Thiourea, properties

The preparation and spectroscopic properties (infrared, ultraviolet, NMR) of iV-alkoxycarbonyl-N -(2-thiazolyl)thioureas (268) have been studied by the Nagano group (78, 264). These compounds react with bromine in acetic acid or chloroform to give 2--alkoxycarbonylimino-thiazolo[3,2-h]thiadiazolines (Scheme 162), whose structures were established by mass spectroscopy, infrared, NMR, and reactivity patterns (481). 

In 1877, Maly (45) discussing formula 34 applied to thiohydantoine found it unable to explain the basic properties of the compound. He preferred a structure in which the -CH2-CO- group would be bonded to only one nitrogen atom. Meyer (46) prepared a monophenyl thiohydantoin (m.p. 178°C) by condensing diloroacetanilide with thiourea and proposed 42 for its structure. 

Physical Properties. Ammonium thiocyanate [1762-95-4] NH SCN, is a hygroscopic crystalline soHd which deHquesces at high humidities (375,376). It melts at 149°C with partial isomerization to thiourea. It is soluble in water to the extent of 65 wt % at 25°C and 77 wt % at 60°C. It is also soluble to 35 wt % in methanol and 20 wt % in ethanol at 25°C. It is highly soluble in Hquid ammonia and Hquid sulfur dioxide, and moderately soluble in acetonitrile. 

Chemical Properties. Ammonium thiocyanate rearranges upon heating to an equiHbrium mixture with thiourea 30.3 wt % thiourea at 150°C, 25.3 wt % thiourea at 180°C (373,375). At 190—200°C, dry ammonium thiocyanate decomposes to hydrogen sulfide, ammonia, and carbon disulfide, leaving guanidine thiocyanate [56960-89-5] as a residue. Aqueous solutions of ammonium thiocyanate are weakly acidic a 5 wt % solution has a pH of 4—6. 

Tellurium pseudohaUdes, such as the dicyanide [14453-24-8] Te(CN)2, the dithiocyanate [83543-04-8] Te(SCN)2, and thiourea complexes with Te(SCN)2, have been prepared. These are similar to the haUdes in properties. 

Although the first all-sulfur macrocycles were prepared many years ago " the first systematic study of such compounds was initiated by Busch and his coworkers , who were interested in the cation binding properties of such ligands. A sequential synthesis was utilized to produce 1,4,8,11-tetrathiacyclotetradecane [tetrathia-14-crown-4 (70)] . In the first step, 1,3-propanedithiol is metallated using sodium and alkylated with 2-chloroethanol. The diol was then treated with thiourea to form the dimercapto-dithioether compound 9. The latter was once again metallated with sodium and allowed to react with 1,3-dibromopropane. The yield of 70 in the ring closure step, conducted at high dilution in absolute ethanol, was 7.5% after recrystallization. The entire sequence is illustrated in Eq. (6.8) . ... 

Properties—Colourless, ihombic prisms (fiom dilute aqueous solution), long silky needles (fiom concentrated solution. ) m. ]i. 172. Very slightly soluble in cold water (i part of thiourea dissolves in about ii parts of water at the ordinary tempei-ature). 

Coatings of tin produced from tin-containing aqueous solutions by chemical replacement may be used to provide special surface properties such as appearance or low friction, but protect from corrosion only in non-aggressive environments. Copper and brass may be tinned in alkaline cyanide solutions or in acid solutions containing organic addition agents such as thiourea. Steel may be first coated with copper and then treated... 

Beneficial Micro Reactor Properties for Desymmetrization of Thioureas... 

The first competitive TRPVl antagonist is capsazepine (3), a conforma-tionally constrained (9-demethyl thiourea analogue of capsaicin that emerged from a programme aimed at the optimization of the agonistic properties of capsaicinoids [66]. The second competitive antagonist to be... 

The earliest NLO studies involving metal pyridyl complexes were reported by Frazier et al. in 1986 who investigated the SHG properties of various group 6 metal pyridyl carbonyls.63 Although most of the complexes tested show little or no activity, (6) and (7) have respective SHG efficiencies of 0.2 and 1.0 times ADP using a 1,064 nm laser.63 Shortly after, Calabrese and Tam reported SHG from the Re1 complex (8).64 Subsequent studies by Eaton and Tam et al.65,66 describe the preparation of inclusion compounds of various metal complexes with thiourea or tris-ort/ o-thymotide. Unfortunately, none of the complexes [W(CO)5L] (L = pyridine, py, or a 4-substituted py) produce SHG-active materials.65,66... 

F. Sansone, E. Chierici, A. Casnati, and R. Ungaro, Thiourea-linked upper rim calix[4]arene neoglycoconjugates Synthesis, conformations and binding properties, Org. Biomol. Chem., 1 (2003) 1802-1809. 

The W types require additional acceleration and ethylene thiourea (ETU), gives the best balance of all properties. However, the use of this accelerator is increasingly being restricted due to fears of its effects on pregnant women, and more recently men. DETU, thiurams and guanidines can also be used. Sulphur is sometimes used to increase the degree of cure in the W types, but this detracts from the ageing performance of the vulcanisate. 

The conformational properties of mono-substituted cyclohexanes, C V, 1111X, in their thiourea inclusion compounds have been studied102. Variable-temperature MAS spectra demonstrate that a chair-chair ring inversion process occurs in the thiourea tunnel, in which the axial and equatorial conformers are interconverted. Predominance of the equatorial conformer is found when X = NH2. 

An important property of the S-nitroso thiourea derivatives is the ability to effect electrophilic nitrosation of any of the conventional nucleophilic centres. This is manifest kinet-ically by the catalysis of nitrous acid nitrosation effected by added thiourea (equation 29). The situation is completely analogous to the catalysis of the same reactions by added halide ion or thiocyanate ion. The catalytic efficiency of thiourea depends on both the equilibrium constant Xxno for the formation of the intermediate and also its rate constant k with typically a secondary amine65. Since Xxno is known (5000 dm6 mol-2), it is easy to obtain... 

A change in ionic adsorption in the presence of organic molecules was also observed by Parsons and Zobel. They found that in the presence of acetanilide in the inner layer, the surface concentration of specifically adsorbed phosphate ions decreases. In another work it was suggested that specific adsorption of nitrate ions is markedly reduced in the presence of thiourea in the solution. Thiourea alters the properties of the mercury electrode, affecting even the adsorption of iodides. ... 

Gritti, F. and Guiochon, G, Influence of the pressure on the properties of chromatographic columns, iii. Retention volume of thiourea, hold-up volume, and compressibility of the C-18-bonded layer, J. Chromatogr. A, 1075, 117, 2005. 

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