Thioureas and Selenoureas

Synthesis.—Diarylthioureas have been made from arylamines and either bis-(alkoxythiocarbonyl) disulphides or CSj and an alumina catalyst. The standard reaction of amines with isothiocyanates was used in the preparation of adamantyl- and glycosyl- thioureas. Benzoyl isothiocyanate, when treated with sterically hindered amines, e.g. Pr jNH or dicyclohexylamine, gives 

Takahashi, N. Nimura, and H. Ogura, Chem. Pharm. Bull., 1979,27,1130. 

The intermediate phosphonium thiocyanate (2) gives phosphinimines with an excess of amine, and acylthioureas and amides when treated with carboxylic acids. A Beckmann rearrangement of amidoximes RCCNOHlNHj with PhSOjCI in pyridine, followed by treatment with HjS, gives thioureas RNHCSNHj in 55—76% yields.  

The radical phenylation of thiourea or of AW -diphenylthiourea to give the iS-phenyl derivatives proceeds better with nitrosoacetanilides than with phenyl-azotriphenylmethane as the source of radicals.  

Addition of HjS to alkyldicyanamides affords 1-alkyl-1-cyanothioureas, and then (with NEtj catalysis) 3-alkyl-dithiobiurets (3). 3-Alkyl-2-thiobiurets are made similarly from 1-alkyl-1-cyanoureas. l-Benzoyl-2-thiobiuret. is obtained from benzoyl isothiocyanate and urea, and it rearranges to l-benzoyl-4-thiobiuret (4) 

Synthesis.—The most common method for the preparation of thioureas is based on the reaction of isothiocyanates with amines, and, not unexpectedly, the majority of the papers dealing with the preparation of new 

Fetter, J. Nyitrai, and K. Lempert, Acta Chim. Acad. Sci. Hung., 1973, 79, 197. 

387—389). More exotic thioureas were the products of interesting reactions of isothiocyanates with ketimines, enamines imino-esters/ amidines, amidrazones, and substituted ammonium salts. Some selenoureas have been synthesized by the reaction of isoselenocyanates with amines, and the phosphorus compounds (300) were obtained analogously by treatment of w-mercaptoalkylphenylphosphines with phenyl isothiocyanate. The action of primary amines on (300) resulted in the formation of N-alkyl-lsT-phenylthioureas in high yields with simultaneous regeneration of the w-mercaptoalkylphenylphosphine.  

Abel and Dunster have reported that dimethyl(trimethylstannyl)amine, on treatment with phenyl isothiocyanate, yields the trimethylstannyl-thiourea (301). On the other hand, Matsuda and his co-workers found that the related reaction of N-trimethylsilyl(diphenylmethylene)amines with isothiocyanates affords equilibrium mixtures of the two rapidly interconvertible tautomeric compounds (302) and (303).  

Synthesis.—Unsubstituted S-labelled thiourea has been synthesized in 88% yield by treating K SCN (obtained from and KCN) with benzoyl chloride, aminolysis of the resulting benzoyl isothiocyanate, and subsequent hydrolysis of the benzoyl[ S]thiourea. The addition of ammonia or amines to isothiocyanates has continued to be the main method for the preparation of substituted thioureas. Williams and Jencks have studied the mechanism of this important reaction [equation (1)], which is first-order in both amine and isothiocyanate and is not catalysed by buffer. 

A very simple, but quite efficient, one-step synthesis of A-aryl-thioureas from primary aromatic amines and ammonium thiocyanate has been reported. Activated isothiocyanates, such as methoxycarbonyl isothiocyanate (1) and acyl or aroyl isothiocyanates, have been applied in the preparation of the JV-heteroaryl-thioureas (2) and (3), or acyl-thioureas (4). Chloroacetyl isothiocyanate 

Numerous alkyl as well as aryl and heteroaryl isothio- 

2-Dichloroethyl isothiocyanate reacts with thioureas R NHC(S)NR 2 at 100 °C to yield thiazolyl-2-thioureas (9), or at 20 °C to give the thiadiazines (10), which may be rearranged, on heating or with base, to the thiazoles (9).  

Watanabe, M. Okano, and S. Uemura, Bull, Chem. Soc. Japan, 1974,47, 2745. 

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Selenourea [630-10-4] ]5k.e urea and thiomea can form channel inclusion compounds (87) with a variety of hydrocarbons. Though the difference in channel diameter between thiourea and selenourea is small, selenourea seems to be much more selective for the inclusion of certain guest molecules (eg, cis/trans isomers). 

Thiourea and selenourea both form canal inclusion compounds. The selenourea compounds, reported only briefly 37), appear to be isostructural with the rhombo-hedral thiourea compounds, although with larger dimensions which are more susceptible to the sizes of guest molecules. For urea, thiourea and selenourea the crystal densities of the compounds are significantly less than those of the hosts values (g cm - 3) for the pairs host/complex are 1.30/1.20 1.40/1.10 2.08/1.60-1.65 for urea, thiourea, selenourea, respectively37). 

