Organic Chemistry Important Reagents-Edit
Organic Chemistry Important Reagents-Edit
Organic Chemistry Important Reagents-Edit
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Organic Chemistry – Specific Name Reactions
Sandmeyer Reaction
The Cl , Br and CN nucleophiles can easily be introduced in the benzene ring of benzene
diazonium salt in the presence of Cu(I) ion. This reaction is called Sandmeyer reaction.
Gatterman Reaction
Chlorine or bromine can be introduced in the benzene ring by treating the benzene diazonium
salt solution with corresponding halogen acid in the presence of copper powder. This is referred
as Gatterman reaction.
Note: The yield in Sandmeyer reaction is found to be better than Gattermann reaction.
Balz-Schiemann Reaction
When arenediazonium chloride is treated with fluoroboric acid, arene diazonium fluoroborate is
precipitated which on heating decomposes to yield aryl fluoride.
Finkelstein Reaction
Alkyl iodides are often prepared by the reaction of alkyl chlorides/ bromides with NaI in dry
acetone. This reaction is known as Finkelstein reaction.
Note: This reaction in forward direction can be favoured by precipitating NaX formed in dry
acetone (according to Le Chatelier’s principle).
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Swarts Reaction
Heating an alkyl chloride/bromide in the presence of a metallic fluoride such as AgF, Hg2F2,
CoF2 or SbF3 gives alkyl fluorides. The reaction is termed as Swarts reaction.
Note: Finkelstein Reaction and Swarts Reaction are known as halogen exchange reaction.
Wurtz Reaction
Alkyl halides react with sodium in dry ether to give hydrocarbons containing double the number
of carbon atoms present in the halide. This reaction is known as Wurtz reaction.
Wurtz-Fittig Reaction
A mixture of an alkyl halide and aryl halide gives an alkylarene when treated with sodium in dry
ether and is called Wurtz-Fittig reaction.
Fittig Reaction
Aryl halides also give analogous compounds when treated with sodium in dry ether, in which
two aryl groups are joined together. It is called Fittig reaction.
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Note: Aromatic carboxylic acids do not undergo Friedel-Crafts reaction because the carboxyl
group is deactivating and the catalyst aluminium chloride (Lewis acid) gets bonded to the
carboxyl group.
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Friedel-Crafts acylation reaction
The reaction of benzene with an acyl halide or acid anhydride in the presence of Lewis acids
(AlCl3) yields acyl benzene.
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Reimer-Tiemann Reaction
On treating phenol with chloroform in the presence of sodium hydroxide, a –CHO group is
introduced at ortho position of benzene ring resulting salicylaldehyde. This reaction is known as
Reimer - Tiemann reaction.
Kolbe’s Reaction
Phenol with sodium hydroxide gives sodium phenoxide ion which with carbon dioxide in acidic
medium results hydroxybenzoic acid (salicylic acid). This is known as Kolbe’s reaction.
Rosenmund Reduction
Acyl chloride (acid chloride) is hydrogenated over catalyst, palladium on barium sulphate. This
reaction is called Rosenmund reduction.
Stephen reaction
Nitriles are reduced to corresponding imine with stannous chloride in the presence of
hydrochloric acid, which on hydrolysis give corresponding aldehyde. This reaction is called
Stephen reaction.
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Etard reaction
Chromyl chloride oxidizes methyl group to a chromium complex, which on hydrolysis gives
corresponding benzaldehyde. This reaction is called Etard reaction.
Clemmensen Reduction
The carbonyl group of aldehydes and ketones is reduced to CH2 group on treatment with
zinc- amalgam and concentrated hydrochloric acid. This is known as Clemmensen
reduction.
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Tollens’ test
On warming an aldehyde with freshly prepared ammoniacal silver nitrate solution (Tollens’
reagent), a bright silver mirror is produced due to the formation of silver metal. The aldehydes
are oxidised to corresponding carboxylate anion. The reaction occurs in alkaline medium.
Fehling’s test
Fehling reagent comprises of two solutions, Fehling solution A and Fehling solution B. Fehling
solution A is aqueous copper sulphate and Fehling solution B is alkaline sodium potassium
tartarate (Rochelle salt). These two solutions are mixed in equal amounts before test. On heating
an aldehyde with Fehling’s reagent, a reddish brown precipitate is obtained. Aldehydes are
oxidised to corresponding carboxylate anion. Aromatic aldehydes do not respond to this test.
Aldol reaction
Aldehydes and ketones having at least one α-hydrogen undergo a reaction in the presence of
dilute alkali as catalyst to form β-hydroxy aldehydes (aldol) or β-hydroxy ketones (ketol),
respectively. This is known as Aldol reaction. The name aldol is derived from the names of the
two functional groups, aldehyde and alcohol, present in the products.
Aldol condensation.
The aldol and ketol readily lose water to give α,β-unsaturated carbonyl compounds which are
aldol condensation products and the reaction is called Aldol condensation.
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Cross aldol condensation:
When aldol condensation is carried out between two different aldehydes and / or ketones, it is
called cross aldol condensation. If both of them contain α-hydrogen atoms, it gives a mixture of
four products.
Cannizzaro reaction:
Aldehydes which do not have an α-hydrogen atom, undergo self oxidation and reduction
(disproportionation) reaction on treatment with concentrated alkali. In this reaction, one molecule
of the aldehyde is reduced to alcohol while another is oxidised to carboxylic acid salt.
Kolbe electrolysis
An aqueous solution of sodium or potassium salt of a carboxylic acid on electrolysis gives alkane
containing even number of carbon atoms.It is decarboxylation reaction. The reaction is known
as Kolbe electrolysis.
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Note: Aromatic primary amines cannot be prepared by this method because aryl halides do not
undergo nucleophilic substitution with the anion formed by phthalimide.
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Carbylamine reaction
Aliphatic and aromatic primary amines on heating with chloroform and ethanolic potassium
hydroxide form isocyanides or carbylamines which are foul smelling substances. This reaction is
known as carbylamines reaction or isocyanide test.
Note: Secondary and tertiary amines do not show this reaction and is used as a test for primary
amines.
Hinsberg’s Test
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Coupling Reactions:
Benzene diazonium chloride reacts with phenol in which the phenol molecule at its para position
is
coupled with the diazonium salt to form p-hydroxyazobenzene. This type of reaction is known
as coupling reaction.
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