CORRESPONDENCE A SIMPLE APPARATUS FOR PREPARING ALDEHYDES To the Editor DEAR SIR: After perusal of the article by C. Johnson and C. E. Burke in the October, 1933, number of the JOURNAL OF CHEMICAL EDUCATION (10, p. 641), I beg to submit the following data. An indicator entitled "A simple apparatus for preparing aldehydes" appeared in the April, 1932, number of The Hormone (6, pp. 72-3). Additional information is given concerning this method of preparing aldehydes, because of various difficulties encountered by other chemists in carrying out this experiment. In the third paragraph, the third sentence reads as follows: "The gas burner is ignited until the copper spiral becomes dull red." The flame must then be removed, as the total heat of oxidation is great enough to keep the copper (on the surface of which the reaction is taking place) warm enough for the immediate formation of copper oxide after the regeneration of metallic copper. The reaction is continuous and requires no external heat [Sabatier and Mailhe, Compt. rend., 142, 1394 (1906); Chem. Zentr., 1906, [2], 402]. The copper oxide is evidently the intermediate step. Sabatier and Mailhe have shown that the oxide of copper has catalytic properties entirely comparable to those of finely divided platinum. When heated in a mixture of oxygen with the vapors of various organic compounds, they become incandescent and maintain themselves so, giving oxidation products of the various organic compounds used. Karpov [Zhur. Prikladnoi Khim., 1 , 121-6 (1928); Chem. Abstr., 23, 4440 (1929)] recommends the use of twice the theoretical amount of air. Orlov [J.Russ. Phys.-Chem. Soc., 40, 203-15 (1908); Chem. Abstr., 2, 3346 (1908)] claims that for propyl alcohol, the theoretical amount of air is sufficient for the oxidation as indicated by the glow of the copper gauze, while for the other alcohols, a much larger quantity is required. This is due to the f a d that the endothermic decomposition of the alcohols into water and hydrocarbons (as the products of oxidation obtained by this method are carbon monoxide, carbon dioxide, water, saturated and unsaturated hydrocarbons, aldehydes, ketones, and unchanged alcohol), which takes place along with their exothermic oxidation, is greater with the other alcohols than with propyl alcohol. Orlov obtained a yield of 66% of acetaldehyde from ethyl alcohol, and a yield of about 50% of the corresponding aldehydes with isobutyl and amyl alcohols. Fokin [J. Russ. Phys.Chem. Soc., 45, 286 (1913); Chem. Abstr., 7, 2227 (1913)] has obtained a 43% to 47% yield of formaldehyde from air and alcohol vapors passed over coppered asbestos, while Trillat [Bull. soc. chim., [3], 29, 35 (1903)] obtained a 48.5% yield of formaldehyde using copper gauze.
The last paragraph of the indicator. referred to above, reads as follows: "If the suction is'removed and a stream of oxygen is forced through the whole apparatus, the apparatus becomes more efficient, as the oxidation is greater and the output is greater." Although a mixture of air and alcohol vapors gives a good yield, oxygen was used to hasten the reaction, as part of the copper gauze remained reduced because of the limited amount of oxygen present in air. The copper gauze continued to glow, and the results were very satisfactory. In using oxygen instead of air, the following precautions must be observed: as soon as the reaction is proceeding smoothly with air, and the copper gauze continues to glow after removal of the flame, the suction is removed and the oxygen admitted slowly. The flow of oxygen must be slow, as the alcohol must be cautiously oxidized to prevent oxidation beyond the aldehyde [Chem. Abstr., 2, 3346 (1908)]. Oxygen was allowed to pass through concentrated sulfuric acid in a gas-washing bottle at the rate of about three to four bubbles per second. The copper gauze continued to glow a t a dull red heat, and the reaction continued without difficulty for several hours. For experimental purposes, the flow of oxygen was increased until it was impossible to count the flow of bubbles through the sulfuric acid. The copper gauze became white-hot instead of red, and there were explosive flashes of the alcohol-oxygen mixture projecting from the white-hot copper gauze. The result was a decrease in the percentage of aldehyde obtained and a corresponding increase in carbon dioxide and water, which must be prevented. A further increase in the flow of oxygen would undoubtedly have led to an explosion, due to the formation of an explosive mixture of alcohol and oxygen in the presence of a copper gauze heated to white heat. Cf. Peronne [Swiss Patent 78,843 (April 16, 1917); Chem. Abstr., 12,484 (1918)], "Ethyl alcohol vapors and oxygen brought into contact with a catalytic agent at high temperature such that the active combustion of the alcohol does not result." Matignon and Trannoy [Compt. rend., 142, 1210 (1906); Chem. Zentr., 1906, [2], 202] have shown the possibility of realizing a lamp without flame by the aid of asbestos fibers impregnated with the oxide of copper suspended in a mixture of air and ether vapors. Copper oxide, when properly impregnated with manganese dioxide made by the method of Fremy [Compt. rend., 82, 1213 (1876)], gives an excellent catalyst which is capable of effecting the catalytic oxidation with great rapidity even a t temperatures somewhat below 0°C. Very truly yours, OLIER L. BARIL HOLY CROSS COLLEGE WORCESTER, MASS. 379
