumice, broken to pieces the size of a bean, and 10 grams of shredded asbestos are added to a solution containing 110 grams of calcium nitrate dissolved in 1000 cc. of water. The calculated amount of 15% sodium carbonate solution is added slowly and with good stirring. The resulting mixture is filtered, washed, and dried. This mixture is enough for four charges. Procedure The combustion tube ( F ) is loosely filled with the catalyst mixture, having a little unmixed pumice a t each end, and clamped into position.
* Catalog 52 of the Hoskins Manufacturing Company from whom the above wires were obtained will be found useful in making the thermocouple. Also tables of temperature millivolt equivalents are given.
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ACETONE FROM ACETIC ACID
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The glacial acetic acid (100 cc.) is placed in the distilling flask ( A ) , and all connections are made tight. The furnace is then heated until the difference in potential between the hot and cold junctions is 30-32 millivolts, which represents a temperature of about 500°C. When the required temperature is attained, the acetic acid in the distilling flask ( A )is heated to boiling, using a Bunsen flame about 4 an.long. In about ten minutes white fumes will be noted in the air condenser (B), which consists of a 500-cc. flatbottomed Florence flask, and in which all the unconverted acetic acid and a little acetone are condensed; also, bubbles will be noted in the water bottle (E). The acetone condenses in the water condenser (C) and is collected in the receiver (D), which is placed in a freezing mixture of ice-water-calcium chloride. Some acetone escapes condensation and passes to the wash bottle (E) where it is dissolved in the water. When almost all of the acid is vaporized-approximately one hour-the distilling flask is removed, the end of the combustion tube is stoppered, and the temperature is allowed to remain a t 500°C. for about 5 minutes longer. Then the current is shut off. The flask in the ice-water-calcium chloride mixture contains the bulk of the acetone, which is obtained by distilling with an efficient fractionating column, collecting the portion boiling up to 57'C. The air condenser contains chiefly unconverted acetic acid and a small amount (ca. 3 cc.) of acetone which may be obtained by fractional distillation. The presence of acetone in the wash bottle is determined by the formation and identification of dibenzalacetone. *' Yield A total yield of fi5-70% calculated from acid vaporized is obtained. Acknowledgment The writer wishes to acknowledge his indebtedness to the following members of the Boston University Chemistry Department: to J. Philip Mason for valuable assistance and suggestions in developing the experiment and preparing the manuscript, and to Edward 0. Holmes, Jr., for timely advice.
