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Practical Organic Pharmaceutical Chemistry 4Th Stage (2Nd Course)

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Practical Organic Pharmaceutical Chemistry 4Th Stage (2Nd Course) Al-ISRAA University College Pharmacy Department ------------------------------------------------------------------------------------------------------------------------ Practical Organic Pharmaceutical Chemistry 4th Stage (2nd course) Lab. 1,2 Prepared by: Assist.Lecturer Ali Amjed 2017-2018 1 Al-ISRAA University College Pharmacy Department ------------------------------------------------------------------------------------------------------------------------ Cannizzaro Reaction Synthesis of Benzoic Acid and Benzyl Alcohol Both Alcohols and Organic Acids are Well Known for their Biological Actions which include: Antibacterial, Preservatives for Food and Pharmaceutics, Local Antiseptic, Local Anesthetic and Antipruritic. Benzyl Alcohol: Benzyl Alcohol can be Prepared by Hydrolysis of Benzyl Chloride with Sodium Hydroxide as shown below: Benzyl chloride Benzyl alcohol Properties of Benzyl Alcohol: 1) Colorless Liquid. 2) Moderate Solubility in Water. 3) Completely Miscible with Organic Solvents like Alcohol and Diethyl ether. 4) Boiling Point: 204-205 °C. 5) Have Low Vapor Pressure and Low Toxicity. 2 Al-ISRAA University College Pharmacy Department ------------------------------------------------------------------------------------------------------------------------ In Pharmaceutical , Benzyl Alcohol used at Low Concentration as: 1) Antiseptic (Bacterio Static). 2) Local Anesthetic. 3) Preservative for Food Industry. 4) In 10% Ointments is used as Antipruritic. In High Concentration Could Cause Hypotension and Respiratory Failure. Benzoic Acid: Benzoic Acid can be Prepared by the Oxidation of Toluene as shown below: Properties of Benzoic Acid: 1) Colorless Crystalline Solid. 2) Soluble in Boiled Water. 3) Melting Point: 122-123 °C. In Pharmaceutical Benzoic Acid used as: 1) Preservative For Food. 2) Cosmetic Industry (Lotions , Mouth Wash and Ointments). 3 Al-ISRAA University College Pharmacy Department ------------------------------------------------------------------------------------------------------------------------ Both Benzyl Alcohol and Benzoic Acid can be Prepared in the Laboratory by Cannizzaro Reaction by the Action of Strong Alkali (Sodium or Potassium Hydroxide) on Benzaldehyde. Benzaldehyde Benzoic acid Benzyl alcohol Cannizzaro Reaction: Is Oxidation-Reduction Reaction of Aldehydes Lacking α-Hydrogen Atoms and in the Presence of Strong Alkali to give a Mixture of Alcohol and Salt of Carboxylic Acid. One Molecule Oxidized to give Salt of Carboxylic Acid and Other Molecule Reduced to give Benzyl Alcohol. Mechanism: 4 Al-ISRAA University College Pharmacy Department ------------------------------------------------------------------------------------------------------------------------ Procedure: 1) Dissolve (3.6g) of Potassium Hydroxide in (5ml) of Water in a Reagent Bottle, then add (3.5ml) of Benzaldehyde. Cork the Bottle Securely and Shake the Mixture Vigorously until it has been Converted to a Thick Emulsion. Allow the Mixture to Stand Overnight, by which Time the Reaction Should have been Completed. 2) At the End of this Period Add (15-20ml) of Water to Dissolve the Potassium Benzoate Completely. 3) Transfer the Mixture to a Separatory Funnel to Separate Two Layer. Organic (Upper) Layer Benzyl Alcohol Aqueous (Lower) Layer Salt of Benzoic Acid 4) Rinse the Bottle with (10ml) of Ether and Again Add to the Solution in the Separatory Funnel to Dissolve Benzyl Alcohol Completely. 5) Shake Well and Separate the Lower Layer (Aqueous) and Wash it Two Times with 10 ml Ether to be Sure that all Benzyl Alcohol Removal from Aqueous Layer. 6) Combine the Ethereal Extracts and Save the Aqueous Layer which Contains the Salt of Benzoic Acid for Later Work-Up. 7) Distill the Ether of Combined Ethereal Extracts on a Water Bath (Until 10-15ml of Liquid Remains). 5 Al-ISRAA University College Pharmacy Department ------------------------------------------------------------------------------------------------------------------------ 8) Cool the Liquid and Shake Twice with (3ml) portions of Saturatd Solution of Sodium Bisulfite NaHSO3 in Order to Remove any Unreacted Benzaldehyde. 9) Separate the Oily Liquid from the Aqueous Sodium Bisulfite Solution.Wash this Oily Liquid with (5ml) of Sodium Carbonate Na2CO3 to Ensure Complete Removal of the Bisulfite Solution, then with (5ml) of Water Separate the Oily Liquid once more. Na2CO3 + 2NaHSO3 2Na2SO3 + CO2 + H2O Excess 10) Dry the Oily Liquid over Anhyrdrous Mg2SO4 or Anhydrous K2CO3 to get Rid of any Water in the Oily Liquid. 11) Remove any Ether with Oily Liquid on a Water Bath and Collect Benzyl Alcohol. 12) Pour the Aqueous Solution Remaining from the Ether Extraction with Stirring into a Mixture of (20ml of Conc. HCl + 10ml of Water), Filter the Precipitated Benzoic Acid, Wash the Precipitate with Cold Water and Collect the Colorless Crystals of Benzoic Acid. 6 Al-ISRAA University College Pharmacy Department ------------------------------------------------------------------------------------------------------------------------ Calculation: 2Benzaldehyde Benzoic Acid 2mole 1mole Density = Wt/Vol. Wt = Vol.*Density 3.6*1.044 = 3.7g Mole = Wt/M.Wt = 3.7/106.12 = 0.035 mole of Benzaldehyde 0.035/2 = 0.0177 mole of Benzoic Acid Mole = Wt/M.Wt 0.0177 = Wt/122.23 = 2.1g Theoretical Wt % Practical Yield = Wt. Actual/Wt. Theoretical *100% % = P.Y = X/2.1 *100% 7 .
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