Paracetamol lab report PDF

Preview

Summary

Lab write up for one of the practicals you will undertake....

Description

An experiment for the preparation, purification and analysis of Paracetamol. Determining its purity and concentration, using the Beer-Lambert law, thin layer chromatography (TLC) and melting point determinations.

Introduction

Paracetamol is a widely used analgesic and antipyretic drug 1. Before a drug can be sold onto the market, tests are performed to determine its purity. In our experiment, we synthesised Paracetamol with Ethanoic anhydride and 4aminophenol, using various analytical techniques to determine the purity of our product.

The aims in our experiment were to prepare a sample of Paracetamol with a yield of 95105%1, complying with the British Pharmacopoeia (BP), and achieve a relatively high purity with a difference of 0.05 in Rf values.

Method

We suspended 4-aminophenol (5.02g) in water (15cm3) in a round bottomed flask (50cm3). Ethanoic anhydride was added (6cm3) and swirled. The flask was clamped to a reflux condenser and heated for ten minutes on a steam bath and swirled. It cooled to hand temperature, cooled further under a cold tap and vacuum filtered using Hirsch apparatus. The solid was transferred into a conical flask (100cm3), and recrystallized from water (40cm3) using a hot plate. The solid was placed on a watch glass and dried in an oven (80°C) overnight.

On silica plates, we drew a line 1cm away from the bottom, marked three spots and transferred our product (0.05g) into a vial of ethyl acetate (~1cm3). We transferred one drop onto our plates and repeated with 4-aminophenol and Paracetamol. The plates were placed into jars of Ethyl acetate (~2cm3) until they travelled to 1cm from the top; we drew a line along the solvent fronts. Under UV light, we drew around the dots.

4-aminophenol, Paracetamol and our product (~3mm) were transferred into capillary tubes and placed in melting point apparatus. The melting point ranges were recorded.

An Infrared spectroscopy (FTIR) machine was used to determine a spectrum for Paracetamol, we could not do this for our product but a given sample was analysed, using a data sheet2.

0.0237g of synthesised Paracetamol was suspended in a volumetric flask (250cm3) with distilled water and mixed until dissolved. We transferred 30, 25, 20, 15, 10, 5 cm3 into 50cm3 volumetric flasks (labelled A-F), added 10cm3 of hydrochloric acid (0.1M) and filled to the mark with distilled water. A spectrophotometer (at 244nm) was used to measure the absorbance of these solutions.

Results

Our yield of Paracetamol was 65.9% (Table 1.0), not meeting the requirements of the BP.

The Rf values (Table 2.0) and melting point ranges (Table 3.0) of standard Paracetamol and synthesised Paracetamol were similar. The IR spectrum of Paracetamol showed all functional groups expected (Table 4.0). The recorded absorbance values (Table 5.0) were plotted onto a graph (Figure 1.0). The synthesised Paracetamol’s concentration was determined by Figure 1.0 from its absorbance value, using the Beer-Lambert law.

Table 1.0- The mass of our watch glass and product, determining the mass of synthesised Paracetamol and its yield. Mass of watch glass(g)

17.4324

Mass of watch glass & Paracetamol product(g)

22.0115

Mass of paracetamol product(g)

4.5791

yield(%)

65.9 (3.s.f)

Table 2.0- Distances from 1cm line on the silica plates, to calculate R f values. Type of powder

Distance to spot

Distance to solvent front

Rf Value

4-Aminophenol

3.00

4.90

0.612

Standard Paracetamol

2.30

4.90

0.469

Synthesised Paracetamol

2.40

4.90

0.490

Table 3.0- The melting point ranges of the samples.

Sample

Melting point Range(°C)

Actual melting point range(°C)

4-Aminophenol

163-166

187.5

Standard Paracetamol

169-171

169-172

Synthesised Paracetamol

168-171

Table 4.0- The wavenumbers of a Paracetamol sample in an Infrared Spectrum to determine functional groups.

IR spectrum wavenumbers(cm-1)

Functional group in Paracetamol

3319

N-H

3109

O-H

1650

C=O

1504

C-C (aromatic)

1434

C-C

1224

C-N

Table 5.0- The expected concentrations of the diluted stock solutions and synthesised Paracetamol, with their recorded absorbance.

Volume of stock solution (cm-3)

A

B

C

D

E

F

30.0

25.0

20.0

15.0

10.0

5.0

Synthesised Paracetamol Solution 0.0237g

Total Volume (cm-3)

50.0

5.0.0

50.0

50.0

50.0

50.0

100

Final Concentration (moldm-3)

1.27x10-4

1.06x10-4

8.48x10-5

6.35 x10-5

4.23 x10-5

2.12 x10-5

6.27x10-5

Absorbance

0.121

0.103

0.0840

0.0650

0.0470

0.0250

0.0580

A linear plot showing the relationship between absorbance and concentration (moldm-3) of paracetamol stock solution. 0.14

Absorbacnce

0.12 f(x) = 981.06 x R² = 1 0.1 0.08 0.06 0.04 0.02 0

0

0

0

0

0

0

0

Concentration (moldm-3)

Figure 1.0- A graph of absorbance against concentration of Paracetamol stock solution.

Discussion

In our experiment, aim of 95-105% yield of synthesised Paracetamol was not achieved (Table 1.0), due to transfer error between the round bottom and conical flasks.

0

From our TLC and melting point determinations we can infer that my sample of Paracetamol was relatively pure since melting point determinations were 1° different to the standard and an Rf difference of 0.021. Unfortunately, we couldn’t obtain an IR spectrum for our sample therefore could not identify ambiguous peaks to test for impurities. Our theoretical concentration of Paracetamol was 6.27x10-5 however, using the BeerLambert law (A=εcl) and our calibration graph, we were able to find the actual concentration of 5.91x10-5 since our molar absorptivity coefficient (ε) was 981.06 dm3mol-1cm-1 (Figure 1.0), therefore similar concentrations. Overall, I achieved a relatively high purity however did not achieve a high enough yield to comply with the BP.

Appendix

Mass of synthesised 22.0115-174324=4.5791 paracetamol %yield (4.5791/6.95) x 100 =65.9 Rf Values 3.00/4.90=0.612 Concentration of 0.058=981.06c synthesised Paracetamol. c=5.91x10-5

IR spectrum

References

1.British Pharmacopoeia [Internet]. Pharmacopoeia.com. cited [12th November 2017] Available at: https://www.pharmacopoeia.com/bp-2018/formulated-specific/paracetamoltablets.html?published-date=2017-08-01&text=paracetamol

2. William Reusch [Internet] Chemistry.MSU.com. cited [13th November 2017] Available at: https://www2.chemistry.msu.edu/faculty/reusch/virttxtjml/spectrpy/infrared/infrared.htm Words:880...