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THE ROLE OF AZOXY FUNCTIONAL GROUPS IN ENHANCING ACARICIDAL
ACTIVITY OF AROMATIC COMPOUNDS.
Pardayev Ulug‘bek Xayrullo ugli
E-mail:
A student of the Chemistry program at the Faculty of
Natural Sciences, Uzbekistan-Finland Pedagogical Institute.
Majidova Gulhayo Abdumalik kizi
E-mail:
A student of the Chemistry program at the Faculty of
Natural Sciences, Uzbekistan-Finland Pedagogical Institute.
Abdumurodova Nozima Akmal
E-mail:
nozimaabdumurodova0614@gmail.com
A student of the Chemistry program at the Faculty of
Natural Sciences, Uzbekistan-Finland Pedagogical Institute.
Xurramova Mubina Olimboy kizi
A student of the Chemistry program at the Faculty of
Natural Sciences, Uzbekistan-Finland Pedagogical Institute.
Annotation:
Azoxy functional groups (-N=N(O)-) have gained considerable attention in
agrochemical research due to their ability to modulate biological activity in aromatic compounds.
This study investigates the influence of azoxy moieties on the acaricidal efficacy of synthetic
aromatic derivatives against selected mite species. A series of azoxybenzene-based compounds
were synthesized and evaluated for their biological activity using standardized bioassay methods.
The structure–activity relationship (SAR) analysis revealed that the presence of azoxy linkages
significantly enhances acaricidal potency compared to their azo or nitro analogs, likely due to
improved electron distribution and target affinity. Spectroscopic (FTIR, NMR) and
chromatographic (GC-MS) techniques confirmed the purity and structure of synthesized
compounds. The findings support the hypothesis that azoxy functionalization contributes to
increased bioefficacy and selectivity, making such derivatives potential candidates for next-
generation eco-friendly acaricides.
Key words:
Azoxy functional group, azoxybenzene, acaricidal activity, aromatic compounds,
structure–activity relationship, bioactive molecules, synthetic pesticides.
Introduction:
The widespread emergence of acaricide-resistant mite populations poses a serious
threat to agricultural productivity and public health, necessitating the development of new,
effective, and environmentally safer compounds. Among the promising candidates, aromatic
compounds bearing azoxy functional groups (-N=N(O)-) have attracted scientific interest due to
their unique electronic configuration, stability, and potential for biological activity. Azoxy
derivatives are structurally related to azo and nitro compounds but possess distinct
physicochemical characteristics that may enhance their interaction with biological targets. This
study aims to explore the role of azoxy linkages in modulating acaricidal efficacy, particularly
focusing on how these groups influence molecular polarity, target binding affinity, and overall
bioactivity. By synthesizing and characterizing a series of azoxybenzene-based compounds and
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evaluating their acaricidal properties, we seek to determine whether the introduction of azoxy
moieties can significantly improve the potency and selectivity of aromatic acaricides.
Literature review:
Previous research has highlighted the potential of aromatic compounds,
particularly those containing nitrogen-based functional groups, as bioactive agents against
arthropod pests. Azo and nitro derivatives have long been studied for their pesticidal properties;
however, their effectiveness is often limited by low selectivity and environmental persistence.
Azoxy compounds, which incorporate both azo and nitroso characteristics within a single
functional group, have been less extensively studied despite their promising chemical properties.
Studies have shown that azoxybenzenes exhibit moderate to high biological activity, including
antimicrobial, insecticidal, and herbicidal effects, suggesting a broad spectrum of action. For
instance, recent investigations into azoxy-substituted triazines and phenyl derivatives
demonstrated enhanced acaricidal activity when compared to their parent structures. The
enhanced efficacy has been attributed to the azoxy group's ability to influence electron
distribution and facilitate molecular interactions with biological targets, such as enzyme systems
in mites. Furthermore, advances in synthetic organic chemistry have enabled the development of
structurally diverse azoxy compounds with tailored activity profiles. However, comprehensive
studies that specifically assess the acaricidal potential of azoxy-functionalized aromatic
compounds remain limited, indicating a need for further exploration in this area.
Methodology:
A series of azoxy-functionalized aromatic compounds were synthesized via the
oxidative coupling of aniline derivatives using hydrogen peroxide in the presence of acetic acid
as a mild oxidant under controlled temperature conditions (0–5 °C). The resulting azoxybenzenes
were purified through recrystallization and characterized by Fourier-transform infrared
spectroscopy (FTIR), proton nuclear magnetic resonance (^1H NMR), and gas chromatography–
mass spectrometry (GC-MS) to confirm structural integrity and purity. The acaricidal activity of
the synthesized compounds was evaluated using a contact bioassay against adult
Tetranychus
urticae
mites under laboratory conditions. Test solutions were prepared by dissolving each
compound in dimethyl sulfoxide (DMSO) and diluting to target concentrations (10, 25, 50, and
100 µg/mL). Mortality rates were recorded after 24 and 48 hours of exposure and compared to
standard commercial acaricides and negative controls. Statistical analysis was conducted using
one-way ANOVA followed by Tukey’s post hoc test (p < 0.05) to assess the significance of the
observed effects. Structure–activity relationships (SAR) were determined by correlating
molecular features (electron-withdrawing/donating substituents) with bioactivity outcomes.
