morsagh
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Test for carboxylic acids
I need some good qualitative test for carboxylic acids and their salts but i know just about bicarbonate test (phenols give positive too, so i find
this just like test for acidity).
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byko3y
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Simple distillation of anhydrous compound (e.g. made from a dry salt and sulfuric acid) or ethir esterification product with alcohols; identification
by esterification with substituted alpha-diazo-acetophenones or alpha-bromo-acetophenones; salt of S-benzyl-thiouronium; ureide via carbodiimide or
urea+NaOEt+pyridine; conversion into amide via acyl chlorides.
But I'm pretty sure phenols can't react with alkali carbonates, unless there's something else in your mixture.
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battoussai114
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I'm with byko3y, deprotonating the phenol group isn't that easy. I'll look around for some reference, but yeah a test with carbonate or bicarbonate
should suffice.
------EDIT------
That was fast: http://www.chemguide.co.uk/organicprops/phenol/acidity.html
[Edited on 8-9-2015 by battoussai114]
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Praxichys
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macckone
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Praxichys chart is very useful.
to make it text searchable:
1) the reaction with phosphorous pentachloride is probably not available to most home chemists. But for those that have it, it will indicate an acid
or alcohol.
2) pH in water of the unknown. Carboxylic acids soluble in water will lower the pH. Most alcohols will not.
3) sodium carbonate test. Carboxylic acids will cause fizzing.
4) esterification test. Alcohols will form ethers in some cases but should be readily distinguishable by smell from carboxylic acids and their formed
esters. Basically mix equal parts with alcohol and unknown (1ml each) with a few drops of sulfuric acid. Heat to 50C on a water bath and hold for 5
minutes. Then neutralize with 20ml of sodium carbonate solution. Modifications would be using less of the reactants and using less sodium carbonate.
Side note.
Phenol should be distiguishable from most carboxylic acids based on melting point and smell. Phenol will also sublimate while carboxylic acids will
not. This last property is useful for isolating phenol from mixtures.
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