Ester

General formula of a carboxylate ester.
In chemistry, esters are organic compounds in which an organic group (symbolized by R' in this article) replaces the hydrogen atom of a hydroxyl group in an oxoacid. A molecule of an oxoacid has an -OH (OH) group from which the hydrogen (H) can dissociate as an H+ ion. Many esters have distinctive odors and flavors, leading to their use as artificial flavorings and fragrances.
The most common esters are the carboxylate esters, where the acid in question is a carboxylic acid. For example, if the acid is acetic acid, the ester is called an acetate. Stable esters such as carbamates, RO(CO)NHR', and dialkyl carbonates, RO(CO)OR, can be formed from unstable carbamic acid or carbonic acid, respectively. Esters may also be formed with inorganic acids; for example, dimethyl sulfate is an ester, and sometimes called "sulfuric acid, dimethyl ester."
Esters are named similarly to salts; although they are not composed of cations and anions as salts are, the terminology used to refer to them follows the same pattern: a more electropositive part followed by a more electronegative part.

Contents

1 Nomenclature
2 Physical properties

2.1 Odors and flavors


3 Ester synthesis
4 Ester reactions
5 See also
6 Notes
7 References
8 External links
9 Credits



An ester can be thought of as a product of a condensation reaction of an acid (usually an organic acid) and an alcohol (or phenol compound), although there are other ways to form esters. Condensation is a type of chemical reaction in which two molecules are joined together and eliminate a small molecule, in this case two-OH groups are joined eliminating a water molecule. A condensation reaction to form an ester is called esterification. Esterification can be catalysed by the presence of H+ ions. Sulfuric acid is often used as a catalyst for this reaction. The name ester is derived from the German Essig-Äther, an old name for acetic acid ethyl ester (ethyl acetate).

Nomenclature
 Ethyl acetate structure
Esters can be produced by an equilibrium reaction between an alcohol and a carboxylic acid. The ester is named according to the alkyl group (the part from the alcohol) and then the alkanoate (the part from the carboxylic acid) which make it up.[1] For example, the reaction between methanol and butyric acid yields the ester methyl butyrate C3H7-COO-CH3 (as well as water). The simplest ester is methyl formate (H-COO-CH3, also called methyl methanoate).
For esters derived from the simplest carboxylic acids, the traditional names are recommended by the International Union of Pure and Applied Chemistry (IUPAC),[2]. Examples of names (from lower molecular-weight acids) are: formate (from formic acid), acetate (acetic acid), propionate (from propionic acid), butyrate (butyric acid), and so forth. For esters from higher molecular-weight acids, the alkane name with an -oate ending is generally preferred—for example, hexanoate from hexanoic acid. Common esters of aromatic acids include benzoates such as methyl benzoate, and phthalates, with substitution allowed in the name.

Physical properties
Esters participate in hydrogen bonds as hydrogen-bond acceptors, but cannot act as hydrogen-bond donors, unlike their parent alcohols. This ability to participate in hydrogen bonding makes them more water-soluble than their parent hydrocarbons. However, the limitations on their hydrogen bonding also make them more hydrophobic than either their parent alcohols or parent acids.
Their lack of hydrogen-bond-donating ability means that ester molecules cannot hydrogen-bond to each other, which makes esters generally more volatile than a carboxylic acid of similar molecular weight. This property makes them very useful in organic analytical chemistry: unknown organic acids with low volatility can often be esterified into a volatile ester, which can then be analyzed using gas chromatography, gas liquid chromatography, or mass spectrometry.

Odors and flavors
Examples of esters with distinctive odors and flavors are given below.



chemical name

molar mass
(g/mol)

♦

♦

♦

image

odor


allyl hexanoate











pineapple


benzyl acetate

150.18

1

1

0



pear, strawberry, jasmine


bornyl acetate











pine tree flavor


butyl butyrate

144.21

2

2

0



pineapple


ethyl acetate

88.12

1

3

0



nail polish remover, model paint, model airplane glue


ethyl butyrate

116.16









banana, pineapple, strawberry


ethyl hexanoate











strawberry


ethyl cinnamate

176.21









cinnamon


ethyl formate

74.08









lemon, rum, strawberry


ethyl heptanoate

158.27









apricot, cherry, grape, raspberry


ethyl isovalerate











apple


ethyl lactate

118.13

1

1

0



butter cream


ethyl nonanoate











grape


ethyl valerate

130.18

1

3

0



apple


geranyl acetate

196.29

0

1

0



geranium


geranyl butyrate











cherry


geranyl pentanoate











apple


isobutyl acetate

116.16

1

3

0



cherry, raspberry, strawberry


isobutyl formate











raspberries


isoamyl acetate

130.19









pear, banana (flavoring in Pear Drops)


