The reaction of isocyanates with bisulphite salts

1972 ◽  
Vol 25 (12) ◽  
pp. 2583 ◽  
Author(s):  
GB Guise ◽  
MB Jackson ◽  
JA Maclaren
Keyword(s):  
Room Temperature ◽  
Order Rate Constant ◽  
Phenyl Isocyanate ◽  
Water Soluble ◽  
First Order ◽  
Rate Of Reaction ◽  
Solids Content ◽  
Ph Range ◽  
Increasing Temperature ◽  
Insoluble Polymers

Aliphatic isocyanates react rapidly and quantitatively with aqueous bi- sulphite solutions to form stable water-soluble adducts which are salts of N-alkyl-carbamyl sulphonio acids. Phenyl isocyanate gives lower yields of the corresponding adduct which is less stable in water. The rate of reaction of n-butyl isocyanate with bisulphite increases with increasing pH and is proportional to [OH-]over the pH range from 5 to 8. The rate of decomposition of the butyl isocyanate-bisulphite adduct increases with increasing temperature and pH. A plot of the logarithm of the initial first-order rate constant for the decomposition of the adduct against pH is linear over the pH range from 2 to 7 and has a slope of 0.57 � 0.05. Water-insoluble polymers with aliphatic isocyanate groups do not form bisulphite adducts under the conditions which are suitable for simple isocyanates. However, the addition of water-soluble organic solvents such as dioxan and the lower alcohols enables the preparation of water-soluble bisulphite adducts which are indefinitely stable at room temperature and low pH. The relative quantity of the organic solvent must be kept within specific limits which depend on the nature of the prepolymer, the solids content of the final product, and the nature of the organic co-solvent.

Kinetic Analysis of Catalytic Reductive Dechlorination of Chlorobenzene in Aqueous Solutions

2013 ◽  
Vol 777 ◽  
pp. 65-70 ◽  
Author(s):  
Hong Yi Zhou ◽  
Si Liang ◽  
Si Si Zeng ◽  
Shuang Jian Lei
Keyword(s):  
Rate Constant ◽  
Organic Contaminants ◽  
Room Temperature ◽  
Solution Ph ◽  
First Order ◽  
Effective Removal ◽  
Chlorinated Organic ◽  
Ph Range ◽  
Increasing Temperature

Deposition of Pd on the surface of zero-valent iron (Pd/Fe) further enhances the ability of the metal to reductively dechlorinate organic contaminants. This work determined the dechlorination of chlorobenzene in water by Pd/Fe and evaluated the effects of Pd loading in Fe, Pd/Fe dosage, solution pH and temperature on the reaction. Pseudo-first-order rate constants were obtained to analyze the reaction kinetics. Chlorobenzene was nearly completely dechlorinated within 60 min by Pd/Fe at room temperature. Benzene was the end product of the reaction, along with the release of chloride into water. The rate constant of chlorobenzene dechlorination increased with increasing Pd loading in Fe and Pd/Fe dosage within the tested ranges of 0.005 - 0.020% and 2.0 - 6.0 g/75 mL, respectively. The rate constant increased with decreasing solution pH over the tested pH range of 4.5 - 6.5, indicating the role of protons in dechlorination. The reaction was considered to occur primarily on the surface of Pd where protons were reduced to hydrogen species and chlorobenzene was subsequently dechlorinated by the hydrogen species. The rate of chlorobenzene dechlorination increased with increasing temperature. The estimated activation energy of the reaction was 47.94 kJ/mol within the temperature range of 15 - 40°C, indicating that the dechlorination of chlorobenzene by Pd/Fe readily occurs at room temperature. Pd/Fe may be a potential reductant for effective removal of chlorinated organic contaminants from water.

Oxidation of Nickel(II) and Manganese(II) by Peroxodisulfate in Aqueous Solution in the Presence of Molybdate. Crystal Structure of the (NH4)6[NiMo9O32].6H2O Product

1992 ◽  
Vol 45 (12) ◽  
pp. 1943 ◽  
Author(s):  
SJ Dunne ◽  
RC Burns ◽  
GA Lawrance
Keyword(s):  
Rate Constant ◽  
Linear Dependence ◽  
Ph Dependence ◽  
Order Rate Constant ◽  
X Ray Diffraction ◽  
X Ray ◽  
First Order ◽  
Oxidant Concentration ◽  
Ph Range ◽  
Kinetics Of

