Acid-catalyzed Research Articles

New Synthesis of 2-Aminopyrimidines by Amination of Biginelli Reaction Products — Oxadiazocines

Abstract Previously, we synthesized methanobenzo[g][1,3,5]oxadiazocines and methanonaphtho[2,3-g]­[1,3,5]oxadiazocines via the Biginelli reaction using thiourea with acetoacetic ester or acetylacetone and salicylaldehyde or 2-hydroxy-1-naphthaldehyde under acidic catalysis and microwave irradiation. These compounds were then subjected to alkylation reaction with ethyl bromide in the presence of potassium carbonate in dimethylformamide. Under these mild reaction conditions, possible thione-thiol tautomerism of the oxadiazocines, as well as their structural analogs of cyclic thioureas, predominantly yielded in S-alkylation products with minor amounts of N-alkylation products. Further nucleophilic substitution reactions of S-ethyl-methanobenzo[g][1,3,5]oxadiazocines and S-ethyl-methanonaphtho[2,3-g][1,3,5]oxadiazocines revealed that alongside nucleophilic substitution by morpholine, elimination of phenol or naphthol occurred, followed by aromatization of the dihydropyrimidinone ring into an aromatic pyrimidine ring, resulting in the formation of 2-morpholinyl-substituted pyrimidines. Only a few examples and multi-step syntheses for obtaining such 2-amino-substituted pyrimidines are presented in the literature. Therefore, our newly discovered method for obtaining widely demanded derivatives of 2-aminopyrimidines is presented both relevant and promising.

Electrically driven proton transfer promotes Brønsted acid catalysis by orders of magnitude.

Electric fields play a key role in enzymatic catalysis and can enhance reaction rates by 100,000-fold, but the same rate enhancements have yet to be achieved in thermochemical heterogeneous catalysis. In this work, we probe the influence of catalyst potential and interfacial electric fields on heterogeneous Brønsted acid catalysis. We observed that variations in applied potential of ~380 mV led to a 100,000-fold rate enhancement for 1-methylcyclopentanol dehydration, which was catalyzed by carbon-supported phosphotungstic acid. Mechanistic studies support a model in which the interfacial electrostatic potential drop drives quasi-equilibrated proton transfer to the adsorbed substrate prior to rate-limiting C-O bond cleavage. Large increases in rate with potential were also observed for the same reaction catalyzed by Ti/TiOyHx and for the Friedel Crafts acylation of anisole with acetic anhydride by carbon-supported phosphotungstic acid.

Supramolecular Polymer‐Based Ionogels Enable Large‐Scale Fabrication of Stable Smart Windows with Room‐Temperature Closed‐Loop Recyclability and Self‐Healing Capability

AbstractCurrent self‐healing ionogels are unable to undergo closed‐loop recycling and are unsuitable for large‐scale fabrication, which increases their manufacturing costs and limits their practical applications. In this study, self‐healing thermochromic ionogels with room‐temperature closed‐loop recyclability and self‐healing capability are large‐scale prepared by the in situ synthesis of imine bond cross‐linked supramolecular polymers in binary ionic liquids. The resulting ionogels show excellent mechanical and environmental stability, high solar modulation capability, and long service life, which can provide spontaneous solar modulation for buildings and vehicles to reduce cooling‐related energy consumption. The temperature‐responsive hydrogen bonding between supramolecular polymers and ionic liquids influences the dissolution state of the supramolecular polymers, allowing the self‐healing thermochromic ionogels to switch between transparent and opaque states through reversible agglomeration of ILs inside the ionogels. Dynamic imine bonds enable the ionogels to spontaneously heal themselves at room temperature and to be depolymerized into monomers in an extremely high yield and purity under hydrochloric acid catalysis at room temperature. The recovered monomers can be used to re‐manufacture self‐healing thermochromic ionogels without losing their original mechanical properties or thermochromic capability. This study provides a new route for developing functional self‐healing ionogels that can be large‐scale fabricated and closed‐loop recycled.

A Water-Stable Boronate Ester Cage.

