Alkylmercury compounds

The photochemical or thermal reaction between petfluoroalkyl iodides and mercury-cadmium amalgams has been used for the synthesis of perfluoro-alkylmercury compounds [150] Functionalized analogues have been prepared similarly via this route [151, 152] (equation 117), and the preparation of bis(tri-fluoromethyl)mercury has been described [153]... 

The reductive decomposition of alkylmercury compounds is also a useful source of radicals.300 The organomercury compounds are available by oxymercuration (see Section 4.1.3) or from organometallic compounds as a result of metal-metal exchange (see Section 7.3.3). 

Mercury (Hg) can occur in a large number of physical and chemical forms with a variety of properties, thus determining complex distribution, bioavailability, and toxicity patterns [1]. The most important chemical forms are elemental Hg (Hg°), ionic Hg (Hg2+ and Hg22+), and alkylmercury compounds. Because of their capability to permeate through biological membranes and to bioaccumulate and to biomagnificate through the trophic chain, alkylmercury compounds are the most toxic mercury species found in the aquatic environment [2]. 

Kimura and Miller [28] collected and determined vapours produced by the decomposition in soil of phenyl alkylmercury compounds. They found that the air above soil containing phenylmercury acetate contained mercury vapour and traces of phenylmercury acetate. 

Vapours of mercury, phenyl, and alkylmercury compounds were collected and measured as described except that the dichromate absorption solution was analyzed by the mercury reduction technique [28] after treatment with an excess of chloride hydroxylammonium chloride solution. 

A method [62] has been described for the determination of down to 2.5pg kg-1 alkylmercury compounds and inorganic mercury in river sediments. This method uses steam distillation to separate methylmercury in the distillate and inorganic mercury in the residue. The methylmercury is then determined by flameless atomic absorption spectrophotometry and the inorganic mercury by the same technique after wet digestion with nitric acid and potassium permanganate [63]. The well known adsorptive properties of clays for alkylmercury compounds does not cause a problem in the above method. The presence of humic acid in the sediment did not depress the recovery of alkylmercury compounds by more than 20%. In the presence of metallic sulphides in the sediment sample the recovery of alkylmercury compounds decreased when more than lmg of sulphur was present in the distillate. The addition of 4M hydrochloric acid, instead of 2M hydrochloric acid before distillation completely, eliminated this effect giving a recovery of 90-100%. 

Figure 2.8 Detection of alkylmercury compounds using flameless atomic absorption detector. Conditions column, Corasil I, 50 cm x 2.1 mm i.d. eluent, n-hexane flow rate, 0.5 ml min-1 detection, flameless atomic absorption spectrometer. Peaks 1, benzene, 2, ethylmercury chloride, and 3, methylmer-cury chloride.

Many organometallic compounds are best prepared by this reaction, which involves replacement of a metal in an organometallic compound by another metal. RM can be successfully prepared only when M is above M in the electromotive series, unless some other way is found to shift the equilibrium. That is, RM is usually an unreactive compound and M is a metal more active than M. Most often, RM is R2Hg, since mercury alkyls372 are easy to prepare and mercury is far down in the electromotive series.397 Alkyls of Li, Na, K, Be, Mg, Al, Ga, Zn, Cd, Te, Sn, etc. have been prepared this way. An important advantage of this method over 2-38 is that it ensures that the organometallic compound will be prepared free of any possible halide. This method can be used for the isolation of solid sodium and potassium alkyls.39R If the metals lie too close together in the series, it may not be possible to shift the equilibrium, For example, alkylbismuth compounds cannot be prepared in this way from alkylmercury compounds. 

Alkyl radicals, prepared in situ, react with pyridine to form mainly 2-alkyl derivatives and this regioselectivity is shown in the free radical reactions of alkylmercurial compounds with pyridines (Scheme 37). 

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... 

Samples of atmospheric mercury were obtained by pre-concentration of mercury on columns of graphitised carbon black (Carbotrap). The columns, at ambient temperature, retained mercury vapour and alkylmercury compounds (Bloom and Fitzgerald, 1988). Methylmercury chloride, ethylmercury chloride and dimethylmercury were held on the column at temperatures as high as 29°C and air flow rates as high as 790cm3min 1. At high flow rates and high temperature,... 

Atomic fluorescence spectroscopy (AFS) has also been used as a means of detection in gas chromatography. Alkylmercury compounds have been determined in air by cold-vapor GC-AFS with limits of detection of about 0.3-2.0 pg [129]. 

Table 15.18 Analytical figures of merit in the determination of alkylmercury compounds by the GLC-MIP system...

Fig. 1. 13. Net reaction (a) for the hydration of atkenes (R = CH3, R" = H) or (b) for the addition of alcohol to alkenes (R = CF3, R" = alkyl) via the reaction sequence (1) solvomercu ration of the alkene (for mechanism, see Figure 3.48 regioselectivity Figure 3.49) (2) reduction of the alkylmercury compound obtained (for mechanism, see Figure 1.14).

At Hg electrodes the oxidation of thiols in aqueous solution occurs at more negative potentials than on Pt and alkylmercury compounds are formed, as in Eqs. (4)-(6) [1,7, 13-15]. 

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