Oxidation of Ni2+,aq, by S2O82- to nickel(IV) in the presence of molybdate ion, as in the analogous manganese system, involves the formation of the soluble heteropolymolybdate anion [MMogO32]2- (M = Ni, Mn ). The nickel(IV) product crystallized as (NH4)6 [NiMogO32].6H2O from the reaction mixture in the rhombohedra1 space group R3, a 15.922(1), c 12.406(1) � ; the structure was determined by X-ray diffraction methods, and refined to a residual of 0.025 for 1741 independent 'observed' reflections. The kinetics of the oxidation were examined at 80 C over the pH range 3.0-5.2; a linear dependence on [S2O82-] and a non-linear dependence on l/[H+] were observed. The influence of variation of the Ni/Mo ratio between 1:10 and 1:25 on the observed rate constant was very small at pH 4.5, a result supporting the view that the precursor exists as the known [NiMo6O24H6]4- or a close analogue in solution. The pH dependence of the observed rate constant at a fixed oxidant concentration (0.025 mol dm-3) fits dequately to the expression kobs = kH [H+]/(Ka+[H+]) where kH = 0.0013 dm3 mol-1 s-1 and Ka = 4-0x10-5. The first-order dependence on peroxodisulfate subsequently yields a second-order rate constant of 0.042 dm3 mol-1 s-1. Under analogous conditions, oxidation of manganese(II) occurs eightfold more slowly than oxidation of nickel(II), whereas oxidation of manganese(II) by peroxomonosulfuric acid is 16-fold faster than oxidation by peroxodisulfate under similar conditions.

scholarly journals Room-Temperature Nitrophenol Reduction over Ag–CeO2 Catalysts: The Role of Catalyst Preparation Method

Catalysts ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 580 ◽  
Author(s):  
Mariia Chernykh ◽  
Natalia Mikheeva ◽  
Vladimir Zaikovskii ◽  
Mikhail Salaev ◽  
Leonarda F. Liotta ◽  
...  
Keyword(s):  
Room Temperature ◽  
Preparation Method ◽  
Order Rate Constant ◽  
Catalyst Preparation ◽  
First Order ◽  
Impregnation Technique ◽  
Nitrophenol Reduction ◽  
Co Precipitation ◽  
N2 Sorption

Ag–CeO2 catalysts (20 mol % Ag) were synthesized using different techniques (co-precipitation, impregnation, and impregnation of pre-reduced ceria), characterized by XRD, N2 sorption, TEM, H2-TPR methods, and probed in room-temperature p-nitrophenol reduction into p-aminophenol in aqueous solution at atmospheric pressure. The catalyst preparation method was found to determine the textural characteristics, the oxidation state and distribution of silver and, hence, the catalytic activity in the p-nitrophenol reduction. The impregnation technique was the most favorable for the formation over the ceria surface of highly dispersed silver species that are active in the p-nitrophenol reduction (the first-order rate constant k = 0.656 min−1).

Kinetics and mechanism of the reaction of dimethyl acetylphosphonate with water. Expulsion of a phosphonate ester from a carbonyl hydrate

1978 ◽  
Vol 56 (13) ◽  
pp. 1792-1795 ◽  
Author(s):  
Ronald Kluger ◽  
David C. Pire ◽  
Jik Chin
Keyword(s):  
Rate Constant ◽  
Electronic Effect ◽  
Order Rate Constant ◽  
Ion Concentration ◽  
First Order ◽  
Cleavage Reactions ◽  
Ph Range ◽  
Rapid Hydrolysis ◽  
Hydrolysis Of ◽  
Mechanism Of The Reaction

Dimethyl acetylphosphonate (DAP) is rapidly cleaved in water to acetate and dimethylphosphonic acid. The half time for reaction at pH 7, 25 °C is estimated to be 3 s. The reaction is first order in hydroxide ion concentration and first order in DAP concentration. Rates of reaction were measured over the pH range 3.8 to 6.5 at 25 °C, 6.5 and 7.0 at 5 °C, 4.5 to 6.5 at 35 °C, and 4.5 to 6.0 at 45 °C. The average observed second-order rate constant at 25 °C is 2.4 × 106M−1 s−1. DAP is converted rapidly to a hydrated carbonyl adduct. The mechanism for the formation of the observed products is proposed to be analogous to cleavage reactions of other carbonyl hydrates, proceeding from a monoanion conjugate in this case. The estimated rate constant for the unimolecular cleavage of the carbonyl hydrate anion is 2 × 103 s−1. The rapid hydrolysis of DAP results from energetically favourable formation of a hydrate due to the electronic effect of the phosphonate diester. This effect also promoles ionization of the hydrate. The ionized hydrate readily expels the phosphonate diester to achieve the overall rapid hydrolysis.

