Chromium dithiocarbamates

Chromium dithiocarbamates are known with the metal in the oxidation states + 2 and + 3. 

Figure 76. Oxygen-expanded chromium dithiocarbamate complexes together with representations of possible resonance hybrids for the expanded ligand.

Mullins [37] has described a procedure for determining the concentrations of dissolved chromium species in seawater. Chromium (III) and chromium (VI) separated by co-precipitation with hydrated iron (III) oxide and total chromium are determined separately by conversion to chromium (VI), extraction with ammonium pyrrolidine diethyl dithiocarbamate into methyl isobutyl ketone, and determination by AAS. The detection limit is 40 ng/1 chromium. The dissolved chromium not amenable to separation and direct extraction is calculated by difference. In waters investigated, total concentrations were relatively high (1-5 xg/l), with chromium (VI) the predominant species in all areas sampled with one exception, where organically bound chromium was the major species. 

Rao, K.R. and D.G. Doughtie. 1984. Histopathological changes in grass shrimp exposed to chromium, pentachlorophenol and dithiocarbamates. Mar. Environ. Res. 14 371-395. 

Complexes of 1,2-dithiolate dianions (225) are of interest, although because they undergo successive one-electron transfer processes which involve orbitals of ligand character so unlike those of the dithiocarbamate type of ligand, it is unprofitable to attempt to assign oxidation states.995,1005 The chromium complexes are shown in Table 89. 

There are two treatability groups of dissolved metals for chemical precipitation, complexed and non-complexed metals. Non-complexed metals can be removed by a direct precipitation with such a chemical as lime (Ca(OH) ), caustic (NaOH), sodium sulfide (Na2S), ferrous sulfide (FeS), or sodium carbonate (NajCOj). Complexed metals require coprecipitation with ferrous sulfate (FeS04), ferrous chloride (FeClj), or sodium dimethyl dithiocarbamate (DTC) in addition to a regular precipitant such as caustic or lime. Electrochemically generated ferrous ion is also effective in removing a wide variety of heavy metals, including hexavalent chromium. 

Four main types of antioxidants are commonly used in polypropylene stabilizer systems although many other types of chemical compounds have been suggested. These types include hindered phenolics, thiodi-propionate esters, aryl phosphites, and ultraviolet absorbers such as the hydroxybenzophenones and benzotriazoles. Other chemicals which have been reported include aromatic amines such as p-phenylenediamine, hydrocarbon borates, aminophenols, Zn and other metal dithiocarbamates, thiophosphates, and thiophosphites, mercaptals, chromium salt complexes, tin-sulfur compounds, triazoles, silicone polymers, carbon black, nickel phenolates, thiurams, oxamides, metal stearates, Cu, Zn, Cd, and Pb salts of benzimidazoles, succinic acid anhydride, and others. The polymeric phenolic phosphites described here are another type. 

Sulfur-based Cr coordination compounds include a series of dithiocarbamates of the type [Cr(S2CNR2)2] (R = Me, Et or R2 = C4H8), which are antiferromagnetically coupled. The diethyl-substituted compound is an S-bridged dimer, making chromium five-coordinate. Square-planar Cr coordinated by sulfur occurs in the violet [NEt4]2[Cr(S2C2H4)2]. Finally, Thiourea and its derivatives form adducts with Cr halides, which are similar to the adducts with O-donors mentioned above. 

Dinuclear niobium sulfido and selenido dithiophosphates, Nb2Q4[S2P(OR)2]4,75,76 (Q = S, Se R = Et) (also xanthates and dithiocarbamates) have been prepared but no crystal structure was reported. Optically active chromium complexes, Cr[S2P(OR)2]3 derived from Z)-borneol and L-menthol, have been described.77... 

Polarographic reduction of chromium(iii) complexes of dithiocarbomates R2NCS J (R = Et, Mr, or Bu") and of heterocyclic amines of the type (CH2)2NCSJ (n = 4,5, or 6) in the presence and absence of the ligands bipy and phen has been studied in DMF. The addition of the first electron occurs reversibly in all cases and the rate of formation of adducts with phen is greater than with bipy. Electrolysis of a solution of Cr(Et2 NCS2)3 in MeCN at — 1.1 V in the presence of bipy gives rise to the sequence of reactions shown in Scheme 4. The Cr product species was identified by e.s.r. spectroscopy. Normal co-ordinate analysis on a series of chromiumfiii) dithiocarbamates... 

Cr(mdtc)3,(CgHg)2, and Cr(mdtc)3,CH2Cl2 (mdtc = morpholinecarbodi-thioate) have been determined. In each case the CrSg unit forms a trigonally distorted octahedron with small deviations from symmetry. Dithiocarbamate, dithiophosphate, and dithioxanthate complexes of chromium(iii) have been found to exhibit Pfeiffer c.d. activity. Further complexes with S-donor ligands are described in Table 5. 

APHA. 1985f. Determination of low concentrations of cadmium, chromium, cobalt, copper, iron, lead, manganese, nickel, silver, and zinc by chelation with ammonium pyrrolidine dithiocarbamate (APDC) and extraction into methyl isobutyl ketone (MIBK)-method 303B. In Standard methods for the examination of water and wastewater. 16th ed. Washington, DC American Public Health Association, 160-162. 

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