The alkali or calcium salt of this acid is used for ethylating purposes in the making of phenacetin and other fine chemicals.

To obtain the salt, or the sulphovinic acid itself, the following procedure may be adopted. To 5 parts of absolute alcohol (by weight), 3 3/4 parts of strong sulphuric acid are slowly added, and then the whole mixed, and heated for four hours on the water-bath. After cooling, ice and water are added, in order to dilute the liquid without greatly raising the temperature. The acid is then neutralised by adding an excess of calcium carbonate mixed into a paste with water, and the liquid filtered from calcium sulphate and excess of carbonate. The solution of calcium ethyl sulphate thus obtained may be made slightly alkaline with lime-water, and concentrated for use if this salt is required. If the potassium compound is wanted, a strong solution of potassium carbonate is added to a concentrated solution of thecalcium salt until the calcium is all precipitated (as calcium carbonate). The potassium ethyl sulphate thus formed is soluble; it is filtered from the precipitate, a little more potassium carbonate added, and the solution evaporated until the salt crystallises out.

If the ethyl hydrogen sulphate itself is wanted, the acid liquid after addition of ice and water is neutralised with barium carbonate or with lead carbonate, instead of with calcium carbonate, as barium or lead can be subsequently eliminated more readily than calcium. The neutralised liquid is filtered from precipitated sulphate and excess of carbonate, and then evaporated. Crystals of barium or lead ethyl sulphate are thus obtained. These are separated and dissolved in water, and sulphuric acid added in quantity just sufficient to precipitate the barium or lead as sulphates. Alternatively, in the case of lead, this metal may be removed as sulphide by a current of hydrogen sulphide gas; or the bulk may be precipitated as sulphate, filtered off, and the elimination of the lead completed by means of hydrogen sulphide. Whichever method is used, the precipitate of barium or lead sulphate or lead sulphide is filtered off, and the filtrate, which now contains the free ethyl hydrogen sulphate, is evaporated in a vacuum over sulphuric acid. It can eventually be obtained as a syrupy liquid, soluble in water and in alcohol, but not in ether.

1 Soc. Anon. Prod. Chim., D.R.P., 1938.30; Friedlander, "Fortsehritto der Teerfarb," 1911, 9, 30. 2 Lassar-Cohn, loc. cit., p. 293.

In preparing sodium ethyl sulphate for technical use an enamelled acid-proof vessel is employed, set in a wooden vessel connected with the water supply and serving as cooler. A charge of 100 kilos. of strong sulphuric acid (96 per cent.) is placed in the former vessel, and 95 per cent. alcohol (47 kilos.) run in with stirring, and slowly, so that no excessive development of heat occurs. After the lapse of twenty-four hours, the mixture is passed into a cold emulsion of well-slaked lime, which must be always present in excess. The mixture is filtered from the calcium sulphate formed, and the latter pressed; the filtrate is then treated with sodium carbonate to precipitate the calcium, and the resulting clear liquid removed, to be finally evaporated in a vacuum.

If the expensive ingredient, alcohol, is to be utilised more completely, it is necessary to remove the water arising from the reaction. This is most conveniently done by means of sulphuric anhydride, with which the alcohol, dissolved in strong sulphuric acid, is treated in the cold.1