Pd/RHA and Pd/BPA as Eco-Friendly Heterogeneous Catalysts: Microwave-Assisted C–S Cross-Coupling Reaction in DMF

Abstract

First time, Pd-Rice Husk Ash (Pd/RHA) and Pd-Banana Peel Ash (Pd-BPA) were used as eco-friendly catalysts in the C–S cross-coupling reaction of 5-bromo-2,1,3-benzothiadiazole with various benzene thiols in DMF under microwave irradiation at 75 °C, 200 W (100 psi) for 15–25 min. These catalysts were produced from agro-industrial wastes, such as rice husk ash and banana peel ash. These can be recycled and reused up to five catalytic cycles without loss of catalytic efficiency.

Key words

Pd/RHA - Pd/BPA - C–S cross-coupling - microwave - DMF - eco-friendly

Publication History

Received: 27 May 2022

Accepted after revision: 25 July 2022

Article published online:
31 August 2022

• References and Notes

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• 20 All chemical reagents and solvents were used without any specific treatment. The reactions were monitored using thin-layer chromatography (TLC) MACHEREY-NAGEL (SIL G/UV254). The purification of the compounds was performed by column chromatography using ethyl acetate and hexane eluents. ¹H and ¹³C NMR spectra were recorded in CDCl₃ on a Bruker spectrometer (400 MHz and 101 MHz, respectively). The infrared spectra were recorded on a FT/IR 4100 type A spectrometer of Jasco. All reactions were carried out in sealed glass tubes with a volume of 10 mL in a commercially available monomode microwave reactor (CEM, Matthews, NC, USA) equipped with infrared monitoring and a noninvasive pressure transducer.§#BLD#§
• 21 Preparation of agro-industrial ashesThe agro-industrial wastes (rice husks and banana peels) were washed with deionized water and dried in an oven at 105 °C for 24 h until water removal, then kept in a desiccator until use. Subsequently, they were milled in a Tekmar A-10 mill and separated in sieves in the 0.5–1.0 mm granulometry range through a JEL 200/80 sieving machine. Samples containing 2.0 g of agro-industrial wastes were calcined in a muffle furnace (400 °C, 4 h), resulting in rice husk ash (RHA) and banana peel ash (BPA). Porosimetric Evaluation (BET Isotherms) of the Obtained AshesN₂ adsorption isotherms were performed on Gemini equipment (Micromeritics, Georgia, USA). Samples were preheated at 70 °C for 8 h under vacuum. The surface area was determined using the Brunauer–Emmet–Teller (BET) method at –196 °C with P/P_atm in the range of 0.01 to 0.35. The mean diameter of mesopores and their distribution were calculated using the Barrett–Joyner–Halenda (BJH) method with Halsey standards for the desorption isotherm. The micropore volume was calculated using the t-plot method and the standard isotherm of Harkins and Jura. Elemental Analysis (CHN)The carbon, hydrogen, and nitrogen compositions (CHN analysis) were determined on a PerkinElmer M-CHNS/O analyzer, model 2400.Palladium Support in the Ashes10 mL of PdCl₂ solution in acetone (0.1 g/L) were added to 600 mg of obtained ash. The mixture was left in the shaker for 24 h. Finally, the resulting solid was filtered and oven dried (80 °C for 1 h). The same procedure was performed for both RHA and BPA. Scanning Electron Microscopy (SEM) and Electron-Dispersive Spectroscopy (EDS) Elemental AnalysisThe morphology of the solids was analyzed using a JEOL model JSM 6610 at 20 kV and a 3000 magnification value. The same instrument was used for the EDS analysis with a Noran detector (20 kV with an acquisition time of 100 s and 1500 magnification). The sample was gold coated for analysis. Fourier-Transform Infrared Spectroscopy (FT-IR)FT-IR analyses were performed using a Shimadzu spectrophotometer (IR Prestige 21), combining 32 scans at a 2 cm^–1 resolution. The samples were analyzed as pellets with an approximate thickness and diameter of 2 mm and 5 mm, respectively. The sample mass dilution was performed with KBr.
