Aspirin Synthesis

Chem December 1st, 2020 Aspirin Synthesis Abstract: The main objective of the experiment is to synthesize acetylsalicylic acid (aspirin) through esterification of salicylic acid and acetic anhydride using phosphoric acid as a catalyst. In analyzing the purity of the product obtained by the given reagent through melting point range, thin layer chromatography and iron chloride test. The amount of crude aspirin synthesized was 0.187 gram and the theoretical yield was 68.24%. Thus, there was error percent in gaining the product while using the technique of crystallization and vacuuming. The iron chloride test proves the presence of pure aspirin as it shows more faint yellowish color instead of dark purple. TLC analysis showed that the acetylsalicylic had a higher Rf value than salicylic acid (0.634 vs. 0.487 Rf value, respectively) which proves that salicylic acid was more polar because of the extra functional group. Thus, pure aspirin was synthesized. Chemical Reaction / mechanism: Physical Properties Table 1: Name of the reagent Salicylic Acid Structure MP 158.6 °C Acetic anhydride −73 °C Acetylsalicylic acid 136 °C Phosphoric acid 42.35°C Acetic acid 16.6°C Procedure: About 50ml of hot water was prepared in a 100-150 beaker about 50 degree Celsius. 0.21grams of salicylic acid was weighed out and placed in a dry 5-ml conical vial. About 0.480 ml of acetic anhydride was added followed by 1 drop of concentrated phosphoric acid. Then a magnetic spin vane was added, and an air condenser was attached to it. 5ml conical vial was partially submerged in the hot bath using the clamp apparatus. Then the mixture was stirred until it was dissolved, and the reaction mixture was heated and stirred for 10 minutes. In doing the crystallization, a conical vial was removed from the hot water bath and was cooled at room temperature. The aspirin was crystallizing as the reaction vial cools. The air condenser was removed when it was cooled at room temperature the spin vane was removed using clean forceps. Again, in doing vacuum filtration, DI water was added to the conical vial and stirred thoroughly. The product was collected by vacuum filtration. Ice DI water was used in transferring remainder of the crystals in vial to Hirsch funnel. Then the crystals were collected with several portion of DI water. The product was air dried for 1 week after transferring to preweighted vial. Results Data The calculations of % yield of aspirin synthesis reaction is showed below Analysis of Product: The experimental melting points of the product obtained were around range of 133.5-135.1 degree Celsius. The melting point of salicylic acid is 158.6 degree Celsius which is higher than the obtained experimental data, this result proves that the obtained product has less percentage of salicylic acid. Again, acetic anhydride the melting point is -73.1 degree Celsius and acetic acid is 16.6 degree Celsius, this melting point of the given compounds proves that the product does not falls in the range of the melting point. The melting point of acetic acid and phosphoric acid is 16.6 degree Celsius and 42.35 degree Celsius, which is very less than the obtained data range. Again, for aspirin the melting point is 135 degree Celsius and this data falls in the range of the obtained experimental data. Therefore, the product contains pure aspirin. TLC: The below TLC analysis showed that the acetylsalicylic had a higher Rf value than salicylic acid (0.634 vs. 0.487 Rf value, respectively) which proves that salicylic acid was more polar because of the extra functional group. FeCl3 Test: Name of the Tube 1 Tube 2 Tube 3 Compounds H2O (0.5 ml) Salicylic Acid Aspirin FeCl3 (1 drop) Color + + + Dark purple + + + Faint yellowish color + + Faint yellowish color Iron chloride test result shows that the tube 1 shows dark purple color due to the presence of salicylic acid. Tube 2 shows faint yellowish color due to the presence of aspirin. Again, in tube 3 unknown shows faint yellowish color due to the absence of salicylic acid. This result proves that the unknown tube contain pure aspirin as the color shows faint yellowish instead of showing dark purple. This data proves that it contains pure aspirin. Conclusion/ Discussion: The main objective of this experiment was successful in determining the aspirin by synthesizing the reagents using the crystallization and vacuum filtration in obtaining pure crystal. Through the TLC, melting point range and FeCl3 test the main product (pure aspirin) was obtained. From FeCl3 test the result indicated that there was no presence of salicylic acid as the percentage of aspirin was more in the product which makes the product pure aspirin. The experimental yield was about 68.24% which clarifies the error obtained in gaining the product. The error might be in collecting the product while using the technique of crystallization and vacuuming. In TLC analysis further confirmed the result observed that the aspirin has a higher Rf value that salicylic acid (0.634 vs 0.487), thus these results demonstrate that one of the polar functional groups had been converted to an ester, which makes the aspirin less acidic. Synthesizing Acetylic acid through esterification of salicylic acid plays an important role in producing drugs which is useful for digestive system. Post lab Questions: 1. Aspirin is made by reaction of salicylic acid with acetic anhydride in presence of acidic catalyst. The presence of acidic catalyst helps to speed up the reaction. In the absence of catalyst salicylic acid reacts slowly with acetic anhydride. Acidic catalyst such as concentrated phosphoric acid protonates the acetic anhydride making it more electrophilic and more prone to attack by nucleophilic phenolic oxygen of salicylic acid, thus, increases rate of reaction. 2. In the mixture of 250mg=0.250g of salicylic acid and excess acetic anhydride the salicylic acid is the limiting reagent therefore the aspirin will be based on the moles of salicylic acid as the reagent of the reaction 3. The relation between grains and milligram 1grain= 65 milli grams. Hence, the conversion faction is 1grain/65mg and 65/1 grain. Hence, 5 grams of acetyl salicylic acid = 5 grain * 65/1 grain = 325 mg. Therefore, there are 325 mg of aspirin in each tablet. Reference “Aspirin Synthesis (Non-Microwave)”-” Laboratory Manual for organic Chemistry, by Kenneth F. Cerny/Schwartz 2017, pp-125