Melting gallium compounds

The gallium chalcogenide halides are hygroscopic compounds that decompose (without melting) at temperatures between 240 and 380°C to a mixture of chalcogenide and halide (see Table XVIII). The tel-luride halides are yellow, and the other compounds are colorless 160, 165). 

In contrast to the non-trivial routes for the syntheses of pure aluminum(I) or gallium(I) subhalides, indium(I) chloride or bromide can simply be prepared by melting mixtures of elemental indium and indium trihalides [39]. When these in-dium(I) halides were treated with bulky alkyllithium compounds, deep violet orga-noelement indium dusters (13-18) were obtained [Eq. (3)] [40, 41]. 

Gallium(III) bromide is a hygroscopic, white solid which sublimes readily and melts at 122.5° to a covalent, dimeric liquid. The solid is ionic and its electrical conductivity at the melting point is twenty-three times that of the liquid.5 The vapor pressure of the liquid at T°K is given by the equation log p(mm.) = 8.554 — 3129/T and the heat of dissociation of the dimer in the gas phase is 18.5 kcal./mol.3 At 125° the liquid has the following properties 5,6 density, 3.1076 dynamic viscosity, 2.780 c.p. surface tension, 34.8 dynes/cm. and specific conductivity, 7.2 X 10-7 ohm-1 cm.-1 Gallium(III) bromide readily hydrolyzes in water and forms addition compounds with ligands such as ammonia, pyridine, and phosphorus oxychloride. 

It will be evident from the preceding account that not all physical methods lend themselves equally well to the detection and specification of the gallium hydrides. There are, for example, obvious difficulties in trying to grow single crystals of a low-melting, thermally unstable compound, and, although the case of hypofluorous acid (62) shows what can be achieved ultimately, X-ray methods do not obviously commend... 

The elements of group Illb, gallium, indium, and thallium, are very rare and have small practical importance. Their principal compounds represent oxidation state - -8 thallium also forms thailous compounds, in which it has oxidation number - -1. Gallium is liquid from 29° C. its melting point, to 1700 C, its boiling point. It has found use as the liquid in quartz-tube thermometers, which can be used to above 1200° C. 

The polycondensation of BHET to PET proceeds in the melt at temperatures of 270-305 °C, under vacuum (< 1 mbar absolute pressure) and in the presence of Lewis acid metal compounds, such as titanium alkoxides, dialkyltin oxide, gallium oxide, germanium oxide, thallium oxide, lanthanide salts, and most commonly, antimony oxide [1,2, 22-26]. Under polymerization reaction conditions, these catalysts are generally converted to their alkoxides with ethylene glycol. Typical of such alkoxides is antimony(III) glycolate, the active catalyst for the majority of the world s PET production [27] (cf. Structure 1). 

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