Extraction, organic examples, with

Solvent extraction techniques are useful in the quantitative analysis of niobium. The fluoro complexes are amenable to extraction by a wide variety of ketones. Some of the water-insoluble complexes with organic precipitants are extractable by organic solvents and colorimetry is performed on the extract. An example is the extraction of the niobium—oxine complex with chloroform (41). The extraction of the niobium—pyrocatechol violet complex with tridodecylethylammonium bromide and the extraction of niobium—pyrocatechol—sparteine complex with chloroform are examples of extractions of water-soluble complexes. Colorimetry is performed on the extract (42,43). Colorimetry may also be performed directly on the water-soluble complex, eg, using ascorbic acid and 5-nitrosahcyhc acid (44,45). 

Contamination by water-insoluble reaction by-products such as l-amino-2,4-dibromoanthraquinone affects the quaUty of dyestuff signiftcandy. Therefore, several methods for purification have been reported. Examples are extraction of impurities with organic solvent (18), or precipitation of bromamine acid from concentrated (60—85%) sulfuric acid (26). 

In Pedersen s early experiments, the relative binding of cations by crown ethers was assessed by extraction of alkali metal picrates into an organic phase. In these experiments, the crown ether served to draw into the organic phase a colored molecule which was ordinarily insoluble in this medium. An extension and elaboration of this notion has been developed by Dix and Vdgtle and Nakamura, Takagi, and Ueno In efforts by both of these groups, crown ether molecules were appended to chromophoric or colored residues. Ion-selective extraction and interaction with the crown and/or chromophore could produce changes in the absorption spectrum. Examples of molecules so constructed are illustrated below as 7 7 and 18 from refs. 32 and 131, respectively. 

The rationale of validation experiments with fatty matrices is the high amount of fat extracted with many organic solvents. If analytes are not fat soluble and extraction is performed with water or aqueous buffer solutions, the troublesome fat is not extracted together with the analyte. Such extractions are typical for, e.g., the class of sulfonylurea herbicides. Examples exist where in such cases the applicability of an analytical method to fatty matrices was accepted by the authority without particular validation. 

However, when considering the use of acid or base in organic solvents for sample extraction, care must be taken to avoid potential artifacts that may arise from side reactions. For example, methylation of active hydroxyl groups or acidic functions on the analyte may sometimes occur when acidic methanol is used as the extractant. Another example is acetylation of an active alcohol on the analyte following partition of the analyte into ethyl acetate from aqueous solution acidified with glacial acetic acid. 

The extraction time has been observed to vary linearly with polymer density and decreases with smaller particle size [78,79]. The extraction time varies considerably for different solvents and additives. Small particle sizes are often essential to complete the extraction in reasonable times, and the solvents must be carefully selected to swell the polymer to dissolve the additives quantitatively. By powdering PP to 50 mesh size, 98 % extraction of BHT can be achieved by shaking at room temperature for 30 min with carbon disulfide. With isooctane the same recovery requires 125 min Santonox is extractable quantitatively with iso-octane only after 2000mm. The choice of solvent significantly influences the duration of the extraction. For example talc filled PP can be extracted in 72 h with chloroform, but needs only 24 h with THF [80]. pH plays a role in extracting weakly acidic and basic organic solutes, but is rarely addressed explicitly as a parameter. 

Example 10.2 An organic product with a flowrate of lOOOkg-h-1 contains a water-soluble impurity with a concentration of 6% wt. A laboratory test indicates that if the product is extracted with an equal mass of water, then 90% of the impurity is extracted. Assume that water and the organic product are immiscible. 

This book presents the basic techniques in the organic chemistry laboratory with the emphasis of doing the work correctly the first time. To this end, examples of what can go wrong are presented with admonishments, often bordering on the outrageous, to forestall the most common of errors. This is done in the belief that it is much more difficult to get into impossible experimental troubles once the student has been warned of the merely improbable ones. Complicated operations, such as distillation and extraction, are dealt with in a straightforward fashion, both in the explanations and in the sequential procedures. 

It is important to keep in mind that any extraction of organic matter from soil will include both naturally occurring organic matter and organic contaminants. Separating the two at some later stage of analysis is thus an essential analytical step. For example, extraction of soil with hexane or dichloromethane will extract both l,l,l-trichloro-2,2-di(4-dicholorphenyl)ethane (DDT), a contaminant, and octadecanoic acid, a natural fatty acid. Also, the herbicide 2,4-dichlorophenoxy acetic acid, a contaminant, and indole-3-acetic acid, a natural plant hormone, are both extracted by water (see Figure 12.3). These... 

There is a continuing demand for selective extractants that can be developed, for example, by tailor making organic molecules with pre-organized metal bind-... 

The extraction of most acids is accompanied by extraction of water. In the extraction of HNO3 by TBP into kerosene, many different species have been identified, several of which involve hydration. The ratio of acid adduct is not very predictable. For example, HCIO4 apparently is extracted into kerosene with 1-2 molecules of TBP, HCl into ethylether with one molecule of ethylether, etc. Also, the extracted acid may dimerize in the organic solvent, etc. Example 2 illustrates the complexity of the extraction of HNO3 by TBP into kerosene. 

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