The reversible condensation of catechols and boronic acids to boronate esters is a paradigm reaction in dynamic covalent chemistry. However, facile backward hydrolysis is detrimental for stability and has so far prevented applications for boronate-based materials. Here, we introduce cubic boronate ester cages 6 derived from hexahydroxy tribenzotriquinacenes and phenylene diboronic acids with ortho-t-butyl substituents. Due to steric shielding, dynamic exchange at the Lewis acidic boron sites is feasible only under acid or base catalysis but fully prevented at neutral conditions. For the first time, boronate ester cages 6 tolerate substantial amounts of water or alcohols both in solution and solid state. The unprecedented applicability of these materials under ambient and aqueous conditions is showcased by efficient encapsulation and on-demand release of β-carotene dyes and heterogeneous water oxidation catalysis after the encapsulation of ruthenium catalysts.

N-Terminal Proline Editing for the Synthesis of Peptides with Mercaptoproline and Selenoproline: Mechanistic Insights Lead to Greater Efficiency in Proline Native Chemical Ligation.

Native chemical ligation (NCL) at proline has been limited by cost and synthetic access. In addition, prior examples of NCL using mercaptoproline have exhibited stalling of the reaction after thioester exchange, due to inefficient S → N acyl transfer. Herein, we develop methods, using inexpensive Boc-4R-hydroxyproline, for the solid-phase synthesis of peptides containing N-terminal 4R-mercaptoproline and 4R-selenoproline. The synthesis proceeds via proline editing on the N-terminus of fully synthesized peptides on the solid phase, converting an N-terminal Boc-4R-hydroxyproline to the 4S-bromoproline, followed by an SN2 reaction with potassium thioacetate or selenobenzoic acid. After cleavage from the resin and deprotection, peptides with functionalized N-terminal proline amino acids were obtained. NCL reactions with mercaptoproline proceeded slowly under standard NCL conditions, with the S-acyl transthioesterification intermediate observed as a major species. Computational investigations indicated that the bicyclic intermediates and transition states for S → N acyl transfer are sufficiently low in energy (10-15 kcal mol-1 above starting material) that ring strain cannot explain the slow S → N acyl transfer. Instead, the bicyclic zwitterionic tetrahedral intermediate has a low barrier for reversion to the S-acyl intermediate, causing reversion to the thioester (reverse reaction) to occur preferentially over elimination to generate the amide (forward reaction). We hypothesized that a buffer capable of general acid and/or general base catalysis could promote S → N acyl transfer and thus achieve greater efficiency in proline NCL. In the presence of 2 M imidazole at pH 6.8, NCL with mercaptoproline proceeded efficiently to generate the peptide with a native amide bond. NCL with selenoproline also proceeded efficiently to generate the desired products when a thiophenol thioester was employed as a ligation partner. After desulfurization or deselenization, the products obtained were identical to those synthesized directly, confirming that the solid-phase proline editing reactions proceeded stereospecifically and without epimerization.

Efficient photo-electro-Fenton catalysis of perfluorooctanoic acid with MOFs based 2D CoFe nanosheets: Oxygen vacancy-mediated adsorption and mineralization ability

In heterogeneous solar photo-electro-Fenton (SPEF) degradation of perfluorooctanoic acid (PFOA), improving the binding energy between the catalyst and PFOA on a surface molecular level to facilitate absorption, diffusion, and degradation is a great challenge. Herein, we attained this goal in two steps: First, developing of two-dimensional (2D) MOFs-based CoFe nanosheets with layered structures as photo-electrocatalysts, which own abundant unsaturated coordination sites to accelerate rapid mass transport and charge transfer. Secondly, the construction of abundant oxygen vacancies (OVs) at low temperatures in 2D CoFe causes hybridization of the d-band of Fe and LUMO orbital of O in PFOA, enhancing PFOA’s binding capacity by theoretical analysis. OVs also reduced the band gap of CoFe and increased the efficiency of electron-hole separation, thereby improving photo-electrocatalytic activity and enabling rapid degradation of PFOA. Moreover, it can maintain a good degradation effect in complex ionic background conditions and actual water samples. These findings extend the applications of catalysts and consolidate the effect of OVs on photo-electrocatalysis for wide environmental applications.

Multivalence-State Tungsten Species Facilitated Iridium Loading for Robust Acidic Water Oxidation.

