Clathrates preparation

The best-known noble gas clathrates are hydrates, hydroquinone and phenol clathrates, which have found an increasing number of uses [131]. Clathrates may serve as convenient storage for noble gases. Because of the different affinity hydroquinone clathrate prepared from an equal mixture of krypton and xenon liberates 3 times the amount of Xe than Kr [132]. Clathrates are also of interest for nuclear technology. Radioactive isotopes of argon, xenon and krypton can more easily be handled in the compact form of a solid rather than in gas form [133-136]. 

Fig. 2 Space-filling representations of (from left to right) empty P-cyclodextrin dimers, a sectioned view showing the empty channel, and sectioned views showing channel occupation by (L)-menthol and (R)-fenoprofen guest molecules in the isostructural clathrates. (Prepared from data in Ref [25].) (View this art in color at www.dekker.com.)...

Electrochemical Clathrate Preparation by the Spark-Plasma Technique... 

Gorbatchuk VV, Gatiatulin AK, Ziganshin MA, Gubaidullin AT, Yakimova LS. Unusually high efficiency of (5-cyclodextrin clathrate preparation by water-free solid-phase guest exchange. J Phys ChemB 2013 117(46) 14544-56. 

Krypton clathrates have been prepared with hydroquinone and phenol. 85Kr has found recent application in chemical analysis. By imbedding the isotope in various solids, kryptonates are formed. The activity of these kryptonates is sensitive to chemical reactions at the surface. Estimates of the concentration of reactants are therefore made possible. Krypton is used in certain photographic flash lamps for high-speed photography. Uses thus far have been limited because of its high cost. Krypton gas presently costs about 30/1. 

The history of iaclusion compounds (1,2) dates back to 1823 when Michael Faraday reported the preparation of the clathrate hydrate of chlorine. Other early observations iaclude the preparation of graphite iatercalates ia 1841, the P-hydroquiaone H2S clathrate ia 1849, the choleic acids ia 1885, the cyclodexthn iaclusion compounds ia 1891, and the Hofmann s clathrate ia 1897. Later milestones of the development of iaclusion compounds refer to the tri-(9-thymotide benzene iaclusion compound ia 1914, pheaol clathrates ia 1935, and urea adducts ia 1940. 

An interesting PLC variation of the nrea clathration techniqne has been proposed by Chaffee and Johns [82]. Component mixtnres are applied onto TLC plates (20 cm X 20 cm X 0.5 mm) coated with Kieselgnhr G/nrea (2 1), prepared from a slnrry in urea-saturated methanol (Iml/g powder). Spotted plates are left in methanolic atmosphere overnight to allow clathrate formation. To remove methanol, plates are air dried for 2 to 3 h at room temperatnre and then developed in -heptane. Two bands of acychc (Rf 0.9 to 1.0) and cyclic (Rf 0.0 to 0.1) hydrocarbons are distinguished, and components are recovered qnantitatively by extraction with chloroform. 

All host compounds except 8-10 have been described in vol. 140 of this series, Molecular Inclusion and Molecular Recognition-Clathrates I . The new host compound (—)-8a was prepared by reaction of PhMgBr and (—)-trans-4,5-bis(ethoxycarbonyl)-... 

Radon forms a series of clathrate compounds (inclusion compounds) similar to those of argon, krypton, and xenon. These can be prepared by mixing trace amounts of radon with macro amounts of host substances and allowing the mixtures to crystallize. No chemical bonds are formed the radon is merely trapped in the lattice of surrounding atoms it therefore escapes when the host crystal melts or dissolves. Compounds prepared in this manner include radon hydrate, Rn 6H20 (Nikitin, 1936) radon-phenol clathrate, Rn 3C H 0H (Nikitin and Kovalskaya, 1952) radon-p-chlorophenol clathrate, Rn 3p-ClC H 0H (Nikitin and Ioffe, 1952) and radon-p-cresol clathrate, Rn bp-CH C H OH (Trofimov and Kazankin, 1966). Radon has also been reported to co-crystallize with sulfur dioxide, carbon dioxide, hydrogen chloride, and hydrogen sulfide (Nikitin, 1939). 

Hydroprocessing, in petroleum refining, 18 654-657 Hydropulping, 10 535 Hydropyrolysis, coal liquefaction, 6 854 Hydroquinolines, 21 198-199 Hydroquinone (HQ) from benzene, 3 620 as a black-and-white chemical reducing agent, 19 205-206 in bleaching preparations, 7 847 clathrates, 14 160 dye releaser, 19 291-292 inclusion compounds in, 14 172, 174 intermediate used in oxidation hair dyes, 7 858t... 

One of the more important recent developments in organometallic aluminum chemistry has been the formation and isolation of low-coordinate compounds, and, in particular, cations. These were first prepared in reactions of various aluminum reagents with crown ethers to form the inclusion compounds known as liquid clathrates. 71,72 Most of the evidence supports the presence of ion pairs as the basis of the solvent inclusion effect. Indeed, the compound [AlMe2-18-crown-6]+[AlMe2Cl2] was isolated from one such system (the cation is shown in Figure 6(a)).73 This was the first time the Me2Al+ unit had been structurally characterized. 

Prior to the generation of 124, one of my students, Samuel K.T. Cheng, in a separate study on the preparation of clathrate inclusion hosts, had prqrared a perfect precursor 131 (Scheme 26). The synthetic routes leading towards 131 and 124 are shown in Scheme 26. As can be seen, a rather synthetically oriented program based on the initial construction of 128 was carried out by Cheng, who achieved... 

R)-1,1 -Bi-2-naphthol was prepared by resolution employing the N-benzylammonium chloride salt of (-)-cinchonidine to form separable diastereomeric clathrate complexes. Hu, Q-S. Vitharama, D. Pu, L. Tetrahedron Asymmetry 1995, 6, 2123. 

It can be used in nucleophilic -displacement reactions of unactivated aryl halides4 that originally were only possible in solutions in HMPT. An example is the reaction of C6C16 or C6F6 with the sodiu m salts of thiols to give hexakis(alkylthio)benzenes in >90% yield4, s. Indeed, hex akis(/ -naphthylthio)benzene (2) was prepared by reaction of hexachlorobenzene and the sodium salt of J -mercaptonaphthalene in 1 in 72% yield. Hexasubstituted ben zenes such as 2 are of interest because they can function as inclusion hosts related to clathrates of phenol.h... 

The solid inclusion (clathrate) complex of oxygen with hydroquinone had been prepared twice previously by a published method which involved saturating a solution of hydroquinone in propanol in an autoclave at 70°C with oxygen at 20—150 bar,... 

Cross-metathesis applications, 11, 200 enynes, 11, 282 in ethenolysis, 11, 198 Lewis-basic substrates, 11, 193 in one-pot reactions, 11, 197 for reagent synthesis, 11, 188 as simple metathesis reaction, 1, 171 Crotyltributyltins, with aldehydes, 9, 352 Crown ether clathrates, diorganozinc compounds, 2, 335 Crown ether-pendant polysilanes, preparation, 3, 577 Crown-ethers, as hosts, 12, 813... 

The inclusion ability of 7.19 is sufficiently robust that it can tolerate a variety of substitutions and still retain (modified) clathrate-forming ability. A wide variety of analogues have been prepared, which exhibit different size and shape cavities by the following modifications ... 

---