Why is synthesis of aspirin important

Limiting reactants are important in chemical reactions because a reaction cannot proceed without all of the reactants. That is to say, a reaction can only occur until one reactant is used up Kirk, Percent yields are related to limiting reactants because the formula to solve for percent yield includes theoretical and actual yield. The theoretical yield is the amount of a product formed when the limiting reactant in completely consumed, and is the maximum amount that can be produced from the amount of reactants used in the reaction.

The theoretical yield is rarely obtained because of sources of error, side reactions, or other complications. The percent yield is the actual yield of a product given as a percentage of the theoretical yield Kirk, How can one prepare aspirin through a reaction between salicylic acid and acetic anhydride? Overall Findings: When the salicylic acid and acetic anhydride were mixed, a white, powdery solution formed. When the sulfuric acid was added, a clear solution formed that produced heat.

After heating, then cooling and scratching the solution, a white precipitate formed. The moisture in the precipitate was filtered overnight and what was left over was the desired product, aspirin. Qualitative Data: The boiling chips calcium carbonate were white, opaque crystals. The acetic anhydride was a clear solution with a vinegar-like odour. The salicylic acid was a find, white solid powder. The ethanol was a clear solution with an odour similar to strong alcohol.

The sulfuric acid was a clear solution with a strong odour when heated. The aspirin acetylsalicylic acid was a white, solid powder. When the acetic anhydride and salicylic acid were mixed, they produced a white, powdery solution. When the sulfuric acid was added to this solution, it turned clear and was warm. Upon heating the solution and adding water, puffs of smoke were produced. Determine whether the limiting reactant is the salicylic acid or the acetic anhydride.

The crystals were rinsed with a small amount of iced tap water and dried. The filter paper and crystals were massed to determine the yield of acetylsalicylic acid. Aspirin Recrystallization The crude product of acetylsalicylic acid crystals were placed in a mL Erlenmeyer flask and diethyl ether, heated on a steam bath, was added drop-wise, while swirling, until all crystals had dissolved. The solution was cooled slowly to room temperature, then transferred to an ice-water bath. The mass of pure acetylsalicylic acid was determined and recorded and the percent yield of the reaction was calculated.

Table 2. Yield of acetylsalicylic acid. Theoretical yield for reaction is 5. Test for Phenols A small amount of distilled water 2 mL was placed in each of 4 test tubes. A small mass of one of four different unknown solid compounds was added to each tube. The procedure was repeated using one drop of molecular iodine solution in place of iron III chloride solution. Table 3. Color changes for iron III chloride and iodine tests of unknowns. Therefore, sulfuric acid was the most effective catalyst, followed by boron trifluoride etherate, pyridine, then sodium acetate.

The general mechanism for catalysation by a base, like the acetate ion or pyridine, is shown in Figure 2. Bases catalyze the reaction by deprotonating the carboxyl group on salicylic acid or the phenol group in the minor pathway , activating the nucleophile. Pyridine also activates the electrophile by reacting with acetic anhydride to form the N-acyliminium ion, as seen in Figure 3. N-acyliminium is a better electrophile than acetic anhydride due to the withdrawal of electron density from the electrophilic carbon by the nitrogen of the pyridyl ring.

This is why pyridine increases the rate of reaction more so than the acetate ion. Figure 2. General mechanism for a basic catalyst major pathway pictured. As seen in Figure 4, the general mechanism for catalyzation by an acidic species such as boron trifluoride or sulfuric acid involves the protonation of the electrophile, increasing its electrophilicity.

This is partially because of the fact that Salicylic acid is a diprotic acid; this means that when Salicylic acid dissolves in water, it releases two Hydronium ions and makes the solution more acidic than if the same number of a monoprotic acid molecules were added.

A monoprotic acid is one that only releases one Hydronium ion when it dissolves in water. In , Felix Hoffmann discovered that there was indeed a way to make this drug less irritating to the throat and stomach: by reacting Salicylic acid with Acetic Anhydride, it would be possible to acetylate the Salicylic acid to remove one of these proton-donating groups and thus make it less irritating to the body.

