Extraction and Evaporation Recrystallization and Melting Point Measurement

Topics: Chemistry, PH, Sodium bicarbonate Pages: 11 (2895 words) Published: October 10, 2014
Chem 231: Organic Chemistry Lab

EXPERIMENT #2 and #3
Extraction and Evaporation
Recrystallization and Melting Point Measurement

PURPOSE:

1. To the components of a simulated pharmaceutical preparation, Panacetin, and identifying the unknown component of the mixture through extraction and separation methods. 2. To learn how to purify by recrystallization, how to dry them and how to obtain a melting point.

PRECAUTION: ACETANILIDE AND PHENACETIN ARE EYE AND SKIN IRRITANTS. Minimize contact with your unknown compound.

THEORY:

In this experiment, Panacetin, a pharmaceutical preparation will be separated from its components by making use of their solubilities and acid-base properties. Panacetin contains aspirin, sucrose and an unknown component that may be either acetanilide or phenacetin. Of the three components, only sucrose is insoluble in the organic solvent dichloromethane (CH2Cl2 or methylene chloride). The insoluble sucrose can be filtered out if Panacetin is dissolved completely in dichloromethane by gravity filtration or centrifugation leaving the soluble aspirin, acetanilide and phenacetin in the solution.

Although the acetanilide and aspirin are both quite insoluble in water at room temperature, the sodium salt of aspirin is very soluble in water but insoluble in dichloromethane. Aspirin, which is a strong acid can be converted to the salt, sodium acetylsalicylate by extraction with an aqueous solution of sodium bicarbonate . This salt will migrate from the dichloromethane layer, in which it is insoluble, to the aqueous layer, in which it is soluble. The unknown component will stay behind in the solution and can be isolated by evaporating the solvent from the dichloromethane solution. Adding HCl to the aqueous solution restores aspirin as an insoluble white solid.

In the third experiment, the identity of the unknown component of Panacetin will be purified. Purification is necessary because the separation procedure may be imperfect leaving traces of small quantities in the compound after separation or chemical reactions may occur prior to or during the separation adding new impurities. The unknown component can be purified by recrystallization, in which an impure solid dissolves in a hot (usually boiling) solvent then crystallizes from the cooled solution in a purer form.

Physical Properties

Mol wt
Melting point
Solubility (c.w)
Solubility (b.w)
acetanilide
135.2

114
0.54
5.0
Phenacetin

179.2
135
0.076
1.22
acetaminophen
151.169
169
0.0143
0.05

After a compound has been purified, it should be analyzed to establish its identity and degree of purity. Through melting point measurement , we will be able to identify the organic compound.

REACTION/CALCULATIONS:



AspirinNaHCO3 Sodium Acetylsalicylate

ASPIRINACETANILIDE

ACETAMINOPHENPHENACETIN

YIELD CALCULATIONS:

A. Experiment 2

a. Sucrose=0.4765 g
b. Aspirin=0.7149 g
c. Unknown= 1.4634 g

B. Experiment 3

METHODS/PROCEDURES:

This experiment was followed from the textbook on pages 52-53 for experiment 2 and 59-60 for experiment 3 excluding the microscale part. First, weigh approximately 3.00 g of Panacetin and transfer it to a clean, dry 125 ml Erlenmeyer flask. Add 50 ml of dichloromethane to the flask , stir the mixture with a stirring rod to break up any lumps. When it appears that no more of the solid will dissolve, filter the mixture by gravity. Collect the undissolved solid on the filter paper and set it aside to dry. Once it has completely dried, reweigh the solid. This compound separated by gravity filtration is known as sucrose.

Next, transfer the filtrate to a separatory funnel and extract it with two 30 ml portions of 5% sodium bicarbonate . For each extraction, use a stirring rod to stir the liquid...
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