"22
KENNETH
B.
W I B E R G AND
KLAUSA. S A E G E B A R T H
Vol. 713
[ CONTRIBUrION FROM T H E DEPARTMENT O F CHEMISTRY, UNIVERSITY OF WASHINGTON]
The Mechanisms of Permanganate Oxidation. IV. Related Reactions
Hydroxylation of Olefins and
BY KENNETH B. WIBERGAND KLAUSA. SAEGEBARTH RECEIVED OCTOBER27, 1956 The oxygen introduced into oleic acid it1 its conversion t o 9,lO-dihydroxystearic acid by permanganate has been found to arise from the oxidizing agent. The reaction of bicyclo[2.2.1]-2-heptenewith permanganate in neutral solution led to a new type of reaction, cleavage t o a dialdehyde. The mechanisms for the formation of the diol, keto1 and dialdehyde from a common intermediate are discussed.
Introduction The hydroxylation of olefins by potassium permanganate has been known for many years and has proved a useful method for this conversion. Wagner, who did much of the early work on this reaction, proposed that it involved the formation of a cyclic ester between the permanganate ion and the olefin. Decomposition of the intermediate with cleavage of the manganese-oxygen bonds would lead to the formation of the glycol.
c' /\
\/
C--0.
, '
.o -
\ \C--OH / - --I C-OH
+ Mn(V)
/\ This hypothesis received strong support from the careful stereochemical investigations of Boeseken and his co-workers2 who determined that the reaction invariably gave the glycol formed by cisaddition of the hydroxyl groups. The formation of a cyclic ester intermediate has been well accepted, particularly since osmium tetroxide, which also gives cis-hydroxylation, has been shown by Criegee? to give an isolable intermediate which almost certainly has the structure
since whereas oleic acid gives quantitatively 9,lOdihydroxystearic acid in alkaline solution, the main product in a neutral solution is a mixture of 9,10and 10,9-ketohydroxystearic acids.6 Results and Discussion I n studying the oxygen transfer from permanganate to oleic acid, it is desirable to effect the reaction under conditions which will minimize oxidation of the double bond by manganate, since it is known that manganate will exchange oxygens with water whereas permanganate will not,' and since the rate of oxidation by manganate is considerably lower than that for permanganate. Thus, if a large part of the oxidation were effected by manganate, the extent of oxygen transfer would be quite low Even with a large excess of permanganate, incomplete oxygen transfer would be expected since it is known that the rate of electron transfer between manganate and permanganate is very rapid,$ permitting some exchange of 01*with the solvent to occur as the reaction proceeds. The oxidation of oleic acid was effected at about pH 12 using the conditions of Lapworth and Mottram6 (1.45 KMn04:l oleic acid) and also using a larger excess of permanganate ( 2 KMn04:l oleic acid). The large excess of permanganate is permissible since it is known that the oxidation of the diol under these conditions is very slow relative to the rate of oxidation6 and since a nearly quantitative yield of diol was obtained in each case. The results are shown in Table I. TABLE I OXYGENTRANSFER IN THE OXIDATION OF OLEIC ACID
The most important evidence which now could be obtained would be a demonstration that the oxygens introduced into the olefin did arise from the permanganate. Since an excellent method for analyzing for 0l8in organic molecules is now available,* ~ 7 ehave studied the oxidation of an olefin with O18-labeledpermanganate. The olefin chosen was oleic acid since it gives an excellent yield of the diol and since the product is easily isolated.6 It was also of interest to study the effect of reaction conditions on the oxidation of other olefins, (1) G. Wagner, J. R U S . Phys.-Chem. Soc., 27, 219 (1895). (2) J. Boeseken, Rec. f r a w ckim., 40, 553 (1921); J. Baeseken and M. C. de Graaff, ibid., 41, 190 (1922); J. BSeseken, ibid., 47, 683 (1928). (3) R. Criegee, Ann., 622, 75 (1936); Angew. Ckcm.,61,519 (1938); K. Criegee, B. Marchand and H. Wannowius, Ann., 660, 99 (1938). (4) W. v. E. Doering and E. Dorfman, T ~ I JOURNAL, S 7 6 , 5595 (1953). (5) A. 1,apworth and IS. N. M o t t r a m , J . Chern. Soc., 127, 1028 \
