1- -3-phenylthiourea, reaction

Several aspects affect the extent and character of taste and smell. People differ considerably in sensitivity and appreciation of smell and taste, and there is lack of a common language to describe smell and taste experiences. A hereditary or genetic factor may cause a variation between individual reactions, eg, phenylthiourea causes a bitter taste sensation which may not be perceptible to certain people whose general abiUty to distinguish other tastes is not noticeably impaired (17). The variation of pH in saUva, which acts as a buffer and the charge carrier for the depolarization of the taste cell, may influence the perception of acidity differently in people (15,18). Enzymes in saUva can cause rapid chemical changes in basic food ingredients, such as proteins and carbohydrates, with variable effects on the individual. 

There are amines such as A-methylnitroamine, that are too weakly nucleophilic to be able to form covalent adducts with arenediazonium ions. The products of the latter appear to be those of salts ArNJ N(N02)CH3, as found by Baranchik et al. (1957). Amides also appear not to be sufficiently nucleophilic, but thioamides are, as is shown by the reaction of A-phenylthiourea in the presence of NaOH (Scheme 13-12 Nesynov et al., 1970). First a (probably homolytic) phenylation-de-diazoniation takes place, followed by A-coupling. Selenourea also reacts a mixture of products is formed, which indicates a reaction of the same type as with thiourea (Nesynov and Aldokhina, 1976). 

Substituted thioureas have been extensively studied over the decades. Reaction of CoX2 (X = C1, Br) with substituted phenylthioureas yield a range of complexes involving halide and thiourea as ligands, characterized by spectroscopy and thermogravimetric analysis.503 Both [Co(Rtu)4(OH2)2]2+ (Rtu = thiourea, phenylthiourea, allylthiourea) and [Co(Rtu)2(OH2)4]2+ (Rtu = diphenylthiourea) have been prepared and characterized as low-spin octahedral species.504 The octahedral bis(phenylthiourea)bis(dithiolate)cobalt(II) complex, one of a number of complexes of phenylthiourea, chlorophenylthiourea and bis(diphenylphospinothioyl)methane prepared and characterized,505 proved the most biologically active of those tested. 

An improved procedure for preparing urea derivatives involves reaction of isocyanates or isothiocyanates with 4(5)-aminoimidazole (25 R = H) in tetrahydrofuran solution [92JCS(P1)2779]. A THF solution of 4(5)-aminoimidazole (25 R=H) generated in situ and then treated with the appropriate reagent gave either lV-imidazole-4-yl-AT-phenylurea (56 X = 0) (32%) or AT-imidazoM-yl-A/ -phenylthiourea (56 X = S) (21%). 

To a solution of triphenyl phosphite (6.2 g, 0.02 mol) and thiomethoxy-acetaldehyde (2.25 g, 0.025 mol) in glacial acetic acid (18 ml), powdered N-phenylthiourea was added in a single portion. The reaction mixture was stirred at room temperature for 30 min and then for 30 min at 80°C. After the mixture was cooled to room temperature, water (5 ml) was added and the solution was maintained at room temperature for 10 h. The precipitate was removed by suction filtration, washed with 1 1 acetic acidtwater (2 x 10 ml), dried over potassium hydroxide in an evacuated dessicator, and recrystallized from chloroform/ methanol. In this manner there was isolated pure 0,0-diphe-nyl 2-methylthio-l-(iV-phenylthioureido)ethylphosphonate (8.61 g, 94%) of mp 136 to 138°C, which exhibited spectra and analytical data in accord with the proposed structure. 

Monosubstituted amino groups (e.g. anilino) in amidinothioureas can participate in this cyclization, as shown by the ready oxidation of l-(2V,jV -diphenylamidino)-3-phenylthiourea (98 R = H, Ar = Ph) (and its analogs) to 5-anilino-2-phenyl-3-phenylimino-AM,2,4-thia-diazoline (99 R = H, Ar = Ph).116 This reaction, in which the alternative cyclization to benzothiazoles might be expected to predominate,68... 

The reaction of thiourea126 with Methylene Blue (MB) is enhanced by an addition of mercaptosuccinic acid. The oxidation of phenylthiourea with MB127 is unaffected by the addition of the corresponding disulfide. The reactions exhibited a zero-order dependence on MB and a first-order dependence on the thiourea. The kinetic features have been explained in terms of reaction between half-reduced MB radical and the thiourea molecule. 

This reaction takes place in three stages. First, the free amino group of the N-terminal amino acid reacts with phenylisothiocyanate to form a phenylthiourea. Second, the phenylthiourea cyclizes to a thiazolinone and expels the shortened peptide chain. Third, the thiazolinone isomerizes to the more stable phenylthiohydantoin. 

The yields of the products from the reaction of phenylthiourea derivatives with bromonitromethane depend largely on the nature of substitution at the nitrogen atom [500] (Scheme 74). 

The reaction of thiourea with [Os(NO)C15]2 is said to give a brown, seven-coordinate association complex , K2[Os(NO)(CN)5 thio].723 The X-ray photoelectron spectrum of OsL2-C12 (L = di-phenylthiourea) has been measured.724... 

