Chlorine hydrates

Chlor-hydrat, n. hydrochloride chlorine hydrate. -hydrin, n. chlorohydrin. 

In 1810 Davy discovered chlorine hydrate when cooling a saturated solution of chlorine in water below 9°C. Research by Villard, de Forcrand and many others subsequently showed that this type of hydrate can be formed by water with a large number of gases or volatile liquids such as Cl2, Br2, H2S, C02, CH4, CHC13 and again the inert gases A, Kr, Xe. It was further established that the process... 

The mechanism responsible for the formation of gas hydrates became clear when von Stackelberg and his school 42 49 in Bonn succeeded in determining the x-ray diffraction patterns of a number of gas hydrates and Claussen6 helped to formulate structural arrays fitting these patterns. Almost simultaneously Pauling and Marsh26 determined the crystal structure of chlorine hydrate. 

The diffraction pattern of the sample of chlorine hydrate consisted of powder lines on which were superimposed a large number of more intense single-crystal reflections for some planes only the latter were visible. The intensities of the lines were estimated by comparison with a previously calibrated powder photograph, and were averaged for several films pre-... 

H. W. B. Eoozeboom has measured the solubility of chlorine and bromine hydrates in water and expressed his results in terms of grams of chlorine per 100 grms. of soln. He found that 100 grms. of soln. contain 0 492 grm. of chlorine at —0 24°, at which temp, the solid phase present is a mixture of ice and chlorine hydrate, C12.8H20. Between 0° and 28 7° the solid phase is the hydrate alone, and the soln. has... 

In the system C12+H20, there are two components, just indicated two solid phases—ice and chlorine hydrate, C12.8H20 two soln.—one a soln. of water in an excess of chlorine, Sol. I, and a soln. of chlorine in an excess of water, Sol. II and a gas phase—a mixture of chlorine and water vapour in varying proportions. The system has not been completely studied, but sufficient is known to show that the equilibrium curves take the form shown diagrammatically in Fig. 20. The two invariant systems L and B have four coexisting phases—... 

F. Wohler 23 found that when chlorine hydrate in a sealed glass tube is exposed to sunlight, it forms two liquids, but does not decompose, since, after a summer s exposure, the two liquids re-form chlorine hydrate when winter returns. The same phenomena occur if the chlorine hydrate is warmed and cooled under similar conditions. A cone. soln. of chlorine water is far less prone to decomposition on exposure to sunlight than is a more dil. soln. J. M. Eder found the same to be the case with bromine water, but he also found that a cone. soln. of chlorine water lost 53 95 per cent, of chlorine while a dil. soln. lost 41 87 per cent, under similar conditions, but he does not state the concentration very exactly. A. Pedler further showed that soln. more cone, than one mols. of chlorine with 64 mol. of water had not decomposed perceptibly after a two months exposure to tropical sunlight, and with that increasing dilution, the action became progressively greater, as illustrated in Table VII. 

Fig. 12-7.—The arrangement of water molecules in the chlorine hydrate crystal. Some of the water molecules are at the corners of pentagonal dodecahedra, as indicated. Some additional water molecules (circles) are needed to complete the structure. Hydrogen bonds are formed along the edges of the d decahedra, and also between adjacent dodecahedra and between the dodecahedra and the interstitial water molecules.

Fig. 12-8.—A portion of the hydrogen-bond framework in the chlorine hydrate crystal. The water molecules are grouped into tetrakaidecahedra as well as dodecahedra.

Clathrate-Cage Model. The final water model which is of major interest is based on clathrate hydrate cage structures. It was originally proposed by Pauling (116), who noted the existence of clathrate hydrates of many inert gases and suggested, by analogy to the chlorine hydrate,... 

However, unlike Davy s experiments, Priestley s temperature (17°F) of the gas mixture was below the ice point, so there is no unequivocal evidence that the frozen system was hydrate. There is also no record of validation experiments by Priestley consequently, Davy s independent discovery of chlorine hydrate is generally credited as the first observance. 

Ditte and Maumene disputed the composition of chlorine hydrates... 

In Table 1.2, the following pattern was often repeated (1) the discovery of a new hydrate was published by an investigator (2) a second researcher disputed the composition proposed by the original investigator and (3) a third (or more) investigator(s) refined the measurements made by the initial two investigators, and proposed slight extensions. As a typical example, in the case of chlorine hydrate after Davy s discovery in 1810, Faraday confirmed the hydrate (1823) but proposed that there were ten water molecules per molecule of chlorine. Then Ditte (1882), Maumene (1883), and Roozeboom (1884) re-examined the ratio of water to chlorine. 

Sir Humphry Davy discovery of chlorine hydrate 1823 - Michael Faraday formula of chlorine hydrate 1841 - C. Schafhautl study of graphite intercalates 1849 - F. Wohler /Lquinol H2S clathrate 1891 - Villiers and Hebd cyclodextrin inclusion compounds... 

A rather unusual instance of a hydrate of an element is chlorine hydrate, C12-8H20, which crystallizes from ice-cold water which is saturated with chlorine. This substance is clearly a molecular compound, for if these crystals are placed in a watch glass and allowed to come to room temperature, chlorine gas escapes and water containing only the amount of chlorine corresponding to an ordinary saturated solution is left. 

Contrast the formation of chlorine hydrate with the action of chlorine and water in sunlight. 

Nevertheless the analogy with clathrate compounds (p. 179) does not go further since it is just the xenon hydrate (1 at. press, at — 3.40 G) which is very much more stable than the argon hydrate (1 at. at —42.8°) likewise the bromine hydrate is more stable than the chlorine hydrate. 

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