Acid-catalyzed Conditions Research Articles

Highly Efficient Synthesis of Substituted 3,4-Dihydropyrimidin-2-(1H)-ones (DHPMs) Catalyzed by Hf(OTf)₄: Mechanistic Insights into Reaction Pathways under Metal Lewis Acid Catalysis and Solvent-Free Conditions.

In our studies on the catalytic activity of Group IVB transition metal Lewis acids, Hf(OTf)4 was identified as a highly potent catalyst for ”one-pot, three-component” Biginelli reaction. More importantly, it was found that solvent-free conditions, in contrast to solvent-based conditions, could dramatically promote the Hf(OTf)4-catalyzed formation of 3,4-dihydro-pyrimidin-2-(1H)-ones. To provide a mechanistic explanation, we closely examined the catalytic effects of Hf(OTf)4 on all three potential reaction pathways in both “sequential bimolecular condensations” and “one-pot, three-component” manners. The experimental results showed that the synergistic effects of solvent-free conditions and Hf(OTf)4 catalysis not only drastically accelerate Biginelli reaction by enhancing the imine route and activating the enamine route but also avoid the formation of Knoevenagel adduct, which may lead to an undesired byproduct. In addition, 1H-MMR tracing of the H-D exchange reaction of methyl acetoacetate in MeOH-d4 indicated that Hf(IV) cation may significantly accelerate ketone-enol tautomerization and activate the β-ketone moiety, thereby contributing to the overall reaction rate.

SYNTHESES OF POLYFLUOROALKYL ESTERS OF MALEOPIMARIC ACID N-PHENYLIMIDE

To meet the challenge of complex processing of plant material, in particular, tall oil rosin, research has been conducted on the synthesis of new polyfluroalkyl maleimides. As is well known, maleopimaric acid’s imides constitute a forward-looking class of organic compounds for pharmacology, agriculture, polymer chemistry and so on. The introduction of a fluorocarbon unit often gives high surface activity, chemical and heat resistance, hydrophobic and oleophobic properties. This paper presents the results of experiments on the synthesis of new N-phenylimides of maleopimaric acid’s polyfluoroalkyl esters by the interaction of the corresponding monosubstituted polyfluorinated maleopimarates with aniline during boiling for 10–16 h in toluene (40–52%). The starting N-phenylimide of maleopimaric acid has been obtained by two methods: by the Diels-Alder reaction from abietic acid and N-phenyl maleimide using sulfuric acid as a catalyst in the melt (40%) and by heating (MPA) with aniline in toluene (80%). 2,2,3,3,4,4,5,5-octafluoroamyl and 2,2,3,3,4,4,5,5,6,6,7,7,7- dodecaftaforpetyl ethers have been obtained by esterification of MPA with fluorinated alcohols under conditions of acid catalysis (70%). It have been identified the ester bonds are quite stable by TLC during long-term treatment of the stock (over 11 hours). The synthesized substances were analyzed with UV-, IR-, 1H NMR and 19F.

Theoretical calculation studies on the rearrangement mechanisms of arenesulfenanilides to generate o- and p-aminodiphenyl sulfides.

The thermal and acid-catalyzed rearrangement mechanisms of arenesulfenanilides were investigated theoretically via density functional theory (DFT) calculations. The results indicate that the o-aminodiphenyl sulfide rearrangement involves a novel S[1,3]-sigmatropic shift followed by tautomerization, while the p-aminodiphenyl sulfide rearrangement proceeds via tandem [3,3]- and [3,3]-sigmatropic shifts followed by tautomerization under thermal conditions. Furthermore, computational studies reveal that water assists the proton shift more efficiently than anilines during tautomerization. Moreover, under the acid-catalyzed conditions, the o-aminodiphenyl sulfide rearrangement involves an S[1,3]-sigmatropic shift similar to that under the thermal conditions, while the p-aminodiphenyl sulfide rearrangement proceeds via cascade S[1,3]- and S[1,3]-sigmatropic shifts followed by water-aided tautomerization. The current theoretical studies provide new insights into the formation mechanism of o/p-aminodiphenyl sulfides in the arenesulfenanilide rearrangement and support the unprecedented suprafacial symmetry-allowed S[1,3]-sigmatropic shift with an inversion of the configuration in the migrating sulfur atom. The mechanism is affected by the reaction medium. Disproportionation of arenesulfenanilides into diaryl disulfides and azobenzenes is a competitive radical pathway during the arenesulfenanilide rearrangements.

