Rates and Isomer Distribution in the Mercuration of Benzene and Toluene. A Proposed Extension of the Quantitative Relationship Governing Isomer Distribution in Aromatic Substitution<sup>1</sup>

Brown, Herbert C.; McGary, C. W.

doi:10.1021/ja01613a081

Cited by 41 publications

(9 citation statements)

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“…The results in Table 5 show that the relative reactivities of the thallation of halobenzenes are in the order F > Cl > Br, The leveling off of the value of the relative reactivities in thallation can be explained by the fact that the activation energy of the reactions in trifluoroacetic acid must be relatively lower than that of mercuration or other electrophilic aromatic substitions of higher selectivity (7).…”

Section: Methodsmentioning

confidence: 99%

Electrophilic mercuration and thallation of benzene and substituted benzenes in trifluoroacetic acid solution

Oláh

Hashimoto

Lin

1977

Proc. Natl. Acad. Sci. U.S.A.

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The mercuration and thallation of benzene and substituted benzenes was studied with mercuric and thallic trifluoroacetate, respectively, in trifluoroacetic acid. With the shortest reaction time (1 sec) at 00, the relative rate of mercuration of toluene compared to that of benzene was 17.5, with the isomer distribution in toluene of: ortho, 17.4%; meta, 5.9%; and para, 76.7%. The isomer distribution in toluene varied with the reaction time, significantly more at 25°than at 00. The competitive thallation of benzene and toluene with thallic trifluoroacetate in trifluoroacetic acid at 150 showed the relative rate, toluene/benzene, to be 33, with the isomer distribution in toluene of: ortho, 9.5%; meta, 5.5%; and para, 85.0%. With increasingly higher reaction temperatures in both mercuration and thallation reactions of aromatics, isomerization (both intramolecular and intermolecular) within the relevant ortho-and para-metallated intermediate ions and/or of the isomers becomes more important. Competitive rates and isomer distributions of mercuration and thallation of benzene and substituted benzenes were also determined. The predominant para substitution in both mercuration and thallation of methylbenzenes reflects, besides some steric factors, the strong stabilizing effect of para methyl groups on the arenium ion intermediates. Under predominantly kinetically controlled conditions, no anomalous increase in the amount of meta substitution was observed.The mercuration of aromatic hydrocarbons with mercuric trifluoroacetate in trifluoroacetic acid at 250 has been studied, predominantly by Brown and coworkers (1-3). The rate ratio of toluene to benzene (kT/kB) was found to be 9.89 and the isomer distribution in toluene was: ortho, 12.2%; meta, 8.6%; and para, 79.2%. From these results, as well as from their preceding studies in acetic acid solution with perchloric acid catalyst giving kT/kB = 3.6-7, and 12-16% meta isomer, it was concluded that the relatively high meta isomer ratio observed was due to the high electrophilic reactivity of the mercurating agent causing the observed low selectivity substitutions. These results were correlated by the so-called Brown selectivity relationship (for a review, see ref. 4).It should be pointed out that, in their original paper on mercuration of toluene and benzene, Brown and Nelson, (5) extending the claimed quantitative selectivity relationship governing isomer distributions in aromatic substitution, commented on the preceding work of Klapproth and Westheimer (6) who found that, in glacial acetic acid with perchloric acid as catalyst, toluene was mercurated by mercuric acetate at 250 to give 6% of the meta isomer. Brown and Nelson claimed to have observed 12% meta isomer under similar conditions and stated "we are, however, unable to account for the differences between the values of the meta isomer." In the former case (6), a precise radiochemical technique was used in establishing orientation, whereas infrared analysis was utilized in the latter. iments at 250 and quenc...

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Section: Methodsmentioning

confidence: 99%

Electrophilic mercuration and thallation of benzene and substituted benzenes in trifluoroacetic acid solution

Oláh

Hashimoto

Lin

1977

Proc. Natl. Acad. Sci. U.S.A.

