Tandem Process Research Articles

Treatment of emerging contaminants in simulated wastewater via tandem photo-Fenton-like reaction and nutrient recovery

Nutrient rich wastewater containing emerging organic contaminants was used for struvite synthesis with a novel tandem process with a heterogeneous Fenton oxidation pretreatment.

A novel synthesis of dihydrofuranyl alcohols through cascade reactions of 1,3-diketones with α,β-unsaturated epoxides

A novel synthesis of highly functionalized dihydrofuranyl alcohols has been developed through a tandem process. These reactions proceeded smoothly in the presence of a PTC, affording a variety of dihydrofuranyl alcohols in good yields of up to 97.1%.

Diastereoselective construction of carbo-bridged polyheterocycles by a three-component tandem annulation reaction.

By a hydroamination-induced tandem annulation process, we herein report a new three-component reaction for room temperature construction of carbo-bridged polyheterocycles with exclusive diastereoselectivity, which features readily available feedstocks, catalyst-free conditions, good substrate and functionality compatibility, no need for transition metal catalysts, and high step and atom efficiency. The products are formed via initial formation of 1,2-dihydro-3H-pyrazol-3-one nucleophiles from but-2-ynedioates and hydrazine followed by 2,4-difunctionalization of N-heteroarenium salts. Given that the obtained products possess structurally important tetrahydroquinoline and pyranopyrazole motifs, the developed chemistry is anticipated to be further applied to the discovery of functional molecules including biomedical ones.

Stereoselective synthesis of 1,6-diazecanes by a tandem aza-Prins type dimerization and cyclization process.

We report the stereocontrolled synthesis of 1,6-diazecanes via a tandem aza-Prins type reaction of N-acyliminium ions with allylsilanes. It involves an aza-Prins type dimerization and cyclization in a single-step operation. This reaction represents the first example of 10-membered N-heterocycle synthesis using an aza-Prins reaction. Also, the interesting formation of an unusual tetracyclic compound through further cyclization of 1,6-diazecane and bicyclic compounds by the intramolecular cyclization of linear allylsilane are described. This tandem aza-Prins protocol provides a new synthetic strategy for the direct synthesis of medium-sized nitrogen heterocycles.

Utilizing ferrocene for doping iron into graphitic carbon nitride (FeIII/g-C3N4): an internal dual photocatalyst for tandem oxidation/cyclization of toluene to benzimidazoles under visible light conditions.

Recently, doping metals into graphitic carbon nitride (g-C3N4) is considered for environmental applications and organic reactions. In this study, we used ferrocene as a source of Fe3+ to dope iron onto g-C3N4. The scaffold of the internal electric field is presented as an impressive strategy to increase photocatalytic activities. Fe3+ was doped onto graphitic carbon nitride (FeIII/g-C3N4) by the calcination method, which was well characterized by FT-IR, Raman, XRF, XRD, XPS, UV-visible DRS, photo-luminescence (PL), photocurrent, SEM, HR-TEM, EDX, BET, EIS, and cyclic voltammetry analyses. The synthesis of benzimidazole derivatives as pharmaceutically active compounds was introduced by using a suitable method under mild reaction conditions without using a base, oxidant, and other reagents or additives. The modification by using iron had a considerable effect on the optical and electronic characteristics in contrast to g-C3N4. The nanocomposite FeIII/g-C3N4 could be employed as a multifunctional photocatalyst to perform the tandem process, oxidation of toluene, and then cyclization with o-phenylenediamines to prepare benzimidazoles under visible light conditions. The existence of the dynamic equilibrium of Fe3+/Fe2+ helped in significantly improving the activity. By changing the reaction conditions and different control experiments as well as Mott-Schottky plot analysis, the superoxide ion (O2˙-) can be obtained as the reactive species in this reaction. The photocatalytic activity of FeIII/g-C3N4 for this one-pot reaction is also investigated in detail.

Photo-induced scandium-catalyzed biomimetic skeleton conversion of lathyrane to naturally rare eupholathone Euphorbia diterpenes.

