A convenient protocol for the synthesis of 2-(2′-Hydroxy-5′- carboxyphenyl)-2H-benzotriazole to avoid decarboxylation when using p-hydroxybenzoic acid as coupling component

Article abstract of DOI:10.1002/jhet.1905

In the study of the synthesis of 2-(2′-hydroxy-5′- carboxyphenyl)-2H-benzotriazole, we found that decarboxy intermediate-4-((2- nitrophenyl)diazenyl)phenol was obtained when using p-hydroxybenzoic acid as coupling component. A convenient protocol for the synthesis of 2-(2′-hydroxy-5′-carboxyphenyl)-2H-benzotriazole is reported with methyl-p-hydroxybenzoate as coupling component. Different dizao components and different coupling components were also used for further investigation of decarboxylation.

Full text of DOI:10.1002/jhet.1905

Month 2014 A Convenient Protocol for the Synthesis of 2-(20-Hydroxy-50-carboxyphenyl)-
2H-benzotriazole to Avoid Decarboxylation When Using p-Hydroxybenzoic
Acid as Coupling Component
*
*
Wei Ma, Tingting Tuo, Jingqiang Hu, Yong Liu, and Shufen Zhang
State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116023, China
*
E-mail: weima@dlut.edu.cn; zhangshf@dlut.edu.cn
Additional Supporting Information may be found in the online version of this article.
Received June 20, 2012
DOI 10.1002/jhet.1905
Published online 00 Month 2014 in Wiley Online Library (wileyonlinelibrary.com).
In the study of the synthesis of 2-(20-hydroxy-50-carboxyphenyl)-2H-benzotriazole, we found that
decarboxy intermediate-4-((2-nitrophenyl)diazenyl)phenol was obtained when using p-hydroxybenzoic
acid as coupling component. A convenient protocol for the synthesis of 2-(20-hydroxy-50-carboxyphenyl)-
2H-benzotriazole is reported with methyl-p-hydroxybenzoate as coupling component. Different dizao
components and different coupling components were also used for further investigation of decarboxylation.
J. Heterocyclic Chem, 00, 00 (2014).
INTRODUCTION
the method, 2-(20-hydroxy-50-methylphenyl)-2H-benzotriazole
was first synthesized, and the hydroxyl group on benzene
ring was acylated for protection. Then through bromination
of methyl group, hydrolyzation, and oxidation, 2-(20-hydroxy-
50- carboxyphenyl)-2H-benzotriazole was obtained.
2-(2-Hydrophenyl)-2H-benzotriazole derivatives are a
very important class of UV absorbers, and they are widely
used as additives in polymers, dyes and pigments, and
textile to improve the light stability of the substrates [1–4].
Introduction of carboxylic groups to UV absorbers can
improve their hydrophilicity and enhance the interaction
with the substrates [5,6].
In this study, to synthesize 2-(20-hydroxy-50-carboxy-
phenyl)-2H-benzotriazole with a convenient method, a
new synthesis route was designed (Fig. 1); methyl-p-
hydroxybenzoate instead of p-hydroxybenzoic acid was
used as coupling component. With this method, the coupling
reaction occurred on the ortho-position of the hydroxyl
group of methyl-p-hydroxybenzoate. The obtained diazo
intermediate was then reduced with reducing agent under
alkali and high temperature conditions. Under the conditions,
not only benzotriazole group was formed but also the
carboxylate group on benzene ring was hydrolyzed to yield
carboxylic group. By this means, 2-(20-hydroxy-50-carboxy-
phenyl)-2H-benzotriazole can be conveniently prepared.
2-(20-Hydroxy-50-carboxyphenyl)-2H-benzotriazole is a
basic structure of benzotriazole type UV absorbers containing
carboxylic groups. Its synthesis had already been reported.
Some concerning references [7,8] reported that the UV
absorber was synthesized through diazotization, coupling,
and reduction. In the reaction, o-nitroaniline was used
as diazo component and p-hydroxybenzoic acid as cou-
pling component. However, when we used the same
method to synthesize 2-(20-hydroxy-50-carboxyphenyl)-
2H-benzotriazole, the target product was not obtained. It was
found that coupling reaction of diazo salt of o-nitroaniline
and p-hydroxybenzoic acid did not occur on the ortho-position
of the hydroxyl group of p-hydroxybenzoic acid; it occurred
on the para-position of the hydroxyl group. Namely, decar-
boxylation product was gained through coupling reaction.
