Thiourea clathrates

Thiourea clathrates may also be applied for geochemical separations. They are similar to the molecnlar complexes of nrea bnt owing to the larger dimensions of the thiourea crystal channels, only branched alkanes, cycloalkanes, and their derivatives participate in clathrate formation. In contrast, the unbranched molecules are too small and hence cannot be held rigidly [77]. 

All -isomers 11,14-dimethylsqualene and 11-methylsqualene were synthesized as reference compounds for biosynthetic studies of squalene synthetase binding sites. 11,14-Dimethylsqualene, obtained in 18% yield by nickel tetracarbonyl coupling of 2-methoxyfamesyl bromide, was isolated from a mixture of geometric and positional isomers as a thiourea clathrate. Condensation between 2-methylfamesyl bromide and the anion of 2-(l-famesylthio)-l-methyl-imidazole followed by Raney nickel desulfuration afforded 11-methylsqualene in 40% yield. 

Chekhova, G.N. Dyadin, Yu.A. Rodionova, T.U. Clath-rates of urea and thiourea. Part IV. Stoichiometry of thiourea clathrates with small molecules and the nature of their packing in the matrix channels. Izv. Sibirskogo Otd. Akad. Nauk SSSR, Ser. Khim. Nauk 1979, N5 (78). 

Allen. A. Fawcett. V. Long. D.A. A Raman spectroscopic investigation of the conformation of the cyclohexyl halides CeHijX (X= chlorine, bromine, and iodine ) in thiourea clathrates. J. Raman Spectrosc. 1976, 4. 285. 

Vibrational Spectroscopy. A Raman investigation of the conformation of cyclohexyl halides trapped in thiourea clathrates has been made. The chloro- and bromo-cyclohexanes are present in the clathrate only as axial conformers whereas the iodide exists in both axial and equatorial forms. From a study of the i.r. spectra of 4-methylcyclohexanone, 4-methylcyclohex-2-enone, and several halogeno-4-methyl-cyclohexanones in the 1350-580 cm region characteristic axial and equatorial (CHj) frequencies were located. This work was subsequently extended to halo-genated 4,4-dimethylcyclohexanones and related t-butyl systems. 

At present, clathrate compounds are considered as both ideal [l] and nonideal solid solutions [2-3] of the guest component in a crystalline framework of the host component. In the absence of the guest component, clathrate 3-modification is considered to be metastable with respect to the stable a-modification under ordinary conditions, i.e. Ap.= i - i <0, where [x, is the chemical potential of the corresponding modification. A number of experimental data on water, urea and thiourea clathrates, hardly consistent with the classical theory, made us study the formation of clathrates with unstable (labile) host frameworks. A comprehensive motivation of such possibility is given in [4]. 

C12H67FO20S, Tri-n-butylsulphonium fluoride hydrate, 27, 781 Cl 2H88Ni,026 f n-Propylamine clathrate hydrate, 39B, 466 Cl2H118N4O41, Trimethylamine clathrate hydrate, 33B, 260 Cl3H22FeN6N3, Ferrocene - thiourea clathrate, 44B, 571 Cl4H18CdN8Ni, catena-M Ethylenediaminecadmium(lI) catena-tetra-M cy-ano-nickelate(II) - bis(pyrrole), 41B, 701 ClgHigCdNeNi, Diamminecadmium tetracyanonickelate benzene clathrate, 40B, 1096... 

Epoxidation of squalene afforded a mixture of squalene 2,3-oxide along with the two trans internal oxides shown above. Controlled acidic hydrolysis allowed selective opening of the terminal epoxide moiety to a diol from which the desired internal oxides were readily separated by thiourea clathrate formation. 

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