Ammonium thiocarbamate

From a kinetic study [1281] of the reaction NH2COSNH4 = 2 NH3 + COS the specific rate expression 2k 

Metal salts of carboxylic acids obviously possess some organic character, but decompositions of these substances can be considered in the present context. Many metal carboxylates decompose at a reactant—product interface and their nucleation and growth processes are similar to the behav- 

The products of decomposition of metal carboxylates vary to some extent with the constituent cation and the final residue is usually either the metal or an oxide, occasionally the carbide and sometimes some elemental carbon deposit. Dollimore et al. [94] have described the use of Ellingham diagrams for the prediction of the composition of the solid products of oxalate decompositions. The complete characterization of residual material can be difficult, however, since the solids may be finely divided, pyrophoric [1010], metallic and amorphous to X-rays. 

Changes in the composition of gaseous products as reaction proceeds may make definition of the fractional decomposition, a, difficult. For example, product CO and residual carbon may be capable of reducing a metallic oxide, particularly at high a and the catalytic properties of an accumulating solid product may result in promotion of secondary gas reactions. 

Kinetic studies of the decomposition of metal formates have occasionally been undertaken in conjunction with investigations of the mechanisms of the heterogeneous decomposition of formic acid on the metal concerned. These comparative measurements have been expected to give information concerning the role of surface formate [522] (dissociatively adsorbed formic acid) in reactions of both types. Great care is required, 

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The reaction is carried out at low temperature in aqueous medium and then allowed to stand overnight (221). Ammonium thiocarbamate is prepared from a cold saturated solution of ammonium thiocyanate, which is gradually added to dilute sulfuric acid at 25°C. The liberated carbonyl sulfide is passed into a saturated solution of alcoholic ammonia at about 10°C (221). The fairly low yield indicates that the reaction has not been greatly developed. 

Thus the condensation of dichloroether or chloroacetone fails to give the parent compound, 2-hydroxythiazole (158a), Rj = R2 = R3 = H (221). However, 2-hydroxythiazole can be obtained in 12% yield from chloro-acetaldehyde (386). The condensation of ammonium thiocarbamate with cf-chloroketones gives the corresponding 2-hydroxy derivatives in 25 to 70% yields (76, 221, 304, 412) (Table 11-24). These compounds condensed with ClP(S)(OEt)2 give the corresponding 2-thiazolyl-thiophosphates (791). 

Carbonyl sulphide may also be obtained by the action of hydrochloric acid on commercial ammonium thiocarbamate, according to the equation ... 

This method, initiated by Marchesini in 1893 (i893G(24)65) (Scheme 177), consists of the condensation of an a-halocarbonyl compound with ammonium thiocarbamate (244 R2 = NH4) or its esters (244 R2 = alkyl). The reaction is carried out at low temperature in aqueous medium and then allowed to stand overnight. 2-Hydroxythiazoles (244 R2 = H) give 2-chlorothiazole derivatives almost quantitatively upon treatment with phosphorus oxychloride. This constitutes a convenient synthetic method for these compounds when the conversion of 2-amino- into 2-chloro-thiazole fails. 

This technique, originated by Marchesini [39,40], in 1893 involves the condensation of a a-halocarbonyl compound with ammonium thiocarbamate to give 2-hydroxythiazole derivatives. 

Salt formation with Brmnsted and Lewis acids and exhaustive alkylation to form quaternary ammonium cations are part of the rich derivati2ation chemistry of these amines. Carbamates and thiocarbamates are formed with CO2 and CS2, respectively the former precipitate from neat amine as carbamate salts but are highly water soluble. 

Tseng et al. [69] determined 60cobalt in seawater by successive extractions with tris(pyrrolidine dithiocarbamate) bismuth (III) and ammonium pyrrolidine dithiocarbamate and back-extraction with bismuth (III). Filtered seawater adjusted to pH 1.0-1.5 was extracted with chloroform and 0.01 M tris(pyrrolidine dithiocarbamate) bismuth (III) to remove certain metallic contaminants. The aqueous residue was adjusted to pH 4.5 and re-extracted with chloroform and 2% ammonium pyrrolidine thiocarbamate, to remove cobalt. Back-extraction with bismuth (III) solution removed further trace elements. The organic phase was dried under infrared and counted in a ger-manium/lithium detector coupled to a 4096 channel pulse height analyser. Indicated recovery was 96%, and the analysis time excluding counting was 50-min per sample. 

Food Wet oxidation with sulfuric acid, complexation with ammonium tetramethylenedi-thiocarbamate followed by extraction with methyl butyl ketone AAS 20 pg/kg No data lARC 1986 (Method 17)... 

The reaction of sucrose 2,3-manno-epoxide with potassium thioacetate and ammonium chloride in aqueous ethanol gave the expected 3-5>-acetyl-3-thio-altropyranoside (101). Treatment of 6,6,-dibromo-6,6,-dideoxysucrose hexaacetate with potassium thioacetate and A/, Ak dimethyl thiocarbamate gave the corresponding derivatives of 6,6,-dithiosucrose. The air oxidation of 6,6,-dithiolsucrose gave the bridged 6,6,-episulfide. A detailed conformational study of sucrose 6,6,-dithiol and sucrose 6,6 -episulfide revealed that they are similar but distinguishable (102). 

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. 

The preparation of alkali and ammonium salts of iV-substituted thiocarbamic acids is usually effected by addition of primary or secondary amines to carbonyl sulfide of carbon disulfide in the presence of ammonia or an alkali hydroxide. Using a strongly basic amine in place of the inorganic base affords the amine salt of the thiocarbamic acid 766,767... 

However, free dithiocarbamic acid, NHz-CS-SH, can be made and isolated by acidifying the ammonium salt in the cold, whereas free carbamic acid, NHa-CO-OH, does not exist. Although thiocarbamic acid is not very stable, its ammonium salt is somewhat more stable and can be synthesized in high yields at atmospheric pressure. When ammonia is passed into a cold solution of CS2 in a solvent in which the ammonium dithiocarbamate... 

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