• 22 General Procedure for the Synthesis of 5-Phenylthio-2,1,3-benzothiadiazoles¹⁵ Benzene thiols (0.45 mmol), 5-bromo-2,1,3-benzothiadiazole (0.3 mmol), a catalytic amount of catalyst (0.025 mol%), K₂CO₃ (0.6 mmol), and DMF (2 mL) were added to a microwave reaction vessel armed with a magnetic stirrer bar. The reaction mixture was subjected to microwave irradiation (a CEM Discover MW reactor) (200W, 75 °C) for 15–25 min. The progress of the reaction was observed by TLC (eluent: EtOAc/hexane, 10:90). The reaction mixture was cooled to room temperature, and the crude residue was extracted with ethyl acetate (3 × 10 mL) and water. Then, all the organic layers were combined and dried over anhydrous Na₂SO₄. The remaining solvent was evaporated under reduced pressure. Further, the crude product was purified by column chromatography over silica gel to afford the corresponding product, and yields were obtained in 51–92% as shown in Scheme 2. We also compared samples with authentic compounds.¹⁵ 5-[(4-Methoxyphenyl)thio]benzo[c][1,2,5]thiadiazole (3a)¹ Yield 74.25 mg (92%); light yellow oil. ¹H NMR (400 MHz, CDCl₃): δ = 8.22 (d, J = 1.5 Hz, 1 H), 7.87 (d, J = 9.2 Hz, 1 H), 7.66 (dd, J₁ = 9.3 Hz, J₂ = 1.8 Hz, 1 H), 7.39 (d, J = 8.8 Hz, 2 H), 6.83 (d, J = 8.8 Hz, 2 H), 3.79 (s, 3 H). ¹³C NMR (101 MHz, CDCl₃): δ = 159.88, 155.25, 153.32, 133.18, 132.61, 128.41, 123.80, 122.15, 114.58, 55.33. MS (ESI): m/z = 275 [M + H]⁺. 5-(Phenylthio)benzo[c][1,2,5]thiadiazole (3b)¹ Yield 67.62 mg (92%); yellow oil. ¹H NMR (400 MHz, CDCl₃): δ = 8.22 (d, J = 1.6 Hz, 1 H), 7.86 (dd, J₁ = 8.9 Hz, J₂ = 5.0 Hz, 1 H), 7.66 (dd, J₁ = 9.3 Hz, J₂ = 1.8 Hz, 1 H), 7.51–7.48 (m, 2 H), 7.30 (dd, J₁ = 10.2 Hz, J₂ = 4.8 Hz, 2 H), 7.22 (q, J = 7.3 Hz, 1 H). ¹³C NMR (101 MHz, CDCl₃): δ = 155.25, 153.31, 137.00, 133.17, 129.02, 127.48, 127.11, 124.49, 123.80, 122.14. MS (ESI): m/z = 245 [M + H]⁺. 5-(p-Tolylthio)benzo[c][1,2,5]thiadiazole (3c)¹ Yield 46.62 mg (60%); yellow oil. ¹H NMR (400 MHz, CDCl₃): δ = 7.84 (d, J = 9.2 Hz, 1 H), 7.41–7.30 (m, 1 H), 7.24 (t, J = 4.9 Hz, 1 H), 7.13–7.06 (m, 2 H), 7.00 (d, J = 7.5 Hz, 2 H), 2.44 (s, 3 H). ¹³C NMR (101 MHz, CDCl₃): δ = 155.37, 153.16, 143.91, 143.37, 141.76, 134.70, 130.16, 129.18, 128.86, 128.00, 121.12, 114.18, 21.40. MS (ESI): m/z = 259 [M + H]⁺.5-(Naphthalen-2-ylthio)benzo[c][1,2,5]thiadiazole (3d)Yield 75.22 mg (85%); yellow solid; mp 118–-120 °C. ¹H NMR (400 MHz, CDCl₃): δ = 8.03 (d, J = 40.3 Hz, 1 H), 7.91–7.40 (m, 9 H). ¹³C NMR (101 MHz, CDCl₃): δ = 155.15, 153.54, 141.26, 133.42, 130.63, 130.24, 129.62, 128.94, 127.78, 127.44, 127.01, 126.63, 126.21, 125.65, 121.35, 118.67. MS (ESI): m/z = 295 [M + H]⁺. Anal. Calcd for (C₁₆H₁₀N₂S₂): C, 65.28; H, 3.42; N, 9.52; S, 21.78. Found: C, 65.24; H, 3.35; N, 9.48; S, 21.73.5-(o-Tolylthio)benzo[c][1,2,5]thiadiazole (3e)¹ Yield 61.38 mg (79%); yellow oil. ¹H NMR (400 MHz, CDCl₃): δ = 7.84 (d, J = 9.2 Hz, 1 H), 7.51–7.40 (m, 4 H), 7.27–7.24 (m, 2 H), 2.41 (s, 3 H). ¹³C NMR (101 MHz, CDCl₃): δ = 155.21, 153.40, 142.53, 139.66, 134.53, 130.70, 130.13, 127.68, 121.14, 117.31, 21.28. MS (ESI): m/z = 259 [M + H]⁺.5-[(2,6-Dimethylphenyl)thio]benzo[c][1,2,5]thiadiazole (3f)Yield 71.25 mg (87%); yellow solid; mp 82–84 °C. ¹H NMR (400 MHz, CDCl₃): δ = 7.84 (d, J = 9.2 Hz, 1 H), 7.39 (dd, J₁ = 9.2 Hz, J₂ = 1.8 Hz, 1 H), 7.31–7.29 (m, 1 H), 7.25 (s, 1 H), 7.10 (d, J = 1.2 Hz, 1 H), 7.01 (s, 1 H), 2.44 (s, 6 H). ¹³C NMR (101 MHz, CDCl₃): δ = 155.38, 153.17, 143.93, 141.77, 130.17, 129.23, 128.86, 128.00, 121.12, 114.16, 21.56. MS (ESI): m/z = 273 [M + H]⁺. Anal. Calcd for (C₁₄H₁₂N₂S₂): C, 61.73; H, 4.44; N, 10.28; S, 23.54. Found: C, 61.70; H, 4.41; N, 10.31; S, 23.49. 5-(Tritylthio)benzo[c][1,2,5]thiadiazole (3g)Yield 108.5 mg (88%); yellow solid; mp 90–92 °C.¹H NMR (400 MHz, CDCl₃): δ = 7.34 (dd, J₁ = 12.6 Hz, J₂ = 6.5 Hz, 9 H), 7.28–7.24 (m, 3 H), 7.17 (d, J = 7.3 Hz, 6 H). ¹³C NMR (101 MHz, CDCl₃): δ = 146.90, 143.94, 129.49, 128.34, 127.97, 127.30, 126.33, 56.88. MS (ESI): m/z = 411 [M + H]⁺. Anal. Calcd for (C₂₅H₁₈N₂S₂): C, 73.14; H, 4.42; N, 6.82; S, 15.62. Found: C, 73.09; H, 4.35; N, 6.77; S, 15.57. 5-(Nenzylthio)benzo[c][1,2,5]thiadiazole (3h)¹ Yield 71.48 mg (92%); yellow semisolid. ¹H NMR (400 MHz, CDCl₃): δ = 8.22 (d, J = 1.6 Hz, 1 H), 7.86 (dd, J₁ = 14.0 Hz, J₂ = 9.2 Hz, 2 H), 7.74 (d, J = 1.5 Hz, 1 H), 7.67 (dd, J₁ = 9.3 Hz, J₂ = 1.8 Hz, 1 H), 7.46–7.39 (m, 3 H), 4.28 (s, 2 H). ¹³C NMR (101 MHz, CDCl₃): δ = 155.22, 153.30, 140.82, 137.34, 133.20, 130.58, 129.39, 128.45, 127.65, 127.40, 123.81, 122.16, 121.00, 116.65, 43.26. MS (ESI): m/z = 259 [M + H]⁺.5-{[4-(Methylthio)phenyl]thio}benzo[c][1,2,5]thiadiazole (3i)Yield 54.12 mg (62%); yellow semisolid. ¹H NMR (400 MHz, CDCl₃): δ = 7.46 (d, J = 8.4 Hz, 1 H), 7.40 (dd, J₁ = 11.5 Hz, J₂ = 5.0 Hz, 3 H), 7.29 (d, J = 8.4 Hz, 1 H), 7.16 (d, J = 8.4 Hz, 2 H), 2.46 (s, 3 H). ¹³C NMR (101 MHz, CDCl₃): δ = 142.56, 139.67, 137.44, 134.54, 133.90, 133.23, 130.72, 130.15, 129.78, 128.55, 124.54, 123.86, 122.20, 121.17, 117.34, 21.04. MS (ESI): m/z = 291 [M + H]⁺. Anal. Calcd for (C₁₃H₁₀N₂S₃): C, 53.77; H, 3.47; N, 9.65; S, 33.12. Found: C, 53.72; H, 3.41; N, 9.59; S, 33.08.4-{Benzo[c][1,2,5]thiadiazol-5-ylthio}aniline (3j)¹ Yield 64.74 mg (83%); yellow semisolid. ¹H NMR (400 MHz, CDCl₃): δ = 8.23 (d, J = 1.3 Hz, 1 H), 7.87 (t, J = 9.4 Hz, 2 H), 7.67 (dd, J₁ = 9.3 Hz, J₂ = 1.7 Hz, 1 H), 7.42–7.38 (m, 2 H), 6.84 (s, 1 H), 4.33 (s, 2 H). ¹³C NMR (101 MHz, CDCl₃): δ = 153.46, 148.74, 136.94, 133.34, 131.71, 123.95, 122.30, 118.35, 115.34. MS (ESI): m/z = 260 [M + H]⁺.5-[(4-chlorophenyl)thio]benzo[c][1,2,5]thiadiazole (3k)¹ Yield 46 mg (55%); light yellow oil. ¹H NMR (400 MHz, CDCl₃): δ = 7.88 (d, J = 9.2 Hz, 1 H), 7.63 (d, J = 1.3 Hz, 1 H), 7.47–7.39 (m, 4 H), 7.27 (d, J = 8.5 Hz, 1 H). ¹³C NMR (101 MHz, CDCl₃): δ = 155.05, 153.54, 140.53, 134.88, 130.53, 130.03, 129.29, 121.55, 118.97. MS (ESI): m/z = 279 [M + H]⁺.5-[(4-Bromophenyl)thio]benzo[c][1,2,5]thiadiazole (3l)Yield 62.2 mg (64%); yellow oil. ¹H NMR (400 MHz, CDCl₃): δ = 7.89 (dd, J₁ = 9.2 Hz, J₂ = 0.4 Hz, 1 H), 7.66 (d, J = 1.2 Hz, 1 H), 7.56–7.53 (m, 2 H), 7.44–7.38 (m, 2 H), 7.35–7.32 (m, 1 H). ¹³C NMR (101 MHz, CDCl₃): δ = 134.98, 132.98, 132.20, 130.64, 129.38, 121.59, 119.20. MS (ESI): m/z = 324 [M + H]⁺. Anal. Calcd for (C₁₂H₇BrN₂S₂): C, 44.59; H, 2.18; N, 8.67; S, 19.84. Found: C, 44.52; H, 2.12; N, 8.71; S, 19.80.5-(Benzo[d]thiazol-2-ylthio)benzo[c][1,2,5]thiadiazole (3m)Yield 50.7 mg (56%); yellow semisolid. ¹H NMR (400 MHz, DMSO): δ = 8.33 (d, J = 1.8 Hz, 1 H), 8.15 (s, 1 H), 8.01 (d, J = 9.2 Hz, 2 H), 7.77 (dd, J₁ = 9.2 Hz, J₂ = 1.6 Hz, 2 H), 7.38 (s, 1 H). ¹³C NMR (101 MHz, DMSO): δ = 164.31, 151.95, 135.63, 132.97, 130.50, 130.43, 127.14, 124.77, 123.79, 121.26, 120.25, 117.21, 115.63. MS (ESI): m/z = 302 [M + H]⁺. Anal. Calcd for (C₁₃H₇N₃S₃): C, 51.81; H, 2.34; N, 13.94; S, 31.91. Found: C, 51.74; H, 2.27; N, 13.87; S, 31.83.2-{Benzo[c][1,2,5]thiadiazol-5-ylthio}aniline (3n)¹ Yield 63.18 mg (81%); yellow semisolid. ¹H NMR (400 MHz, CDCl₃): δ = 8.23 (d, J = 1.4 Hz, 1 H), 7.90 (d, J = 9.2 Hz, 1 H), 7.69 (dd, J₁ = 9.2 Hz, J₂ = 1.8 Hz, 1 H), 7.17 (t, J = 7.2 Hz, 2 H), 6.73 (d, J = 7.6 Hz, 1 H), 6.60 (t, J = 7.5 Hz, 1 H), 4.36 (s, 2 H). ¹³C NMR (101 MHz, CDCl₃): δ = 155.30, 153.37, 148.65, 136.84, 133.24, 131.62, 123.85, 122.20, 118.25, 115.25. MS (ESI): m/z = 260 [M + H]⁺.5-[(4-Fluorophenyl)thio]benzo[c][1,2,5]thiadiazole (3o)¹ Yield 55.23 mg (70%); yellow oil. ¹H NMR (400 MHz, CDCl₃): δ = 7.88 (d, J = 9.2 Hz, 1 H), 7.56 (ddd, J₁ = 15.4 Hz, J₂ = 9.4 Hz, J₃ = 1.5 Hz, 3 H), 7.17 (t, J = 8.6 Hz, 2 H), 7.02 (t, J = 8.6 Hz, 1 H). ¹³C NMR (101 MHz, CDCl₃): δ = 164.69, 162.20, 155.13, 153.45, 141.78, 136.63, 131.33, 130.02, 121.41, 117.71, 117.29, 116.40. MS (ESI): m/z = 263 [M + H]⁺.
• 23 General Procedure for the Synthesis of Bisarylsulfenyl- benzo-2,1,3-thiadiazolesBenzene thiols (0.6 mmol), 4,7-dibromo-2,1,3-benzothiadiazole (0.3 mmol), a catalytic amount of Pd/RHA (0.025 mol%), K₂CO₃ (0.9 mmol), and DMF (2 mL) were added to a microwave reaction vessel armed with a magnetic stirrer bar. The reaction mixture was subjected to microwave irradiation (a CEM Discover MW reactor) (200W, 75 °C) for 20 min. The progress of the reaction was observed by TLC (eluent: EtOAc/hexane, 10:90). The reaction mixture was cooled to room temperature, and the crude residue was extracted with ethyl acetate (3 × 10 mL) and water. Then, all the organic layers were combined and dried over anhydrous Na₂SO₄.The remaining solvent was evaporated under reduced pressure. Further, the crude product was purified by column chromatography over silica gel to afford the corresponding product, and yields were obtained in 83–94% as shown in Scheme 3.4,7-Bis(phenylthio)benzo[c][1,2,5]thiadiazole (4a)Yield 77.6 mg (88%); yellow solid; mp 125–127 °C. ¹H NMR (400 MHz, CDCl₃): δ = 7.49–7.35 (m, 8 H), 7.30 (d, J = 7.3 Hz, 1 H), 7.22 (d, J = 7.2 Hz, 1 H), 6.94 (s, 2 H). ¹³C NMR (101 MHz, CDCl₃): δ = 152.97, 136.98, 134.40, 133.52, 132.23, 131.50, 129.62, 129.00, 128.66, 127.72, 127.48, 127.10. MS (ESI): m/z = 353 [M + H]⁺. 