Thiocyanate conversion

In general, thiocyanate salts are used for the epoxide-thiirane conversions. The reaction proceeds by nucleophilic attack on the epoxide by thiocyanate ion followed by cyclization as shown for (121) (125). The formation of a... 

Replacement of iodine in (perfluoroalkyl)ethyl iodides predominates over the usual conversion to olefins when the reagent is very nucleophilic and weakly basic Soft nucleophiles like sodium thiocyanate and sodium thiolates react well in displacements [46, 47] (equation 42)... 

There is virtually no recent literature on quinoxaline cyanates or isocyanates, and most of what little there is on quinoxaline thiocyanates, isothiocyanates, or nitrones has been covered already the preparation of thiocyanatoquinoxalines from halogenoquinoxalines (Section 4.4.1) the conversion of the thiocyanatoquinoxalines into alkoxyquinoxalines (Section 4.4.1), into quinoxalinethiones (Section... 

It is well known that palladium on carbon catalysts are poisoned by hydrogen cyanide and thiol products or hydrogen sulfide (6). Therefore, it was of interest to investigate the reduction of perfluoroalkyl thiocyanates as a function of tin concentration, keeping the concentration of palladium and reaction conditions constant. Figure 15.1 delineates the % conversion vs. Sn/Pd ratio, under the same reaction conditions of 175°C, 700 psig H2 for 2 hours with 5% Pd on carbon catalysts in ethyl acetate solvent at a 1000 1 substrate catalyst molar ratio. The increase in... 

Cyanide and thiocyanate anions in aqueous solution can be determined as cyanogen bromide after reaction with bromine [686]. The thiocyanate anion can be quantitatively determined in the presence of cyanide by adding an excess of formaldehyde solution to the sample, which converts the cyanide ion to the unreactive cyanohydrin. The detection limits for the cyanide and thiocyanate anions were less than 0.01 ppm with an electron-capture detector. Iodine in acid solution reacts with acetone to form monoiodoacetone, which can be detected at high sensitivity with an electron-capture detector [687]. The reaction is specific for iodine, iodide being determined after oxidation with iodate. The nitrate anion can be determined in aqueous solution after conversion to nitrobenzene by reaction with benzene in the presence of sulfuric acid [688,689]. The detection limit for the nitrate anion was less than 0.1 ppm. The nitrite anion can be determined after oxidation to nitrate with potassium permanganate. Nitrite can be determined directly by alkylation with an alkaline solution of pentafluorobenzyl bromide [690]. The yield of derivative was about 80t.with a detection limit of 0.46 ng in 0.1 ml of aqueous sample. Pentafluorobenzyl p-toluenesulfonate has been used to derivatize carboxylate and phenolate anions and to simultaneously derivatize bromide, iodide, cyanide, thiocyanate, nitrite, nitrate and sulfide in a two-phase system using tetrapentylammonium cWoride as a phase transfer catalyst [691]. Detection limits wer Hi the ppm range. 

According to an O.S. amendment sheet, the procedure as described [1] is dangerous because the reaction mixture (dicyanodiamide and ammonium nitrate) is similar in composition to commercial blasting explosives. This probably also applies to similar earlier preparations [2]. An earlier procedure which involved heating ammonium thiocyanate, lead nitrate and ammonia demolished a 50 bar autoclave [3], TGA and DTA studies show that air is not involved in the thermal decomposition [4], Explosive properties of the nitrate are detailed [5], An improved process involves catalytic conversion at 90-200°C of a molten mixture of urea and ammonium nitrate to give 92% conversion (on urea) of guanidinium nitrate, recovered by crystallisation. Hazards of alternative processes are listed [6],... 

Compound 129, an intensely blue compound, was obtained by direct functionalization of DDTOMe 20b with LDA and chloro(chloromethyldimethylsilane) at one of the terminal positions followed by conversion of chloride to NCS using sodium thiocyanate in acetone (Scheme 12). The other isothiocyanates were prepared via Stille coupling of mono or dibrominated rigid cores with appropriate thienyl or phenyl stannanes followed by conversion of the chlorine atom of Si(CH3)2CH2Cl attached to a phenyl group into isothiocyanate occurred in rather low yield. 

A quite different use of a thiocyanate salt is the conversion of an epoxide (oxirane) to an episulfide (thiirane) this normally heterogeneous reaction is markedly accelerated by the use of silica gel coated with, or finely ground with, potassium thiocyanate, rather than with the thiocyanate salt alone.17... 

