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Palladium-mediated base-free and solvent-free synthesis of aromatic azo compounds from anilines catalyzed by copper acetate

  • Bo Jiang , Yue-Yue Du and Guo-Zhi Han EMAIL logo
Published/Copyright: August 19, 2022
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Green Processing and Synthesis
From the journal Green Processing and Synthesis Volume 11 Issue 1

Abstract

Herein, we report a new one-step direct synthesis of aromatic azo compounds from anilines under mild conditions. With the catalysis of copper acetate mediated by palladium salt, rapid conversion of anilines to aromatic azo compounds can be observed under the conditions of base-free along with solvent-free. Furthermore, the cross-coupling nitridation reaction based on this strategy was also studied. This research provides not only a new way for the synthesis of symmetrical and asymmetrical aromatic azo compounds but also a strategy and platform for exploring catalytic applications of transition metal compounds.

Keywords: base-free; solvent-free; azo compounds; copper acetate; palladium mediated

1 Introduction

Aromatic azo compounds are an important class of molecules with chromophore moiety of –N═N– bond and larger conjugated systems [1,2], which endows aromatic azo compounds with wide applications in organic dyes [3–7], radical reaction initiators [8,9], pigments [10,11], photosensitive molecular skeleton [12], and indicators [13–15]. Moreover, aromatic azo compounds are also intermediates in many organic conversion processes [16,17]. To synthesize the aromatic azo compounds, conventional methods mainly proceed via diazonium coupling or Mills reaction [18–22]. As for diazonium coupling reaction, the method has the advantages of fast reaction rate and high yield. However, the reaction has high restrictions on the substituent types of aromatic rings, resulting in a very narrow scope of substrate. The Mills reaction usually needs acetic acid as catalyst with raw materials of nitroso aromatic compounds and primary aromatic amines. Due to the instability of nitroso compounds, many side reactions often occur [23–25]. In the past decade, many efforts of scientists have been devoted to developing a number of new catalytic protocols for the synthesis of aromatic azo compounds by the direct oxidative coupling of anilines as shown in Table 1 [26–32]. Despite numerous improvements compared with conventional methods, several drawbacks remain in these new strategies including: (1) environmentally unfriendly oxidants [33] and undesirable over-oxidation products; (2) asymmetric aromatic azo compounds are not easy to prepare; (3) the additives of strong base or other organic ligands [34–38]; and (4) the usage of large amount of solvent makes these processes unfriendly for large-scale preparation. Especially, those additives in the above catalytic methods are great challenges for the rapid synthesis of azo compounds with groups on aromatic ring intolerant to strong base or oxidant. Therefore, the development of heterogeneous catalytic synthesis of aromatic azo compounds under mild conditions in the absence of side-additives is highly desirable [39,40].

Table 1

Catalytic protocols for the direct synthesis of aromatic azo compounds from anilines

Entry Solvent Oxidant Temperature (°C) Catalyst Additives
1 Toluene O2 100 Cu Pyridine/NH4Br
2 MeCN / 85 RuO2/Cu2O NPs /
3 DMSO / RT Ag NPs KOH
4 p-Xylene / 20 Pt NWs KOH/H2
5 DMF O2 80 Cu salt Cryptand
6 Toluene O2 110 meso-Mn2O /
7 THF O2 60 / t-BuOK
8 Toluene O2 60 Cu Pyridine
Our work / Air 100 Cu(OAc)2/Pd salt /

Herein, we develop a novel approach to synthesize aromatic azo compounds from available anilines under mild conditions of base-free along with solvent-free in air atmosphere, only with cheap copper acetate as catalyst mediated by small amount of palladium salt as shown in Scheme 1. To the best of our knowledge, this research is the first convenient catalytic process for synthesis of symmetric and asymmetric aromatic azo compounds from anilines without those above-mentioned side additives. There is no doubt that this strategy can provide a simple way to construct aromatic azo compounds with substituents which are not tolerant to strong bases.

Scheme 1 Palladium salt mediated catalytic synthesis of aromatic azo compounds from anilines.
Scheme 1

Palladium salt mediated catalytic synthesis of aromatic azo compounds from anilines.

