Organic Compounds of Metals and Metalloids

PART 5 DEGRADATION OF ORGANIC COMPOUNDS OF METALS AND METALLOIDS 

Although knowledge on the biodegradation of these compounds is sparse, a number of them are important in industrial processes. Formation of methylated derivatives may take place in metals and metalloids belonging to groups 15 and 16 of the periodic table, and a few of group 14. These have been discussed in a critical review (Thayer 2002) and in Chapter 3, Part 4, and they have been noted in the context of the bacterial resistance to metals and metalloids. Since carbon monoxide has been considered as an organic compound (Chapter 7, Part 1), it is consistent to make brief comments on metal carbonyls. 

There are distinct structural types of organic compounds containing metals and metalloids. The first contain covalent carbon-metal bonds and are strictly organometallic compounds, for example, the alkylated compounds of Hg, Sn and Pb, and of Li, Mg, and A1 (and formerly Hg), which have been extensively used in laboratory organic synthesis, and A1(C2H5)3 that is a component of the 

Ziegler-Natta catalyst for polymerization of alkenes. Considerable attention has been directed to double-bonded Fischer carbenes of Cr and W, the Schrock carbenes of Ta and Ti, and cyclic polyene ligands of Fe, Co, Cr, and U. Carbonyls of transition metals from groups 6 to 10 of the periodic table include both the monomeric compounds such as Cr(CO)g, Fe(CO)5, Ni(CO)4 and those with two metal groups such as Mn2(CO)io and Co2(CO)s, which is used industrially for hydroformylation. Although their source has not been identified, it has been shown that volatile compounds from landfills contain carbonyls of Mo and W (Feldmann and Cullen 1997). 

Metals may also be linked through an oxygen or nitrogen atom to form a stable metal complex without a carbon-metal bond. These include metal complexes of ethylenediamine tetraacetate (EDTA), diethylenetriamine pentaacetate (DTPA), or ethylenediamine tetramethylphosphonate (EDTMP). Metalloid compounds include antimonyl gluconate and bismuth salicylate. 

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Parts 1 through 5 of this chapter provide an outline of the reactions involved in the biodegradation of aliphatic esters, ethers, nitramines, phosphonates and sulfonates, and organic compounds of metals and metalloids. 

Thousands of compounds have been proposed as heat stabilizers and as combination heat and light stabilizes for various plastics. The principal classes of such compounds are (1) Group II metal salts of organic acids (primarily the barium, cadmium, and zinc salts of fatty acids, and phenols, the most important group). (2) Organotin stabilizers. (3) Epoxy stabilizers. (4) Salts of mineral acids, e.g., carbonates, sulfates, silicates, phosphates, and phosphates. (5) other organic compounds of metals and metalloids, e.g., alcoholates and mercaptides. Heat stabilizers are used nearly exclusively with vinyl resins. 

Production of metals has been among the first human industrial activities, and thus sinee ancient times man influences the state of metals in nature. Thanks to human activity metals are redistributed in ways different from natural ones and new metal compounds are obtained and released into the environment. Thus the natural cycle of metals is disturbed. Sinee metals and metalloids are distributed everywhere in nature and cover a large concentration interval between mg/kg and more to ng/kg and less, and partieipate in a number of important geochemical and biochemical processes this disturbanee leads to serious impaet on living organisms. This is one of the reasons that determination of metals and metalloids in environmental materials is an object of constant interest. 

The term speciation refers to the determination of the chemical form of metals and metalloids and according to lUPAC it is the process yielding evidence of the atomic or molecular form and oxidation state of an analyte. Included in this definition are the organometallic compounds and those of N, P, S and Si. The determination of organic substances is not referred to. 

Contents Trifluoromethyl Aromatic Compounds (R. Filler) Aliphatic Fluoro-amino Acids (F. Loncrini and R. Filler) Fluoro-alcohols (S. K. De and S. R. Palit) Polyfluoroaromatic Derivatives of Metals and Metalloids (S. C. Cohen and A. G. Massey) The Chemistry of Organic Nitrogen Fluorides (J. P. Freeman) Fluorine Compounds of lenium and Tellurium (B. Cohen and R. D. Peacock) Madelung Constants as a New Guide in the Structural Chemistry of Solids (R. Hoppe). 

Metals and metalloids that form alkyl compounds, eg, methylmercury and methylarsenic acid, tributjltin, deserve special concern because these compounds are volatile and accumulate in cells they are poisonous to the central nervous system of higher organisms. Because methylmercury or other metal alkyls may be produced at a rate faster than it is degraded by other organisms, it may accumulate in higher organisms such as fish. Hg species are also reduced to elementary Hg which is soluble in water but lost by volatilization to the atmosphere (40). 

Is tetramethyldiarsine an organometallic compound By definition, arsenic is a so-called metalloid or semi-metal , not a metal, and thus organoarsenic compounds like the organic compounds of boron or silicon are not per se organometallics. There is no doubt that the preparation of tetramethyldiarsine and the elucidation of its structure may in retrospect be linked to the development of organometallic chemistry, but it would be far beyond the scope of this book, if the chemistry of the organic compounds of the metalloids in its entirety was discussed. 

Metals and metalloids that form alkyl compounds (e.g., methylmercury) deserve special concern, because these compounds are volatile and accumulate in cells they are poisonous to the central nervous system of higher organisms. 

The native species of most metals and metalloids, such as mercury, lead, tin, arsenic, and selenium, are generally present as ionic forms in sample matrices. For GC-based coupling techniques, these compounds need to be extracted from the sample matrix and to be converted to volatile and thermally stable derivatives. Frequently, the derivatives are then concentrated by cry-otrapping or extracting into an organic solvent prior to injection onto a GC column [1]. 

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