CBSE Class 12 Chemistry Revision Aldehydes Ketones Carboxylic Acids.Learning the important concepts is very important for every student to get better marks in examinations. The concepts should be clear which will help in faster learning. The attached concepts made as per NCERT and CBSE pattern will help the student to understand the chapter and score better marks in the examinations.
ALDEHYDES, KETONES AND CARBOXYLIC ACIDS
• Aldehydes, Ketones and Carboxylic acids are important classes of organic compounds containing carbonyl groups.
• They are highly polar molecules.
• They boil at higher temperatures than the corresponding hydrocarbons and weakly polar compounds such as ethers.
• Lower members are soluble in water because they can form H-bond with water.
• Higher members are insoluble in water due to large size of their hydrophobic group.(alkyl/aryl)
•Aldehydes are prepared by-
a. Dehydrogenation of primary alcohols
b. Controlled oxidation of primary alcohols.
c. Controlled and selective reduction of acyl halides
• Aromatic aldehydes can be prepared by-
a. Oxidation of toluene with chromyl chloride or CrO3 in the presence of acetic anhydride
b. Formylation of arenes with carbon monoxide and Hydrochloric acid in the presence of anhydrous aluminiumchloride / Cuprous chloride
c. Hydrolysis of benzal chloride
• Ketones are prepared by-
a oxidation of secondary alcohols
b. Hydration of alkenes
c. Reaction acyl chlorides with dialkylcadmium
d. By friedel crafts reaction
• Carboxylic acids are prepared by –
a. oxidation of primary alcohols, aldehydes and alkenes
b. hydrolysis of nitriles
c. Treatment of grignard reagent with carbondioxide.
ALDEHYDES AND KETONES
1. ROSENMUND REDUCTION:
Acyl chlorides when hydrogenated over catalyst, palladium on barium sulphate yield aldehydes.
2. STEPHEN REACTION
Nitriles are reduced to corresponding imines with stannous chloride in the presence of Hydrochloric acid, which on hydrolysis give corresponding aldehyde.
3. ETARD REACTION
On treating toluene with chromyl chlorideCrO2Cl2, the methyl group is oxidized to a chromium complex, which on hydrolysis gives corresponding benzaldehyde.
4. GATTERMAN-KOCH REACTION
When benzene or its derivative is treated with CO and HCl in the presence of anhyd. aluminium chloride or cuprous chloride, it gives benzaldehyde or substituted benzaldehyde.
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