Dialkylmercury

A further kinetic investigation of the rates of cleavage of diphenylmercury (and some dialkylmercurials) showed similar kinetic features608. The first-order rate for the reaction of diphenylmercury with acetic acid at 25 °C was 4.98 x 10", which agreed quite well with the value from the above determination (2 x 10-4 at 42 °C with dioxan). In the presence of perchloric acid, second-order kinetics were found to be obeyed (for dineophyl mercury and presumably for diarylmercurials as well) for a twofold concentration change in both mercurial and perchloric acid. Two separate mechanisms were proposed for the reactions in the absence, and presence, of perchloric acid. Under the former conditions an SEi process (244) was... 

Organolithium reagents stabilized by ct-silyl groups have been recently used for the synthesis of mononuclear derivatives such as compounds 8, 9 which the bulky (PhMe2Si>3C and (Me3Si>3C as ligands directly attached to the mercury center.30 Other examples include the dialkylmercury products shown in Equations (2) and (3).31 32... 

Because mercury is easily reduced, dialkylmercury compounds are useful reagents for preparing a large number of alkyls of other metals by group transfer reactions. This is illustrated by the following equations ... 

Rice has shown that the cracking of hydrocarbons at high temperatures gives free radicals.48 Only the methyl and ethyl radicals survive long enough to react with mercury to give dialkylmercury. Presumably the others decomposes by a beta cleavage process. 

Diaryl- or dialkylmercury compounds can be used for the synthesis of mixed aryltin chlorides326, or for alkylation of SnF2338 or SnX4339 (Scheme 26). Functional halostan-nanes can be prepared by a variety of methods. 

Some other organogermyl-, organohalogermyl- and organopolygermylmercury derivatives have been prepared by hydrogermolysis of dialkylmercury compounds (equations 37 and 38)43,44. 

Simple dialkylmercury reagents react with phosphorus trichloride replacing a single halogen and leading to the alkyldichlorophosphine in reasonable yield (Equation 4.12).23... 

For secondary alkyl iodides, the two one-electron polarographic waves are more separated. Reduction of 2-iodooctane at the potential of the first wave alfords the dialkylmercury and 7,8-dimethyl-tetradecane by reactions of the sec-octyl radical. At the potential of the second wave only octane and octenes are isolated [37]. 2-Bromooctane shows only one polarographic wave and yields octane and octene on reduction at any potential [37]. Radicals generated by reduction of primary and secondary iodoalkanes will react with other cathode materials including tin, lead and thallium to form metal alkyls [48,49],... 

Radical intermediates are also trapped by intramolecular reaction with an alkene or alkyne bond. At a mercury cathode this process competes with formation of the dialkylmercury [51], At a reticulated vitreous carbon cathode, this intramolecular cyclization of radicals generated by reduction of iodo compounds is an important process. Reduction of l-iododec-5-yne 5 at vitreous carbon gives the cyclopentane... 

The preparation of a number of 5-(alkyl)thianthrenium perchlorates has been performed from the thianthrene cation radical with dialkylmercurials and tetraalkyltins (R4Sn) <1983JOC143>. Thianthrene as well as phenoxathiin cation radical perchlorates react with alkenes. The former add stereospecifically to cycloalkenes although the latter afforded a mixture of mono- and bis-adducts in which the configuration of the alkene was retained <2003JOC8910>. 

Mercury compounds are often used as electrophiles in displacements on organomercurials. There are five possible combinations of reactants in such mercury exchange reactions. A dialkylmercurial substrate may be attacked either by a mercury salt (Reaction 4.43) or by a monoalkylmercurial (Reaction 4.44) and likewise a monoalkylmercurial may react either with a mercury salt or with another monoalkylmercurial (Reactions 4.45 and 4.46). Finally, a dialkylmercurial may react with another dialkylmercurial (Reaction 4.47). (In Reactions 4.43-4.47 and in other reactions in this section, one of the reactants, and the fragments derived from that reactant in the products, are written in italics. This is done to make it easier to follow the course of the reaction.)... 

The possibility of electrophilic substitution at saturated carbon as an independent mechanism was considered by Hughes and Ingold2 in 1935, but this mechanism was not kinetically demonstrated with metal alkyls as substrates until 1955, when Winstein and Traylor3 published their results on the acetolysis of dialkylmercurys. At about the same time, stereochemical studies on electrophilic substitutions at saturated carbon were commenced by Winstein and by Reutov, again using alkylmercury compounds as substrates. Notable studies on the kinetics and stereochemistry of substitution at saturated carbon have been carried out by Ingold and his co-workers and by Reutov and his co-workers. Ingold4... 

SECOND-ORDER RATE COEFFICIENTS (l.mole- .Sec- ) AT 25 °C AND ACTIVATION PARAMETERS FOR THE SUBSTITUTION OF DIALKYLMERCURYS BY MERCURIC IODIDE... 

The two-alkyl exchange (15) has also been studied by Dessy et al.29,33 the reported rate coefficients at 25 °C and the activation parameters are collected in Table 7. Dessy and Lee33 suggested that the dialkylmercurys were attacked by mercuric iodide in dioxan to give a four-centre transition state (XII) (of the SE2(cyclic) type) or a transition state (XIII) derived from an ion-pair attack, viz. 

ACIDOLYSIS OF DIALKYLMERCURYS BY ACETIC ACID AND BY PERCHLORIC ACID IN SOLVENT ACETIC ACID... 

When dialkylmercurys are allowed to react with acetic acid, the latter also acting as the solvent, one alkyl group only is cleaved from the mercury atom, viz. 

Winstein and Traylor27 showed that under the above conditions, that is with an excess of acetic acid, reaction (19) follows kinetics first-order in dialkylmercury their reported first-order rate coefficients are collected in Table 5. Relative rates of acetolyses at 25 °C are thus ... 

FIRST-ORDER RATE COEFFICIENTS (sec" ) FOR THE ACETOLYSIS OF DIALKYLMERCURYS,... 

The acidolysis of dialkylmercurys by hydrogen chloride in solvent DMSO-(10) dioxan (1) was shown by Dessy et al.28, to proceed by the simple reaction... 

Rate coefficients and activation parameters for the substitution of a number of dialkylmercurys are in Table 6. 

Jensen and Rickborn60 have severely criticised the work of Dessy on the acidolysis of dialkylmercurys by hydrogen chloride. They state that, in their view, no firm mechanistic conclusions can be drawn from the published results , although a four-centred mechanism at present seems to be reasonable. 

Over a period of years, Kharasch et al.32,33, and also Whitmore and Bernstein34, studied the cleavage of unsymmetrical dialkylmercurys by hydrogen chloride in solvent ethanol, viz. 

The SE1 mechanism, equations (24) and (25), implies that dialkylmercurys should ionise according to equation (24) in solvent ethanol, even in the absence of hydrogen chloride. But dialkylmercurys are quite stable in ethanolic solution and thus reaction (24) would seem to be unrealistic Winstein and Traylor27 have already pointed out that the typical dialkylmercurys used in the studies of Kharasch do not follow an SE1 mechanism. There is thus very little theoretical basis for regarding (23) as an electronegativity series. 

Results46 on the rate of gas evolution on stirring dialkylmercurys with concentrated aqueous hydrochloric acid are hence not included, since in this case the reaction medium is probably heterogeneous. 

The formation of butyl derivatives of methylmercury and ethylmercury was studied as a means of providing stable, volatile derivatives for the gas chromatographic determination of these compounds (Quimby and Sullivan, 1990). The resulting dialkylmercury species were separated satisfactorily on a capillary... 

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