RuCl₃ anchored onto imine functionalized silica for the aerobic oxidation of benzylic alcohols under liquid phase catalysis

Figures & data

short-legendScheme 1. Synthesis of RuCl3 anchored onto imine functionalized silica [SiO2-RuCl3].

Figure 1.  TGA of SiO₂-RuCl₃.

Figure 2.  XRD diffraction patterns of SiO₂-RuCl₃.

Figure 3.  SEM image of SiO₂-RuCl₃.

Figure 4.  (a) TEM micrograph of SiO₂-RuCl₃. (b) TEM micrograph of SiO₂-RuCl₃ after 5th use.

short-legendScheme 2. Selective oxidation of benzylic alcohols to benzaldehydes in the presence of SiO2-RuCl3 by stirring in acetonitrile at 80 °C using molecular oxygen as an oxidant.

Table 1. Effect of different solvents and catalyst loading for SiO₂-RuCl₃ catalyzed oxidation of 4-chlorobenzylic alcohol at 80°C.

Effect of solvent^a			Effect of catalyst loading^b
Entry	Solvent	Yield (%)	Entry	Catalyst (mol% Ru)	TOF (h^−1)	Yield (%)
1	Acetonitrile	85	1	0.5	14	70
2	Toluene	60	2	1.5	5.2	78
3	Water	40	3	2.5	3.2	80
			4	3.5	2.43	85
^aReaction conditions: 4-Chlorobenzylic alcohol (0.143 g, 1 mmol), SiO2-RuCl3 (0.2 g, 3.5 mol% Ru), K2CO3 (2 mmol), solvent (5 mL), 80°C as the reaction temperature. The reaction was carried out in the presence of molecular oxygen for 10 h.
^bReaction conditions: 4-Chlorobenzylic alcohol (0.143 g, 1 mmol), K2CO3 (2 mmol), SiO2-RuCl3 (0.5–3.5 mol% Ru), acetonitrile (5 mL), 80 °C as the reaction temperature and the reaction was carried out using molecular oxygen as an oxidant for 10 h.

Figure 5.  Recyclability of SiO₂-RuCl₃. Reaction conditions: 4-chlorobenzylic alcohol (0.143 g, 1 mmol), SiO₂-RuCl₃ (0.2 g, 3.5 mol% Ru), K₂CO₃ (2 mmol), acetonitrile (5 mL) at 80 °C for 10 h.

Table 2. SiO₂-RuCl₃ catalyzed selective oxidation^a of benzylic alcohols to corresponding aldehydes by stirring in acetonitrile at 80°C using molecular oxygen as an oxidant.

Entry	Substrate	Time (h)	Yield (%)^b	Melting point (m.p.) or boiling point (b.p.)/literature m.p. or b.p. (°C)
1		10	85	Liquid/178 36
2^c		13	65	72–75/73–76 36
3		10	85	45–47/47 36
4		12	80	20–21/20–22 36
5		13	82	43–44/44 36
6		13	79	56–57/55–58 36
7		12	84	100–103/103 36
8^c		13	55	Liquid/162 36
9		12	83	Liquid/250 36
10^c		10	25	Liquid/74.8 36
^aReaction conditions: Alcohol (1 mmol), SiO2-RuCl3 (0.2 g, 3.5 mol% Ru), K2CO3 (2 mmol), acetonitrile (5 mL), 80 °C as the reaction temperature and molecular oxygen as an oxidant.
^bIsolated yield by column chromatography.
^cRest being the starting material.

Figure 6.  Proposed mechanism for the SiO₂-RuCl₃ catalyzed selective oxidation of benzylic alcohols to the corresponding aldehydes using molecular oxygen.

Aldrich Advancing Science Handbook of Fine Chemicals , 2007 .

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