isopropyl acetate

102.1

1

3

0



fruity


linalyl acetate











lavender, sage


linalyl butyrate











peach


linalyl formate











apple, peach


methyl acetate

74.08

1

3

0



peppermint


methyl anthranilate

151.165









grape, jasmine


methyl benzoate

136.15









fruity, ylang ylang, feijoa fruit


methyl benzyl acetate











cherry


methyl butyrate

102.13









pineapple, apple


methyl cinnamate











strawberry


methyl pentanoate

116.16









flowery


methyl phenyl acetate











honey


methyl salicylate (oil of wintergreen)

152.1494









root beer, wintergreen, Germolene™ and Ralgex™ ointments (UK)


nonyl caprylate











orange


octyl acetate

172.27









fruity-orange


octyl butyrate











parsnip


amyl acetate (pentyl acetate)

130.19









apple, banana


pentyl butyrate (amyl butyrate)

158.24









apricot, pear, pineapple


pentyl hexanoate (amyl caproate)











apple, pineapple


pentyl pentanoate (amyl valerate)

172.15









apple


propyl ethanoate











pear


propyl isobutyrate











rum


terpenyl butyrate











cherry

Ester synthesis
Esters can be prepared in the laboratory in several ways:

by esterification of carboxylic acid derivatives and alcohols
by transesterifications between other esters
by Dieckmann condensation or Claisen condensation of esters carrying acidic α-protons
by Favorskii rearrangement of α-haloketones in presence of base
by nucleophilic displacement of alkyl halides with carboxylic acid salts
by Baeyer-Villiger oxidation of ketones with peroxides
by Pinner reaction of nitriles with an alcohol
Ester reactions
Esters react in a number of ways:

Esters may undergo hydrolysis - the breakdown of an ester by water. This process can be catalyzed both by acids and bases. The base-catalyzed process is called saponification. The hydrolysis yields an alcohol and a carboxylic acid or its carboxylate salt.
Esters also react if heated with primary or secondary amines, producing amides.
Phenyl esters react to hydroxyarylketones in the Fries rearrangement.
Di-esters such as diethyl malonate react as nucleophile with alkyl halides in the malonic ester synthesis after deprotonation.
Specific esters are functionalized with an α-hydroxyl group in the Chan rearrangement
Esters are converted to isocyanates through intermediate hydroxamic acids in the Lossen rearrangement.
See also
Carboxylic acid
Alcohol
Notes

↑ Specific Classes of Compounds: Salts and Esters. (IUPAC naming of esters.) Retrieved May 24, 2007.

↑ Carboxylic acids and related groups: Unsubstituted parent structures. (IUPAC parent groups using traditional names.) Retrieved May 24, 2007.


ReferencesISBN links support NWE through referral fees
McMurry, John. Organic Chemistry, 6th ed. Belmont, CA: Brooks/Cole, 2004. ISBN 0534420052.
Morrison, Robert T., and Robert N. Boyd. Organic Chemistry, 6th ed. Englewood Cliffs, NJ: Prentice Hall, 1992. ISBN 0136436692.
Solomons, T.W. Graham, and Fryhle, Craig B. Organic Chemistry, 8th ed. Hoboken, NJ: John Wiley, 2004. ISBN 0471417998.
External links
All links retrieved August 15, 2017.

Simon Cotton Ethyl acetate. Uppingham School, Rutland, UK.
Project shum Making an Ester Homepage.
IUPAC Compendium of Chemical Terminology - the Gold Book. International Union of Pure and Applied Chemistry.




Functional groups


Chemical class: Alcohol • Aldehyde • Alkane • Alkene • Alkyne • Amide • Amine • Azo compound • Benzene derivative • Carboxylic acid • Cyanate • Ester • Ether • Haloalkane • Imine • Isocyanide • Isocyanate • Ketone • Nitrile • Nitro compound • Nitroso compound • Peroxide • Phosphoric acid • Pyridine derivative • Sulfone • Sulfonic acid • Sulfoxide • Thioether • Thiol • Toluene derivative


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