Base-catalyzed Research Articles

Synthesis and Characterization of Zinc (II) Phthalocyanine for Screening Potential Solar Cell Dye Application

Phthalocyanine molecules have the potential to be used in select Dye Sensitized Solar Cells (DSSCs) and Luminescent Solar Concentrators (LSCs), due to UV-Vis absorbance in the 300-450 (nm) Soret Band, corresponding to π HOMO-1 to π* LUMO transition and 550-690 (nm) Q-band, corresponding to π HOMO to π* LUMO transitions. In this study Tetranitro Zinc (II) Phthalocyanine is synthesized via base catalysis before the product is characterized via IR, 1H NMR & UV-Vis analysis. Assessing the desirability of the Tetranitro Zinc (II) Phthalocyanine as a solar organic semiconducting dye in DSSCs and LSCs. The desirability is assessed by novel computational DFT calculations, of the aggregation binding mode to deduce if Aggregation-Caused Quenching (ACQ) is occurring in the aggregated sample. ACQ is known to reduce DSSCs and LSCs generation of useful photo-active current. Aggregation-Caused Quenching (ACQ) is mathematically indicated in Phthalocyanine aggregation and Tetranitro Zinc (II) Phthalocyanine’s desirability is assessed for further use in DSSCs and LSCs.

Chiral Sulfide/Phosphoric Acid Cocatalyzed Enantioselective Intermolecular Oxysulfenylation of Alkenes with Phenol and Alcohol O -Nucleophiles

Chiral Sulfide/Phosphoric Acid Cocatalyzed Enantioselective Intermolecular Oxysulfenylation of Alkenes with Phenol and Alcohol <i>O</i> -Nucleophiles

Stereoselective Michael Additions of Arylacetic Acid Derivatives by Asymmetric Organocatalysis

AbstractBecause of the versatility of chiral 1,5-dicarbonyl structural motifs, the development of stereoselective Michael additions of arylacetic acid derivatives to electron-deficient alkenes is an important challenge. Over recent decades, an array of enantio- and diastereoselective methods of this type have been developed through the use of chiral organocatalysts. In this article, three distinct strategies in this research area are highlighted. Catalytic generation of either a chiral iminium electrophile (iminium catalysis) or a chiral enolate nucleophile (Lewis­ base catalysis) has allowed the efficient construction of stereogenic C–C bonds. We also introduce a synergistic catalytic approach involving the merger of these two catalytic cycles that provides selective access to all four stereoisomers of products with vicinal stereocenters.1 Introduction2 Iminium Catalysis3 Lewis Base Catalysis4 Synergistic Organocatalysis5 Summary

The role of Na+ in catalysis by the 8-17 DNAzyme.

The 8-17 DNAzyme is the most studied deoxyribozyme in terms of its molecular mechanism; hence it has become a model system to understand the basis behind DNA catalysis. New functional studies and the recent attainment of high-resolution X-ray structures, in addition to theoretical calculations have offered a great opportunity to gain a broader comprehension of its mechanism; however many aspects are unclear yet, especially regarding the precise role of metal ions in catalysis. Recently, molecular dynamics simulations have suggested for the first time a specific and dynamical participation of Na+ in the mechanism through the reaction pathway, besides the roles proposed for divalent metal cofactors. Herein, we present experimental evidence of a cooperative role of the monovalent cation Na+ in catalysis that is in line with these theoretical suggestions. Our findings show a clear influence of the concentration of Na+ on the activity of the 8-17 DNAzyme when Pb2+ is used as the cofactor. Interestingly, this effect is not noticed with Mg2+, indicating a particular contribution of the monovalent ion to catalysis that would operate preferentially with Pb2+. We have also found that Na+ affects the pKa of the general base and the general acid, indicating its influence on general acid-base catalysis, already identified as part of the mechanism of the 8-17 DNAzyme. Finally, our results emphasize the need to consider Na+ carefully in the design and analysis of functional studies of catalytic DNAs and its possible specific role in their mechanisms.

Water as a monomer: synthesis of an aliphatic polyethersulfone from divinyl sulfone and water.

