Question

I have 4 possibilities for an unknown Aldehyde compound, what would be the best path to differentiate between them to find the right one in an Organic Chemistry lab.

Benzaldehyde

Nonyl Aldehyde

Phelyclacetalaldehyde

2-Hydroxybenzaldehyde (salicylaldehyde)

Answer 1

Specific Test for salicylaldehyde: Dissolve the sample in ethanol and add ferric chloride solution. If the solution turns to dark purple color, will indication for salicylaldehyde. moreover, if you add dil. HCl to this solution, it turns yellow.

Specific Test for nonanal (nonyl aldehyde): Add dilute KMnO₄ solution followed by addition of HNO₃ to get nonanoic acid. Excess KMnO₄ can be decolourized by oxalic acid. Then add glacial acetic acid few drops and heat it gently to get fruity grape or winey odour.

Specific Test for Phenyl acetaldehyde: It gives fehling test.

Specific Test for Benzaldehyde: It wont give any of the above reactions.