A rate and equilibrium study of the addition of acetone enolate ion to the 2-methyl-5-nitroisoquinolinium cation in aqueous solution

1986 ◽  
Vol 64 (5) ◽  
pp. 973-979 ◽  
Author(s):  
John W. Bunting ◽  
James W. Tam
Keyword(s):  
Equilibrium Constants ◽  
Reaction Times ◽  
Order Rate Constant ◽  
Hydroxide Ion ◽  
First Order ◽  
Carbonate Buffer ◽  
Equilibrium Study ◽  
Analogous Data ◽  
Enolate Anion ◽  
Ph Range

Rate and equilibrium constants for the reaction between acetone and the 2-methyl-5-nitroisoquinolinium cation to give 1-acetonyl-1,2-dihydro-2-methyl-5-nitroisoquinoline (2) have been evaluated over the pH range 10.0–11.3 in aqueous solutions at 25 °C. This reaction is shown to occur under much milder conditions (temperature, pH) and in much shorter reaction times than previously used for the synthesis of this adduct. Analogous data for the reaction of hexadeuteroacetone with this heterocyclic cation are also presented. The formation of 2 is shown to be first order in each of acetone, isoquinolinium cation, and hydroxide ion, and is not catalyzed by carbonate buffer species. These data are consistent with the rate-determining attack of the acetone enolate anion upon the isoquinolinium cation. The microscopic reverse of this reaction is the uncatalyzed decomposition of 2, which is consistent with the observed pH independence of the first-order rate constant for this process. Quantitative comparisons of rates and equilibria for the addition of hydroxide ion and acetone enolate ion to this isoquinolinium cation and to substituted benzaldehydes are now available.

scholarly journals Acid Hydrolysis of Bis(2,2'; 6',2''–Terpyridyl) Iron(II) Complex in the Water Pools of CTAB/Hexane/Chloroform Reverse Micelles-A Kinetic Study in Confined Medium

2020 ◽  
Vol 15 (3) ◽  
pp. 853-860
Author(s):  
K. V. Nagalakshmi ◽  
P. Shyamala
Keyword(s):  
Ionic Strength ◽  
Acid Hydrolysis ◽  
Reverse Micelles ◽  
Order Rate Constant ◽  
Micellar Medium ◽  
First Order ◽  
First Order Kinetics ◽  
Rate Of Reaction ◽  
Kinetics Of ◽  
Hydrolysis Of

The kinetics of acid hydrolysis of bis(2,2';6',2''–terpyridyl) iron(II) complex has been studied in CTAB/Hexane/Chloroform reverse micelles. The reaction obeys first order kinetics with respect to each of the reactants at all values of W, {W= [H2O]/[CTAB]}. In the reverse micellar medium, the reaction is much slower compared to aqueous medium due to low micropolarity of the water pools which does not facilitate a reaction between reactants of same charge. The effect of variation of W {W=[H2O]/[CTAB]} at constant [CTAB] and variation of [CTAB] at fixed W has been studied. The second order rate constant (k2) of the reaction increases as the value of W increases up to W = 8.88 and remains constant thereafter and it is independent of concentration of [CTAB] at constant W. The variation of rate of reaction with W has been explained by considering variation of micropolarity and ionic strength of water pools of reverse micelles with W. Copyright © 2020 BCREC Group. All rights reserved 

scholarly journals Photoinitiated Polymerization of 2-Hydroxyethyl Methacrylate by Riboflavin/Triethanolamine in Aqueous Solution: A Kinetic Study

2013 ◽  
Vol 2013 ◽  
pp. 1-7 ◽  
Author(s):  
Iqbal Ahmad ◽  
Kefi Iqbal ◽  
Muhammad Ali Sheraz ◽  
Sofia Ahmed ◽  
Tania Mirza ◽  
...  
Keyword(s):  
Initial Rate ◽  
Hydroxyl Group ◽  
Hydroxyethyl Methacrylate ◽  
First Order ◽  
First Order Kinetics ◽  
Rate Of Polymerization ◽  
Rate Of Reaction ◽  
Ph Range ◽  
Kinetics Of ◽  
Increased Activity

The polymerization of 1–3 M 2-hydroxyethyl methacrylate (HEMA) initiated by riboflavin/triethanolamine system has been studied in the pH range 6.0–9.0. An approximate measure of the kinetics of the reaction during the initial stages (~5% HEMA conversion) has been made to avoid the effect of any variations in the volume of the medium. The concentration of HEMA in polymerized solutions has been determined by a UV spectrophotometric method at 208 nm with a precision of ±3%. The initial rate of polymerization of HEMA follows apparent first-order kinetics and the rates increase with pH. This may be due to the presence of a labile proton on the hydroxyl group of HEMA. The second-order rate constants for the interaction of triethanolamine and HEMA lie in the range of 2.36 to  M−1 s−1 at pH 6.0–9.0 suggesting an increased activity with pH. An increase in the viscosity of HEMA solutions from 1 M to 3 M leads to a decrease in the rate of polymerization probably as a result of the decrease in the reactivity of the flavin triplet state. The effect of pH and viscosity of the medium on the rate of reaction has been evaluated.

