DATE: Friday February 18th 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
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DATE: Friday 4th 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 /oC = 250oC - 255oC
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DATE: Friday 11th 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 x 5
0.3457 g
= 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
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DATE: Friday 25th 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
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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:
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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
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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.
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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.
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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
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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 85oC 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
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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 /oC = 250oC - 255oC
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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 cm3)
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.
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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 x 5
0.3457 g
= 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
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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
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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.
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EXERCISE:
1) Mechanism for the reaction of salicylic acid with acetic anhydride
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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
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