Expt 4 formal report

Topics: Solvent, Solubility, Acetic acid Pages: 7 (1967 words) Published: October 19, 2014
Purification of Acetanilide by Recrystallization Method
Dupaya, Julian Victor M.
Estacio, Jerwin Caesar A.
Farnacio, Rebecca Ruth
Gabito, Jose Luis F.
Gallo, Cian Carlo M.
Galvez, Joshua M.
Group no.4, 2D-Medical Technology, Faculty of Pharmacy, University of Santo Tomas

ABSTRACT

Recrystallization is a method for purifying solid organic compounds. The process is dissolving the solid to be purified in a hot solvent and cooling the solution slowly, this allows impurities with different solubility to separate from the solution in each step. The objective of the experiment was to synthesize acetanilide by the acetylation of aniline and to purify crude acetanilide product by recrystallization. The group determined water as the recrystallizing solvent. The group performed acetylation of aniline and acetic anhydride for the formation of crude acetanilide. The recrystallizing solvent dissolved the crude acetanilide and was heated in a water bath, after heating, the solution was cooled in an ice bath causing crystals to form. The percent recovery was computed to be 38.49% while the percent yield was computed to be 34.46%.

INTRODUCTION

Compounds that are obtained from natural sources or from reaction of chemicals almost always contain impurities. The impurities may include some combination of insoluble, soluble, and colored impurities. To obtain a pure compound these impurities must be removed. Recrystallization is a method in which two crystallization processes was performed. It is referred to the second crystallization. (Pavia, Lampman, Kriz, & Engel, 1999) Recrystallization is a widely used purification process that removes these impurities from the compound. In performing recrystallization, solubility tests will be used to find a suitable recrystallization solvent for the compound. To determine which the most suitable recrystallizing solvent is, the compound should have a high solubility in the hot solvent and a low solubility in the cold solvent.

The recrystallization method can effectively produce pure compounds. With the difference in solublity, the substances can be separated by dissolving the solvent then filtering the impurities. As the solution is cooled, a small seed crystal is formed then it gradually increases layer by layer. Although the recrystallization method is not perfect, it does increase the purity of the product.

Solubility, which is the main factor that affects crystallization, is the quantity of a solute that can dissolve in a specific solvent. It is important to identify the recrystallizing solvent to be used in the experiment. Purification of a substance can occur when both the desired substance and impurity have the same solubility at its boiling point temperature, and when the impurity is only a small percentage of the total solid.

Figure I Structural formula of Aniline

Aniline [C6H5NH2] 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. Aniline is a clear to slightly yellow liquid although pure aniline is a highly poisonous, oily, colorless substance with a pleasant odor. It is commercially prepared by the catalytic hydrogenation of nitrobenzene or by the action of ammonia on chlorobenzene. It is an organic base used to make products such as dyes, drugs, explosives, plastics and photographic and rubber chemicals.

• Molar Mass – 93.13 g/mol
• Density – 1.0217 g/cm3
• Melting Point – -6.3°C

Figure II Structural formula
of acetic anhydride

Acetic anhydride or ethanoic anyhride [(CH3CO)2O] is a clear, colorless liquid with a very pungent, penetrating, vinegar-like odor that combines with water to form acetic acid. It is soluble in ether, chloroform and benzene.

Acetic anhydride is used as a raw material for cellulose acetate fibers and plastics. Acetic anhydride is also a significant raw material for aspirin, acetaminophen and other...


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