DATE: Friday February 18 th 2011 Experiment #3 (A) : p - acetotoluidide TITLE: PABA and its Chemistry RESULTS: p toludine mass of container (g) = 1.0888 mass of container and sample (g) = 3.1923 mass of sample (g) = 2.1035 Sodium Acetate mass of container (g) = 1.094 mass of container and sample (g) = 3.893 mass of sample (g) = 2.799 p-acetotoluidine Mass of watch glass, and filter paper (g) = 25.3530 Mass of watch glass, filter paper and sample (g) = 29.8520 Mass of crystallized sample (g) = 4.499 1
DATE: Friday 4 th March 2011 Experiment #3 (B) : p acetamidobenzoic acid TITLE: PABA and its Chemistry RESULTS: For p-acetotoluidide mass of container (g) = 0.8391 mass of container and sample (g) = 2.7318 mass of sample (g) = 1.8927 For MgSO4.7H2O mass of container (g) = 0.6224 mass of container and sample (g) = 5.6212 mass of sample (g) = 4.9988 For potassium permanganate mass of container (g) = 0.8385 mass of container and sample (g) = 5.9677 mass of sample (g) = 5.1292 Volume of ethanol used = 3 ml Mass of watch glass, and filter paper (g) = 19.4540 Mass of watch glass, filter paper and sample (g) = 20.0322 Mass of crystallized sample (g) = 0.5782 Temperature/Melting Point / o C = 250 o C - 255 o C 2
DATE: Friday 11 th March 2011 Experiment #3 (C) : p aminobenzoic acid TITLE: PABA and its Chemistry RESULTS: Mass of Acetamidobenzoic Acid from the previous step: mass of watch glass (g) = 25.2261 mass of watch glass and sample (g) = 25.5718 mass of sample (g) = 0.3457 1g of acetamidobenzoic acid : 5 ml of 18% HCl therefore 0.3457 g : 0.3457 g x 5 = 1.7285 ml HCl For each 30 ml of solution, add 1 ml of glacial acetic acid therefore, 75 ml of solution 75 ml = 2.5 ml of glacial acetic acid Mass of filter paper (g) = 0.0640 Mass of watch glass (g) = 25.2256 Mass of watch glass and filter paper (g) = 25.2896 Mass of product, watch glass and filter paper (g) = 25.3977 Mass of product (g) = 0.1081 therefore, mass of product = 0.1081 g 3
DATE: Friday 25 th March 2011 Experiment #3 (D) : benzocaine TITLE: PABA and its Chemistry RESULTS: For p-aminobenzoic acid Mass of Empty container (g) = 0.8852 g Mass of container and PABA (g) = 1.5444 Mass of PABA (g) = 0.6592 For benzocaine Mass of empty container and cover (g) = 32.9968 Mass of residue, container and cover (g) = 33.3889 Mass of end product (crystals) (g) = 0.3921 Therefore the mass of benzocaine obtained was 0.3921g 4
DATE: NAME OF PARTNERS: Yohance Matsimela, Nadia Asgarali EXPERIMENT #3 TITLE: PABA and its chemistry OBJECTIVES: To produce a benzocaine sample from four steps starting initially with paratoluidine 1. p-toluidine p-acetotoluidide 2. p-acetotoluidide p-acetamidobenzoic Acid 3. p-acetamidobenzoic Acid p-aminobenzoic acid 4. p-aminobenzoic acid BENZOCAINE THEORY: P-aminobenzoic acid (PABA) is associated with the Vitamin B Complex. It is the central unit of Folic Acid (vitamin B10). Folic acid is made up of three main components: 1. pteridine unit 2. glutamic acid unit 3. p-aminobezoic unit P-aminobenzoic acid (PABA) is required for folic acid synthesis by certain bacteria, and this process is disrupted by Sulfa Drugs. PABA is usually made from p-nitroluene by oxidation to p-nitrobenzoic acid, and subsequent reduction of the nitro group catalytically or by iron or zinc with HCl. There is another method of manufacture of PABA that is better suited for small scale laboratory production. This method includes the following steps: 5
1. p-toluidine reacts with acetic anhydride in the presence of NaO2CCH3 and HO2CCH3 to give p-acetotoluidide. 2. p-acetotoluidide is oxidized by KMnO4. This reaction is buffered by MgSO4 which avoids hydroxylation of protective acetyl groups. This reaction produces p-acetamidobenzoic Acid 6