As decarboxylation in coupling reaction of diazo salt of
o-nitroaniline with p-hydroxybenzoic acid was not previ-
ously reported, in this article, not only decarboxylation was
proved through characterization of the coupling product but
also the phenomenon was illustrated through changing
different diazo components and coupling components.
Different synthesis route for 2-(20-hydroxy-50-carboxy-
phenyl)-2H-benzotriazole was reported by Koutsimpelis
et al. [9]. However, the method was a little complex. With
RESULTS AND DISCUSSION
Synthesis of azo intermediate of 2-(20-hydroxy-50-
carboxyphenyl)-2H-benzotriazole.
In the synthesis of
2-(20-hydroxy-50-carboxyphenyl)-2H-benzotriazole, the
intermediate 4-hydroxy-3-((2-nitrophenyl)diazenyl)benzoic
acid was first prepared according to the reference [5].
However, when the intermediate was synthesized
through coupling reaction of diazo salt of o-nitroaniline
and p-hydroxybenzoic acid, decarboxylation was
detected. It was found that the molecular weight of the
intermediate was 243 on the basis of MS of the product,
which was just 44 less than that of 4-hydroxy-3-
((2-nitrophenyl)diazenyl)benzoic acid (MW = 287).
© 2013 HeteroCorporation

W. Ma, T. Tuo, J. Hu, Y. Liu, and S. Zhang
Vol 000
Figure 1. Synthesis of 2-(20-hydroxy-50-carboxyphenyl)-2H-benzotriazole.
1H NMR (DMSO-d6) was also used to determine the
structure of the intermediate. The data were as follows:
6.97 ppm (d, J = 8.80 Hz, 2H), 7.70 ppm (d, J = 2.69 Hz,
2H), 7.78 ppm (d, J = 9.05 Hz, 3H), 8.02–8.12 ppm
(m, 1H) and 10.58 ppm (s, 1H).
coupling reaction happened on the ortho-position of the
hydroxyl group of methyl-p-hydroxybenzoate. The
obtained diazo intermediate was then reduced with
reducing agent (sodium hydrosulfite or zinc dust) under
alkaline and high temperature conditions; carboxylate
group was at the same time hydrolyzed to yield the target
product 2-(20-hydroxy-50-carboxyphenyl)-2H-benzotriazole.
The final product with this new synthesis method was
characterized by FTIR, MS, 1H NMR, and UV absorption
spectrum.
It is clear that if the product is 4-hydroxy-3-((2-nitrophe-
nyl)diazenyl)benzoic acid, there should be seven hydrogen
atoms on the benzene ring. However, it showed altogether
1
eight hydrogen atom on the benzene ring from H NMR
spectrum, which indicated decarboxylation during the
reaction in combination with the analysis of the result of
the MS. The real reaction procedure was shown in Figure 2.
For comparison, phenol instead of p-hydroxybenzoic acid
was used in the aforementioned coupling reaction to yield
diazo product 4-((2-nitrophenyl)diazenyl)phenol (Fig. 3).
TLC and UV absorption spectrum were employed to make
comparison the coupling products synthesized with both
p-hydroxybenzoic acid and phenol as coupling components.
It shows that the Rf values of both products are 0.42
(developing agent CH2Cl2), and the maximum absorption
wavelength in UV–vis absorption spectra of the two azo
compounds are both 361 nm. In addition, the melting point
of both products was 160ꢀ162ꢁC. These results demon-
strated that decarboxylation really occurred in the coupling
reaction of diazo salt of o-nitroaniline and p-hydroxybenzoic
acid, and the coupling product is 4-((2-nitrophenyl)diazenyl)
phenol, not the aimed intermediate-4-hydroxy-3-((2-
nitrophenyl)diazenyl)benzoic acid.
It is shown in Figure 4 the FTIR (KBr) spectrum of the
benzotriazole derivative. The absorption peak at 3458cmꢀ1
was assigned to the stretching vibration of O-H on the
benzene ring. The absorption peak at 1697cmꢀ1 was attrib-
uted to the stretching vibration of C═O of aromatic carboxyl
group. The absorption peaks at 1598 and 1476 cmꢀ1 were
assigned to the vibration of skeleton of aromatic ring.
