A-Thiocyanations

Sinapine, CjgHjjOgN, was isolated as a thiocyanate from black mustard seeds (Brassica nigra) by Henry and Garot." Will and Laubenheimer first noted that sinapine occurs in white mustard seed in the form of the alkaloidal glucoside sinalbine, CajH jOuNgSg, which, on hydrolysis by the enzyme myrosin, also present in the seed, furnished dextrose, p-hydroxybenzylthiocarbimide and sinapine sulphate. Owing to its instability sinapine is unknown in the free state. The thiocyanate can be recrystallised from water and converted into the acid sulphate by treatment with sulphuric acid. 

A. Thiocyanate method Discussion. Iron(III) reacts with thiocyanate to give a series of intensely red-coloured compounds, which remain in true solution iron(II) does not react. Depending upon the thiocyanate concentration, a series of complexes can be obtained these complexes are red and can be formulated... 

NH,C1 + 8TiCl4 + 4H20 The excess Ti trichloride is then back-titrated with a std ferric ammsulfate so In to a thiocyanate end-point. A blank is run concurrently on the Ti trichloride soln. The % AP in the sample is calcd by the formula ... 

A corrosion inhibitor that is the adduct of a carbonyl compound, an amine, and a thiocyanate has been described [1431]. The product provides protection against ferrous corrosion in severe environments. 500 ppm by weight is sufficient. The inhibitor is employed in wells producing both oil and water and in high-temperature environments around 120° C. 

An azide group can be transformed into a thiocyanate group by reduction with LiAlH4 followed by treatment with NJSl -thiocarbonyldiimidazole.[ 14]... 

Using a triazole-/pyrimidine-containing hybrid ligand, terminally coordinated in a thiocyanate-bridged copper(II) dimer, Haasnoot et al. reported250 the structure of the f3 isomer of complex (288), revealing that the Cu-SCN distance is relatively short compared to other Cu-SCN... 

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... 

Unisulf [Unocal sulfur removal] A process for removing sulfur compounds from petroleum fractions, similar to the Stretford process, but including in the catalytic solution vanadium, a thiocyanate, a carboxylate (usually citrate), and an aromatic sulfonate complexing agent. Developed by the Union Oil Company of California in 1979, commercialized in 1985, and operated in three commercial plants in 1989. 

Katayama Y, Narahara Y, Inoue Y, et al. 1992. A thiocyanate hydrolase of Thiobacillus thioparus. A novel enzyme catalyzing the formation of carbonyl sulfide from thiocyanate. J Biol Chem 267(13) 9170-9175. 

Second, in comparing either the behavior of [65] vs. [67], or that of [66] vs. [68], one sees that the rate of intramolecular displacement of CN- from —SCN by —S02 is about 30 times faster than the rate of intramolecular displacement of SO, from —SSOj by —SOj. This is striking because it contradicts the belief sometimes expressed in the literature, but not apparently founded on any real experimental data, that Bunte salts are considerably more reactive as sulfenylating agents than thiocyanates. The data in (178)—(181) clearly indicate that a thiocyanate can be more reactive than a Bunte salt as a sulfenylating agent. 

A) Thiocyanate inhibits the binding of iodide to thyroid hormone receptors. 

The three-carbon component in this subgroup is either a /3-dicarbonyl compound or a /3-keto nitrile. The N and C-N components in the reactions with /3-dicarbonyl compounds come from formamide, a nitrile, a thiocyanate, or a cyanamide <1994HC(52)1>. 

Four minor metabolites, psammaplins B-D (503-505) and presammaplin A (506) were isolated from Psammaplysilla purpurea, in addition to psammaplin A (500). Psammaplin B (503) is a thiocyanate bromotyrosine derivative, while psammaplin C (502) is a sulfanamide. Psammaplin D (505) displayed antimicrobial activity and mild tyrosine kinase inhibition [429]. The psammaplins Ai (507) and A2 (508) and aplysinellins A (509) and B (510) were isolated from Aplysinella rhax from both Pohnpei and Palau. These compounds inhibit famesyl protein transferase and leucine aminopeptidase [430]. Another sample of A. rhax from the Great Barrier Reef, Australia contained psammaplin A 11 -sulfate (511) and bisaprasin ll -sulfate (512), both of which inhibited [3H]-l,3-dipropyl-8-cyclopentylxanthine binding to rat brain adenosine Ai receptors [431]. 

