Oxidation and reduction reactions of aldehydes and ketones

(a) OXIDATION BY DILUTE HNO3, KMnO4 AND K2Cr2O7: aldehydes are oxidised straight through to the corresponding carboxylic acid by any of these three oxidants, provided the reaction medium is acidic -- e.g. R-CHO, with K2Cr2O7 and dilute H2SO4, gives R-COOH directly. Ketones, by contrast, genuinely RESIST oxidation under these same conditions, because oxidising a ketone would require breaking a strong carbon-carbon bond rather than simply removing a hydrogen the way an aldehyde does; but sufficiently STRONG oxidants -- CrO3, alkaline KMnO4, or hot concentrated HNO3 -- CAN still oxidise a ketone, by actually cleaving one of its C-C bonds, giving a genuine MIXTURE of two carboxylic acids, each carrying fewer carbon atoms than the original ketone did. Worked examples: acetone (a SYMMETRICAL ketone) with CrO3 gives only ONE product, acetic acid, by symmetry (both sides of the cleavage give the identical fragment); but butan-2-one (an UNSYMMETRICAL ketone) with CrO3 gives a genuine mixture of TWO different acids, acetic acid AND propanoic acid, since its two sides of the carbonyl are chemically different. (b) CLEMMENSEN AND WOLF-KISHNER REDUCTION: both of these named reactions reduce the carbonyl group, >C=O, all the way through to a plain methylene group, -CH2-, with the oxygen effectively replaced by two hydrogen atoms in the process. CLEMMENSEN REDUCTION uses zinc amalgam together with concentrated hydrochloric acid, under heat: >C=O + 4[H], with Zn-Hg/conc.HCl and heat, gives -CH2- + H2O; worked examples show acetone reduced this way straight through to propane, and propanal reduced through to propane as well. WOLF-KISHNER REDUCTION instead proceeds in two distinct stages: the carbonyl compound FIRST forms a hydrazone with hydrazine (H2N-NH2), losing a molecule of water in the process (>C=O + H2N-NH2 gives >C=N-NH2 + H2O); that hydrazone is THEN heated, separately, with potassium hydroxide in a high-boiling solvent such as ethylene glycol, which drives off nitrogen gas and gives the final methylene product (>C=N-NH2, with KOH/HO-CH2-CH2-OH and heat, gives -CH2- + N2). Worked examples: ethyl phenyl ketone reduced this way gives n-propylbenzene, and propanal similarly reduces through to propane. The Wolf-Kishner route is specifically valued, and specifica …