Moreover, the absorption peak indicating deformation
vibration of O-H of carboxylic acid was observed at
1420 cmꢀ1. The absorption peaks indicating stretching
vibration of C-O of carboxyl group and the phenol deriva-
tive were found at 1297 and 1228 cmꢀ1, respectively. In
addition, the absorption peaks at 895 and 804 cmꢀ1 were
assigned to the deformation vibration of ═C-H of 1,2,
4-substituted benzene and 744 cmꢀ1 to deformation
vibration of ═C-H of 1,2-substituted benzene.
Mass spectrometry of the product that presented
the molecular weight was just in accordance with that of
2-(20-hydroxy-50-carboxyphenyl)-2H-benzotriazole.
Synthesis of 2-(20-hydroxy-50-carboxyphenyl)-2H-benzotriazole.
As decarboxylation occurred in the synthesis of the
intermediate of 2-(20-hydroxy-50-carboxyphenyl)-2H-
benzotriazole, the target UV absorber cannot be obtained.
In the study, methyl-p-hydroxybenzoate instead of
p-hydroxybenzoic acid was designed to use as coupling
component to avoid decarboxylation. It was found that
1
The results of H NMR spectrum of the final product
were as follows: 7.26 (d, J = 8.53 Hz, 1H) 7.55
(dd, J = 6.65, 2.89 Hz, 2H) 7.98–8.03 (m, 1H) 8.06
(dd, J = 6.53, 3.01 Hz, 2H) 8.32 (s, 1H).
Figure 2. Diazo coupling reaction with o-nitroaniline as diazo compo-
nent and p-hydroxybenzoic acid as coupling component.
Figure 3. Synthesis of 4-((2-nitrophenyl)diazenyl)phenol.
Figure 4. IR spectrum of 2-(20-hydroxy-50-carboxyphenyl)-2H-benzotriazole.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2014
A Convenient Protocol for the Synthesis of 2-(20-Hydroxy-50-carboxyphenyl)-2H-
benzotriazole
UV absorption spectrum of the product was shown
in Figure 5. The characteristic absorption peaks of
2-(20-hydroxy-50-carboxyphenyl)-2H-benzotriazole
were observed at 298 and 331 nm.
confirm this phenomenon, aniline and p-methylaniline
whose diazo salts show weaker electropositivity was
selected instead of o-nitroaniline to proceed coupling
reaction with p-hydroxybenzoic acid. It was presented
when aniline was used as diazo component; the product
(mp151–152ꢁC) showed peaks at m/z: 197 and 233 in
MS which are assigned to [M ꢀ H]ꢀand [M + Cl]ꢀ,
respectively. This indicated the molecular weight of the
yielded compound is 198. However, if carboxyl group is
not substituted, the molecular weight of the product should
be 242, which is just 44 larger than the result obtained in MS.
So we predicted that decarboxylation also occurred in the
reaction. In addition, the same result was obtained with
p-methylaniline as diazo component. The molecular weight
of the obtained azo compound (mp146–148ꢁC) was also 44
less than that of the target product bearing carboxyl group.
As diazo salt of p-methylaniline can even substitute the
carboxyl group of p-hydroxybenzoic acid, the diazo salt
of o-nitroaniline with higher electropositivity should
inevitably substitute the carboxyl group and obtain the
decarboxylation product.
On the basis of the results of the aforementioned charac-
terization, the structure of the final product 2-(20-hydroxy-
50-carboxyphenyl)-2H-benzotriazole was confirmed.
A number of methods have been reported for the conver-
sion of o-nitrophenylazophenols to benzotriazoles [10].