With a name, Bayer proceeded to commercialize the Acetylsalicylic Acid in , though it was not until that Aspirin was released as an over-the-counter non-steroidal anti-inflammatory drug.

A few concepts are understood to be known in this experiment. The first of these is the concept of a limiting reactant. Whenever two or more reactants are brought together to do something, they react in particular whole-number ratios.

As such, any reactant that exists in an amount more than this whole number ratio is known as an excess reactant and some will be left over when the reaction is completely finished. The reactant that is used up in its entirety is known as the limiting reactant.

By using molar masses and these whole number molar ratios, it is also possible to calculate the theoretical yield of the reaction. By comparing the actual yield of the reaction and the theoretical yield, one can then find the yield percentage of the experiment.

As no experiment is perfect, the yield percent will always be less than 1. Another chemical concept used in this lab is that of a catalyst. A catalyst is something that changes the rate of a reaction, but is not actually consumed in the reaction itself. In this experiment, the catalyst of Phosphoric Acid is used to catalyze the formation of Aspirin, which can be seen in the mechanism of the reaction in Figure 2. Catalysts do not change the composition of the final product, however, and this is also visible in Figure 2.

Many different laboratory techniques are used in the synthesis of Aspirin. The first of these that is used is the procedure of weighing by difference. To do this, place an arbitrary amount of the substance to be weighed greater than the desired amount on the Fischer balance and press the tare bar to reset the balance to zero.

Then, after resetting the balance, take the large arbitrary amount of substance and transfer some of the substance to the desired beaker or other receptacle. By replacing the arbitrary large amount of substance that was on the balance at first, it is then possible to view the total amount of substance removed from the large arbitrary amount and is, consequentially, in the desired receptacle.

It is possible to repeat this process in order to end up with the desired amount of substance in the end. Another laboratory procedure used in this procedure is reading and recording liquid volumes.

There are many instruments that can be used to measure liquid amounts that differ in measuring capacity and accuracy, but the one used in this experiment is the graduated cylinder. To measure an amount of a liquid, the liquid to be measured is poured into the graduated cylinder.

When liquid is placed in a narrow vertical glass tube, the forces of adhesion and cohesion will cause to form a curve in the tube. This curve, whether the liquid in the middle is higher or lower than the outside, is called the meniscus. In order to get a correct reading while looking at a graduated cylinder, one must look at the middle of the meniscus.

If the meniscus curves up, then the correct reading will be at the bottom of the meniscus. Conversely, if the meniscus curves down and forms a sort of dome, the proper measurement is at the top of the meniscus.

Another laboratory technique used in this experiment is vacuum filtration. The process of vacuum filtration uses a filter crucible, an aspirator, and a vacuum hose in order to separate a liquid from a solid.

The crucible is placed in the aspirator with a rubber stopper between the two pieces of equipment to ensure the seal between them. Turning the aspirator on will cause a low-pressure area in the vacuum hose, which will in turn pull air and anything else through the crucible that can get through the filter liquid. It wasn't until the 's, when British pharmacologist John Vane, Ph. Vane and his colleagues found that aspirin inhibited the release of a hormone like substance called prostaglandin.

This chemical regulates certain body functions, such as blood vessel elasticity and changing the functions of blood platelets. Thus can aspirin affect blood clotting and ease inflammation. Procedure The reaction for synthesis of acetylsalicylic acid is shown in the following figure. In previous experiments, we used Fischer esterification reaction to produce some esters that we detected by odor. The current experiment uses, instead of glacial acetic acid concentrated acetic acid , another carboxylic acid derivative, acetic anhydride for ester formation.

The advantage of using acetic anhydride is that you do not produce water which can be used for hydrolysis of the newly formed ester. Concentrated phosphoric acid will be used to keep everything in the acidified, protonated state. Acetic anhydride is the preferred acid derivative to synthesize aspirin commercially because the acetic acid produced in this reaction can be used again, by converting it back into acetic anhydride. In a mL erlenmeyer flask, add 2 g salicylic acid put the flask on the balance, and zero it.

In the hood, carefully add 5 mL of acetic anhydride severe irritant, handle carefully to the flask. Stir the mixture with a stirring rod. Place the flask and its contents in a boiling water bath and stir untill all the solid dissolves.