Organomercury compounds,

Alkenylmercury compounds can be prepared by hydroboration of an alkyne with catecholborane, followed by reaction with mercuric acetate.185 

Organomercury compounds are weak nucleophiles and react only with very reactive electrophiles. They readily undergo electrophilic substitution by halogens. 

Organomercury reagents do not react with ketones or aldehydes but Lewis acids cause reaction with acyl chlorides.187 With alkenyl mercury compounds, the reaction probably proceeds by electrophilic attack on the double bond with the regiochemistry being directed by the stabilization of the (3-carbocation by the mercury.188 

Most of the synthetic applications of organomercury compounds are in transition metal-catalyzed processes in which the organic substituent is transferred from mercury to the transition metal in the course of the reaction. Examples of this type of reaction 

Several organomercury compounds of formula CH3HgX are water-soluble, which makes them very poisonous to organisms [20], They dissociate according to Eq. (6). 

The biological methylation of mercury (e.g., from weathering, volcanism, fossil fuels, chloralkali electrolysis) is effected by microorganisms that utilize methylco-balamin (2c) see Section 5.1.2. 

The water-soluble organometallic 2 is the only natural product able to transfer the methyl group as a carbanion (cf. Eq. 7). As a soft Lewis acid (in the classification of Pearson), the methylmercuronium ion [CH3Hg]+ is soluble in the presence of hard bases such as [N03]- or [S04]2. In turn, soft bases such as (organic) sulfides thus make it lipophilic and enable its uptake by living organisms. 

The catastrophy of Minamata in Japan (1953-1960), with 55 people killed and more than 1200 poisoned, for the first time focused attention on the environmental consequences of water-soluble organometal species. In this particular case, it was mercury-containing waste water that had access to marine organisms [3 a, 20]. Fish, particularly, accumulates mercury, up to 250 ppb. In another case (Iraq, 1970-1971), the seed disinfectant ethylmercury p-toluenesulfonic anilide (4) had been applied to wheat and caused severe poisoning of consumers. 

Organomercury compounds derive their toxicity from their solubility in both aqueous and lipophilic systems. They primarily affect the central nervous system. The reversible ionic/covalent bonding in organomercury compounds distributes them in the body. Thus, water-soluble species such as 3 are converted in the stomach into lipophilic 5 (cf. Eq. 8) X = [N03]-, etc., where they are then absorbed. 

There are several useful means for preparation of organomercury compounds. The general metal-metal exchange reaction between mercury(II) salts and organolithium or magnesium compounds is applicable. The oxymercuration reaction discussed in Section 

The organomercury compounds can be used in situ, or they can be isolated as organomercuric halides. 

Their extreme toxicity necessitates stringent precautions during their preparation and handling. The toxicity of organomercury compounds is often greater than that of the mercury in them the volatile alkylmercury class is particularly dangerous. 

Organomercury compounds have only slight reactivity. They are also completely indifferent to atmospheric oxygen and to water under normal conditions and can thus be prepared and used under conditions that are not permissible for the more reactive organometallic compounds discussed above. 

Some alkyl iodides react with metallic mercury in sunlight and in presence of a little elemental iodine, yielding alkylmercury iodides,159 but the reaction is very slow. 

A generally applicable method of preparing dialkyl- and diaryl-mercury compounds is by treatment of alkyl or aryl halides or alkyl sulfates with sodium amalgam 160 

Dimethylmercury 161 A mixture of methyl iodide (10 parts by wt.) and anhydrous methyl acetate (1 part by wt.) is placed in a round-bottomed flask carrying an efficient condenser 

See also page 403, Section 1 for reduction of cnynes and diynes to dienes. Reviews  

Onishchenko, Diene Synthesis, D. Davey Co., New York (1964) Houben-Weyl, Vol V / lc, G. Thieme, Stuttgart (1970) 

SECTION 7.3. ORGANIC DERIVATIVES OF GROUP nB AND GROUP niB METALS 

The chromatographic system used in this method consisted of two Laboratory Data Control (LDC) (Riviere Beach, FL, USA) Constametric ITT pumps with a gradient controller and a Rheodyne Model 7125 injection valve (Rheodyne Corp., Cotati, CA, USA) fitted with a 200pL loop. The separation was performed on two Waters Resolve columns (Waters Assoc., Milford, MA, USA), SpmCig stationary phase, 15 cm x 3.9mm id placed in series with a mobile phase consisting of 0.06M ammonium acetate and 0.005% V/V 2-mercaptoethanol with a gradient from 15 to 75% of acetonitrile. A flow-rate of 1.0ml min was used for all analyses. The post-column reaction system has been described by Bushee et al. [247] and is shown schematically in Fig. 4.7. An aqueous solution of 0.5% m/V 

Source Reproduced by permission from the Royal Society of Chemistry. London [246] 

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Addition of several organomercury compounds (methyl, aryl, and benzyl) to conjugated dienes in the presence of Pd(II) salts generates the ir-allylpalladium complex 422, which is subjected to further transformations. A secondary amine reacts to give the tertiary allylic amine 423 in a modest yield along with diene 424 and reduced product 425[382,383]. Even the unconjugated diene 426 is converted into the 7r-allyllic palladium complex 427 by the reaction of PhHgCI via the elimination and reverse readdition of H—Pd—Cl[383]. 

