Oxidative Self-coupling Research Articles

Exploring the Role of Titanate Perovskites in the Oxidation of Amines to Imines via Photocatalysis.

Considering that structural differences could affect the photocatalytic efficiency of titanate perovskites, cubic SrTiO3 (STO) and tetragonal CaTiO3 (CTO) were synthesised as models to elucidate the structure-activity relationship. STO and CTO materials were produced through hydrothermal approaches, adjusting parameters such as temperature and pressure to optimise material purity. Among the perovskite photocatalysts, two stand out for their exceptional photocatalytic capacity and crystalline purity: CaTiO3, prepared at 180 ºC for 36 h, and SrTiO3, synthesised at 200 ºC for 24 h. Notably, we explore the selective ability of these materials for the photocatalytic oxidative self-coupling of benzylamine (BZA) to produce N-benzylidenebenzylamine (BZI), with CaTiO3 emerging as the most efficient catalyst for this reaction. The CTO material prepared at 180 ºC for 36 h (CTO180T-36) achieved a peak BZI production of 0.5 mM, with a total conversion of BZA after 7 h of irradiation. This study also emphasises the crucial role of reaction conditions and perovskite morphologies in fine-tuning photocatalytic performance. These findings highlight opportunities for developing efficient and selective photocatalytic processes, holding the compromise for applications in organic synthesis and sustainable green chemistry.

Synthesis of fluorescein-containing polymeric heterogeneous photocatalyst and its applications

A novel fluorescein-containing polymeric photosensitizer (FS-PHEMA) was successfully synthesized and used as an excellent heterogeneous photocatalyst for aerobic photooxidation of thioethers, hydroxylation of aryl boric acids, and oxidative self-coupling of amines. All the reactions could run smoothly upon irradiation of blue LED under aerobic conditions at room temperature. This heterogeneous photosensitizer can be easily separated, recovered, and reused at least 5 times without significant loss of catalytic activity, showing a good potential in practical applications.

Novel chromatic reaction based on the redox reaction between tertiary aromatic amines and gold(Ⅲ) or cerium(Ⅳ)

Abstract Herein, a novel chromatic reaction based on the oxidative self-coupling of tertiary aromatic amines and driven by a redox reaction with gold(III) or cerium(IV) is developed. The dimers resulting from the oxidation of tertiary aromatic amines with gold(III) or cerium(IV) show colors depending on their chemical structures. Substituting a hydrogen atom on the aromatic ring with a methyl or methoxy group induces a bathochromic shift in the color developed via oxidation. This redox reaction is highly selective for gold(III) and cerium(IV) because of their high redox potentials and complexation abilities with tertiary aromatic amines, thus suggesting the development of a selective analytical method for gold(III) and cerium(IV). Cyclic voltammograms and ultraviolet–visible light absorption spectra confirm that the oxidative coupling of tertiary aromatic amines develops color. The addition of reductants, such as l-ascorbic acid, degrades the color of the resultant colored species, thus indicating that the quinoid structure of the colored species caused color development. Thus, the developed redox reaction of tertiary aromatic amines with gold(III) or cerium(IV) provides a new chromogenic platform for determining gold(III), cerium(IV), and ascorbic acid.

Direct access to pyrrole anhydrides via oxidative self-coupling of pyrrole carboxaldehydes.

An elegant synthesis of pyrrole-2-carboxylic acid anhydrides from pyrrole-2-carboxaldehydes using TBAI as a catalyst and tert-butyl hydroperoxide (TBHP) as an oxidant is described herein. Unlike the previous reports wherein pyrrole-2-carboxylic acids were invariably used, we report here for first time the oxidative self-coupling of N-benzyl pyrrole-2-carboxaldehydes for the synthesis of 1-benzyl-1H-pyrrole-2-carboxylic anhydrides. In addition, a one-pot synthesis of novel pyrrole-2-carboxamides from pyrrole-2-carboxaldehydes is also reported. The mechanistic investigation supports a previously unexplored oxidative self-coupling of a pyrrole acyl radical, leading to the synthesis of a carboxylic anhydride.

