Phillips Condensation of O-phenylenediamine and Glycolic Acid to Afford 2(hydroxymethyl)benzimidazole
Sam Jacob
Chemistry 338
Experiment 8
Abstract:
O-phenylenediamine and glycolic acid underwent a Phillips Condensation in acidic conditions to
form the product of 2-(hydroxymethyl)benzimidazole. The final product was white solid. The final
product had a mass of 0.207g, a 30% yield, and a melting point of 167.4-169.2°C. The product’s IR
spectrum showed considerable peaks at: 3233.7cm-1 (alcohol and secondary amine) and 1777.2-1900cm1
(aromatic overtones).
Introduction:
The purpose of this experiment was to synthesize 2-(hydroxymethyl)benzimidazole from ophenylenediamine and glycolic acid in acidic conditions, obtaining valuable synthetic lab techniques in
the process of doing so. The product, a benzimidazole, was synthesized via Phillips Condensation. A
benzimidazole is a ten electron aromatic heterocyclic compound comprised of benzene bonded to an
imidazole ring. An imidazole ring is a heterocyclic aromatic containing two nitrogens. Both imidazole
and benzimidazole are amphoteric, meaning they are capable of functions as both an acid and base.
Ammonia hydroxide is specifically used in the reaction to neutralize the product, making it more basic.
If sodium hydroxide were used, the product would dissolve in the reaction mixture.2
Figure 1: Overall reaction of o-phenylenediamine with glycolic acid to form 2(hydroxymethyl)benzimidazole.
In the above reaction, o-phenylenediamine reacted with glycolic acid in acidic conditions. The
mixture was crystallized into 2-(hydroxymethyl)benzimidazole.
Figure 2: Part one of reaction mechanism of o-phenylenediamine with glycolic acid to form 2(hydroxymethyl)benzimidazole.
Reaction begins with the carbonyl in glycolic acid attacking a hydrogen forming a positive charge
on oxygen. One of the amines from o-phenylenediamine then attacks the carbonyl carbon, pushing the
pi electrons to the oxygen. One of the hydrogens bonded to the positively charged nitrogen then shifts
to one of the hydroxyls forming a water substituent and a neutral charge on nitrogen.
Figure 3: Part two of reaction mechanism of o-phenylenediamine with glycolic acid to form 2(hydroxymethyl)benzimidazole.
The water then breaks off from the molecule and the hydrogen from the hydroxyl leaves
reforming the carbonyl. The second amine substituent then attacks the carbonyl carbon and the
carbonyl oxygen attacks another hydrogen, closing the ring and forming a positive charge on nitrogen.
Figure 4: Part three of reaction mechanism of o-phenylenediamine with glycolic acid to form 2(hydroxymethyl)benzimidazole.
Proton shift occurs from the positive charged nitrogen to the hydroxyl, forming a water
substituent. The water substituent leaves and one of the hydrogen bonded to nitrogen breaks off to
form the product 2-(hydroxymethyl)benzimidazole.
The product of the reaction, 2-(hydroxymethyl)benzimidazole, will be characterized by the
melting point, TLC, and obtained IR spectrum from both the reactants and product. The theoretical
melting point of 2-(hydroxymethyl)benzimidazole is 170.5-171.5°C.1 Theoretically, the IR spectra for 2(hydroxymethyl)benzimidazole will show the corresponding peaks: 3200cm-1 (alcohol and secondary
amine), 1700-1900cm-1 (aromatic overtones). Theoretical IR spectra values of o-phenylenediamine
would be: 3350cm-1 (primary amine stretch) and 1800-1950cm-1 (aromatic overtones). The IR spectra
for glycolic acid would show theoretical peaks: 3241.9cm-1 (carboxylic acid stretch) and 1703.5cm-1
(carbonyl stretch).
Procedure:
0.505g of o-phenylenediamine and 0.706g of glycolic acid were mixed together in 10mL of 4N
HCl and refluxed. Mixture was cooled then neutralized with concentrated ammonia hydroxide. Solution
was vacuum filtrated and dried. Product was then recrystallized with hot ethyl acetate. Weight, percent
yield, melting point, IR, and TLC were taken and product was turned in to the lab TA.
Results:
Figure 5: 2-(hydroxymethyl)benzimidazole product formed from reaction.
Balanced Equation: C6H8N2 + C2H4O3 → C8H8N2O + 2H2O
Pre-crystallization Yield
Post-Crystallized Yield
Theoretical Yield
Percent Yield
Melting Point
Literature Melting Point
0.313g
0.207g
0.692g
30%
167.4-169.2°C
170.5-171.5°C
TLC
Rf Values
2-(hydroxymethyl)benzimidazole
0.75
Ethyl Acetate
0.625
Glycolic Acid
0.75
See attached documents for notable IR spectrum peaks.
Calculations
𝑆𝑀(𝑔)
= 𝑀𝑜𝑙𝑒𝑠 ∗ 𝑀𝑊(𝑝) = 𝑇ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑌𝑖𝑒𝑙𝑑
𝑀𝑊 𝑆𝑀
0.505 𝑔
= 0.00467𝑚𝑜𝑙 ∗ 148.16𝑔/𝑚𝑜𝑙 = 0.692𝑔
108.16 𝑔/𝑚𝑜𝑙
𝐸𝑥𝑝(𝑔)
∗ 100% = % 𝑌𝑖𝑒𝑙𝑑
𝑇ℎ𝑒𝑜(𝑔)
0.207𝑔
∗ 100% = 30%
0.692𝑔
Discussion:
O-phenylenediamine and glycolic acid underwent a Phillips Condensation in acidic conditions to
form 2-(hydroxymethyl)benzimidazole. After calculating the percent yield and obtaining TLC, IR spectra,
and melting point for the product, the experiment was shown to be successful. The IR spectra of the
product showed a peak at 3233.7cm-1, showing a secondary amine and alcohol, and aromatic overtones
between 1777.2-1900cm-1. The melting point of the product, 167.4-169.2°C, is fairly close to the
literature value, 170.5-171.5°C.1 The TLC was done and analyzed incorrectly. The plate shows the
product travelling the same distance as the glycolic acid, however, the IR spectrum and melting point
indicate that the product is not contaminated with glycolic acid. During the experiment the reaction
mixture was refluxed for about an hour, however, a magnetic spin vane was not placed in the round
bottom flask for the reflux. The lack of the spin vane hindered the reaction from occurring. At the end
of the experiment, the product was given time to dry before recording its mass. To speed up the
process of drying, the product was placed in an oven. The product melted because of the contamination
of the reactants, however, a small portion didn’t melt because some product did form from the reaction.
This small portion was used to take the melting point, IR spectra, and TLC spotting. The mass of the final
product was 0.207g, while the theoretical mass was 0.692g. A low 30% yield was achieved. Placing a
spin vane in the reaction mixture during reflux would have improved the overall experiment. Without
the spin vane, the mixture did not react properly and the obtained product contained a large amount of
contamination, explaining why a majority of it melted.
References:
1. The Allylic Character of 2-(α-Chloroalkyl)-benzimidazoles1. Herman Skolnik, John G. Miller, and
Allan R. Day. Journal of the American Chemical Society 1943 65 (10), 1854-1858.
2. Skibo, Edward. Phillips Reaction. Recitation Powerpoint Presentations. Slides 1-11. 2014.