scholarly journals Alkali metal cations can inhibit non-covalent catalysis

2021 ◽  
Author(s):  
Nazar Rad ◽  
Volodymyr Sashuk
Keyword(s):  
Reaction Rate ◽  
Metal Cations ◽  
Inorganic Salts ◽  
Phenyl Acetate ◽  
Supramolecular Catalysis ◽  
Hydronium Ions ◽  
Binding Data ◽  
Covalent Catalysis ◽  
Hydrolysis Of ◽  
Acetate Derivative

The study concerns the effect of inorganic salts on supramolecular catalysis. The model reaction is the acid hydrolysis of the ammonium phenyl acetate derivative promoted by cucurbit[7]uril macrocycle. When salt is absent, the macrocycle is insensitive to the ionic strength of the solution, and the reaction rate linearly depends on the concentration of hydronium ions (H3O+). After the addition of inorganic salts, in particular, Na+ and K+ ions, the catalytic effect of the macrocycle is suppressed. The kinetic and binding data collected by us evidence the formation of the ternary complexes between the cations, macrocycle, and substrate, which are less prone to H3O+ attack. This type of inhibition corresponds to a rare uncompetitive model in contrast to a more common competitive one that relies on the displacement of the substrate. This study shows that special care must be taken when studying catalysis in solutions that contain metal cations, such as regular water and inorganic buffers.

Upgrading to nutrient removal by means of internal carbon from sludge hydrolysis

1994 ◽  
Vol 29 (12) ◽  
pp. 31-40 ◽  
Author(s):  
Pia Prohaska Brinch ◽  
Kim Rindel ◽  
Kathryn Kalb
Keyword(s):  
Reaction Rate ◽  
Wastewater Treatment Plants ◽  
Secondary Treatment ◽  
N Removal ◽  
Sludge Hydrolysis ◽  
Speed Up ◽  
On Line ◽  
Full Scale Tests ◽  
Biological Phosphorus ◽  
Hydrolysis Of

Due to the introduction of stricter nutrient effluent standards, many existing wastewater treatment plants performing only primary or secondary treatment are about to be upgraded. As the space available at the plants is, however, often limited, processes are required which will accommodate the need for increased treatment capacity without requiring much more space. In the hydrolysis of primary or pre-precipitated sludge direct-degradable organic carbon is produced which can speed up the reaction rate and increase both biological phosphorus and nitrogen removal. Full-scale tests with dosing of hydrolysate for biological P and N removal, respectively, have shown that this is a most viable process. The use of on-line monitoring has improved the process further.

Cyclization and acid-catalyzed hydrolysis of O-benzoylbenzamidoximes

1986 ◽  
Vol 51 (12) ◽  
pp. 2786-2797
Author(s):  
František Grambal ◽  
Jan Lasovský
Keyword(s):  
Reaction Rate ◽  
Kinetic Isotope ◽  
Acid Base Equilibrium ◽  
Mineral Acids ◽  
Kinetics Of Formation ◽  
Acid Catalyzed ◽  
Ph Scale ◽  
Kinetics Of ◽  
Hydrolysis Of ◽  
Derivatives Of

Kinetics of formation of 1,2,4-oxadiazoles from 24 substitution derivatives of O-benzoylbenzamidoxime have been studied in sulphuric acid and aqueous ethanol media. It has been found that this medium requires introduction of the Hammett H0 function instead of the pH scale beginning as low as from 0.1% solutions of mineral acids. Effects of the acid concentration, ionic strength, and temperature on the reaction rate and on the kinetic isotope effect have been followed. From these dependences and from polar effects of substituents it was concluded that along with the cyclization to 1,2,4-oxadiazoles there proceeds hydrolysis to benzamidoxime and benzoic acid. The reaction is thermodynamically controlled by the acid-base equilibrium of the O-benzylated benzamidoximes.

scholarly journals Vinyl ether hydrolysis. XIV. 2-Methoxy-2,3-dihydropyran: concurrent reaction of vinyl ether and acetal functional groups

1980 ◽  
Vol 58 (21) ◽  
pp. 2199-2202 ◽  
Author(s):  
R. A. Burt ◽  
Y. Chiang ◽  
A. J. Kresge
Keyword(s):  
Vinyl Ether ◽  
Isotope Effect ◽  
Reaction Rate ◽  
Functional Group ◽  
Minor Amount ◽  
Cyanoacetic Acid ◽  
Buffer Solutions ◽  
Hydrogen Isotope Effect ◽  
A Minor ◽  
Hydrolysis Of

The hydrolysis of 2-methoxy-2,3-dihydropyran shows a normal isotope effect (kH/kD > 1) under catalysis by the hydrogen ion and gives an accurately linear dependence of reaction rate upon undissociated acid concentration in cyanoacetic acid and formic acid buffer solutions. This substrate, therefore, unlike its higher homolog, 9-methoxyoxacyclonon-2-ene, provides no evidence in support of an anything but a normal mechanism for vinyl ether hydrolysis. Analysis of the hydrogen isotope effect suggests that a minor amount (8%) of this hydrolysis occurs via reaction of the acetal functional group.

