UNIT 4B Laboratory techniques and their application
Esters are non-hydrocarbon chemical compounds that are formed when a carboxylic acid
reacts with an alcohol. They can be found in nature and can also be made synthetically.
Fatty acids and glycerol, as well as pheromones and fragrances from fruits like apples, pears,
and strawberries, contain natural esters. Smaller esters have lower boiling points and are
more volatile than larger esters. Small esters are water soluble, but as the carbon chain
length increases, solubility diminishes.
Ethyl ethanoate is one of the most commonly used small esters. It's a flammable, colourless
liquid with a pleasant odour that's used in perfumes, flavourings, and medications. Ethyl
ethanoate is a common ingredient in nail polish removers and lacquer thinners because it
serves as an organic solvent. Because of its low boiling point, it has evaporative qualities and
can be used in plasticizers and glues. Polystyrene cement, for example, is made out of
polystyrene dissolved in ethyl ethanoate.
METHOD:
1. In a 250cm3 round-bottomed flask, carefully combine 50cm3 ethanol and 50cm3
glacial ethanoic acid.
2. Slowly pour in 10cm3 of concentrated sulphuric acid while cooling and shaking.
3. Make sure the mixture is uniform, then attach a reflux water-condenser to the flask
and slowly boil the mixture for 10 minutes.
4. Reposition the condenser for distillation and remove approximately two-thirds of the
mixture.
5. Pour roughly 25 cm3 of 30 percent sodium carbonate solution into a separating
funnel with the distillate. Stopper the funnel, flip it, and shake it, sometimes opening
the tap.
6. Allow the two layers to separate, then gently run off and discard the lower layer,
ensuring that all sodium carbonate is eliminated.
7. Mix saturated calcium chloride solution with the ethyl ethanoate, stir it, and then
remove the lowest watery layer.
8. Fill a beaker halfway with ethyl ethanoate, then add a few lumps of solid anhydrous
calcium chloride and shake vigorously. Fill a flask halfway with ethyl ethanoate.
9. Pour the liquid into a clean, dry 100 cm3 round-bottom flask, add some anti-
bumping granules, and set up the apparatus for distillation, including a 0-100oC
thermometer. Place the distillation flask in a cold water bath that is progressively
heated.
At 35-40oC, the ether that is produced in this reaction will distil and can be discarded.
Continue to heat, collecting the percentage that boils between 74 and 79 degrees Celsius.
, UNIT 4B Laboratory techniques and their application
Precautions taken:
• -The concentrated sulphuric acid on dilution gives out a lot of heat; the slow addition
with cooling is necessary to avoid splashing if the mixture gets hot.
• Because concentrated sulphuric acid is substantially denser than any of the other
chemicals, the mixture must be homogeneous. When mixing happens later in the
reaction, if the solution is not adequately mixed at the start, it is likely to get
excessively hot and boil uncontrolled.
• The neutralisation with sodium carbonate creates carbon dioxide gas, the tap was
opened from time to time to release this gas and avoid a build-up of pressure that
may blow the stopper out of the funnel.
• keeping the equipment clean and dry to avoid any mistakes and anomalies in the
results.
Measuring purities
Measuring purity’s is not accurate as other methods. This is because boiling point will
change due to impurities, but a constant boiling point doesn't indicate a pure compound
(melting point does). It would be wise to compare purifies with a pure sample.
We use Infrared spectroscopy to identify samples and their purity levels. When an infrared
beam is focused towards a sample, the amount of radiation absorbed by the sample at
various frequencies may be used to determine the sort of molecules that make up the
sample. The most popular type of infrared spectrometer is the Fourier transform infrared
(FTIR) spectrometer. It keeps track of the information gathered and converts it into a
spectrum. The spectrum is shown by a graph that indicates the frequency of absorption and
the amount of absorption. Because various molecules absorb different frequencies of light
in varying quantities, the spectrum can be used to identify the sample at a molecular level.
it’s used because it can be used on all states of matter. It is also easily prepared.
Production of ethyl ethanoate in The Industry
The industrial production of ethyl acetate may be divided into three categories.
The first involves the traditional Fischer esterification of ethanol with acetic acid in the
presence of an acid catalyst. Acid catalyst2 is required for this process, such as sulphuric
acid, hydrochloride acid, and ptoluene sulfonic acid, among others. At room temperature,
this combination changes to the ester in about 65 percent of the time.
CH3COOC2H5 + H2O = CH3CH2OH + CH3COOH
Acid catalysis can speed up the process, while removing water from the equation can move
the equilibrium to the right.
The Tishchenko Reaction of Acetaldehyde with Aluminum Triethoxide as a Catalyst is the
second. The Tishchenko procedure is used to make the majority of ethyl acetate in Germany
and Japan.
2 CH3CHO → CH3COOC2H5
Two distinct approaches have been proposed for this method: I the dehydrogenative
process, which utilises copper or palladium-based catalysts, and (ii) the oxidative process,
which uses PdO-supported catalysts.
