Mild Acid Catalyst Research Articles

Glycerol Acetalization in Cyclopentyl Methyl Ether with Mild Acid Catalysts

AbstractReaction of glycerol with aldehydes and ketones is a strategy widely studied in literature to valorize this bioproduct. A Brønsted or Lewis acid is normally used to activate the carbonyl function and various strategies adopted to drive the equilibrium to the products. In this study ammonium salts as catalysts, and removal of water by azeotropic distillation of cyclopentyl methyl ether, permit the conversion of glycerol into acetals obtained as mixture of dioxanes and dioxolanes determined by 1H‐NMR. Under the optimized conditions, the products could be obtained in excellent yield without using excess of reactants and the solvent was recycled efficiently.

Mild Acidic Charcoal Catalyzed Synthesis of 3,4-dihydropyrimidin-2(1H)-one/-thione Derivatives

A green and efficient method for the multicomponent synthesis of 3,4-dihydropyrimidin-2(1H)-ones and -thiones using acetic acid supported on activated charcoal as a mild acid catalyst in ethanol under both conventional as well as microwave irradiation conditions has been developed. The catalyst system found more efficient under microwave irradiation conditions than conventional conditions with shorter reaction times and excellent yields.

Study of scrambling in porphyrin forming reactions: Synthesis, structure, photophysical, electrochemical and antimicrobial studies

Three classes of scrambled porphyrins (Class 1–3) were synthesized by MacDonald type 2+2 condensation reactions of electron deficient dipyrromethanes with aldehyde and its complementary reactions in presence of mild acid catalysts. Overall, BF3·OEt2 catalyzed reactions yield more scrambled products than TFA catalyzed. All the scrambled porphyrins were characterized by the conventional spectroscopic methods. A marginal red shift (2–3nm) was observed in Soret band upon installation of two or three 4-cyanophenyl/4-carboxymethylphenyl groups at the meso-position of porphyrin 1 with the subsequent removal of pentafluorophenyl groups. The first emission exhibits a bathochromic shift of 4–5nm when a pentafluorophenyl ring detached from 1 with the subsequent addition of 4-cyanophenyl group; first emission intensity is less compared to the second one which increases as it moves from 2 to 5. The copper complex, Cu-8 has been structurally characterized by single crystal X-ray diffraction analysis and the role of weak intermolecular interactions in their crystal packing has been analyzed and quantified using Hirshfeld surface analysis. Electrochemical studies revealed that a gradual increase of positive shift in the first reduction/oxidation potentials of Class 1 and 2 porphyrins upon installation of pentafluorophenyl ring with subsequent removal of 4-cyanophenyl/4-carboxymethylphenyl ring on either H2T(4-CNP)P or H2T(4-CMP)P; the HOMO−LUMO energy gap is found to be decreased in Class 1 porphyrins whereas it is increased in Class 2 porphyrins. The highest antimicrobial activity is observed for porphyrin 5.

Fructo-Oligosaccharide Production from Inulin Through Partial Citric or Phosphoric Acid Hydrolyses

Purified inulin from Dahlia tubers was partially hydrolyzed to form fructo-oligosaccharides by using citric or phosphoric acids (pH, 2.0-2.5) as mild acid catalysts. The ideal kinetic conditions to ensure a high yield of fructo-oligosaccharides relative to free fructose were a temperature range of 85°C-95°C, a hydrolysis time of 15-25 minutes, and a catalyst pH of 2.5. At the higher temperature and the longest hydrolysis time, an inversion of the product ratio occurred. Under these conditions, co-generation of hydroxymethylfurfural occurred, and it was eliminated by activated charcoal. Unlike in classic hydrolysis with hydrochloric or sulfuric acid, deionization of the actual hydrolysates was not necessary because the catalyst neutralization with common bases results in the formation of co-nutrients with alternative uses as foods or fermentation substrates. These whole hydrolysates can be advantageously added as nutraceuticals to carbonated beverages and acidic foods, such as soft drinks and yogurts.

First application of hexaaquaaluminium(III) tetrafluoroborate as a mild, recyclable, non-hygroscopic acid catalyst in organic synthesis: a simple and efficient protocol for the multigram scale synthesis of 3,4-dihydropyrimidinones by Biginelli reaction

For the first time hexaaquaaluminium(III) tetrafluoroborate has been used as a mild acid catalyst in organic synthesis. A simple method of its preparation based on the reaction of aluminium triisopropoxide and tetrafluoroboric acid in isopropanol afforded catalyst of high purity and activity. The three-component Biginelli condensation of acetoacetate esters, urea and aldehydes catalyzed by 10 mol % of [Al(H 2O) 6](BF 4) 3 in refluxing acetonitrile afforded 3,4-dihydropyrimidonones in good to high yields on multigram scales. The tolerance to acid sensitive reactants such as thienyl and furyl carbaldehydes, applicability to sterically hindered β-ketoesters and simple recyclability without losing catalytic activity make this catalyst as good replacement to literature methods. The mechanism of the reaction includes formation of the so called ‘ureido-crotonate’ rather than corresponding acylimino intermediate as found with Brønsted type catalysts.

