Recrystallization of Crude Acetanilide

Introduction

The aim of the experiment was to purify a sample of acetanilide through recrystallization using experimental techniques such as hot filtration, vacuum filtration, thin layer chromatography and melting point estimation. Acetanilide is an organic compound produced by reacting aniline and acetic anhydride. Commonly used as an alternative pain reliever other than aspirin before its toxic side effects were discovered.

Organic compounds are frequently not pure due to other soluble and insoluble impurities present. Recrystallization is a technique used in the purification of solid organic compounds.

In the case of acetanilide, the compounds property of being slightly soluble in water allows for both the soluble and insoluble impurities to be removed. The soluble impurities are removed along with the solvent, water in this experiment, and the insoluble impurities by filtration.

Procedure

Three grams of the crude acetanilide were weighed out in a weighing boat on a zeroed mass balance. This sample was poured into a two hundred and fifty millilitre conical flask along with thirty millilitres of water.

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The mixture was boiled on a hot plate and was stirred and swirled often. A small amount of water was added once the mixture had boiled. This was repeated a couple of times until all the acetanilide had dissolved in the hot water. The conical flask was removed from the hot plate and a spatula of activated charcoal was added with four boiling chips into the mixture. The conical flask was placed back onto the hot plate again and boiled until the mixture was clear and the charcoal had aggregated together into small clumps.

The charcoal and any insoluble impurities where removed from the solution by hot filtration. A fluted piece of filter paper was put inside of a heated funnel and the solution was poured through and was allowed filter for a few minutes.

The filtrate was placed inside of an ice bath to recrystalize the acetanilide. The filtrate was poured into the Büchner funnel, containing a wet piece of filter paper. The vacuum pump was turned on and the apparatus was left for a few minutes. The purified acetanilide was scrapped off the inside of the Büchner funnel and the dried filter paper into a container that was then weighed. The percentage yield was then calculated and recorded. A sample of the purified acetanilide was then placed inside of a melting point apparatus and the approximate melting point and the melting range was recorded. Thin layer chromatography analysis was carried out on a sample of the crystals and the rf value was recorded. A final sample was placed onto a slide and viewed under a microscope. The shapes of the crystals were then drawn. The results were then compared with the results of a pure sample of acetanilide.

Results

Shape of crystals – Mostly hexagonal prisms

Mass of Impure acetanilide = 3g

Mass of Pure acetanilide = 0.622g

Percentage Yield=(Mass of pure crystals)/(Mass of impure crystals) ×100

Percentage Yield=0.622/3 ×100=20.73%

The melting point range of the acetanilide recrystalized was 108 oC to 110 oC. Compared to the melting point of pure acetanilide which is 114oC I conclude that my sample was not completely pure, and some impurities must have been present in the recrystalized acetanilide.

A sample of pure acetanilide was taken, and thin layer chromatography was carried out on it to analyse its purity. The crystals were dissolved and spotted on the silica gel part of the aluminium chromatography plate. This was placed in a mobile phase, chloromethane, and the different components separated according to their solubility in the mobile phase and their relative affinities for the stationary phase.

The crystals obtained were mostly hexagonal prisms. The percentage yield of pure acetanilide was calculated to be 20.73%, indicating the effectiveness of the purification process. However, the melting point range (108°C to 110°C) suggested the presence of impurities, as the expected melting point for pure acetanilide is 114°C.

Thin layer chromatography revealed the relative purity of the acetanilide sample, with comparisons drawn against a pure acetanilide reference. The rf values obtained aided in assessing the degree of impurity in the sample.

Discussion

The presence of impurities in the purified acetanilide likely affected its melting point range, demonstrating the necessity for further purification steps or optimization of the recrystallization process. Thin layer chromatography provided valuable insights into the composition of the sample, offering a qualitative assessment of its purity.

Conclusion

In conclusion, the experiment successfully demonstrated the recrystallization of acetanilide as a purification technique. While the percentage yield indicated a reasonable recovery of the compound, the observed melting point range suggested the presence of impurities. Further refinement of the recrystallization procedure could enhance the purity of the obtained acetanilide.