The naturally scarce eupholathone-type euphornin E (1) was efficiently prepared from abundant lathyrane-type Euphorbia factor L1via a visible-light-induced Sc(OTf)3-catalyzed tandem process. Eupholathones 2 and 3 were also smoothly obtained by changing the reaction solvent. This route provides a convenient method for easily constructing scarce eupholathone- from lathyrane-type Euphorbia diterpenes, and confirms the biogenetic relationship between them from a chemical standpoint. Notably, compound 1 exhibited good anti-HIV activity.

N-Allylbenzimidazole as a strategic surrogate in Rh-catalyzed stereoselective trans-propenylation of aryl C(sp2)-H bond.

A Rh-catalyzed C(sp2)-H propenylation has been reported by taking N-allyl benzimidazole as an allylamine congener. This transformation has been observed for the first time, where a tandem process of C-H allylation followed by alkene isomerization delivers a highly stereoselective trans-propenylated product. Detailed mechanistic studies including the characterization of rhodacycle-intermediates have been conducted to understand the mechanism.

Hydroaminomethylation of Natural Allylic and Homoallylic Alcohols: A Ligand‐Controlled Route to New Amines

AbstractHydroaminomethylation (HAM) is a tandem catalytic process that allows accessing amines from olefin scaffolds and is perfectly aligned with green chemistry precepts. In this work, HAM was applied to the natural hydroxyolefins: isoprenol, linalool, nerolidol, and isopulegol. Employing 4‐methylpiperidine, morpholine, and 1,2,3,4‐tetrahydroisoquinoline as counterparts, several new, structurally complex amines were prepared from biorenewable, low‐cost substrates, opening a path to exploit this structure diversity in biological activity. By the appropriate choice of rhodium‐based catalytic systems, as well as the reaction conditions, the necessary fine tuning for each counterpart was achieved. The unpromoted rhodium system leaded mostly to aminoalcohols, while certain phosphorus(III)‐promoted rhodium systems afforded amines containing a tetrahydropyran or a tetrahydrofuran moiety in moderate to high yields.

Tandem chemocatalysis and biological funneling to valorize lignin

In 2014, Linger et al. presented a tandem process for lignin valorization by integrating chemical and biological catalysis. Chemical pretreatment of corn stover generated mixed lignocellulose-derived monomers that were converted to a single product, polyhydroxyalkanoates, by Pseudomonas putida. Tandem processes have since been developed for diverse feedstocks to support the bioeconomy.

A Copper‐Catalyzed [5+1] Cycloaddition of Terminal Alkynes with Diazo Esters through a Tandem 1,5‐H‐Shift Cyclization

Comprehensive SummaryA copper‐catalyzed [5+1] cycloaddition reaction of terminal alkynes with diazo esters for the rapid construction of protected naphthalen‐1(2H)‐one derivatives in moderate to good yields has been disclosed along with good functional group compatibility and a broad substrate scope. The mechanistic investigations reveal that this tandem cyclization process proceeds through a Cu(I)‐catalyzed coupling of terminal alkyne with diazoacetate, a 1,5‐H shift process and a thermally induced pericyclic reaction via an allene intermediate. The synthetic utility and the further transformations of the obtained cycloadduct to naphthalenone, naphthol and dihydronaphthol have been also presented in this paper.

Research on the effect of alignment form of strip welding on strip breaking in tandem cold rolling

The tandem cold rolling process is continuous production, and it is desired to achieve a stable operation process, the incoming materials need to be welded in the length direction before cold rolling. Usually the head and tail of the incoming material have a thickness dimension positive deviation, and there are two alignments in the thickness direction of the front and rear strip, so that different weld zone profiles can be formed. In this research, we built an FEA (finite element analysis) model of strip rolling with weld zone and relevant simulation conditions are designed to reveal the effect of alignment on the rolling process of the strip with weld zone. The risk of strip breaking between two alignment forms of the weld zone during the rolling process is further discussed and compared. It provides a reference for the setting of the alignment method of the laser welding machine in welding the strip in order to reduce the probability of weld zone breaking during the cold rolling process.

