Liquid clathrates examples

Liquid clathrates, analogues of the gas clathrates but present in the liquid phase, are unusual two phase systems in which an upper layer of solvent lies above a denser layer of solvent saturated with ionic species. Some interesting examples are found in Atwood s work. Initially a salt, such as sodium chloride, is added to an aromatic solvent in which it is insoluble. Another reagent, an aluminium alkyl in one example, is added and the salt is solublized to form a dense phase [1] which may be interpreted as ... 

Temperature is all important to the existence of liquid clathrates. K[Al2(CH3)6N3] benzene is reasonably stable (Reaction 4) at 25°C and completely stable at 40°C. Cs[A1o(CH3)gN03] benzene is exceedingly unstable (Reaction 4) at 25°C but completely stable at 80°C. K[AL(CH3)gN3] p-xylene does not exist at 25°C, but it is stable at 130 °C. It does not seem unreasonable that the proper combination of cation, anion, and guest might form a liquid clathrate at slightly elevated temperatures, but at room temperature it would form a solid with a structure similar to that of the liquid clathrate. We now have what may be an example of this in the crystal structure of K[CH3Se Al(CH3)3 3] 2CgHg. 

Liquid clathrate is a term coined by Professor Jeny L. Atwood, then at The University of Alabama.This term was used to describe the serendipitous discovery of the biphasic behavior of a wide selection of salts with aromatic solvents, such as toluene and benzene. These semiordered liquids containing complex salt hosts and aromatic hydrocarbons represent the most common examples of liquid clathrates. 

The first examples of materials that supported liquid clathrate phase formation, in contact with aromatic hydrocarbons, were highly reactive air-sensitive salts containing alkylaluminum anions, first described by At-wood. " Their applications for separations of aromatics from hydrocarbons and in coal liquefaction were extensively explored. However, a drawback of the initial systems studied was their air-sensitivity and reactivity. 

These observations appear to hold for all known alkylaluminum-based liquid clathrates. For example, a selenonium ion-based liquid clathrate having the inclusion formula [(CH3)3Se] [C1A1(CH3)2(C1)A1(CH3)3] (aromatic solvent), can accommodate 8.5 benzene molecules or 8.3 toluene molecules per parent compound. 

In studies to determine the miscibility of ionic liquids with aromatic solvents, Holbrey et al. found that ionic liquid-aromatic mixtures form liquid clathrate systems. For example, ionic liquids of current interest, such as hydrophobic 1-alkyl-3-methylimidazolium salts ([Cn-mim]X) with hexafluorophosphate, / w(trifyl)imide, and tetrafluoroborate anions were observed to form liquid clathrates with benzene, toluene, and xylenes (Fig. 2). In... 

Liquid clathrates essentially consist of a liquid made out of guest molecules entrapped in a host species. They are primarily based on low-melting organometallic salts, which have a high solubility in aromatic liquids, as well cts a high selectivity for liquid aromatic hydrocarbons. For example,... 

In addition, when ILs are used as solvents, how will the supramolecular structures of ILs themselves affect the formation of supramolecular assemblies. For example, when the surfactant is added into the IL/oil mixture, two cases would happen. If the hydrophobic interactions between oil and surfactant are stronger than the interactions between IL and oils, liquid clathrate can be destroyed and O/IL microemulsions form. Otherwise, a new state would exist instead of O/IL microemulsions. However, in the reference, this field has not been mentioned. Moreover, because trivial water is difficult to be removed and could be included in the supramolecular framework of imidazolium ILs, ILs are not pure, which makes the system more complicated. This supramolecular structure may also affect the formation of supramolecular assemblies. Recently, we noticed that water plays the key role in the formation of IL based microemulsions. A small quantity of water can lead to great change in the phase diagram of IL/TX-100/ oil ternary systems. Therefore, the effect of the supramolecular structures of ILs on the formation of supa-amolecular assemblies is another valuable subject. 

Cram [49a] elaborated further on this concept by enclosing space in his carcerands and hemicarcerands (See Scheme 1) to form a new inner phase which he has referred to as a new phase of matter . In contrast to the hollow space found inside clathrates and zeolites for instance, the cages of these molecules are independent of the form and physical state. For example, hemicarcerands and related supramolecular systems (i.e. hemicarceplexes) prevail in the solid, liquid, or gas phase. This characteristic-hollow space, the inside surface — is maintained across all phase transitions. The inner surfaces and spaces of these systems are not manifested as bulk properties. An extensive review on the synthesis of these materials has been published recently [205]. 

Finally, we wish to comment briefly on a recent development in inclusion polymerization. As already discussed, this reaction can be carried out on the pure clathrate or in the presence of an excess monomer. Consequently, the vapor pressure of a volatile monomer during polymerization ranges from the decomposition pressure of the clathrate to the vapor pressure of the saturated solution of the host in the guest, which is generally very close to that of the pure liquid monomer. For example, the vapor pressure... 

In the last twenty five years there has been a number of studies devoted to the reactions of the organic solids subjected either to a physical agent (light, heat) or a chemical one which can be a solid, a liquid or a gas The molecular constituents of a highly ordered medium such as a crystal lattice may undergo physical or chemical modifications which are far more selective than those experienced in solution or in the gas-phase. In the bimolecular crystalline edifices of the clathrates, attention is turned to the guest molecules as incipient reactive species. For example, it has recently been reported that inclusion polymerization of prochiral... 

Though there do not seem to be any generally available technical reports, there are genuine stories of explosions and burn accidents caused by the inadvertent formation and subsequent decomposition of hydrates of hydrocarbons in railway tank cars in the cold climate of Canada. Incidents occurred due to the practice of washing empty tank carr following their use for transporting liquid hydrocarbons. In a cold winter climate, it is possible to form hydrates with small amounts of hydrocarbon residues, which later decompose when the tank car warms up, e.g., when exposed to sunshine. For example, the clathrate hydrate of isobutene (2-methyl-propene, b.p. -6.9" C) needs only 1.12 bar at 273 K to be stable. Precautions were not taken around such nominally clean and empty tankers, and exposure to sparks or naked flames led to flash fires and explosions. While the main content of the tankers was butane, other hydrocarbons were present. In another kind of industrial accident, a worker was killed by H2S gas liberated from H2S hydrate residue in a heavy water production plant, during a shutdown for maintenance. 

In addition to simple binding there are many examples where a low molecular weight species enters either the crystal interior or the interlamellar space with compound formation. These situations, although not uncommon, must obviously be very specific in nature and are termed inclusion compounds or clathrates. An example is given by the phase diagram of Fig. 3.25 for polyethylene-perhydrotriphenylene mixtures.(112) A compound is formed that melts congruently at 178.2 °C. This inclusion compound does not exist in the liquid phase and does not form mixed crystals with the pure species. 

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