Organic Starting Material and Other Volatiles

Volatile impurities in an ionic Hquid may have different origins. They may result from solvents used in the extraction steps during the synthesis, from unreacted starting materials from the alkylation reaction (to form the ionic liquid s cation), or from any volatile organic compound previously dissolved in the ionic liquid. 

In theory, volatile impurities can easily be removed from the nonvolatile ionic liquid by simple evaporation. However, this process can sometimes take a considerable time. Factors that influence the time required for the removal of all volatiles from an ionic liquid (at a given temperature and pressure) are a) the amount of volatiles, b) their boiling points, c) their interactions with the ionic liquid, d) the viscosity of the ionic liquid, and e) the surface of the ionic hquid. 

A typical example of a volatile impurity that can be found as one of the main impurities in low-quality ionic Hquids with aLkylmethylimidazolium cations is the methylimidazole starting material. Because of its high boiling point (198 °C) and its strong interaction with the ionic Hquid, this compound is very difficult to remove from an ionic hquid even at elevated temperature and high vacuum. It is therefore important to make sure, by use of appropriate alkylation conditions, that no unreacted methylimidazole is left in the final product. 

Traces of bases such as methylimidazole in the final ionic liquid product can play an unfavorable role in some common applications of ionic liquids (such as bipha-sic catalysis). Many electrophilic catalyst complexes will coordinate the base in an irreversible manner and be deactivated. 

A number of different methods to monitor the amount of methylimidazole left in a final ionic liquid are known. NMR spectroscopy is used by most academic groups, but may have a detection limit of about 1 mol%. The photometric analysis described by Holbrey, Seddon, and Wareing has the advantage of being a relatively quick method that can be performed with standard laboratory equipment [13]. This makes it particularly suitable for monitoring of the methylimidazole content during commercial ionic liquid synthesis. The method is based on the formation and colorimetric analysis of the intensely colored complex of 1-methylimidazole with copper] 11) chloride. 

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In the late nineteenth century and up to World War II coal was the major starting material for the organic chemical industry. When coal is heated in the absence of oxygen, coke and volatile by-products called coal tars are created. All sorts of organic chemicals can be isolated from coal tar - benzene, toluene, xylenes, ethylbenzene, naphthalene, creosotes, and many others (including Hofmann and Perkin s aniline). The organic chemical industry also draws upon other natural products, such as animal fats and vegetable oils, and wood by-products. 

This colorless, volatile, and air-stable solid is the starting material for synthesis of many Cr derivatives. Commercially available, it is seldom synthesized however, Reductive Carbonylation (e.g. equation 5) gives higher yields and is more reliable than other methods. Cr(CO)6 melts at 130 °C, sublimes at room temperature in vacuo, and dissolves slightly in organic solvents. It exhibits perfect octahedral symmetry, as determined by electron and neutron diffraction and X-ray crystallography. The IR spectrum of this material in CCI4... 

Carbon disulfide is a volatile organic solvent, used mainly as a starting material in rayon manufacture in the viscose process. It was important historically in the cold vulcanization of rubber. Although no longer used in this form, carbon disulfide is still a major industrial precursor in rubber industry chemical synthesis and has a number of other industrial applications. Carbon disulfide is also widely used as a solvent in a variety of laboratory settings. Carbon disulfide is a metabolite of the drug disulfiram (see pp 186) and is a spontaneous breakdown by-product of the pesticide metam sodium. 

The tris(silylamide) complexes, [(Me3Si)2N]3Ln, are isolated from a pentane solution as needle crystals readily hydrolysed on air. They are well soluble in common organic solvents and posses a rather high volatility. These properties as well as the simplicity of their synthesis and the high reactivity of Ln-N bonds make REM amides one of most suitable starting material for the preparation of other organic and inorganic compounds of lanthanoids. The last method can be used as well for the preparation of mixed chloride/amides of lanthanoids [29]. 

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