Pearson BTEC Applied Science (Distinction) Unit 14: Applications of Organic Chemistry Assignment 14D: Investigate organic chemistry reactions in order to gain skills in preparative organic chemistry

H.
L3 EXTENDED DIPLOMA IN APPLIED SCIENCE
Unit 14: Applications of Organic Chemistry
Assignment 14D: Investigate organic chemistry
reactions in order to gain skills in preparative organic
chemistry

Preparation of a compound with a carbonyl functional group

For preparation of a compound with a carbonyl functional group (C=O), an ester
was prepared from a carboxylic acid. As part of this preparation, the reaction
mixture was heated, refluxed, and then purified to reach the final preparation.
This preparation can also be referred to as an acid-catalysed esterification
reaction- the balanced chemical equation can be seen below:
conc H2SO4
CH3COOH + CH3CH2OH ⇋ CH3COOCH2CH3 + H2O

The reaction shown above involves ethanoic acid, a carboxylic acid that has a
carbonyl group (C=O) which is the functional group. The central carbon atom in
ethanoic acid is bonded to two hydrogen atoms and one oxygen atom. Also, the
carbon atom has a double bond with the oxygen atom, forming the functional
group- C=O. The ethanol used to react with the ethanoic acid accepts a proton
from the ethanoic acid which causes an ethanoate and ethylammonium ion to be
formed. The overall formation of these ions leads to the functional group of
ethanoic acid to be converted to an ester functional group (R-C(=O)-O-R'). The R
and R’ represent alkyl groups with the carbonyl carbon having a double bond to
an oxygen atom and the other oxygen bonded to the R’. As ethanol and ethanoic
acid are reacted together, ethyl ethanoate is formed along with water as a by-
product since the ethanol used neutralises the ethanoic acid causing it to form a
molecule with an ester functional group.

The reaction mechanism for this reaction involves many steps:
1. Protonation of the carboxylic acid
2. Nucleophilic attack by alcohol
3. Proton transfer
4. Ester formation
In the first step of this mechanism, the ethanoic acid gains a proton from the
concentrated sulfuric acid (1). The proton attaches to one of the lone pairs on the
carbonyl oxygen of ethanoic acid (1). In the next step of this mechanism, one of
the lone pairs on the ethanol molecule attacks the positively charged carbon
atom as it is attracted to the positive charge (1). The ethanol molecule acts as a
nucleophile in this step and the attack on the carbon atom causes an
intermediate to be formed. Following on from this, a proton is transferred from an
oxygen atom at the bottom of the intermediate to a different oxygen atom in the
intermediate (1). An ester is formed as a result since a water molecule is lost and
a hydrogen is removed (1). Also, the sulfuric acid catalyst is reformed at the end
of this reaction.

In terms of reaction conditions, for the reaction performed, ethanoic acid was
heated under reflux with ethanol in the presence of concentrated sulfuric acid.
The concentrated sulfuric acid acts as a catalyst for this esterification reaction by
helping to protonate the ethanoic acid and form the ester. Protonation of the
ethanoic acid makes it more prone to nucleophilic attack by the alcohol. This
leads to the formation of an ester, so it is important that this concentrated

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, H.
L3 EXTENDED DIPLOMA IN APPLIED SCIENCE
Unit 14: Applications of Organic Chemistry
sulfuric acid is used for this reaction. Moreover, this esterification reaction is
performed under reflux conditions using the heating mantle to heat the reactants
and the reflux condenser to condense and return vapours. The reflux condenser
helps to constantly remove water from the reaction mixture, which helps to shift
the position of equilibrium in the direction of the ester forming. This means that
the yield of the ester will be higher, forming more product. The temperature for
this reaction occurred from 50-70˚C and lasted for a duration of 10 minutes. High
temperatures are used for this esterification reaction to maximise the rate of
reaction as the process can take a long time to reach completion. The reflux
conditions used in this reaction allow the temperature to be maintained, ensuring
the reaction runs smoothly to form the ester.

Also, the functional group involved in this practical is the carbonyl functional
group as the ester and carboxylic acid both consist of a carbonyl functional
group:
- Ester functional group, -COO
- Carboxylic acid functional group, -COOH

Equipment list

 Safety goggles
 Heating mantle
 Test tubes
 Ethanol
 Ethanoic acid
 Sulfuric acid
 Anti-bumping granules
 Clamp stand
 Sodium carbonate solution
 Conical flask
 Condenser
 Tubes
 Clips
 Thermometer
 Pear flask
 Capillary tube (5-6cm)
 Dropper
 Rubber band
 Clamp stand
 Bunsen burner
 Hot plate
 Heatproof mat
 Beaker

Health and safety assessment

Hazard Risk Control
Glassware Can break and cut the Handle with care and if
skin cut, run under water
immediately
Ethanoic acid Flammable, can cause Wear eye protection at
burns all times and handle with

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