Experiment No 6 Jerry.docx

EXPERIMENT NO: 6

EXPERIMENT TITLE: PREPARATION OF ACETYL SALICYLIC ACID NAME: Phenyo Jerry Mmereki ID: 201602475 DATE OF THE EXPERIMENT: Friday8 March 2019

AIM The aim of this experiment is to synthesis aspirin (acetyl salicylic acid) from salicylic acid and acetic anhydride thus calculate it percentage yield.

ABSTRACT The purpose of this experiment was to synthesize aspirin by reacting salicylic acid and acetic anhydride in the presence of acid to form acetylsalicylic acid. Once synthesized , acetylsalicylic acid was purified by recrystallization. The actual yield of aspirin synthesized was 1.49 grams and the theoretical yield was 2.61 grams, hence the percent yield of 57.1% giving a percent error of 42.9%. The melting point range of the product was found to be 138.2-140.3 oC.

INTRODUCTION Over history, many compounds obtained from nature have been used to cure ills or to produce an effect in humans. These natural products have been obtained from plants, minerals, and animals. In addition, various transformations of these and other compounds have led to even more medically useful compounds. Analgesics are compounds used to reduce pain, antipyretics are compounds used to reduce fever. One popular drug that does both is aspirin (Chickos, Garin, & D'Souza, 2017). Aspirin is the common name for the compound acetylsalicylic acid, widely used as a fever reducer and as a pain killer. Salicylic acid is administered in the form of aspirin which is less irritating to the stomach than salicylic acid. To prepare aspirin, salicylic acid is reacted with an excess of acetic anhydride. A small amount of a strong acid (concentrated sulfuric acid ) is used as a catalyst which speeds up the reaction. The excess acetic acid is be quenched with the addition of water. The aspirin product is not very soluble in water so the aspirin product will precipitate when water is added. The synthesis reaction of aspirin is shown below:

This reaction results in the removal of a hydrogen atom of the hydroxyl group attached to the ring on salicylic acid being replaced by an acetyl group. This reaction must take place in an anhydrous environment or the acetic anhydride will react with the water. The sulfuric acid initiates the acetylation reaction at low temperatures. Without the addition of the catalyst, sulfuric acid, this reaction is very slow. According to (El-Magbri, 2014) and (Postu, 2014), despite the medicinal and wonderful properties of aspirin, negative effects have been associated with this drug. Symptoms associated with aspirin include nausea, vomiting, rashes, swelling, and hives. Aspirin can still cause stomach irritation resulting in the risk of internal bleeding and ulcers. Aspirin has also been known to interfere with platelet functioning and may cause Reyes syndrome in children.

EXPERIMENTAL PROCEDURE 5ml of acetic anhydride was added to a clean dry flask which contained 2.0ml of salicylic acid. 5 drops of concentrated sulfuric acid was added slowly while swirling. The mixture was stirred for until the salicylic acid dissolved. The mixture flask was heated in a hot water bath for about 10 minutes. The flask was removed from the hot water bath then allowed to cool to room temperature. The walls of the flask was scratched with a glass stirring rod to enhance precipitation of the aspirin. 50ml of water was added to the precipitate then the flask was placed in a cold water bath. Hirsh funnel was used to vacuum filter the precipitate, the flask was then rinsed cold water. The precipitate was air dried for about 10 minutes. Crude aspirin was transferred into a 200ml beaker then 25ml of an aqueous sodium bicarbonate (saturated). The mixture was stirred until the bubbling subsided. The polymers were removed by filtering the solution through a Hirsch funnel. 10ml of water was used to rinse. 3.5ml of concentrated HCl was added to the 200ml beaker which contained 10ml water, the filtrate was the poured in small portions into the 200ml beaker while constantly stirring. The solution was cooled in ice water bath then vacuum filtered through Hirsch funnel, ice cold water was used to wash the precipitate. The precipitate was left to dry overnight. The purified dried acetyl salicylic acid was weighed and it melting point range was determined.

