Dithiocarbamate complexes chromium

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

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. 

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... 

Inorganic Derivatives.- 1,6-Anhydro 2-chloro-2,4-dideoxy-4-(diphenylphosphoryl)-P-D-glucopyranose, the P-in-the-ring sugar analogues (27) and (28)," the natural arsenic-containing riboside (29), methyl 4,6-0-benzylidene-3-deoxy-3-C-triphenylstannyl-a-D-altropyranoside, two isomeric chromium(III) complexes with 1,3,5-triamino-1,3,5-trideoxy-cw-inositol in the one structure, the vanadium(in) complex (30),and the platinum(Il)-dithiocarbamate complex (31). ... 

It is not clear when dithiocarbamates were first prepared, but certainly they have been known for at least 150 years, since as early as 1850 Debus reported the synthesis of dithiocarbamic acids (1). The first synthesis of a transition metal dithiocarbamate complex is also unclear, however, in a seminal paper in 1907, Delepine (2) reported on the synthesis of a range of aliphatic dithiocarbamates and also the salts of di-iTo-butyldithiocarbamate with transition metals including chromium, molybdenum, iron, manganese, cobalt, nickel, copper, zinc, platinum, cadmium, mercury, silver, and gold. He also noted that while dithiocarbamate salts of the alkali and alkali earth elements were water soluble, those of the transition metals and also the p-block metals and lanthanides were precipitated from water, to give salts soluble in ether and chloroform, and even in some cases, in benzene and carbon disulfide. 

Chromium(III) tris(dithiocarbamate) complexes, [Cr(S2CNR2)3], were first prepared by Delepine (2). Now a large number of chromium(III) complexes are known, while other oxidation states are also accessible, including zero, +2 and... 

Figure 74. Crystallographically characterized chromium tris(dithiocarbamate) complexes.

Bis(2-hydroxyethyl)dithiocarbamate complexes of a range of metals including cobalt, chromium, nickel, copper, and platinmn have been separated by... 

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. 

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... 

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. 

Chromium(VI) can be quantitated without coprecipitation by forming a metal chelate. Method 7196A provides a procedure to prepare the diphe-nylcarbazone complex with Cr(VI) in an aqueous matrix. The method is not sensitive in that it is useful for a range of concentrations between 0.5 and 50 mg/L Cr. A more sensitive colorimetric method converts Cr(VI) to Cr(VI) chelate with ammonium pyrrolidine dithiocarbamate (APDC), followed by LLE into methyl isobutyl ketone (MIBK). The molecular structure for APDC is as follows ... 

Examples of applications involving preconcentration may be found in references (79-85). Modified electrodes capable of preconcentrating the analyte onto the electrode surface have been employed to enhance the analytical sensitivity and selectivity. The most common applications appear to be in the area of metal analysis. Preconcentration has been achieved on the basis of electrostatic attraction for analysis of chromium as Cr207" (78). For more selective preconcentration, however, complexation has been employed (79-81). Dimethylglyoxime has been employed for nickel determinations (81), and dithiocarbamates (79, 80, 82, 83) for copper determination. Dithiocarba-mate modified electrodes have been used for mercury analysis (84, 85). 

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