[Reprinted from the .Journalof Organic Chemistry'.{0. i]r77 ( 1975).l Copvright 19?5by the American Chemical Societvand reprinted bv permissionof the copyright owner. The Oxidation of Terminal Olefins to Methyl Ketones by Jones Reagent Is Catalyzed,by Mercury(Il)t Harold R. Rogers, Joseph X. McDermott,2 and George M. Whitesides* Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 ReceiuedJune 11. 1975 The oxidation of terminal olefins by Jones reagent in the presence of a catalytic quantity of mercury(II) affords good yields (>lO"t") of the corresponding methyl ketones. Similar oxidations of 1,2-disubstituted olefins gives fair (20-70%) yields; in the caseof unsymmetrically substituted olefins, mixtures of ketones are produced. The Wacker process for oxidation of olefins to ketones products) different from those of the Wacker oxidation. has three mechanistically distinct parts:3 first, activation of Mercury(Il) is an obvious candidate for the catalyst for the olefinic double bond toward nucleophilic attack by new oxidation reactions: it resembles palladium(Il) in its coordination with Pd(II) and addition of a hydroxide moi- ability to activate olefins for nucleophilic attack,a but dif- ety to this electrophilic double bond; second, conversion of fers in that decomposition of the oxymercuration products the resulting 2-hydroxyethylpalladium(Il) compound to normally generates cations by loss of mercury(0) rather ketone and a (formally) Pd(O) atom by a series of palladi- than olefins by loss of mercury hydride.s Unfortunately, um(II) hydride addition-eliminations involving vinylic al- neither we nor others6 have been able to discover a satisfac- cohol intermediates; third, reoxidation of the palladium(0) tory solution to the principal problem in developing a mer- to palladium(Il) by copper(Il). Wacker oxidation is an ex- cury(II)-catalyzed analog of the Wacker oxidation: viz., an tremely useful and general reaction. It is, nonetheless, efficient regeneration of mercury(Il) from mercury(0). In worthwhile to try to develop procedures for oxidizing ole- the absence of a solution to this problem, there are, how- fins that use as catalysts metals less expensive than palla- ever, ways of involving mercury(II) in catalytic oxidation of dium, and which involve reactions (and possibly generate olefins other than in a direct analog of a Wacker oxidation. 3578 J. Org.Chem., Vol.40, No.24, 1975 Rogers,McDermott, and Whitesides Table I Oxidation of Terminal Olefins by Jones Reagent Catalvzed bv Mercury(II) Isolated Registry no. Reqistry no. yield, oi 1-Octene 111-66-0 2-Octanone 111-13 - ? 82 Undecylenic acid 112-38-9 10-Oxoundecanoicacid 676-00-6 83 3, 3-Dimethyl- I -butene 558-3 ?- 2 3, 3-Dimethyl- 2-butanone 75-9?-B B6 o 2 - Allylcyc Iododec anone 32539-89- 2 t:-Oxo- 2-pr opylcyclododec anone 56666- 10- 5 70 Styrene 100-42-5 Acetophenoneb 98-86-2 26 1, 3-Hexadiene 592-48-3 Polymer d In addition. a ?7oyield of 2 -al lyl- 2 -hydroxycyclododecanone was obtained- b Benzoic acid (16%) was also isolated, together vtith pol,\/mer. One, explored in this paper, utilizes mercury(II) in oxymer- too curation of an olefin, oxidizes the hydroxyl moiety of the resulting 2-hydroxyalkylmercury(II) compound to an acid- labile 2-ketoalkylmercury(Il) derivative, and regenerates 50 mercury(II) by proteolysis of the carbon-mercury bond of this substance (eq 1). Thus, the mercury(Il) performs the OH o RCH:cH, * fHgoacl**9 nJucu,H*oa. too I Itot (i) t-- V I 950 oo o llH*ll ; RCCH, + [HgOAc]* ." RCCHTHgOAc essential function of olefin activation, but is regenerated o without leaving the mercury(II) oxidation level. This cycle roo is, in a sense,one in which mercury(Il) catalyzesthe hydra- tion of the double bond, and in which the reaction is driven in the direction of the thermodynamically less stable hy- 50 drated form by trapping this form by oxidation to ketone. Results and Discussion Jones reagent (CrO:rHzSO+-HzO) oxidizes alcohols to o ketones efficiently, and is relatively unreactive toward ole- o.o o.5 l.o fins.? When Jones reagent is added to an acetone solution Hq(tt/olefin. of an olefin at 20", a slow, nonselective oxidation takes place. Addition of mercuric acetate or mercuric propionate Figure l. The vield of'ketonedepends on the ratio of equiva- lentsof mercury(II)to olefinpresent at the startof the reaction:A, o/obased on olefin) to the solution results in a rapid ?ZOmol (EICO2)2Hg-catalyzedoxidation of 1-octeneto 2-octanone(25o, Terminal olefins are converted consumption of the oxidant. acetone,Jones reagent, t8 hr); B, (EICO2)2Hg-catalyzedoxidation (Table to methyl ketones in yields of 80-90o/o I); 1,2-disub- of 1-octene to 2-octanone (25', dioxane, NazCr:Oz'2HzO- stituted olefins react readily, but give low yields of ketones CF:rCOuH, 18hr); C, (FltCO2)2Hg-catalyzedoxidation of a mixture (25o, under these conditions. The yield of methyl ketones result- <rfcr.s- and trans-2-octeneto a mixtureof 2- and 3-octanclne 18 