Preparation of Salicylic Acid By Hydrolysis of Methyl Salicylate .pdf

Preparation of Salicylic Acid By Hydrolysis of Methyl Salicylate .pdf

• 1.
  Preparation of SalicylicAcid By Hydrolysis of Methyl Salicylate Medicinal chemistryIII practice 4th stage Lab2 prepared by: Dr. Narmin hamaamin Hussen
• 2.
  Purpose  Hydrolyze theester known as methyl salicylate under base conditions in order to synthesize salicylic acid, a carboxylic acid. Techniques 1. • Hydrolysis of an ester 2. • Heating under reflux 3. • Filtration 4. • Crystallization 5. • Melting point
• 3.
   Methyl salicylateis an ester easily recognized by its odor and is known as oil of wintergreen because of its natural source.  This ester will be treated with aqueous base. The hydrolysis reaction that occurs will form methanol, water, and the sodium salt of salicylic acid.  Salts of organic compounds usually are soluble in water or will dissolve in water with a bit of heating. Later in the work-up, the salt is acidified with sulfuric acid to convert the organic salt into the protonated carboxylic acid Formula: C8H8O3 Boiling point: 220° C Molar mass: 152.1494 g/mol
• 4.
  Salicylic acid  Salicylicacid is a monohydroxy benzoicacid, a type of phenolic acid and a beta hydroxyacid.  Formula: C7H6O3  Melting point: 159° C  Molar mass: 138.121 g/mol Physical Features  Salicylic Acid is a white crystalline powder.  Soluble in acetone, ether, alcohol, boiling water, benzene and turpentine, sparingly soluble in chloroform benzene, slightly soluble in water.  Melts at 159°C. .
• 5.
  1. Salicylic aciditself has strong antiseptic and germicidal properties it is used as preservative for foods and pharmaceuticals. 2. S.A. has anti-inflammatory, analgesic and antipyretic properties. 3. In addition, it has good keratolytic properties which make it useful in the local treatment of warts, corns, hyperkeratosis, dandruff and psoriasis as well as in the treatment of fungal skin infections.
• 6.
  Salicylic acid caneither be prepared from phenol by the Kolbe’s process or from methyl salicylate by hydrolysis: A-Kolbe’s Synthesis The Kolbe–Schmitt reaction/Kolbe process is a carboxylation chemical reaction proceeded by heating sodium phenolate (the sodium salt of phenol) with carbon dioxide, then treating the product with sulfuric acid. The final product is an aromatic hydroxy acid which is also known as salicylic acid
• 8.
  B-Hydrolysis of methylsalicylate:  Methyl salicylate is an ester easily recognized by its odor and it is known as oil of wintergreen.  This ester will be treated with aqueous base. The hydrolysis reaction that occurs will form methanol, water, and the sodium salt of salicylic acid. Salts of organic compounds usually are soluble in water or will dissolve in water with a bit of heating. Later in the work-up, the salt is acidified with sulfuric acid to convert the organic salt into the protonated carboxylic acid. Therefore, the major organic products of this reaction are methanol and salicylic acid.
• 10.
  Procedure: Preparation of Salicylicacid by hydrolysis of Methyl- salicylate: 1. Place 5 ml of methyl salicylate in a flask(conical flask); add 50ml of 20% w/v aqueous solution of sodium hydroxide and mix well. 2. Heat the mixture for about 15-20 minute with stirring. 3. Cool and acidify the mixture with dilute H2SO4. Use blue litmus paper, the color changes from blue to pink. When the mixture becomes completely acidic, the salicylic acid will separate out. 4. Filtrate the mixture, allow drying.
• 11.
  M.Wt Wt  Methylsalicylate 152.15 5gm  Salicylic acid 138.12 ?  Theoretical weight = ?  Practical weight: by weighing your filtered product after drying. Practical weight %Yield = × 100% Theoretical
• 12.
  QUESTIONS 1. What isthe white solid formed immediately when the methyl salicylate was introduced to the aqueous solution of sodium hydroxide? 2. Write a good definition for what a catalyst is. Is the sodium hydroxide a catalyst in this experiment? Explain. 3. Why the phenolic hydroxyl group is converted to sodium salt during basic hydrolysis?