The development of the proton exchange membrane water electrolyzer (PEMWE) is still limited by the prohibitive cost and scarcity of iridium (Ir)-based oxygen evolution reaction (OER) catalyst. This work presents a novel catalyst synthesized by precursor-atomization and rapid joule-heating method, successfully doping iridium atoms into polyvalent tungsten blends (W0, W5+, W6+) based on titanium substrate. The vacancy engineering of unsaturated tungsten oxide (W5+, W6+) reconstructs the electronic structure of the catalyst surface, which resulting in the low-valence state iridium species, avoiding excessive oxidation of iridium and accelerating the catalytic kinetics. Meanwhile, metallic tungsten (W0) improves the conductivity of catalyst and guarantees the stable existence of oxygen vacancy. The TiIrWOx possesses excellent performance in acidic OER catalysis, requiring overpotential of only 181mV to drive 10.0mAcm-2, and exhibiting a high mass activity of 753AgIr -1 at an overpotential of 300mV. The membrane electrode assembly (MEA) with TiIrWOx as anode electrocatalyst can reduce the Ir consumption amount by >60% compared to commercial IrO2, and it can operated over 120h at a current density of 1.0Acm-2.

Mechanochemical Activation of DNAzyme by Ultrasound.

Controlling the activity of DNAzymes by external triggers is an important task. Here a temporal control over DNAzyme activity through a mechanochemical pathway with the help of ultrasound (US) is demonstrated. The deactivation of the DNAzyme is achieved by hybridization to a complementary strand generated through rolling circle amplification (RCA), an enzymatic polymerization process. Due to the high molar mass of the resulting polynucleic acids, shear force can be applied on the RCA strand through inertial cavitation induced by US. This exerts mechanical force and leads to the cleavage of the base pairing between RCA strand and DNAzyme, resulting in the recovery of DNAzyme activity. This is the first time that this release mechanism is applied for the activation of catalytic nucleic acids, and it has multiple advantages over other stimuli. US has higher penetration depth into tissues compared to light, and it offers a more specific stimulus than heat, which has also limited use in biological systems due to cell damage caused by hyperthermia. This approach is envisioned to improve the control over DNAzyme activity for the development of reliable and specific sensing applications.

Unveiling a Strategy for Ring Opening of Epoxides: Synthesis of 2-Hydroxyindolinylidenes Using α-Ester Sulfoxonium Ylides.

The untapped potential of α-carbonyl sulfoxonium ylides in epoxide ring-opening reactions has been a notable gap in current research, with such reactivity predominantly associated with the highly reactive dimethylsulfoxonium methylide. This study introduces an innovative approach wherein an epoxide indole, formed in situ from 2-hydroxyindoline-3-triethylammonium bromide, undergoes reaction with α-ester sulfoxonium ylides. The outcome is the efficient synthesis of a range of 2-hydroxyindolin-3-ylidenes, demonstrating favorable yields (41-81%) and Z/E ratios from 4:1 to those of exclusive Z isomers. Additionally, the photophysical properties of the synthesized indolinylidenes are explored, along with their derivatization using various nucleophiles under acid catalysis.

Enantioselective Flow Synthesis of a Tetrahydroquinoline SERM Enabled by Immobilized Chiral Phosphoric Acid Catalysis and Diboronic Acid Mediated Selective Nitro Reduction

AbstractAn asymmetric enantioselective flow process is reported for the formal synthesis of a 1,2,3,4‐tetrahydroquinoline selective estrogen receptor modulator. Starting from an easily available 2‐nitrochalcone, the first part of the process comprised a telescoped nitro reduction/intramolecular cyclocondensation sequence using diboronic acid as a simple reductant. Subsequent enantioselective transfer hydrogenation in the presence of an immobilized phosphoric acid organocatalyst followed by telescoped N‐alkylation furnished the targeted chiral intermediate. The approach ensures flexibility regarding the scale of the synthesis, whilst minimizing the need for intermediate purifications and ensuring environmentally benign metal‐free conditions.

Heteropoly acid catalysis in the valorization of bio-renewables: Acetylation of 1,4-cineole and 1,8-cineole (eucalyptol) in green solvents

In this work, a novel synthesis of monoterpenic acetate esters potentially valuable as flavoring agents was developed. It involves the reactions of 1,4-cineole and 1,8-cineole with acetic anhydride giving the desired products in 80–88 % total yields. The process is performed under ambient conditions in green solvents such as methyl isobutyl ketone, methyl ethyl ketone, dimethyl carbonate or diethyl carbonate in the presence of acidic cesium salt of phosphotungstic acid, Cs2.5H0.5PW12O40, as an efficient solid acid catalyst. The catalyst is stable toward leaching in the reaction system and can be reused. The process produces mixtures of acetate esters with different flavor bouquets which can be used directly as ingredients in fragrance compositions without separating individual compounds.

