To thioureas

When the potassium cyanate used in the above preparation is replaced by potassium thiocyanate (or sulphocyanide), the ammonium thiocyanate formed undergoes partial rearrangement to thiourea (or sulpho-urea). Even above... 

The formation of a sulfur-containing ring was justified by the attack of the halogenated carbon of the cMoroacetyl derivative by the sulfur atom of thiourea, a fact in accordance with the results just discussed by Wallach (49,50) and Claus (51). The new formula (37) of thiohydantoine explained why, contrary to thiourea, its desulfuration was difficult. 

Other Accelerators. Amine isophthalate and thiazolidine thione, which are used as alternatives to thioureas for cross-linking polychloroprene (Neoprene) and other chlorine-containing polymers, are also used as accelerators. A few free amines are used as accelerators of sulfur vulcanization these have high molecular weight to minimize volatility and workplace exposure. Several amines and amine salts are used to speed up the dimercapto thiadiazole cure of chlorinated polyethylene and polyacrylates. Phosphonium salts are used as accelerators for the bisphenol cure of fluorocarbon mbbers. 

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. 

At approximately 160°C, some of the ammonium thiocyanate is converted to thiourea [62-56-6] H2NCSNH2, iulow yield. With alcohoHc ammonia, ammonium dithiocarbamate [513-74-6] forms ... 

The dihaloalkane (10 mmol) is added to thiourea (20 mmol) in EtOH (25 ml) over 10 min and then stirred under reflux for ca. 3 h. The EtOH is removed under reduced pressure and aqueous NaOH (20%, 30 ml), TEBA-CI (0. II g, 0.5 mmol), and the haloalkane (20 mmol) is added. The mixture is heated at 60°C for ca. 1.5 h and then cooled, filtered, and acidified to pH 2.0 with aqueous HC1 (6M) to yield the bis-sulphide. 

For organizational reasons, several catalytic systems possessing multiple hydrogen bond donating functionalities have been included in this section which may not be classified as BBAs. For example, the bistrifylamide Mikami catalyst could perhaps be classified as a double-hydrogen bond donor catalyst akin to thiourea catalysis. 

Ammonium thiocyanate is stable in air however, upon heating it isomer-izes to thiourea ... 

Amino-1,2,4-thiadiazoles liberate iodine, though not quantitatively, from potassium iodide in mineral acid solution.6 Hydrogen sulfide in acid solution degrades the parent compound completely to thiourea, sulfur, and ammonium chloride, but it is without effect on the acetyl derivative.8... 

As is well known, simple stoichiometry of a compound is not a good guide to the coordination number of the central atom. This is well shown in (BiCl3)3-7tu (tu = thiourea), where bismuth is octahedrally coordinated to thiourea via the sulfur atom.240 The structure was found to consist of bismuth cations and anions, [Bi2Cl4tu6]2+[BiCl5tu]2- (82). 

Dihydro-1,3-thiazine derivatives (208) and (210) are prepared by the addition of alkyl propiolates to thioureas and dithiocarbamic acids respectively. In the latter case it is necessary to cyclize the initial products (209) with acetic anhydride (Scheme 96) (70AJC51). Ring expansion of isothiazolium chlorides (211) by the action of potassium cyanide provides a route to imine derivatives (212 Scheme 97) (79TL1281). 

One of the most commonly used class of derivatization agents for diasteromer formation are isothiocyanates and isocyanates. Enantiomers of /3-blockers, amphetamine, epinephrine, methamphetamine, and mexiletine have been resolved after derivatization with these agents. Isothiocyanates produce thiourea derivatives upon reaction with primary and secondary amines. Thiourea derivatives also provide a strong UV absorbance for the detection of enantiomers lacking a strong UV chromophore. Isocyanates produce ureas when reacted with amines. The physical properties of these ureas are similar to thiourea derivatives. Isocyanates will also react with alcohols to yield carbamates. 

The simultaneous use of urea, or thiourea [76] and DABCO catalyst was introduced by the Connon group for the addition of methyl acrylate and benzaldehyde [39]. The study revealed that, although both ureas and thioureas accelerated the reaction relative to the uncatalyzed process, urea was superior to thiourea in terms of stability and efficiency. Chiral thiourea derivatives may offer, however, superior enantioselectivity. It was postulated, that the catalysts operate mainly via a Zimmerman-Traxler-type transition state 69 for addition of the resulting enolate anion to the aldehyde (Scheme 5.15). 

Dithiazolylium salts and related compounds with S—S bonds are readily reduced both to thiols and to radicals. Thus, the thione (30) is reduced quantitatively to thiourea and CS2 by Sn/HCl (1897JCS607), and for the electrochemical reduction of the salt (31) to dithiobiuret (80) at a Pt electrode, the half-cell potential E q -0.251 V at pH 0 decreases with increasing pH, indicating that the equilibrium favours the cation (31) (47JA2632). The same cation, when refluxed in EtOH with dithiomalonamide, is converted quantitatively... 

The most general synthetic route to thioureas (104) is probably by treatment of an alkyl or aryl isothiocyanate (105) with ammonia or a primary or secondary amine (Scheme 56). 

Irradiation of the thiopyran derivative (292a) results in extrusion of HNCS and the formation of the pyridine (292b, 63.3%) as the major product. The photochemical reactivity of the pyranthione (293) is concentration dependent in 3-methylpentane as solvent. At low concentrations the thione reacts with the solvent but at higher concentrations the main reaction is the production of thiyl radicals. Laser flash photolysis has been used to identify that the triplet excited state of (294) is involved in addition reactions which occur to electron deficient alkenes such as acrylonitrile giving (295), for example. Other compounds related to thiourea are also photochemically reactive. Thus the photochemical cyclisation of (296) to afford (297) has been reported. ... 

When these reaction conditions were applied to thioureas as heterocyclization components, the purities of the resulting aminothiazolylpyrroles were poor. However, this drawback was overcome by changing to DMF/AcOH 95 5 as solvent (Fig. 6.16b, d). The variation of amines and thioureas provided crude products with HPLC-purities of 50% to 92 %, the majority having purities > 80 %. 

Ammonium thiocyanate is used as a corrosion inhibitor in ammonia-handling systems. At 160°C, the ammonium thiocyante is converted to thiourea. 

Thiosemicarbazides are structurally similar to thioureas. In regard to their effect and mode of action, however, they differ sharply, as these active substances also have a powerful fungicidal activity in vitro. Of the derivatives investigated so far... 

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