This is usually prepared by the action of iodine on alcohol in the presence of red phosphorus, much as described under "ethyl bromide." Various proportions of ingredients have been recommended. Thus Wurtz indicates phosphorus 7 parts, alcohol 35, and iodine 23; whilst Frankland used these in the ratio of 7: 35: 14. According to Beilstein,

1 Trans. Chem. Soc, 1915, 107, 1489. 2 D.R.P. 52982.

1 part of red phosphorus is placed in a retort with 5 parts of 90 per cent. alcohol, and then 10 parts of iodine are added gradually, and the mixture allowed to stand for twenty-four hours. At the end of that period the retort is warmed, and the ethyl iodide distilled off. The crude product is purified by washing first with dilute solution of sodium hydroxide, and then with water, after which treatment it is dried over fused calcium chloride, and redistilled if necessary.

Walker1 recommends the use of both red and yellow phosphorus, in equal quantities, and obtains about 570 grams of the iodide for 500 grains of iodine used, or 93 per cent. of the theoretical yield. As the dissolving of the iodine in the alcohol is tedious, he has devised an arrangement to shorten the time and labour. This consists essentially in an adaptation of the principle of the Soxhlet extractor to the purpose. A wide-mouthed, round-bottomed flask, of about 1 litre capacity, carries a two-holed cork into which are fitted an adapter, serving as receptacle for the iodine and a wide side-tube, up which the alcohol vapour passes. These are connected at the top with a tube which passes to a reflux condenser. The arrangement is such that when alcohol placed in the flask is boiled, its vapour passes up the side tube, is condensed in the reflux condenser, falls back on the iodine contained in the adapter, dissolves more or less of this iodine, and carries it down into the flask, where the solution of iodine in alcohol reacts with the phosphorus present.

To obtain about 550 grams of ethyl iodide the ingredients used are 500 grams of iodine, 250 of alcohol, 30 of yellow phosphorus, and 30 of red phosphorus. The alcohol and the two kinds of phosphorus are placed in the flask, with a few fragments of porous tile to prevent bumping, and 100 grams of the iodine are packed tightly in the adapter. The flask is then connected up, and heated on a water-bath to boil the alcohol. Distillation should not be allowed to proceed too rapidly, as much heat is disengaged during the reaction. When all the iodine has been dissolved, the heating is continued until there is no longer any coloration in the liquid due to iodine. The flask is then cooled, and a fresh charge of iodine placed in the adapter, after which the heating is re-commenced, and the operations repeated until the whole 500 grams of iodine have been worked up.

When the reaction is completed, a small quantity of water is poured down the condenser to destroy any phosphonium compounds which may have been formed. The flask is then detached, and the liquid distilled off by means of a water-bath. The distillate, after being washed with water, separated from the aqueous layer, and dried, is practically pure ethyl iodide.

1 Trans. Chem. Soc, 1892, 61, 717.

The chief precaution to be taken is the proper regulation of the temperature when the final charge of iodine is being dealt with. Too much heat should be avoided, and the last stages conducted slowly until experience has been gained.

Methyl iodide can be prepared in a similar manner.

In Crismer's method of preparation, the iodine is dissolved in liquid paraffin. Yellow phosphorus is then added, and afterwards alcohol.1

Ethyl iodide has the sp. gr. 1944 at 14°, and boils at 723°.