Microwave-Assisted Production of 5-Hydroxymethylfurfural from Fructose Using Sulfamic Acid as a Green Catalyst

The development of safe-by-design synthesis of valuable chemicals from biomass derivatives is a key step towards sustainable chemical transformations in both academia and industry. 5-Hydroxymethylfurfural (5-HMF) is a biomass derivative chemical of high commercial interest due to its wide range of chemical and biofuel applications. In this scenario, the present work contributes to a methodology for producing 5-hydroxymethylfurfural (5-HMF) through fructose dehydration reaction under microwave irradiation. The proposed protocol uses a simple sodium chloride–saturated aqueous-i-PrOH biphasic system and catalysis of sulfamic acid, a low-cost solid Brønsted–Lowry inorganic acid, which presents pivotal features of a sustainable catalyst. A 23 full factorial design was applied to achieve the highest conversion and 5-HMF yield, allowing the identification of the main factors involved in the process. Under the optimized conditions, fructose at the concentration of 120 g L−1 was converted with 91.15 ± 6.98% after 20 min at 180 °C, using 10 mol% of catalyst. 5-HMF was produced in 80.34 ± 8.41% yield and 73.20 ± 8.23% selectivity. Thus, the present contribution discloses a new optimized methodology for converting the biomass derivative fructose to 5-hydroxymethylfurfural (5-HMF).

Synthesis and characterization of biodiesel obtained from castor oil transesterification

The objectives of this work were to optimize the variables affecting transesterification process for biodiesel production from castor oil, non edible oil, by acid catalysis (sulphuric and phosphoric acid) and basic catalysis (potassium methoxide and potassium hydroxide); and to characterize the biodiesel for its use as fuel in compression ignition motors. The studied operation variables were methanol/oil molar ratio (3:1, 6:1, 9:1, 12:1), temperature (25, 35, 45, 55, 65 ºC), and catalyst amount (2, 3, 4 wt.% in acid catalysis, and 0.5, 1.0, 1.5 wt.% in basic catalysis). Evolution of each process was followed by gas chromatography, determining the content of methyl esters at different reaction times. Biodiesel was characterized by a set of parameter according to European Standard, EN 14214. The best conditions for transesterification process were 9:1 methanol/oil molar ratio, 65 ºC, and the use of potassium methoxide as catalyst with concentration 1.0 wt.%. In these conditions, obtained biodiesel presents satisfactory values of water content, iodine and saponification values, flash and combustion points, and temperature of 50% of distillate. However, values of density, kinematic viscosity, cetane index and cold filter plugging point, that are heavily dependent on oil, move away from those required by the European Standard.

Increased ACSL6 Expression Predicts a Favorable Prognosis in Triple-negative Breast Cancer.

Long-chain acyl-coenzyme A synthases (ACSLs) are responsible for the catalysis of fatty acids into their corresponding fatty acyl-CoAs. The dysregulation of ACSLs has been increasingly recognized in cancer patients. However, the function of ACSL6 in triple-negative breast cancer (TNBC) is still completely unknown. In this study, immunohistochemistry was applied to detect ACSL6 protein expression using a TNBC tissue microarray. Additionally, the mRNA levels of ACSL6 in human normal tissues and pancancer tissues were analyzed using Genotype Tissue Expression (GTEx) datasets and The Cancer Genome Atlas (TCGA) database. The correlations between the levels of ACSL6 expression and clinical characteristics were analyzed. The survival analysis of ACSL6 in TNBC was carried out using the Kaplan‒Meier Plotter online tool. Associations of ACSL6 with immune infiltration analyses were conducted using the ESTIMATE, CIBERSORT, and TISIDB databases. The relationship between ACSL6 and sensitivity to drugs was analyzed from Genomics of Drug Sensitivity in Cancer (GDSC). The results indicated a significant increase in ACSL6 expression in TNBC tissues compared to adjacent normal tissues. However, high ACSL6 expression was significantly associated with favorable survival outcomes in TNBC patients. Enrichment analysis revealed that coexpressed genes of ACSL6 were significantly enriched in various immunity processes. ACSL6 was positively correlated with the infiltration of memory CD4 T cells, while a negative correlation was found between ACSL6 and M2 macrophages and resting dendritic cells. Further analysis revealed that high levels of ACSL6 correlated with increased survival outcomes in cancer patients who received immunotherapy. Altogether, the current findings highlight the potential value of ACSL6 as a diagnostic and prognostic marker in the treatment of TNBC.