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“…a t $15" C for 3 7 G3 G 250 ml 11 hr 600/0 I-ICI04 possibility that equilibrium is not always attained a t once in systems where the mercurated nitrobenzenes are not equally stable. Likewise, as is shown for toluene mercuration in Table 11, Brown and McGary (9) formed mercurials seems to be occurring, and that mercuration, like sulphonation ( l l ) , is reversible. A similar opinion (12) had been aflirmed earlier.…”

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confidence: 59%

“…Indeed, the substitution of more than one anionomercuri group is so likely that most worliers have been troubled by it. Attempts t o avoid it (9) The analyses of the products have been accon~plished, after solvent-extractive separation of pl~enylmercuric chloride from the physically intractable benzenepolymercuric chlorides, b17 quantitative conversion t o the polybromobenzenes. The inethods used previously (14, 15) have been lnodified slightly.…”

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The Reversibility of Aromatic Mercuration

Malaiyandi¹,

Sawatzky²,

Wright³

1961

Can. J. Chem.

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!iBSl'1<.4C.l', .I hc ratio of isomeric bispcrchloratomcrc~~ribenze~~es obtairietl from the monomercurial ancl mercuric perchloratc in perchloric acicl varies slightly with concentration of the acid, but is prepondera~~tly meta. Howe\.er, more para than meta isomcr is o b t a i~~e d under conditions \\here the para isomer is insoluble ill thc s~~s t c~n .This indicates a mobile equilibri~~m among the isomers, which is found to estencl to all of the polymercuration p r o d~~c t s .The postulated intermediate for the equilibratio~~, which is 1,2,4-triclilorato~~iercuribenzene, is inclicated by the isolation of the similarly orie~~tecl 1,2,4,5-percliloratomercuritetral;ie1ze1ie. i\lthough nolle of the ortho-diperrhlorato~nerc~~ribe~~zene can be found fro111 this reaction in perchloric acicl, it is the principal isomer \\hen phenylmercuric acetate is acetos~~mercurated neat.

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“…Electrophilic metallation of mercury(II), 18 thallium(II) 19,20 or lead(IV), 20 salts to aromatic rings is well known and several examples of metallation of aliphatic carbons are also reported. [22][23][24] The attack could be either on the aromatic ring followed by rearrangement or directly on the benzylic carbon.…”

Section: Resultsmentioning

confidence: 99%

Efficient C-H activation of alkylbenzenes and methylcyclohexenes to benzyl esters by Pd(OAc)2/Sn(OAc)2 catalyst system

Ohishi

Tanaka

Yamada

et al. 1997

Appl. Organometal. Chem.

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Rates and Isomer Distribution in the Mercuration of Benzene and Toluene. A Proposed Extension of the Quantitative Relationship Governing Isomer Distribution in Aromatic Substitution¹

Cited by 41 publications

References 0 publications

Electrophilic mercuration and thallation of benzene and substituted benzenes in trifluoroacetic acid solution

Electrophilic mercuration and thallation of benzene and substituted benzenes in trifluoroacetic acid solution

The Reversibility of Aromatic Mercuration

Efficient C-H activation of alkylbenzenes and methylcyclohexenes to benzyl esters by Pd(OAc)2/Sn(OAc)2 catalyst system

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Rates and Isomer Distribution in the Mercuration of Benzene and Toluene. A Proposed Extension of the Quantitative Relationship Governing Isomer Distribution in Aromatic Substitution1

Cited by 41 publications

References 0 publications

Electrophilic mercuration and thallation of benzene and substituted benzenes in trifluoroacetic acid solution

Electrophilic mercuration and thallation of benzene and substituted benzenes in trifluoroacetic acid solution

The Reversibility of Aromatic Mercuration

Efficient C-H activation of alkylbenzenes and methylcyclohexenes to benzyl esters by Pd(OAc)2/Sn(OAc)2 catalyst system

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Product

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Rates and Isomer Distribution in the Mercuration of Benzene and Toluene. A Proposed Extension of the Quantitative Relationship Governing Isomer Distribution in Aromatic Substitution¹