OUR LADY OF THE ROSARY COLLEGE CHEMISTRY
PRACTICAL MANUAL



Advanced Level, F.6
Experiment should be carried out under the supervision of a Chemistry teacher
Safety precaution must be noted.
Division of work: individual
The Preparation and Hydrolysis of Phenyl Benzoate
Introduction
A.
Preparation of aromatic ester.
They may be prepared by methods similar to those for aliphatic esters. These include:
(1) From the acid.
By refluxing an aromatic acid (1 mole) with an excess (up to 10 moles) of methanol or ethanol
in the presence if a small proportion of concentrated sulphuric(VI) acid or hydrogen chloride,
the ester may be obtained in good yield. The excess of methanol or ethanol may be largely
removed by distillation from a water bath or, less conveniently, by pouring into a large excess
of water. For higher alcohols, e.g. butanol, the proportion of alcohol may be considerably
reduced (say, 1 mole of monobasic acid to 2 moles of alcohol) if a volume of pure dry benzene
approximately equal to that of the alcohol is added. The following examples are given:
Esterification with an aromatic alcohol may be readily achieved by using an excess of the
acid. The acid is readily removed by washing with water and/or treatment with sodium
bicarbonate solution.
(2) From the nitrile
By refluxing mixture of the aromatic nitrile (with -CN group in side chain) with alcohol and
concentrated sulphuric acid, simultaneous hydrolysis and esterification occurs, for example:
(3) From the acid chloride:
The interaction of the acid chloride of an aromatic acid with the calculated quantity of an
alcohol or a phenol affords a good yield of the ester, for example,
(4) By the Schotten-Baumann reaction:
Under the usual Schotten-Baumann conditions, esters are readily formed, for example,
(5) From Grignard's reagent
B. Hydrolysis of esters.
Aliphatic esters are hydrolysed by boiling with 2 M sodium hydroxide under reflux until the
odour of the ester can no longer be detected (about 1 hour). Distil off the alcohol. The residue in the
flask is acidified with dilute sulphuric acid and distil off to get the organic acid. A slight
modification in the procedure for isolating the products of hydrolysis is necessary for phenolic (or
phenyl) esters. After refluxing with 2 M NaOH for 1 hour, the solution is allowed to cool and dilute
sulphuric acid is added. Both the organic acid and phenol are extracted with ether. The ethereal
solution is washed with sodium hydrogencarbonate solution by using a separating funnel. The
ethereal solution is dried and ether is evaporated away to get phenol. Acidify the aqueous washings
with dilute sulphuric acid to get the organic acid.
Apparatus
Quickfit apparatus, Buchner funnel, suctional pump and flask, rubber tubing for condenser, melting
point apparatus and capillary tubes, evaporating dish, separating funnel.
Chemicals
Phenol (4.0 g), 3.0 M sodium hydroxide (70 cm3), ether (30 cm3), methylated spirits (50 cm3),
benzoyl chloride, red litmus paper, ice, anhydrous potassium carbonate, phenylbenzoate.
Bench solution: sulphuric acid, sodium carbonate solution,
Hot water should be prepared by using an electric hot plate or cooker.
Procedure A. Preparation of phenyl benzoate [2 periods]
1. Dissolve 2.0 g of phenol in 30 cm3 of 2.0 M sodium hydroxide solution in a 250 cm3 conical
flask.
2. Add 4.0 cm3 of benzoyl chloride, stopper the flask securely and shake vigorously for 15
minutes.
3.
4.
5.
6.
At the end of this time, a solid product should be obtained which can be filtered off with
suctional pump, breaking up any lumps on the filter paper with a spatula.
Wash thoroughly with water and drain.
Re-crystallise the crude ester from methylated spirits using a quantity of hot solvent
approximately 1.5 times the minimum required for complete solution. This is to ensure that the
phenol benzoate does not separate until the temperature of the solution has fallen below the
melting point of the ester.
