Separating Acid and Neutral Compounds by solvent Extraction
Ziyue Zhu
2015/2/8
 Introduction:
The goal of this lab was to use solvent extraction techniques to spparate a mixture
consisting of p-Toluic Acid, p- tert-Butylphenol and acetanilide.
Extraction is a process that selectively dissolves one or more of the mixture
compounds into an appropriate solvent. The solution of there dissolved compounds is
often referred to as the extract. A compound can be separated from impurities in a
solution by extracting the compound from the original or first solvent into a second
solvent. The compound must be more soluble in the second solvent than in the first
solvent, and impurities must be insoluble in the second solvent. Also, to effect the
extraction, the two solvents selected must be immiscible or not soluble in one another,
so that they produce two separate solvent layers. Washing is the reverse process, in
which the impurities are removed to the second solvent. Leaving the desired
compound in the original solvent. An emulsion is a suspension of small droplets of
one liquid in another liquid. Emulsions are generally opaque or cloudy in appearance
and are often mistaken as a third layer. Some organic compounds are sufficiently
polar to be quite soluble in water. Extraction of such polar compounds into a nonpolar
solvent is often difficult. The process can be facilitated by using the technique called
salting out.
The first step of the lab was to add aqueous NaHCO3 to the ether solution in the
centrifuge tube. After mixing thoroughly, the identity of the layers were confirmed by
using a pipet to introduce one drop of water just below the surface of the top layer.
The second step was to add NaOH into ether solution remaining in the centrifuge tube.
After confirming the identity of two layers,HCl was added in the NaHCO3 solution
which was extracts from the second step in order to precipitate the p-toluic acid. Then
the NaOH solution was heated to 60oC so that the ether remained in the solution could
be removed. After cooled down the solution, HCl was added into the solution to
isolate p-tert-Butylphenol. In the third step, Na2SO4 was added into the remaining
solution in the centrifuge tube to remove water. The ether was evaported by warming
the beaker in a sand bath. After that the Acetanilide could be isolated by putting the
beaker into a ice bath to cool down. After all three compounds was dried, measured
their weights and melting points.
 Data
Table 1: The composition of the given mixture
Acetanilide
P-toluic Acid
Mass
6.0283
10.1323
P-tert-butylphenol
10.3118
Table 2: The expected composition of the sample mixture
Acetanilide
P-toluic Acid
Mass
0.2961728812
0.49780410447
P-tert-butylphenol
0.5066230142
Table 3: The actual composition of the sample mixture
Acetanilide
P-toluic Acid
Mass
0.5975
0.144
% of yield
201.74%
28.927%
P-tert-butylphenol
0.1398
27.59%
Table 4: The melting points of three compounds
Acetanilide
P-toluic Acid
o
o
Melting points
62 C - 67 C
176oC - 179oC
P-tert-butylphenol
95oC - 98oC
 Results and Discussion
The table 1 indicates the composition of the mixture of acetanilide, p-toluic Acid
and p-tert-butylphenol and table 3 shows the expected weight of the three compounds
in the lab. Whereas, table 3 indicates the three compounds recovered from the lab.
The yield of acetanilide was 201.74% and that of p-toluic Acid and p-tert-butylphenol
were 28.927% and 27.59%. In addition, the melting pointing points of the actenilide
was 62oC to 67oC which was very inaccurate. However, the melting points range of
p-toluic acid and p-tert-butylphenol was 176oC to 179oC and 95oC to 98oC which
were very close to the pure sample.
The most possible reason for the impossible high yield was that when decanting the
solution into the clean beaker, the Na2SO4 was also decanted into the beaker. Besides,
when filtered the acetanilide solution, some solution was wasted because it stayed in
the filtered flask. It also explained why the melting point range of the actenilide was
board and not even close to the true melting point range which was 112oC to 113oC.
The reason that could explain the low yield of the other two compounds was that the
HCl was added too fast so that lots of precipitation was left in the containers because
of the foaming.
 Post-Lab questions:
1. See table 3
2. Because the OH- ions in the NaOH would react with the HCO3- ions in the
NaHCO3. The Na2CO3 would be formed. In that case, no HCO3- ions can react with
the p-toluic acid to form crystals.
3. P- C4H9-C6H4ONa
4. When testing the identity of two layers, the drop of water will not stay in the under
layer. However, it will flow up to the top layer.
6. See results and discussion section.