2 Materials and methods

2.1 General information

The chemicals used were purchased from Sinopharm, Aladdin, and McLean Chemical Reagent Co, Ltd. All chemicals and reagents were of analytical grade and used without extra purification. All reactions were monitored by thin layer chromatography, and finally determined by gas chromatography-mass spectrometer (GC-MS). GC analysis was conducted with flame ionization detector and TG-5MS gas chromatography column (0.25 mm × 0.25 μm × 30 m). The products were purified by silica gel column chromatography. The structures of all target products were characterized by 1H-NMR and 13C-NMR at 400 MHz using CDCl3 as solvent.

2.2 Experimental procedure

First, the aromatic primary amine was added to a reaction tube in proportion to copper acetate and palladium chloride, and then heated at 100°C for 8 h in the air. After the reaction, an appropriate amount of ethyl acetate was added to the system to fully dissolve the products, and GC-MS was used for detection and analysis of target aromatic azo compounds, followed by characterization by 1H NMR and 13C NMR after purification.

As for cross-coupling reaction, two different aromatic amines were equivalently mixed and reacted under the same conditions.

3 Results and discussion

This work originates from our attempt to catalyze the C–N coupling reaction by Cu(OAc)2. We inadvertently found that this reaction can easily form aromatic azo compounds even in the absence of strong base and strong oxidant, whereas no aromatic azo compounds was observed with traditional palladium catalyst in this reaction. In order to fully understand the reaction and investigate the reaction mechanism, a series of parallel experiments were conducted using aniline as the model substrate (Table 2). We first mixed aniline with 10% Cu(OAc)2 in the absence of palladium salt, the yield of azobenzene was only 31%, whereas no azobenzene was observed only with the palladium catalyst (Table 2, Entries 1–2). Interestingly, with a mixture of palladium salt (1 mol%) and Cu(OAc)2 (10 mol%) as catalyst, the product yield greatly increased to 74% (Table 2, Entry 3). Furthermore, increasing the amount of palladium salt significantly leads to the decrease of product yield (Table 2, Entries 4–5). Similarly, increasing the amount of copper salt did not improve the yield (Table 2, Entry 6).

Table 2

Screening of various reaction parametersa

Entry PdCl2 (mol%) Cu(OAc)2 (mol%) Temp. (°C) Time (h) Yield (%)b
1 0 10 100 8 31
2 1 0 100 8 0
3 1 10 100 8 74
4 3 10 100 8 54
5 5 10 100 8 38
6 1 20 100 8 60
7 1 10 (CuSO4) 100 8 0
8 1 10 (CuNO3) 100 8 0
9 1 10 (CuCl) 100 8 26
10 1 10 100 6 68
11 1 10 100 4 65
12 1 10 120 4 46
13 1 10 140 4 42
14 1 10 80 4 51
15 1 10 60 4 47
16 1 10 40 4 0

aStandard reaction conditions: aniline (1 mmol), Cu(OAc)2 (0.1 mmol), PdCl2 (0.01 mmol), air (1 atm), 100°C, 8 h. bThe yield was measured by GC-MS.

In order to explore the role of copper acetate in the reaction, catalysts of other copper salts were further screened. However, attempts to use other bivalent copper salt such as copper nitrate and copper sulfate were unsuccessful (Table 2, Entries 7–8). Although monovalent copper salts can catalyze the conversion with yield of 26% (Table 2, Entry 9), similar catalytic studies have been reported previously with necessary oxidant such as air (or dioxygen) and base of pyridine by Zhang and Jiao [41]. In our discovery, this diazotization reaction can be carried out under the condition of alkali-free and solvent-free with Cu(OAc)2 as catalyst in air. In particular, the addition of a small amount of palladium salt can greatly improve the yield. However, it should be noted that palladium acetate cannot catalyze this reaction under the same conditions. As for reaction time, due to solvent-free conditions, the reaction mixture gradually solidified with prolonging the reaction time and could not be stirred after 8 h. Thus, we optimized the reaction time at 8 h. The experimental results also showed that the best yield was obtained after 8 h (Table 2, Entries 10–11).

Subsequently, we investigated the effect of reaction temperature on the reaction. Experimental results indicated that the reaction worked more efficiently at an enhanced temperature of 100°C. With unchanged reaction time of 8 h, a lower yield of the product was obtained when the reaction was conducted at lower or higher reaction temperature. When the reaction temperature was increased to 120°C and 140°C, the product yield decreased to 46% and 42%, respectively (Table 2, Entries 12–13). When the reaction temperature conversely dropped to 80°C and 60°C, the product yield decreased to 51% and 47%, respectively (Table 2, Entries 14–15). Moreover, when the temperature is further lowered to 40°C or room temperature, no target products were observed (Table 2, Entry 16).