With reducing agent and alkali, o-nitrophenylazophenols
was converted to benzotriazoles through reductive cycliza-
tion under high temperature. In this study, sodium hydro-
sulfite was used as reducing agent in consideration of
both the reaction efficiency and cost. The reaction proce-
dure was described in the Experimental section. Ethanol
and water were employed as mixed solvent for dissolving
the reactant and alkali. Sodium hydroxide with high
concentration (18%) was used to promote reduction. Al-
though high temperature is beneficial to the conversion
of the intermediate to the product 2-(20-hydroxy-50-
carboxyphenyl)-2H-benzotriazole, the highest temperature
for this reaction was about 80ꢁC limited by the boiling point
of the solvent. And the effect of the dosage of the reducing
agent (the molar ratios of the reactant to the reducing agent
was 1:2, 1:3.5, 1:5, and 1:7, respectively) on the yield of the
product was investigated. It showed when the molar ratio of
the reactant to the reducing agent was 1:2 and 1:3.5, the
yield of the product was 63.4% and 72.0%, respectively;
when the molar ratio increased to 1:5 and 1:7, the yield of
the product reached 77.0% and 81.5%. Therefore, under
the selected reaction system, increasing addition amount of
sodium hydrosulfite can increase the yield of the product.
For further investigation, two isomers of p-hydroxybenzoic
acid, o-hydroxybenzoic acid, and m-hydroxybenzoic acid
were both used as coupling components to proceed coupling
reaction with diazo salt of o-nitroaniline. At this time,
decarboxylation phenomenon was not observed. The
coupling product of diazo salt of o-nitroaniline and
o-hydroxybenzoic acid was pure (the reaction scheme was
shown in Fig. 6) and confirmed to be 2-hydroxy-5-((2-
nitrophenyl)diazenyl)benzoic acid (mp 221–222ꢁC). The
1
data of H NMR (DMSO-d6) were as follows: 6.81 ppm
(d, J= 9.03 Hz, 1H), 7.60–7.68 ppm (m, 1H), 7.68–7.75 ppm
(m, 1H), 7.75–7.86 ppm (m, 2H), 8.02 ppm (d, J=8.03Hz, 1H)
and 8.26 ppm (d, J = 1.51 Hz, 1H).
Study on decarboxylation.
Coupling reaction is an
electrophilic substitution reaction, and the cation of
diazonium salt attacks the carbon that shows relatively
strong electronegativity on aromatic ring. It was analyzed
that it may be the strong electrophilicity of diazo salt of
o-nitroaniline resulted in the decarboxylation, so to
When m-hydroxybenzoic acid was used as coupling
component (Fig. 7), it was found through HPLC–MS
detection that there are three components in the product,
and their molecular weight is all 287, indicating no decar-
boxylation product yielded. The primary component is
5-hydroxy-2-((2-nitrophenyl)diazenyl)benzoic acid, and
its content is 95.27% (mp 257–258ꢁC). This means that the
coupling reaction mainly occurred on the para-position of
1
hydroxyl group. H NMR (DMSO-d6) data of the primary
component (content: 95.27%) is as follows: 7.05 ppm (dd,
J= 8.91, 2.38 Hz, 1H) 7.12 ppm (d, J=2.51Hz, 1H) 7.58ppm
(dd, J= 10.79, 8.78 Hz, 2H) 7.73 ppm (t, J=7.65Hz, 1H)
7.85 ppm (t, J= 7.65 Hz, 1H) 8.10 ppm (d, J=7.78Hz, 1H).
It can be concluded from the aforementioned results that
only when carboxyl group was on the para-position of the
Figure 5. UV absorption spectrum of 2-(20-hydroxy-50-carboxyphenyl)-
2H-benzotriazole.
Figure 6. Diazo coupling reaction with o-nitroaniline as diazo compo-
nent and o-hydroxybenzoic acid as coupling component.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

W. Ma, T. Tuo, J. Hu, Y. Liu, and S. Zhang
Vol 000
Figure 7. Diazo coupling reaction with o-nitroaniline as diazo component and m-hydroxybenzoic acid acid as coupling component.
standard. HPLC analysis and MS were recorded on HP1100LC-
MSD (Agilent Technologies Inc., Santa Clara, California, USA).
The HPLC conditions were as follows: XBridge C18 column
(150 mm length, 2.1 mm ID, 5 mm particle) Mobile phase: H2O
(0.5% HAc)/CH3OH = 60/40 (30 min)-0/100(40 min), flow rate
0.3 mL/min (Water Alliance 2695–2996 system, l = 335nm).
