Question

How do you separate acetic acid and formic acid; and how do you separate acetaldehyde from formaldehyde?

Answer 1

So you want to (i) separate acetic acid and formic acid; and (ii) separate the formyl compounds. (i) is trivial; (ii) is a non-trivial process.

Explanation:

Acetic acid and formic acid are relatively easy. They have an appreciable difference in boiling point (`20` `""^@C`), which should be (almost) enough for fractional distillation. Extraction with petroleum ether would also be feasible and more successful. Methanol is INSOLUBLE in hexanes; ethanol is SOLUBLE. Formic acid (as I recall) should be relatively insoluble in hexanes also; whereas acetic acid should be soluble.

Why this differential solubility? This is an important inorganic principle in that length of the carbon chain influences the physical properties of the molecule. Short chains such as methanol or formic acid should have very limited solubility in NON-POLAR solvents.

So how do you separate the aldehydes? This is non-trivial. I think you must use preparative column chromatography. You must run the aldehydes down a column in a suitable solvent and rely on their different adsorption to the column. You will find details to do this nowhere. You must design and perform the experiment yourself, and do what works.

Note that if this is not a practical problem, and simply a conceptual question, the answers above are acceptable. If you actually need to do the experiment, this is non-trivial. Chromatography takes %££# hours.

Other chemists here might have input, if this is actually a practical problem. All suggestions welcome. Cheers.