Using water as a monomer in polymerization reactions presents a unique and exquisite strategy towards more sustainable chemistry. Herein, the feasibility thereof is demonstrated by the introduction of the oxa-Michael polyaddition of water and divinyl sulfone. Upon nucleophilic or base catalysis, the corresponding aliphatic polyethersulfone is obtained in an interfacial polymerization at room temperature in high yield (>97%) within an hour. The polyethersulfone is characterized by relatively high molar mass averages and a dispersity around 2.5. The polymer was tested as a solid polymer electrolyte with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as the salt. Free-standing amorphous membranes were prepared by a melt process in a solvent-free manner. The polymer electrolyte containing 15 wt% LiTFSI featured an oxidative stability of up to 5.5 V vs. Li/Li+ at 45 °C and a conductivity of 1.45 × 10−8 S cm−1 at room temperature.

Brønsted base-catalyzed 1,2-addition/[1,2]-phospha-Brook rearrangement sequence providing functionalized phosphonates.

A new methodology for the introduction of functional groups into an organic molecule in which a keto or a formyl group is used as the connecting site was developed by utilizing the 1,2-addition/[1,2]-phospha-Brook rearrangement sequence under Brønsted base catalysis. The reaction of aromatic aldehydes and ketones with phosphinates having functional groups such as alkynyl, bromoalkyl, N-Boc amino, and boryl groups efficiently proceeded with the aid of phosphazene base P2-tBu as the catalyst, providing densely functionalized phosphonates in good yields.

Dual functional catalysis of [Nb6O19]8--modified Au/Al2O3.

A catalyst prepared by modifying the surface of Au nanoparticles (NPs) on Al2O3 with [Nb6O19]8- clusters had specific base and reduction abilities, and the reduction of p-nitrophenol to p-aminophenol using H2 as a reductant proceeded efficiently with the dual functional catalyst. At the interface between Au NPs and basic [Nb6O19]8-, heterolytically cleaved hydrogen species are generated, which can efficiently react with nitrophenolate ions generated by base catalysis. Moreover, this surface modification strategy was applicable to the reduction of other nitro compounds.

Improved accessibility of Na-LTA zeolite catalytic sites for the Knoevenagel condensation reaction

The use of zeolites in basic catalysis is limited when large molecules are involved, such as in the manufacture of fine chemicals, due to difficulty in accessing the micropores of the catalyst. A solution to this problem is to synthesize zeolites containing mesopores that improve the accessibility of the active sites. This work investigates the synthesis of zeolites 4A according to a bottom-up method employing the organosilane surfactant [3-(trimethoxysilyl) propyl] octadecyldimethylammonium chloride (TPOAC), at different concentrations in the synthesis mixture (TPOAC/Al2O3 = 0–0.09), to produce mesopores. The zeolites were evaluated in the Knoevenagel condensation reaction, which is strongly influenced by the accessibility of the catalytic sites, due to the large sizes of the molecules involved. Zeolites 4A with mesopores, showing higher external surface areas, were formed in the presence of TPOAC at the different concentrations tested. Higher conversions were achieved using the zeolites with mesopores, compared to conventional zeolite 4A, due to improved access of the reactant molecules to the catalytic sites. In addition, the reaction catalyzed by the zeolite with mesopores had lower activation energy, compared to use of the conventional zeolite 4A.

Concurrent base and silver(I) catalysis pulsed by fuel acid.

Treatment of a crown-ether receptor and a silver(I)-loaded cyclam derivative (NetState-I) with a fuel acid reversibly afforded the protonated cyclam and the silver(I)-loaded crown ether (NetState-II). While NetState-I was catalytically OFF, a base-catalysed Michael addition and a silver(I)-catalysed oxime cyclisation reaction was pulsed under dissipative conditions in NetState-II.

Prebiotic triose glycolysis promoted by co-catalytic proline and phosphate in neutral water.

Proline and phosphate promote a near-quantitative aldol reaction between glycolaldehyde phosphate and formaldehyde at neutral pH in water. Our results demonstrate the important role of general acid-base catalysis in water and underscore the essential role that amino acid catalysis may have played in early evolution of life's core metabolic pathways.

Ni@C catalyzed hydrogenation of acetophenone to phenylethanol under industrial mild conditions in a flow reactor

The catalytic hydrogenation of organic substrates containing plenty of unsaturated functional groups is an important step in the industrial preparation of fine chemicals and has always been a hot spot in basic catalysis research.

