J . Org. Chem., Vol. 58,No. 9, 1975 1681
OXIDATION OF OLEFINSBY PALLADIUM(II) This oil was chromatographed on basic alumina IV. The material was eluted with petroleum ether (trace of ether) solvent to yield 0.6 g (92%) of 2-methyl DMAMF (4). Nmr data: 6 1.95 (s,3.0), 2.13 (s,6.0), 3.26 (ABquartet, 2.1, V I = 3.21, v2 = 3.30, J = 13.0), 4.00 (m, 8.0).
Registry No.-1, 38744-26-2; 2, 38641-31-5; 2a, 12214-99-2; 4, 12111-28-3; 5, 38641-34-8; sa, 3864135-9; 5b, 12111-89-6; 6 , 38e41-37-1; 7, 38641-38-2; 8, 38641-39-3.
Oxidation of Olefins by Palladiurn(I1). VI. Ethylene Oxidation by Palladium(I1) Acetate in Acetic Acid Promoted by Various Oxidants' PATRICK M. HENRY^ Contribution No. 1606 from the Research Center, Hercules Incorporated, Wilmington, Delaware 19899 Received November 19, 19Y8 Palladium(I1) salts alone in acetic acid oxidize ethylene to vinyl acetate. I t has been previously reported that CuClz and NOa- increase the rate of oxidation and change the product from vinyl acetate to 1,2-disubstituted ethanes such as ethylene glycol mono- and diacetate and 2-chloroethyl acetate. The present study was undertaken to determine the generality of this new reaction. A number of oxidants, including KzCrz07, NaN02, CuBm, MnOz, Pb(OAc)r, Tl(OAc)a, TlCla, and HAuC14, were also found to be active in this reaction. Others which had little or no activity include p-quinone, FeCls, Fe(OAc)a, Hg(OAo)z, MoCIS,and hfOOCl4. CuBrz gave Z-bromoethyl acetate. In addition to the 1,2-disubstituted ethanes, Tl(OAc)a, TlCla, and HAuC14 also formed appreciable quantities of ethylidene diacetate. The reactioii probably proceeds by a mechanism similar to that of the previously studied aromatic substitution reaction. This mechanism involves formation of an intermediate with a palladium(I1)-carbon bond. This intermediate reacts with the oxidant to give the observed products.
In the absence of other oxidants palladium(I1) salts of the acetoxypalladation intermediate, 1, by oxidant in acetic acid oxidize ethylene to vinyl acetate3 and t o give saturated products (X = OAc, C1, or OH). other olefins to mixtures of vinyl and allylic a c e t a t e ~ . ~ 1 2cuc12 + x- ---f A study of the product distributions obtained from AcOCHGHzX + PdClz 2CuCl + OAC- (4) oxidation of 1 and 2 olefins with palladium(I1) acetate The reaction is not limited to CuC12, as it has been HOAc demonstrated that nitrate can replace CuC12.' The CzHa + PdZ+ f 20Ac- +CzHaOAc + HOAc + Pd" (1) present study is aimed at defining the scope of this new reaction. In particular a number of oxidants will be - HPdOdc Pd(0Ac)z CzH4 +AcOPdCHzCHzOAc -+ surveyed to determine what types of oxidants are effec1 tive in interacting with Pd(I1). CHz=CHOAc (2) A related reaction is the Pd(I1)-catalyzed aromatic substitution reaction, which also requires a second indicated that the reaction proceeds by way of an oxidant* (X- = OAc-, NS-, C1-, NOZ-, Br-, CN-, or acetoxypalladation-Pd(I1)-hydride eliminati~n.~ SCN -). Addition of copper(I1) chloride to these reaction mixtures causes the rate of olefin oxidation to increase. Pd(I1) + oxidant + X I n addition the main product changes from vinyl acetate to 1,2-disubstituted alkanesa6 It has been demonstrated that both PdC12 and CuClz are required for this reaction This reaction very likely proceeds by way of a Pd(1I)aryl intermediate analogous to 1 although Pd(IV) PdClz species cannot be eliminated by the experimental CtHd CuClz OAC- * evidence. HOAC + H20
+
+
+
-
+
+
AcOCHzCHzCl AcOCHzCHzOAc AcOCHzCHzOH
+ CuCl
(3)
to take place.6b On the basis of studies with the butenes6b and cyclohexene' the mechanism for this reaction has been postulated to involve the interception (1) Paper V: P. M. Henry, J . Amer. Chem. Soc., 94, 7305 (1972). (2) Address correspondence to author at the Department of Chemistry, University of Guelph, Guelph, Ontario, N1G 2W1, Canada. (3) (a) I. I. Moiseev, M. N. Vargaftik, and Ya. K. Sirkin, Dokl. Akad. Nauk S S S R , 133, 377 (1960); (b) E. W. Stern and M. L. Spector, Proc. Chsm. SOC., 370 (1961). (4) (a) M. N. Vargaftik. I. I . Moiaeev, and Ya. K. Sirkin, Izu. Akad. Nauk S S S R , Otd. K h i m . Nauk, 930 (1962); (b) I. I. Moiseev, A. P . Belov, and Y s . K. Sirkin, Im.Akad. Nauk SSSR.Ser. K h i m . , 1527 (1963). ( 5 ) W. Kitching, Z. Rappoport, S. Winstein, and W. G. Young, J. Amer. 88, 2054 (1966). Chsm. SOC., (6) ( a ) D . Clark, P . Hayden, and R . D . Smith, Amer. Chem. Soc., Diu. Petrol. Chem., Prep?., 14 ( Z ) , B10 (1969); (b) P . M. Henry, J . Org. Chem., Sa, 2575 (1967).
Results A number of oxidants were tested for their ability to change the nature of the oxidation of olefins in the same fashion as CuClz or nitrate. In the present work ethylene was the olefin used. There are two criteria for a given reagent to be capable of interacting with Pd(I1) : first, the rate of ethylene oxidation in the presence of this reagent and Pd(I1) as compared t o the rate of oxidation in the absence of Pd(I1); and second, the product distributions obtained in the oxidations containing Pd(I1) and the reagent. Of course, Pd(I1) alone gives only vinyl acetate. Gas Uptake Experiments.-In Table I are listed the results of a series of experiments in which the Pd(0Ac)Z (7) M. Tamura and T. Yahui, Kogyo Kagaku Zasshz, 73, 578, 581 (1969). (8) P. $4. Henry, J.Org.Chem., 36,1856 (1971).
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HENRY
TABLE I EFFECT OF VARIOUS OXIDANTS ON THE RATEOF ETHYLENE UPTAKEBY Pd(0Ac)z SOLUTIONS IN ACETICACID AT 25' A N D ATMOSPHERICPRESSURE" Oxidant
Initial rate, M hr-1
None 0.017 p-Quinoneb 0.015 Pb(0Ac)a 0.09 CuBrz 0.047 MnOz 2.0c FeC13