4,7-Bis(p-tolylthio)benzo[c][1,2,5]thiadiazole (4b)Yield 102.6 mg (90%); orange oil. ¹H NMR (400 MHz, CDCl₃): δ = 7.72 (s, 1 H), 7.58 (d, J = 7.8 Hz, 1 H), 7.50 (s, 1 H), 7.41 (d, J = 8.1 Hz, 2 H), 7.28 (s, 1 H), 7.19 (d, J = 8.0 Hz, 2 H), 6.82 (s, 1 H), 6.75 (d, J = 7.8 Hz, 1 H), 2.42 (s, 3 H), 2.36 (s, 3 H). ¹³C NMR (101 MHz, CDCl₃): δ = 152.92, 152.07, 139.12, 134.93, 134.13, 132.24, 130.73, 130.44, 129.35, 127.49, 126.84, 125.37, 113.88, 110.14, 21.20. MS (ESI): m/z = 381 [M + H]⁺. 4,7-Bis[(4-methoxyphenyl)thio]benzo[c][1,2,5]thiadiazole (4c)Yield 116 mg (94%); orange oil. ¹H NMR (400 MHz, CDCl₃): δ = 7.50 (d, J = 8.8 Hz, 4 H), 6.93 (d, J = 8.8 Hz, 4 H), 6.71 (s, 2 H), 3.83 (s, 6 H). ¹³C NMR (101 MHz, CDCl₃): δ = 160.58, 152.51, 137.45, 136.59, 129.92, 127.62, 125.83, 121.03, 115.78, 115.34, 114.61, 55.39. MS (ESI): m/z = 413 [M + H]⁺.4,7-Bis(o-tolylthio)benzo[c][1,2,5]thiadiazole (4d)Yield 94.6 mg (83%); yellow oil. ¹H NMR (400 MHz, CDCl₃): δ = 7.72 (s, 1 H), 7.58 (s, 1 H), 7.46 (d, J = 7.6 Hz, 1 H), 7.40 (d, J = 3.1 Hz, 1 H), 7.33–7.29 (m, 3 H), 7.20 (dd, J₁ = 5.1 Hz, J₂ = 2.9 Hz, 1 H), 6.61 (s, 1 H), 6.55 (d, J = 7.7 Hz, 1 H), 2.42 (s, 6 H). ¹³C NMR (101 MHz, CDCl₃): δ = 152.78, 141.92, 136.31, 135.38, 132.21, 130.98, 129.47, 127.11, 125.88, 124.44, 113.86, 109.92, 20.53. MS (ESI): m/z = 381 [M + H]⁺. Anal. Calcd for (C₂₀H₁₆N₂S₃): C, 63.13; H, 4.24; N, 7.36; S, 25.27. Found: C, 63.09; H, 4.17; N, 7.28; S, 25.18.4,7-Bis(naphthalen-2-ylthio)benzo[c][1,2,5]thiadiazole (4e)Yield 116.6 mg (86%); yellow solid; mp 105–107 °C. ¹H NMR (400 MHz, CDCl₃): δ = 8.04 (s, 2 H), 7.85–7.76 (m, 6 H), 7.54–7.48 (m, 6 H), 6.96 (s, 2 H). ¹³C NMR (101 MHz, CDCl₃): δ = 153.10, 133.86, 133.01, 130.07, 129.38, 129.05, 128.76, 127.98, 127.68, 126.95, 126.78. MS (ESI): m/z = 453 [M + H]⁺. Anal. Calcd for (C₂₆H₁₆N₂S₃): C, 69.00; H, 3.56; N, 6.19; S, 21.25. Found: C, 68.92; H, 3.46; N, 6.12; S, 21.14.4,4′-{Benzo[c][1,2,5]thiadiazole-4,7-diylbis(sulfanediyl)}dianiline (4f)Yield 100.8 mg (88%); yellow oil. ¹H NMR (400 MHz, CDCl₃): δ = 7.45 (dd, J₁ = 7.7 Hz, J₂ = 1.5 Hz, 1H), 7.25–7.21 (m, 1 H), 7.14 (ddd, J₁ = 7.2 Hz, J₂ = 3.9 Hz, J₃ = 1.5 Hz, 3 H), 6.71 (ddd, J₁ = 9.6 Hz, J₂ = 8.5, J₃ = 4.4 Hz, 3 H), 6.60–6.54 (m, 2 H), 4.34 (s, 4 H). ¹³C NMR (101 MHz, CDCl₃): δ = 162.47, 152.60, 149.09, 148.56, 136.71, 131.50, 126.71, 124.65, 118.12, 115.15, 111.52. MS (ESI): m/z = 383 [M + H]⁺. Anal. Calcd for (C₁₈H₁₄N₄S₃): C, 56.52; H, 3.69; N, 14.65; S, 25.14. Found: C, 56.46; H, 3.62; N, 14.60; S, 25.08.