The Preparation of Acetaminophen (Paracetamol) with Thin Layer Chromatography (Tlc) to Monitor the Reaction.

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Experiment 3: The preparation of acetaminophen (paracetamol) with thin layer chromatography (TLC) to monitor the reaction.

Abstract:

This experiment is to demonstrate the preparation of paracetamol and its properties. Reflux and filtration of 4-aminophenol and acetic anhydride formed the crude sample. Further analysis of dry white crystals were used to give quantitative measurements and a percentage yield of 46% was obtained. The overall conclusion is that the acetic anhydride reacted with the –NH2 group.

Materials and Methods:

1. We weighed out (on a top-pan balance) 4-aminophenol (about 11.0g) in a weighing boat and transfer the powder to a 250cm3 round-bottomed flask (RBF) using a powder funnel. 2. Then recorded the amount of 4-aminophenol added. Then added distilled water (30cm3) followed by ethanoic anhydride (acetic anhydride, 12cm3). 3. I then removed the powder funnel and wiped the inside of the ground glass joint to remove any powder that may have adhered to the joint. Then applied fine smears of silicone grease to the neck of the reflux condenser and fit it to the RBF. 4. Then refluxed the mixture for a period of 30 minutes.

5. At the end of this period the sample was removed (using the extended teat pipette provided) for tlc analysis. 6. Cool the mixture and filter the solid at the pump using a Büchner flask and funnel. 7. The solid residue was washed thoroughly with distilled water (35cm3) this was repeated and washed with a further 35cm3 of distilled water and then the crystals were sucked as dry as possible using the pump. 8. They were then spread as thinly as possible onto a pre-weighed and labelled watchglass, and then placed it in the drying cabinet

9. Using a large silica tlc plate (20 cm by 15 cm approx) the sample was spotted from each batch onto the plate with a separation of about 2cm.

10. The 4-aminophenol and paracetamol spots are standards with the same separation, using relatively diluted solutions.

11. This was then allowed to dry and elute the plate in a suitable tank with cyclohexane (ethyl acetate for a miniplate).

12. When elution is complete, allow the plate to dry again (or use hairdryer) and then examine it under a uv lamp.

13. All the observed spots were marked with a soft pencil. The plate was exposed to iodine vapour in a suitable tank and then photocopied for a permanent record

Results:

1. Calculate the Percentage Yield (crude product) of your reaction.

To calculate % yield you have to use the following equation:

(Actual amount of product in mols / Theoretical amount of product in mols) x100

-The first step I carried out was finding out the amount in mol of 4-aminophenol used:

• To work out the mol I did: mass (g) / Mr (molecular weight)

• Mass is equal to: 11.06(g) as this is how much I used.

• Mr is:

-C6H7NO = (12x6)+(1x7)+14+16

=109

• Mol is equal to: Mass (g) / Mr = 11.06 / 109

= 0.101mol

-The ratio for this equation is 1:1 therefore 0.101mol of 4-aminophenol should give 0.101mol of paracetamol. Resulting in this being the theoretical yield.

-The second step is to find out the Actual amount of paracetamol formed:

• To work out the mol I did: mass (g) / Mr (molecular weight)

• The Mass is: 7.02(g) I worked this out using the weight of the watchglass and crude sample which was 30.51(g) – the weight of just the watchglass which was 23.49(g)

• Mr is:

-C8H9O2N = (12x8)+(1x9)+(16x2)+14

= 151

• Mol is equal to: Mass (g) / Mr = 7.02 / 151

= 0.046mol

-This is the actual amount of paracetamol formed in this reaction.

-Finally to work out % Yield:

(Actual amount of product in mols / Theoretical amount of product in mols) x100

= 0.046 / 0.101 x 100

=45.8

=46% this is the percentage yield of paracetamol obtained from my sample.

2. Dissolve a...
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