Strategies to reduce the extent of product dilution in a tandem simulated-moving-bed process for ternary separation without loss of throughput

One of highly-efficient separation processes for recovery of a target product in the pharmaceutical and fine chemical industries is a simulated-moving-bed (SMB) process. Although an SMB can ensure high separation capability and high throughput, it always has a problem of product dilution, which increases the energy consumption for post-processing of SMB product streams. This issue is even more important in a tandem SMB, which uses two subordinate SMB units in series for implementing a ternary-separation task. To address this issue, we sought to develop effective strategies for reducing the extent of product dilution in a tandem SMB without loss of throughput. For this task, a standing-wave-design (SWD) method was used to find a clue to reducing the extent of a tandem-SMB product dilution, which revealed the following results. First, for the considered issue, it could be effective to increase the column length of the SMB unit under the influence of column-efficiency limiting factor while decreasing the column length of the other SMB unit accordingly for the purpose of keeping total bed volume constant. It could also be effective to place more columns in the zones containing both edges of solute band for a target component. The two aforementioned strategies (called “S1” and “S2” respectively) were applied to the tandem SMB for recovery of neoagarotetraose from neoagarooligosaccharides. It was found that when the S1 method was utilized, the extent of product dilution in the tandem SMB was reduced by 56%. Furthermore, if the S1 and S2 methods would be used together, the extent of the tandem-SMB product dilution could be reduced by up to 85%. It is thus expected that the proposed strategies can contribute to a substantial improvement in the energy efficiency for post-processing of product stream from a tandem SMB process for ternary separation.

Tandem Copper(I)‐Catalyzed N‐Arylation–1,4‐Conjugate Addition to Access Tetrahydroacridinones

AbstractA copper‐catalyzed tandem process integrating N‐arylation and 1,4‐conjugate addition is disclosed through the reaction of cyclic enaminones and ortho‐halochalcones. The reaction appears to proceed through chemoselective arylation on the nitrogen of enaminone with ortho‐halochalcones and Michael addition of α‐carbon of the enaminone to the chalcone to furnish a diverse range of tricyclic tetrahydroacridinone derivatives in moderate to excellent yields.magnified image

Solvent Effects Enable Efficient Tandem Conversion of Cellulose and Its Monosaccharides Towards 5-Hydroxymethylfurfural.

The biomass-derived platform compound 5-hydroxymethylfurfural (HMF) has been hailed as the "Sleeping Giant" due to its promising applications, and it occupies a critical spot in the biomass upgrading roadmap. HMF is typically produced from cellulose and its monosaccharides via a complex tandem conversion with multiple steps (i. e., cellulose depolymerization, glucose isomerization, fructose dehydration, etc.). Previous investigations have confirmed the irreplaceable contribution of solvents in regulating the tandem conversion of cellulose and its monosaccharides to HMF. However, the potential effects of solvents in contributing to this multi-step tandem process have not yet been clearly elucidated. In this context, this Review aims to provide in-depth insights into the intrinsic interactions between solvent system and substrate conversion (cellulose and its monosaccharides conversion), reaction regulation (reaction activity and selectivity regulation), as well as product acquisition (humins formation inhibition and product purification). It attempts to elucidate specific solvent effects to promote a more efficient tandem conversion of cellulose and its monosaccharides towards HMF. The insights provided in this Review may contribute to a more sustainable HMF production from biomass feedstocks and a further development of greener solvent systems.

Solid Single-Atom Catalysts in Tandem Catalysis: Lookout, Opportunities and Challenges.

Tandem catalysis stands out as a major instrument towards the intensification of existing and future chemical processes. Initially formulated in the field of homogeneous catalysis, the concept relies on the single-pot integration of two (or more) catalysts showing high specificity for mechanistically decoupled reactions, while being operational and compatible under a single set of operation conditions. Isolated metal atoms stabilized on solid carriers in single-atom catalysts (SACs) hold the potential to reconcile the high reaction specificities of mononuclear sites in molecular catalysts with an intrinsic catalyst compartmentalization on inorganic matrices. Understandably, SACs have started to be considered as platforms in tandem catalysis. Tandem (electro)catalytic processes based on SACs have been showcased recently. While this sets excellent prospects for the expansion of this research subarea, challenges are faced, particularly as to the verification of the tandem nature of the processes.

Tunable Reaction Mode of Bifunctional Peroxides with Ketones to Access α-Oxacyclic Ketones and Enals.