Synthesis of Isocoumarin via PTSA-Catalyzed Annulation of Diarylalkynes

p-Toluenesulfonic acid (PTSA) in ethanol was used as a mild acid catalyst for the annulation of various functionalized diarylalkynes under microwave irradiation. This metal-free process allowed the synthesis of a range of 3-aryl-substituted isocoumarins in good yields.

First Principles Studies on Boron Sites in Zeolites

A systematic computational investigation on protonated and nonprotonated boron-containing zeolites (boralites), performed by using different periodic density functional theory approximations, is presented. Both minimum energy structures and finite temperature behavior of model boron sodalites were analyzed. All of the adopted computational schemes agree in predicting an acid site composed of a silanol Si-OH group loosely linked to a planar BO(3) structure in the protonated system and a BO(4) tetrahedral site in the sodium-containing zeolite. Calculated structural and vibrational properties are in line with experimental data. Comparisons of the protonated boralite site with Al and Ga zeolitic acid sites are discussed as well. Results indicate that this class of mild acid catalysts is characterized by significant framework flexibility and pronounced thermal effects due to the loosely bound acid site.

PVP-SO2 complex as a solid mild acid catalyst for efficient one pot, three component, Strecker synthesis of α−aminonitriles

Solid poly(4-vinylpyridine)-SO2 complex was prepared and used as a mild solid acid catalyst for simple and efficient three component Strecker synthesis of α-aminonitriles in high yield and purity.

Effect of Steam Treatment of Alperujo on the Composition, Enzymatic Saccharification, and in Vitro Digestibility of Alperujo

The solid waste from two-phase olive oil extraction or "alperujo" was submitted to steam treatment at high pressure or temperature, 200 degrees C for 5 min, in the presence and absence of mild acid catalyst. This treatment made easier the separation of the solid and liquid fractions. Besides the recovery of certain valuable components from the liquid fraction (the antioxidant hydroxytyrosol, low molecular weight oligosaccharides, glucose, mannitol, etc.), the major components of the solid residue could be also exploited. In this study, changes in composition of alperujo due to steam treatment were determined. The process reduced appreciably the hemicellulose concentrations (75-88%), removed a substantial portion of Klason lignin and protein (50%), and led to an extensive solubilization of alperujo (55-67%). Cellulose was very resistant to autohydrolysis and acid-catalyzed hydrolysis, so the solid residue was enriched in fat (13-18 g/100 g of dry steam-treated alperujo) and cellulose (15-25 g/100 g of dry and defatted steam-treated alperujo). The steam-treated material can be efficiently saccharified with commercial cellulase. The best hydrolysis yields were attained, up to 80%, when the treated material was post-treated with NaOH. The possibility of using this steam-treated alperujo in animal feeding was evaluated by an in vitro digestibility test, using the pepsin-cellulase method. The treatment affected positively the nutritional characteristics of alperujo with an increase in its in vitro (dry and organic matter) digestibility (8-10% higher than untreated material). In vitro digestibility and cellulose accessibility to enzymatic hydrolysis were improved by the alkali post-treatment.

A Survey of Acid Catalysis and Oxidation Conditions in the Two‐Step, One‐Flask Synthesis of Meso‐Substituted Corroles via Dipyrromethanedicarbinols and Pyrrole.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A survey of acid catalysis and oxidation conditions in the two-step, one-flask synthesis of meso-substituted corroles via dipyrromethanedicarbinols and pyrrole.

The reaction of dipyrromethanedicarbinols with pyrrole leading to meso-substituted corroles was investigated to determine whether mild acid catalysts [Dy(OTf)(3), Yb(OTf)(3), Sc(OTf)(3), and InCl(3)] known to provide porphyrins from dipyrromethanecarbinol species while suppressing undesired reversibility (resulting in scrambling) are applicable to reactions affording corrole, and to explore the requirements of the oxidation step. We examined a model reaction leading to meso-triphenylcorrole (TPC) to survey the effect of acid catalyst, acid concentration, ratio of pyrrole to dipyrromethanedicarbinol, oxidant, oxidant quantity, and reaction time on the yield of TPC (by UV-vis) in reactions performed at room temperature in CH(2)Cl(2). Key to this survey was a modification of the well-known spectrophotometric method for monitoring reactions leading to porphyrin. The survey revealed that TPC could be prepared via a subset of the mild acid catalysts [Dy(OTf)(3) and Yb(OTf)(3)], and a preparative-scale reaction afforded an isolated yield of TPC of 49%, devoid of porphyrin. Suppression of reversible processes was further demonstrated by the synthesis of three corroles bearing different meso substituents in defined locations in isolated yields ranging from 50% to 80%. The reaction conditions were applicable to a dipyrromethanedicarbinol bearing electron-withdrawing pentafluorophenyl substituents-provided that the reaction time of the condensation step was increased. We identified circumstances under which DDQ can cause severe interference with the detection and isolation of some corroles, we found that the yield and purity of the corrole depend on judicious selection of oxidation conditions, and we assessed the sensitivity toward light of dilute solutions of the corroles prepared in this study.

