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MHT-CET : Chemistry Entrance Exam

MHT - CET : Chemistry - Aldehydes and Ketones Page 2

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6.

Chemical Properties

 

The order of reactivity of carbonyl compounds is HCHO > RCHO > RCOR.

  1. Addition Reactions

    a. Addition of Hydrogen Cyanide (HCN):
     
        

 

(i)  

H

l

R C = O

 

aldehyde

 + HCN  

base

H

l

  R  C OH

l

  CN

cyanohydrin

  1.  

 

(ii)  

R

l

R C = O

ketone

 

 

 + H CN 

base

R

l

  R C OH

l

  CN

cyanohydrin


  1. b. Addition of Sodium Bisulphite (NaHSO3):

 

(i)  

H

l

R C = O

 

 

 + NaHSO

H

l

  R C OH

l

        SO3Na

  1.  

 

(ii)  

R

l

R C = O

 

acetone

 + NaHSO

H

l

  R C OH

l

        SO3Na


  1. c. Addition of Ammonia (NH3) [Ammonolysis]:

 

 

(i) With Formaldehyde:

 6HCHO - 4NH3

(CH2)6N4

+ 6H2O

 

hexamethylene
tetramine
[Urotropine]

 


Urotropine is used as a drug for rheumatism, gout and urinary antiseptic.

(ii) With Acetaldehyde:



(iii) With Acetone:




  1. d. Addition of Grignard Reagent:

    (i) Formaldehyde + RMgX Primary alcohols
    (ii) Other aldehydes + RMgX Secondary alcohols

 

 

  1.  

 

 


  1. (iii) Ketones + RMgX Tertiary alcohols

 

 

  1.  

 

 

  1.  
  2. Condensation Reactions:

    Presence of >C = O group can be detected by these reactions.

    a. Action of Hydroxylamine [NH2OH]:

 

 


  1. b. Action of Phenyl Hydrazine (C6H5NHNH2):

 

(i)

  1.  

 

(ii)

  1.  
  2. Aldol Condensation

    This reaction is given by aldehydes and ketones containing a-hydrogen atom.

 

(i)

  1.  

 

(ii)


  1. NOTE: Since formaldehyde, benzaldehyde, trimethyl acetaldehyde, etc. do not contain an
    a-hydrogen atom, they do not undergo aldol condensation.

 

 

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