Under the optimized reaction conditions, the substrate scope of the reaction was explored by applying these conditions to a series of substituted anilines (Scheme 2).

Scheme 2 The optimum reaction conditions for synthesis of azo compounds.
Scheme 2

The optimum reaction conditions for synthesis of azo compounds.

Experimental results indicated that this method has a high degree of functional-group tolerance as shown in Scheme 3. Both electron-donating and electron-withdrawing substrates were well-tolerated, giving a moderate to satisfactory yield. Even aromatic primary amine with considerable steric bulk also afforded the corresponding azo compounds with moderate yield. It is noteworthy that electron-withdrawing substituents adjust well to the reaction and lead to higher yields. For example, aromatic primary amine with electron-withdrawing groups such as fluorine, chlorine, and bromine (Scheme 3a–g) can obtain yield of 60–87%. However, when the halogen substituent is in the ortho position, the yield decreases sharply, and even the target product was not observed (Scheme 3h–j). On the other hand, with electron-donating groups on aromatic rings, yield of the azo compounds decreased to between 8% and 73% (Scheme 3k–q), and yield of azo compounds from ortho-substituted amine is still lower, that is considered here is the effect of steric hindrance. For example, when the methoxy group locates in the para position, the yield can reach 66% whereas the yield decreased to 18% for the ortho position. Furthermore, for multi-substituted aniline, this strategy can still achieve a mild yield from 43% to 80% (Scheme 3r–t). For aromatic primary amines with fused ring, the yield of the target product decreased to 30% (Scheme 3u). If there is another amino group on the aromatic ring, the yield decreases obviously, which may be due to the interference of substituents on the reaction sites (Scheme 3v–w).

Scheme 3 Substrate scope of synthesis of azo compounds (3a–3w) catalyzed by Cu(OAc)2.
Scheme 3

Substrate scope of synthesis of azo compounds (3a–3w) catalyzed by Cu(OAc)2.

For further extending the utility of the synthetic strategy, we next turned our attention toward examining its application for synthesis of asymmetrically substituted aromatic azo compounds as shown in Scheme 4.

Scheme 4 Synthesis of asymmetric azo compounds.
Scheme 4

Synthesis of asymmetric azo compounds.

Generally, asymmetrically substituted azo compounds are synthesized through reaction of the diazonium salt with aromatic compounds with electron-rich substituents. There is no doubt that the traditional method has great limitations for constructing azo compounds with only electron-withdrawing groups on aromatic rings. Scheme 5 shows the results of synthesis of asymmetric azo compounds by this method. Experimental results clearly indicated that this method is favorable for synthesis of asymmetrical azo compounds containing electron-withdrawing substituents. Electron-withdrawing substituents in the aromatic rings advance the yields of desired cross-coupling products and perform better than electron-donating substituents. 4-Fluoroaniline and 4-chloroaniline can give desired asymmetric azo products with the yield of 55% (Scheme 5a), whereas yield of 45%, 25%, and 21% were obtained for 4-methylaniline and 4-methoxyaniline, p-methylaniline and 3,5-xylidine, and aniline and p-methylaniline, respectively (Scheme 5b–d). Importantly, different types of substituents in aromatic ring also resulted in a moderate yield of 48% (Scheme 5e). However, with the decrease of pulling-electron ability of electron-withdrawing, the yield also decreased (Scheme 5f).

Scheme 5 Application of the method for synthesis of asymmetrical azo compounds (5a–5f).
Scheme 5

Application of the method for synthesis of asymmetrical azo compounds (5a–5f).

Based on the above results, we put forward a plausible mechanism as shown in Scheme 6, which is similar to that proposed by Suib et al. [42]. Obviously, for understanding the mechanism of this reaction, the transfer of hydrogen of the amino group is a key factor. Since our parallel experiments indicated that only copper acetate can catalyze this reaction, we speculate that the acetate ions in Cu(OAc)2 promote the transfer of hydrogen, and the transferred hydrogens of amino groups combine with acetate ions to form acetic acid. On the other hand, in some previous reports [41], oxygen in the atmosphere played an important role in the circulation of the catalyst. In the plausible mechanism proposed by us, the aromatic primary amine is first oxidized by divalent copper ion to form radical species 2, then the radical species attack another aromatic primary amine to form compound 3 with a 3 e–б bond. Under the promotion of acetate ion, the successive loss of a proton, an electron, and another proton happens to form intermediate 5, i.e., 1,2-diphenylhydrazine. Subsequently, the intermediate 5 goes through all the aforesaid steps once again to provide the final azo compound 7. However, 1,2-diphenylhydrazine can be rearranged and converted to benzidine under acidic conditions, resulting in a decrease of yield. When a small amount of palladium salt is added, palladium ions can act with 1,2-diphenylhydrazine to inhibit its rearrangement and enhance the yield of the target product, which originates from the strong complexation between palladium and nitrogen atoms [43]. In order to verify this conclusion, we conducted an additional experiment as shown in SI. When palladium chloride was mixed with amino compounds at room temperature, the characteristic peaks of amino groups in the infrared spectra changed greatly. In addition, this complexation also weakens the N–H bond and makes the leaving of molecular hydrogen more easily.

