ALDEHYDES AND KETONES

Aldehydes and Ketones

  • Possess Carbonyl group (>C=0)

  • General formula - CnH2nO

  • Aldehydes and ketones are collectively called Carbonyl Compounds.

  • In Aldehydes, carbonyl group is linked to one Alkyl group and to one H-atom (monovalent)

  • In ketones,carbonyl group.is joined to two alkyl groups which may be same or different. It is a divalent group.

                                                   

                                               

                                                

Preparation of Aldehydes and Ketones-

By oxidation and dehydrogenation of alcohols

1. Oxidation of alcohols :

CH3−CH2−OH−→−−−−−−−−−−−−−−−−−ORPCC(or)PDCK2Cr2O7/H+(or)KMnO4 /H+CH3CHO PCC = Pyridiniumchlorochromate,(C5H5N+HCrO3Cl−) PDC = Pyridiniumdichromate

 

2. Dehydrogenation of alcohols:

(CH3COO)2Ca+(HCOO)2Ca−→−−−−−−−Drydistillation2CH3CHO+2C aCO3 Ethylalcohol

 

3. STEPHEN REACTION:

RCN+SnCl2+HCl→RCH=NH−→−H2ORCHO

Uses of aldehydes and ketones

USES (ACETALDEHYDE)                                                                                                                                           1. In the preparation of Acetic acid, Acetic anhydride ethyl acetate, chloral, 1,3-butadiene (used in Rubber) dyes and drugs.                                                                                                                                        2. Used as antiseptic inhalent in nose troubles.

 

USES (ACETONE)                                                                                                                                                     1) As a solvent for cellulose accetate, cellulose nitrate, celluloid, resins etc.                                                2) Used in storing of acetylene.

DISTINCTION OF ALDEHYDES AND KETONES

TEST

ALDEHYDE

KETONE

With Schiffs reagent

Pink colour

No colour

With Fehling’s Solution

Red ppt of Cu2O

No ppt

With Tollen’s Reagent

White silver ppt

No ppt

 

Hope you benefitted from this article, and it helped you clear your basics for aldehydes and ketones.