CHEMISTRY TEXTBOOK

Can you think?

What is the alcohol formed when

benzoyl chloride is reduced with

pure palladium as the catalyst?

hydrochloric acid which on acid hydrolysis

give corresponding aldehydes. This reaction

is called Stephen reaction.

R - C ≡ N + 2[H] SnCl^2 , HCl R - HC = NH.HCl

(Alkane nitrile) (imine hydrochloride)

H^3 O

⊕

R - CHO + NH 4 Cl

(Aldehyde)

For example,

H 3 C - C ≡ N + 2[H]

SnCl 2 , HCl

(reduction)^

(Ethanenitrile)

CH 3 - HC = NH.HCl H^3 O

⊕

CH 3 -CHO+NH 4 Cl

(ethanimine hydrochloride) (Ethanal)

C 6 H 5 - C ≡ N + 2[H] SnCl^2 , HCl

(Benzonitrile)

C 6 H 5 - HC = NH.HCl H^3 O

⊕

C 6 H 5 -CHO+NH 4 Cl

(Benzanimine hydrochloride) (Benzaldehyde)

Alternatively, nitriles are also reduced by

diisobutylaluminium hydride (DIBAl-H)

or AlH (i-Bu) 2 to imines followed by acid

hydrolysis to aldehydes. An advantage of this

method is that double or triple bond present in

the same molecule is not reduced..

H 3 C - CH = CH - CH 2 - C ≡ N

AIH (i-Bu) 2

H 3 O⊕

(Pent-3-enenitrile)

H 3 C - CH = CH - CH 2 - CHO

(Pent-3-enal)

• Preparation of ketones from nitriles :
  Ketones are prepared by reacting nitriles
  with Grignard reagent in dry ether as solvent
  followed by acid hydrolysis.

Use your brain power

Write the structure of the

product formed on Rosenmund

reduction of ethanoyl chloride and benzoyl

chloride.

b. Preparation of ketone (aliphatic and
aromatic) from acyl chloride :

i. Preparation of aliphatic ketones from
acyl chloride: ketones are obtained from acyl
chloride by reaction with dialkyl cadmium
which is prepared by the treatment of cadmium
chloride with Grignard reagent.

2R - MgX + CdCl 2 R 2 Cd + 2Mg(X)Cl

2R' - COCl + R 2 Cd 2 R' - CO - R
(Acyl chloride) (Ketone)

• CdCl 2

For example,

2CH 3 - COCl + (CH 3 ) 2 Cd
(Ethanoyl chloride) (Dimethyl cadmium)
2CH 3 -CO-CH 3 + CdCl 2
Propanone (Acetone)

2C 6 H 5 - COCl + ( CH 3 ) 2 Cd
(Benzoyl chloride) (Dimethyl cadmium)
C 6 H 5 - CO - CH 3 + CdCl 2
(Acetophenone)

ii. Preparation of aromatic ketones from
acyl chloride : Aromatic ketones are prepared
by Friedel Craft's acylation reaction (Std. XI
Chemistry Textbook, Chapter 15, sec. 15.4.6)

b. From nitriles : Aldehydes and ketones both
can be obtained from nitriles but by different
reaction.

• Preparation of aldehydes from nitriles :

Nitriles are reduced to imine hydrochloride
by stannous chloride in presence of

H 3 C - C ≡ N + H 3 CMgCl dry ether

CH 3 - C = NMgCl

H 3 C

H 3 O⊕

CH 3 - CO - CH 3

+ NH 3 + Mg(Cl)OH

(Ethanenitrile)

(Acetone)

C H^3 O⊕

6 H 5 - C = NMgBr

C 6 H 5

C 6 H 5 - C ≡ N + C 6 H 5 - MgBr dry ether

C 6 H 5 - CO - C 6 H 5

+ NH 3 +Mg(Br)OH

(Benzonitrile)

(Benzophenone)