A rapid method based on advanced polymer chromatography for analyzing the products of the acid-catalyzed depolymerization of lignosulfonate

In this study, a fast and efficient method for the separation and analysis of the products in the acid-catalyzed depolymerization of commercially available sodium lignosulfonate has been developed. The depolymerized lignosulfonate products were well separated and characterized by advanced polymer chromatography (APC) employing four ACQUITY APC XT columns in series and a ultraviolet detector. The developed method enabled the detection of relative-low-molecular-mass lignin degradation products with peak molecular weights (Mp) of 720, 490, and 260 Da, and an extremely low polydispersity index (PDI) of 1, indicating almost complete conversion of lignosulfonate to smaller molecules. The effects of reaction temperature, time, and catalyst/lignin ratio on the reaction products were systematically investigated. High yields of depolymerization (>80%) could be obtained under the mild acid-catalyzed conditions at 130℃ for 60 min using a catalyst/lignin ratio of 2.334:1. Preliminary studies also indicated that the mild acid-catalytic mechanism is unaffected by the reaction time, temperature, or catalyst concentration, thus suggesting the specificity of the catalytic procedure employed.

Synthesis of meso-Tetraaryl Triphyrins(2.1.1).

A simple, straightforward [2+1] condensation of 5,6-diaryldipyrroethene dicarbinols with pyrrole under mild acid-catalyzed conditions resulted in the formation of highly desirable aromatic β-free meso-tetraaryl [14]triphyrins(2.1.1) in 15-18% yields. The triphyrins(2.1.1) are very novel monoanionic tridentate ligands that form metal complexes readily as demonstrated here by preparing Re(I) complexes.

BIS-DEACETYLATION OF TETRAACETYLGLYCOLURYL UNDER ACTION OF UREAS

It is established that tetraacetylglycoluril under the action of urea, some N-substituted ureas and benzylidenebisurea in the acid-catalyzed conditions undergoes only bis-deacetylation with the formation of syn- and anti-regio-substituted N,N-diacetylglycolurils, rather than N-acetylation as it was previously shown in a similar reaction for a number of aromatic and heterocyclic amines. In the course of individual experiments, the absence of independent effect of organic solvents during boiling for several hours (alcohols, dioxane, tetrahydrofuran, dimethylsulfoxide) on the deacetylation of tetraacetylglycoluril was revealed, since in these conditions the original substrate remained unchanged. Based on the NMR spectroscopy data, by comparison the integrated intensities of methine and acetyl protons of glycoluryl fragments, we found that the bis-deacetylation of tetraacetylglycoluril in the studied conditions occurs regioselectively with an overwhelming majority of anti-N,N-diacetylglycoluril (up to 92-94%) except for benzylidenebisurea, when the content of the trans-isomer reaches 75%. A marked increase in the cis-isomer (up to 25%) of N,N-diacetylglycoluril in the case of benzylidenebisurea seems to be dictated by the specific effect on the intermediates of reaction of phenylmethylureido carbocation from eliminating urea molecule in acid-catalyzed conditions. It is shown that N,N-diacetylglycoluril in similar conditions under the action of urea and its derivatives does not undergo further deacetylation to the progenitor of bicyclic bisureas – glycoluril, primarily related to the high hydrolytic and steric resistance of these compounds. On the basis of the above research results, the reaction mechanisms of bis-deacetylation of tetraacetylglycoluril in the acid-catalyzed conditions under the action of urea and its N-methyl (phenyl) derivatives through an intermediate process of nucleophilic addition of ureas is proposed.Forcitation:Hoang N.P., Bakibaev A.A., Malkov V.S. Bis-deacetylation of tetraacetylglycoluryl under action of ureas. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 7. P. 49-53

Skeletal Rearrangements of Rings C and D of the Kaurene and Beyerene Tetracyclic Diterpenoids

The skeletal rearrangement of the bicyclo[3.2.1]octane portion of rings C and D of the kaurene and beyerene tetracyclic diterpenoids are reviewed, revealing the tendency of the secondary carbocations to rearrange to tertiary carbocations with the eventual preferential formation of bicyclo[2.2.2]octanes. Under acid-catalysed conditions the variations in the products with the nucleophilicity of the counter ions suggest that the intervention of discrete rather than completely delocalised non-classical carbonium ions may be contributing to the reaction pathway.

