Organic compounds, extraction using green solvents

Carbon dioxide, 4 an important green house gas,45 is obtained in combustion of carbon and hydrocarbons, calcination of CaC03, and so on. It forms complexes with transition metals (Section 7-14) and inserts into MH and other bonds (Section 21-3). The gas is very soluble in ethanolamines, which are used to scrub C02 from gas streams. Liquid C02 at pressures up to 400 bar is a solvent for some organic compounds and is used to extract caffeine from coffee beans many studies of other applications of supercritical C02 have been conducted.46... 

Another green approach involving technology is the use of solid-phase extraction (SPE) columns (see Technique 12, Section 12.14). Using SPE columns, extractions such as removing caffeine from tea can be carried out more quickly and with less-toxic solvents. In other applications, SPE columns can be used to carry out the synthesis of organic compounds more efficiently with less use of toxic reagents. 

Most of the recent literature in this field is concerned with synthetic organic reactions, supramolecular chemistry and crystal engineering. However, solvent free approaches can also be used in the extraction of natural products, although less information is available in the mainstream literature. Juice extractors can be used to afford aqueous solutions of biologically active compounds from undried plant material. An extract of Capsicum annum L. was recently prepared in this way, and then used in the green synthesis of silver nanoparticles. The actual synthesis of the nanoparticles was conducted in the aqueous phase and therefore this work will not be discussed further here. However, this solvent free approach to extraction is probably worthy of greater representation in the green chemistry literature. 

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