A new annulation reaction between allylic/benzylic peroxides and ketones has been developed to provide the α-oxacyclic ketones in moderate yields under the KOtBu basic conditions. Mechanistic studies reveal that these peroxides undergo the Kornblum-DeLaMare rearrangement to release the aldehyde intermediates and subsequently initiate the aldol/etherification tandem process to deliver the final products. Accordingly, these peroxides serving as "masked" enals have also been utilized to prepare the previously hard-to-achieve α-enal-tethered ketones in one step.

Electrochemical Palladium-Catalyzed Oxidative Carbonylation-Cyclization of Enallenols.

Herein, we report an electrochemical oxidative palladium-catalyzed carbonylation-carbocyclization of enallenols to afford γ-lactones and spirolactones, which proceeds with excellent chemoselectivity. Interestingly, electrocatalysis was found to have an accelerating effect on the rate of the tandem process, leading to a more efficient reaction than that under chemical redox conditions.

Electrochemical Palladium‐Catalyzed Oxidative Carbonylation‐Cyclization of Enallenols

AbstractHerein, we report an electrochemical oxidative palladium‐catalyzed carbonylation‐carbocyclization of enallenols to afford γ‐lactones and spirolactones, which proceeds with excellent chemoselectivity. Interestingly, electrocatalysis was found to have an accelerating effect on the rate of the tandem process, leading to a more efficient reaction than that under chemical redox conditions.

Nitrogen-rich cobalt (II) MOFs as efficient bifunctional catalysts for single or tandem oxidation and CO2 conversion reactions

The development of efficient catalysts that include the advantages of homogeneous and heterogeneous catalysts is a challenge that can be achieved with metal-organic frameworks (MOFs) since they can incorporate different functionalities in their structure that make them promising catalysts for different processes. Herein, two new isoreticular nitrogen-rich naphthalene cobalt-MOFs, Co-NDTz and Co-NDPhTz, were successfully prepared under solvothermal conditions from the corresponding linkers (H2NDTz=2,6-naphthaleneditetrazole and H2NDPhTz=2,6-bis(4-(1H-tetrazol-5-yl)phenyl)naphthalene). These Co-tetrazole-based MOFs combine Lewis acid and redox functionalities and good CO2 adsorption and after being thermally activated resulted to be excellent efficient catalysts for the epoxidation of alkenes and CO2 cycloaddition to epoxides yielding cyclic carbonates, reaching turnover numbers up to 2500. Furthermore, these two reactions take place following a highly desired one-pot tandem process and a cyclic carbonate was obtained from styrene and CO2 under solvent-free conditions. In addition, the heterogeneous catalysts are easily recycled without noticeable loss of catalytic activity and without important structural deterioration.

Calcium looping of CO2 capture coupled to syngas production using Ni-CaO-based dual functional material

Calcium looping (CaL), which involves carbonation of CaO by CO2 and regeneration of CaO through the conversion of the captured CO2 into useful products, shows promise for carbon capture and utilization. By integrating CaL with methane dry reforming (DRM), the captured CO2 can be converted into syngas, a valuable chemical feedstock and fuel. Herein, a dual functional material (DFM) composed of CaO (CO2 adsorbent), Ni (DRM catalyst) and CeO2 (promoter for DRM) had been developed to drive the CaL-DRM tandem processes. The CaO-Ni-CeO2 DFM possessed high performance of cyclic CaL-DRM: high CO2 uptake efficiency (10.3 mmolCO2/gCaO), high H2 and CO yields (754.4 mmolH2/gNi and 454.6 mmolCO/gNi), moderate required temperature for carbonation (450 °C) and subsequent methane dry reforming (680 °C), and sufficiently high stability. The carbonation of CaO was strongly influenced by the basicity of the material, and the conversion of CH4 with the captured CO2 was affected by the Ni dispersion in the material. Overall, our work demonstrates a prototype study of using a temperature-programmed reaction platform for a quantitative, real-time analysis on CaL-DRM kinetics. The mechanistic understanding of CaL-DRM by the CaO-Ni-CeO2 DFM were elucidated, showing promise for the catalyst optimizations.