Design, One-Step Highly Selective Synthesis and Enhancing Insecticidal Activity and Photo-Self-Degradation of Phenylpyrazole Esterified Derivatives as GABA and nACh Receptor Inhibitors.

In the pursuit of novel insecticides with high activity and a unique mode of action on the GABA receptor, a series of phenylpyrazole esterified derivatives (PEs) were synthesized using an improved Pinner reaction with high selectivity. Lewis acid catalysis was employed in a one-step solvent-thermal method to convert the cyano group of fipronil into an ester unit. FeCl3 was found to exhibit the highest selectivity for PEs synthesis, yielding PEs at 96.4%, with the byproduct being phenylpyrazole amide (PE0) at 2.1%. Initial biological assays indicated superior insecticidal activity of the target compounds against Plutella xylostella and Mythimna separata compared to fipronil. Particularly, the smaller and shorter ester units, PE3, PE5, and PE8, demonstrated 2-2.5 times higher insecticidal activity against P. xylostella than fipronil. The higher activity of ester units compared to amide and acylhydrazone units can be attributed to the enhanced lipid solubility of PEs. Additionally, it may be due to the impact of PEs on the neurotransmitter nACh or the coordination of calcium and chloride ions with the ester's -C═O and -O- bonds, blocking the chloride ion channel. Hydrophobic parameters were confirmed by reversed-phase high-performance liquid chromatography (HPLC), indicating the enhanced lipophilicity conferred by the ester units of PEs. Molecular docking and CoMFA analysis preliminarily validated the strong interactions and structure-activity relationships between PEs and the GABA receptor and nACh receptor in P. xylostella. Furthermore, under simulated natural sunlight, PEs exhibited photodegradation capabilities, transforming back into fipronil parent fragments and enhancing their insecticidal activity. Moreover, PEs displayed excellent fluorescent properties, enabling self-detection of residues. These research findings provide new insights and directions for the development of efficient pesticides, with potential wide applications in the fields of medicine and biosensors.

A Catalytic Method to Activate Nitromethane by the Cooperation of Homo‐ and Heterogeneous Catalysis

AbstractThe achievement of directly activating and utilizing bulk small molecules has remained a longstanding objective in the field of chemical synthesis. The present work reports a catalytic activation method for bulk chemical nitromethane (MeNO2). This method combines homogeneous Lewis acid with recyclable heterogeneous Brønsted acid catalysis, featuring practicality, sustainability, and low cost, thus solving the inherent drawbacks of previous Nef processes where stoichiometric reductants or activators were required. By combining the advantages of both homo‐ and heterogeneous catalysts, this chemistry may not only offer new opportunities for the further development of MeNO2 as a nitrogen source for organic synthesis, but also promote the catalysis design in synthetic chemistry.

Bilocus phylogenetic diversity and biogeographic distribution of isopods infesting Egyptian fishes

Phylogenetic diversity studies of parasitic isopods in Egyptian fisheries are very limited, based on a few records of the single mitochondrial gene, COI. Consequently, there has been no mapping study to monitor the phylogenetic diversity and biogeographic distribution of parasitic isopods among a wide range of Egyptian fisheries, leading to gaps in our understanding of the origin and expansion of these parasites. Hence, this study focused on validating the taxonomy and phylogenetic distribution of parasitic isopods using two marker genes, nuclear 18S rDNA and mitochondrial COI. Isopods were collected from seven fish species, Liza ramada, Solea aegyptiaca, Tilapia zillii, Pomadasys sp., Dicentrarchus sp., Atherinomorus lacunosus, and Nemipterus japonicus at four distant Egyptian lakes, Lake Qarun, Bitter Lakes, Lake Burullus, and Lake Manzala; and two marine localities, Red Sea and Suez Gulf, respectively. Sequence analysis revealed 10 and 19 haplotypes of 18S rDNA and COI, respectively. Lake Qarun showed the highest haplotype intra-diversity and is considered a pool of haplotypes with ancestors from other distant lakes. The Red Sea and Suez Gulf haplotypes showed genetic divergence from those recovered from lakes, implicating endemic isopod species. Some haplotypes had mutations in COI-deduced catalytic amino acids. The lake haplotypes belonged to Livoneca redmanii, suggesting a biogeographic expansion of this species among distant Egyptian fisheries. A new genus belonging to the family Cymothoidae was recorded in the Red Sea fish A. lacunosus. Elthusa vulgaris-like haplotypes were recorded in the Suez Gulf fish N. japonicus. Hence, this study clarified the expansion of isopod phylogenetic diversity among varieties of fish species from distant localities.