Scheme 6 Plausible mechanism of the synthesis of azo compounds catalyzed by copper acetate.
Scheme 6

Plausible mechanism of the synthesis of azo compounds catalyzed by copper acetate.

On the other hand, in the catalytic cycle, Cu2+ will be reduced to Cu+, which is then re-oxidized to Cu2+ by the oxygen in the air, followed by formation of corresponding lattice oxygen from O2 (Scheme 6, cycle 2). The lattice oxygen finally combines with the protons released from HOAc and electrons released in cycle 1 to form water, and the released acetate ions enter the next cycle. The role of oxygen in the catalytic cycle is consistent with our observations of a highly diminished yield when the reaction was conducted under nitrogen gas. On the contrary, the increase of the amount of palladium salt will reduce the yield, because palladium salt can also complex with anilines, thus inhibiting the first step of the conversion.

4 Conclusion

In summary, we have developed a novel and simple method for the rapid synthesis of symmetric and asymmetric aromatic azo compounds directly from anilines by using Cu(OAc)2 as catalyst under base-free and solvent-free conditions. Moreover, with the aid of a small amount of palladium salt, the yield of the aromatic azo compounds can be greatly improved. In addition, the cross-coupling nitridation reaction based on this strategy also obtained satisfactory results. This research provides a new green way to synthesize aromatic azo compounds not only solving the harsh reaction requirements but also laying a new way for the synthesis of asymmetrical aromatic azo compounds.

  1. Funding information: This work was partly supported by “Research and Development (R&D) Plan of Jurong City” (ZY2019006, Jiangsu Province, China).

  2. Author contributions: Bo Jiang: writing – original draft, editing, and completing the manuscript; Yue-Yue Du: modifying and perfecting manuscript; Guo-Zhi Han: review and editing – methodology and content of the manuscript.

  3. Conflict of interest: Authors state no conflict of interest.

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Received: 2022-04-13
Revised: 2022-06-04
Accepted: 2022-06-14
Published Online: 2022-08-19

© 2022 Bo Jiang et al., published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 International License.