Cobalt-nanoparticle catalysts derived from zeolitic imidazolate framework@MXene composites for efficient oxidative self-coupling of benzylamines

Cobalt-nanoparticle catalysts derived from zeolitic imidazolate framework@MXene composites for efficient oxidative self-coupling of benzylamines

Efficient synthesis of imines using carbon nitride as photocatalyst

Heterogeneous photocatalytic systems can provide green organic synthesis at cost-effective processes. In the present work, an efficient, environment-friendly and sustainable heterogeneous photocatalyst, the metal-free exfoliated carbon nitride (GCN-T), is used in the oxidative self-coupling of benzylamine (BZA) to produce N-benzylidenebenzylamine (BZI) within the visible light range of irradiation (LEDs with λmax = 417 nm) under mild reaction conditions. The issue of selectivity is successively addressed with complete conversion of BZA achieved upon 45 min of reaction, under irradiation, for 97 % selectivity towards BZI production. Electron paramagnetic resonance (EPR) spectroscopy is used to investigate the main reactive species involved in the photocatalytic reaction. This analysis revealed that superoxide and singlet oxygen radicals played the leading role in the amine conversion in the heterogeneous photocatalytic mechanism. A reaction pathway is proposed to include all identified species generated during the oxidative self-coupling of BZA under visible light irradiation. The results described here add to the portfolio of customisable heterogeneous photocatalytic solutions towards efficient solar synthesis.

Ultrathin Niobate Nanosheet Assembly with Au NPs and CdS QDs as a Highly Efficient Photocatalyst.

Niobate nanosheets have aroused widespread interest in recent years for their prospects in catalysis. The exploration of 2D niobate catalysis with stable and efficient properties is still the focus in chemistry and materials science. Herein, the successful fabrication of 2D CdS/Au/HNb3 O8 catalyst is demonstrated which revealed efficient photocatalytic properties in H2 evolution, oxidative self-coupling of amines to imines, and degradation of dyes. Especially the assembled architecture can give a rate of 5.85 mmol ⋅ g-1 ⋅ h-1 of photocatalytic H2 evolution, an ∼254-fold enhancement, compared with bare HNb3 O8 nanosheets under identical conditions. In accordance with density functional theory (DFT) and X-ray adsorption fine structure (XAFS) analyses, the vast improvements are benefited from efficient migration and separation of charge carriers. Besides, the surface plasma resonance (SPR) effect of Au NPs enhances the light harvesting capacity and boosts the generation of hot electrons, efficiently improving the visible-light absorption.

Metal-free and green synthesis of a series of new bis(2-alkylsulfanyl-[1,3,4]thiadiazolyl)-5,5′-disulfides and 2,2′-Dibenzothiazyl disulfide via oxidative self-coupling using hydrogen peroxide

Many disulfide and 1,3,4-thiadiazole-1,2-dithiol compounds have been extensively investigated in the pharmaceutical industry due to their unique biological properties. A series of new bis(2-alkylsulfanyl-[1,3,4]thiadiazolyl)-5,5′-disulfide derivatives containing two 1,3,4-thiadiazole rings linked by SS bond spacer were synthesized via the oxidative self-coupling of 5-alkylsulfanyl-[1,3,4]thiadiazole-2-thiol using hydrogen peroxide and ethanol as green oxidant and solvent, respectively. The excellent yields of 93–97% with 100% conversion were achieved with a simple one-pot synthesis. There is no over-oxidation of 5-alkylsulfanyl-[1,3,4]thiadiazole-2-thiol and 2-mercaptobenzothiadiazole that leads to the formation of by-products such as thiosulfinate, thiosulfonate, and sulfonic acid. In this process, a straightforward, short reaction time, metal-free, reusable solvent, and mild reaction conditions are applied to produce bis(2-alkylsulfanyl-[1,3,4]thiadiazolyl)-5,5′-disulfides and 2,2′-dibenzothiazyl disulfide. Therefore, the oxidative self-coupling is potential for other disulfide compounds.

