Salt complexes, dithiocarbamate solubility

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). 

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. 

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... 

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. 

In other work, a new high-yield synthesis of the known alkoxide complexes, [NbCl(OR)2(S2CNR2)2], has been reported from [NbCl3(OR)2] and 4 equiv of dithiocarbamate salt in THF. All are soluble in polar solvents, but insoluble in alkanes (721). 

In the final variation of the METSCAN instrument, the use of the water soluble, complexing agent, zinc bis(2-hydroxyethyl)dithiocarbamate Zn(hedtc)2, is used as an alternative to salts of diethyldithiocarbamate or p3Trolidinedithiocarbamate. Zn(hedtc)2 has a low stability constant relative to other metals of interest and participates in exchange reactions with many divalent and trivalent metal ions (equa-... 

---