Hydroxy acids, detection paper chromatography

Hydroxamic acid gives a strong color with ferric chloride. This reaction is suitable for the detection of aldehydes in the presence of ketones. Aromatic / -hydroxyaldehydes, / -aminobenzaldehyde, vanillin, / -dimethyl-aminobenzaldehyde, salicylaldehyde, and aliphatic aldehydes with a hydroxy group in the y-position do not react. A positive reaction is observed with benzyl ketones in strongly alkaline media. It is necessary, therefore, to keep the mixture distinctly but not excessively alkaline. This reaction can be utilized for the separation of aldehydes from their mixture with ketones by converting the acid to its insoluble copper salt. Paper chromatography can be used for the identification of aldehydes in mixtures (41). 

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