Penicillin is the basis for most of the antibiotics in the world just as aspirin is the basis for many drugs. Therefore, if there had been only two drugs to invent, it would be down to penicillin and aspirin. Hippocrates, the father of modern medicine lived sometime between 460 B.C and 377 B.C. Hippocrates has left historical records of pain relief treatments, including the use of a powder made from the bark and leaves of the willow tree to help heal headaches, pains and fevers. By 1829, scientists discovered that it was the compound called salicin in willow plants, which gave the pain relief. We need to wait a quarter century for Charles Frederic Gerhardt to find a way to neutralize salicylic acid by buffering it with sodium (sodium salicylate) and acetyl chloride, creating acetylsalicylic acid (aspirin) 46 years later Felix Hoffmann, who worked for Bayer, rediscovered Gerhardt's formula. Hoffmann then convinced Bayer to market the new drug. Bayer patented aspirin on February 27, 1900. The drug was first sold as a powder. In 1915, the first Aspirin tablets were made. After Germany lost World War I, Bayer was forced to give up his trademarks as part of the Treaty of Versailles in 1919. Nowadays, Aspirin is the most consumed drug worldwide, with an annual consumption estimated at 40,000 tons, the equivalent of 120 billion tablets. We use it for migraine, prevention of heart attacks, diabetes, and to reduce pain and fever. How and why to make aspirin?
Nobel Prize winner Sir John Vane discovered in 1971 that acetylsalicylic acid inhibits the biosynthesis of certain messenger molecules known as prostaglandins. These prostaglandins perform a number of different functions in the body. They play a particularly important role in the processes of pain and inflammation, in which they act as mediators. They are formed whenever a cell is damaged or even destroyed by factors such as mechanical effects, heat or aggressive chemicals. When damage such as this occurs, the fatty acid arachidonic acid is released from the cell membrane. Prostaglandins are immediately synthesized from this substance with the aid of two enzymes. Acetylsalicylic acid (ASA) inhibits the activity of both of these enzymes, thus preventing the biosynthesis of pain-exacerbating and pro-inflammatory prostaglandins. The main ingredient in aspirin is acetylsalicylic acid obtained by acetylation of salicylic acid. Acetylsalicylic acid can be found naturally in certain plants (willow bark for example) or chemically synthesized from phenol C6H5OH. Indeed, if every year about 40,000 tons of aspirin are consumed worldwide we should therefore have to plant and produce 15 106 willows per year over a land area of 3,104 ha to extract the powder that we need to transform as aspirin. Hence the need for pharmaceutical plants to synthesize it chemically. Purpose: Synthesizing aspirin
Bayer A.G. of Germany had become one of the world’s leading producers of synthetic dyestuffs, created through the manipulation and synthesis of organic chemical molecules. In 1896, Bayer established a laboratory to synthesize and test dyestuff formulations for medicinal effects in humans. One of its candidates, acetylsalicylic acid, proved to be as effective against fever and headaches as its parent molecule, salicylic acid, but with far milder side effects. The new formulation was named “aspirin,” which was patented, trademarked, licensed, and sold profitably by Bayer throughout the world. While the aspirin production process varies between pharmaceutical companies, dosage forms and amounts, the process is not as complex as the process for many other drugs. In particular, the production of hard aspirin tablets requires only four ingredients: the active ingredient (acetylsalicylic acid), corn starch, water, and a lubricant. The purpose of this experiment is to show how to crate this active ingredient the Acetylsalicylic Acid. The basis of this experiment will be salicylic acid that we will mix with acetic anhydride in the presence of a catalyst, it should produce an acid of which we do not know the purity or the PH. We will have to Insulate and purify the Acetylsalicylic acid or aspirin. Then, we will have to do some required tests to be able to tell if the product thus obtained can be eaten and in what form. The experiment
The experiment evolves in three distinct parts:
Synthesis of salicylic acid (C7H6O3) and acetic anhydride (C4H603) in the presence of a catalyst (phosphoric acid or H3PO). Isolation and purification of aspirin.
Estimation of the purity of the final product.
Synthesis: The synthesis involves the following reaction
Isolation and Purification: Once the aspirin is prepared, it must be isolated from the reaction solution and purified. The aspirin is insoluble in cold water, so can be isolated by filtering the chilled reaction solution. Purification is necessary to remove any unreacted salicylic acid and acetic anhydride, as well as the acetic acid product and phosphoric acid. Acetic anhydride will decompose by the addition of water once the formation of aspirin is complete:
Final purification is accomplished by the process of recrystallization. The impure aspirin is dissolved in warm ethanol. The solution is then cooled slowly. The aspirin crystallizes out of the solution leaving the salicylic acid and other impurities behind. Estimation of Purity: The melting point of the compound can be used to identify it and also to estimate its purity. Generally, an impure compound will exhibit a lower melting point than that of the pure compound. Therefore, if your aspirin melts at a temperature below the accepted melting point, two possibilities exist: either your product is impure or it is not aspirin. Procedure:
1. Weigh out 3.0 g of salicylic acid (C7H6O3) and place it in a 250 ml Erlenmeyer flask. 2. Measure out 6.0 ml of acetic anhydride (C4H603) and add this to your flask. Be sure to do this in the hood and wear your goggles. Do not let the acetic anhydride contact your skin and don't get the vapors in your eyes. 3. Still in the hood, carefully add 5 to 10 drops of 85% phosphoric acid (H3PO), a catalyst, to the flask and swirl to mix everything thoroughly. 4. Still in the hood, heat the mixture for about 10 min. in a beaker of warm water (70-80°C). It is heated in the presence of a catalyst to accelerate the result because the reaction is both complete and faster when subjected to warm temperatures.
