In this experiment you will be preparing the ester ethyl benzoate by warming ethanol and benzoic acid in a plastic pipette in a water bath.

Class practical

The ester, ethyl benzoate, is prepared using a microscale technique, from benzoic acid and ethanol mixed in a plastic pipette and warmed in a waterbath. The ester is identified by smell.

Lesson organisation

An organic preparation suitable as a class experiment for post-16 students, using a microscale technique that produces an identifiable product in about 20 minutes.

Apparatus Chemicals

Eye protection

Each group will require:

Measuring cylinder, 5 cm3

Beaker, 10 cm3

Plastic dropping pipettes, 4

Thermometer, 0 -110°C

Beaker, 100 cm3

Heat resistant mat

Access to top-pan balance, weighing to 0.01 g

Bunsen burner, tripod and gauze

or

Access to an electric hotplate, with thermostatic control

or

Access to thermostatically controlled water bath set at 70 - 80°C

Ethanol, (IDA, Industrial Denatured Alcohol) (HIGHLY FLAMMABLE, HARMFUL), 1 cm3

Benzoic acid (HARMFUL), about 0.5 g

Concentrated sulfuric acid (CORROSIVE), access to small quantity

Refer to Health & Safety and Technical notes section below for additional information.

Health & Safety and Technical notes

Read our standard health & safety guidance

 Wear eye protection. 

Ethanol or IDA (Industrial Denatured Alcohol), C2H5OH(l), (HIGHLY FLAMMABLE, HARMFUL) - see CLEAPSS Hazcard.

Benzoic acid, C6H5COOH(s) (HARMFUL) - see CLEAPSS Hazcard. 

Concentrated sulfuric acid, H2SO4(l), (CORROSIVE) - see CLEAPSS Hazcard.  

Each group requires the stem of one of the three plastic dropping pipettes to be shortened, and a second pipette’s stem to be cut off completely, as illustrated:

This may be done in advance as part of technician preparation, but teachers may decide to leave this to the students. If so, they will require a sharp knife or scissors.

Procedure

a Weigh 0.24 g of benzoic acid into the 10 cm3 beaker.

b Add 1 cm3 of ethanol and swirl to dissolve.

c Hold the shortened dropping pipette upside down. Carefully transfer, using a normal plastic dropping pipette, the contents of the beaker into the shortened dropping pipette.

d Using a clean, normal dropping pipette, add one drop of concentrated sulfuric acid to the mixture.

e Place the cut-off pipette bulb over the shortened pipette end.

f Set up a waterbath at 70 - 80°C using a small beaker about one-third full with water, and leave the assembled reaction vessel in the bath for 10 minutes.

g Remove from the water bath, take off the top and waft the vapour towards your nose. Describe the smell, and compare with the smell of other esters.

Teaching notes

Class activity after the practical:

Write an equation for the reaction that has occurred in this preparation.

The advantages of microscale techniques for organic preparation lie not only in the use of less reagents and safer conditions, but also in the speed with which a detectable product can be obtained.

Health & Safety checked, 2016

Credits

This Practical Chemistry resource was developed by the Nuffield Foundation and the Royal Society of Chemistry.

© Nuffield Foundation and the Royal Society of Chemistry

Page last updated October 2015