3. p-acetamidobenzoic Acid is hydrolyzed by heating with HCl to produce PABA The Ethyl ester of p-acetamidobenzoic Acid is used as a local anaesthetic (benzocaine), as well as a sunburn preventative. It may also cause dermatitis in sensitive individuals. 7
PART A TITLE: p-acetotoluidide PROCEDURE: 1. 2.1g (0.02 mole) of p-toluidine, 50ml water and 1.7ml (0.02 mole ) of HCl were placed in a 125ml Erlenmeyer flask in that specific order. 2. A solution of 2.8g (0.022mole) of sodium acetate crystals (CH3CO2Na.3H2O) was mixed with 7ml of water. 3. After both solutions were prepared 2.7ml of acetic anhydride was added to the amine HCl solution 4. The contents of the flask were gently swirled to dissolve the anhydride 5. The sodium acetate solution was then added and the flask was vigourously swirled to ensure proper mixing of the reactants while the products crystallized. 6. The crystals produced were then collected by suction filtration, washed with cold water and allowed to dry. 7. After the crystals dried, they were collected and placed into a container and the mass of crystals obtained was determined using a scale balance. 8. A small portion of the crystals was then used for melting point determination. 8
RESULTS: For p toludine mass of container (g) = 1.0888 mass of container and sample (g) = 3.1923 mass of sample (g) = 2.1035 for Sodium Acetate mass of container (g) = 1.094 mass of container and sample (g) = 3.893 mass of sample (g) = 2.799 p-acetotoluidine Mass of watch glass, and filter paper (g) = 25.3530 Mass of watch glass, filter paper and sample (g) = 29.8520 Mass of crystallized sample (g) = 4.499 9
PART B TITLE: p-acetamidobenzoic acid PROCEDURE: 1. 1.9g of p-acetotoluidide from the previous step together with 5g of magnesium sulphate crystals and 125ml of water was placed into a 250ml Erlenmeyer flask. 2. The contents of the flask were then heated to about 85 o C on a steam bath. 3. A solution of 5.1g of Potassium permanganate was prepared in 20ml of boiling water in an Erlenmeyer flask 4. The hot permanganate in the solution was added in small portions over a 30 minute period while swirling the acetotoluidide solution vigorously 5. When all the permanganate was added, the mixture was swirled vigorously 6. A fluted filter paper was then used to filter off the precipitated manganese dioxide from the hot solution, and the manganese dioxide was then washed with a little water. 7. The colourless filtrate obtained was then cooled and acidified with 20% aq. H2SO4 to a ph of approx. 3 to 4 8. The p-acetamidobenzoic acid was collected by suction filtration and pressed dry. 9. The dried crystals were place into a container and the mass of crystals obtained was determined using a scale balance. 10. A small portion of the dried crystals was then used for melting point determination. RESULTS: For p-acetotoluidide mass of container (g) = 0.8391 mass of container and sample (g) = 2.7318 mass of sample (g) = 1.8927 10
For MgSO4.7H2O mass of container (g) = 0.6224 mass of container and sample (g) = 5.6212 mass of sample (g) = 4.9988 For potassium permanganate mass of container (g) = 0.8385 mass of container and sample (g) = 5.9677 mass of sample (g) = 5.1292 Volume of ethanol used = 3 ml Mass of watch glass, and filter paper (g) = 19.4540 Mass of watch glass, filter paper and sample (g) = 20.0322 Mass of crystallized sample (g) = 0.5782 Temperature/Melting Point / o C = 250 o C - 255 o C 11
