Aldehydes, Ketones and Carboxylic Acids - Methods of preparation

Oxidation of Alcohols: Primary alcohols are oxidized to aldehydes using mild oxidizing agents like $PCC$ (Pyridinium chlorochromate) or $CrO_3$ in anhydrous media to prevent further oxidation to carboxylic acids. Secondary alcohols are oxidized to ketones using $K_2Cr_2O_7/H_2SO_4$ or $KMnO_4$.

Rosenmund Reduction: Acid chlorides ($R-COCl$) are reduced to aldehydes by hydrogenating them over a catalyst of palladium ($Pd$) supported on barium sulphate ($BaSO_4$), which is 'poisoned' with sulfur or quinoline to prevent further reduction to alcohols.

Stephen Reaction: Nitriles ($R-CN$) are reduced to corresponding imines with stannous chloride ($SnCl_2$) in the presence of $HCl$, which on hydrolysis yield aldehydes.

Etard Reaction: Toluene ($C_6H_5CH_3$) is oxidized to a chromium complex using chromyl chloride ($CrO_2Cl_2$) in $CS_2$, which on hydrolysis gives benzaldehyde ($C_6H_5CHO$).

Gatterman-Koch Reaction: Benzene or its derivatives react with carbon monoxide ($CO$) and hydrogen chloride ($HCl$) in the presence of anhydrous $AlCl_3$ or $CuCl$ to give benzaldehyde.

Preparation of Carboxylic Acids: Carboxylic acids can be prepared by the hydrolysis of nitriles ($R-CN$) or amides ($R-CONH_2$) in the presence of dilute mineral acids or alkalies as catalysts.

Grignard Reagent Method: Reaction of Grignard reagents ($R-MgX$) with dry ice (solid $CO_2$) followed by hydrolysis yields carboxylic acids with one more carbon atom than the starting Grignard reagent.