Phenol clathrates

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). 

The history of inclusion compounds (1,2) dates back to 1823 when Michael Faraday reported the preparation of the clathrate hydrate of chlorine. Other early observations include the preparation of graphite intercalates in 1841, the 3-hydroquinone H2S clathrate in 1849, the choleic acids in 1885, the cyclodextrin inclusion compounds in 1891, and the Hofmann s clathrate in 1897. Later milestones of the development of inclusion compounds refer to the tri-o-thymotide benzene inclusion compound in 1914, phenol clathrates in 1935, and urea adducts in 1940. 

Figure 2. Four phase equilibrium lines for phenol clathrate of carbon dioxide , pure water , pure phenol , phenol clathrate-carbon dioxide-rich liquid-water-rich liquid-vapor line ...

The experiment began by charging the equilibrium cell with about 30 cm3 of either phenoPp-cresol or phenol-water solution mixture. The cell was then pressurized with either methane or carbon dioxide until the phenol clathrate formed under sufficient pressure. The systems were cooled to about 5 K below the anticipated clathrate-forming temperature. Clathrate nucleation was then induced by agitating the magnetic spin bar. After the clathrates formed, the cell temperature was slowly increased until the clathrate phase coexisted with the liquid and vapor phases. The nucleation and dissociation steps were repeated at least twice in order to diminish hysteresis phenomenon. The clathrates, however, exhibited minimal hysteresis and the excellent reproducibility of dissociation pressures was attained for all the temperatures and found to be within 0.1 K and 1.0 bar at each time. When a minute amount of phenol or p-cresol clathrate crystals remains and the system temperature was kept constant for at least 8 hours after attaining pressure stabilization, the pressure was considered as an equilibrium dissociation pressure at that specified temperature. 

Equilibrium hydrate and phenol clathrate conditions for water—carbon dioxide,... 

The hydrate and phenol clathrate equilibrium data of the water-carbon dioxide, phenol-carbon dioxide, and water-phenol-carbon dioxide systems are presented in Table 1 and depicted in Figure 2. In order to establish the validity of the experimental apparatus and procedure the hydrate dissociation pressures of carbon dioxide measured in this work were compared with the data available in the literature (Deaton and Frost [7], Adisasmito et al. [8]) and found that both were in good agreement. For the phenol-carbon dioxide clathrate equilibrium results, as seen in Figure 2, the dramatic increase of the dissociation pressures in the vicinity of 319.0 K was observed. It was also found in the previous study (Kang et al. [9]) that the experimental phenol-rich liquid-phenol clathrate-vapor (Lp-C-V) equilibrium line of the binary phenol-carbon dioxide system could be well extended to the phenol clathrate-solid phenol-vapor (C-Sp-V) equilibrium line (Nikitin and Kovalskaya [10]). It is thus interesting to note that a quadruple point at which four individual phases of phenol-rich liquid, phenol clathrate, solid... 

For the ternary water-phenol-carbon dioxide system, several interesting phenomena were observed. As shown in Figure 2, the four-phase, water-rich liquid-phenol-rich liquid-phenol clathrate-vapor (Lw-Lp-C-V), dissociation pressures were measured at several temperatures near 293.0 K. Like above the phenol-carbon dioxide clathrate equilibrium results, the dramatic increase of the four-phase dissociation pressures was observed in a vicinity of 293.0 K. One of the most interesting results observed in this work is that a quintuple point at which the five phases of water-rich liquid, phenol-rich liquid, carbon dioxide-rich liquid, phenol clathrate, and vapor coexist in equilibrium was carefully measured and found to be 293.7 K and 57.2 bar. 

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]. 

The phenol clathrates of argon, krypton, and xenon have been prepared by Lahr and Williams [148] by direct combination of the gas with crystalline... 

Fig. 14.31. Plan of the clusters of six phenol molecules in the structure of the phenol clathrates. The hydroxyl groups lie at the comers of a plane hexagon and the axes of the phenol molecules are inclined alternately above and below this plane. Hydrogen bonds between hydroxyl groups are represented by broken lines.

Fig. 14.32. Clinographic projection of the unit cell of the rhombohedral structure of the phenol clathrates. Clusters (fig. 14.31) of six phenol molecules are represented schematically, and these are disposed about the comers of the cell in the manner shown, for clarity, at only one comer. Guest molecules can occupy the interstices A at the centres of the cell and the interstices B at its corners.

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. 

Not only hydroquinone, but also phenol and a number of related substances have been reported20,21 33,44 to form clathrate compounds of a similar type. But this class of substances proves to be... 

Classifying particles, in filtration, 11 326 Class I hybrids, 13 536, 543, 544 Class II hybrids, 13 536, 543 Clastogenesis, 25 206 Clathrate hydrates, 14 170—171 Clathrate receptor chemistry, 16 797 Clathrates, 12 374 14 159, 170-182 formation of, 10 633-635 26 869 Hofmann- and Werner-type, 14 171-172 phenol-type, 14 180 tri-o-thymotide, 14 179 Claus catalysts... 

Krypton is an inert gas element. Its closed-shell, stable octet electron configuration allows zero reactivity with practically any substance. Only a few types of compounds, complexes, and clathrates have been synthesized, mostly with fluorine, the most electronegative element. The most notable is krypton difluoride, KrF2 [13773-81-4], which also forms complex salts such as Kr2F3+AsFe [52721-23-0] and KrF+PtFF [52707-25-2]. These compounds are unstable at ambient conditions. Krypton also forms clathrates with phenol and hydroquinone. Such interstitial substances are thermodynamicahy unstable and have irregular stoichiometric compositions (See Argon clathrates). 

Not all clathrates are hydrates. Other well-known examples have host lattices formed from hydrogen bonded aggregates of hydroquinone, phenol, and similar organic compounds. Non-hydrogen bonded host structures are also known. One example is a cyclotriphosphazene. (C6H402PN). that traps molecules such as benzene in tunnels in the crystal.2 In addition, coordination polymers are formed by ambidentate ligands, such as CN and SCN, which coordinate to metal ions at both ends (Chapter 12). Perhaps the best known of this type of compound is the series of Ni(CN)2NHj M compounds, where M may be benzene, thiophene, furon. pyrrole, aniline, or phenol. 

Clathration is the third sorption situation. Guests are incorporated during the growth of the host lattice. Their liberation occurs on heating or lowering the pressure with lattice breakdown. This situation is found for water, phenol, quinol, cresol, urea, and Dianin s compound. 

In clathrate solutions the bonds holding together the units of the host lattice are weaker, and the resistance to collapse, even of only partially guest-free host lattices, is much less. Thus it may not be possible to realize the whole isotherm as illustrated in Figure 1 (76) for Kr in the porous 0-phenol lattice at 195, 212, 222.2, and 228°K. A critical pressure pc of Kr and loading of 0-phenol by Kr are essential before 0-phenol forms from ordinary nonporous a-phenol. If pa and M/3 are the chemical potentials of phenol in these two forms, the critical condition can be expressed as ... 

Some phenolic compounds can form flat hexagonal structures with the aromatic rings facing outward, and linked by hydrogen bonds. The internal space thus formed contains solvent. Such compounds are called inclusion compounds or clathrates. An example is dianin (2.14), which can form clathrates in more than 50 different solvents. 

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... 

Hydroquinone and phenol based clathrates including Dianin s compound are based upon cages made up of 6-membered hydrogen bonded rings of hydroquinone and are subject to considerable synthetic variation. 

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