Ester is one of the functional groups in organic chemistry. It is formed by combining alcohols and carboxylic acids in a process called esterification.

2. What are Esters?

3. KEY POINTS
• Esters are a functional group commonly encountered in
organic chemistry. They are characterized by a carbon bound
to three other atoms: a single bond to a carbon, a double
bond to an oxygen, and a single bond to an oxygen. The singly
bound oxygen is bound to another carbon.
• Ester names are derived from the parent alcohol and the
parent acid. While simple esters are often called by
their common names, all esters can be named using the
systematic IUPAC name, based on the name for the acid
followed by the suffix "-oate."

4. Cont.
• The odors of flowers and the odors and flavors
of fresh fruits are a result of a complex mixture
of many chemical compounds, but one of the
major constituents is a type of compound called
an ester.

5. Nomenclature
The word "ester" was
coined in 1848 by German
chemist Leopold Gmelin,
probably as a contraction of the
German Essigäther, meaning
acetic ether.
Ester names are derived from
the parent alcohol and acid.

6. In the case of esters formed from common carboxylic
acids, more colloquial terms are sometimes used. For
example, ethanoic acid is more commonly known as acetic
acid, and thus its esters contain "acetate" instead of
"ethanoate" in their names. Other such substitutions include
"formate" instead of "methanoate," "propionate" instead of
"propanoate," and "butyrate" instead of "butanoate."

7. Properties of Esters
*Polar
-Less than alcohols, carboxylic acids
-Soluble in water
*Smell Fruity
*Can form Polymers
Esters are more polar than ethers, but less so than alcohols. They
participate inhydrogen bonds as hydrogen bond acceptors, but cannot act
as hydrogen bond donors, unlike their parent alcohols and carboxylic
acids. This ability to participate in hydrogen bonding confers some water-
solubility, depending on the length of the alkyl chains attached. Since they
have no hydrogens bonded to oxygens, as alcohols and carboxylic acids do,
esters do not self-associate. Consequently, esters are more volatile than
carboxylic acids of similar molecular weight.

8. Condensed Structural
Formula
Name Melting
Point (°C)
Boiling Point
(°C)
Aroma
HCOOCH3 methyl formate −99 32
HCOOCH2CH3 ethyl formate −80 54 rum
CH3COOCH3 methyl acetate −98 57
CH3COOCH2CH3 ethyl acetate −84 77
CH3CH2CH2COOCH3 methyl butyrate −85 102 apple
CH3CH2CH2COOCH2CH3 ethyl butyrate −101 121 pineapple
CH3COO(CH2)4CH3 pentyl acetate −71 148 pear
CH3COOCH2C6H5
isopentyl acetate −79 142 banana
CH3CH2CH2COO(CH2)4CH3 benzyl acetate −51 215 jasmine
CH3CH2CH2COOCH4CH3 pentyl −73 185 apricot

9. Preparation of Esters
The most common way to make simple esters is by Fischer
Esterification, named after the German chemist Emil Fischer, who
won the Nobel Prize in Chemistry in 1902. Fischer esterification
involves mixing a carboxylic acid and an alcohol with a small
amount of acid. This mixture is generally refluxed for a brief time to
drive the reaction to completion. This is the process you will be
using today.

10. Esterification is the chemical process for making
esters, which are compounds of the chemical structure R-
COOR', where R and R' are either alkyl or aryl groups. The
most common method for preparing esters is to heat a
carboxylic acid, R-CO-OH, with an alcohol, R'-OH, while
removing the water that is formed. A mineral acid catalyst
is usually needed to make the reaction occur at a
useful rate.

11. Esters are produced when carboxylic acids are heated with alcohols
in the presence of an acid catalyst. The catalyst is usually
concentrated sulphuric acid. Dry hydrogen chloride gas is used in
some cases, but these tend to involve aromatic esters (ones where
the carboxylic acid contains a benzene ring).
Making esters from carboxylic acids

12. Saponification
This is the process by which an ester is hydrolyzed in the presence
of a base. The products of this reaction are the alcohol and the salt
of the carboxylic acid used to create the ester. An example of this
reaction is presented below:

13. Making an ester – Higher tier
You can make a variety of esters by reacting different carboxylic
acids with different alcohols.
ethanol + ethanoic acid → ethyl ethanoate + water

14. methanol + butanoic acid → methyl butanoate + water
A catalyst is needed to speed up the reaction.
Concentrated sulfuric acid is often used.

15. Introduction to Esters’ Reactions
• Esters can be converted into other esters (transesterification),
the parent carboxylic acid (hydrolysis) or amides (see above).
– Transesterification : heat with alcohol and acid catalyst
– Hydrolysis : heat with aq. acid or base (e.g. aq. H2SO4 or aq.
NaOH) (see hydrolysis of esters for more details)
– Amide preparation : heat with the amine, methyl or ethyl
esters are the most reactive
Hydrolysis of Esters

16. Naming Esters
Systematic names of esters are based on the name
of the corresponding carboxylic acid. Remember esters
look like this:

17. The alkyl group is named like a substituent using
the -yl ending. This is followed by a space. The acyl
portion of the name (what is left over) is named by
replacing the -ic acid suffix of the corresponding
carboxylic acid with -ate.
* Look for the organic acid and alcohol used during the
esterification reaction.

18. Example:

20. 1-methylethyl propanoate

21. 1. methyl hexanoate
2. propyl pentanoate

22. Benzyl and Phenyl
Benzyl - can be seen as a phenyl attached to a CH2 before
attaching to the parent compound.
Phenyl - the phenyl group or phenyl ring (often abbreviated as
-Ph) is the functional group with the formula C6H5
- This functional group differs from the benzyl functional
group in that benzyls have an extra CH2.

23. Right or Wrong??
1.
3.
2.

24. Cyclic Esters
A cyclic ester is called a lactone. IUPAC names of lactones are
derived by adding the term lactone at the end of the name of the
parent hydroxycarboxylic acid it came from.

25. Lactones
Lactones are usually named according to the precursor acid
molecule (aceto = 2 carbons, propio = 3, butyro = 4, valero = 5, capro =
6, etc.), with a -lactone suffix and a Greek letter prefix that specifies the
number of carbons in the heterocyle — that is, the distance between
the relevant -OH and the -COOH groups along said backbone. The first
carbon atom after the carbon in the -COOH group on the parent
compound is labelled α, the second will be labeled β, and so forth.
Therefore, the prefixes also indicate the size of the lactone ring: α-
lactone = 3-membered ring, β-lactone = 4-membered, γ-lactone = 5-
membered, etc.
The other suffix used to denote a lactone is -olide, used in substance class
names like butenolide, macrolide, cardenolide or bufadienolide

26. Caprolactone

27. Butyrolactone

28. Propiolactone

29. Uses and Examples of Esters
There are various uses of esters.
1. Esters that are have fragrant odors are used as a constituent of
perfumes, essential oils, food flavorings, cosmetics, etc
2. Esters are used as an organic solvent
3. Natural esters are found in pheromones
4. Naturally occurring fats and oils are fatty acid esters of glycerol
5. Phospoesters form the backbone of DNA molecules
6. Nitrate esters, such as nitroglycerin, are known for their explosive
properties
7. Polyesters are used to make plastics
8. Esters are used to make surfactants
E.g. soap, detergents