Used to purify compounds with small amounts of

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Used to purify compounds with small amounts of impurity Involves dissolving the crude solid in a hot solvent at high concentration More solute dissolves in hot solvents As the solvent cools, the compound begins to crystallize but impurities remain in the solution Impurities aren’t concentrated in the solvent Purer solid is collected by filtration
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Technique Choose a solvent that is sparingly soluble at room temperature but very soluble at higher temp Add small amounts of hot solvent to crude solid until fully dissolved
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Technique Allow solvent to cool to room temp May further cool in ice bath Vacuum filter crystals
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Things to keep in mind: Crude solid should only have minor amount of impurity Requires a slow cooling and crystallizing process Often times allows hydrates to form which can be difficult to dry
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Task: Separate these 3 compounds using extraction techniques We could use partition coefficient (K) values, but… Another technique is to make a salt (water soluble) Can separate acids from bases or neutrals pKa determines acid or base to use
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Acid wash –removes aniline Base wash –removes benzoic acid Neutral is left in the organic layer pKa of aromatic H ~43
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The acid and base have been isolated as salts Need to convert them back to their original species We will use the insolubility of the acid and base in water to our advantage Benzoic acid will crystallize out of water solution NaCl and remaining HCl are water soluble Filtration to purify acid
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Flow Chart Percent Recovery (no reaction performed) = (mass recovered / mass initial) x 100 Do not confuse with % yield Percent Yield (when a reaction is performed) =(mass isolated / theoretical yield) x 100 Take melting points and IR’s Annotate the spectra…major functional groups Compare to literature (annotate this too)
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