Abstract:In the 20 types of heterogeneous and homogenous catalysts screened, Nb2O5 shows the highest activity for synthesis of N-phenylsuccinimide by dehydrative condensation of succinic anhydride and aniline. Nb2O5 is applicable to the direct imidation a wide range of carboxylic anhydrides with NH3 or amines with various functional groups and is reusable. Kinetic studies show that Lewis acid catalysis of Nb2O5 is more water-tolerant than a Lewis acidic oxide (TiO2) and a homogeneous Lewis acid (ZrCl4), which results in higher yield of imides by Nb2O5.Cyclic imides and their derivatives are an important class of substrates for biological and chemical applications [1,2] and used as intermediates in the industrial production of drugs, dyes and polymers. [1a,1b,2] However, sustainable synthetic methods of cyclic imides from readily available starting materials are limited. General methods for synthesis of cyclic imides are the dehydrative condensation of a dicarboxylic acid [3] or its anhydride [3f,4,5] with an amine under harsh conditions (250-380 °C, ~330 bar) [3a,b] or under microwave heating, [5] and the cyclization of an amic acid with the help of acidic reagents or in the presence of excess amount of promoter (Lewis acid, base, dehydrating agent). These methods suffer from some of the drawbacks of low atom-efficiency, limited substrate scope, production of stoichiometric amount of byproducts, and need of special procedure (microwave heating). New synthetic routs from nitriles, [7] halides, [8] alkynes, [9] aryl boronic acids, [10] aromatic amides, [11] aliphatic amides, [12] cyclic amines [13] have been developed, but these homogeneous catalytic methods have drawbacks of low atom-efficiency, narrow substrate scope, needs of toxic reagents or additives, and difficulties in catalyst/products separation and catalyst reuse. For example, a reusable heterogeneous catalytic system by Pd/C[8d] suffers from needs of halides and CO as less environmentally benign reagents. One of the most effective synthesis of cyclic imides via dehydrogenative coupling of diols and amines (or nitriles) catalyzed by a Ru complex [1a,14] still suffers from limited substrate scope of diols and amines. Catalytic synthesis of cyclic imides by condensation of cyclic anhydrides with amines is one of the most deriable route. A few catalytic methods using TaCl5/SiO2 [15a,15b] or DABCO [15c] were reported to synthesize cyclic imides from cyclic anhydrides with amines. These methods [15] suffer from some of the drawbacks such as quite limited substrate scope, no results on the catalyst reuse, and needs of large catalyst loading and special method (microwave heating). [15a,15b] Potentially, the reaction is catalyzed by Lewis acid, but co-presence of water as byproduct can suppress Lewis acidity by hindering coordination. Inspired by recent reports that several metal oxides, such as Nb2O5, [16a] act as water-tolerant Lewis acid catalysts, [16] we have recently reported that Nb2O5 acts as water-tolerant Lewis acid catalyst for direct imida...

Pt metal nanoparticles loaded on various supports and carbon-supported various metal catalysts are tested for dehydrogenation of 6-methyl-1,2,3,4-tetrahydroquinoline to 6-methyl-quinoline under oxidant-free conditions. In the 20 types of the catalysts screened, carbon-supported Pt catalyst (Pt/C) shows the highest activity. Pt/C is reusable after the reaction and is effective for dehydrogenation of various N-heterocycles (tetrahydroquinolines and indoline). Pt/C is also effective for hydrogenation of quinoline under 3 bar H 2 . The results demonstrate that this catalytic method may be useful for an organic hidride-based hydrogen storage system.

Niobic acid catalyzes the condensation of biomass-derived dicarboxylic acids into cyclic anhydrides, key intermediates of carbon-neutral and biodegradable polyesters.

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