Gaseous Chloride Complexes Containing

Gaseous Chloride Complexes Containing Halogen Bridges Harold Schafer... 

The complex hydride reductions of nitriles to aldehydes compare favorably with the classical Stephen reduction which consists of treatment of a nitrile with anhydrous stannous chloride and gaseous hydrogen chloride in ether or diethylene glycol and applies to both aliphatic and aromatic nitriles [183,285, 1152]. An advantage of the Stephen method is its applicability to polyfunctional compounds containing reducible groups such as carbonyl that is reduced by hydrides but not by stannous chloride [1153]. 

A gaseous alkene was passed into a cooled autoclave containing the complex, initially with agitation, and later without. Later, when the alkene was admitted to a pressure of 5.6 bar at 2°C, a slight exotherm occurred, followed by an explosion. The autoclave contents were completely carbonised. Mixtures of ethylene, aluminium chloride and nitromethane had exploded previously, but at 75°C. 

Thus, the direct synthesis of phenylchlorosilanes produces a complex mixture, which, apart from phenyltrichlorosilane, diphenyldichlorosilane, phenyldichlorosilane and triphenylchlorosilane, also contains silicon tetrachloride, trichlorosilane, benzene, solid products (diphenyl and carbon) and a gaseous product (hydrogen). It also forms high-boiling polyolefines, which are part of tank residue and can deposit on contact mass, reducing its activity. It should be kept in mind that the production of phenylchlorosilanes requires silicon with a minimal impurity of aluminum, because the aluminum chloride formed contributes to the detachment of the phenyl group from phenylchlorosilanes at higher temperature. The harmful effect of aluminum chloride is counteracted by the addition of metal salts to contact mass, which form a nonvolatile and nonreactive complex with aluminum chloride. 

This causes problems with product recovery at the end of the reaction as the reaction mixture must be quenched in water to destroy this complex (Figure 16.13). This in turn leads to the production of heat due to the exothermic nature of the quench, large volumes of aluminium-containing aqueous effluent which is contaminated with organics, and gaseous hydrogen chloride emission. The suspected links between Alzheimer s disease and aluminium have also led to increased concern about the safe disposal of such effluent. 

Thallium is one of the most difficult elements for GF AAS, at least when it has to be determined in complex matrices, as will be shown in more detail in Sections 8.2.6 and 8.2.7. Thallium forms a chloride that is volatile at temperatures above 400 °C and easily lost without being atomized, as the gaseous molecule HCl is thermally very stable. Palladium, the most frequently used modifier to avoid such losses, has an absorption line close to the T1 line, causing a spectral interference. Iron, a frequent concomitant in many samples, also has an absorption line close to the T1 line. Finally, sulfur-containing samples produce a molecular absorption spectram with a pronounced rotational fine stfucture, which is another source of spectral interferences [141]. 

The vapor pressures of several organic chemicals are listed in Table 2.1. Comparing vapor pressures makes it possible to predict the relative tendencies of liquids to evaporate. Let s assume, for example, that pure benzene, pure dioxin, and pure vinyl chloride are discovered in three separate puddles at a hazardous chemical waste site. Based on the vapor pressures listed in Table 2.1,132 billion times more benzene should evaporate than dioxin, while 27.9 times more vinyl chloride should evaporate than benzene. The actual amounts that enter the atmosphere depend, of course, on how big the puddles are. If the benzene puddle is not 132 billion times larger than the dioxin puddle, it will not contribute 132 billion times more benzene. Other real-world factors may also affect the relative amounts of chemical that evaporates. Vapor pressures are determined in closed containers under standard conditions of temperature and pressure, yet at a typical hazardous chemical waste site, temperatures change continuously, and chemicals are exposed to the weather. In complex open systems such as these, equilibrium between the liquid and gaseous states of a chemical is never reached. Thus, vapor pressures determined under... 

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