hr). Note that the maxi- ing from the catalyzed Jones oxidation of terminal olefins dioxane,NazCr.:O;.2H2O-CF3COzH, mum yield shownin A doesnot correspondto an optimizedyield is relatively insensitive to the amount of mercuric salt (seethe text for a discussionof this point). added (Figure 1). The catalyzed oxidation of terminal ole- fins by sodium dichromate-trifluoroacetic acid solution (Table II); showed similar insensitivity to the amount of mercuric salt be impr<lved using different reaction conditions required different added; the yields were, however, substantially lower than however, each 1,2-disubstituted olefin oxymercurates ole- those obtained using Jones reagent (Figure 1). Note that optimum conditions. Mercuric acetate or dioxanea'8 the plots in Figure 1 are based on data collected under fins efficiently in aqueous tetrahydrofuran proved as oxidation media. ,o,rghly comparable conditions, but that these conditions and these solvents also useful were carried out using sodi- are not necessarily those that generated the highest yield of Experiments in these solvents solution acidic product. In particular, in plot A of Figure 1, the maximum um dichromate as oxidant, and making the The yields of ketones from the ox- ietected yield of 2-octanone was approximately 507o,while with trifluoroacetic acid. olefins were significantly poor- the best yield isolated under optimized synthetic condi- idation of 1,2-disubstituted Jones reagent, hydrogen per- tions was 82olo(see the Experimental Section for details). er when other chromate salts, ion were used as oxidants. Yields The major function of the plots in Figure 1 is to establish oxide, or hypochlorite mercury(Il) chloride, nitrate, and the relative sensitivities of primary and secondary olefins were also poorer when in place of mercury(Il) propionate. to catalysis by mercury(Il) and to provide a qualitative es- tosylate were used ions other than mercury(Il) were explored timation of the absolute activity of mercury(Il) as a cata- Several metal be unsatisfactory as catalysts. No re- lyst in reactions based on Jones reagent and dichromate briefly, and found to place treating 2-octene with sodium dichro- ion as oxidants. action took on acid solution in the presence of thalli- The vield of ketones from 1,2-disubstituted olefins can mate-trifluoroacetic Oxidation of Terminal Olefins to Methvl Ketones J. Org.Chem., Vol.40, No.24, 1975 3579 Table II Oxidation of 1,2-Disubstituted Olefins bv Sodium Dichromate-Trifluoroacetic Acid Solution Catalyzed by lllercury( II ) Isolated Olefin Registry no, Product Registry no, yield, % cis-2-Octene 7642-04-8 2-Octanone (64Vd+ 560 3-octanone (9670) 106- 68- 3 trans-2-Octene 13389-42-I 2-Octanone (Og7o)+ 540 3-octanone (37Va) Cyclohexene 110-83-8 Cyclohexanone 108-94- 1 4lb Cyclododecenec 1501 -82-2 Cyclododecanone 830-13-? 36D Norbornene 498-66-8 Norcamphord 497-38- 1 20" a2'3-Cholestene 15910-23- 3 No reaction d Oxidation was car ed out in the presenceof0.2 equiv of mercuricpropionate. b Oxidation was canied out in the presenceof 0.5 equiv of mercuricpropionate. ' A mixture ofcis and trans isomers.d The product was isolatedas the 2,4-dinitrophenylhydrazone. um(I), suggesting that olefin activation was slow. Similar cipitates, but no metallic mercury is formed and no organic treatment of 2-octene in the presenceof gold(III), palladi- solvolysis products can be detected. Thus, it appears that um(II), and rhodium(Ill) afforded mixtures of 2- and 3- the rapid disappearance of 1 when treated with Jones re- octanone in yields of 30, 10, and 296,respectively. Gold(0) agent may be an oxidative reaction (eq 2). Cyclohexanol and palladium(0) deposited on the walls of the reaction can be detected in ca. 5oloyield after 5 min reaction time. vessel in substantial amounts during the oxidation. Evidence for the mechanism of the mercury(Il)-cata- ( J ones ( FHgoAc- ;:-rhagenr FHgocro,H lyzed oxidations (eq 1) is inferential. Treatment of cyclo- \_J \_J hexene with aqueous mercury(Il) acetate gives trans-2- 3J hydroxycyclohexylmercuric acetatee (1), which is oxidized to cyclohexanone in yields very similar to those obtained [,2-f I from cyclohexene under the same reaction conditions. Sim- *l * Hgrrrr* crrrVr(2) ilarly, 2-(chloromercuri)cyclohexanone (2) is converted L\_/ rapidly and in high yield to cyclohexanone by aqueous sul- lir o furic or trifluoroacetic acid. Compound I is itself relatively +- ..lones (3%, ( Fu<- ( FOH Jones reagent' acebone) reagent -/-,-,//O \--l \--i (-'{'n + | T G)8/,, NarCrpr, aqumus V"n*oo. \-/ d.ioxane.H+) Conclusions 1 Jones reagent or trifluoroacetic acid-sodium dichromate fln solution oxidizes olefins to ketones in the presence of cata- aY" :tt1H,S(), or | | | | (100/,) lytic quantities of mercury(Il); of the various metals tried r'q (-f 'Co-H \--\, -HeCl \-/ as catalysts for the oxidation-thallium(I), gold(III), palla- dium(II), rhodium(III), and mercury(II)-mercury(II) 2 gives the best yields.