Group Medical Technology Organic Chemistry Laboratory
Recrystallization is one of the simplest and most widely used technique for purifying organic solids through the differences in solubility at different temperatures. It is also the process in which the solid to be crystallized is dissolved to either a hot solvent or a hot solvent mixture and is cooled in a solution.In this experiment, acetanilide, the crude product of acetylation of aniline and acetic anhydride, was used as the pure organic compound. Crude acetanilide underwent crystallization process using the preferred recrystallizing solvent, water. The crystallization process was when crude acetanilide was placed in hot water bath and was cooled after in an ice bath which would then yield to the formation of crystals of pure acetanilide. The percentage yield form the crude acetanilide was 94.59%. The percentage recovery of the experiment was 46.43%.
Organic compounds that are synthesized in laboratories or isolated from natural recourses are often tainted by impurities. Different purification methods can be used to remove the impurities present in a compound. One example of these is recrystallization. It is a method which purifies organic solids base on its solubility. It is also a process which dissolves solid to be crystallized in a hot solvent mixture and cools it afterward. The dissolve solid decreases insolubility at a low temperature and separates as it cools resulting to small seed crystals. Crystallization was done twice. During the first crystallization a crude product would be formed which would still have some impurities that needs to be remove. This was the reason for doing crystallization for a second time yield to a pure product which contained fewer or no impurities at all. The level of purity of the product can be checked through its melting point range. Formation of crystals was due to the difference insolubility of the solid with the solvent. Solutes or compounds tend to be more soluble in hot solvents than they were in cold solvents. The crystals formed have a lattice structure that is a fixed and rigid arrangement of atoms, molecules or ions. Solubility refers to the degree of substance in which the solute is to be dissolved in solvent. It was the main factor that affects crystallization. Identifying the recrystallizing solvent was very important in crystallization process. The substance to be crystallized must exhibit ideal solubility behavior in the chosen solvent. Purification of substances could take place when both the desired substance and the impurities have similar solubility at its boiling point temperature; and the impurities correspond to only a small portion of the total solid. The desired compound will crystallize in cooling temperature while impurities will not.
Figure 1. Structure of Aniline
Aniline (C6H5NH2) also known as aminobenzene or benzenamine is a primary amine in which the amino group is directly attached to the benzene ring and the final product of the reduction of most nitrogen derivatives of benzene. Its IUPAC name is Phenlyamine, has a density of 1.0217 g/ml and a molecular weight of 93.13 g/mol. Aniline is a clear to slightly yellow liquid with a characteristic odor. It does not readily evaporate at room temperature. Aniline is slightly soluble in water, 3.6g/100mL at 20°C, and mixes readily with most organic solvents. It is used to make a wide variety of products such as polyurethane foam, agricultural chemicals, synthetic dyes, antioxidants, stabilizers for the rubber industry, herbicides, varnishes and explosives. When exposed to light and air, it slowly changes it color and darkens because of atmospheric oxidation of an impurity usually present in the benzene from which the aniline was prepared. Aniline is acetylated by warming a mixture of aniline and acetic anhydride, forming N-phenylacetamide, which is more commonly known as...
References: From books:
. Ault (1983). Techniques & Experiments fo Organic Chemistry (4th Ed.). Massachusets: Ally & Bacon Incorporated.
. Martin & Gilbert (2011). Organic Laboratory Experiment (5th Ed.). Boston: Cengage Learning.
. University of Santo Tomas. Faculty of Pharmacy. Organic Chemistry Group. (2014). Laboratory Manual in Organic Chemistry (Revised Edition). Quezon City: C&E Publishing Inc.
. ACETANILIDE (N-PHENYLACETAMIDE). (n.d.). Retrieved September 28, 2014 from http://chemicalland21.com/lifescience/phar/ACETANILIDE.htm
. ACETIC ANHYDRIDE (ACETYL ETHER). (n.d.). Retrieved September 28, 2014, from http://chemicalland21.com/petrochemical/ACETIC%20ANHYDRIDE.htm
. PURIFYING ACETANILIDE BY RECRYSTALLIZATION. Retrieved September 24, 2014,from http://www.cerlabs.com/experiments/1087540703X.pdf
. RECRYSTALLIZATION.Retrieved September 27,2014 from http://chemistry.barnard.edu/orgolab/lab2 and http://web.centre.edu/muzyka/organic/lab/24_recrystallization.htm
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