Living cationic polymerisation of styrene in an ionic liquid.

For the first time, living cationic polymerisation of styrene has been carried out in room temperature ionic liquids under mild reaction conditions and using mild acid catalysts (e.g. organoborate acids) to obtain polymers of narrow polydispersity.

AlPO4catalyzed Diels-Alder reaction of cyclopentadiene with (-)-menthyl acrylate. Influence of catalyst surface properties

Different synthetic AlPO4 systems are effective yet mild acid catalysts for the heterogeneous cycloaddition reaction of cyclopentadiene with (-)-menthyl acrylate. The reaction proceeds selectively under mild conditions and in a relatively short reaction time with an almost total conversion, a high endo/exo ratio, and a reasonable asymmetric induction. When the reactions are carried out without solvent, some correlations are obtained between the number of acid sites, titrated with pyridine, and reaction yields, endo/exo and diastereofacial selectivities. The positive influence of surface area of catalysts is also determined. However, the lack of good correlations between reaction results and surface properties of the catalysts indicates the influence of some other factors.

Synthesis of Alkyl Fructosides

AbstractThe anomeric alkylation of D‐fructose is efficiently catalyzed by mild acid catalysts. Degradation of fructose is negligible under the conditions applied.

A New, Mild Heterogeneous Catalyst for the Tetrahydropyranylation of Alcohols and Phenols

The hydrochloride salt of a cross-linked macroreticular poly(4-vinylpyridine) resin in bead form is an effective, yet mild acid catalyst for the tetrahydropyranylation of alcohols (primary, secondary, and tertiary) and phenols. The reaction is carried out in the presence of excess dihydropyran without the formation of troublesome oligomeric pyrans. High yields of the desired ethers are obtained even in reactions with alcohols having steric restrictions or acid sensitive amine functionalities.

Acid catalysed reactions between diols and vinyl-ethers in basic solvents towards a selective protection of polyols by 2,3-dihydro-4H-pyran

Acid catalysed synthesis of THP ethers of 1,3-butanediol takes place much more selectively and in high yields if DMSO is used as solvent, instead in CHCl 3, even with mild acid catalysts, rearranged 1,3-dioxans are obtained.

A quantitative study of crosslinking cotton with N‐methylol acrylamide

AbstractCotton was acrylamidomethylated by applying N‐methylol acrylamide to it with the aid of a mild acid catalyst. When the molal ratio of N‐methylol acrylamide to anhydroglucose exceeded about 0.2, the efficiency of this reaction was suddenly reduced and the variation of density with addon departed from linearity. These and other available facts indicated that only one of the three hydroxyls in cellulose, probably the one in the 6‐position, was involved in the acrylamidomethyl ether formation and that cotton was about 20% accessible to this reagent. When acrylamidomethylated cotton was treated with free radical or alkaline catalysts, the double bonds became partially saturated and the mechanical properties changed in a spectacular manner. In particular, the resilience of the fabric, as measured by crease recovery, was improved. Analysis of double bond reaction at various levels of acrylamidomethyl content of the fabric indicated that free radical catalysis caused homopolymerization of the pendant double bonds, that alkaline catalysis in the presence of water resulted in Michael condensation between double bonds and the hydroxyls of cellulose, and that these two reactions competed with each other when the alkaline aftertreatment was conducted in dry state. These reactions crosslinked the fabric, and the crosslink content could be calculated from the difference of molal methylene and double bond contents.The crease recovery reached the maximum attainable value characteristic for the method of catalysis when the ratio of accessible anhydroglucose units to crosslinks was 4 to 5. When the crosslinked fabrics were hydrolyzed in acid, the crease recovery increment produced by crosslinking was eliminated after about half of the crosslinks were broken. The residual crosslinks did not contribute to crease recovery. Dry state crosslinking treatments reduced the moisture regain, increased the density, and had no effect on the x‐ray pattern. In contrast to this, wet state crosslinking in‐increased the moisture regain, changed the x‐ray pattern, and, under certain conditions, reduced the density. These results indicate that wet state crosslinking increased the amorphous portion of cotton. Wet state crosslinking lead to higher wet than dry crease recovery whereas the opposite was true for dry state crosslinking. Although the alkaline catalyst did not degrade the fabric, alkali catalyzed crosslinking substantially reduced the tensile strength. Free radical catalysis was more favorable for tensile strength, in spite of the fact that it degraded the fabric in the absence of crosslinking agent.