C-Glycosidation of Unprotected Di- and Trisaccharide Aldopyranoses with Ketones Using Pyrrolidine-Boric Acid Catalysis

C-Glycoside derivatives are found in pharmaceuticals, glycoconjugates, probes, and other functional molecules. Thus, C-glycosidation of unprotected carbohydrates is of interest. Here the development of C-glycosidation reactions of unprotected di- and trisaccharide aldopyranoses with various ketones is reported. The reactions were performed using catalyst systems composed of pyrrolidine and boric acid under mild conditions. Carbohydrates used for the C-glycosidation included lactose, maltose, cellobiose, 3'-sialyllactose, 6'-sialyllactose, and maltotriose. Using ketones with functional groups, C-glycosides ketones bearing the functional groups were obtained. The pyrolidine-boric acid catalysis conditions did not alter the stereochemistry of non-C-C bond formation positions of the carbohydrates and led to the formation of the C-glycosidation products with high diastereoselectivity. For the C-glycosidation of the carbohydrates under the pyrrolidine-boric acid-catalysis, the hydroxy group at the 6-position of the reacting aldopyranose was necessary to afford the product. Our analyses suggest that the carbohydrates form iminium ions with pyrrolidine and that boric acid forms B-O covalent bonds with the carbohydrates during the catalysis to forward the C-C bond formation.

Stable Core-Modified Doubly N-Fused Expanded Dibenziporphyrinoids.

We describe one-pot synthesis of stable doubly N-fused expanded dibenziporphyrinoids using readily available precursors under acid-catalyzed conditions. The doubly N-fused expanded dibenziporphyrinoids have been synthesized by adopting an inversion followed by fusion strategy. The studies showed that the dibenziporphyrinoids undergo mono fusion initially, but due to the high stability of doubly fused dibenziporphyrinoids, the monofused macrocycles undergo further fusion to form doubly fused dibenziporphyrinoids. The mono fusion and double fusion in these dibenziporphyrinoids were established by X-ray crystallography.

Nitrogen self-doped carbon aerogels derived from trifunctional benzoxazine monomers as ultralight supercapacitor electrodes.

Ultralight benzoxazine-derived porous nitrogen self-doped carbon aerogels with good yield can be prepared by direct polymerization of trifunctional benzoxazine monomers under acid catalysis using concentrated hydrochloric acid. This allows for a significantly widened density range (0.8-4.5 mg cm-3) and avoids any sacrificial etching. When serving as electrode materials for supercapacitors, the resulting hierarchical porous carbon aerogels show ultrahigh specific capacitance, excellent rate performance and good cycling stability (retention of 97.3% even after 10 000 continuous charge-discharge cycles). Besides energy storage devices, the interconnected nanoporous carbon aerogels can also find applications in oil/water separation, heavy metal removal, catalyst supports, and so forth.

Synthesis of chalcones from 3-formyl-substituted pyrrolo[3,4-f]indole-5,7-diones

General methods to access new 3-formyl-substituted 1-methoxypyrrolo[3,4-f]indole-5,7-diones were developed. The synthesized 3-formylindoles react with heterocyclic aceto-phenones under acid-catalyzed conditions to give different chalcones.

Gas Phase Oxidation of Campholenic Aldehyde and Solution Phase Reactivity of its Epoxide Derivative.

The rate constant for the OH reaction with campholenic aldehyde (CA) was measured using the flow tube-chemical ionization mass spectrometry method with a relative rate kinetics technique and was found to be (6.54 ± 0.52) × 10-11 cm3 molecule-1 s-1 at 100 Torr pressure and 298 K. A mechanism for the formation of the observed products was developed for both NO-free and NO-present conditions. On the basis of measurements of the pressure dependent yields of the products, between 5 and 20% of the CA oxidation at atmospheric pressure is predicted to lead to campholenic aldehyde epoxide (CAE). The aqueous solution reaction rate constants for CAE were determined via NMR spectroscopy and were found to be (2.241 ± 0.036) × 10-5 s-1 for neutral conditions and 0.0989 ± 0.0053 M-1 s-1 for acid-catalyzed conditions at 298 K. The products of the CAE aqueous solution reaction were identified as an isomer of CAE and the aldehyde group hydrated form of this isomer. Unlike the isoprene-derived epoxide, IEPOX, a nucleophilic addition mechanism was not observed. On the basis of the rate constants determined for CA and CAE, it is likely that these species are reactive on atmospherically relevant time scales in the gas and aerosol phases, respectively. The results of the present study largely support a previous supposition that α-pinene-derived secondary organic aerosol may be influenced by the multiphase processing of various intermediate species, including those with epoxide functionality.

