Silica-Alumina Catalyst Support, an Efficient Catalyst for Synthesis of Halogen Substituted 2,6-Bis(imino)pyridines

Abstract

Silica-alumina catalyst support was found to be an efficient catalyst for the condensation reaction of 2,6-, 2,5-, and 2,4-difluoroaniline and ortho-halogen-aniline with 2,6-diacetylpyridine to afford corresponding 2,6-bis(imino)pyridines in 56-75% isolated yields under extremely mild reaction conditions. The catalyst can be recovered and reused

Key words

silica-alumina catalyst support - halogen substituted 2,6-bis(imino)pyridine - condensation reaction

References

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• 21a

  Zeolite H-Beta Si/Al = 19.98, specific surface area 554.4 m²/g, average pore size 6.6-6.7, 5.6-5.6 Å.

• 21b

  Zeolite H-Y Si/Al = 3.35, specific surface area 739.3 m²/g, average pore size 7.4 Å, cage diameter 12 Å.

• 21c

  Si-Al(II) Si/Al = 1.0, specific surface area 240.4 m²/g.

7

We applied a China patent (CN1322717A) in January 2001. BASF Company promulgated a WO Patent (01/07491) in February, 2001, in which two halogen substituted 2,6-bis(imino)pyridyl iron complexes, 2,6-bis-diacetyl-pyridinebis(2,6-dibrom-4-methylanil)FeCl₂ and 2,6-bis-diacetyl pyridinebis(2,6-dichloroanil)FeCl₂, appeared, but there was no characterization of the complexes.

15

The condensation reaction of 2,6-dibromoaniline with 2,6-diacetylpyridine catalyzed by p-TsOH in refluxing toluene, with removing water by azeotropic distillation gave corresponding 2,6-bis(imino)pyridine in 58% yield if purified by recrystallization, However, it gave 30% yield when purified by flash column. See ref. [6]

18

Silica-alumina catalyst support (Grade 135) was purchased from Aldrich. Si/Al = 5.62, its specific surface area is 421.3 m²/g, average pore size 61.0545 Å. In our study, silica-alumina catalyst support (Grade 135) combined with 4 Å MS is found to be excellent catalyst for the condensation reaction of arylaldehydes with anilines, which gave almost quantitative yield.

19

Typical Experimental Procedure: Under an argon atmosphere, a mixture of 2,6-difluoroaniline (0.77 g, 6.0 mmol), 2,6-diacetylpyridine (0.41 g, 2.5 mmol), silica-alumina catalyst support (0.2 g) and molecular sieves 4 Å (0.5 g) in 8 mL toluene was stirred at 30-40 °C for 24 h. The reaction mixture was filtered and the filtration was condensed in vacuo. Anhydrous MeOH (5 mL) was added to the residue. A yellow solid was collected by filtration to yield 1a in 65% yield. ¹H NMR (300 MHz, CDCl₃): d = 8.39 (d, 2 H, J = 8.0 Hz), 7.93 (t, 1 H, J = 7.9 Hz), 7.07 (m, 4 H,), 6.99 (t, 2 H, J = 7.6 Hz), 2.46 (s, 6 H). IR (KBr): n = 1636, 1576, 1465, 1369, 1277, 1237, 1215, 1126, 1032, 1002, 827, 789, 759 cm^-1. MS (EI): m/z 349 (M⁺). Anal. Calcd for C₂₁H₁₅F₄N₃: C, 72.19; H, 4.90; N, 12.03. Found: C, 71.88; H, 4.96; N, 11.96.