Kimia Sintesa

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    [Repr inted rom the .Journal f Organic Chemis t ry ' . 0. i ] r77 ( 1975) . lCopvr ight 19?5 y the Amer ican Chemical Soc ietvand repr inted bv permiss ionof the copyr ight owner .

    The Oxidation of Terminal Olefins to Methyl Ketones by Jones ReagentIs Catalyzed,by Mercury(I l ) t

    Harold R. Rogers, Joseph X. McDermott,2 and George M. Whitesides*Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139

    Receiued une 11. 1975

    The ox idation of terminal olefins by Jones reagent in the presenceof a catalytic quantity of mercury(II) affordsgood 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 ketoneshas three mechanistically distinct parts:3 first, activation ofthe olefinic double bond toward nucleophilic attack bycoordination with Pd(II) and addition of a hydroxide moi-ety to this electrophilic double bond; second, conversion ofthe resulting 2-hydroxyethylpalladium(Il) compound toketone and a (formally) Pd(O) atom by a series of palladi-um(II) hydride addition-eliminations involving vinylic al -cohol intermediates; third, reoxidation of the palladium(0)to palladium(Il) by copper(Il). Wacker oxidation is an ex-tremely useful and general reaction. It is, nonetheless,worthwhile to try to develop procedures for oxidizing ole-fins that use as catalysts metals less expensive than palla-dium, and which involve reactions (and possibly generate

    products) different from those of the Wacker oxidation.Mercury(Il) is an obvious candidate for the catalyst fornew oxidation reactions: it resembles palladium(Il) in itsability to activate olefins for nucleophilic attack,a but dif-fers in that decomposition of the oxymercuration productsnormally generates cations by loss of mercury(0) ratherthan olefins by loss of mercury hydride.s Unfortunately,neither we nor others6have been able to discover a satisfac-tory solution to the principal problem in developing a mer-cury(II)-catalyzed analog of the Wacker oxidation: viz., anefficient regeneration of mercury(Il) from mercury(0). Inthe absence of a solution to this problem, there are, how-ever, ways of involving mercury(II) in catalytic oxidation ofolefins other than in a direct analog of a Wacker oxidation.

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    3578 J. Org.Chem., o l .40,No.24, 975 Rogers,McDermott, and WhitesidesTable IOxidation of Terminal Olefins by Jones Reagent Catalvzed bv Mercury(II)

    Regist ry no . Reqist ry no .Iso atedy i e l d , o i

    One, explored in this paper, uti l izes mercury(II) in oxymer-curation of an olefin, oxidizes the hydroxyl moiety of theresulting 2-hydroxyalkylmercury(II) compound to an acid-labi le 2-ketoalkylmercury(Il) derivative, and regeneratesmercury(II) by proteolysis of the carbon-mercury bond ofthis substance (eq 1). Thus, the mercury(Il) performs th e

    OH

    RCH:cH, * fHgoacl* 9 nJucu,H*oa.ool lH* l lRCCH, + [HgOAc]* . RCCHTHgOAc

    essential function of olefin activation, but is regeneratedwithout leaving the mercury(II) oxidation level. This cycleis, n a sense,one in which mercury(Il) catalyzes he hydra-tion of the double bond, and in which the reaction is drivenin the direction of the thermodynamically less stable hy-drated form by trapping this form by oxidation to ketone.

    Results and DiscussionJones reagent (CrO:rHzSO+-HzO) oxidizes alcohols to

    ketones efficiently, and is relatively unreactive toward ole-fins.? When Jones reagent is added to an acetone solutionof an olefin at 20 , a slow, nonselective oxidation takesplace. Addition of mercuric acetate or mercuric propionate?ZOmol o/obased on olefin) to the solution results in a rapidconsumption of the oxidant. Terminal olefins are convertedto methyl ketones n yields of 80-90o/oTable I); 1,2-disub-stituted olefins react readily, but give low yields of ketonesunder these conditions. The yield of methyl ketones result-ing from the catalyzed Jones oxidation of terminal olefinsis relatively insensitive to the amount of mercuric saltadded (Figure 1). The catalyzed oxidation of terminal ole-fins by sodium dichromate-trifluoroacetic acid solutionshowed similar insensitivity to the amount of mercuric saltadded; the yields were, however, substantially lower thanthose obtained using Jones reagent (Figure 1). Note thatthe plots in Figure 1 are based on data collected under,o,rghly comparable conditions, but that these conditionsare not necessarily hose that generated the highest yield ofproduct. In particular, in plot A of Figure 1, the maximumietected yield of 2-octanone was approximately 507o,whilethe best yield isolated under optimized synthetic condi-tions was 82olo see the Experimental Section for details).The major function of the plots in Figure 1 is to establishthe relative sensitivities of primary and secondary olefinsto catalysis by mercury(Il) and to provide a qualitative es-timation of the absolute activity of mercury(Il) as a cata-lyst in reactions based on Jones reagent and dichromateion as oxidants.