Phenyl benzoate separates as colourless crystals. (If the solution is not clearly, filter the hot
solution, but you must consult with the teacher in advance.) Determine the melting point and
7.
yield of the product. [N.B. Suctional filtration: A Buchner funnel, with filter paper, is placed
on the top of a vacuum flask. This flask is connected to vacuum pump which is fitted to tap.
When tap water flows, a low pressure is resulted in the flask and it speeds up the rate of
filtration.
Determination of melting point. A capillary tube, sealed at one end, is inserted into the sample
solid. Allow the capillary tube falling from the top of a long erect tube. The sample solid will
then accumulated at the closed end of the tube. Repeat the above steps several times until the
height of the sample in the tube is about 4 mm. The sample is ready for the determination of
melting point.
Procedure B. Hydrolysis of phenyl benzoate [3 periods]
1. Obtain 4.0 g of phenyl benzoate from your teacher. Mix it with 40 cm3 of 3.0 M sodium
hydroxide in a 50 cm3 Quickfit flask and boil the mixture under reflux until molten ester has
2.
3.
4.
5.
6.
7.
8.
completely disappeared (about 1 hour).
During the boiling, a small quantity of unchanged ester may have volatilized in the steam and
recrystallised in the condenser; therefore pour about 3 cm3 of the sodium hydroxide solution
down the condenser to dislodge the ester and continue boiling until the solution is clear.
Cool the solution in ice cold water and then add dilute sulphuric acid with stirring until a faint
but permanent precipitate of benzoic acid is produced (test with pH paper to ensure the
solution is acidic.
Add sodium carbonate solution with vigorous stirring until the precipitate is just redissolved
and the solution is alkaline to red litmus paper.
Extraction of phenol from the mixture (a) Transfer the reaction mixture into a separating
funnel. Add about 15 cm3 ether into the funnel and stir vigorously. Allow most of the ethereal
solution to run off into a small beaker. Repeat this step once again. (b) Add anhydrous
potassium carbonate to dry the united ethereal extract. Filter the mixture and discard the solid.
(c) Distil off the greater part of the ether. Pour the remainder whilst hot into an evaporating
basin dish and leave the phenol to crystallise out.
Extraction of benzoic acid from the mixture (a) The aqueous layer obtained in step 12(a)
contains benzoic acid. Run off the small amount of ethereal solution and discard it. (b) Add
hydrochloric acid to the aqueous solution to precipitate out the benzoic acid.
Filter at the pump (i.e. suctional filtration), wash the residue with water and recrystallise from
boiling water (i.e. dissolve the residue with minimum amount of hot water. When the water
cools, the acid will appear in the form of crystals. An ice-bath may help crystallization.)
Determine the yield and melting point of the benzoic acid and the yield of phenol. % yield =
mass of crystal/ mass of theoretical quantity
Questions
1. Propose synthetic route for the following conversion. Reaction conditions must be specified.
Organic reagents are limited to contain 3 or less carbon atoms only. C6H5 in the following
equations represent the phenyl group.
(a) C6H5COOCH3 -------> C6H5CH2COOCH3
(b) C6H5CH2OOC6H5 -------> C6H5CO2CH2OC6H5
2. Explain the solubility of phenol in 2 M sodium hydroxide (refer to step A1).
3. Give an equation for step A2.
4. Draw a diagram to show the experimental set-up for suctional filtration. (step A3). What are the
advantages and disadvantages of employing suctional filtration? Solute particles in milk
(mainly colloidal proteins) can not be separated by using filtration. Explain.
5. In step 3, the solubility of the product in water is very low. Explain.
6. Recrystallization is a common and important method to obtain a pure substance. Explain.
7. If you got low yield when step 6 was completed, give reasons to explain the low yield.
8. Propose a reaction mechanism together with an energy profile for the reaction in step B8.
9. Explain the purpose of adding dilute sulphuric acid in step B3.
10. Sodium carbonate is added to the resulting solution of step B4. What is the pH range when
you add no more sodium carbonate? Why is this pH range chosen?
11. List advantages and disadvantages when (a) ethoxyethane (b) ethanol is used for the
recrystallization of an organic compound.