SrCl2 as an efficient cocatalyst for acidic hydrolysis of methyl glycosides

SrCl2 was found to be the most efficient cocatalyst for the acidic hydrolysis of methyl glycosides after 26 kinds of most representative metal salts were screened. The SrCl2-cocatalyzed acidic hydrolysis of methyl glycosides is highlighted by short reaction times, less byproducts and high yields. A possible mechanism for the SrCl2-cocatalyzed hydrolysis is also proposed.     

Hydrolysis of Cellobiose in Dilute Sulpuric Acid and Under Hydrothermal Conditions

The sulfuric acid hydrolysis rate of cellobiose between pH 2 and 3 is directly proportional to the acid concentration. In good agreement with other authors, an activation energy of 133 kJ/Mol was found under these acidic conditions. The relation of the reaction rate constants for the glucose formation and glucose degradation (k₁/k₂) shows, in contrast to the hydrolysis of cellulose, little dependence on the temperature. Hydroxymethylfurfural, and to a lesser extent furfural, are glucose degradation products, which are also consumed but at a lower reaction rate than glucose. At pH values between 3 and 4.7 (pure water) strong deviations of the hydrolysis rates were observed. The formation of organic acids decreases the pH but has no influence on the reaction rate. This fact indicates that hydrothermolysis follows a reaction mechanism different from that of acidic hydrolysis.     

Hydrolytic reactions of diadenosine 5',5'-triphosphate

The hydrolysis of diadenosine 5',5'-triphosphate to AMP and ADP has been studied over a wide pH-range. Under acidic conditions the reaction shows a first-order dependence on the hydronium ion concentration. Below pH 3 the rate-increase begins to level off. From pH 6 to 9 the hydrolysis is slow and pH-independent. Base-catalysed hydrolysis is observed in NaOH-solutions. Under alkaline conditions an intramolecular nucleophilic attack on the phosphate producing 3',5'-cAMP is also observed, but it is slower than the intermolecular reaction. Depurination of the adenosine moieties competes with the hydrolysis both under acidic and alkaline conditions, but the mechanisms are different. The temperature-dependence of the hydrolysis of Ap(3)A and the depurination of adenosine moieties were studied under acidic conditions, and the activation parameters of the reactions were calculated. The results of the work reflect the fact that the negatively charged polyphosphate group is very resistant towards nucleophilic attack. An efficient catalysis is only observed under acidic conditions, where the phosphate group becomes protonated. General acids or bases did not catalyse the hydrolysis. Furthermore, hydroxide ion catalysed cleavage is only observed at high base concentrations and other negatively charged nucleophiles did not attack the phosphate groups of diadenosine polyphosphates.     

Role of the electrostatic interactions on the basic or acidic hydrolysis kinetics of poly-(d,l-lactide) monolayers

The hydrolysis kinetics of insoluble poly-(d,l-lactide) monolayers spread on basic or acidic aqueous subphase were followed by measuring simultaneously the decrease in the surface area at constant surface pressure and the evolution of the surface potential. An approach to analyse the role of the electrostatic interactions during the hydrolysis at alkaline pH, interpreting the surface potential data was developed. The theoretical predictions based on the idea of a random fragmentation of polymer molecules leading to the interfacial accumulation of charged insoluble products and solubilisation of small fragments describes well the experimental results. The reversibility of the hydrolysis/esterification reaction at acidic pH is taken into account.     

Theoretical study of hydrolysis of an imine oxime in aqueous solution and crystal structure and spectroscopic characterization of a platinum(II) complex containing the hydrolysis product

The hydrolysis of an imine oxime (ppeieoH) in neutral and acidic aqueous solutions was studied using DFT at the B3LYP/6-311G(d,p) level. The rate-determining step at the neutral and acidic aqueous solutions is the nucleophilic attack of the water molecules to the neutral or protonated imine C atom of ppeieoH. The activation energy is much lower in the acidic hydrolysis. The hydrolysis of ppeieoH results in the parent carbonyl oxime (inapH) and amine compounds with ΔG _cal values of 8.66 and 11.02 kJ mol^?1 in the neutral and acidic solutions, respectively. The hydrolysis of ppeieoH was observed experimentally during its reaction with K₂[PtCl₄] in an aqueous solution. The reaction yielded [PtCl(inap)(DMSO)], which contains only the hydrolysis product inap. The new platinum(II) complex was characterized spectroscopic techniques and X-ray diffraction. The platinum(II) ion is coordinated by chlorido, carbonyl oxime (inap), and DMSO ligands forming a distorted square-planar arrangement. The molecules of the platinum(II) complex were connected by weak non-conventional C–H···O and C–H···π hydrogen bonds.     

