Solubility, dithiocarbamate complexes

Considerably less is known about the chemistry of palladium and platinum 1,1-dithio complexes. Of late, there has been only one report that dealt with the synthesis of a large number of palladium dithiocar-bamates 392). Twenty-five yellow palladium dithiocarbamate complexes were obtained by reaction of PdCla with NaR2dtc in methanol solution. Several other reports have appeared in which a few dithiocarbamate complexes of palladium were synthesized. Thus, the novel [Pd (OH)2dtc 2], which is soluble in water, was isolated 393). The synthesis of optically active palladium(II) complexes of AT-alkyl-a-phen-ethyldithiocarbamates, similar to (XXIV), via the reaction between the optically active amine, CS2, and PdCl2, has been described. From ORD and CD spectra, it has been established that the vicinal contribution of a remote, asymmetric carbon center could give rise to optical activity of the d—d transitions of palladium 394). Carbon disulfide has been shown to insert into the Pt-F bond of [PtF(PPh3)3]HF2, and X-ray studies indicated the structure (XXIX). 

Standard official methods have been described for the determination of nitric-perchloric acid-soluble nickel [174] and acetic acid-extractable nickel [175] in soil. To determine nitric acid-perchloric acid-soluble nickel [174], the acid digest is dissolved in hydrochloric acid and the nickel is determined by atomic absorption spectrometry. To determine extractable nickel, the nickel is first extracted from the soil with 0.5 M acetic acid and the nickel is then converted to the ammonium pyrrolidine dithiocarbamate complex. Extraction of the complex with chloroform provides an extract for the determination of nickel by atomic absorption spectrometry. 

Closely related are the 1-benzylamino-l-deoxylactitol dithiocarbamate salts developed by Eybl and co-workers316 317 for the same purpose. However, the most important application of 175 is, probably, its use as a nontoxic, water-soluble nitric oxide probe in vivo. In view of the central importance that this gaseous free-radical species plays in regulating a broad range of important biological functions, its detection and quantification near its site of production and action is of prime importance. For this purpose, the ferrous salt of MGD, which forms a stable water-soluble mononitrosyl iron-dithiocarbamate complex (176) with a characteristic electron spin resonance (ESR) spectrum at room temperature, is currently used.318-323... 

The bismuth forms a sparingly soluble metal complex with the pyrrolidine dithiocarbamate. The potentiometric method of titration is highly sensitive for small quantities of bismuth. An evaluable jump is still obtained with the standard solution. However, no explanation has yet been given as to why there is a potential jump at all. During potentiometric titration there is presumably a small quantity of a reversible oxidation product present, with the result that a measurable redox potential may be formed between the... 

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. 

Suzuki et al. (1680) reported that ESR spectra of bis(dithiocarbamate) complexes in various media at —196°C show a typical spectrum with narrow hyperfine splittings. However, spectral differences between water soluble and insoluble complexes are seen, which leads them to suggest they differ both structurally and in their interaction with solvents in frozen solution. Further, the water-soluble complexes are permeable in tissues and this has allowed their ESR spectra to be measured for the first time in this medium. 

Bond and Scholz (606) calculated thermodynamic data for solid mercury bis(dithiocarbamate) complexes mechanically attached to the surface of a paraffin-impregnated graphite electrode. Two-electron reduction generates mercury and the soluble dithiocarbamate anions in a chemically reversible couple during the second and subsequent scans. The formal potential of the reaction has been measured, which enables the calculation of conventional stability constants (P2) for 17 mercury complexes, and a previously unrecognized correlation between log p2 and molecular weight is found (see Section III.G). 

A second approach adopted by O Brien and co-workers (1841, 1849) is the preparation of bis(dithiocarbamate) complexes generated from trimethylethy-lene and trimethylpropylene diamines. The former gives fairly insoluble products that were not pursued, but the latter are soluble in toluene and benzene and were successftdly used to deposit thin films of ZnS and CdS on glass, which gave better quality films than [Cd(S2CNEt2)2]. 

We screened the cytotoxicity of metal-dithiocarbamate complexes against melanoma cell cultures and found that Cu, Zn and Fe DTC conqjlexes decreases melanoma viability, but that Ni complex enhance it. As the first con5>lexes had low solubility in water, we then investigated several water-soluble DTC Cu conq)lexes, such as the N-methyl glutamate derivative Cu(mgDTC)2, but all were... 

LONG-TERM MONITORING OF METAL CONCENTRATIONS VIA COMPLEXES FORMED BY EXCHANGE PROCESSES WITH A WATER SOLUBLE ZINC DITHIOCARBAMATE COMPLEX... 

More recendy, molecular molybdenum-sulfur complexes and clusters have been used as soluble precursors for M0S2 in the formulation of lubricating oils for a variety of appHcations (70). Presumably, the oil-soluble molybdenum—sulfur-containing precursors decompose under shear, pressure, or temperature stress at the wear surface to give beneficial coatings. In several cases it has been shown that the soluble precursors are trifunctional in that they not only display antifriction properties, but have antiwear and antioxidant characteristics as weU. In most cases, the ligands for the Mo are of the 1,1-dithiolate type, including dithiocarbamates, dithiophosphates, and xanthates (55,71). 

Neutral or alkaline salts, eg, KCl, K SO, K CO, or Na PO, are often present in synthetic latices in quantities of - <1%, based on the weight of the mbber. During emulsion polymerization the salts help control viscosity of the latex and, in the case of alkaline salts, the pH of the system. Many polymerizations are carried out at high pH, requiring the use of fixed alkaH, eg, KOH or NaOH. Very small amounts of ferrous salts can be employed as a component of the initiator system, in which case a sequesteriag agent, eg, ethyldiaminotetraacetic acid (EDTA) may be iacluded to complex the iron. Water-soluble shortstops, eg, potassium dithiocarbamate, may also be iacluded ia very small amounts (ca 0.1 parts). 

Discussion. Because of the specific nature of atomic absorption spectroscopy (AAS) as a measuring technique, non-selective reagents such as ammonium pyrollidine dithiocarbamate (APDC) may be used for the liquid-liquid extraction of metal ions. Complexes formed with APDC are soluble in a number of ketones such as methyl isobutyl ketone which is a recommended solvent for use in atomic absorption and allows a concentration factor of ten times. The experiment described illustrates the use of APDC as a general extracting reagent for heavy metal ions. 

The most widely applied reagents have been chelating agents which will complex with many metals, e.g. dithizone and the various thiocarbamate derivatives such as diethyldithiocarbamate and pyrrolidine dithiocarbamate. The latter agent as the ammonium salt (APDC) has been shown to complex some thirty elements [19] most of which can be readily extracted into various solvents. 4-Methylpentane-2-one (methyl isobutyl ketone or MIBK) is usually the favoured solvent because of its excellent compatibility with flames. The solubility of MIBK in water is not negligible and this limits the available concentration factor to ten higher molecular weight ketones (e.g. decan-2-one) offer better concentration factors and chloroform up to fifty times, but this latter solvent is only really suitable for electrothermal atomisation. 

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