Cyanates and Thiocyanates

Low detection limits (low ng/mL) have been achieved using a headspace/gas chromatographic (GC) technique (Seto et al. 1993). The sample is acidified and incubated, and the headspace analyzed by GC with a nitrogen-specific detector (NPD) (Carseal et al. 1993 Levin et al. 1990 Seto et al. 1993). Reported recovery is good (>90%) (Carseal et al. 1993), and precision is good as well (<15% RSD) (Carseal et al. 1993 Levin et al. 1990 Seto et al. 1993). Blood samples may be treated with chloramine T priorto incubation to produce a derivative which can be determined by GC with electron capture detection (ECD). Cyanate and thiocyanate do not interfere in this method (Odoul et al. 1994). The detection limit is 5 pg/L (ppb) precision is good (<15% RSD) (Odoul et al. 1994). 

The pseudohalides and related compounds have been investigated by a number of workers. Thallium(I) cyanate and thiocyanate are both known, and the latter has been shown to be ionic in the solid state 288 differing values have been reported for the stability constants in the T1/NCS system in aqueous or mixed water/non-aqueous systems, but the overall evidence is that the complexes are extremely weak.289 The ionic selenocyanate has been reported, but the chemistry has not been investigated.1... 

Cyanates and Thiocyanates.—Three reasonable structures can be written for hydrogen cyanate ... 

Syntheses of cyanate and thiocyanate in the coordination sphere of a metal 237... 

Diaryl tellurium iodide cyanates and thiocyanates have been prepared. They arc colored, crystalline solids with sharp melting points, soluble in organic solvents and stable at 20 ... 

With evolution of COj or COS, respectively, cyanate and thiocyanate anions react with HFA to form an ionic hexafluoropropaneimine 113, whose crystal structure shows the anion to be dimeric in the solid state (237). 

A striking difference to the reactions with cyanate and thiocyanate [Eq. (95)] has been found with potassium selenocyanate. Elemental selenium is precipitated and cyanide ion is the reactive species in accordance with Eq. (86) (237). 

An important area of inorganic carbon chemistry is that of compounds with C—N bonds. The most important species are the cyanide, cyanate, and thiocyanate ions and their derivatives. We can regard many of these compounds as being pseudohalogens or pseudohalides, but the analogies, although reasonably apt for cyanogen, (CN)2, are not especially valid in other cases. 

Dielectrophilic species are 1,4-diketones, certain 1,3-dienes, a,B-unsaturated isocyanates, isothiocyanates, cyanates, and thiocyanates bearing electron-withdrawing (e.g., polyfluorinated and perfluorinated) substituents the most frequently used 1,1-dinucleophiles are water, potassium sulfide, primary amines, and ammonia. From this repertoire of building blocks many combinations are possible. Tetrakis(trifluoro-methyl)furans, thiophenes, and pyrroles have been synthesized from per-fluoro-3,4-dimethylhexa-2,4-diene on addition of water, potassium sulfide, or aniline (90CC1127) (Scheme 39). 

Details of interatomic distances and bond angles within the ions and in their hydracids are given in Table I. Similar parameters will be given for complexes of these ions in Section IV. Iqbal 398) has collated data on the lattice parameters of the ionic cyanates and thiocyanates. The ions are linear, although in many cases this is not confirmed by direct measurement but is assumed for the purposes of the subsequent calculation. Increasingly, thiocyanates of Group I and II metals are... 

Infrared spectra of a number of single crystals of cyanates and thiocyanates have been recorded and correlations made with the crystal structure. However, these results are not listed here since they have been reviewed recently by Iqbal 398). 

The NMRs of aqueous solutions of potassium cyanate and thiocyanate are — 1.1 and —5.7 ppm (relative to benzene) 504) and comparison of these data with those from related compounds suggests that the ions have a small or zero formal charge on the carbon, in general agreement with the results. 

Decomposition of sulphur dicyanide in aqueous solution is a general-base catalysed reaction , leading to formation of cyanate and thiocyanate. Catalytic coefficients have been estimated for acetate and hydroxide ions. With thiocyanate ion, side reactions also occur these are responsible for some apparent dependence of rate coefficients on sulphur dicyanide concentrations previously found. At 20 °C, /c(OH ) = 5.8 x 10 l.mole- sec" and it(CH3COO") = 7.7 X 10 1.mole sec ... 

No simple reactions between CO2 or CS2 and group IVB hydrides have been reported. On the other hand, a vast literature exists on insertion of CO2 and CS2 into N-H bonds. The reactions of NH3 with CO2 and CS2, to form ammonium carbamate and dithiocarbamate, respectively, are of commercial importance in the synthesis of urea, cyanates, and thiocyanates but are properly considered in the realm of organic chemistry. Secondary phosphines react with CS2 in the presence of a base ... 

In this chapter we deal first with compounds formed by metals containing the isoelectronic groups CN , Cl, and CO. (HCN and non-metal cyanides, and also cyanates and thiocyanates are included in Chapter 21.) We then describe briefly compounds of metals with hydrocarbon radicals or molecules other than olefine compounds of Pd and Pt (Chapter 27) and certain compounds of Cu and Ag (Chapter 25). 

All the crystalline metal fulminates and the heavy metal azides explode and detonate on the application of thermal shock and in some cases in the presence of an electric field, while the heavy metal cyanates and thiocyanates only deflagrate at high temperatures. According to Bowden and Williams (83) the stability to thermal shock increases in the order fulminate heavy metal salts are more thermally unstable. During the last decade Yoffe and co-workers have tried to explain the thermal and photochemical behaviour of these meterials in terms of their electronic structure. This work has been extensively reviewed by Yoffe (2) and will not be considered here. We will however explore briefly a few ideas which qualitatively correlate the geometry of the electronic and atomic configurations with the kinetic stability of these materials. 

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