Effects of critical points of two microemulsion systems on the reaction rate of basic hydrolysis of crystal violet

2017 ◽  
Vol 231 ◽  
pp. 655-662 ◽  
Author(s):  
Lvjie Yang ◽  
Yunhui Xiang ◽  
Lin Chen ◽  
Dan Zhang ◽  
Chenyi Wu ◽  
...  
Keyword(s):  
Crystal Violet ◽  
Critical Points ◽  
Reaction Rate ◽  
Basic Hydrolysis ◽  
Hydrolysis Of

Basicity and acidity promote hydrolysis of methyl nitrate in aqueous aerosols

2020 ◽  
Author(s):  
Fatemeh Keshavarz ◽  
Theo Kurtén ◽  
Hanna Vehkamäki
Keyword(s):  
Nitric Acid ◽  
Nitrous Acid ◽  
Rate Coefficients ◽  
Alkyl Nitrates ◽  
Hydronium Ions ◽  
Hydroxyl Ion ◽  
Solvent Model ◽  
Methyl Nitrate ◽  
Hydrolysis Of ◽  
Aqueous Aerosols

<p>The chemistry of organic nitrates (ONs), also known as alkyl nitrates (RONO<sub>2</sub>), controls the lifetime of nitrogen oxides in continental areas, which in turn affects air quality and varies ozone concentration throughout the troposphere. ONs can be emitted to the troposphere from marine sources. Also, they can be produced in the atmosphere through addition of NO to peroxy radicals or through the reaction of NO<sub>3</sub> radicals with volatile organic compounds. Atmospheric ONs may subsequently undergo oxidation or photolysis, in both gas and aerosol phases, or hydrolysis in aqueous aerosols. Though some recent studies have believed acid-catalysis promotes hydrolysis of ONs, earlier studies have claimed that acids have no effect on ON hydrolysis, and that it is the hydroxyl ion that can improve the hydrolysis process. The limited number of experimental studies performed so far have left this conflict with no appropriate answer, as mechanistic insight and full kinetics details have been partially or completely missing for the studied ONs. We report the detailed mechanism of methyl nitrate hydrolysis in acidic, neutral and basic conditions, in addition to analyzing the degradation of methyl nitrate into formaldehyde and nitrous acid in the presence of water and hydronium ions. According to the potential energy surfaces obtained at the CCSD(T)/cc-pVDZ//ωB97X-D/def2-TZVP level of theory (including the SMD solvent model) along with the rate coefficients estimated using asymmetric Eckart tunneling-corrected transition state theory (TST), mediation of water molecules and hydronium ions hinders degradation of methyl nitrate into formaldehyde and nitrous acid and, in general, this decomposition reaction is kinetically unfavorable. Furthermore, neutral hydrolysis of methyl nitrate is extremely slow with pseudo-first order rate coefficients (k; 298 K and 1 atm) falling below 10<sup>-27</sup> s<sup>-1</sup>. Similarly, hydrolysis of methyl nitrate by hydronium ions is observed to be extremely slow (k < 10<sup>-27</sup> s<sup>-1</sup>). However, under acidic conditions, protonation of methyl nitrate is quite feasible with the protonation Gibbs free energy of -429.1 kJ mol<sup>-1</sup>, at 298 K and 1 atm, and protonated methyl nitrate can hydrolyze into protonated methanol and nitric acid much faster relative to the hydronium ion-based and neutral hydrolysis (k = 3.83 s<sup>-1</sup>). On the other hand, the hydroxyl ions generated under basic conditions can hydrolyze methyl nitrate readily to give methanol and nitric acid (k = 6.63 × 10<sup>3</sup> s<sup>-1</sup>), or formaldehyde, nitrate and water (k = 9.40 × 10<sup>6</sup> s<sup>-1</sup>). In addition, regardless of the limitation on the rate of solvent-phase chemical reactions by the rate of diffusion, basic hydrolysis can produce methoxy ions and nitric acid quite fast (k = 8.95 × 10<sup>9</sup> s<sup>-1</sup>). In other words, methyl nitrate hydrolysis is faster in basic aerosols (i.e. some marine aerosols) and, to a less extent, in highly acidic aqueous aerosols (e.g. haze and urban aerosols).       </p>

scholarly journals Catalysis of Rice Straw Hydrolysis by the Combination of Immobilized Cellulase fromAspergillus nigeronβ-Cyclodextrin-Fe3O4Nanoparticles and Ionic Liquid

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Po-Jung Huang ◽  
Ken-Lin Chang ◽  
Jung-Feng Hsieh ◽  
Shui-Tein Chen
Keyword(s):  
Ionic Liquid ◽  
Rice Straw ◽  
Reaction Rate ◽  
Magnetic Particles ◽  
Initial Reaction Rate ◽  
Initial Reaction ◽  
High Concentration ◽  
Solid Reaction ◽  
Immobilized Cellulase ◽  
Hydrolysis Of

Cellulase fromAspergillus nigerwas immobilized ontoβ-cyclodextrin-conjugated magnetic particles by silanization and reductive amidation. The immobilized cellulase gained supermagnetism due to the magnetic nanoparticles. Ninety percent of cellulase was immobilized, but the activity of immobilized cellulase decreased by 10%. In this study, ionic liquid (1-butyl-3-methylimidazolium chloride) was introduced into the hydrolytic process because the original reaction was a solid-solid reaction. The activity of immobilized cellulase was improved from 54.87 to 59.11 U g immobilized cellulase−1at an ionic liquid concentration of 200 mM. Using immobilized cellulase and ionic liquid in the hydrolysis of rice straw, the initial reaction rate was increased from 1.629 to 2.739 g h−1 L−1. One of the advantages of immobilized cellulase is high reusability—it was usable for a total of 16 times in this study. Compared with free cellulase, magnetized cellulase can be recycled by magnetic field and the activity of immobilized cellulase was shown to remain at 85% of free cellulase without denaturation under a high concentration of glucose (15 g L−1). Therefore, immobilized cellulase can hydrolyze rice straw continuously compared with free cellulase. The amount of harvested glucose can be up to twentyfold higher than that from the hydrolysis by free cellulase.

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