PART C TITLE: p aminobenzoic acid PROCEDURE: 1. The acetamidobenzoic acid from the previous step was weighed using a scale balance. 2. For each gram obtained 5ml of 18% HCl was used for the hydrolysis. 3. The materials were placed into a 50ml round bottomed flask with an attached reflux condenser and gently boiled for 25-30 minutes. 4. Following this the reaction mixture was cooled and half of its volume of cold water was added (0.915 cm 3 ) 5. The resulting solution was then made barely alkaline (ph 7-8) by adding 10% NH3 6. 1ml of glacial acetic acid was added for each 30ml of solution, this was stirred vigorously and then cooled in an ice bath. 7. The resulting product was collected by suction filtration and allowed to dry 8. The mass of final product was the determined using a scale balance 9. A small portion of the crystals was then used in order for melting point determination. 12
RESULTS: Mass of Acetamidobenzoic Acid from the previous step: mass of watch glass (g) = 25.2261 mass of watch glass and sample (g) = 25.5718 mass of sample (g) = 0.3457 1g of acetamidobenzoic acid : 5 ml of 18% HCl therefore 0.3457 g : 0.3457 g x 5 = 1.7285 ml HCl For each 30 ml of solution, add 1 ml of glacial acetic acid therefore, 75 ml of solution 75 ml = 2.5 ml of glacial acetic acid Mass of filter paper (g) = 0.0640 Mass of watch glass (g) = 25.2256 Mass of watch glass and filter paper (g) = 25.2896 Mass of product, watch glass and filter paper (g) = 25.3977 Mass of product (g) = 0.1081 therefore, mass of product = 0.1081 g 13
PART D TITLE: benzocaine PROCEUDRE: 1. 0.66g of p-aminobenzoic acid, 5ml ethanol, and 0.5ml conc. Sulphuric acid were added in a 25 ml round bottomed flask (reflux for 1 hour). 2. The solution was cooled to room temperature and neutralized using sodium carbonate. 3. The solution was then extracted using two 5ml portions of methylene chloride. 4. The combined organic layers was extracted twice using 15ml portions of water and then dried over anhydrous MgSO4 5. The methylene chloride was removed by distillation using a steam bath 6. A suction filter was set up 7. The residue from the methanol - H2O was recrystallized using the suction filter 8. The white crystals obtained was then dried and weighed using an analytical balance 9. A small portion of the crystals was then used for melting point determination. RESULTS: For p-aminobenzoic acid Mass of Empty container (g) = 0.8852 g Mass of container and PABA (g) = 1.5444 Mass of PABA (g) = 0.6592 For benzocaine Mass of empty container and cover (g) = 32.9968 Mass of residue, container and cover (g) = 33.3889 Mass of end product (crystals) (g) = 0.3921 Therefore the mass of benzocaine obtained was 0.3921g 14
DISCUSSION: Benzocaine is a white crystalline powder that is used as a topical anaesthetic. It is also widely used in first aid creams and sunburn remedies. A similar chemical procaine (novocaine) is used by dentist to numb the gums before dental work. Another anaesthetic similar to benzocaine is lidocaine, which is used to relive the pain of shingles infection. However lidocaine is considered an amide anaesthetic rather than an ester anaesthetic. In lidocaine the alcohol from the ester is replace by an amide nitrogen group. The amide is metabolized by the liver and is less prone to cause allergic reactions. 15
EXERCISE: 1) Mechanism for the reaction of salicylic acid with acetic anhydride 16
Reaction of salicylic acid with acetic anhydride The reaction conditions include: conc. H2SO4, heat and a catalyst 2) Upon conversion of salicylic acid to acetylsalicylate, the major changes in the IR spectrum that would be expected are as follows: For NH2, NH 3200 For C=O 1700 For CH3 stretchy 2900 17