Ester in Daily Life.

In our daily life, we use energy and we sweat. Sweating makes our body smell and thus, a superb creation is created, the perfume. Perfumes are known as esters.


Esters have a very sweet fruity smell.  Naturally occurring esters are found in fruits.  An ester is a product of the reaction of an acid (usually organic) and an alcohol (the hydrogen of the acid R-COOH is replaced by an alkyl group R').  Esters mainly result from the condensation (a reaction that produces water) of a carboxylic acid and an alcohol.  The process is called esterification.  This reaction can be catalyzed by the presence of H⁺ ions.  Sulphuric acid, H₂SO₄, is often used as a catalyst for this reaction.  The name ester is derived from the German Essig-Aether, an old name for acetic acid ethyl ester (ethyl acetate).  Esters have the general formula R-COOR',

Esters are named in the same manner as salts (although esters and salts have completely different properties): two-word names are used.  Note that in the general formula, R-COOR' (the carbon is double-bonded to one oxygen atom and single-bonded to another), the alkyl group (R') is always attached to an oxygen atom.  This alkyl group (R') is named as the first word of the two-word name.  The second word is derived by adding the ending -oate to the stem of the acid name (-oic in the acid name is replaced by -oate).
A reversible reaction between an alcohol and a carboxylic acid causes loss of water and the formation of an ester:

Alcohol + Carboxylic Acid  Ester + Water

R'OH + RCOOH  RCOOR' + H₂O.

Esters are named as derivatives of the carboxylic acid from which they are formed.   Condensation of ethanoic acid with methanol will produce methyl ethanoate.   As stated above the ending of the acid -oic is changed to -oate, much as if the ester were a salt of the acid.  The esterification reactions are generally easily reversible by addition of water; the reverse reaction is called the hydrolysis of the ester and proceeds in the presence of aqueous base.

Methyl ethanoate

CH₃OH + CH₃COOH  CH₃COOCH₃ + H₂O

methanol  + ethanoic acid  methyl ethanoate + water

The esterification process will proceed more nearly to completion if a substance which removes water without reacting with the acid or the alcohol is added to the reaction, such as sulfuric acid.   For example, the reaction between ethanoic acid and ethanol produces the ester ethyl ethanoate.

Ethyl ethanoate

CH₃COOH + CH₃CH₂OH  H₂SO₄  CH₃COOCH₂CH₃+ H₂O

ethanoic acid + ethanol  H₂SO₄  ethyl ethanoate + water

The concentrated H₂SO₄ removes water from the products and is a dehydrating agent.  Most esters have very pleasant odors (see below).  Many flavoring and scenting agents are made from esters.  Esters are volatile liquids which are not ionized and they are soluble in organic solvents but not in water.
The simplest ester is H-COO-CH₃ (methyl methanoate).

Methyl methanoate

In the laboratory, methyl methanoate can be produced by the condensation reaction of methanol  and methanoic acid, as follows:

HCOOH + CH₃OH  HCOOCH₃ + H₂O

methanoic acid + methanol  methyl methanoate + water

Industrial methyl methanoate, however, is usually produced by the combination of methanol and carbon monoxide in the presence of a strong base:

CH₃OH + CO  HCOOCH₃

methanol + carbon monoxide  methyl methanoate

As shown in the diagram above the hydrogen atom on the right can be replaced with a CH₃ group or additional CH₂ units, producing other methyl esters, such as:

Ethyl methanoate

For esters derived from the simplest carboxylic acids, the traditional names are recommended by IUPAC, such as, formate, acetate, propionate, butyrate, though out of these only acetate may carry further substituents.  For esters from higher acids, the alkane name with an -oate ending is generally preferred, e.g., hexanoate.   Common esters of aromatic acids include benzoates such as methyl benzoate, with substitution allowed in the name.
Common names of esters are derived from the organic acid and the alcohol from which they are derived.  For example, when acetic acid reacts with ethyl alcohol, the ester formed is called ethyl acetate.  The IUPAC name is different.  Acetic acid is called ethanoic acid by the IUPAC rules.  Thus the ester formed is called ethyl ethanoate.  IUPAC names ester from two words: first from the prefix of the alcohol and the second from the name of the acid.

