Oxidation of Alkenes by Mercuric Salts

Abstract

The 0-osymercurials of cyclohesene, 2-methyl-I-phenylpropene-I, and the geoisomers of stilbene have been shown t o be the intermediates in the oxidation of these alkenes by mercuric nitrate ant1 other salts, ~isually in methanol. 'l'hese intermediates are stable in the osidation environment ant1 their alkosy groups appear illtact in thc osidation product; indeed organomercurials without vicinal allcosy groups are likewise oridizcd. The rcaction protlucts from allce~lcs in . methanol are 1,2-dimethosyethanes, 1,l-tlin1etl1os~ethanes, and (with nlercuric nitrate) 1-111ethosy-2-nitrosyetl1anes, formation of the latter being most rapitl. The osidation is stereospecific, each gcoisomer yielding its characteristic diastcreomeric protl~rcts. I t is catalyzed by acids such as nitric acid but not by nitrate ion, though neither affect thc ratio of procluc~s. This over-all second-order reaction, k t -o r t l c r in orgnnomerc~~rial and Lirst-order in mercuric salt, becomes ovcr-all first-order with mercuric acetate when it is catalyzed by boron fl~roritle. Combination of the catalyst with the organoinercurial must be rate-controlling. The similarity of the oxitlation ant1 the acid decomposition reactions of organomercurials is discussed.The oxidation of allcenes by mercuric salts is not a new reaction (3, 2, 25) but interest has recently been revived because of its application to sterol dehydrogenation (4, 5 , 38, 39). A meclianism for the sterol dehydrogenation has been proposed involving a "mercurinium ion" (33) but it seems t o be inconsistent with the observed formation of mercurous salts rather than metallic mercury. On the other hand, another mechanism has been sug~ested (11) for the oxidation of cycloalltene by mercuric salts (20, 36, 37) which does not take into account the equilibration: 2HgOAc I l g f H g ( 0 A~)~. Neither mechanism is consistent with the earlier observations that two equivalents of mercuric salt are involved in the oxidation of an alkene to an allcadiene or an allcenyl ester as well as to a glycol derivative (7) or rearrangement product (10, 30).The consun~ption of two equivalents of mercuric salt per e q u i v a l e~~t of alliene was confirmed by Broolc and Wright (10) who also proposed a mechanism for the conversion of cyclohesene to forrn~~lcyclopentane not illvolving the intermediacy of an oxyn~ercurial. These workers thought that an oxymercurial could not be involved because "hydroxymercuration with n~ercuric nitrate is not a significant reaction in water". \Ye have now found this statement t o be incorrect.The error of Brook and Wright lay in dilution of their reaction aliquots with excess aqueous sodium chloride. 'The hydrochloric acid generated in this way decomposed the mercurial. Alternatively if cyclohexene is mixed with an equivalent each of mercuric nitrate and nitric acid (1 molar) and diluted after 10 min. into one eqz~ivalent of cold aqueous sodium chloride a maximal 80% yield of 2-hydl-oxy-1-chloromercuricyclohexane may be isolated. The equilibrium is shifted to afford a...

The Autooxidation of Organomercuric Salts

“…The isolated non-mercurial has been shown to be I-methoxy-1-methylcyclohexane (X, estin~ated yield 25%) by coinparison of its physical constants (5) and its Rf 011 a chromatoplate (6). This product is the expected one from the hoinolytic oxidation described in earlier reports (1,2).…”

One-pot synthesis of oligomeric aryl-substituted PPV analogs with extended π-conjugation

“…This was done by carrying out a one-pot synthesis of the same tetramers 6, directly from the corresponding monomers 4, in four consecutive steps [eqn. (11)]. The tetramers were obtained in high yields (86-90%) within an overall reaction time of one hour!…”

The Mechanism of Organomercurial Oxidation by Mercuric Salts

“…In the earlier publication (1) it was shown that the reaction of benzylmercuric nitrate with mercuric nitrate in methanol led to benzyl methyl ether and benzyl nitrate. Additional examples have now been sought.…”

“…I t has been shown previously (1) that the oxidation of organomercuric salts in which the anion is nitrato is much more facile than maiiltains for systems in which the salts are acetates. Because of this difference in reactivity we have found it convenie~lt to discuss the nitrato and acetato systems separately.…”