Other reactions readily available for the detection of a thiosulphate include reduction to hydrogen sulphide by most reducing agents, for instance by zinc and hydrochloric acid, oxidation to sulphuric add or a sulphate, and formation of a thiocyanate on warming with an alkaline solution of a cyanide 5... 

An important method of preparing carbonyl sulphide consists in the decomposition of a thiocyanate with moderately concentrated (14-/V) sulphuric acid, the liberated thiocyanic acid being hydrolysed thus ... 

The Detection and Estimation of Thiocyanates.—A thiocyanate may be detected by its behaviour with sulphuric acid (p. 281) and by the blood-red colour produced with ferric chloride, which colour is dis-... 

By the interaction of a thiocyanate and selenious acid in the presence of hydrochloric acid, thiocyanoselenious acid is formed ... 

Thiocyanate salts. The earliest publication describing additii m of a thiocyanate aalt to an epoxide appeared in 1046 from the Culvenor laboratory.3 7 Since then a number of papers have dealt will Ihr useful reaction, which may be utilized to transform ethylene oxides into ethylene sulfides conveniently in a single operation. It is general h agreed117- 1177 that the course of events may be depicted as slu>wn in Eq. (673) for the general case. 

Crystal structure data are available for Ag(tu)2Cl,343 Ag(tu)3C104344 and Ag(tu)2SCN.345 In the latter compound the Ag atoms were coordinated by two thiourea S atoms (Ag—S = 248.2 and 246.2 pm) and one S of a thiocyanate ligand (Ag—S = 260.8 pm). The three S atoms formed an almost planar arrangement with the central Ag atom. A fourth sulfur atom was much more weakly bound (Ag—S = 311.1 pm) and completed a highly distorted tetrahedron. In addition, it acted as a bridge to the second half of the centrosymmetric dimer (43). 

The presence of a thiocyanate group can be very easily deduced from the IR spectrum, which contains a sharp, but weaker in intensity, IR band around 2150 cm-1 and an NMR carbon resonance between 112 and 115 ppm. In the case of psamaplin B (172), C-NMR additivity effects applied to the methylene carbon linked to the thiocyanate were used to distinguish between a thio- and isothiocyanate group [142]. Chemical proof can be provided by LAH reduction of the thiocyanate, which gives a thiol rather than a methylamine group as the reaction product of the reduction of the isothiocyanate [195]. 

The classical, Fischer7 synthesis of sugar isothiocyanates involves treatment of an acylated glycosyl halide with an inorganic thiocyanate in a polar solvent. Depending on the reactivity of the halide and the reaction conditions, either a thiocyanate or an isothiocyanate is formed directly. 

Grayson and Whitham have found the regiochemistry of addition of ISCN (from LiSCN and I2) to vinyl silanes to be consistent with the intermediacy of an iodonium ion which is particularly stabilized at one of the carbons due to the -silicon effect.129 The products were a thiocyanate in one case and an isothiocyanate in the other (Scheme 65).129... 

The purity of the crystallized product, determined volu-metrically by Volhard s method, exceeds 98%. In this procedure, 10 ml. of a 1% solution of methylisourea hydrochloride is acidified with a few drops of nitric acid and treated with 20 ml. of 0.1 N silver nitrate. After removal of the silver chloride by filtration, the excess of the silver nitrate is estimated with 0.1 A thiocyanate solution, using ferric alum as indicator. Alternatively, 10-ml. portions of 0.1 N silver nitrate, acidified with nitric acid, may be titrated directly with the 1% methylisourea hydrochloride solution in the presence of tartrazine. 

Film also takes longer to fix at low temperatures. When temperatures drop below 65F/18C fixing time will need to be extended. Observe how long the milkiness takes to disappear from the surface of the film and multiply that time by three. Below freezing a thiocyanate fixer should be used (Formulas Fixers Defender 9-F RapidThiocyanate Fixer). 

Figure 4. Schematic representation of the medium effect on the reaction of methyl iodide with (a) thiocyanate ion and (b) p-nitrophenoxide ion.

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