The conversion of functionalized arenes as represented by the general formula 97, into isothiazolium compounds (99) has been achieved by the sequence shown in Scheme 117.180 From a synthetic viewpoint, transformation of cyclopalladated products into thiocyanate derivatives is more efficiently achieved using monomeric dithiocarbamato complexes (98) rather than dimeric compounds. The generation of analogous dithiolylium perchlorates by a related procedure is described later (see Section IV,H). 

Oh, S.Y., S. Jalaludin, R.H. Davis, and A.H. Sykes. 1987. Detoxication of cyanide in the chicken by conversion to thiocyanate, as influenced by the availability of transferable sulphur. Comp. Biochem. Physiol. 86B 129-133. 

Plasma levels of cyanide in unexposed, healthy adults average 0 to 10.7 figHOO mL (mean, 4.8, g/100 mL) (Feldstein and Klendshoj 1954). Following mild exposures to cyanide, plasma levels return to this normal range within 4 to 8 h after cessation of exposure the half-life for the conversion of cyanide to thiocyanate from a nonlethal dose in humans was between 20 min and 1 h. 

The metabolism of cyanide has been studied in animals. The proposed metabolic pathways shown in Figure 2-3 are (1) the major pathway, conversion to thiocyanate by either rhodanese or 3-mercapto-pyruvate sulfur transferase (2) conversion to 2-aminothiazoline-4-carboxylic acid (Wood and Cooley 1956) (3) incorporation into a 1-carbon metabolic pool (Boxer and Richards 1952) or (4) combining with hydroxocobalamin to form cyanocobalamin (vitamin B12) (Ansell and Lewis 1970). Thiocyanate has been shown to account for 60-80% of an administered cyanide dose (Blakley and Coop 1949 Wood and Cooley 1956) while 2-aminothiazoline-4-carboxylic acid accounts for about 15% of the dose (Wood and Cooley 1956). The conversion of cyanide to thiocyanate was first demonstrated in 1894. Conversion of cyanide to thiocyanate is enhanced when cyanide poisoning is treated by intravenous administration of a sulfur donor (Smith 1996 Way 1984). The sulfur donor must have a sulfane sulfur, a sulfur bonded to another sulfur (e.g., sodium thiosulfate). During conversion by rhodanese, a sulfur atom is transferred from the donor to the enzyme, forming a persulfide intermediate. The persulfide sulfur is then transferred... 

The nervous system is the most sensitive target for cyanide toxicity, partly because of its high metabolic demands. High doses of cyanide can result in death via central nervous system effects, which can cause respiratory arrest. In humans, chronic low-level cyanide exposure through cassava consumption (and possibly through tobacco smoke inhalation) has been associated with tropical neuropathy, tobacco amblyopia, and Leber s hereditary optic atrophy. It has been suggested that defects in the metabolic conversion of cyanide to thiocyanate, as well as nutritional deficiencies of protein and vitamin B12 and other vitamins and minerals may play a role in the development of these disorders (Wilson 1965). 

Persons with a metabolic disturbance in the conversion of cyanide to thiocyanate may be at greater risk. A defect in the rhodanese system and vitamin B12 deficiency have been associated with tobacco amblyopia and Leber s hereditary optic atrophy in persons exposed to cyanide in tobacco smoke (Wilson 1983). 

Erythrocyte suspension Sample purged absorption of hydrogen cyanide in sodium hydroxide conversion of thiocyanate to cyanide by potassium permanganate oxidation Spectrophotometry (thiocyanate- cyanide determination) No data 93-97 McMillan and Svoboda 1982... 

Baskin S, Kirby S. 1990. Effect of sodium tetrathionate on cyanide conversion to thiocyanate by enzymatic and non-enzymatic mechanisms [Abstract], The Toxicologist 10 326. 

Himwich WA, Saunders JP. 1948. Enzymatic conversion of cyanide to thiocyanate. Am J Physiol... 

Maduh EU, Baskin SI. 1994. Protein kinase C modulation of rhodanese catalyzed conversion of cyanide to thiocyanate. Res Comm Mol Pathol Pharmacol 86(2) 155-173. 

Pettigrew AR, Fell GS. 1973. Microdiffusion method for estimation of cyanide in whole blood and its application to the study of conversion of cyanide to thiocyanate. Clin Chem 19 466-471. 

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