Pd(II) salts promote the carbonylation of organomercury compounds. Reaction of phenylmercury chloride and PdCh under CO pressure affords benzophenone (429)[387]. Both esters and ketones are obtained by the carbonylation of furylmercury(Il) chloride in alcohol[388]. Although the yields are not satisfactory, esters are obtained by the carbonylation of aryl- and alkylmercuryfll) chlorides[389,390]. One-pot catalytic carbonylation of thiophene, furan, and pyrrole (430) takes place at the 2-position via mercuration and transmetallation by the use of PdCb, Hg(N03), and CuCl2[391]. 

With mercuric acetate (Hg(OOCCH2)2), olefins and / fZ-butyl hydroperoxide form organomercury-containing peroxides (66,100). The organomercury compound can be treated with bromine or a mild reducing agent, such as sodium borohydride, to remove the mercury. 

The reactivity of mercury salts is a fimction of both the solvent and the counterion in the mercury salt. Mercuric chloride, for example, is unreactive, and mercuric acetate is usually used. When higher reactivity is required, salts of electronegatively substituted carboxylic acids such as mercuric trifiuoroacetate can be used. Mercuric nitrate and mercuric perchlorate are also highly reactive. Soft anions reduce the reactivity of the Hg " son by coordination, which reduces the electrophilicity of the cation. The harder oxygen anions leave the mercuric ion in a more reactive state. Organomercury compounds have a number of valuable synthetic applications, and these will be discussed in Chapter 8 of Part B. 

Another major route to fluorinated organomercury compounds is thermal or photochemical decarboxylation offluonne-conlaining mercury carboxylates [/-Si, 169, 170,171, 172], as shown for example in equation 125 [153, 169] Via similar methodology, C6HjHgCF3 (60-75%) [171], (CF3)2Hg (92%) [/i59T, (02NCFCl)2Hg (58%) [172], and [(CF3)3C]2Hg (80%) [157] were synthesized, and several of these mercurials have been used as fluorocarbene precursors [166],... 

Larock, R C Organomercury Compounds in Organic Synthesis Springer-Verlag Berlin, 1985 Seyferth D Acc Chem Res 1972, 5 65... 

The reaction between an excess of Li and an organomercury compound is a useful alternative when isolation of the product is required, rather than its direct use in further synthetic work ... 

These reactions work best with X = I but the less-expensive RBr can be used in conjunction with a Zn-Cu alloy instead of pure Zn. Diaryls are best obtained from appropriate organoboranes or organomercury compounds ... 

An enormous number of organomercury compounds are known. They are predominantly of the same stoichiometries as those of Zn and Cd, viz. RHgX and HgR2, and may be prepared by the action of sodium amalgam on RX ... 

Interaction of the thiophene-containing organomercury compounds 272 (R = H, Me, Et) [74MI1, 79JCS(D)2037] with potassium tris(3-methylpyrazolyl) borate (KTp ) yields 273 [96JOM(515)213],... 

Abstraction of H+ from the protonated enol by water gives an organomercury compound. 

Organomercury compounds, reaction with NaBH4, 222 Organometallic compound, 345 polarity of, 143... 

Reviews of the use of organomercury compounds in organic synthesis have been published by Brilkina and Shushunov (1970), by Larock (1978, 1982, 1985), and by Wardell (1988). 

Organomercury compounds undergo a similar reaction. Alkyl and aryl Grignard reagents can be converted to carboxylic esters with Fe(CO)5 instead of CO. Amides have been prepared by the treatment of trialkyl or triarylboranes with CO and an imine, in the presence of catalytic amounts of cobalt carbonyl ... 

For a review of this and other free-radical reactions of organomercury compounds, see Barluenga, J. Yus, M. Chem. Rev., 1988, 88, 487. 

For a discussion of conversions of organomercury compounds to sulfur-containing compounds, see Larock, R.C. Ref. 300, p. 210. 

The reaction has not been elucidated. Presumably Michler s thioketone reacts with organomercury compounds to yield intensely colored, mesomer-stabilized diphenyl-methane derivatives. 

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