Hydrates double

Mak, T.C.W. McMullan, R.K. (1965). Polyhedral Clathrate Hydrates. X. Structure of the Double Hydrate of Tetrahydrofuran and Hydrogen Sulfide. J. Chem. Phys., 43... 

A similar, if somewhat sketchier, study of the photolysis of d-UpU (16b, R = H) has been carried out,73 and comparison with the photolysis of UpU is interesting. The close similarity of d-UpU and UpU, differing only in the sugar moiety, and there only slightly, would lead to the expectation that the photolyses should be very similar in outcome. The differences are, however, appreciable. d-UpU forms only two dimers, and both the single and double hydrate are separable by paper chromatography, leading to a reaction scheme as shown in Chart 4. 

Each act of covalent hydration introduces a center of asymmetry, and a double hydration can provide the opportunity for geometrical isomerism. 

Double hydrates was initially reserved for structure II hydrates in which one component is hydrogen sulfide or hydrogen selenide. It has come to mean hydrates in which each size cage is primarily occupied by a different type of molecule. Von Stackelberg proposed that double hydrates were stoichiometric due to their almost invariant composition. Van der Waals and Platteeuw (1959) suggested this invariance was caused instead by azeotropic composition (i.e., hydrate and gas phase compositions are the same). 

Structural Changes in Binary (Double) Hydrates. Although CH4 and C2H6 are both si hydrate formers, Subramanian et al. (2000) showed that a binary CH4/C2H6 mixture can exhibit sl/sll transitions with varying pressure and/or composition. In contrast, a binary CH4/CO2 mixture, where again both pure components are si hydrate formers, forms only si hydrate. 

Figure 2.15 (Ripmeester, 2000) correlates the observations of double hydrates and demonstrates the complexity of the structure-size relationship for hydrates containing two types of guest molecules. The combinations of two different types of guests forming sll and sH double hydrates are also listed in Tables 2.6 and 2.7, respectively.

Hester and Sloan (2005) extended the size-structure correlations for double hydrates. A simple scheme of guest size-structure boundaries was proposed to predict the sl/sll structural transitions for double hydrates consisting of si hydrate formers (Figure 2.16). Raman spectroscopy and neutron diffraction measurements were performed to test the limits of these structural transitions. 

The peptide group can be fixed at the ice lattice with p = 0127. Ice-like distances of the H-bond acceptors are in different molecules for example Biotin. Thymine, Triglyceride, 1,4-Quinone etc.141. Hechter gave a model for biologic membranes too142. In the membrane surface Hechter assumes a water double hydrate lamella of 4.9 A thickness in which K+ could be placed, but Na+ would be too big. 

The ideal stoichiometric formulas for the hydrates prepared with the aid of H2S are, for example, 6C12-2H2S-46H20, or 8C3H816H2S136H20 for types I and II hydrates, respectively. They are referred to as double hydrates. It is also possible to occupy the voids with mixtures of appropriate gases such as the mixture of methane, ethane, and propane, which occurs in natural gas, to yield mixed hydrates. 

Mak TCW, McMullan RK (1965) Polyhedral clathrate hydrates. X. Structure of the double hydrate of tetrahydrofuran and hydrogen sulfide. J Chem Phys 42 2732- 2737... 

Crude 10% sodium hydroxide containing sodium chloride is purified in a similar manner to the product of the causticization process. The water is evaporated in nickel or nickel-clad steel (to reduce corrosion) multiple-effect evaporators to about 50% sodium hydroxide concentration. At this concentration, sodium chloride is only about 1% soluble (2%, on a dry basis) in the more concentrated caustic so that the bulk of it crystallizes out and is filtered off. This quite pure sodium chloride is recycled to the cells. Lor many purposes, such as for pulp and paper production, this purity of 50% sodium hydroxide is quite acceptable. If higher purities are required, sodium hydroxide may be separated from residual water and salt by chilling to the double hydrate crystals NaOH 2HiO, m.p. about 6°C, or as NaOH 3.5HiO, with a m.p. of about 3°C, or by counter-current extraction [9]. The sodium hydroxide obtained after these steps contains 2-3 ppm sodium chloride, equivalent to the purity of the mercury cell product ( rayon grade ) [10]. Concentrations of 73% and 100% sodium hydroxide (see details, Section 7.5) are also marketed. 

The requirements for highly hydrated dolomitic lime, (also called di-hydrated or double hydrated lime) are specified in [20.15, 20.16]. It is required to contain less than 8 % of free lime, to ensure that it is sound. 

Fig. 3 The P.T decomposition curves of the simple and double hydrates. The melting curves of different ices are given.

II maq occur depending on P.T conditions and relative concentrations. Guests of Type Ila. la. or Ib together with lib or 11c give double hydrates of Structure II, and guests of Type la. Ila. or Ib with Ha give structure H. (J.A. Ripmeester. Ann. N. Y. Acad. Sciences 2000. 912. 1.) View this art in color at www. 

Because a hydrate ean contain, volume for volume, a large amount of gas, this is potentially a useful solid storage aud transport medium, though it has to compete economically with liquefied gas. There is active research to find storage systems that will work at pressures less than 1 MP, involving "additives" to give double hydrates that are more stable. 

The formation is explained by oxidation of two 3-methyl-2-butenyl side chains, giving rise to an allylic hydroperoxide and a trisubstituted epoxide. Dismutation of the hydroperoxide and double hydration afford two diol units, which generate compound 246 (Fig. 99) by intramolecular dehydrations. 

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