MANA TV programme
KOLBE-SCHMITT REACTION
P. Kiran Kumar Lecturer in Chemistry SGA Government Degree College Yellamanchili Kolbe-Schmitt reaction
One of the finest experimentalists of the 19th century
Coined the word “synthesis”
Published the synthesis of acetic
acid(from carbon disulfide), first Adolph Wilhelm example of total synthesis of an Hermann Kolbe organic compound
Contributed a number of new chemical reactions- Kolbe electrolysis, Kolbe nitrile synthesis
Kolbe-Schmitt reaction
Received his PhD for his work on Sulfanilic acid
In 1884, he described the modification of the Kolbe reaction(carbonation was carried out under pressure which resulted Rudolf Schmitt in higher yields) Due to an explosion of a glass tube filled with hydrogen sulfide he lost his right eye in 1869 Kolbe-Schmitt reaction
Phenoxide ion undergoes electrophilic aromatic substitution reaction with carbon dioxide (under a pressure of 4 to7 atmospheres) to form an unstable intermediate which undergoes a proton shift(a keto- enol tautomerisation) to form sodium salicylate. Subsequent acidification of the mixture produces salicylic acid(o-Hydroxybenzoic acid)
p-Hydroxybenzoic acid is also obtained in small amount
Kolbe-Schmitt reaction
Phenol Salicylic acid (o-Hydroxybenzoic acid)
Carbon dioxide acts as the electrophile Kolbe reaction-Mechanism
Phenol Phenoxide ion Kolbe-Schmitt reaction-Mechanism(Cont’d)
The Phenoxide ion is resonance stabilized
Resonance structures of Phenoxide ion Kolbe-Schmitt reaction-Mechanism(Cont’d)
Phenoxide Carbon Sodium salicylate ion dioxide Kolbe-Schmitt reaction-Mechanism(Cont’d)
Sodium salicylate Salicylic acid Applications of Kolbe-Schmitt reaction
Salicylic acid obtained from the Kolbe reaction is used for the synthesis of
Aspirin (Acetylsalicylic acid)
Oil of winter green (Methyl salicylate) Aspirin (Acetylsalicylic acid)
One of the most widely used medicine in the world
Non-steroidal anti-inflammatory drug (NSAID)
Analgesic: pain reliever
Anti-inflammatory: Lowers inflammation
Antipyretic: Reduces fever Aspirin from salicylic acid Reaction of salicylic acid with acetic anhydride yields Aspirin
Salicylic acid Acetylsalicylic acid (aspirin) Methyl salicylate (Oil of winter green)
Present mainly in oil extracted from the leaves of wintergreen tree (Gaultheria procumbens)
Gaultheria procumbens Wintergreen oil Methyl salicylate Methyl salicylate (Oil of winter green)
Analgesic: relieve pain in joints and muscles
Antiseptic: used in Listerine
Flavoring agent: sweet wintergreen minty aroma flavour- used in foods, chewing gums and beverages Perfume
Cosmetic Methyl salicylate from salicylic acid Reaction of salicylic acid with Methanol yields Methyl salicylate(Oil of wintergreen)
Salicylic acid Methyl salicylate (Oil of winter green)