HALIDES OF SULPHUR

Comparatively little kinetic work has been done on the halides of sulphur. As in the case of the nitrogen, the greatest attention has been given to the fluorides, and kinetic studies of SF6 and S2F10 are reported below. At the time of writing no other sulphur halides have been investigated in sufficient detail to warrant 

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Sulphur exhibits its highest oxidation state +6 in sulphur hexafluoride. Though a number of halides of sulphur are known (SF, SCl, SClj etc.) only hexafluoride is the stable compound among hexahalides. Hexachloride, hexabromide and hexaiodide are not known. This may be attributed to the small size of the fluorine atom. 

Nickel forms yellow anhydrous halides NiXjlX = F. Cl. Br) and a black iodide Nil2 all these halides are made by direct combination of the elements, and the chloride by reaction of sulphur dichloride oxide with the hydrated salt. All dissolve in water to give green solutions from which the hydrates can be crystallised the solutions contain the ion [NifHjOls], and the chloride crystallises as NiCl2.6H2O, nickel(II) chloride hexahydrate. 

A. Amino-derivatives.—The reactions of sulphur halides with the mono-amino-derivative, NaPgFs NHa, have been described in which the phos-phazene ring stays intact despite very forcing conditions ... 

When an organic compound is heated with a mixture of zinc powder and sodium carbonate, the nitrogen and halogens are converted into sodium cyanide and sodium halides respectively, and the sulphur into. zinc sulphide (insoluble in water). The sodium cyanide and sodium halides are extracted with water and detected as in Lassaigne s method, whilst the zinc sulphide in the residue is decomposed with dilute acid and the hydrogen sulphide is identified with sodium plumbite or lead acetate paper. The t for nitrogen is thus not affected by the presence of sulphur this constitutes an advantage of the method. 

When iodine is dissolved in hydriodic acid or a soln. of a metallic iodide, there is much evidence of chemical combination, with the formation of a periodide. A. Baudrimont objected to the polyiodide hypothesis of the increased solubility of iodine in soln. of potassium iodide, because he found that an extraction with carbon disulphide removed the iodine from the soln. but S. M. Jorgensen showed that this solvent failed to remove the iodine from an alcoholic soln. of potassium iodide and iodine in the proportion KI I2, and an alcoholic soln. of potassium iodide decolorized a soln. of iodine in carbon disulphide. The hypothesis seemed more probable when, in 1877, G. S. Johnson isolated cubic crystals of a substance with the empirical formula KI3 by the slow evaporation of an aqueous-alcoholic soln. of iodine and potassium iodide over sulphuric acid. There is also evidence of the formation of analogous compounds with the other halides. The perhalides or poly halides—usually polyiodides—are products of the additive combination of the metal halides, or the halides of other radicles with the halogen, so. that the positive acidic radicle consists of several halogen atoms. The polyiodides have been investigated more than the other polyhalides. The additive products have often a definite physical form, and definite physical properties. J. J. Berzelius appears to have made the first polyiodide—which he called ammonium bin-iodide A. Geuther called these compounds poly-iodides and S. M. Jorgensen, super-iodides. They have been classified 1 as... 

In the halide group the most active lone pair is found in the phosphortrihalides. The stability of the boron complexes AXZ.BXZ decreases in the sequence PXj -> AsXz SbX3, no antimony compounds being observed. The halides of the sulphur group do not form compounds at all it seems improbable that the only reason for this behaviour is the disproportionation of these halides. 

The most important range for inorganio chemicals is between 1 40 and 1 70. But there are some substances, such as certain oxides and sulphides, whose indices lie well above this range, or even well above 2 0. Media which are liquid at room temperature and have such high refractive indices are not available, but certain mixtures of substances which solidify to glasses may be used. A little of the medium is melted on a microscope slide, the substance under examination is dusted into the melt, a cover-glass is pressed on, and the slide is then allowed to cool. Substances which have been used in this way are mixtures of piperine with arsenic and antimony tri-iodides (for indices 1 7-2 1), mixtures of sulphur and selenium (2-0-2-7)—for details, see Larsen and Berman (1934)—and mixtures of the halides of thallium (Barth, 1929). 

This behaviour contrasts with that of the halides of oxygon, which witli water produce halogen oxyaeids. Sulphur and selenium do not combine with iodine. 

Halogenation in the presence of sulphur, or by means of sulphur halides, is also available. When chlorine is conducted into a mixture of vanadium pentoxide and sulphur, or when powdered vanadium pentoxide is treated with sulphur monochloride vapours, an immediate reaction sets in, with formation of vanadium oxytrichloride.2 A quantitative yield of this compound is also obtained when vanadium trichloride is heated in oxygen at 500° to 600° C.3... 

Hydrated Vanadium Tri-iodide, VT3.6H20, is prepared by reducing, electrolytically, a solution of vanadium pentoxide, V2Os, in hydriodic add, until the product becomes green more hydriodic add is then added and the whole allowed to stand over lime and concentrated sulphuric add at 0° C. Small green needles separate, which have the same crystalline form as the hydrated trivalent halides of titanium, iron, and chromium. These crystals are extremely hygroscopic and deliquesce in air to a brown liquid8 which is extremely unstable. 

In the case of aromatic bodies the temperature has an important influence on the part of the molecules the chlorine or bromine will attack in the cold in the presence of carriers, the halogen enters the nucleus, while at the boiling point the side chain is attacked. The carriers most frequently used are iron, aluminium-mercury couple, iodine, halides of phosphorus, antimony, iron, aluminium, sulphur or pyridine. The halogen is always more active in sunlight, or in ultra-violet light. 

This recalls the parallel case of the addition of hydrogen halides to the unsaturated hydrocarbons observed by A. P. Eltekoff. As in the case of sulphurous and nitrous acids, the facts can also be explained by assuming the desmotropic change ... 

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