2-(20-Hydroxy-50-carboxyphenyl)-2H-benzotriazole. A mixture
of 4.21 g (0.03mol) of o-nitroaniline, 75mL of deionized water, and
7.12g (0.07 mol) of hydrochloric acid (12mol/L) was heated with
stirring until it was completely dissolved. The solution was cooled
to 0ꢀ5ꢁC in ice-water bath, and 7.4 mL of 30% sodium nitrite
solution was quickly added. Diazotization reaction was carried out
for 1 h with stirring. The excess nitrous acid was decomposed
with sulphamic acid.
A solution of 4.56 g (0.03 mol) of methyl-p-hydroxybenzoate,
20 mL of alcohol, and 20 mL of deionized water were cooled to
below 10ꢁC and adjusted to pH 8 using 10% sodium carbonate
solution. The diazo salt of o-nitroaniline was added slowly into
the solution within 30 min. The pH of the reaction solution was
maintained at 8. After 2 h, the pH of the solution was adjusted to
2, and a red precipitate was observed. The red solid was collected
and dried under vacuum to yield 6.68g (74%) product. A mixture
of 6.02g (0.02 mol) of red azo product, 40 mL of alcohol, 8.4 g of
sodium hydroxide, and 38mL of water was heated under 80ꢁC with
continuous stirring. A 13.54 g of sodium hydrosulfite (90%) was
added batchwise; the color of the solution changed from garnet to
flavovirens. After a 2-h reaction, the temperature was decreased to
room temperature. The pH of the solution was adjusted to 1–2;
reseda fine powders were precipitated. The product was collected
by filtrating and drying, and then recrystallized with alcohol and
water, yield 3.67 g (72.0%). Melting pointing is 246–248ꢁC.
Diazo compound with o-nitroaniline as diazo component and
hydroxyl group on benzene ring, decarboxylation occurred
during coupling reaction. As coupling reaction was carried
out under alkaline condition for hydroxy-containing
coupling component, the electronegativity of the carbon
on the para-position of hydroxyl group was even strong.
Thus, under the attack of diazo salt and alkaline condition,
the carboxyl group seemed to be much easy to leave away
and the decarboxylation product was yielded.
CONCLUSIONS
Study of preparation of 2-(20-hydroxy-50-carboxyphenyl)-
2H-benzotriazole presents decarboxylation occurred in the
coupling reaction of diazo salt of o-nitroaniline and p-
hydroxybenzoic acid. A new facile synthesis method was
proposed with methyl-p-hydroxybenzoate as coupling
component. The target product was finally obtained with
good yield, and its structure was confirmed. Aniline and
p-methylaniline whose diazo salts show weaker electrophilic-
ity, instead of o-nitroaniline, were used as diazo components,
and decarboxylation products were also obtained when
being coupled with p-hydroxybenzoic acid. In addition,
o-hydroxybenzoic acid and m-hydroxybenzoic acid,
instead of p-hydroxybenzoic acid, were used as coupling
components. It was found that the carboxyl groups on
ortho-position and meta-position of hydroxyl groups did
not leave away during the coupling reaction with diazo salt
of o-nitroaniline. And the main product was always the
para-position substituted product of hydroxyl group of cou-
pling component. Therefore, the reason of decarboxylation
in coupling reaction of diazo salt with p-hydroxybenzoic
acid was mainly speculated to be the high electronegativity
of para-position of hydroxyl group on benzene ring under
the coupling condition.
phenol as coupling agent.
A mixture of 4.21 g (0.03 mol)
o-nitroaniline, 75 mL deionized water, and 7.12 g (0.07 mol)
hydrochloric acid (12 mol/L) was heated with stirring until it was
completely dissolved. The solution was cooled to 0–5ꢁC in ice-
water bath, and 7.4 mL of 30% sodium nitrite solution was quickly
added. Diazotization reaction was carried out for 1 h with stirring.
The excess nitrous acid was decomposed with sulphamic acid.
A solution of 2.85 g (0.03 mol) phenol and 100mL deionized
water was cooled to below 10ꢁC and adjusted to pH 7 using 10%
sodium carbonate solution. The diazo salt of o-nitroaniline was
added slowly into the solution within 30 min. The pH of the reaction
solution was maintained at 7. The reaction was carried out for 3 h,
and red azo product was precipitated. The red solid was collected
and dried under vacuum to yield 6.66 g (91.4%) product.
