Preparation Of Recrystallization Of Aspirin Biology

This experiment serves 2 aims – the production of Aspirin from esterification of salicylic acid with extra acetic anhydride and obtaining it in a purer province by recrystallisation, hence determines the runing point of the acetylsalicylic acid ( ASA ) that was synthesised and purified.

To accomplish this, salicylic acid is reacted with extra acetic anhydride in the presence of the sulfuric acid as the accelerator, which produces precipitate ASA and aqueous acetic acid. I applied suction filtration to roll up the ASA as the residue holding acetic acid as the filtrate.

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Pure acetylsalicylic acid is a white crystalline solid. The acetylsalicylic acid ab initio produced by synthesis may be light sunburn, bespeaking the presence of drosss. The ASA synthesis earlier is purified by recrystallization. In recrystallization, the impure solid is dissolved in a hot dissolver ( aqueous ethyl alcohol ) and the resulting solution is allowed to chill easy. As the solution cools, crystals of the merchandise will organize and soluble drosss will stay in solution.

From this experiment, the per centum output of ASA is about 49 % , utilizing capillary trial the runing point of ASA falls in the fury of 137.9-140.5 0 C. The visual aspect of ASA is an odourless, white, acerate and glistening solid. In decision, experiment is a success. Despite merchandise had a low per centum output and was found to be impure due to its low thaw point.

2. Introduction

Aspirin is the trade name for the molecule acetylsalicylic acid.

The earliest known usage of this molecule has been traced back to the 5th century B.C. The Grecian doctor Hippocrates described an infusion of willow tree bark, a acrimonious pulverization that could be used to cut down febrilities. In 1829, Salicin was isolated from willow bark and used as a hurting stand-in. Unfortunately Salicin was non really popular since it was found to be really acidic and a tummy thorn.

In 1897 Felix Hoffman, a German chemist, was working for the Bayer chemical company. Hoffman wanted to explicate for a less acidic hurting stand-in as his male parent could devour for his arthritis. His surveies led to the synthesis of acetylsalicylic acid ( ASA ) or acetylsalicylic acid. Bayer patented the name and commenced to market the merchandise in 1899. It was a immense success and gross revenues grew quickly. In fact, the company set up by Friedrich Bayer & A ; Company is by and large considered to hold been the first pharmaceutical company, and the production of acetylsalicylic acid has indisputably laid the base of the modern pharmaceutical industry.


Merely until the 1970 ‘s that scientists starts to grok the construct on how aspirin map as a hurting stand-in. Today 80 billion aspirin tablets are taken every twelvemonth over the Al the states to cut down febrilities, relieve hurting, and even assist forestall bosom onslaughts. Bayer In commercial acetylsalicylic acid merchandises, a little sum of ASA ( 300 to 400 milligram ) is bound together with a amylum binder and sometimes caffeine and buffers to do an aspirin tablet. The basic conditions in the little bowel break down the ASA to give salicylic acid, which is absorbed into the blood stream. The add-on of a buffer reduces the annoyance caused by the carboxylic acid group of the acetylsalicylic acid molecule.

3. Theory

Esters are organic compounds with the general expression RCOOR ‘ , where Roentgen and R ‘ can be an alkyl group or an aromatic group. Alkyl group is an methane series that is short of one H since it needs one bond to be branched from the parent concatenation. Aromatic compounds are a category of molecules incorporating benzine, a 6-membered C rings with delocalized pi negatrons. This type of group is found in salicyclic acid and ASA.

Esters are readily synthesized by the reaction between a carboxylic acid, RCOOH, and an intoxicant, R’OH, as shown in the undermentioned reaction.

The reaction above is besides known as esterification. It is a condensation reaction, whereby two molecules combine to organize one individual molecule, while taking a little molecule ( e.g. H2O ) in the procedure.