Synthesis and Quantum Mechanical Studies of a Highly Stable Ferrocene-Incorporated Expanded Porphyrin.

We present the first evidence for an unusual stable metallocene-containing expanded porphyrinoid macrocycle that was synthesized by condensing one equivalent of 1,1'-bis[phenyl(2-pyrroyl)methyl]ferrocene with one equivalent of 5,10-di(p-tolyl)-16-oxa-15,17-dihydrotripyrrane under acid-catalyzed conditions. The formation of ferrocene-incorporated expanded porphyrin macrocycle was confirmed by HR-MS and 1D/2D NMR spectroscopy. The macrocycle was nonaromatic and displayed absorption bands in the region of 420-550 nm. The molecular and electronic structure of the ferrocene-incorporated expanded porphyrin was investigated by DFT methods. The DFT calculations indicated a partially twisted structure of the molecule, and the extent of torsional distortion was larger than previously observed for ruthenocenoporphyrinoids and ferrocenothiaporphyrin. The HOMO and LUMO states that were obtained from the DFT calculations indicated partial charge density on all four pyrrole nitrogen atoms and the furanyl oxygen atom in the HOMO state and partial charge density on the α and β carbon atoms in the LUMO state. In addition, the ferrocene moiety displayed the presence of partial charge density on the Fe atom and the cp rings in both the HOMO and LUMO states. Moreover, DFT studies of the diprotonated form of macrocycle indicated that the diprotonated form also retained a synclinal conformation and that its torsional strain was slightly higher than its free base form.

Influence of preparation method on the physicochemical properties and catalytic activity of SiO2–TiO2 mixed oxides

In this study, SiO2–TiO2 mixed oxides with different physicochemical properties and various activities were prepared by sol–gel method under acid-catalyzed and base-catalyzed conditions. X-ray diffraction (XRD), scanning electron microscope, and energy dispersive X-ray spectroscopy (EDX) analysis methods were used for the characterization of prepared samples. The photocatalytic activity was evaluated vs. the decolorization of methyl orange (MO) under black-light radiation. The influence of synthesis method on the physicochemical properties such as crystalline structure, crystal size, morphology, and photocatalytic activity of samples was investigated. The XRD patterns showed that the sample prepared by sol–gel method under acid-catalyzed conditions has pure anatase phase, whereas the sample prepared by sol–gel method under base-catalyzed conditions has anatase-rutile mixed phase. SiO2–TiO2 mixed oxides prepared under acid-catalyzed conditions showed higher photoactivity in comparison with SiO2–TiO2 mixed oxides prepared under base-catalyzed conditions for the sake of reducing the crystallite size and agglomerations. The figures-of-merit based on electric energy consumption (electrical energy per order (EEO)) were evaluated in the photodecolorization of MO in the presence of prepared samples. The results showed that less energy is consumed during the decolorization of MO in the presence of SiO2–TiO2 mixed oxides prepared by sol–gel method under acid-catalyzed conditions.

Catalytic dehydration of 2,3-butanediol over P/HZSM-5: effect of catalyst, reaction temperature and reactant configuration on rearrangement products

As a type of important bio-based vicinal diol, 2,3-butanediol could be transformed into methyl ethyl ketone and 2-methyl propanal through a pinacol rearrangement mechanism under acid catalysis conditions.

The Synthesis of New Organoselenium Heterocyclic Compounds: 2‐aryl‐4‐phenyl‐5,6,7,8‐tetrahydro‐4H‐selenochromenes

AbstractWe have explored the reactions of 2‐(3‐oxo‐1‐aryl‐3‐phenylpropyl)cyclohexanone (1–3) with hydrogen selenide in situ in conditions of acid catalysis, and synthesized new 2‐aryl‐4‐phenyl‐5,6,7,8‐tetrahydro‐4H‐selenochromenes (4–6).

Direct synthesis of carbon microspheres under acidic conditions and fenofibrate release

Mesoporous carbon microspheres were prepared through a novel direct method under acid-catalyzed conditions, which not only avoided the complicated, time-consuming property of hard-template method, but also avoided the nonporous nature of carbon microspheres by hydrothermal method. Fenofibrate (FFB) was selected as a model drug and was loaded through incipient wetness impregnation. In vitro drug release results further showed that FFB incorporation into the materials significantly increased its release rate compared with that of pure crystalline FFB.