Metal-free and Green Synthesis of a Series of New bis(2-alkylsulfanyl-[1,3,4]thiadiazolyl)-5,5'-disulfides and 2,2’-dibenzothiadiazole disulfide ‎via Oxidative Self-Coupling Using Hydrogen Peroxide

Many disulfide and 1,3,4-thiadiazole-1,2-dithiol compounds have been extensively investigated in pharmaceutical industry due to their unique biological properties. A series of new bis(2-alkylsulfanyl-[1,3,4]thiadiazolyl)-5,5’-disulfide derivatives containing two 1,3,4-thiadiazole rings linked by S-S bond spacer were synthesized via the oxidative self-coupling of 5-alkylsulfanyl-[1,3,4]thiadiazole-2-thiol using hydrogen peroxide and ethanol as green oxidant and solvent, respectively. The excellent yields of 93-97% with 100% conversion was achieved with simple one-pot synthesis. There is no over-oxidation of 5-alkylsulfanyl-[1,3,4]thiadiazole-2-thiol and 2-mercaptobenzothiadiazole that lead to formation of by-product such as thiosulfinate, thiosulfonate, and sulfonic acid. In this process, a straightforward, short reaction time, metal-free, reusable solvent and mild reaction conditions are applied to produce bis(2-alkylsulfanyl-[1,3,4]thiadiazolyl)-5,5'-disulfides‎ and 2,2’-dibenzothiadiazole disulfide. This suggested that oxidative self-coupling is potential for other disulfide compounds.

Exerting charge transfer to stabilize Au nanoclusters for enhanced photocatalytic performance toward selective oxidation of amines

Atomically precise gold nanoclusters have received increasing attention in photocatalysis but suffered from self-oxidation coalescence induced by photo-generated holes. Herein, we report an efficient charge engineering strategy to improve the photo-oxidation activity and stability of Au25(PPh3)10(SC3H6Si(OC2H5)3)5Cl2 nanocluster (AuNC) taking advantage of Z-scheme AuNC/ultrathin BiOCl nanosheets (2D-BiOCl) heterojunction for visible light oxidative self-coupling of amines. The turnover frequency (TOF) over AuNC/2D-BiOCl for benzylamine can reach 1916 h―1, much higher than that of most previously reported gold catalysts with a TOF usually less than 500 h―1. Moreover, the heterojunction can be stabilized for six cycles with the intact structure of AuNC remained. The enhanced photocatalytic activity of AuNC/2D-BiOCl was predominantly attributed to the formation of Z-scheme heterojunction, which effectively accelerated the transfer and separation of photo-generated carriers. Especially, the consumption of holes in AuNC by injected electrons from 2D-BiOCl can inhibit the self-oxidation of AuNC, thus improve its stability. This study provides some insights into the design of metal nanocluster catalysts with Z-scheme charge transfer for the application of photocatalysis.

Interfacial engineering by creating Cu-based ternary heterostructures on C3N4 tubes towards enhanced photocatalytic oxidative coupling of benzylamines.

Benzylamine coupling is a very important reaction for the synthesis of imine but still faces many challenges. Herein, we present a highly effective strategy towards the coupling reaction by using environmentally friendly catalysts. These catalysts are composed of Cu/Cu2O/Cu3N heterostructures supported by C3N4 tubes and the composites were synthesized by one-step hydrothermal treatment followed by calcination. Cu2O, Cu3N, and C3N4 all are responsive to visible light and the heterojunction formed can greatly enhance the charge separation. When used as photocatalysts for oxidative self-coupling of benzylamine at a low temperature of 323 K in air, Cu/Cu2O/Cu3N/C3N4 was able to give conversion and selectivity values of up to 99% and 98%, respectively. The high efficiency of the catalysts is attributable to their ability to generate large quantities of free radicals (such as ·OH and ·O2−) under visible-light irradiation.