The reaction to I have used synthesis ASA is really similar to the one above. Salicylic acid a phenol consisting of a phenyl bonded to the hydroxyl ( -OH ) which is really much alike to alcohol and acetic

Anhydride is a dehydrated carboxylic acid ( acetic acid ) . In the below reaction we use concentrated sulfuric acid as the accelerator. After the warm bath to finish the reaction, we added cold H2O to slake the reaction ( hydrolysis of acetic anhydride ) to forestall farther reaction to take topographic point. The cold H2O must be added rapidly as to let fast crystal formations due to the drastic bead in temperature. Stir and rub the walls can make uneven surfaces therefore bring oning crystallisation. ) .

As such, in this experiment, 2.4 gms of salicylic acid should give 3.13 gms of Aspirin, it is stated that acetic anhydride is in surplus. This is proven by the undermentioned computation:

Mol of salicylic acid in this experiment:

2.4 ( 2d.p ) /138 = 0.0174 ( 3 s.f. )

Mol of salicylic acid: Mol of Aspirin

1: 1

Therefore, Mol of Aspirin:

0.0174/1 ten 1 = 0.0174 ( 3 s.f. )

Expected mass of Aspirin:

0.017391 ten 180 = 3.130 ( 3 December. )

The solid ASA formed contains drosss and should be recrystallised to accomplish a purer province. Recrystallization is possible because most solids are more soluble in hot dissolvers than in cold dissolvers.

The solubility of ASA additions as temperature additions. This means that if acetylsalicylic acid is dissolved in ethyl alcohol to bring forth a concentrated solution and that solution is cooled, the acetylsalicylic acid will crystallise during the chilling.

Ethanol has been chosen as the dissolver because the polar nature of the hydroxyl group causes ethanol to fade out many ionic compounds, furthermore the ethyl alcohol molecule besides has a non-polar terminal, and it will besides fade out non-polar substances.

While chilling, crystallisation takes topographic point. In crystallisation, there is a slow, selective formation of the crystal model ensuing in a pure compound. Alternatively in precipitation, due to the rapid formation it will pin down drosss in the solid ‘s crystal model. For this ground, we should include crystallisation to acquire a purer solid substance.

The alternate manner of synthesizing the acetylsalicylic acid can be produced by replacing the acetylizing agent from acetic anhydride to an even more acidic acid known as acetyl chloride CH3COCl. This can increase the per centum output of ASA, since ethanoyl group chloride is more acidic. The reaction of acetyl chloride with salicylic acid is showed below. However, the byproduct is hydrochloric acid ( HCl ) alternatively of acetic acid.

However, Acetic anhydride is preferred because it is less risky to utilize and less expensive than acetyl chloride. In industry, the acetic acid produced in this reaction can be recovered and converted back into acetic anhydride by the procedure known as desiccation:

We may besides make or Salicylic acid from Kolbe ‘s reaction whereby we start with a phenol:

4. Procedure

Approximately 2.4 gms of salicylic acid is weighed and placed in a dry, 100ml conelike flask.

6ml of acetic anhydride is added into the same conelike flask, along with 3-4 beads of concentrated H2SO4 as accelerator.

The conelike flask is so heated at 80-100 grade C in a H2O bath for 10 to 15 proceedingss to rush the reaction.

1ml of distilled H2O is added into the conelike flask instantly after it is removed from H2O bath.

40ml of cold distilled H2O is so added to the conelike flask.

A stirring rod is used to gently ‘rub ‘ the side of the conelike flask. This is to rub off crystals which have formed.

Suction filtration is so carried out to take the crystals from the solution.

The crystals are removed from the filter paper. To guarantee truth, cold distilled H2O is used to rinse away staying crystals from the filter paper.

The crystals are so dissolved in 5ml of ethyl alcohol.

30ml of hot, distilled H2O is added into the solution, and easy cooled.

Crystallization of Aspirin will take topographic point as the solution is cooled to room temperature.

Suction filtration is done to take the Aspirin from the solution. The residue is so placed on a ticker glass along with the filter paper.