ethyl alcohol + acetic acid  ethyl acetate + water (common names)

ethanol + ethanoic acid  ethyl ethanoate + water (IUPAC names)

(1)

General formula RCOOR'.  In the following example R is H- while R' is a methyl group -CH₃.  This will produce the simplest of esters.  The reaction of methanoic acid HCOOH and methanol CH₃OH can form this ester.  From the IUPAC rules, the ester will take its first name from the prefix of the alcohol, in this case methyl, and the second name from the acid, in this case it is methanoate.  Thus HCOOCH₃ is named methyl methanoate by the rules laid down for  IUPAC nomenclature for esters.  The common name of this ester is methyl formate.

methyl methanoate, methyl formate HCOOCH₃

formic acid + methyl alcohol  methyl formate + water (common names)

methanoic acid  + methanol  methyl methanoate + water (IUPAC names)

(2)
General formula RCOOR'.  In the following example R is H- while R' is an ethyl group -C₂H₅.  The reaction of methanoic acid HCOOH and ethanol C₂H₅OH can form this ester.  From the IUPAC rules, the ester will take its first name from the prefix of the alcohol, in this case ethyl, and the second name from the acid, in this case it is methanoate.  Thus HCOOC₂H₅ is named ethyl methanoate by the rules laid down for  IUPAC nomenclature for esters. The common name for this ester is ethyl formate.

ethyl methanoate, ethyl formate, HCOOC₂H₅

formic acid + ethyl alcohol  ethyl formate + water (common names)

methanoic acid + ethanol  ethyl methanoate + water (IUPAC names)

(3)

General formula RCOOR'.  In the following example R is CH₃- while R' is also a methyl group -CH₃.  The reaction of ethanoic acid CH₃COOH and methanol CH₃OH can form this ester.  From the IUPAC rules, the ester will take its first name from the prefix of the alcohol, in this case methyl, and the second name from the acid, in this case it is ethanoate.  Thus CH₃COOCH₃ is named methyl ethanoate by the rules laid down for  IUPAC nomenclature for esters.  The common name of this ester is methyl acetate.

methyl ethanoate, methyl acetate CH₃COOCH₃

acetic acid + methyl alcohol  methyl acetate + water (common names)

ethanoic acid + methanol  methyl ethanoate + water (IUPAC names)

(4)

General formula RCOOR'.  In the following example R is CH₃- while R' is an ethyl group -C₂H₅.  The reaction of ethanoic acid CH₃COOH and ethanol C₂H₅OH can form this ester.   From the IUPAC rules, the ester will take its first name from the prefix of the alcohol, in this case ethyl, and the second name from the acid, in this case it is ethanoate.  Thus CH₃COOC₂H₅ is named ethyl ethanoate by the rules laid down for  IUPAC nomenclature for esters. The common name of this ester is ethyl acetate.

ethyl ethanoate, ethyl acetate CH₃COOC₂H₅

acetic acid + ethyl alcohol  ethyl acetate + water (common names)

ethanoic acid + ethanol  ethyl ethanoate + water (IUPAC names)

(5)

General formula RCOOR'.  In the following example R is CH₃-CH₂- while R' is a methyl group -CH₃.  The reaction of propanoic acid CH₃CH₂COOH and methanol CH₃OH can form this ester.   From the IUPAC rules, the ester will take its first name from the prefix of the alcohol, in this case methyl, and the second name from the acid, in this case it is propanoate.  Thus CH₃CH₂COOCH₃ is named methyl propanoate by the rules laid down for  IUPAC nomenclature for esters.

CH₃CH₂COOH + CH₃OH  CH₃CH₂COOCH₃ and H₂O

Propanoic Acid + Methanol  Methyl Propanoate + Water

Many esters have distinctive odors, which has led to their use as artificial flavorings and fragrances. For example: