Benzilic acid rearrangement solid state

Toda, F., Tanaka, K., Kagawa, Y., Sakaino, Y. Benzilic acid rearrangement in the solid state. Chem. Lett. 1990, 373-376. 

Benzilic acid rearrangement is usually carried out by heating benzil derivatives and an alkali metal hydroxide in aqueous organic solvent. This reaction also proceeds efficiently in the solid state. For example, a mixture of finely powdered benzil (35a) (0.5 g, 2.38 mmol) and KOH (0.26 g, 4.76 mmol) was heated at 80 °C for 0.2 h, and the reaction mixture was mixed with 3N HCl (20 ml) to give benzilic acid (39a) as colorless needles (0.49 g, 90% yield) [13]. Since the product is collected simply by filtration, this method is very simple and economical. Similar treatment of benzil derivatives (35b-g) in the solid state also gave the corresponding benzilic acid (39b-g) in good yields (Table 15-8) [13],... 

By ESR studies, the benzilic acid rearrangement in solution has been proven to proceed via a radical intermediate [14], For the benzilic acid reanangement in the solid state, a radical intermediate was also detected. For example, a freshly prepared mixture of finely powdered 35e and KOH showed a strong ESR signal (g=2.0049), and this signal declined as the reaction proceeded. 

Microwave-assisted heterogeneous benzilic acid rearrangement in solid state has been reported by Yu et al The reported method provides a new route to the synthesis of interesting anticonvulsant dilantin. Powdered KOH and benzil were ground together along with two drops of water and... 

A range of reactions has been described. In Baeyer-Villiger oxidation of ketones with m-chloroperbenzoic acid the reaction proceeds significantly faster in the solid state than in solution. For example, when a mixture of a powdered ketone and two equivalents of the perbenzoic acid are reacted at room temperature, significantly improved yields were obtained with the solid state mixture than from solution. Values are given in Table 6.2. Similarly, the benzilic acid rearrangement proceeded faster as a solid state reaction than in solution. A typical procedure involved heating at 80°C... 

A new procedure for carrying out the benzil-benzilic acid rearrangement in the solid state has been developed by Yu et al. (1999). 

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