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Synthesis lab 1b (MOL126)Preparation form experiment 4.4a (LJV011)
Lisa Verhoeven, s1014716
4-3-2022
Synthesis of bis(2,4,6-
trichlorophenyl) oxalate
Experimental aim
This experiment aims to synthesise bis(2,4,6-trichlorophenyl)oxalate by reacting 2,4,6-
trichlorophenol with triethylamine and oxalyl chloride in a 2:2:1 stoichiometry. Moreover, the aim is
to isolate as pure as possible bis(2,4,6-trichlorophenyl)oxalate and to analyse it with solid IR
spectroscopy, C-NMR spectroscopy, and by melting point analysis.
Background
Chemiluminescence is the process whereby light is produced via a chemical reaction with the
evolution of minimal heat. It is fueled by the reaction of an oxalic ester with hydrogen peroxide,
which generatse the intermediate 1,2-dioxetanedione. This intermediate can undergo a
decarboxylation reaction to produce two carbondioxide molecules which releases a large amount of
energy. The addition of a fluorescer to this reaction allows the excitation of an electron of this
fluorescent molecule into the excited state by the energy that the reaction releases. Subsequently,
this electron releases a photon that we can detect as a result of the excited electron returning to the
ground state.
The reaction rate of the oxalic ester reacting with the hydrogen peroxide can be determined by the
total light output of the reaction, as this is directly proportional to the reaction rate. It is known that
the type of flueorescer, the purity and the identity of the ester, as well as the pH have a large
influence on the rate of this reaction.
To investigate the dependence of the reaction rate on the oxalic ester type, various types of oxalic
esters are synthesised via the reaction as indicated in figure 1, dependent on the type of phenol
used.
Figure 1. Mechanism of the synthesis of bis(2,4,6-trichlorophenol)oxalate.
Triethyl amine is a non-nucleophilic very strong base that is used for the deprotonation of phenols in
many well-known reactions. The phenolate generated upon deprotonation of phenol can act as a
nucleophile for the attack of the carbonyl groups of oxalyl chloride. During this step in the reaction,
electrons flow from the phenol oxygen via the carbonyl oxygen to the chloride atoms, which expels a
chloride ion and results in a newly formed ester bond with the phenol. If the phenolate ions are
present in excess to the oxalyl chloride, the reaction will proceed in a 2:1:1 (phenolate:oxalyl
chloride: product) stoichiometry to yield diesters of the phenol.
Next to deprotonation of phenols, the purpose of triethylamine is to push the reaction forward in
two other ways. Protonated triethyl amine will precipitate with cloride ions during the reaction,
, thereby lowering the rate of the backward reaction. Moreover, triethylamine forms an intermediate
by reacting with oxalyl chloride as shown in figure 2. Nucleophilic attack of the carbonyl carbons of
oxalyl chloride by triethylamine in a 1:2 stoichiometry forms the charged intermediate.
Figure 2. Nucleophilic catalysis by trietylamine in the synthesis of bis(2,4,6-trichlorophenol)oxalate. Oxalyl chloride reacts in
a 1:2 stoichiometry with triethylamine to form the charged intermediate.
This intermediate catalyses the reaction via a mechanism called ‘nucleophilic catalysis’. This results
from the increased electrophilicity of the carbonyl carbon of this intermediate, which in turn
increases its susceptibility to nucleophilic attack by the phenolate. It is expected that this complex
also increases the reaction rate by the attractive, very strong long-range electronic force it exerts on
phenolates in the reaction mixture, as this increases the chance of the reactants coming in close
proximity and reacting.
Experimental
1. build the experimental set up as shown in the figure 3
2. Prepare a 35mL 0.57M (=20mmol) solution of 2,4,6-trichlorophenol in DCM
and cool to 5◦C
3. Prepare a 2M solution of triethylamine in DCM and add dropwise to the
phenol solution make sure that the temperature of the reaction mixture
stays below 10◦C
4. Dropwise add a 1M solution of oxalyl chloride in DCM again the
temperature should remain below 10◦C and make sure that the
dropping/separatory funnel has been cleaned thoroughly (otherwise oxalyl
chloride reacts therein)
5. Monitor the reaction with TLC start with the eluent 70%heptane:30%ethyl Figure 3. Experimental set up
acetate
6. After stirring the solution at RT, filter off the precipitate
7. Wash the mixture with 1M HCl, water, and brine carefully analyse the DCM layer with TLC
to monitor the purity; if not pure perform more extractions
8. Dry the organic phase over sodium sulphate
9. Remove the solvent (DCM) by rotary evaporation, the product will be available as an off-
white solid
10. Analyse the product with C-NMR, solid IR, and melting point analysis, and weigh the product
Expected result(s)
It is expected that the diester will be obtained as a pure white solid powder. Moreover, it is expected
that during the reaction a precipitate is formed and that heat is released. Furthermore, it is expected
that the obtained spectra will be similar to the spectra shown below.
C-NMR:
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