organic chemistry lab report help due in 12 hours.

Aspirin Synthesis Lab

Kendyl Tom Partner: Damaris Ochoa

TA: Subhadeep Dutta Lab: Thursday, 3:30PM Room# PSE 307

Abstract: An experiment of chemical synthesis was performed to extract acetylsalicylic acid from

salicylic acid. Acetylsalicylic acid was extracted by heating a reaction that consisted of the

reactant, salicylic acid, the reagent, acetic anhydride, and a catalyst, phosphoric acid. It was then

isolated by the use of crystallization, which involves the hydrophobic effect and cooling the

temperature. Finally, acetylsalicylic acid is purified using methods of recrystallization. Then the

product was characterized using melting point range and IR spectroscopy. Our results concluded

in a melting point range of 133.1 – 137.8C and a 31.6% yield of pure acetylsalicylic acid.

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Introduction

Chemical synthesis is a method that manipulates starting structures using a series of

chemical reactions to break and build bonds to form more complex structures. This method also

usually consists of multiple tasks that generally proceeds as: the performance of the reaction, the

isolation of the product, the purification of the product and the characterization of the product. In

synthesis the use of chemical reactions usually means the breaking and making of covalent bonds

to convert one chemical structure into another. It also relates to the aspect of the order in which

bonds are made and broken. In this reaction, Equation 1 and 2, the breaking of a bond must come

first, meaning it requires a high amount of energy for this break to occur; this is also known as

the activation energy. To help reach this activation energy this reaction will be heated because by

increasing temperature it allows the reaction to go faster. A catalyst will also be added to increase

the reaction rate. The reactant is shown as the salicylic acid, reagent in this experiment is

identified as acetic anhydride and the phosphoric acid is the catalyst.

(1)

(2)

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In the next step the reaction product must now be isolated and in this experiment the

method of crystallization was used. First, by decreasing the temperature, the solubility will also

decrease, allowing the solution reform a solid. Then by adding water to this solution, it induces

the hydrophobic effect due to the fact that most organic compounds have lower solubility in

water. Therefore, by adding water to the solution and then rinsing with cold water after it has

been filtered by the Hirsch, the isolated crystals of the product will be found.

Finally, the isolated product must be purified through recrystallization using the

centrifuge. Then, after the purification of the product the yield is found by converting the weight

of both the starting chemical and the final product to moles into a ratio of products over reactants

times 100 and it is characterized by finding the product’s melting point range and its IR

spectrum.

Experimental

The method described in this experiment called for 250mg of salicylic acid in a test tube

added with 0.5mL of acetic anhydride and one drop of 85% phosphoric acid. The reaction was

then performed by heating it on a hotplate and dissolving it into a solution. Then while the

solution was still warm, 1.5mL of deionized water was added. Next, the solution was then cooled

and placed into an ice bath to let crystals form. After the solution had cooled, it was filtered

through a Hirsch funnel and rinsed with cold water to isolate the crystals. The impure synthetic

aspirin was then transferred into a Craig tube. Where it was again dissolved by adding hot

ethanol. The white inner plug was then placed into the Craig tube and was allowed to cool to

room temperature before being transferred into an ice bath for 10-15 minutes.

Next, after 10-15 minutes in the ice bath, the ethanol is then separated from the pure

aspirin using centrifugation. The pure aspirin crystals are then extracted from the Craig tube and

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left to dry. The weight of these crystals is then found for the percent yield, as well as the melting

point range and the IR spectrum.

Results

In this chemical synthesis, salicylic acid is converted into acetylsalicylic acid. To test for

accuracy, melting point range test was run resulting in 133.1 – 137.8C. The chemical yield of

this can then be found by comparing the number of moles of reactant and product using Equation

4. The moles are attained from converting the measured weight into moles Eq. 2 and 3. The yield

of pure acetylsalicylic acid is then determined to be 31.6%.

Moles of Salicylic Acid =0.262 g x 1 mol

138.12 g =.001897 mols (2)

Moles of Acetylsalicylic Acid =0.108 g x 1mol

180.16 g =.0005995 mols (3)

Yield of pure acetylsalicylic acid = moles of product moles of reactant

x 100= .0005995 .001897

x 100=31.6 (4)

TABLE 1. Weight used to find percent yield and the melting point range of the pure product

Chemical Weight (g) Moles Melting Point (C) Starting Salicylic Acid 0.262g .001897 N/A Purified Aspirin Product 0.108g .0005995 133.1 – 137.8C

The infrared spectra of the pure aspirin reaction product is illustrated in Figure 1. The

characteristic peak frequencies for the vibrational peaks that can be designated to specific

functional groups are shown in Table 2 with assignments of the peaks with vibration frequencies

greater than 1500 cm-1.

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FIGURE 1. IR spectrum of pure aspirin product

TABLE 2. Significant peak frequencies and assignments for pure aspirin product

Vibration Frequency (cm-1) Functional Group Specific Bond Vibration 2980.70 Alkyl O - H 2585.77 Alkyl C (sp2)– H & C (sp3) - H 1749.50 Ester Ester 1679.89 Conjugate C = O 1604.59 Benzene Ring Benzene Ring

Discussion

In this experiment acetylsalicylic acid was synthesized from salicylic acid. In step one,

the performance of the reaction, salicylic acid was converted into acetylsalicylic acid, Equation 1

(Arizona State University, 2016). Acetic anhydride is used as a reagent and phosphoric acid is

used as a catalyst to increase the rate of reaction, as shown in the mechanism in Scheme 1.

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SCHEME 1. The mechanism of the formation of actylsalicylic acid from salicylic acid

The IR spectrum of both the beginning structure, salicylic acid, (Figure 2) and the final

product structure, acetylsalicylic acid, (Figure 1) shows the conversion between one structure to

the other. When looking at Figure 2 of salicylic acid it can noted that the OH bond circled,

corresponding to the peak that is circled, has disappeared from the IR spectrum of acetylsalicylic

acid in Figure 1 due to the bond breaking to form acetyl. In the acetylsalicylic acid IR spectrum

it also shows and additional peak that formed due to the ester in salicylic acid.

FIGURE 2. IR Spectrum of salicylic acid

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Due to the low percent yield of pure acetylsalicylic acid, a few errors that could have

occurred. During the filtration and transfers between tubes crystals could have been lost. As well

as during the reaction losses could have occurred due to incomplete formation of products.

Conclusion

The purpose of this lab was to convert salicylic acid into acetylsalicylic acid. The melting

point range was 133.1 – 137.8C meaning that the product produced is indeed pure

acetylsalicylic acid due to the almost matching ranges of melting points. The chemical yield of

the overall reaction was 31.6%. This is considerably low, most likely due to the fact that this

reaction had produced unwanted side-products and by-products, making losses in the reaction.

This method of chemical synthesis demonstrates an excellent way to convert simple structures

into the more wanted complex ones.

References Cited

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Arizona State University (2016, October 13). Aspirin Synthesis Lab Package.

Retrieved from https://myasucourses.asu.edu/

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