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  37. Optimization of biochar preparation process and carbon sequestration effect of pruned wolfberry branches
  38. Anticancer potential of biogenic silver nanoparticles using the stem extract of Commiphora gileadensis against human colon cancer cells
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  45. Anti-colon cancer activities of green-synthesized Moringa oleifera–AgNPs against human colon cancer cells
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  47. A low-cost and eco-friendly fabrication of an MCDI-utilized PVA/SSA/GA cation exchange membrane
  48. Synthesis, microstructure, and phase transition characteristics of Gd/Nd-doped nano VO2 powders
  49. Biomediated synthesis of ZnO quantum dots decorated attapulgite nanocomposites for improved antibacterial properties
  50. Preparation of metal–organic frameworks by microwave-assisted ball milling for the removal of CR from wastewater
  51. A green approach in the biological base oil process
  52. A cost-effective and eco-friendly biosorption technology for complete removal of nickel ions from an aqueous solution: Optimization of process variables
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  55. Effectiveness of different accelerated green synthesis methods in zinc oxide nanoparticles using red pepper extract: Synthesis and characterization
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  57. A numerical study on the effects of bowl and nozzle geometry on performances of an engine fueled with diesel or bio-diesel fuels
  58. Liquid-phase hydrogenation of carbon tetrachloride catalyzed by three-dimensional graphene-supported palladium catalyst
  59. The catalytic performance of acid-modified Hβ molecular sieves for environmentally friendly acylation of 2-methylnaphthalene
  60. A study of the precipitation of cerium oxide synthesized from rare earth sources used as the catalyst for biodiesel production
  61. Larvicidal potential of Cipadessa baccifera leaf extract-synthesized zinc nanoparticles against three major mosquito vectors
  62. Fabrication of green nanoinsecticides from agri-waste of corn silk and its larvicidal and antibiofilm properties
  63. Palladium-mediated base-free and solvent-free synthesis of aromatic azo compounds from anilines catalyzed by copper acetate
  64. Study on the functionalization of activated carbon and the effect of binder toward capacitive deionization application
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  73. Off-gas detection and treatment for green air-plasma process
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  75. Construction of mercury ion fluorescence system in water samples and art materials and fluorescence detection method for rhodamine B derivatives
  76. Hydroxyapatite/TPU/PLA nanocomposites: Morphological, dynamic-mechanical, and thermal study
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  79. Nitrogen removal characteristics of wet–dry alternative constructed wetlands
  80. Structural properties and reactivity variations of wheat straw char catalysts in volatile reforming
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  86. Chemical synthesis, characterization, and dose optimization of chitosan-based nanoparticles of clodinofop propargyl and fenoxaprop-p-ethyl for management of Phalaris minor (little seed canary grass): First report
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  88. Green synthesis of silver nanoparticles and their antibacterial activities
  89. Review Articles
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  91. Applications of polyaniline-impregnated silica gel-based nanocomposites in wastewater treatment as an efficient adsorbent of some important organic dyes
  92. Green synthesis of nano-propolis and nanoparticles (Se and Ag) from ethanolic extract of propolis, their biochemical characterization: A review
  93. Advances in novel activation methods to perform green organic synthesis using recyclable heteropolyacid catalysis
  94. Limitations of nanomaterials insights in green chemistry sustainable route: Review on novel applications
  95. Special Issue: Use of magnetic resonance in profiling bioactive metabolites and its applications (Guest Editors: Plalanoivel Velmurugan et al.)
  96. Stomach-affecting intestinal parasites as a precursor model of Pheretima posthuma treated with anthelmintic drug from Dodonaea viscosa Linn.
  97. Anti-asthmatic activity of Saudi herbal composites from plants Bacopa monnieri and Euphorbia hirta on Guinea pigs
  98. Embedding green synthesized zinc oxide nanoparticles in cotton fabrics and assessment of their antibacterial wound healing and cytotoxic properties: An eco-friendly approach
  99. Synthetic pathway of 2-fluoro-N,N-diphenylbenzamide with opto-electrical properties: NMR, FT-IR, UV-Vis spectroscopic, and DFT computational studies of the first-order nonlinear optical organic single crystal
https://doi.org/10.1515/gps-2022-0070
Keywords for this article
base-free; solvent-free; azo compounds; copper acetate; palladium mediated
Creative Commons
BY 4.0