Highly selective oxidation of amines to imines by Mn2O3 catalyst under eco-friendly conditions

Enhancing the selectivity of imines for the oxidative self-coupling of primary amines was found to be challenging in the heterogeneous catalysis. Three different manganese oxides (M-3, M-4, M-5) were synthesized by controlling the calcination temperature using a simple template-free oxalate route. The prepared manganese oxides were systematically characterized using XRD, N2 sorption, SEM, TEM, XPS, H2-TPR techniques. M-4 gave 96.2% selectivity of imine at 100% conversion of benzylamine, which was far more superior than other existing protocols. Mn3+/Mn4+ ratio was found to affect the selectivity of the imines. The probable reaction pathway for amines oxidation catalyzed by manganese oxides was proposed for the first time.

Suspending Ion Electrocatalysts in Charged Metal-Organic Frameworks to Improve the Conductivity and Selectivity in Electroorganic Synthesis.

Electroorganic synthesis is an environmentally friendly alternative to traditional synthetic methods; however, the application of this strategy is heavily hindered by low product selectivity. Metal-organic frameworks (MOFs) exhibit high selectivity in numerous catalytic reactions; however, poor conductivity heavily limits the application of MOFs in electroorganic synthesis. To realize the electrocatalytic application of MOFs in selective electroorganic synthesis, a practically applicable strategy by suspending ion electrocatalysts in charged MOFs is herein reported. This approach could markedly improve the product selectivity in electroorganic synthesis. In the electrocatalytic oxidative self-coupling of benzylamine experiments, the imine product selectivity is markedly improved from 61.3 to 94.9 %, when the MOF-based electrocatalyst is used instead of the corresponding homogeneous electrocatalyst under the identical conditions. Therefore, this work opens a new route to improve the product selectivity in electroorganic synthesis.

Copper-Catalyzed Oxidative Self-Coupling of α-Amino Carbonyl Compounds for the Synthesis of Tetrasubstituted 1,4-Enediones

A protocol for the copper-catalyzed oxidative self-coupling of α-amino carbonyl compounds has been developed for the synthesis of tetrasubstituted 1,4-enediones (Z-isomers) in moderate to good yields through the cleavage of four sp3C–H bonds and the simultaneous formation of one C=C double bond in the α-amino carbonyl compound. The strategy has the advantages of using readily available starting ­materials and of high stereoselectivity.

Selective aerobic oxidation of halides and amines with an inorganic-ligand supported zinc catalyst.

A practical, efficient and environmentally benign catalytic protocol for the oxidative cross-coupling reaction of halides with amines, oxidative self-coupling of amines and oxidation of halides was developed with inorganic-ligand supported ZnPOM (NH4)4[ZnMo6O18(OH)6] using molecular oxygen. This method mainly utilizes an inorganic polymolybdate ligand to support the Zn2+ ion, avoiding the use of complicated organic ligands.

TBAI-catalyzed oxidative self-coupling of benzyl bromides under solvent-free conditions: A new pathway toward synthesis of benzyl benzoates

A new pathway was developed for the synthesis of benzyl benzoates via TBAI-mediated oxidative self-coupling of benzyl bromides in the presence of tert-butyl hydroperoxide (TBHP) as an oxidant under solvent-free conditions. Various derivatives of precursors including electron donating and withdrawing groups as well as heteroaromatic and polycyclic benzyl bromides were subjected to the reaction conditions and converted to the corresponding benzylic esters in good to high yields. Mechanistic studies showed that this reaction did not take place via the radical pathway and tert-butyl peresters and benzoic acids are two key intermediates in this transformation.

Metal-free oxidative self-coupling of aldehydes or alcohols to symmetric carboxylic anhydrides

Abstract A metal-free synthesis of symmetrical anhydrides has been developed starting from aldehydes, both aliphatic and aromatic or primary benzylic alcohols. The reaction occurs at room temperature and makes use of trichloroisocyanuric acid (TCCA) as an oxidant providing the desired carboxylic anhydrides in satisfactory yields.

Oxidative self-coupling of aldehydes in the presence of CuCl2/TBHP system: direct access to symmetrical anhydrides

A simple synthesis of symmetrical anhydrides has been developed. Using tert-butylhydroperoxide (TBHP) as the oxidant and copper(II) chloride as the catalyst in acetonitrile, various aromatic and heteroaromatic aldehydes were reacted to provide symmetrical anhydrides in modest to good yields.