Lewis Base Catalyzed Allylation Reaction of N-Aryl Amides with Morita–Baylis–Hillman Carbonates

Lewis Base Catalyzed Allylation Reaction of N-Aryl Amides with Morita–Baylis–Hillman Carbonates

Succinylated isoniazid potential prodrug: Design of Experiments (DoE) for synthesis optimization and computational study of the reaction mechanism by DFT calculations

Tuberculosis represents a worldwide public health concern, showing high rates of incidence and mortality annually. There is a recommended therapeutic regimen, in which isoniazid is indicated. This drug has a recognized action on Mycobacterium tuberculosis and presents pharmacokinetic problems, which can be improved using prodrug design. Considering that, this paper aimed to apply Design of Experiments (DoE) methods to optimize the synthetic procedure of succinylated isoniazid, a kind of isoniazid prodrug. For this reason, a factorial study 33, varying (1) reaction time (X1) at 6, 12 and 18 h; (2) proportion of excess succinic anhydride (X2) at 1.2, 1.4 and 1.6 equivalents and (3) the different catalysts (X3), pyridine, triethylamine and DMAP were carried out in 19 different experiments (performed in triplicate). It was observed that the condition containing DMAP, 18 h of reaction, presented the best result (85% yield). Additionally, DFT calculations were extremely important for understanding two competitive reaction mechanisms: via a basic DMAP catalysis (Pathway 1) and via self-catalyzed by the succinylated isoniazid (Pathway 2). The presence of a base was fundamental to generate a catalytic amount of product in order to start the Pathway 2. As the reaction goes on and the self-catalyst concentration increases, the Pathway 2 becomes the favorable mechanism, explaining the low influence of the base in the factorial test.

Recent Advances in Lewis Base-Catalysed Chemo-, Diastereo- and Enantiodivergent Reactions of Electron-Deficient Olefins and Alkynes.

Lewis base catalysis provides powerful synthetic strategies for the selective construction of carbon-carbon and carbon-heteroatom bonds. Thus continuous efforts have been deployed to develop effective methodologies involving Lewis base catalysis. The nucleophilicity and steric hindrance of Lewis base catalyst often plays a major role in catalytic reactivity and selectivity in the reaction. In the past decades, tremendous progress has been made in the divergent construction of valuable motifs under Lewis base catalysis. In this review, we provide a comprehensive and updated summary of Lewis base-catalysed chemo-, diastereo- and enantiodivergent reaction, as well as the related mechanism will be highlighted in detail.

Revisiting the Structural Evolution of Hydrotalcite‐Derived Mixed Metal Oxides upon Alkali Metal Doping and Its Impact on Base Catalysis

AbstractThe structural evolution of classic coprecipitation‐derived Mg−Al mixed oxide (MMO) upon doping of different alkali metals in a wide level (1–20 wt.%) was revisited. The pristine lateral MMO of aggregates into particulates, accompanied with the dramatic loss of the surface areas and the formation of aluminates. These phenomena become severer with the decrease of the atomic radius. The formation of NaAlO2 likely occurs via the gradual dealumination of the MMO, which is highly dependent on both the dopant content and the activation temperature. This leads to ultimately a new ensemble with MgO as the core decorated by NaAlO2 in the outer surfaces at high Na doping level and above 973 K. When evaluated in the base‐catalyzed transesterification and acylation model reactions, the Na‐doped MMO show enhanced performance and a plateau at increasing doping that might be explained by an interplay between the number and strength of strong basicity.

New insights into the exploitation of oxidized carbon nitrides as heterogeneous base catalysts

In this work, the development of a novel efficient heterogeneous catalytic system capable of driving Knoevenagel condensation reactions between benzaldehydes and malononitrile was reported. Specifically, we explored a post-synthetic modification of graphitic carbon nitride (g-CN) through a strong oxidation treatment by acid mixture (HNO3/H2SO4). The as-prepared oxidized CN material (CNO) shows a large number of surface acidic moieties, that can be easily deprotonated through an aqueous alkaline wash with different bases (NaOH, K2CO3, t-BuOK), to introduce a high density of reactive basic sites. The best catalyst is obtained with NaOH as the base (CNO-NaOH), and displays high reactivity and good tolerance towards functional group variations of the reagents, thus emerging as a potential new recyclable carbon nitride-based structure for organic base catalysis.

