Author Topic: oxidation of hydroquinone  (Read 1488 times)

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demorol

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oxidation of hydroquinone
« on: December 29, 2002, 01:46:00 PM »
Rhodium, I think this might be something for your page.

Oxidation of Hydroquinones, Catechols, and Phenols using Ceric Ammonium Nitrate and Ammonium Dichromate Coated on Silica: An Efficient and Convenient Preparation of Quinones

Oxidation of Hydroquinone by the Cerium(IV)/SiO2 Reagent; Typical Procedure

Hydroquinone (0.11g, 1 mmol) in dichloromethane (15mL) is added with stirring to cerium(IV)/SiO2 reagent [6.94g, 2.1 mmol of cerium(IV)]. The mixture was stirred for 5 minutes and filtered. The residue is washed with dichloromethane (2 × 15mL). Evaporation of solvent from the combined filtrates gives product (0.106g) as a bright yellow crystalline solid which is found to be pure p-benzoquinone by 1H-N.M.R. (authentic sample from Aldrich). It is furthes purified by recrystallization from ether; mp 116° C.

Repetition of the oxidation on a 5 mmol scale yields 0.525g of p-benzoquinone.

Oxidation of Hydroquinone by the Chromium(VI)/SiO2 Reagent

Hydroquinone (0.11g, 1 mmol) in dichloromethane (10mL) is added with stirring to the chromium(VI)/SiO2 reagent [2.07g, 2.4 mmol of chromium(VI)]. The mixture is stirred for 5 minutes and filtered. The residue is washed with dichloromethane (2 × 15mL). Evaporation of solvent from the combined filtrates gave pure p-benzoquinone (0.104g). A 5 minute reaction with 5 mmol of hydroquinone yields 0.52g of pure p-benzoquinone.



Cerium(IV)/SiO2 and Chromium(VI)/SiO2 Reagents

To an efficiently stirred solution of ceric ammonium nitrate (20g) in MeOH (200mL), dichloromethane (200mL) followed by silica (200g, Baker Analyzed, 40-140 mesh) is added. The mixture is stirred for additional 15 minutes and the solvents are evaporated on a rotavapor. The resulting solid is dried for 3 h at 55° C on rotavapor, when free-flowing yellow powder is obtained. At this stage the yellow powder of cerium(IV)/SiO2 reagent weights 221.2g, suggesting that 1.2g of the solvent is retained. It is used as such for the oxidations. For this reagent 6.06g contain 1 mmol of cerium(IV).

A similar procedure using ceric ammonium nitrate (40g), silica (200g), MeOH (300mL) and dichloromethane (200mL) gives the 20% cerium(IV)/SiO2; yield: 242g [3.32g of the reagent contain 1 mmol of cerium(IV)].

Ammonium dichromate (40g) is dissolved in warm (50° C) 50:1 MeOH/H2O (600mL MeOH and 12mL H2O) and to this silica (200g) is added with stirring. After 10 minutes, the solvent is evaporated and the residue is dried for 10 h at 55° C on rotavapor. The 20% chromium(VI)/SiO2 reagent is obtained as a free-flowing orange powder; yield: 250.4g [0.79g of the reagent contain 1 mmol of chromium(VI)].

Reference: Synthesis, 1985, No. 6/7, pp 641



carboxyl

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Quick
« Reply #1 on: December 29, 2002, 02:28:00 PM »
This process certainly has the advantage of time, only 5 minutes :) !