5. After heating, cautiously add 20 drops of distilled water. 6. Next, add 20 ml of distilled water and cool in an ice bath. If crystals do not appear, you can scratch the walls of the flask with a stirring rod to induce crystallization. 7. Filter the solid aspirin through a piece of pre-weighed filter paper using a Buchner funnel and an aspirator. Wash the crystals with 2-3 ml of chilled water. The liquid is mostly water and can be washed down the sink. Allow the air to be drawn through the solid and filter paper for 15 minutes. Be sure to record the filter paper weight in your notebook. 8. Preweigh a watch glass, and place the filter paper with the product on it and weigh. Obtain the weight of the aspirin by subtracting the weights of the filter paper and the watch glass from the total weight. 9. At this point, the aspirin contains traces of water and salicylic acid, and further purification is required. Place a small amount of this impure aspirin in a small-labeled beaker, cover with a tissue, and set aside to dry. The amount to be placed in the beaker, enough to measure a melting point, will be indicated by the instructor. 10. Transfer the remainder of the impure aspirin to a 100 mL beaker. Add 10 mL of 95% ethanol to the beaker and warm (do not boil) the mixture in a water bath to dissolve the crystals. If the crystals do not all dissolve, add 5 mL more of the ethanol and continue to warm the mixture. When the crystals are all dissolved, add 20 mL of warm water, cover the beaker with a watch glass, and let the solution cool slowly. Crystals of aspirin will form. Complete the recrystalization by cooling in an ice bath. 11. Collect the purified aspirin by filtration as before. Dry the crystals by pulling air through them for about 15 minutes. Put the product into a small beaker, cover with a tissue, and set aside to dry further. 12. Measure the melting points of both the impure aspirin, and the recrystallized aspirin. Observations:
1 The Acetyl Acid smells very strongly, and the container cannot be open very long. 2 The Salicylic Acid is a very fine, white powder.
3 After mixing the reactants, the product smells almost like vinegar. 4 Once the beaker is set in ice water the liquid become almost like a white slush or paste. 5 At the end of Purification the crystals forms rather quickly. Unlike before, these are pure crystals and not a paste.
The Buchner funnel is a filtering device. Place the solution on top of the filter that only allows liquids to pass through. Using the vacuum for liquids, in this case water, pull through the water until only the aspirin remains. Compare the melting points of the impure aspirin and of the recrystallized aspirin with that of pure aspirin, 138-140oC……………………..
Aspirin is a wonder drug. This magic powder is the basis of most currently used drugs. Indeed, acetylsalicylic acid powder is incorporated into many medicinal compounds all over the world. In France for example, 237 marketed drugs contain aspirin. Today, Americans alone consume 16,000 tons of aspirin tablets a year, equaling 80 million pills, and spend about $2 billion a year for non-prescription pain relievers, many of which contain aspirin or similar drugs. But, after more than a hundred years of marketing, in 2010, Professor Peter Rothwell of Oxford University and his team showed that aspirin had almost universal preventive effect to certain cancers when it is taken in small doses for years (Le Figaro 12/07/2010). The researchers point out that the benefits appear after five years consumption for colorectal cancer, cancers of the esophagus, pancreas, brain, stomach, lung and prostate. Their studies proved it could block or restrict certain cancer process before they are visible. The main disadvantage is that the grains of aspirin remain a long time in the stomach before being dissolved, absorbed and then reach a specific target in the body. Thus, aspirin can cause burns and ulcers to the lining of the stomach as acetylsalicylic acid has aggressive, even corrosive properties, when in contact with it in solid form. Other side effects can also be observed like allergies or rashes. According to the pH and form of aspirin, a particular property will match on its scope. This is why chemists and pharmacists are creative in shaping the aspirin powder. To act optimally and pass into the bloodstream, the active ingredient will be administered under the aspect that best suits to reach its target in the body. Hence, the importance of having gastro-resistant tablets such as coated tablets for the coating will prevent the aspirin from dissolving in the stomach. You can also find aspirin in other forms: tablets simple, soluble tablets and effervescent, buffered tablets, powder in sachets, capsules or suppositories. All those forms help to meet therapeutic requirements such as efficiency, security, stability, tolerance, and ease of use. Aspirin we obtained is of great quality but it is not advisable to use it directly as a drug because it is too acidic. To eat it, it should be put in the presence of a carrier that will make the active ingredient administered, modulate its release in the body, then deliver the drug to the absorption site. This excipient will also improve the conservation and taste of aspirin administered orally. Aspirin is now rivaled by paracetamol, which would also be interesting to manufacture and study because it has no counter-effects on the gastric level to fight against mild pains and fevers. In spite of its 3 millenia, aspirin has yet a lot to offer and hasn’t finished surprising its consummers and it’s researchers. As of the latest discoveries it is very useful for the prevention of cardiovascular risks and some cancers, who knows what it will bring in the next century? Only science will say. But, remember, even the most remarkable drug of the world should be used and administered with caution.