室温下二氧化氮催化带有给电子取代基的苯和萘的氧化溴化

在室温下,以8.2%的二氧化氮为催化剂,反应管中残留的空气为氧化剂,分子溴为溴化试剂,研究了带有给电子取代基的苯和萘的氧化溴化.使用的低沸点非金属催化剂易于从产物中去除,很少玷污最终产品;但反应后有少量的苯环硝化副产物生成,这会造成催化剂二氧化氮的损耗.反应具有较高的原子经济性,大部分溴原子被转化到产物中.反应产物具有可控性:可通过改变溴源的用量,分别得到单溴化和二溴化产物.初步的机理分析结论为:反应可能经历分子溴和芳环的反应,生成溴代芳烃和溴化氢;然后在氧化氮类物种催化下,生成的溴化氢被氧气氧化为具有反应活性的溴.

Nitrogen Dioxide-Catalyzed Oxidative Bromination of Benzenes and Naphthalines with Electron-Donating Substituents at Room Temperature

Oxidative bromination of benzenes and naphthalines with electron-donating substituents was investigated by using 8.2 mol% nitrogen dioxide as the catalyst, the residual oxygen in the reaction tube as the oxidant, and molecular bromine as the brominating reagent at room temperature. The used heavy metal waste-free catalyst can be easily removed from the products and scarcely stains the final products. But a small amount of by-product from the nitration of the benzene ring was observed, which led to the consumption of nitrogen dioxide. The reaction is highly atom economic, and a majority of bromine atoms in bromine source were transferred to the bromination products. The bromination is controllable: mono- and di-bromination products were controllably obtained by changing the loading amount of the brominating reagent. Preliminary mechanistic investigation suggests that the bromination firstly undergoes the reaction between molecular bromine and aromatic ring to give aryl bromide and HBr, which is followed by oxygenation of the resulting bromine hydride to form the reactive bromine under the catalysis of the catalytic species.