Microscale preparation of ethyl benzoate
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.
Read our standard health & safety guidance
Lesson organisation
An organic preparation suitable as a class experiment for post-16 students, using a microscale technique that produces an identifiable produce in about 20 minutes.
Apparatus and 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
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
Heat resistant mat
Access to top-pan balance, weighing to 0.01 g
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
Technical notes
Ethanol, (IDA, Industrial Denatured Alcohol) (Highly flammable, Harmful) Refer to CLEAPSS Hazcard 40A
Benzoic acid (Harmful) Refer to CLEAPSS Hazcard 13A
Concentrated sulfuric acid (Corrosive) Refer to CLEAPSS Hazcard 98A
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
HEALTH & SAFETY: Wear eye protection.
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.
Write an equation for the reaction that has occurred in this preparation.
Teaching notes
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, June 2008
Updated 12 Feb 2009
