scholarly journals Rate constants for cyanate hydrolysis to urea: A Raman study

1994 ◽  
Vol 72 (4) ◽  
pp. 1099-1106 ◽  
Author(s):  
Nanping Wen ◽  
Murray H. Brooker
Keyword(s):  
Rate Constant ◽  
Room Temperature ◽  
Pure Water ◽  
Spectroscopic Studies ◽  
Raman Spectroscopic ◽  
Intensity Measurements ◽  
Equilibrium Reaction ◽  
Hydrolysis Process ◽  
Parallel Reactions ◽  
Hydrolysis Of

Raman spectra of aqueous solutions of potassium cyanate have been obtained at suitable time intervals. It was found that the peaks attributed to cyanate became less intense, while the peaks attributed to urea, carbamate and carbonate, centred at 1003, 1034, and 1065 cm−1, respectively, enhanced greatly with the passage of time. Further Raman spectroscopic studies revealed that the cyanate ion hydrolysed slowly and spontaneously at room temperature. Urea, carbamate, and carbonate were formed even without additional ammonium. Raman intensity measurements were used to monitor species concentrations as a function of time. The results suggested a complicated hydrolysis process: the hydrolysis of cyanate ion to form carbonate and ammonium, a rearrangement type reaction of aqueous cyanate ion with aqueous ammonium to formed urea, and an equilibrium reaction of carbonate and ammonium to form carbamate. The initial hydrolysis of cyanate with pure water was found to be first order with rate constant k1 = (2.67 ± 0.53) × 10−4 min−1 at 22 °C. The reaction of cyanate with aqueous ammonium was found to be second order with rate constant k2 = (4.64 ± 0.93) × 10−4 mol−1•L•min−1. The equilibrium reaction of carbonate and ammonium to form carbamate was very fast. Urea and carbamate were formed in parallel reactions. It was not possible to convert urea to carbamate or carbamate to urea at room temperature.

Structural and Raman spectroscopic studies of the two M0.50SbFe(PO4)3 (M = Mg, Ni) NASICON phases

2017 ◽  
Vol 32 (S1) ◽  
pp. S40-S51
Author(s):  
Abderrahim Aatiq ◽  
Asmaa Marchoud ◽  
Hajar Bellefqih ◽  
My Rachid Tigha
Keyword(s):  
Room Temperature ◽  
Structural Information ◽  
Rietveld Analysis ◽  
Spectroscopic Studies ◽  
X Ray Diffraction ◽  
X Ray ◽  
Raman Spectroscopic ