Class: S.5D
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Wang KwunSing (41)
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Ester
Structural formula of a
general ester group
(RCOOR').
A carboxylic acid ester. R
and R' denote any alkyl or
aryl group, respectively
Introduction to Ester
Esters are derived from carboxylic acids. A carboxylic acid contains the -COOH group, and in an
ester the hydrogen in this group is replaced by a hydrocarbon group of some kind. This could be an
alkyl group like methyl or ethyl, or one containing a benzene ring like phenyl.
Physical properties (Simple esters)
Boiling points
The small esters have boiling points which are similar to those of aldehydes and ketones with the
same number of carbon atoms.
Like aldehydes and ketones, they are polar molecules and so have dipole-dipole interactions as well
as van der Waals dispersion forces. However, they don't form hydrogen bonds, and so their boiling
points aren't anything like as high as an acid with the same number of carbon atoms.
Solubility in water
The small esters are fairly soluble in water but solubility falls with chain length. Although esters
can't hydrogen bond with themselves, they can hydrogen bond with water molecules. One of the
slightly positive hydrogen atoms in a water molecule can be sufficiently attracted to one of the lone
pairs on one of the oxygen atoms in an ester for a hydrogen bond to be formed. There are
dispersion forces and dipole-dipole attractions between the ester and the water molecules which
release energy. This helps to supply the energy needed to separate water molecule from water
molecule and ester molecule from ester molecule before they can mix together. As chain lengths
increase, the hydrocarbon parts of the ester molecules start to get in the way.
By forcing themselves between water molecules, they break strong hydrogen bonds between water
molecules without replacing them by anything as good. This makes the process energetically less
profitable, and so solubility decreases.
Physical properties (Fats and oils)
Solubility in water
They are insoluble in water. The chain lengths are now so great that far too many hydrogen bonds
between water molecules would have to be broken, so it isn't energetically profitable.
Melting points
The melting points determine whether the substance is a fat (a solid at room temperature) or an oil
(a liquid at room temperature).
Fats normally contain saturated chains. These allow more effective van der Waals dispersion forces
between the molecules. That means you need more energy to separate them, and so increases the
melting points.
The greater the extent of the unsaturation in the molecules, the lower the melting points tend to be
because the van der Waals dispersion forces are less effective.
Uses of Esters in our daily life
Food additive
Mono- and diacylglycerols are common food additives used to blend together certain ingredients,
such as oil and water, which would not otherwise blend well.
The commercial source may be either animal (cow- or hog-derived) or vegetable, derived primarily
from soy bean and canola oil. They may also be synthetically produced. They are often found in
bakery products, beverages, ice cream, chewing gum, shortening, whipped toppings, margarine, and
confections.
Nail polish remover comprising fatty acid ester and alkyl lactate
A nail polish remover is formulated from a combination of solvents derived from naturally
occurring materials, which combination consists essentially of
1. a major proportion by weight of esters of fatty acids having from 16 to 18 carbon atoms
wherein the content of linoleic acid ester in the source vegetable oil is less than 60%.
2. a minor proportion by weight of a lower (C1–C5) alkyl lactate.
The nail polish remover is highly effective yet has good skin conditioning properties, is non-toxic
and non-flammable. A visible residue several micrometers thick provides a desirable gloss on the
cleaned nails unless it is washed off.
Other solvents typically used in nail polish removers include ethyl acetate, and combinations
including ethylene and/or propylene carbonate or diethers and diesters, each of which has several
undesirable effects similar to those of acetone.
Perfume

Esters are used in products which have a fruity smell.

Properties includes low molecular mass and low boiling point

They are volatile and so are easy to smell and flammable.

The smell doesn't linger long.
List of ester odorants
Many esters have distinctive fruit-like odors, which has led to their commonplace use in artificial
flavorings and fragrances, such as
Ester Name
Structure
Odor or occurrence
Allyl hexanoate
pineapple
Benzyl acetate
pear, strawberry, jasmine
Isobutyl formate
raspberry
Isopropyl acetate
fruity
Linalyl acetate
lavender, sage
Methyl acetate
glue
Methyl anthranilate
grape, jasmine
Methyl benzoate
fruity, feijoa
Propyl acetate
pear
Methyl acetate

normally a flammable liquid

smell like certain glues or nail polish removers

used as a solvent, being weakly polar and lipophilic

has a solubility of 25% in water at room temperature

at elevated temperature its solubility in water is much higher

not stable in the presence of strong aqueous bases or acids.

major use of methyl acetate is as a volatile low toxicity solvent in glues, paints, and nail
polish removers
Ethyl acetate

widely employed as a solvent for nail varnishes and nail varnish removers

Industrially, it is used to decaffeinate coffee beans and tea leaves.

In chemistry, it is often mixed with a non-polar solvent such as hexanes as a
chromatography solvent. It is also used as a solvent for extractions.

It is used in confectionery and perfumes. It is used in perfumes because it confers a fruity
smell (as many esters) and evaporates quickly, leaving the scent of the perfume on the skin.

It is used in paints as an activator or hardener.

In the field of entomology, ethyl acetate is an effective poison for use in insect collecting
and study. In a killing jar charged with ethyl acetate, the vapors will kill the collected
(usually adult) insect quickly without destroying it because it is not hygroscopic, ethyl
acetate also keeps the insect soft enough to allow proper mounting suitable for a collection.
Phthalate Esters, PAEs

Phthalates are used in a large variety of products

esters of phthalic acidand are mainly used as plasticizers (substances added to plastics to
increase their flexibility, transparency, durability, and longevity)

used primarily to soften polyvinyl chloride

Phthalates are easily released into the environment because there is no covalent bond
between the phthalates and plastics in which they are mixed. As plastics age and break down,
the release of phthalates accelerates. People are commonly exposed to phthalates, and most
Americans tested by the Centers for Disease Control and Prevention have metabolites of
multiple phthalates in their urine. Because phthalate plasticizers are not chemically bound to
PVC, they can easily leach and evaporate into food or the atmosphere. Phthalate exposure
can be through direct use or by indirect means through leaching and general environmental
contamination.
Carbonate ester
Laboratory methods for the synthesis of carbonate ester in the laboratory are:
 from the corresponding diols.

by double oxidation of ketones in a Baeyer-Villiger rearrangement,although this method is
plausible,there is no evidence that it is effective.

by reaction of an epoxide with carbon dioxide catalysed by a zinc halide
Use as solvents
A large number of organic carbonates are used as solvents They are classified as polar solvents
and have a wide liquid temperature range. One example is polypropylene carbonate with melting
point −55 °C and boiling point 240 °C. Other advantages are low ecotoxicity and good
biodegradability. The industrial production of carbonates is not green because methods for
production of linear carbonates rely on phosgene and those of cyclic carbonates rely on propylene
oxide.
Use in batteries
Organic carbonates are used as a solvent in lithium batteries; due to their high polarity they can
dissolve lithium salts. The problem of high viscosity is circumvented by using carbonate mixtures
for example mixtures of dimethyl carbonate, diethyl carbonate and dimethoxy ethane.