Results:
The synthesized azoxybenzene derivatives exhibited a concentration-dependent
acaricidal effect against
Tetranychus urticae
. Compounds bearing electron-withdrawing
substituents (e.g., nitro, halogen) on the aromatic ring demonstrated significantly higher
mortality rates, with the para-nitroazoxybenzene derivative achieving 94% mortality at 100
µg/mL after 48 hours. In contrast, derivatives with electron-donating groups (e.g., methoxy,
methyl) showed moderate activity, with maximum mortality rates ranging from 55% to 70%.
Control groups treated with DMSO alone exhibited less than 5% mortality, confirming that
observed effects were compound-specific. Statistical analysis revealed that four of the
synthesized compounds were significantly more effective than the reference acaricide (p < 0.05),
especially at higher concentrations. FTIR and ^1H NMR spectra confirmed the successful
formation of the azoxy linkage, with characteristic bands at ~1500 cm⁻¹ and chemical shifts
between 7.2–8.4 ppm. GC-MS analysis showed purity levels exceeding 95% for all bioactive
compounds. The structure–activity relationship (SAR) analysis indicated that increased polarity
and electron deficiency in the aromatic ring enhanced acaricidal performance, likely by
promoting stronger interactions with biological targets in mite physiology.
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Figure 1. FTIR Spectrum of Azoxybenzene Derivative.
The FTIR spectrum displays characteristic absorption bands of the synthesized azoxybenzene
derivative. A strong and sharp absorption peak is observed around 1500 cm⁻¹, corresponding to
the azoxy (-N=N(O)-) functional group. Additional bands near 1600 cm⁻¹ are attributed to
aromatic C=C stretching vibrations, while peaks around 1300 cm⁻¹ may indicate C–N stretching
modes or contributions from substituted aromatic rings. The presence of a prominent peak at
~1500 cm⁻¹ confirms the successful formation of the azoxy functional group within the aromatic
framework. This spectral evidence supports the structural integrity of the synthesized compound
and is consistent with previously reported data for azoxy-containing compounds. The intensity
and sharpness of the band indicate good purity and minimal side product interference.
Figure 2. ¹H NMR Spectrum of Azoxybenzene Derivative.
The proton NMR spectrum exhibits multiple peaks in the aromatic region, specifically at 7.2
ppm, 7.8 ppm, and 8.4 ppm, consistent with the expected chemical shifts of protons on
substituted aromatic rings containing an azoxy group. The signal multiplicity and chemical shift
dispersion suggest symmetrical substitution patterns and electron-withdrawing effects induced
by the azoxy linkage.
The chemical shifts between 7.2–8.4 ppm are indicative of deshielded aromatic protons, likely
due to the electronegative influence of the azoxy group. The absence of extraneous signals
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outside the aromatic region and the clarity of peak resolution support the high purity of the
compound. These results corroborate the FTIR findings and validate the successful synthesis of
the target azoxybenzene structure.
The table 1 below presents the efficacy of various azoxybenzene derivatives against
Tetranychus
urticae
mites at concentrations of 50 µg/mL and 100 µg/mL, expressed as percentages of
mortality.
Table 1:
№ Compound
Substituent group
Mortality at 50
μg/ml
Mortality
at
100
μg/ml
1
AzB-1
-NO
2
(para)
72
94
2
AzB-2
-Cl (meta)
65
88
3
AzB-3
-OMe (para)
48
70
4
AzB-4
-CH
3
(ortho)
44
61
5
AzB-5
-H (unsubstituted)
36
50
The table presents the acaricidal efficacy of five synthesized azoxybenzene derivatives (AzB-1 to
AzB-5) against
Tetranychus urticae
at concentrations of 50 µg/mL and 100 µg/mL. Among the
tested compounds, AzB-1, which contains a para-nitro substituent (-NO₂), exhibited the highest
mortality rate of 94% at 100 µg/mL and 72% at 50 µg/mL. This is attributed to the strong
electron-withdrawing nature of the nitro group, which enhances the molecule’s electrophilicity
and binding affinity to biological targets.
AzB-2 (meta-chloro) also showed strong activity with 88% mortality at 100 µg/mL. In contrast,
AzB-3 and AzB-4, bearing electron-donating substituents (-OMe and -CH₃ respectively),
displayed only moderate activity. The unsubstituted compound AzB-5 had the lowest efficacy,
achieving just 50% mortality at the highest tested concentration.