Role of the electrostatic interactions on the basic or acidic hydrolysis kinetics of poly-( , -lactide) monolayers

The hydrolysis kinetics of insoluble poly-( , -lactide) monolayers spread on basic or acidic aqueous subphase were followed by measuring simultaneously the decrease in the surface area at constant surface pressure and the evolution of the surface potential. An approach to analyse the role of the electrostatic interactions during the hydrolysis at alkaline pH, interpreting the surface potential data was developed. The theoretical predictions based on the idea of a random fragmentation of polymer molecules leading to the interfacial accumulation of charged insoluble products and solubilisation of small fragments describes well the experimental results. The reversibility of the hydrolysis/esterification reaction at acidic pH is taken into account.     

Equatorial contra axial polar substituents. The relation of a chemical reaction to stereochemical substituent constants

The established rates of glycoside hydrolysis reactions were analyzed using free energy relationship plots based on substituent constants that depend on whether the substituent is axial or equatorial. In all cases good correlations were found when assuming either that the transition state had a charged ring-oxygen atom or that it had a charged anomeric carbon atom. The spontaneous hydrolysis of 2,4-dinitrophenyl beta-glycopyranosides and the acidic hydrolysis of methyl beta-D-glycopyranosides were found to give a good correlation, when 100% charge at the ring-oxygen in the transition state of these reactions is assumed. The acidic hydrolysis of methyl alpha-glycopyranosides was found to give good correlations regardless of whether 100% charge at the ring-oxygen or 100% charge at the anomeric carbon was assumed. The findings clearly demonstrate how crucial the stereochemistry of even remote polar substituents is for their electronic effect on chemical reaction.     

Vibrational spectroscopic studies in the hydrolysis and condensation of chlorotrimethylsilane

Raman and infrared spectroscopy were used to study the hydrolysis and condensation of chlorotrimethylsilane (CTMC) in aqueous organic solvents. From the recorded spectra and their intensity variation with time, we were able to identify trimethylsilanol as the reaction intermediate or the hydrolysis product as well as hexamethyldisiloxane (HMDS) as the final condensation product. The measured Raman intensity of CTMS at different time revealed that hydrolysis of CTMS is first order in terms of the CTMS concentration. From the Raman spectra collected under different conditions, it was noted that condensation reaction rates is faster in neutral condition than in acidic condition.     

Controlled acid hydrolysis and kinetics of flavone C-glycosides from trollflowers

Acid hydrolysis mechanisms of orientin-2"-O-galactopyranoside(OGA),orientin and other flavone C-glycosides in the trollflowers[Trollius chinensis Bunge) were studied in this report for the first time.Hydrolysis parameters including temperature,acidity,solvent and reaction time were comprehensively investigated.OGA could be hydrolyzed to orientin,followed by an isomerization to isoorientin via a reversible Wessely-Moser rearrangement reaction under stronger acidic conditions.A first-order kinetic model fitted the hydrolysis process of OGA well.Under the optimal hydrolysis conditions of 80 ℃,1.0 mol/L H~+ and 7 h reaction time,about 77%OGA was transformed to orientin with no detectable isoorientin.These results could be helpful for better understanding of the acid hydrolysis kinetics of flavone C-glycosides,as well as the preparation of these valuable components under controlled acid hydrolysis conditions.     