EXPERIMENTAL
General. All chemicals and reagents were analytical grade
and used without further purification. UV spectra were recorded
on Agilent 8453 UV–vis spectrophotometer (Agilent Technologies
Inc., Santa Clara, California, USA). Fourier transform infrared
(FTIR) spectra were recorded with KBr pressed disks on a
NICOET FT/IR-460 infrared spectrophotometer (Thermo Nicolet
Corp., Madison, Wisconsin, USA). 1H NMR spectra were
recorded in DMSO-d6 on a Varian Inova 400 MHz spectrometer
(Varian Inc. Palo Alto, California, USA) with TMS as internal
General procedure for the preparation of azo compounds with
aniline derivatives as diazo components and hydroxybenzoic acids
as coupling components.
A mixture of 0.03 mol of aniline
derivatives (o-nitroaniline, aniline, or p-methylaniline), 75mL of
deionized water, and 7.12 g (0.07 mol) of hydrochloric acid
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2014
A Convenient Protocol for the Synthesis of 2-(20-Hydroxy-50-carboxyphenyl)-2H-
benzotriazole
(12mol/L) was completely dissolved. The solution was cooled to
0–5ꢁC in ice-water bath, and 7.4 mL of 30% sodium nitrite
solution was quickly added. Diazotization reaction was carried
out for 1 h with stirring. The excess nitrous acid was
decomposed with sulphamic acid.
Acknowledgment. The authors gratefully thank the financial support
of the National Nature Science Funds of China (Nos. 20806013,
20923006 and 20836001) and the National Key Technology
R&D Program (No. 2011BAE07B08).
A solution of 0.03 mol of hydroxybenzoic acids (p-hydroxy-
benzoic acid, o-hydroxybenzoic acid, or m-hydroxybenzoic acid),
20 mL of alcohol, and 20 mL of deionized water were cooled to
below 10ꢁC and adjusted to pH 8 using 10% sodium carbonate
solution. The diazo salt of the aniline derivative was added slowly
into the solution within 30 min. The pH of the reaction solution
was maintained at 8. After 2 h, the pH of the solution was adjusted
to 2–3, and a red precipitate was observed. The red solid was
collected and dried under vacuum to yield the product. The yield
of different compounds is as follows: diazo compound with
o-nitroaniline as diazo component and p-hydroxybenzoic acid as
coupling agent, yield 69.6%; diazo compound with aniline as
diazo component and p-hydroxybenzoic acid as coupling agent,
yield 76.0%; diazo compound with p-methylaniline as diazo
component and p-hydroxybenzoic acid as coupling agent, yield
70.4%; diazo compound with o-nitroaniline as diazo component
and o-hydroxybenzoic acid as coupling agent, yield 71.6%;
diazo compound with o-nitroaniline as diazo component and
m-hydroxybenzoic acid as coupling agent, yield 88.7%.
REFERENCES AND NOTES
[1] Jurgen, K.; Horst, E. A. K.; Helmut, P.; Thomas, H.; Peter, F.;
Gerhard, R. J Phys Chem 1996, 100, 14468.
[2] Akrman, J.; Prikryl, J. J. Appl. Polym. Sci. 2008, 108,334.
[3] Rajan V. V.; Waeber, R.; Wieser, J. J Appl Polym Sci 2012,
124, 3988.
[4] John C. Crawford. Prog. Polym. Sci. 1999, 24, 7.
[5] Tsatsaroni, E. G.; Eleftheriadis I. C. Dyes Pigment. 2004,
61, 141.
[6] Oda, H. Dyes Pigment. 2008, 76, 270.
[7] Belusa, J.; Janousek, Z.; Knoflickova, H. Chemicke Zvesti
1974, 28, 673.
[8] Kashimura, T. N. EP0363839, Jun 10, 1989.
[9] Koutsimpelis, A. G.; Screttas, C. G.; Igglessi, M. O.
Heterocycles 2005, 65, 1393.
[10] Liu, G. B.; Zhao, H. Y.; Yang, H. J.; Gao, X.; Li, M. K.; Thies,
T. Adv. Synth. Catal. 2007, 349, 1637.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet