This section is from the book "Alcohol, Its Production, Properties, Chemistry, And Industrial Applications", by Charles Simmonds. Also available from Amazon: Alcohol: Its Production, Properties, Chemistry, And Industrial Applications.
According to Berthelot,4 ethyl alcohol vapour when heated begins to decompose at 500°, yielding on the one hand ethylene and water, and on the other aldehyde and hydrogen; but secondary reactions also take place, with the formation of acetylene, ethane, benzene, naphthalene, carbon monoxide, and carbon dioxide.
Jahn5 found that in the presence of zinc dust ethyl alcohol decomposes into ethylene and water at 300-350°.
Ipatieff6 has shown that at 600°, in the presence of zinc and litharge, aldehyde and hydrogen are formed from ethyl alcohol, and at 580-680°, when the alcohol is distilled over aluminium powder, divinyl is yielded, in addition to the products of the decomposition of aldehyde and ethylene.
Ehrenfeld7 passed the vapour of ethyl alcohol over carbon heated to dull redness, and found that the alcohol is decomposed into equal volumes of methane, carbon monoxide, and hydrogen, according to the equation: -
C2H6O = CH4 + CO + H1.
At a lower temperature, large quantities of ethane are formed, probably as a primary reduction product. When distilled over aluminium below a dull red heat, the products are ethylene and water, the latter being to a large extent further reduced to hydrogen.
1 Compt. rend., 1898, 126, 616. 2 Biochem. Zeitsch., 1909, 20, 136.
3 Ibid., 126. 4 Traite de Chimie organique, 1872, 164.
5 J. Chem. Soc, 1880, 38 (Abst.), 794.
6 Ibid., 1902, 82, i, 4, 335; and 1903, 84, i, 453.
7 J. pr. Chem., 1903, [ii], 67, 49.
At a dull red heat, decomposition into methane, carbon monoxide, and hydrogen also takes place, and, at a bright red heat, is pre-dominant.
Sabatier and Senderens1 have studied the action of reduced copper, nickel, cobalt, and spongy platinum as catalysts in the decomposition of alcohols generally by heat. When ethyl alcohol is passed over reduced copper, a reaction begins at 200° and is very vigorous at 250°, the alcohol being decomposed exclusively into aldehyde and hydrogen. Up to a temperature of 300°, the same change occurs, and at this temperature as much as half the alcohol is decomposed. At 420°, the gas evolved consists of equal volumes of methane (12.5 per cent.) and carbon monoxide (12.5 per cent.), together with hydrogen (75 per cent.). The two gases first-mentioned are formed at the expense of the aldehyde, which, in the presence of reduced copper, begins to decompose at 400°.
When reduced nickel is used as the catalyst, decomposition of the alcohol begins at 150°, and is rapid at 170°. At 178°, some aldehyde is formed, but nearly half is destroyed again; the evolved gases at this temperature consist almost wholly of carbon monoxide, methane, and hydrogen. Decomposition of the carbon monoxide into carbon dioxide and carbon begins at 230°, and is very rapid at 300°; at 330°, the gas consists of carbon dioxide, methane, and hydrogen. Reduced cobalt acts in the same manner as nickel. Spongy platinum begins to decompose ethyl alcohol at 270° - a much higher temperature than is required with copper or nickel. The action increases regularly with the temperature; at 310°, the gas evolved consists of carbon monoxide, methane, and hydrogen. Only a small quantity of aldehyde is obtained, most of it being destroyed, with the production of carbon monoxide and methane.
J. B. Senderens2 finds that the oxidation of ethyl alcohol occurs at temperatures of 405° to 450° by simple heating, without the aid of a catalyst. If a current of dry air is passed through ethyl alcohol at the rate of 100 c.c. per minute, and the mixture of alcohol vapour and air then led through a heated glass tube, oxidation is found to commence at about 405°, and at 450° all the oxygen is used up. The main products are carbon monoxide, carbon dioxide, and water, with much smaller quantities of aldehyde and acid. Magnesium, zinc, and aluminium are therefore regarded as having no great value as catalysts in this reaction, since the oxidation takes place almost as readily without them as with them.
1 Compt. rend., 1903, 136, 738, 921, 983.
2 Ibid., 1913, 156, 1909-1912.