Kinetics and Mechanism of the Reaction of Mercury(II) with a Water-soluble Octabromoporphyrin

1998 ◽  
Vol 02 (05) ◽  
pp. 397-403 ◽  
Author(s):  
N. NAHAR ◽  
M. TABATA
Keyword(s):  
Rate Constant ◽  
Activation Parameters ◽  
High Reactivity ◽  
Kinetics And Mechanism ◽  
Water Soluble ◽  
First Order ◽  
Rate Expression ◽  
Ph Range ◽  
Mechanism Of The Reaction

The reaction of mercury(II) hydroxide with 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin, [Formula: see text]( H 2P4−), to form the mercury(II) porphyrin [( TPPSBr 8) Hg ]4−( HgP 4−) was investigated in the pH range 6.2-8.5. The observed rate constant was first-order with respect to the mercury(II) concentration and decreased with increasing pH from pH 6.2 to 7.5 and then increased from pH 7.5 to 8.5. The rate expression was written as d [ HgP 4−]/dt = (kHPK−1[ H +]−1 + k H 2 P + k H 3P K 1[ H +])(1 + K1[ H +] + K−1[ H +]−1)−1[ Hg ( OH )2][ H 2 P 4−]. The kHP, kH2P and kH3P values were found to be (1.33 ± 0.02) × 108, (5.50 ± 0.08) × 106 and (1.40 ± 0.08) × 108 M −1 s−1 respectively, with K1 = [ H 3 P 3−][ H 2 P 4−]−1[ H +]−1 = 104.83 ± 0.04 and K−1 = [ HP 5−][ H +][ H 2 P 4−]−1 = 1010.02 ± 0.02. The activation parameters were [Formula: see text] and ΔS‡ HP = 226 ± 22 J K −1 mol −1 for the k HP path, [Formula: see text] and [Formula: see text] for the k H 2 P path and [Formula: see text] and [Formula: see text] for the k H 3 P path. The kinetic results show the high reactivity of mercury(II) hydroxide towards the protonated porphyrin.

Tyrosine-Selective Bioconjugation with Iminoxyl Radicals

2020 ◽  
Author(s):  
Katsuya Maruyama ◽  
Takashi Ishiyama ◽  
Yohei Seki ◽  
Kounosuke Oisaki ◽  
Motomu Kanai
Keyword(s):  
Reaction Time ◽  
Steric Hindrance ◽  
Room Temperature ◽  
Water Soluble ◽  
Light Irradiation ◽  
Sodium Ascorbate ◽  
Iminoxyl Radical ◽  
Short Reaction Time ◽  
Modified Peptides ◽  
The Stability

A novel Tyr-selective protein bioconjugation using the water-soluble persistent iminoxyl radical is described. The conjugation proceeded with high Tyr-selectivity and short reaction time under biocompatible conditions (room temperature in buffered media under air). The stability of the conjugates was tunable depending on the steric hindrance of iminoxyl. The presence of sodium ascorbate and/or light irradiation promoted traceless deconjugation, restoring the native Tyr structure. The method is applied to the synthesis of a protein-dye conjugate and further derivatization to azobenzene-modified peptides.

Molecular, rheological and physicochemical characterisation of puka gum, an arabinogalactan-protein extracted from the Meryta sinclairii tree

2020 ◽  
Author(s):  
MSM Wee ◽  
Ian Sims ◽  
KKT Goh ◽  
L Matia-Merino
Keyword(s):  
Hydrodynamic Radius ◽  
Average Molecular Weight ◽  
Gum Arabic ◽  
Water Soluble ◽  
Arabinogalactan Protein ◽  
Type Ii ◽  
Weight Average Molecular Weight ◽  
Soluble Polysaccharide ◽  
Physicochemical Characterisation ◽  
Increasing Temperature

© 2019 Elsevier Ltd A water-soluble polysaccharide (type II arabinogalactan-protein) extracted from the gum exudate of the native New Zealand puka tree (Meryta sinclairii), was characterised for its molecular, rheological and physicochemical properties. In 0.1 M NaCl, the weight average molecular weight (Mw) of puka gum is 5.9 × 106 Da with an RMS radius of 56 nm and z-average hydrodynamic radius of 79 nm. The intrinsic viscosity of the polysaccharide is 57 ml/g with a coil overlap concentration 15% w/w. Together, the shape factor, p, of 0.70 (exponent of RMS radius vs. hydrodynamic radius), Smidsrød-Haug's stiffness parameter B of 0.031 and Mark-Houwink exponent α of 0.375 indicate that the polysaccharide adopts a spherical conformation in solution, similar to gum arabic. The pKa is 1.8. The polysaccharide exhibits a Newtonian to shear-thinning behaviour from 0.2 to 25% w/w. Viscosity of the polysaccharide (1 s−1) decreases with decreasing concentration, increasing temperature, ionic strength, and at acidic pH.

Sign in / Sign up

Export Citation Format

Share Document