    The vield of ketones from 1,2-disubstituted olefins can

    1 1 1 - 3 ?676- 0-675-9? -B56666-10- 598- 6 -2

    8283B6702 6

    t o o

    5 0

    ot o o

    oroo

    5 0

    o o.o o.5 l.oHq(tt /olefn.Figure l . The vield of'ketonedepends n the ratio of equiva-lentsof mercury(II) o olefinpresent t the startof the reaction: ,(EICO2)2Hg-catalyzedxidationof 1-octeneo 2-octanone25o,acetone, ones eagent,8 hr); B, (EICO2)2Hg-catalyzedxidationof 1-octene to 2-octanone 25', dioxane, NazCr:Oz'2HzO-CF:rCOu, 18 hr); C, (FltCO2)2Hg-catalyzedxidation f a mixture

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    Oxidation of Terminal Olefins to Methvl Ketones J. Org.Chem.,Vol.40,No.24,1975 3579Table IIOxidation of 1,2-Disubsti tuted Olefins bv Sodium Dichromate-Trif luoroacetic Acid SolutionCatalyzed by lllercury( II )

    Olef in Regist ry no , Product Registry no ,Isolatedyield, %

    cis-2-Octene

    trans-2-OcteneCyclohexeneCyclododecenecNorbornenea2 '3-Choles tene

    7642-04-813389-42-

    110-83 -8150182-2498- 6-815910-23-

    2-Octanone (64Vd+3-octanone (9670)2-Octanone (Og7o)3-octanone (37Va)CyclohexanoneCyclododecanoneNorcamphordNo reaction

    106- 68- 3

    108-94-830-13 -?497- 8 -

    5 6 0

    5404lb3 6 D20

    dOxidation was car ed out in the presence f0.2 equiv of mercuricpropionate.bOxidation was canied out in the presence f 0.5 equiv ofmercuricpropionate. A mixture ofcis and trans somers. The productwas solatedas he 2,4-dinitrophenylhydrazone.um(I), suggesting that olefin activation was slow. Similartreatment of 2-octene n the presenceof gold(III), pal ladi-um(II), and rhodium(Il l) afforded mixtures of 2- and 3-octanone in yields of 30, 10, and 296, espectively. Gold(0)and palladium(0) deposited on the walls of the reactionvessel n substantial amounts during the oxidation.Evidence for the mechanism of the mercury(Il)-cata-lyzed oxidations (eq 1) is inferential. Treatment of cyclo-hexene with aqueous mercury(Il) acetate gives trans-2-hydroxycyclohexylmercuric acetatee (1), which is oxidizedto cyclohexanone in yields very similar to those obtainedfrom cyclohexene under the same reaction conditions. Sim-i larly, 2-(chloromercuri)cyclohexanone (2) is convertedrapidly and in high yield to cyclohexanone by aqueous sul-furic or trifluoroacetic acid. Compound I is itself relatively

    cipitates, but no metallic mercury is formed and no organicsolvolysis products can be detected. Thus, it appears thatthe rapid disappearance of 1 when treated with Jones re -agent may be an oxidative reaction (eq 2). Cyclohexanolcan be detected in ca. 5olo ield after 5 min reaction time.

    J ones( FHgoAc ;:- ( FHgocro,H\_J - rhagenr \_J3J[,2-f IL\_/ *l * Hgrrrr crrrVr 2)

    l iro+-(-'{'nV n*oo.

