Learning Activity 1
Preparation of Acetanilide
Recrystallization is a common method of purifying organic substances through the difference in solubility at different temperature. In this experiment, acetanilide was produced by acetylation of aniline with acetic anhydride. The crude acetanilide was dissolved in a solvent in a heating water bath. The solution was cooled slowly in an ice bath as crystals form out. As the compound crystallizes from the solution, molecules of other compounds dissolved in solution are excluded from growing crystal lattice, yielding pure acetanilide. Acetanilide is slightly soluble in water, and stable under most conditions. Pure crystals are plate shaped and colorless to white. This experiment involves four functional groups common in organic chemistry. Solids prepared in this manner serve a derivative, whose melting point may be correlated with known values and thus is a means of identification and serves as a test for homogeneity or purity.
Acetic anhydride is a colorless liquid with a pungent vinegar-like odor when it reacts with water to form acetic acid. The boiling point of acetic anhydride is 140°C and the melting point is -73°C. It is soluble in ether, chloroform and benzene. It is soluble in water when acetic anhydride decomposes. The density of acetic anhydride is 1.082 g/ml in liquid state and its molecular weight is 102.09 g/mol. Acetic anhydride is most widely used for the conversion of cellulose to cellulose acetate, which is a component of photographic film and other coated materials. It plays an important role in the acetylation of aniline to form acetanilide.
Acetanilide is in the general category of organic chemicals, since its main element is carbon. More specifically, it is an amide since it contains a carbon double bonded to an oxygen atom, while that same carbon is also connected to a nitrogen atom. It is also classified as an aromatic compound because the six carbon phenyl ring is contained in its molecular structure. Its chemical formula is CH3CONHC6H5. This chemical goes by numerous other names, including acetaminobenzene and acetanil.
Years ago, pharmacists dispensed acetanilide under the trade name Antifebrin to reduce fevers. Pharmacies have since moved on to different drugs for this purpose, but the chemical industry still employs acetanilide for a variety of purposes, primarily as an intermediate for synthesizing other chemicals.
Acetanilide which can be obtained by acetylation of aniline undergoes nitration at low temperature and yields highly the para-nitro products. Acetyl group can then be removed by acid-catalyzed hydrolysis to yield para-nitroaniline. Although the activating affection of the amino group can be reduced, the acetyl derivative remains an ortho/para-orientation and activating substituent.
Organic compounds that are solid at room temperature are usually purified by crystallization. Crystallization is the deposition of crystals from a solution. During the process of crystal formation, a molecule have the tendency to be attached to a growing crystal composed with the same type of molecules because of a better fit in a crystal lattice of a molecule of the same structure than for other molecule. (Pastro, John, & Miller) Lattice is a fixed and rigid arrangement of atoms, molecules or ions. (Mullin, 1961 ) Recrystallization is a method in which two crystallization processes was performed. It is referred to the second crystallization. (Pavia, Lampman, Kriz,& Engel, 1999) It depends on the difference of solubility of a substance in a hot and in a cold solvent.
Acetanilide was the first aniline derivative serendipitously found to possess analgesic as well as antipyretic properties, and was quickly introduced into medical practice under the name of Antifebrin by A. Cahn and P. Hepp in 1886. But its (apparent) unacceptable toxic effects, the most alarming being cyanosis due to methemoglobinemia, prompted the...
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