These results confirm that the type and position of substituents on the azoxybenzene ring
significantly influence acaricidal potency. Electron-withdrawing groups in particular enhance
bioactivity, likely by increasing molecular polarity and improving interaction with enzymatic
systems in mites. The structure–activity relationship (SAR) observed supports the potential for
rational design of more potent azoxy-based acaricides through strategic substitution on the
aromatic core.
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SAR Model 1: Effect of Substituent Electronics and Hydrophobicity:
SAR Model 2: 3D Surface of Bioactivity Prediction
:
The SAR Model 1 (3D scatter plot) illustrates the correlation between electronic effects
(Hammett σ values), hydrophobicity (logP), and acaricidal activity. The data reveal that
compounds with higher σ values—indicative of stronger electron-withdrawing substituents such
as nitro (-NO₂) and chloro (-Cl)—demonstrated significantly greater mortality rates against
Tetranychus urticae
. For instance, the para-nitro-substituted derivative (σ ≈ 0.78) showed the
highest activity at both tested concentrations. This suggests that electron-deficient aromatic rings
facilitate stronger interaction with the biological target, possibly through enhanced
electrophilicity or hydrogen-bond acceptor capacity.
SAR Model 2 (3D surface plot) further supports these findings by visualizing a smooth
bioactivity gradient across the σ–logP space. The peak region of the surface corresponds to
compounds with both high electronic withdrawal and moderate hydrophobicity (logP ≈ 1.2–1.5),
indicating that optimal acaricidal efficacy is achieved when electronic effects and lipophilicity
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are balanced. Compounds with low σ values and higher logP—associated with electron-donating
substituents such as -OMe and -CH₃—tended to cluster in regions of lower mortality on the
surface, confirming their reduced bioactivity.
Together, the models underscore the critical role of substituent electronics and physicochemical
properties in designing potent azoxy-based acaricides. Rational modification of substituents to
fine-tune σ and logP could therefore be a viable strategy for optimizing acaricidal performance.
Discussion:
The structural and biological evaluation of azoxybenzene derivatives revealed a
strong correlation between molecular structure and acaricidal activity. The FTIR spectrum
confirmed the presence of the azoxy functional group through a prominent absorption band near
1500 cm⁻¹, which is characteristic of the -N=N(O)- linkage. Additional peaks associated with
aromatic C=C and C–N vibrations supported the formation of the targeted azoxy framework.
Complementary to this, the ¹H NMR spectrum displayed deshielded proton signals within the
7.2–8.4 ppm range, typical of substituted aromatic systems, further validating the successful
synthesis and structural integrity of the azoxybenzene core.
The biological assays demonstrated that acaricidal activity increased significantly with the
incorporation of electron-withdrawing substituents. According to the data in the table, the para-
nitro derivative (AzB-1) achieved 94% mortality at 100 µg/mL, while unsubstituted and
electron-donating variants showed comparatively lower efficacy. These results suggest that the
electronic properties of the substituents significantly impact bioactivity, likely by influencing
molecular polarity and binding affinity to biological targets within
Tetranychus urticae
.
This trend was further supported by the SAR Model 1, a 3D scatter plot showing that compounds
with higher Hammett sigma constants (σ) and moderate logP values clustered in regions of
higher acaricidal effect. The SAR Model 2 surface plot provided a predictive landscape of
bioactivity, indicating that optimal biological performance is achieved when substituents
contribute to a balanced combination of electrophilicity and hydrophobicity. The peak region of
this model centered around σ values of 0.4–0.8 and logP values of 1.2–1.5, aligning precisely
with the properties of the most potent compounds identified experimentally.
Together, these spectroscopic, biological, and SAR modeling results strongly suggest that the
azoxy group enhances acaricidal activity not only by contributing to the molecule's reactivity but
also by enabling precise modulation through aromatic substitution. These findings offer a
strategic platform for the rational design of azoxy-based acaricides with improved potency,
selectivity, and potentially lower environmental impact. Future work should focus on extending
these investigations to in vivo systems and broader pest targets to assess their practical
applicability and safety profile in agricultural settings.
Conclusion:
This study demonstrates that azoxy-functionalized aromatic compounds exhibit
significant acaricidal activity, with their efficacy strongly influenced by the electronic nature and
position of substituents on the aromatic ring. Spectroscopic analyses (FTIR and ¹H NMR)
confirmed the successful synthesis of structurally pure azoxybenzene derivatives. Among the
tested compounds, those bearing strong electron-withdrawing groups, particularly para-nitro
substituents, showed the highest mortality rates against
Tetranychus urticae
. Structure–activity
relationship (SAR) modeling revealed that optimal acaricidal activity is achieved when
electronic effects (Hammett σ values) and hydrophobicity (logP) are finely balanced, suggesting
that both properties synergistically contribute to enhanced bioactivity. These findings provide
valuable insight into the design of next-generation acaricides and support the use of azoxy
groups as a promising scaffold in agrochemical development. Further studies involving
environmental safety and in vivo efficacy are warranted to confirm their applicability in
integrated pest management.
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