CBSE Class 12 Chemistry Aldehydes Ketones And Carboxylic Acids Notes Set D

 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 

NAME REACTIONS 

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.GATTERMAN-KOCH REACTION 

On treating toluene with chromyl chloride(CrO2Cl2), 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.

8. ALDOL CONDENSATION

Aldehydes and ketones having at least one α-hydrogen condense in the presence of dilute alkali as catalyst to form β-hydroxy aldehydes (aldol) or β-hydroxy ketones (ketol) which on condensation forms αβ unsaturated aldehyde or ketone.

10. CANNIZARO REACTION

Aldehydes which do not have an α-hydrogen atom, undergo self oxidation and reduction (dispropotionation) reaction on treatment with concentrated alkali,to yield carboxylioc acid salt and an alcohol respectively.

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