Extractive distillation with soluble salt

Saponification of esters. Aqueous sodium hydroxide method. To hydrolyse an ester of an alcohol, reflux 5-6 g. with 50 ml. of 20 per cent, sodium hydroxide solution for 1-2 hours or until the ester layer disappears. Distil the alkahne mixture and collect about 6 ml. of distillate. This will contain any volatile alcohol formed in the saponification. If the alcohol does not separate, i.e., is water-soluble, saturate the distillate with sohd potassium carbonate an upper layer of alcohol is then usually formed. (The alcohol may be subsequently identified as the 3 5-dinitrobenzoate see Section 111,27,2.) Cool the residual alkahne mixture, and acidify it with dilute sulphuric acid. If no crystalline acid is precipitated, the acid may frequently be isolated by ether extraction, or it may be distilled from the acidified solution and isolated from (or investigated in) the distfllate. (The acid may be subsequently identified, e.g., as the S benzyl wo-thiuronium salt see Section 111,85,2.)... 

With dinitriles a slightly different procedure is necessary due to their water solubility. After the reaction has cooled, 150 ml of chloroform is added to the flask, and this mixture is then poured into saturated salt solution. Enough water is added to dissolve precipitated salt and the chloroform layer is separated. The aqueous layer is extracted once with chloroform. The combined extracts are then washed twice with salt solution, dried, and distilled. 

This process can also be applied to purification of the substance if it is an acid, a phenol or a base, by extracting into the appropriate aqueous solution to form the salt which, after washing with pure solvent, is again converted to the free species and re-extracted. Paraffin hydrocarbons can be purified by extracting them with phenol (in which aromatic hydrocarbons are highly soluble) prior to fractional distillation. 

Trimethylborate forms an azeotropic mixture with the excess of methyl alcohol, which boils approximately at 55 °C. To separate the mixture and extract pure trimethylborate, there are several techniques to flush methyl alcohol with sulfuric acid to separate methyl alcohol with the help of calcium chloride, lithium chloride or other alcohol-soluble salts to distil methyl alcohol (in the form of azeotropic mixture with trimethylborate, which boils under a lower temperature than both components) with subsequent extraction of trimethylborate with mineral oil, etc. 

One possibility to separate the enantiomers of rac- 1-phenylethanamine is to form diastereomeric salts with an enantiomerically pure chiral acid, e.g. (R,R) tartaric acid or (S)-2-hydroxysuccinic acid. These can be separated from each other by recrystallisation as a consequence of their different solubilities. Note, however, that the separation process is not complete at this stage since the amines are now present as salts. The separated salts must be treated with a strong base, e.g. aqueous sodium hydroxide, to convert them back to the free amines which can then be extracted into an organic solvent. After drying the extract distillation of the solvent leaves the pure amine. 

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