Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

ETHYL IODIDE FKOM ETHYL ALCOHOL 95
verted into ethyl bromide. The proportions used in the above
experiment have been adapted to this consideration. Theoretically
39 g. of alcohol are required for 100 g. of KBr, whilst actually 86 g.
(90 g. of 95 per cent) are used, i.e. more than double the theoretical
quantity. Hence when the theoretically possible yield is calculated
here the amount of potassium bromide used must be taken as the
basis of reckoning. If it is desired to convert an alcohol which is
more valuable than KBr into its bromide, the inorganic substance
would naturally be used in excess.
The preparation is used for making diethyl eihylmalonate (p. 254).
Methyl Bromide.—The simplest alkyl bromide is prepared in
an esentially similar way (Bygden, J. pr. Chem., 1911, 83, 421).
Since it boils at 4-5° it is difficult to keep in stock, but its direct
application in the Grignaxd reaction, in place of the dearer iodine
compound, is very much to be recommended. Uses analogous to
those of ethyl bromide.
2. ETHYL IODIDE FROM ETHYL ALCOHOL J
Absolute alcohol (50 c.c.) is poured into a small flask (capacity
about 200 c.c.) containing 5 g. of red phosphorous and then, during
the course of a quarter of an hour, 50 g. of finely powdered iodine
are gradually added with frequent shaking and occasional cooling
by dipping the flask into cold water. An efficient water condenser
is then attached to the flask, the mixture is left for two hours with
frequent shaking and heated for two hours on the water bath under
reflux. Then the ethyl iodide is distilled through a downward
condenser, preferably with the flask dipping into the vigorously
boiling water. If the last part of the material distils only with
difficulty, the water bath is removed and the flask, after drying, is
heated over a luminous flame which is kept in constant motion. The
distillate, which is coloured brown by dissolved free iodine, is shaken
in a separating funnel first with water (repeatedly) to remove the
alcohol, then with a few drops of bisulphite solution to remove the
iodine, and, finally, with an equal volume of sodium hydroxide solution.
The colourless oil so obtained is drawn off from the funnel,
dried with a little granulated calcium chloride, and distilled directly
over a small flame. If the calcium chloride should float on the ethyl
1 F. Beilstein, Annalen, 1863, 126, 250.