Acetylsalicylic acid, also known as aspirin is a common use medicine. It is a product of the chemical reaction between salicylic acid and acetic anhydride. In this experiment aspirin will be made, using recrystallization; distillate twice with a Buchner funnel. 5g (36mmol) salicylic acid, 35ml (330mol) toluene and 5g (48,98mmol) acetic anhydride gives in the end 1,98g (42,5mmol) crystals of acetylsalicylic acid. These crystals had a lower melting point then acetylsalicylic acid (137 °C) only because also acetic acid (16,5°C) is formed, which has a lower melting point. The IR spectra before and after the distillation maintain almost the same peaks. Only after distillation there is 1 high peak (wave number 3400 cm-1). This because of added demi water after the first distillation.
A common use pain killer is acetylsalicylic acid, also known as aspirin. The crystal form of acetylsalicylic acid plays an important role in the 'healing' effect of acetylsalicylic acid. There are a various different types of crystals. Each crystal dependent on how it is made.
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A popular method how aspirin is made is the esterfication reaction. Salicylic acid in combination with an acetic anhydride gives a reaction witch produces mainly acetylsalicylic acid, it produces also a bit acetic acid (see equation 1).
Equation : Process of Aspirin
Acetylsalicylic acid are reaction with one group of the acetic acid (see equation 2). After cooling down the first crystals are formed. For a higher concentration of acetylsalicylic acid, it became filtered twice with a Buchner funnel. This causes recrystallization.
Equation : Electron transport
In this experiment acetylsalicylic acid is made throw the chemical reaction of salicylic acid and acetic anhydride.
Materials and Methods
Placed a reflux condenser on 100ml three necked round bottom flask. Added 5g (36mmol) salicylic acid, 35ml (330mmol) Toluene and added slowly 5g (48,98mmol) acetic anhydride. Taken a sample for the IR spectrum. Reflux for 1,5h (at 220 °C). Cooled with ice. Filtered with a Buchner funnel. Washed the filter with small amount toluene. Heated 10,90g (13,97mol) of 96% ethanol (till 65°C) and added to the crystals. When dissolved, added 10,90g (same amount as 96% ethanol) warm demi water. Cooled down till room temperature. Filtered (for the second time) with a Buchner funnel, an dried the crystals.
Determine the yield of the product, melting point determination and characterized it.
Molar mass (g/mol)
Table : Concentrations of substances
Figure : Reflux preparation
Figure : Buchner funnel filtration
Results and Discussion
Determination of the Yield
To determinate of yield, the amount of mol of salicylic acid has to multiply with the molar mass of acetylsalicylic acid. The amount of mol of salicylic acid is used because in the reaction it is this the restrictive factor.
Amount of mol of Salicylic acid
Molar mass of acetylsalicylic acid
Density of acetylsalicylic acid
Table : Concentrations
Yield (in g) = 0,0362 * 180,16 = 6,53 g.
Yield (in ml) = = 4,66 ml
The actually obtained amount of acetylsalicylic acid is 1,98 g (42,5mmol). This means that 30,3 % of the yield has formed into acetylsalicylic acid.
We could explain this low percentage; before the second Buchner filtration, a small amount of hot 96% (10,90g) of ethanol was added. This has to dissolved the product. To increase the percentage, less ethanol has to be add, then less of the product would be dissolved.
Melting point determination
Theoretic melting point
137 °C (of acetylsalicylic acid)
16,5 °C (of acetic acid)
Table : Melting points
Equation 1 shows that not only acetylsalicylic acid id formed but also acetic acid.
De result from the melting point determination shows that the melting point is lower than we expect from acetylsalicylic acid, (see table 3).
Around 97 °C all the solid has was gone. The reason for this low melting point could be that in the solid there is a high concentration acetic acid present. This high concentration provides for a lower melting point than expected.
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There were taken two IR spectra, one before the reflux and Buhner filtration and one after the two Buhner filtrations.
IR spectrum before (salicylic acid, toluene , anhydride)
(see attachment 1)
Wave numbers (cm-1)
Table : IR spectrum before distillation
In table 4 we could see that at a wavelength from 695 cm -1 it is unlikely that there is a C-Br bond in the solution. Because we did not use any Br in this experiment.
All the other bindings that we have in the solution, are represented in the IR spectrum.
Acetylsalicylic acid (see attachment 2)
Table : IR spectrum after distillation
In table 5 there is, in comprising with table 4, a high peak with a wavelength of 3400cm-1. This is explainable, because after the first Buchner funnel there was added (warm) demi water (10,90g). This causes the high peak.
The other peaks are in the same area as in attachment one. This means that there are the same kind of bonds, and this is true. Some bonds are on a different location but they still exists.
From 5 g (36mmol) Salicylic acid, 35ml (330mmol) Toluene and 5 g (48,98mmol) acetic anhydride we should be getting a yield of 6,52 g (4,66ml) of acetylsalicylic acid. The results shown that the actually obtained volume has a yield of 1,98 g (1,41ml; 30,3%).
There is to many of 96% ethanol added, through that too many of the crystals were solutes and the total yield is lower than expected (6,52g; 4,66ml).
The melting point determination shows that there was a high concentration of acetic acid present in the solid. This causes a lower melting point (97 °C ) than the melting point from acetylsalicylic acid alone ( 137 °C). This was not very surprising because acetic acid is a product of this reaction.
Looking at the IR values, table 4 and table 5 shows that the same bonds are present in the first solution as in the final solid. Looking at equation 1 this is true. All de bond are still remain only the location of some bonds is different. The only different peak is (in attachment 2) the peak with wave number 3400 cm-1. The explanation is that after the second Buchner filtration, demi water (10,9g) is added.
This causes the high peak in the IR spectrum.