Boronic Acid/Palladium Hybrid Catalysis for Regioselective O-Allylation of Carbohydrates.

Novel imidazole-containing boronic acid and palladium hybrid catalysis for regioselective O-allylation of carbohydrates has been developed. This catalytic process enables the introduction of a useful allyl functional group into the equatorial hydroxy group of cis-1,2-diols of various carbohydrates with low catalyst loading and excellent regioselectivities. This is the first report on hybrid catalysis in combination with a Lewis base-containing boronic acid and a transition metal complex.

Co-Immobilization of Laccase and Mediator into Fe-Doped ZIF-8 Significantly Enhances the Degradation of Organic Pollutants.

Co-immobilization of laccase and mediator 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) for wastewater treatment could simultaneously achieve the reusability of laccase and avoid secondary pollution caused by the toxic ABTS. Herein, Fe-induced mineralization was proposed to co-immobilize laccase and ABTS into a metal-organic framework (ZIF-8) within 30 min. Immobilized laccase (Lac@ZIF-8-Fe) prepared at a 1:1 mass ratio of Fe2+ to Zn2+ exhibited enhanced catalytic efficiency (2.6 times), thermal stability, acid tolerance, and reusability compared to free laccase. ABTS was then co-immobilized to form Lac+ABTS@ZIF-8-Fe (ABTS = 261.7 mg/g). Lac@ZIF-8-Fe exhibited significantly enhanced bisphenol A (BPA) removal performance over free laccase due to the local substrate enrichment effect and improved enzyme stability. Moreover, the Lac+ABTS@ZIF-8-Fe exhibited higher BPA removal efficiency than the free laccase+ABTS system, implying the presence of a proximity effect in Lac+ABTS@ZIF-8-Fe. In the successive malachite green (MG) removal, the MG degradation efficiency by Lac@ZIF-8-Fe was maintained at 96.6% at the fifth reuse with only an extra addition of 0.09 mM ABTS in each cycle. As for Lac+ABTS@ZIF-8-Fe, 58.5% of MG was degraded at the fifth cycle without an extra addition of ABTS. Taken together, this research has provided a novel strategy for the design of a co-immobilized laccase and ABTS system for the degradation of organic pollutants.

Insight into the reaction mechanism of photocatalytic production of solketal

In this work, the behavior of a commercial TiO2 (Evonik P25) and synthesized CeO2 and Bi2WO6 photocatalysts in the photoacetalization of glycerol with acetone to obtain solketal under simulated sunlight was studied. The solids were characterized by X-ray diffraction (XRD), N2 adsorption desorption isotherms, Raman spectroscopy and UV–Vis spectroscopy techniques. The influence of the oxygen content in the reaction atmosphere (1–40% O2) was analyzed. It was concluded that oxygen is essential for the reaction taking place, suggesting the participation of the superoxide radical as an intermediate in the transfer of electrons. To confirm this point, p-benzoquinone, a known superoxide radical scavenger, was used to evaluate the role of O2. However, two opposite effects were observed for p-benzoquinone depending on the amount added to the reaction medium. Thus, for small amounts of p-benzoquinone a negative effect on the yield of solketal was observed, in agreement to its superoxide radical scavenger character. On the contrary, at high concentrations, p-benzoquinone enhanced the solketal yield obtained in the process. A mechanism is proposed by which the semiquinone radical formed acts as an intermediate capable of facilitating the transfer of electrons in the process, thereby improving the overall process. The catalyst showing the lowest catalytic activity was CeO2, whereas Bi2WO6 had a higher reaction rate and activity than TiO2 (P25), with both reaching approximately 78% conversion under optimum conditions. These results are promising because the conversion achieved is comparable to that obtained by acid catalysis, using sunlight as energy source.