Dithiocarbamate absorbances

Chloroacetone, phenacylbromide, a-bromoisobutyrophenone, 3-bromo-3-methyl-2-butanone, 1 -alkylsulfonyl-3-bromo-2-propanone, and ethyl-y-chloroacetoacetate give with ammonium dithiocarbamate the corresponding 4-hydroxythiazolidine-2-thiones (177), which have a characteristic absorption between 273 and 279 nm. Dehydration by heating with dilute HCl can be followed by ultraviolet spectroscopy because the products formed (175) absorb at 315 to 340 nm. 

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. 

Various spectroscopic methods have been used to probe the nature of the copper centers in the members of the blue copper oxidase family of proteins (e.g. see ref. 13). Prior to the X-ray determination of the structure of ascorbate oxidase in 1989, similarities in the EPR and UV-vis absorption spectra for the blue multi-copper oxidases including laccase and ceruloplasmin had been observed [14] and a number of general conclusions made for the copper centers in ceruloplasmin as shown in Table 1 [13,15]. It was known that six copper atoms were nondialyzable and not available to chelation directly by dithiocarbamate and these coppers were assumed to be tightly bound and/or buried in the protein. Two of the coppers have absorbance maxima around 610 nm and these were interpreted as blue type I coppers with cysteine and histidine ligands, and responsible for the pronounced color of the protein. However, they are not equivalent and one of them, thought to be involved in enzymatic activity, is reduced and reoxidized at a faster rate than the second (e.g. see ref. 16). There was general concurrence that there are two type HI... 

In order to characterize the adsorption species on mineral surface, DDTC is oxidized into the dimmer by adding definite H2O2 into the DDTC solution, which then is extracted by cyclohexane to determine its UV spectrum. As seen from the UV spectrum in Fig. 4.33, there are three UV absorbance peaks at 230 nm, 261 nm, 280 nm respectively. The maximum absorbance peak is at 230 nm, the next peak is at 260 nm, and the weak peak is at 280 nm. The peak at 230 nm can serve as a characteristic absorbance peak, and the peak at 260nm results from absorbance overlapping of diethyl dithiocarbamate and its dimmer. 

Polar functional groups of the additives are adsorbed on metal surfaces and this provides a barrier to prevent corrosive materials from contacting the metallic surfaces. Zinc dithiophosphates, dithiocarbamates and benzotriazoles are commonly used to protect copper-lead bearings from the type of corrosion present at concentrations of 50 to 300 mg/kg of oil. Rust inhibitors derived from sulfonates and amines also form absorbed films on ferrous metal, which prevents corrosive material from reaching the metal surface. 

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. 

Although it is evident from the above studies that the dithiocarbamate uv stabilisers function primarily as peroxide decomposers and only to a minor extent at uv absorbers, it is not clear to what extent they act as triplet quenchers. In the case of NlOx, it is known that this is not a hydroperoxide decomposer (37) and this is confirmed in Figure 11 which shows that it does not inhibit thermal oxidation to carbonyl and unlike NiDBC, its main effect in uv degradation is to retard the photo-oxidation process. In order to study the behaviour of these complexes in photo-... 

Dithiocarbamates are absorbed from the gastrointestinal tract, lungs, and skin. The absorption of ethyl-enebisdithiocarbamates from the gastrointestinal tract may be altered by the presence of cations occurring naturally in food. 

Typical examples of the stabilizers generally used to prevent the above chain reaction are (a) UV absorbers — 2(2-hydroxy-3-tert-butyl-5-methylpheny l)-5-c hi or ob en zo tr ia zo le and 2-h yd ro xy-4-octoxybenzophenone (b) Antioxidants — 3,5-di-tert-butyl-4-hydroxy-toluene and octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propa-noate (c) Peroxide decomposers — dilauryl thiodipropionate. In addition quenchers such as the organic nickel complex, Ni(II) bis-(diisopropyl dithiocarbamate) are used for the deactivation of the excited states of the chromophoric groups responsible for light initiation. 

Maneb or mancozeb. Like with many other dithiocarbamate pesticides, the most commonly used methods of detecting maneb or mancozeb involve degrading the active ingredient in the pesticide to carbon disulfide, CS2. The CS2 is then detected by spectrophotometry of a colored complex (Keppel et al. 1971) or by gas chromatography of the gas either in the headspace (McCleod and McCully 1969) or absorbed in a solvent layer (Headley 1996). The CS2 evolution method is the AO AC method used widely to identify amounts of dithiocarbamates in pesticide formulations (HSDB 1999). 

Rao et al. (1993) present a modification of the usual CS2 evolution method (which measures CS2 by spectrophotometry) with a method that converts maneb to a manganese-PAN complex that is extracted in isobutyl methyl ketone (MIBK) the complex then absorbs at 550 nm and can be measured from 0.37 to 3.75 micrograms/mL. Their method determines micro-quantities of maneb in commercial formulations, synthetic mixtures, grain, and in the presence of various other dithiocarbamates. The authors note that this method is particularly selective since other pesticides like ziram, zineb, and ferbam which usually interfere in other methods did not interfere under their experimental conditions. 

---