Sister Laetitia Marie Lariviere,' and Joseph E. Weber Bowling Green State university Bowling Green, Ohio
A Simplified Electrolytic Preparation of lodoform An anodic organic laboratory experiment
W e suggest here a simple electrolytic oxidation experiment as a complement to the electrolytic reduction experiment previously de~cribed.~A simplified anodic preparation of iodoform can he carried out utilizing the G. A. Roush3 auxiliary cathode technique for controlling the pH of the reaction mixture and the lead dioxide coated graphite anode developed by F. D. G i b ~ o n . ~ We also describe an inexpensive reactifier and variable dc source, and the preparation of a lead-dioxide-coated anode as well as the electrolytic preparation of the iodoform. A compact source of direct current can be assembled from readily available parts5 (Fig. 1) in a Bud nfnibox
Figure 1.
Low voltage dc power source.
Port. List C Flar Rect. RL Rl,z A,,? T
N
Capacitor, Sprogue 5 5 0 0 MF @ 2 5 v Fuses, 2 % amp. 3 A G SB type RectBer. Bridge type-Motorola MDA 952-1 220K Resistor, % w. 10% ccomporition Rheostat, 12.5 w ohmite, 15 ohms Ammeters-Emico 5 v range Tronrformer, Allied Electronic 12.6 v @ 3 amp Neon bulb Nc 2
in effectiveness but is more economical. Graphite rods 0.5 in. in diameter were used for both electrodes. When the cathode vas immersed about 2'/%in. in the solution a current density of 5 amps resulted; an anode immersion of 4 in. produced a current density of 3 amps. The cell was operated a t G v. The graphite rods should be soaked in water for a period preceeding electroplating to displace the air and thus prevent the formation of pinholes in the coating. Also to insure a smooth even coat the anode should he rotated. An electric stirrer can be adapted by connecting the anode to the shaft by means of rubber tubing. The second method mould be to use a simple motor-such as an adjustable phase wave generator7-run with a single dry cell and a rheostat to control speed. The shaft is fitted with a wooden cam through which a hole allows a wire to make the contact between electrode and motor. Rubber tubing was also used to secure the anode to the cam. The plating bath consists of 50 g lead nitrate, 2.5 g copper nitrate, 2.5 g nickel nitrate, 1 ml conc. nitric acid, 0.125 g sodium fluoride, and 5 drops Triton X-1008 per 250 ml of solution. A two hour electrolysis time results in a shiny smooth black coating of lead dioxide on the graphite core. Preparation of lodoform
The Roush cell was assembled (Fig. 2) using the lead dioxide rod for the anode, and t~i-ocgpper rods 0.23
cabinet S X G X 31/1in. Another source of power can be a 12-v automobile battery used in connectian with a Heathkit6variahleresistor set in series with an ammeter. Preparation of Lead Dioxide Electrode
Although platinum electrodes can be used successfully, the lead dioxide electrode is not only comparable 1 Present address: Holy Redeemer High School, Detroit, Michigan. Work supported by the National Science Founda tion in a three phase sequential summer institute. WEBER,J. E., AND MEISTER,A., J. CHEM.EDUC.,27, 671 (1950). a ROUSE.G. A,. J. Trans. Amer. Electroehem. Sac., 8, 283 (1905). 4 GIBSON, F. D., U.S . Patent 2,94.5,791, July 19, 1960. 6 Allied Radio Corporation, Allied Industrial Electronics Catdolog, 100 N. Western Ave., Chicago, Illinois, 6ffi80. 6 Heath Company, Heilthkit Catalog, Benton Harbor, Michigan, 4902'3. 'Maonlaster Scientific Corporation, Watertown, Mass., 02172. 8 Triton X-100, Alkyl-phenoxy polyethoxy ethanol, Rohm & Haas, Philadelphia, Pennsylvania.
54 / Jovrnol of Chemical Education
Figure 2.
Ceii far the prepamtion of iodoform.
in. in diameter as cathodes. One cathode was placed in a 50-ml porous cup. The electrolytic solution consisted of 8.3 g potassium iodide per 100 ml of solution. Part of this solution was placed in the porous cup, the remainder in a 250-ml beaker. One milliliter of acetone Tvas added to the beaker. The electrodes were submerged about 1 in. into the solution and the current turned on. The current through the two cathodes was regulated t.o maintain a 3 2 ratio between the regular and auxiliary cathodes. The reaction was permitted to run for 1 hr with occasional stirring. The pH may be monitored by Hydrion paper and should he kept at about pH S hy adjusting the cathode current. At the conclusion of the electrolysis any remaining free iodine is removed by adding a few drops of a 10yo solution of sodium thiosulfate until the color disappears.
The product is filtered and recrystallized from hot isopropyl alcohol. Although the preparation of iodoform provides an easy application of an anodic method for organic synthesis the creative student mill find that the equipment suggested here is sufficiently versatile that many variations in the procedure can be made including the use of organic compounds that can he directly oxidized at the anode. A review paper by Wilson8 suggests that the area of electro-organic chemistry has tremendous potential in both pure and applied science. Therefore there would seem to be a definite place in the organic laboratory for an electrochemical experiment. 'WILSON,C . L.,Science and Technology, 82, (Mar. 1966).
Volume 45, Number 7, lonuory 7968
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