The Hydrolysis of Phosphinates and Phosphonates: A Review

Phosphinic and phosphonic acids are useful intermediates and biologically active compounds which may be prepared from their esters, phosphinates and phosphonates, respectively, by hydrolysis or dealkylation. The hydrolysis may take place both under acidic and basic conditions, but the C-O bond may also be cleaved by trimethylsilyl halides. The hydrolysis of P-esters is a challenging task because, in most cases, the optimized reaction conditions have not yet been explored. Despite the importance of the hydrolysis of P-esters, this field has not yet been fully surveyed. In order to fill this gap, examples of acidic and alkaline hydrolysis, as well as the dealkylation of phosphinates and phosphonates, are summarized in this review.     

甲基丙烯酸3-三甲氧基硅丙酯/苯乙烯细乳液共聚合过程中的水解及缩合反应

研究了甲基丙烯酸3-三甲氧基硅丙酯(MPS)和苯乙烯(St)细乳液聚合过程中的水解及缩合反应.用气相色谱仪测定聚合过程中水解产物——甲醇的含量来研究MPS的水解度.MPS分子主要在细乳液液滴与水的界面以及乳胶粒与水的界面上发生水解反应.MPS和St比例、介质pH值、乳化剂用量、引发剂类型和用量都会影响MPS的水解程度.缩合产物用29Si固态核磁共振表征,中性条件下,缩合反应受到抑制,在高MPS/St比例的体系中也只生成少量缩合产物.酸性和碱性条件下,缩合产物量均增加,但碱性条件下,体系中仍有一定数量未缩合的硅氧烷存在,这与细乳液聚合独特的液滴成核机理及聚合过程中较少液滴间物质交换有关.     

Theoretical studies on the mechanism of acid-promoted hydrolysis of N-formylaziridine in comparison with formamide

[reaction: see text] We present an ab initio study of the acid-promoted hydrolysis reaction mechanism of N-formylaziridine in comparison with formamide. Since the rate of amide hydrolysis reactions depends on the formation of the tetrahedral intermediate, we focused our attention mainly on the reactant complex, the tetrahedral intermediate, and the transition state connecting these two stationary points. Geometries were optimized using the density functional theory, and the energetics were refined using ab initio theory including electron correlation. Solvent effects were investigated by using polarizable continuum method calculations. The proton-transfer reaction between the O-protonated and N-protonated amides was investigated. In acidic media, despite that the N-protonated species is more stable than the O-protonated one, it is predicted that both N-protonated and O-protonated pathways compete in the hydrolysis reaction of N-formylaziridine.     

丙烯酸β-羧乙酯-苯乙烯共聚物缩合异烟肼的合成及其水解释放研究

<正> 大分子载体药物是精细高分子合成的一个重要研究领域,作为药物载体的大分子骨架需有良好的生物相容性及控制释放能力。本文采用具有较长柔性侧支链的丙烯酸β-羧乙酯(APA)-苯乙烯(St)共聚物作载体,并通过羧基与抗结核药物异烟肼反应,制备出毒性较低并能控制释放的大分子载体异烟肼药物。     

Kinetic study of cyanoguanidine resin formation: acid hydrolysis of hydroxymethyl and methoxymethyl cyanoguanidine

The hydrolysis of hydroxymethyl cyanoguanidine and methoxymethyl cyanoguianidine in acidic aqueous media were studied by analyzing the eluted formaldehyde and the reaction products. Dihydroxymethyl cyanoguanidine released two formaldehydes with different rates because one of the two hydroxymethyl groups is intramolecularly interactive through the hydrogen bond. Methanol dissociation from methoxymethyl cyanoguanidine was seven to eight times faster than the dissociation of hydroxymethyl group, and the overall hydrolysis kinetics were similar to those of hydroxymethyl cyanoguanidine.     

Mechanistic insights into the hydrolysis of a nucleoside triphosphate model in neutral and acidic solution

Nucleoside triphosphate hydrolysis is an essential component of all living systems. Despite extensive research, the exact modus and mechanism of this ubiquitous reaction still remain elusive. In this work, we examined the detailed hydrolysis mechanisms of a model nucleoside triphosphate in acidic and neutral solution by means of ab initio simulations. The timescale of the reaction was accessed through use of an accelerated sampling method, metadynamics. Both hydrolyses were found to proceed via different mechanisms; the acidic system reacted by means of concerted general acid catalysis (found to be a so-called D(N)A(N)A(H)D(xh) mechanism), whereas the neutral system reacted by way of a different mechanism (namely, D(N)*A(N)D(xh)A(H)). A neighboring water molecule took on the role of a general base in both systems, which has not been seen before but is a highly plausible reaction path, meaning that substrate-assisted catalysis was not observed in the bulk water environment.     

