593-74-8 mercury dimethyl

The thermal decomposition of dimethyl mercury in the presence of radical scavengers has been thoroughly investigated61-65. The basic mechanism, the preexponential factor and the activation energy are all well established. There is still considerable doubt about the mechanism of the pyrolysis in the absence of chemically active additives. Consequently, the quantitative interpretation of rate data from such systems is of doubtful value. Systems using effective scavengers will be discussed first. The quantitative results from these systems will be used in assessing the data obtained in the absence of additives. 

The overall process given by reaction (1) and reaction (2) is common to all mechanisms proposed for the decomposition of this alkyl. Whether this process occurs as written or by the simultaneous release of both methyl radicals is uncertain. Gowenlock et al.66 tried to resolve this problem and the similar problem that arises with other mercury alkyls by determining D(RHg-R) [R = CH3, C2H5, (CH3)2CH, CH3CH2CH2CH2] from appearance potential measurements. 

For the fully inhibited decomposition Russell and Bernstein61 give kt = 5,0x 1015 exp(—57,900/RT) sec 1. This result has been criticized by Cattanach and Long67 who point out that the presence of hydrogen from the decomposition of cyclopentane should initiate the chain process 

Weston and Seltzer62, who have also studied the cyclopentane inhibited decom- 

The gas-phase thermal decomposition of dimethyl mercury by itself and in the presence of inert gas has been extensively investigated61,63,67,71-79. The 

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The length of the axial bond would be expected on all theories to be important. The barrier height does decline from ethane to methyl silane to methyl germane, but of course the bonded atoms are different. Unfortunately reliable values are not available for dimethyl mercury, dimethyl acetylene, and similar molecules with still longer bonds. An apparent exception is provided by methyl mercaptan and methyl alcohol. The latter, with the shorter axial bond, has the lower barrier. 

Thus, both elemental mercury and the mineral form cinnabar (HgS) can release Hg++, the mercuric ion. Bacteria can then methylate it to form sequentially CH3 Hg+, the methyl mercuric cation, and dimethyl mercury. The latter, like elemental mercury, is volatile and tends to pass into the atmosphere when formed. The methylation of mercury can be accomplished in the environment by bacteria, notably in sediments. 

Dimethyl mercury Iron Silver sulphide Hydrides... 

Photolysis of acetone forms methyl radicals, isolated as dimethyl-mercury, and acetyl radicals isolated as diacetyl. Photolysis of benzo-phenone forms phenyl radicals which remove a tellurium mirror to give diphenyltellurium. 

Fig. 3. Arrhenius plots for the decomposition of dimethyl mercury. All rate coefficients are at or near the high-pressure limit. If a radical scavenger has been used it is shown in brackets following the authors names. 1, Krech and Price (benzene) 2, Kallend and Purnell (propene) 3, Russell and Bernstein (cyclopentane) 4, Russell and Bernstein 5, Laurie and Long 6, Kominar and Price (toluene) O, Weston and Seltzer (cyclopentane) , point calculated from the steady-state equation of Kallend and Purnell.

The mechanism proposed by Kallend and Purnell explains many features of the dimethyl mercury pyrolysis but two difficulties arise. Their explanations are valid only if addition of NO does, in fact, increase the methyl radical concentration. The process by which this occurs has not been specified and none comes readily to mind. In fact, the equilibrium CH3+NO CH3NO might reasonably be expected to lower the methyl radical concentration. The second difficulty arises when high pressure limiting values of calculated from Kallend and Purnell s steady-state equation... 

Based on the loss of dimethyl mercury kovcraI1 = 5.0 xlO13 exp(—49,900/RT) sec-1. Laurie and Long72 propose an alternate scheme in which reactions (1) and (2) are the only processes involving dimethyl mercury. On this basis they calculate kx = 1.9 x 1014 exp(—51,300/RT) sec-1. The methyl radicals released are assumed to undergo reactions (12) and (21), viz. 

Fig. 4. Arrhenius plots for the pressure-dependent flow system decomposition of dimethyl mercury. 1, Gowenlock, Polanyi and Warhurst (7 torr C02+3 torr toluene), Kominar and Price (4.4 torr toluene) 2, Price and Trotman-Dickenson (16 torr toluene, rate coefficients corrected for methyl radicals found as ethylbenzene) 3, Krech and Price (16 torr benzene). O, Lossing and Tickner (6-20 torr helium).

The available kinetic and thermochemical data are summarized in Table 7. Based on the approximate equality of E and D1+D2 and on the magnitude of the frequency factor, Billinge and Gowenlock98 would place dimethyl mercury, di-B-propyl mercury, di-isopropyl mercury (above 230 °C) and (on the basis of the frequency factor only, since thermochemical data are not available) di-n-butyl mercury in class II (simultaneous rupture into mercury and two alkyl radicals). If the high frequency factors are simply due to a general softening of the vibrations in the activated state, then in the case of di-isopropyl mercury D2 — 0, while for dimethyl and di-B-propyl mercury D2 is small but finite (2-3 kcal.mole" ). However, within the limits of experimental error all of these alkyls for which thermochemical data are available may have E = Dl+D2, and thus all may belong to class II. At the same time it must be noted that some metal alkyls which are... 

The mean bond dissociation energies (E ) given in Table 12 are based on thermochemical data at 25 C19. Unless previously discussed, the heat of formation of the metal alkyl used is that given by Long60. The higher values of E and D2 for dimethyl mercury are obtained when Long s recommended value for the heat... 

Compounds Methyl mercury ethyl mercury chloride, dimethyl mercury... 

TICs are threats to water systems, but are not as problematic as chemical or biological agents. Consider cyanide with a lethal dose of 25 mg. To contaminate the reservoir mentioned above would require 25 x 200 x 10 mg, or roughly 5,000 kg (5 tons). Dimethyl mercury is lethal at 400 mg more than 50 tons would be required. Of course, it is possible to contaminate a small reservoir or simultaneously a group of several reservoirs. 

CsHuN, Ethanamine, A-ethyl-A-methyl-tungsten complex, 26 40, 42 C6HF5, Benzene, pentafluoro-gold complexes, 26 86-90 C H4I2, Benzene, 1,2-diido-iridium complex, 26 125 CJT, Phenyl platinum complex, 26 136 C,H,N, Pyridine osmium complex, 26 291 OHtS, Benzenethiol osmium complex, 26 304 QH7P, Phosphine, phenyl-cobalt-iron complex, 26 353 QH 1-Butyne, 3,3-dimethyl-mercury-molybdenum-ruthenium complex, 26 329-335 C6H 4P, Phosphine, triethyl-platinum complex, 26 126 platinum complexes, 26 135-140 CsHisPO, Triethyl phosphite iron complex, 26 61... 

As dangerous as mercur r vapor is, it is by no means the most toxic form of the metal. This distinction belongs to a compound of mercury, dimethyl mercury. The world found out about the deadly nature of this substance in the 1950s, when dozens of people died and thousands experienced symptoms of mercury toxicity in the Japanese fishing village of Minamata. A nearby chemical company had been using mercury in the production of acetylene, and it had routinely discharged the used mercury into the ocean. Mercury isn t soluble in water, and it should have simply accumulated harmlessly at the bottom of the sea. But it didn t. 

Professor Wetterhahn addressed this very question in 1997 by conducting an experiment that involved adding a tiny amount of dimethyl mercury to a sample. Working in a fume hood, wearing latex gloves, Wetterhahn carefully added the liquid. Then Murphy s Law kicked in, and she accidentally spilled a couple of drops on her gloved hand. She performed a quick cleanup and went back to what she was doing. 

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