Esters
Esters have got the same
functional group with carboxylic acids.
The structural formula of esters
is
General formula is CnH2nO2. Here
R´=R or R´≠R.
Besides, R can never be a hydrogen
atom as in carboxylic acids.
Nomenclature of Esters
As esters are made up of two
groups, one is from carboxylic acid and the other is from alcohol, so they are
named after they are di- vided into two groups as follows:
1. The first name of ester belongs to the alkyl group
bonded to the oxygen atom in alcohol group.
2. The remaining name is written by adding –oate suffix to the
alkane part of the carboxylic acid.
Do you know that
Esters which are found in fruits
and vegetables have pleasant odors and therefore they are used as sweetener in
foods, perfumes and kids’ foods?
Preparation of Esters
Esters can be synthesized through
many methods such as the reaction of alcohols and carboxylic acids. Besides, by
adding pyridine to produce HCl, carboxylic acid chloride is obtained and with
its reaction with alcohol, esters are prepared.
Physical Properties of Esters
Esters can ionize. They don’t form
hydrogen bonds between their molecules. Therefore, their boiling points are
lower than those of carboxylic acids with the same number of carbons. Most
esters don’t dissolve in water but dissolve in many organic solvents. Besides,
these substances are used as good solvents for many organic compounds.
Chemical Properties of Esters
Esters undergo following reactions.
a) Reaction of Esters with Water
in Acidic Solution
This reaction is the opposite of
esterification reaction which is synthesis of esters from alcohols and
carboxylic acids. Here H2SO4 and HCl are used as catalysts. Esters react with
water and form carboxylic acids and alcohols.
b) Reaction of Esters with Water
in Basic Medium
Esters react with water molecules
in basic solution such as NaOH. At the end of the reaction, sodium salt of
carboxylic acid and alcohol are formed. This reaction is very important as it
is used in soap production. Therefore, it is also known as saponification
reaction. Besides, it is used to differentiate esters as shown in the following
reaction:
Apples and beeswax contains esters.
See also
1. Alcohols: nomenclature – synthesis - Properties
2. Alkyl halides: nomenclature - synthesis - Properties
References
1. K. J. Denniston c J. J.Topping c and R. L.Caretc
“General Organic and Biochemistry”c Mc-Graw- Hillc New York
(2004).
2. K.W. Whittenc R.E. Davis and L. M. Peckc “General Chemistry” 7th ed. Holt
Rinehart and Winstonc New York (2010).
3. Clayden, J.; Greeves, N. and Warren, S. (2012) Organic
Chemistry. Oxford University Press. pp. 1–15. ISBN 0-19-927029-5.
4. Streitwieser, Andrew; Heathcock, Clayton H.; Kosower,
Edward M. (2017). Introduction to Organic Chemistry. New Delhipages=3–4:
Medtech (Scientific International, reprint of revised 4th edition, Macmillan,
1998). ISBN 978-93-85998-89-8.
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