α-甲基丙烯酸甲酯-二乙烯苯共聚体碱性水解反应的研究

本文合成3α-甲基丙烯酸甲酯-二乙烯苯大孔共聚体(MMA-DVB),研完了诸因素对碱性水解反应的影响.结果表明,以10—100％糖醇为溶胀剂,以60％ NaOH热水溶液为水解剂,在150℃反应4—10小时,酯基水解率可达90—95％。制得的弱酸离子交换树脂,其交换容量为9meq/g。树脂机械强度良好。     

A Cascade‐Reaction Nanoreactor Composed of a Bifunctional Molecularly Imprinted Polymer that Contains Pt Nanoparticles

This study was aimed at addressing the present challenge of cascade reactions, namely, how to furnish the catalysts with desired and hierarchical catalytic ability. This issue was addressed by constructing a cascade‐reaction nanoreactor made of a bifunctional molecularly imprinted polymer containing acidic catalytic sites and Pt nanoparticles. The acidic catalytic sites within the imprinted polymer allowed one specified reaction, whereas the encapsulated Pt nanoparticles were responsible for another coupled reaction. To that end, the unique imprinted polymer was fabricated by using two well‐coupled templates, that is, 4‐nitrophenyl acetate and 4‐nitrophenol. The catalytic hydrolysis of the former compound at the acidic catalytic sites led to the formation of the latter compound, which was further reduced by the encapsulated Pt nanoparticles to 4‐aminophenol. Therefore, this nanoreactor demonstrated a catalytic‐cascade ability. This protocol opens up the opportunity to develop functional catalysts for complicated chemical processes.     

Effect of acid and base catalyzed hydrolysis on the yield of phenolics and antioxidant activity of extracts from germinated brown rice (GBR)

The influence of both acidic and basic hydrolysis on the yield, total phenolic content and antioxidative capacity of methanolic extract of germinated brown rice (GBR) was studied. Total phenolic content (TPC), total flavonoid content (TFC), 2,2'-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging, 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid (ABTS) radical cation scavenging, and ferric reducing antioxidant power (FRAP) tests were used for the measurement of antioxidant ability. There was a significant difference p < 0.05) in the TPC and DPPH radical scavenging assay results when comparing neutral with acidic and basic catalysed hydrolysis. The yield of the crude extract was slightly higher in acidic hydrolysis than in basic hydrolysis p > 0.05). The TPC and TFC were highest in acidic hydrolysis. A significant correlation was observed between ABTS radical cation scavenging and FRAP. The antioxidant activity measured using DPPH radical scavenging assay showed high activity in acidic hydrolysis, while the ABTS radical cationscavenging activity and FRAP showed the highest values in basic hydrolysis. The samples were further evaluated using HPLC to determine the individual phenolic concentrations in different hydrolytic media contributing to the antioxidant effects. This study revealed that acidic and basic hydrolysis can improve the yield, phenolic content, and antioxidant activity of germinated brown rice.     

Regioselective Lactonization of α‐(2→8)‐Trisialic Acid

A simple and selective method has been developed to obtain both monolactones of the title compound, a model compound for biologically important polyneuraminic acid derivatives: acidic lactonization and alkaline hydrolysis of dilactone 1 . The two monolactonized trimers can be separated by capillary electrophoresis, and then distinguished by enzymatic hydrolysis with neuraminidase; only the 2‐monolactone undergoes reaction.     

Synthesis of primary amines by the electrophilic amination of Grignard reagents with 1,3-dioxolan-2-one O-sulfonyloxime

Primary amines are prepared by the electrophilic amination of Grignard reagents with 4,4,5,5-tetramethyl-1,3-dioxolan-2-one O-phenylsulfonyloxime and the acidic hydrolysis of the resulting imines. [reaction: see text]