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  37. Optimization of biochar preparation process and carbon sequestration effect of pruned wolfberry branches
  38. Anticancer potential of biogenic silver nanoparticles using the stem extract of Commiphora gileadensis against human colon cancer cells
  39. Fabrication and characterization of lysine hydrochloride Cu(ii) complexes and their potential for bombing bacterial resistance
  40. First report of biocellulose production by an indigenous yeast, Pichia kudriavzevii USM-YBP2
  41. Biosynthesis and characterization of silver nanoparticles prepared using seeds of Sisymbrium irio and evaluation of their antifungal and cytotoxic activities
  42. Synthesis, characterization, and photocatalysis of a rare-earth cerium/silver/zinc oxide inorganic nanocomposite
  43. Developing a plastic cycle toward circular economy practice
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  45. Anti-colon cancer activities of green-synthesized Moringa oleifera–AgNPs against human colon cancer cells
  46. Phosphorus removal from aqueous solution by adsorption using wetland-based biochar: Batch experiment
  47. A low-cost and eco-friendly fabrication of an MCDI-utilized PVA/SSA/GA cation exchange membrane
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  49. Biomediated synthesis of ZnO quantum dots decorated attapulgite nanocomposites for improved antibacterial properties
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  52. A cost-effective and eco-friendly biosorption technology for complete removal of nickel ions from an aqueous solution: Optimization of process variables
  53. Protective role of Spirulina platensis liquid extract against salinity stress effects on Triticum aestivum L.
  54. Comprehensive physical and chemical characterization highlights the uniqueness of enzymatic gelatin in terms of surface properties
  55. Effectiveness of different accelerated green synthesis methods in zinc oxide nanoparticles using red pepper extract: Synthesis and characterization
  56. Blueprinting morpho-anatomical episodes via green silver nanoparticles foliation
  57. A numerical study on the effects of bowl and nozzle geometry on performances of an engine fueled with diesel or bio-diesel fuels
  58. Liquid-phase hydrogenation of carbon tetrachloride catalyzed by three-dimensional graphene-supported palladium catalyst
  59. The catalytic performance of acid-modified Hβ molecular sieves for environmentally friendly acylation of 2-methylnaphthalene
  60. A study of the precipitation of cerium oxide synthesized from rare earth sources used as the catalyst for biodiesel production
  61. Larvicidal potential of Cipadessa baccifera leaf extract-synthesized zinc nanoparticles against three major mosquito vectors
  62. Fabrication of green nanoinsecticides from agri-waste of corn silk and its larvicidal and antibiofilm properties
  63. Palladium-mediated base-free and solvent-free synthesis of aromatic azo compounds from anilines catalyzed by copper acetate
  64. Study on the functionalization of activated carbon and the effect of binder toward capacitive deionization application
  65. Co-chlorination of low-density polyethylene in paraffin: An intensified green process alternative to conventional solvent-based chlorination
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  67. Recovery of cobalt from spent lithium-ion battery cathode materials by using choline chloride-based deep eutectic solvent
  68. Synthesis of insoluble sulfur and development of green technology based on Aspen Plus simulation
  69. Photodegradation of methyl orange under solar irradiation on Fe-doped ZnO nanoparticles synthesized using wild olive leaf extract
  70. A facile and universal method to purify silica from natural sand
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  72. Endophytic bacterial strain, Brevibacillus brevis-mediated green synthesis of copper oxide nanoparticles, characterization, antifungal, in vitro cytotoxicity, and larvicidal activity
  73. Off-gas detection and treatment for green air-plasma process
  74. Ultrasonic-assisted food grade nanoemulsion preparation from clove bud essential oil and evaluation of its antioxidant and antibacterial activity
  75. Construction of mercury ion fluorescence system in water samples and art materials and fluorescence detection method for rhodamine B derivatives
  76. Hydroxyapatite/TPU/PLA nanocomposites: Morphological, dynamic-mechanical, and thermal study
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  81. Microfluidic plasma: Novel process intensification strategy
  82. Antibacterial and photocatalytic activity of visible-light-induced synthesized gold nanoparticles by using Lantana camara flower extract
  83. Antimicrobial edible materials via nano-modifications for food safety applications
  84. Biosynthesis of nano-curcumin/nano-selenium composite and their potentialities as bactericides against fish-borne pathogens
  85. Exploring the effect of silver nanoparticles on gene expression in colon cancer cell line HCT116
  86. Chemical synthesis, characterization, and dose optimization of chitosan-based nanoparticles of clodinofop propargyl and fenoxaprop-p-ethyl for management of Phalaris minor (little seed canary grass): First report
  87. Double [3 + 2] cycloadditions for diastereoselective synthesis of spirooxindole pyrrolizidines
  88. Green synthesis of silver nanoparticles and their antibacterial activities
  89. Review Articles
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  91. Applications of polyaniline-impregnated silica gel-based nanocomposites in wastewater treatment as an efficient adsorbent of some important organic dyes
  92. Green synthesis of nano-propolis and nanoparticles (Se and Ag) from ethanolic extract of propolis, their biochemical characterization: A review
  93. Advances in novel activation methods to perform green organic synthesis using recyclable heteropolyacid catalysis
  94. Limitations of nanomaterials insights in green chemistry sustainable route: Review on novel applications
  95. Special Issue: Use of magnetic resonance in profiling bioactive metabolites and its applications (Guest Editors: Plalanoivel Velmurugan et al.)
  96. Stomach-affecting intestinal parasites as a precursor model of Pheretima posthuma treated with anthelmintic drug from Dodonaea viscosa Linn.
  97. Anti-asthmatic activity of Saudi herbal composites from plants Bacopa monnieri and Euphorbia hirta on Guinea pigs
  98. Embedding green synthesized zinc oxide nanoparticles in cotton fabrics and assessment of their antibacterial wound healing and cytotoxic properties: An eco-friendly approach
  99. Synthetic pathway of 2-fluoro-N,N-diphenylbenzamide with opto-electrical properties: NMR, FT-IR, UV-Vis spectroscopic, and DFT computational studies of the first-order nonlinear optical organic single crystal
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