CHEMISTRY TEXTBOOK

(ResonatedVirtue) #1
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)
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