Aspirin is so dried by puting it in the oven for 20 proceedingss, along with the ticker glass and filter paper.

It will so be transferred to the desiccators for 15 proceedingss to farther dry it.

The crystals remained on the filter paper would be pure, dry, Aspirin.

The undermentioned measurings are taken:

-Actual weight of salicylic acid is weighed at ( 1 ) .

-Weight of filter paper and ticker glass is taken.

-Weight of Aspirin, along with ticker glass and filter paper, is taken after ( 15 ) .

After obtaining Aspirin, the runing point of Aspirin is so determined utilizing the capillary method.

5. Consequences and Calculation


Mass of salicylic acid ( a ) = 2.39 g

Mass of filter paper & A ; ticker glass ( B ) = 33.11 g

Mass of dried, recrystallised acetylsalicylic acid, filter paper & A ; ticker glass ( degree Celsius ) = 34.64 g

Mass of dried, recrystallised acetylsalicylic acid ( vitamin D ) = ( degree Celsius ) – ( B )

= 34.64-33.11

= 1.53 g

Percent output

Number of moles of salicylic acid used ( vitamin E ) = 0.0173 mol

( Molecular weight of salicylic acid = 138 )

Expected figure of moles of acetylsalicylic acid ( degree Fahrenheit ) = 0.0173 mol

Expected mass of acetylsalicylic acid ( g ) = 3.12 g

( Molecular weight = 180 )

Melting point

Temperature scope 137.9-140.5 oC


Needle shaped, white, and shiny.

6. Discussion

My per centum output ASA is comparatively low since it is merely 49 % . This may happen due to several factors:

While reassigning the salicylic acid, some of the solid may remain at the side of the conelike flask and even your spactula, and ensuing in lesser salicylic acid take parting in the procedure of esterification compared to what hold been weighed earlier. Therefore, this will ensue in lower output of the crystal ASA. It will be advisable to rinse the walls with distilled H2O to guarantee more salicylic acid will take part in the reaction.

When fade outing the initial sum of salicylic acid in the solution of acetic anhydride and concentrated sulfuric acid, it did non wholly fade out into the solution, even when it was heated. This could hold a little impact on the consequences of the overall output of acetylsalicylic acid because it was possible that non all of the salicylic acid was synthesized. To find if this affected the synthesis of acetylsalicylic acid at all, the experiment should hold been ran a 2nd clip to see if the same thing occurred. The Fe ( III ) chloride trial besides could hold been ran to find if any of the acetylsalicylic acid degraded to salicylic acid or ne’er converted from salicylic acid.

During the suction filtration we should rinse the solid ASA formed in the conelike flask and the glass rod during the synthesis before pouring into the Buchner funnel repeatedly. After the concluding suction filtration, another mistake causes the per centum output to drop. This is due to the crystals non being to the full collected on the filter paper, but instead, remains on the side of the Buchner funnel. This loss can be minimized by the crystals from the side of the Buchner funnel to the filter paper traveling utilizing a metal spatula before roll uping the filter paper and puting it on the ticker glass.

During recrystallization, one common mistake of adding excessively much dissolver ( ethyl alcohol ) will ensue in less per centum output while chilling. We should forbear from traveling or switching the solution while it is chilling as it will disrupt the crystal formation since the atoms are by and large held by weak scattering forces, dipole-dipole forces, and H bond. We should besides let slow crystal formation as fast crystal formation will do the trap of drosss and giving higher per centum output.

With the presence of drosss the runing point will diminish and change in a larger scope.

7. Decision

In decision, the experiment is a success since I have managed to synthesis and recrystallise the ASA although we have comparatively low per centum output of 49 % that may originate due to several factors as stated in the treatment. I was able to analysis the runing point of the recrystallised acetylsalicylic acid and it is by and large low in temperature which implies the presence of drosss.

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Preparation Of Recrystallization Of Aspirin Biology. (2017, Jul 14). Retrieved from