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Reactive Exns
When the extracting solvents are apolar, their ability to extract the polar compounds such as organic acids, amino acids, and phenols is low.
About 30 years ago extraction with the help of a chemical reaction or strong physical interaction between the extracting solvent and the sample was used to solve the problem in LLE.
In this method usually a small amount of a reactant is added to the extracting solvent to:
1) Increase solvent polarity
2) Have specific interactions with analyte
3) Increase the extraction selectivity
Applications of Reactive Extractions in LLE Systems
1) Separation and purification of heavy metal ions such as platinum, Ga (e.g. selective extraction of Ga from coal), etc using organic ligands or strong Lewis bases
2) Extraction of organic compounds from aqueous solutions have also been extensively studied:
a) Separation of amino acids using bis(2-ethylhexyl) phosphoric acids
b) Separation of Penicillin using Amberlite LA-2
Reactive Extraction of Carboxylic Acids in a LLE system
Organic extractants already used are divided into 3 major categories:
1- Hydrocarbons and oxygen containing extractants.
2- Solvents containing oxygen and phosphorous.
3- High molecular weight aliphatic amines
a)higher efficiency
b)cheaper than organophosphorous solvents
c)reversible reaction with carboxylic acids
d)high selectivity
Use of amines in the reactive extraction is limited to tertiary amines with long alkyl chain
primary amines are water soluble
secondary amines are changed into imines when distilled or their pH is changed dramatically for separation of amine from acid
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