This reaction is used to synthesize heterocyclic compounds from orfAo-substituted phenylthioureas." ... 

When urea (or thiourea) reacts with a-hydroxy ketones or a-diketones the products are imidazolin-2-ones (or -thiones) (70AHC(12)103,66RCR122). The reaction is limited to the preparation of 4,5-alkyl(or aryl)- or l,4,5-trialkyl(or triaryl)-imidazoles since an oxygen or sulfur function appears at C-2. Benzoin condenses with iV-phenylthiourea in hexanol in the presence of catalytic quantities of HCl to give l,4,5-triphenylimidazoline-2-thione (131) in 50-60% yield (Scheme 69). While 1-methylurea can also take part in the reaction. 

The preparations of 1,2,4-thiadiazoles and 1,2,4-thiadiazolidines from thioureas are well known and have been summarized in three reviews those of Bambas, Sherman, and Kurzer. Contained in these reviews are discussions of the controversies that surrounded some of the products, notably Hector s bases, which resulted from oxidation of substituted thioureas.Subjects covered in the above reviews, but too extensive to outline in detail here, are the oxidation of amidinothioureas to 3,5-diamino-l,2,4-thiadiazoles (71), the oxidation of phenylthiourea and of substituted amidinothioureas to 3,5-diimino-1,2,4-thiadiazolidines (72, Hector s bases), the reaction of thiopseudoureas with trichloromethanesulfenyl chloride to form 3-alkylthio-5-chloro-l,2,4-thiadiazoles (73), the reaction of thiopseudoureas with sodium thiocyanate and bromine and the oxidation... 

Reaction of aromatic or heterocyclic amines with formaldehyde and urea or phenylthioureas gave 2-(oxo)thioxohexahydro-l,3,5-triazines 90. Regioselective cyclization and isomerization of propargylthio-l,2,4-triazinones were achieved to give the fused heterocycles 91-93. Cyclization of isatin 3-thiosemicarbazones gave 94 which can be alkylated to 95 . The imidazotriazepines 96 were obtained from heating a mixture of hydrazide and ortho-ester. 

Hydrazine hydrate reacts with 3-benzoylimino-5,6-dihydro-3/f-imidazo[2,l-c][l,2,4]dithiazole (19) opening the dithiazole ring and forming a triazole ring, giving (123). Reaction with aniline leads to the formation of imidazolidine-2-thione (120) and l-benzoyl-3-phenylthiourea (124) (Scheme 6)... 

Hoar Ci J found that in the corrosion inhibition of iron in hydrochloric acid by g-naphthoquinoline, the corrosion potential increases monotonically with increasing inhibitor concentration, while in the case of o-tolylthiourea one observes first a decrease of the corrosion potential followed by an increase at higher inhibitor concentrations. A similar predominant inhibition of the cathodic partial reaction at small inhibitor concentrations is exhibited also by phenylthiourea according to Kaesche. Furthermore, in the series of the thiourea derivatives one often finds corrosion acceleration at small concentrations, as for instance in the case of phenylthiourea at concentrations of 10- moles per liter. This appears to be due to a small cathodic decomposition of thiourea and its derivatives in the course of which hydrogen sulfide is formed. As is well known, hydrogen sulfide tends to accelerate corrosion, in particular the anodic partial reaction of dissolution of iron, which has been demonstrated independently by other authors (17). 

Metal compounds have found some application as desulfurization catalysts, and a novel reaction of N-phenylthiourea has been reported. The reaction of PhNCSNH2 with ethanolic Cu(OAc)2 in the presence of 2,2 -bipyridine results in the formation of the phenylcarbodiimido complex [(bipy)Cu(/i-PhN=C=N)2Cu(bipy)]. The same group have also described a related partial desulfurization of 3-methylimidazoline-2(l if)-thione to yield di( 1-methyl-imidazolyl)sulfide (41) upon reaction with copper(II) salts. These reactions are mechanistically obscure. 

Carbohydrate-integrated isoxazolines have been synthesized from 2-nitroglycals and sulfur ylides, with 1-phenylthiourea as catalyst. The reactions proceed via [4 - -l]-annulations and subsequent rearrangement gives the isoxazolines with high diastere-oselectivity (Scheme 83). ... 

Edman Degradation (Section 27.4B) Treatment with phenyl isothiocyanate followed by acid removes the N-terminal amino acid as a substituted phenylthiohydan-toin, which is then separated and identified. The mechanism involves reaction of the electrophilic C atom of phenyl isothiocyanate with the nucleophilic terminal amino group to give an N-phenylthiourea intermediate that decomposes upon heating by cy-clization to give a thiazoKnone intermediate as the C-terminal peptide bond is cleaved. The thiazolinone intermediate isomerizes to the phenylthiohydantoin product. 

Instead of thiourea, N-phenylthiourea can also be used for the reaction with alkyl halogenides, and the S-alkyl-N-phenylthiuronium halo-genides formed can be converted to sharply melting picrates, picrolonates or styphnates (8). 

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