Synthesis of Aspirin

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Lab 1: Synthesis of Aspirin

Introduction:

The purpose of this lab was to demonstrate the ability to easily alter the molecular structure of a compound to greatly increase its utility. In this case, an acetyl group was added to salicylic acid, a naturally occurring compound with significant pharmaceutical value. Without the addition of the acetyl group, salicylic acid is an irritant to the gastro-intestinal (GI) tract. Once the acetyl group is added via a simple reaction, acetylsalicylic acid (commonly referred to as aspirin) is formed. Aspirin does not have the same negative effect on the GI tract as salicylic acid and has shown itself to be not only one of the safest and most effective analgesics, but vital in the prevention of heart attacks and strokes in those with history of these conditions or otherwise predisposed to them. This lab facilitated an in depth look at both acid-catalyzed and base-catalyzed reactions to produce aspirin from salicylic acid and the critical differences between the two. The lab demonstrated both the simplicity of the overall reaction, but also a number of considerations regarding the final come which will be discussed in great detail below. The process of the lab included two acid-catalyzed reactions (using BF3(MeOH) and H2SO4)., and two catalyzed with bases (anhydrous sodium and pyridine). Salicylic acid was combined with acetic anhydride in four test tubes, and one of the four catalysts was added to each. The reactions were monitored and timed to track their rates, and then all four test tubes were combined, washed in water solution, and the aspirin produced was massed.

Equation Used:
% Yield = Mass of Products (g)/Expected Mass (g) X 100% (equation 1)

Results:
Structures:
The following compounds and their structures were used in this experiment (figure 1; figure2; figure 3; figure4; figure5; figure6; figure7):

Reaction Mechanisms:

Figure 8. Un-catalyzed production of aspirin

Step 1 Step 2 Step 3

Figure 9. Acid-Catalyzed production of aspirin

Figure 10. Base-Catalyzed production of aspirin

Data:

Table 1:
Catalyst| Acid/Base role played| Time (in sec.)|
1g Anhydrous sodium acetate| Base| 120|
3 drops pyridine| Base| 35|
3 drops BF3(MeOH)| Acid (Lewis)| 6|
3 drops H2SO4| Acid| 23|

Table 1 shows the four catalysts used in the experiment, the role they played in the formation of acetylsalicylic acid, the duration of time in which the temperature of the reactants rose by 4 °C (signaling the rate of the reaction).

Table 2. Masses taken during the experiment (in grams)

Reagent| Total mass| grams/mole| Moles|
Salicylic acid| 2.023g| 138.121| 0.014646578|
Acetic Anhydride| 4.32g| 102.089| 0.042316018|

Product| Total mass| grams/mole| Moles|
Acetylsalicylic acid| 0.133g| 180.157| 0.000738|

Calculations:

Mass of Salicylic acid:

(test tube 1) +(test tube 2) + (test tube 3) + (test tube 4) = Total mass

0.507g + 0.508g + 0.506g + 0.502g =2.023g

Mass of Salicylic acid= 2.023g (see table 2 above)

Mass of Acetic Anhydride:

Convert 1ml of acetic anhydride to grams:

1ml of acetic anhydride X 1.08g/ml = 1.08g

(test tube 1) +(test tube 2) + (test tube 3) + (test tube 4) = Total mass

1.08g + 1.08g + 1.08g + 1.08g = 4.32 (see table 2 above)

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Conversion to moles:

2.023g of Salicylic acid / (138.121g/mol) = 0.0146 moles

4.33g of Acetic anhydride / (102.089g/mol) = 0.042 moles
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***If 0.0146 moles of Salicylic acid (the limiting reactant) used in the reaction, 0.0146 moles of Acetylsalicylic acid are expected.*** -------------------------------------------------

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