CM1501 Expt 2

Topics: Chemistry, Solvent, Solubility Pages: 7 (1292 words) Published: October 15, 2013
National University of Singapore

CM1501
Organic Chemistry for Engineers

Lab Report
Experiment 2: Separation and Identification of Two Organic Compounds

10th October 2013

Abstract
This experiment involves the separation and identification of 2 organic compounds (1 Neutral Compound and 1 Acidic Compound) in a mixture. Separation techniques used in this experiment include solvent extraction, simple distillation and recrystallization using a suitable solvent determined through a solubility test. The identification method used was through Melting Point Determination. By obtaining data of the melting points of the 2 purified compounds and cross-referencing from a list of possible organic compounds, the 2 organic compounds were identified to be Dibenzalacetone (Neutral) and o-Chlorobenzoic acid (Acidic). Results

A solubility test was conducted to determine the recrystallization solvent to be used for the 2 compounds. The solvents used in the test were water and ethanol, both under room temperature and near boiling conditions. The results are tabulated in Table 1 below. Table 1: Results for Solubility Tests

Solvent
Neutral Compound
Acidic Compound

Room Temp
Hot
Room Temp
Hot
Water
Not Soluble
Not Soluble
Not Soluble
Not Soluble
Ethanol
Not Soluble
Soluble
Not Soluble
Soluble

From the results in Table 1, the method of recrystallization using 100% ethanol is determined to be most suitable for both compounds. Using 100% ethanol as the solvent for recrystallization, the purified compounds were obtained in the form of crystals. Table 2 below summarises the primary data of the 2 purified compounds. Table 2: Primary Data of Purified Compounds

Neutral Compound
Acidic Compound
Appearance
Yellow crystals
White powder
Mass obtained (g)
0.6844
0.5893

After obtaining the purified compounds, their melting points are then determined. The experimentally obtained melting point data are then checked against a list of possible compounds and identified. The results are shown in Table 3 below. Table 3: Identification of Purified Compounds by Melting Point Determination

Neutral Compound
Acidic Compound
Measured Melting Point (°C)
111.2 °C -111.8 °C
140.9 °C – 141.3 °C
Theoretical Melting Point (°C)
110.0 °C – 112.0 °C
140.0 °C – 142.0 °C
Chemical Name
Dibenzalacetone
o-Chlorobenzoic acid

Chemical Structure1,2

Discussion
Yield
From Table 2, the yield of the neutral and acidic compounds can be calculated. Yield of Neutral Compound (Dibenzalacetone) =
= 34.2%
Yield of Acidic Compound (o-Chlorobenzoic acid) =
= 29.5%
The appearance of the yellow crystals obtained tallies with the reference physical appearance of Dibenzalacetone1. The appearance of the white powder obtained also tallies with the reference physical appearance of o-Chlorobenzoic acid2. The yields of the compounds are relatively low at 34.2% and 29.5%. This may be due to some possible sources of error and limitations which will be discussed in the next section. Limitations and Sources of Error

Loss of compounds was an important factor that caused the yield of the purified compounds to be reduced. This may have occurred first during the extraction phase where extraction may not be complete. During the filtration and vacuum filtration processes, there was also a high level of difficulty in retrieving all the wanted products due to the products forming on the edges of the filter paper or sticking to the sides of the apparatus. Although the yield can be improved by increasing the number of extractions, the increase will not be significant enough (explained under exercise question 1) to overcome the loss of the compounds due to frequent transferring of the products. The usage of the separatory funnel to separate the 2 organic and aqueous layers limited the accuracy of the experiment due to potential contamination. There was difficulty in determining the exact boundaries between the...
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