Acid-catalyzed cascade radical addition/cyclization of arylacrylamides with ketones

A Brønsted acid catalyzed cascade radical addition/cyclization of arylacrylamides with ketones was described. The reaction tolerates a series of functional groups, such as nitro, methoxyl, carbonyl, bromo, chloro, fluoro, and trifluoromethyl groups. γ-Peroxyketones were also prepared using N-arylsulfonyl-acrylamides as substrates under acid-catalyzed conditions.

Out of the Blue! Azuliporphyrins and Related Azulene-Containing Porphyrinoids

Carbaporphyrinoids, porphyrin analogues that have one or more of the usual pyrrolic units replaced by carbocyclic rings, have been widely studied in recent years. These systems exhibit a wide range of properties and varying degrees of macrocyclic aromaticity. Azuliporphyrins have an azulene ring incorporated into the porphyrin framework and exhibit intermediary aromatic character. They were first prepared by reacting tripyrranes with 1,3-azulenedicarbaldehyde under acid-catalyzed conditions, although several alternative routes have been developed for preparing this intriguing carbaporphyrinoid system. Azuliporphyrins are easily protonated and this greatly enhances the diatropic properties for the macrocycle. Azuliporphyrins are also superior organometallic ligands and afford stable derivates with Ni(II), Pd(II), Pt(II), Ir(III) and Rh(III). Furthermore, tetraarylazuliporphyrins have been shown to undergo an oxidative metalation with copper(II) salts to generate a nonaromatic copper(II) complex. Treatment of azuliporphyrins with tert-butyl hydroperoxide under basic conditions triggers a ring contraction reaction to afford benzocarbaporphyrins. This appears to involve initial nucleophilic attack onto the seven-membered ring, followed by a Cope rearrangement and elimination of tert-butyl alcohol. These observations have led to investigations into related macrocyclic systems, including heteroazuliporphyrins with furan, thiophene or selenophene rings. In addition, an azulisapphyrin has also been reported. Dicarbaporphyrinoids with azulene-subunits have also been investigated. Azulene-containing fulvene dialdehydes have been shown to react with dipyrrylmethanes under acidic conditions to give 22-carbaporphyrins, and this system also shows intermediary aromatic character. In addition, a bis-azulenylmethane dialdehyde was shown to react with dipyrrylmethanes to give, following oxidation with DDQ, examples of diazuliporphyrins. This system was only stable in a protonated form but retained a degree of diatropic character. Reaction with palladium(II) acetate gave an unusual zwitterionic palladium(II) organometallic complex. These results demonstrate that azulene-containing porphyrinoids have unique properties and are superior precursors to organometallic derivatives.

Stable nonaromatic [20]dithiaporphyrin (2.1.1.1) macrocycles: synthesis, structure, spectral, electrochemical, and metal ion sensing studies.

Stable nonaromatic [20]dithiaporphyrin (2.1.1.1) macrocycles were synthesized in decent yields by condensing readily available butene-2,3-diyl-bisthiophene-2,5-diyl-bis(p-methoxyphenylmethanol) with different meso-aryl dipyrromethanes under mild acid-catalyzed conditions. The [20]dithiaporphyrin (2.1.1.1) macrocycles are the first members of the expanded porphyrin analogues of [18]dithiaporphyrin (1.1.1.1) and consist of two pyrroles and two thiophenes connected through five meso-carbon bridges. The [20]dithiaporphyrin macrocycles were confirmed by mass spectroscopy, 1D and 2D NMR spectroscopy, and X-ray crystallography. The X-ray structure revealed that the macrocycle is highly distorted and that the two thiophene rings are completely out-of-plane from the "mean-plane" defined by the dipyrromethene moiety and the two meso-carbons. In the absorption spectrum, the macrocycles showed one strong band at ∼420 nm and one weak band at ∼720 nm. The electrochemical studies revealed that the macrocycles are stable under redox conditions. The metal sensing studies indicated that these macrocycles have the potential to sense specific metal ions such as Hg(2+) ions. Two covalently linked dithiahomoporphyrin-fluorophore dyads were synthesized by coupling iodo-functionalized dithiahomoporphyrin with an ethynyl-functionalized fluorophore such as boron-dipyrromethene (BODIPY) and BF2-smaragdyrin under mild Pd(0) coupling conditions. The potential of these dyads as a fluorescent sensor for Hg(2+) was explored, and the studies indicated that both dyads can be used as fluorescent sensors.