Efficient oxidative self-coupling of polystyrene bearing chain-end primary amines

A series of well-defined linear polystyrenes (PSs) with different degree of polymerization (DP) was synthesized via atom transfer radical polymerization (ATRP) using tert-butyloxycarbonyl (t-boc)-protected 4-(aminomethyl)phenyl 2-bromoisobutyrate (BAPB) as an initiator. The resulting polymers were deprotected by cleavage of the t-boc protecting groups via treatment with trifluoroacetic acid (TFA) to generate the chain-end primary amine functionality. The chain-end primary amine groups of the polymers were self-coupled in the presence of 2,2′-azobisisobutyronitrile (AIBN) under an oxygen atmosphere via imine bond formation. The coupling efficiency decreased slightly as the chain length of the PS increased. The imine linkages of the coupled PSs were hydrolyzed in the presence of HCl to individual PS chains.

ChemInform Abstract: tert‐Butyl Hydroperoxide (TBHP)‐Mediated Oxidative Self‐Coupling of Amines to Imines over a α‐MnO2 Catalyst.

ChemInformVolume 45, Issue 36 Isocyclic Compounds ChemInform Abstract: tert-Butyl Hydroperoxide (TBHP)-Mediated Oxidative Self-Coupling of Amines to Imines over a α-MnO2 Catalyst. Zhe Zhang, Zhe Zhang State Key Lab. Catal., Dalian Inst. Chem. Phys., Dalian 116023, Peop. Rep. ChinaSearch for more papers by this authorFeng Wang, Feng Wang State Key Lab. Catal., Dalian Inst. Chem. Phys., Dalian 116023, Peop. Rep. ChinaSearch for more papers by this authorMin Wang, Min Wang State Key Lab. Catal., Dalian Inst. Chem. Phys., Dalian 116023, Peop. Rep. ChinaSearch for more papers by this authorShutao Xu, Shutao Xu State Key Lab. Catal., Dalian Inst. Chem. Phys., Dalian 116023, Peop. Rep. ChinaSearch for more papers by this authorHaijun Chen, Haijun Chen State Key Lab. Catal., Dalian Inst. Chem. Phys., Dalian 116023, Peop. Rep. ChinaSearch for more papers by this authorChaofeng Zhang, Chaofeng Zhang State Key Lab. Catal., Dalian Inst. Chem. Phys., Dalian 116023, Peop. Rep. ChinaSearch for more papers by this authorJie Xu, Jie Xu State Key Lab. Catal., Dalian Inst. Chem. Phys., Dalian 116023, Peop. Rep. ChinaSearch for more papers by this author Zhe Zhang, Zhe Zhang State Key Lab. Catal., Dalian Inst. Chem. Phys., Dalian 116023, Peop. Rep. ChinaSearch for more papers by this authorFeng Wang, Feng Wang State Key Lab. Catal., Dalian Inst. Chem. Phys., Dalian 116023, Peop. Rep. ChinaSearch for more papers by this authorMin Wang, Min Wang State Key Lab. Catal., Dalian Inst. Chem. Phys., Dalian 116023, Peop. Rep. ChinaSearch for more papers by this authorShutao Xu, Shutao Xu State Key Lab. Catal., Dalian Inst. Chem. Phys., Dalian 116023, Peop. Rep. ChinaSearch for more papers by this authorHaijun Chen, Haijun Chen State Key Lab. Catal., Dalian Inst. Chem. Phys., Dalian 116023, Peop. Rep. ChinaSearch for more papers by this authorChaofeng Zhang, Chaofeng Zhang State Key Lab. Catal., Dalian Inst. Chem. Phys., Dalian 116023, Peop. Rep. ChinaSearch for more papers by this authorJie Xu, Jie Xu State Key Lab. Catal., Dalian Inst. Chem. Phys., Dalian 116023, Peop. Rep. ChinaSearch for more papers by this author First published: 21 August 2014 https://doi.org/10.1002/chin.201436085Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume45, Issue36September 9, 2014 RelatedInformation