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) .