ON THE E L E C T R O L Y T I C P R E P A R A T I O N O F IODOFORM FROM A C E T O N E BY HOWE ABBOTT
In 1884E. Schering' patented a process for the preparation of iodoform, bromoform and chloroform by the electrolysis of the corresponding halogen compound of an alkali or an alkaline earth metal in warm aqueous alcohol, aldehyde or acetone solution with the simultaneous introduction of a current of carbon dioxide. Elbs and Hem2 have conducted experiments to determine the most favorable conditions for the preparation of iodoform from alcohol. They suggest that if an alkali carbonate is added to the anode solution the introduction of carbon dioxide is unnecessary. When they tried to substitute acetone for alcohol, using as anode solutions 3, 6 and 1 2 grams of sodium carbonate, 10-15 grams of potassium iodide, 93 cc of water, 2 7 cc acetone, at temC and current densities from 0.5-4.0 peratures from 20'-40' amperes per square decimeter, they obtained no iodoform during the electrolysis, but instead a dark brown body and free iodine. If, however, they added a warm solution of sodium hydrate to the body it dissolved and, on cooling, a small quantity of iodoform together with some impurities precipitated. This led them to substitute the hydrate for the carbonate in the anode solution. Under otherwise similar conditions after one ampere hour no solid separated and only the odor of the anode solution showed the formation of a small quantity of iodoform. I n this case they state that there was no free iodine, but that the solution was colored brown by condensation products of acetone. From their experiments they conclude that iodoform cannot be successfully prepared from acetone. I
* D. R. P. 29, 771, May 6 , 1884. Zeit. Elektrochemie, 4, 113 (1897).
Pyeparation of lodofoorm f i w w i Acetoze
85
I duplicated their conditions with the same experimental result. Knowing from experiments in this laboratory that a ternperature of 75" C gave the best yield of iodoform from alcohol, I next tried to prepare iodoform froin acetone at this temperature. T h e apparatus was constructed as follows: T h e cathode chamber consisted of an ordinary beaker of about 500 cc capacity. I n this was placed a porous cup, of about 1 2 0 cc capacity, containing the anode solution of 6 grams sodium carbonate, I O grams potassium iodide, 80 cc water and 20 cc acetone. A cork with two perforations was placed in the mouth of the porous cup. Through one of these passed a thermometer and through the second a reflux condenser to prevent loss of acetone by distillation. T h e cathode was a cylinder of iron wire gauze and the cathode liquid a I O pct solution of sodium carbonate. The apparatus was maintained at a constant temperature by means of a water-bath. After electrolyzing for two hours with a current density of one ampere per square decimeter, the anode solution contained a small quantity of iodoform, an excess of free iodine and but little of the brown body described by Elbs and Herz. Thinking that possibly the acetone could be kept from oxidizing and frum forming condensation products (thus increasing the yield of iodoform), if only a small quantity was present i n the anode solution at one time, the next experiment was to add the acetone gradually during the electrolysis. T h e result was that a considerable quantity of fairly pure iodoform was obtained. T h e concentratioii of the anode solution was next varied. Instead of IOO cc of water 2 5 0 cc were used. With the other conditions the same, the yield was perceptibly increased and the anode solution was little colored with free iodine. I n all these cases, however, the iodoform was more or less colored froin the presence of a small quantity of the brown body mentioned above. Seeing that the temperature had a great influence on the quantity of the brown body formed, I next tried a
Howe Abbott
86
temperature of 9 0 O - 9 5 " C with the hope of either decomposing this body or preventing its formatioil altogether. T h e result was that the iodoform obtained was of a beautiful yellow color and no trace of the other body was found. These preliminary experiments were not quantitative, but indicated the most favorable conditions for a good yield of iodoform. I next tried by a systematic series of experiments to determine the most favorable conditions for the preparation of iodoform from acetone. T h e apparatus was the same as that used in the preliminary experiments with the exception that a copper voltameter and an ammeter were placed in the circuit in addition to the resistance and the electrolytic cell. T h e sodium carbonate used was anhydrous and chemically pure as was also the potassium iodide and acetone. T h e effect of all conditions of experiment, namely : current density, temperature, the amount of sodium carbonate and potassium iodide, the concentration of the anode solution and the gradual addition of definite aniounts of acetone at regular intervals during the electrolysis, were tried and the results are given in the tables below. A temperature of 9 0 O - 9 5 " C was used i n the first five series of experiments, as the preliminary test indicated that this was the most favorable temperature. T h a t this is not the case is evident from the temperature table (VI).
TABLE I. Gffect of varying amounts of sodium carbonate. Anode solution: I O grams potassium iodide, I O cc acetone, 250 cc water and varying . - amounts of sodium carbonate. _______-
-
-
~ o . 1Sodium 1 ampere Current Temp. Voltage. 1 carbonate.\ hours. density. ~
I
-1
I I 3 grams! 1.675 215 1 1.692 1.654 3 ) 6 4 ,I2 I 1.456 ~
93O 92O 92O 910
c,
:
1.95 I .go 2.0
1.9
Yield grams.
1.4079 1.2511 1.4323 0.9002
1
Current yield.
'
34.7 PCt
I ~
1
I
30.2
35.3 25.2
TABLE 11. Effect of varying amounts of potassium iodide. Anode solution : 6 grams sodium carbonate, I O cc acetone, 250 cc water and varying amounts of potassium iodide. -
NO
I Potassium Ampere hours. iodide
-
Current yield.
~
-
I 2
j IO I5
3
10.05 pct
gram4 2.16 1.6j4 I 1.85
35.30 30.45
TABLE 111. Effect of current density Anode solution : 6 grams sodium carbonate, iodide, I O cc acetone and 250 cc water.
1
No.
1 I
I
Ampere hours.
'
,
grams potassium
I
I
I
Current density.
IO
Temp'
I
4
Yield gr