Borrowing Hydrogen and Acceptorless Dehydrogenative Coupling in the Multicomponent Synthesis of N‐Heterocycles: A Comparison between Base and Noble Metal Catalysis

AbstractAcceptorless dehydrogenative coupling reactions (ADC) and hydrogen transfer strategies (HT) provide a powerful tool in the multicomponent formation of N‐heterocycles. A broad variety of complex products can be obtained starting from simple, cheap and commercially available reagents. The protocols are highly atom‐efficient, as water, dihydrogen, or in some cases hydrogen peroxide, are the only by‐products. Moreover, neither further reducing or oxidizing agents, nor external hydrogen are in general required. Especially base metal‐catalyzed strategies become ever more important. Therefore, in recent years, various different manganese, iron, cobalt, nickel and copper catalysts have been developed. This Minireview highlights the progress that has been made by using abundant metal complexes to promote multicomponent cyclizations for the formation of N‐heterocycles and compares their performance with available noble metal catalyst systems.

Production and Evaluation of Fractionated Tamarind Seed Oil Methyl Esters as a New Source of Biodiesel

Biodiesel has attracted considerable interest as an alternative biofuel due to its many advantages over conventional petroleum diesel such as inherent lubricity, low toxicity, renewable raw materials, biodegradability, superior flash point, and low carbon footprint. However, high production costs, poor low temperature operability, variability of fuel quality from different feedstocks, and low storage stability negatively impact more widespread adoption. In order to reduce production costs, inexpensive inedible oilseed alternatives are needed for biodiesel production. This study utilized inedible tamarind (Tamarind indica) seed oil as an alternative biodiesel feedstock, which contained linoleic (31.8%), oleic (17.1%), and lauric (12.0%) acids as the primary fatty acids. A simple and cost-effective high vacuum fractional distillation (HVFD) methodology was used to separate the oil into three fractions (F1, F2, and F3). Subsequent transesterification utilizing basic, acidic, and enzymatic catalysis produced biodiesel of consistent quality and overcame the problem of low temperature biodiesel performance. The most desirable biodiesel with regard to low temperature operability was produced from fractions F2 and F3, which were enriched in unsaturated fatty acids relative to tamarind seed oil. Other properties such as density and cetane number were within the limits specified in the American and European biodiesel standards.

Evidence of Rate Limiting Proton Transfer in an SNAr Aminolysis in Acetonitrile under Synthetically Relevant Conditions.

An early synthetic step in the synthesis of adavosertib, AZD1775, is the SNAr reaction between 4-fluoronitrobenzene and 1-methylpiperazine in acetonitrile. A simple kinetics-based design of four reaction profiling experiments was used to investigate the kinetics of the reaction for the purpose of building a kinetic model. Fitting of the reaction profile data from two experiments conducted at 70 °C with a different excess of 1-methylpiperazine showed the reaction to follow a third-order rate law with a second-order dependence upon 1-methylpiperazine. This was rationalized in terms of the reaction following a rate-limiting proton transfer mechanism (base catalyzed) in which the progress to product is driven by a proton transfer involving a second molecule of 1-methylpiperazine. The experimentally determined entropy of activation of -180 J K-1 is consistent with this mechanism. The formation of a low level impurity was found to be due to the presence of traces of piperazine in the 1-methylpiperazine, which was shown to react approximately 15 times faster than 1-methylpiperazine at 70 °C. The rate constants for the 1-methylpiperazine catalyzed reaction of piperazine, 1-methylpiperazine, and the piperazine derived impurity were found to correlate in a Brønsted type analysis with the pKa's (acetonitrile) of the amine nucleophile.

Synthesis of Enantioenriched 3,4-Disubstituted Chromans through Lewis Base Catalyzed Carbosulfenylation.

A method for the catalytic, enantioselective, carbosulfenylation of alkenes to construct 3,4-disubstituted chromans is described. Alkene activation proceeds through the intermediacy of enantioenriched, configurationally stable thiiranium ions generated from catalytic, Lewis base activation of an electrophilic sulfenylating agent. The transformation affords difficult-to-generate, enantioenriched, 3,4-disubstituted chromans in moderate to high yields and excellent enantioselectivities. A variety of substituents are compatible including electronically diverse functional groups as well as several functional handles such as aryl halides, esters, anilines, and phenols. The resulting thioether moiety is amenable to a number of functional group manipulations and transformations. Notably, the pendant sulfide was successfully cleaved to furnish a free thiol which readily provides access to most sulfur-containing functional groups which are present in natural products and pharmaceuticals.