Iron dithiocarbamates

The alternative approach is to add a photodegradant which is an ultraviolet light absorber. However, instead of dissipating the absorbed energy as heat (as with conventional ultraviolet absorbers) the aim is to generate highly reactive chemical intermediates which degrade the polymer. One such material is iron dithiocarbamate. 

Trivalent iron dithiocarbamate complexes have been extensively studied, because of the existence of "spin equilibria in these complexes. Table II outlines the tris(l,l-dithiocarbamate) iron(III) complexes and, some of their physical properties. 

Increase the oxidation rate of polymers, e.g. metal ions which increase the hydroperoxide decomposition rate. Photodegradation and thermal degradation are enhanced by transition metal ion containing pro-oxidants, such as iron dithiocarbamate (as opposed to nickel dithiocarba-mate, which acts as a photo-antioxidant). 

It is widely assumed that NO is responsible for the pharmacological effects of nitroglycerin, which has been used to treat angina since 1879. However, this has been challenged by Kleschoyov et al. who, using a colloidal iron-dithiocarbamate preparation to trap the radical in vascular segments, showed that the ability of the compound to induce vasorelaxation is not related to its ability to donate NO.289... 

Dithiocarbamates are normally prepared as alkali metal salts by the action of primary or secondary amines on CS2 in the presence of, say, NaOH. The zinc, manganese, and iron dithiocarbamates are extensively used as agricultural fungicides, and zinc salts as accelerators in the vulcanization of rubber. Alkali metal dithiocarbamates are usually hydrated and are dissociated in aqueous solution. When anhydrous, they are soluble in organic solvents in which they are associated. 

AO-21 AO-22 AO-23 AO-24 Robec Z bud Iron dithiocarbamate Nickel dithiophosphate Nickel xanthate... 

Manganese, zinc and iron dithiocarbamates, whether they are 1 1 or 2 1 complexes, react with copper-containing complex compounds, thus with proteins,... 

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 key reaction in the time-control step is quantised photolysis or thermal oxidation of the antioxidant system under environmental conditions. Parallel antioxidant and prooxidant reactions occur when the iron dithiocarbamates are exposed to light between 290 and 350 nm. 

Scheme 5.4 Iron dithiocarbamate (FeDRC) antioxidant-prooxidant inversion in a polyolefin (P represents a polyolefin chain)...

Data adapted with permission from Vanin A et al. (2000) Redox properties of iron-dithiocarbamates and their nitrosyl derivatives Implications for their use as traps of nitric oxide in biological systems. Biochimica Biophysica Acta 1474 365-377. 

Phosphites can react with ROOH to give alcohols and phosphates, avoiding the decomposition of the hydroperoxide to free radicals. They include the tristearyl, diphenyl or tri-isodecyl phosphite, and di-isodecyl pentaerythritol diphosphite. Besides phosphites, sulphur compounds can be used, such as thioesters, thioethers, thiodipropionates (including the dilauryl and distearyl thiodipropionates) and the metal dithiolates, e.g., iron dithiocarbamate. 

Fig. 5. Time-controlled photodegradation of LDPE stabilized with different concentrations of the photosensitize iron dithiocarbamate (FeDRC) and the photostabilizer nickel dithiocarbamate (NiDRC). Numbers on curves are antioxidant concentration in 10- mol/100g(156).

Iron dithiocarbamate Nickel dithiophosphate Nickel xanthate... 

In this analysis of the nmr data we have that the results for a variety of solvents and over a wide temperature range may be interpreted as arising from small changes in the crystal field environment of the iron atom due to two solvent interactions - a term which is an intrinsic property of the solvent and a second term arising from a solute-solvent interaction. Although the application of the model has been simplified the results nevertheless give an insight into the effect of the solvent on the nmr shifts of these iron dithiocarbamate complexes. 

Figure 9.3 Comparison of the controlled degradation of LORE sensitized with an iron dithiocarbamate with the stabilizing behaviour of a nickel dithiocarbamate. (Numbers on curves are additive concentration in mol/100 g x 10". ) (From S Al-Malaika, A. Marogi and G. Scott, J. App. Polym. Sci., 31,685 (1986), with permission.)...

Scheme 9.1 Mechanism of the photoinversion of the iron dithiocarbamates to photoactive iron carboxylates.

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