    1

    -/-,-,//O (3%, Jones reagent' acebone)+ | T G)8/,, NarCrpr, aqumus\-/ d.ioxane.H+)

    . . lones( F u < - ( F O H\--l reagent \--i

    f l naY :tt1 ,S(), r| | | | (100/ , )\--\, r'q (-f 'Co-H \-/HeCl

    2stable toward the acid conditions encountered in the oxida-tion. Oxidation products arising directly from the ti-hy-droxyalkylmercury(II) cation therefore seem unlikely. Mer-cury(0) has been observed to form in small amounts only atelevated temperatures; no Hg(0) was observed under theconditions described. The B-hydroxymercury(Il) cationshave previously been shown to be stable in acid solution.l0The difference in the yields of ketones from 1- and 1,2-di-substituted olefins under strongly acidic (Jones reagent) orweakly acidic (NazCrzO?-CF3CO2H) conditions is reason-ably attributed to differences in the oxidative and/or solvo-lyticll stabilities of primary and secondary carbon-mercu-ry bonds. We have tested these stabilities under the condi-tions of these reactions by examining the behavior of cyclo-hexylmercuric acetate (3) and n-hexylmercuric acetate (4 )toward Jones reagent in acetone. Compound 3 reacts rapid-ly; oxidation is complete in 30 min at 20o, yielding cyclo-hexanone in 65% yield. Under the same conditions, the car-bon-mercury bond of 4 does not react appreciably: n-hex-ylmercuric sulfate can be recovered in good yield. Com-pound I does not solvolyze appreciably when treated withthe components of the Jones reagent without the chromi-um trioxide (that is, acetone, water, and sulfuric acid): asmall quantity of 2-hydroxycyclohexylmercuric sulfate pre-

    ConclusionsJones reagent or trifluoroacetic acid-sodium dichromate

    solution oxidizes olefins to ketones in the presenceof cata-lytic quantit ies of mercury(Il); of the various metals triedas catalysts or the oxidation-thal l ium(I), gold(III), pal la-d ium(I I ) , rhod ium(I I I ) , and mercury ( I I ) -mercury ( I I )gives the best yields. Qualitative evidence described abovesuggests hat these transformations occur by the sequenceof reactions outlined in eq 1. This oxidation provides a use-ful alternative to several of the procedures presently usedto convert olefins to ketones. It is less complex than Wack-er oxidation: the problems that arise in applying Wackeroxidation to high molecular weight, water-insoluble sub-stancesdo not seem to be important, and it is unnecessaryto have present the large excess of copper salts normallyused to make the Wacker oxidation catalytic. It can be ap-plied to unprotected olefinic carboxylic acids, where dibo-rane-chromic acid results in destruction of the carboxylicacid moiety. It is more direct and more economical than theseveral procedures (oxymercuration-reduction, epoxida-tion-reduction) that generate an alcohol preliminary to aJones oxidation.

    Experimental SectionGeneral. Melting points,determinedon a Thomas-Hoover ap-illary meltingpoint apparatus, re not corrected.GLC analysiswasperformedusinga 10 t X 0.125 n. 15%Carbowax 0M columnona F & M Model 810gaschromatograph quippedwith a hydrogenflamedetectorand a Hewlett-PackardModel 33738electronic n-

    tegrator.All solventswere reagentgradeand were used withoutfurtherpurif ication. -Octene,-octenea mixtureof cisand ransisomers),is-2-octene,nd cns-2-

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    3580 J Org. Chem. , Vol . 40, No. 24, 1975

    dec ene a mix tu re o f ' c i sand t r ans s omers ) . , l l - d imethy l - 1 -bu tene ,and undecy lenicac id (Aldr ich) were used as suppl ied. Mercur ic ac -etate and sodium dichromate dihydrate (Mal l inck rodt ) , t r i f luo-roacet ic ac id (Matheson Coleman and l lel l ) , gold( I I I ) chlor ide,pal -l ad ium( I I ) c h l o r i de , and tha l l i um( I ) ac e ta te (F i s her Sc ien t i f i c ) .and rhodium( I I I ) chlor ide (Al fa) were used wi thout fur ther pur i f i -cat ion. Elemental analyseswere per formed by Rober tson l ,abora-tory, Florham Park , N. .J .

    Mercur ic Propionate. Red mercur ic ox ide (108g) was added inl0-g por t ions to 100 ml of hot propionic ac id. The ox ide dissolved.giv ing a s l ight ly yel lowish solut ion which was f i l tered and al lowedto cool t