Reactions of hydrazonoyl halides with thiourea and selenourea were reported to give products that depend on the structure of the halide used. Thus, while reactions of thiourea with C-heteroacyl-N-arylhydrazonoyl halides 30e and 34 yield the corresponding 5-arylazo-2-aminothiazole derivatives 282a and b [88PS(40)243 90MI3], its reaction with the halide 28b gives 5-iminothiadiazoline derivatives 283 (88MI1). 

II. Classical Channel Inclusion Compounds of Urea, Thiourea, and Selenourea. 155... 

It. CLASSICAL CHANNEL INCLUSION COMPOUNDS OF UREA, THIOUREA, AND SELENOUREA... 

A brief review on the crystal structures of urea, thiourea, and selenourea is included for understanding the properties of hydrogen-bonded channel frameworks in their inclusion compounds. The N-H—E (E = O, S, Se) hydrogen bonds which play an instrumental role in the structures of urea/thiourea/selenourea inclusion compounds are discussed in this section. 

There are more striking differences in the unit-cell dimensions of the selenourea inclusion compounds than are observed for the thiourea inclusion compounds, as adaptation of the selenourea lattice to the shape and size of the included molecules is apparently relatively easy [57-Si]. A theoretical study of the conformations and vibrational frequencies in urea, thiourea, and selenourea compounds has been reported [54]. Studies on the complexation of TT with I" and urea, thiourea, or selenourea (and their Me derivetives) using a horizontal zone electromigration method have indicated that the complexing capacities of the urea derivatives increase in the order urea < thiourea < iV,N, N -tetramethylthiourea < selenourea [55]. 

Our studies on the generation of novel urea, thiourea, and selenourea-anion inclusion compounds have shown that novel anionic host lattices can be constructed from urea derivatives and many types of anions as building blocks. The versatility of urea, thiourea, or selenourea as a key component in the construction of novel host lattices is clearly demonstrated by the occurrence of many new types of linkage modes, which include various discrete units, chains or ribbons, and composite ribbons with corresponding anions. These motifs are shown in Tables 14, IS, and 16, respectively. 

In summary, we have shown that novel anionic host lattices can be constructed from urea, thiourea, or selenourea molecules and various anions as building blocks, which readily adopt different topologies for the accommodation of tetraalkylam-monium ions of various sizes. By employing organic cations as templates and suitable counter anions as an ancillary host material, with or without neutral molecules such as H2O as a third component, the lattice engineering of new urea, thiourea, and selenourea inclusion compounds by self-assembly may be further explored. 

Thiourea and selenourea and their applications, particularly, in the preparation of heterocycles 06COS439. 

Hofmann-type clathrates Werner clathrates clathrate hydrates inclusion compounds of urea, thiourea, and selenourea cyclodextrins calixarenes gossypol hexa-hosts hydroquinone phenol and Dianin s compounds graphite intercalates natural and pillared clays and others. Such studies contributed to the birth of supramolecular chemistry, with relevance to a new understanding of the world of materials that was emphasized with a Nobel Prize. 

Gopal, R. Robertson. B.E. Rutherford, J.S. Adamantane inclusion complexes with thiourea and selenourea. Acta Crystallogr. 1989. C45. 257. 

Hollingsworth MD, Harris KDM (1996) Urea, thiourea, and selenourea. Comprehensive Supramolecular Chemistry, vol. 6. Pergamon, UK, pp 177-237 Cannarozzi GM, Meresi GH, Void RL, Void RR (1991) J Phys Chem 95 1525 Sozzani P, Bovey FA, Schilling FC (1989) Macromolecules 22 4225 Schilling FC, Bovey FA, Sozzani P (1990) Polymer Preprints 31... 

Phenylurea added to a soln. of startg. furan-2,3-dione in glacial acetic acid, and heated for 1 h - 3-phenyl-5-phenacylideneimidazolidine-2,4-dione. Y 79%. F.e. and 2-thioxo- and 2-selenoxo-analogs from thioureas and selenoureas, respectively, s. Y.S. Andreichikov et al., Khim. Geterotsikl. Soedin. 1988, 1411-3. 

Takemoto, K., and Sonoda, N., 1984, htclnsion compoimds in urea, thiourea and selenourea, in Inclusion Compounds Structural Aspects of Inclusion Compounds Formed by Organic Host Lattices, Vol. 2 (J. L. Atwood, J. E. D. Davies, and D. D. MacNicol, eds.). Academic Press, New York, pp. 47-67. 

The inclusion properties of urea were discovered by Ben-gen in 1940 and this tubulate host has since become one of the most studied. Thiourea and selenourea form related, but slightly different, clathrate structures. Figure 1 illustrates the structure of the (thiourea)3 -(carbon tetrachloride) compound. Many 1,3-diarylurea derivatives also include guest molecules, but these produce hydrogen-bonded complexes with acceptor guest species, rather than clathrates. " ... 

Rate constants and activation parameters (Table 2) have been reported for reactions of [PdCl and [PdBr with thiourea and selenourea. Two steps were monitored,... 

Reactions of [PdXsL]" and of [PdXL3]+ were too fast even for stopped-flow monitoring, owing to the very high trans effects of thiourea and selenourea. The reactions of [PdClJ " with l,3-diamino-2-methylenepropane [diampr (9)] and its NN -dimethyl derivative have also been studied (Table 2). 

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