RESULTS ANALYSIS Table 1: The amount of acetyl salicylic acid prepared Description

Mass (g)

Mass of petri dish + filter paper

48.98

Mass of petri dish+ filter paper + acetyl salicylic acid

50.47

Mass of acetyl salicylic acid

1.49

The equation for this reaction is: Salicylic acid + acetic anhydride → acetyl salicylic acid + ethanoic acid C7H6O3 + C4H6O3 → C9H8O4 + CH3COOH

Determining the limiting reactant Acetic anhydride

Mass = volume * density = 5ml * 1.08g/ml = 5.4g

Moles

𝑚𝑎𝑠𝑠 𝑚𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠

=

5.4𝑔 102.09𝑔/𝑚𝑜𝑙

= 0.0528mol

Since the ratio of C4H6O3 : C9H8O4 is 1:1, acetic anhydride is going to yield 0.0528mol of acetyl salicylic acid.

Salicylic acid

𝑚𝑎𝑠𝑠

2.0𝑔

Moles =𝑚𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠 = 138.121𝑔/𝑚𝑜𝑙 = 0.0145mol

Since the ratio of C7H6O3 : C9H8O4 is 1:1, Salicylic acid is going to yield 0.0145mol of acetyl salicylic acid. Thus Salicylic acid is the limiting reactant since it yields lower moles of product.

Determining the percentage yield of acetyl salicylic acid

Theoretical mass = moles * molar mass = 0.0145mol * 180.158g/mol = 2.61g

𝟏.𝟒𝟗𝒈

= 𝟐.𝟔𝟏𝒈 * 100 = 57.1% Melting point range = 138.2-140.3 oC QUESTIONS 1) IR spectrum: 1751.4 and 1679.2 cm-1 → C=O bond 1604 cm-1 → aromatic ring 1456.6 and 1292 cm-1→ C-H bond 1185 cm-1→ C-O bond

2) The salicylic acid spectrum has a 3228.3 cm-1 peak which shows OH bond while aspirin spectrum don’t have.

DISCUSSION Acetyl salicylic acid was synthesized from salicylic acid and acetic anhydride. In the reaction the hydroxyl group on the benzene ring in salicylic acid reacted with acetic anhydride to form an ester functional group. This method of forming acetylsalicylic acid is an esterification reaction. Since this esterification reaction is not spontaneous, sulfuric acid was used as a catalyst to initiate the reaction. The actual mass of 1.49g was obtained which was a percentage yield of 57.1%, which is a low yield. The IR spectra of aspiring and salicylic acid both have OH broad peak between 3500-3000cm-1. The –CH, -C-C- stretching and bending in both for benzene ring is shown by some peaks occurs between 6001200cm-1. Both the structures have similar features, which is due to the derivative nature of acetyl salicylic acid from salicylic acid, resulting in similar peaks of their spectra. Each has a strong peak near 1689 cm-1 due to stretching of the C=O bond of the acid group [-(C=O)-O-H]. The two compounds both have a large peak near 1605 cm-1 due to a skeletal vibration of the benzene ring. Some of the differences’ observed between aspiring and salicylic acid is that Acetylsalicylic acid indicates two strong peaks in the carbonyl (C=O) stretching region (1650 – 1800 cm-1), as it has two different carbonyl group, while salicylic acid has only one. The other difference between aspiring and salicylic acid is the presence of carboxylic ester in aspirin and –OH in salicylic acid. Aspirin show peaks at 1790, 1240 and 1090cm-1 carboxylic ester which is not present in salicylic acid. The sources of low yield might be loss of product during vacuum filtration which lead to reduction of product mass. The acetyl salicylic acid melting point range was found to be 137.2-139.0 oC which correlates with the literature value of 138-140 °C’

CONCLUSION The aspirin was synthesized from acetic anhydride and salicylic acid and the yield was found to be 53.6%.

REFERENCES Chickos, J., Garin, D., & D'Souza, V. (2017, september 1). Retrieved from chem.libretexts: https://chem.libretexts.org/Ancillary_Materials/Laboratory_Experiments/Wet_Lab_Experiment s/Organic_Chemistry_Labs/Experiments/1%3A__Synthesis_of_Aspirin_(Experiment) El-Magbri, M. (2014). The Synthesis and Analysis of Aspirin. Journal of Chemical Education. Postu, A. C. (2014). Esterification reaction: the synthesis and purification of 2-Acetoxybenzoic acid and subsequent analysis of the pure product (acetylsalicylic acid ) via Thin-Layer Chromatography. Department of Chemistry, American University, Washington, D.C. 20016.