Conversion of Aldoximes to Carboxylic Acids by Means of Hot Alkali. The Elimination of Water from Aldoximes

Abstract

The common statement that a P-aldoxime loses water to form a nitrile more readily than its a-isomer has been based presumably on the wellknown fact that, in the presence of certain reagents, as for example acetic anhydride followed by alkali, the P-aldoxime forms nitrile, whereas the a-isomer usually gives only negligible amounts of this product. Under these conditions, however, the nitrile is not formed by the elimination of water from the &aldoxime; the latter is first converted to its acetyl derivative which eliminates acetic acid to form nitrile.2 Apparently there has been no direct evidence that in general, a P-aldoxime loses water more easily than its aisomer.I n this paper it is shown that certain P-aldoximes in 2 Nsodium hydroxide solution4 a t 97-100° are slowly converted into mixtures of the corresponding carboxylic acids, ammonia and the aaldoximes ;s the latter are more slowly converted into carboxylic acids. The yields of acid and (1) This paper is from a portion of a thesis presented by Earl Jordan in partial fulfilment of the requirements for the Ph.D. degree a t Duke University.(2) For a recent discussion of this reaction see Hauser and Jordan, THIS JOURNAL, 67, 2450 (1935); Hauser and Sullivan, ibid., 85, 4611 (1933). (3) This has been pointed out by Brady, Science Progress, 29, 485 (1935). I n this connection it should be mentioned that Hantzsch and Lucus [Bcr., 88, 748 (1895)] have reported that 8-mesitylaldoxime with hot alkali gives nitrile whereas the a-isomer is stable under similar conditions: also, Hantzsch [ibid., 84, 47 (lS91)I has reported that 8-thiophenaldoxime with hot sodium carbonate gives nitrile. For references to the thermal decomposition of aldoximes see Hurd, "The Pyrolysis of Carbon Compounds," Chemical Catalog Co., N. Y., 1929, p. 659.(4) Aldoximes in alkaline solutions are quite stable a t room temperatures. See Freudenberg, "Stereochemie," Vol. VII, 1933, p. 987. In this Laboratory 8-3,4-methylenedioxybenzaldoxime (m. p., 1 4 6 O ) , after being kept in 2 N sodium hydroxide solution a t 30' for thirty-six hours was recovered in a yield of 93% melting a t 133-135'; the a-isomer melts a t 110'.(5) I t is well known that there is a tendency for the 8-benzaldoximes to revert to the a-isomers. See Freudenberg, "Stereochemie,"Vol. VII, 1935, p. 488.oxime isolated after certain periods of time are given in Table I. It can be seen that after the same periods of time the yields of acid obtained from P-aldoximes are higher than those from the a-isomers. Since these carboxylic acidss are probably formed by the hydrolysis of intermediate nitriles produced from the aldoximes by elimination of water, 6-aldoximes apparently do lose water more readily than their a-isomers; however, this reaction is not recommended for distinguishing a pair of geometrically isomeric aldoximes7 because, under the conditions used to effect the elimination of water, a considerable portion of the P-aldoxime is converted into the aisomer.The rate of conversion5 of /3-3,4-methylenedioxybenzaldoxime into the a-i...