The benzil–benzilic acid rearrangement in high-temperature water

Abstract

The rearrangement of benzil is base (and not acid) catalyzed under conventional conditions (water-dioxane mixture around 100 uC). We examined this reaction in high-temperature water (HTW) between 300-380 uC with the intent of studying a reaction that proceeds solely by base catalysis in this more environmentally benign medium. The rearrangement proceeds in neutral HTW without addition of base, but the yield of rearrangement products is nearly insensitive to pH at near-neutral conditions. Adding larger amounts of base, however, leads to much higher yields and 100% selectivity to rearrangement products. Likewise, adding larger amounts of acid leads to comparable yields, but less than 100% selectivity. The selectivity to rearrangement products generally increased with pH at near-neutral and basic conditions whereas the selectivity to benzil decomposition products (a competing thermal pathway) exhibited a maximum at nearneutral conditions. We conclude that the benzil rearrangement is catalyzed by acid, base, and water in HTW. The dominant mechanism shifts as the pH changes. This system shows that mechanisms that are unimportant at conventional reaction conditions can become dominant in HTW. It also demonstrates the ability to use pH to direct the selectivity of a reaction in HTW.

Redox Cascades and Making of a C–C Bond: 1,2-Benzodiazinyl Radicals and a Copper Complex of a Benzodiazine

“…Py Cn • has been established as a catalyst for the oxidative cleavage of benzil to benzoic acid in methanol in air. Oxidative cleavage of benzil to benzoic acid is not common, generally in the presence of base benzil undergoes rearrangement to benzilic acid . However, the reaction of benzil (2.0 mmol) with Py Cn • (0.07 mmol) in methanol in the presence of triethylamine (0.03 mmol) and air at RT for 48 h affords benzoic acid (3.44 mmol), corresponding to 86% conversion (see experimental section in SI).…”

“…The preliminary investigation establishes that Py Cn • acts as a catalyst for the oxidative cleavage of benzil to benzoic acid in methanol in the presence of air. Oxidative cleavage of benzil to benzoic acid is not common, generally in the presence of base benzil undergoes rearrangement to benzilic acid . Thus, modeling of a catalyst for this redox reaction is significant in metallo-organic chemistry, and in this regard, the activity of Py Cn • is worthy.…”

Copper-Catalyzed Aerobic Oxidative Cleavage of C–C Bonds in Epoxides Leading to Aryl Ketones

“…On the basis of these preliminary results and previous studies, , the catalytic cycle of this transformation was hypothesized as shown in Scheme . Ring opening of 2,3-diphenyloxirane 1a with aniline gives intermediate A .…”

Kinetic Analysis of a Solid Base-Catalyzed Reaction in Sub- and Supercritical Water Using Aldol Condensation with Mg(OH)2 as a Model

“…Among the most widely researched types of reactions are base-catalyzed reactions. Many types of reactions, such as aldol condensation, − the Cannizzaro reaction, Michael addition, benzylic acid rearrangement, and hydrolysis, − have been investigated. Recently, the control of base-catalyzed reactions in sub- and supercritical water using solid catalysts has attracted much attention.…”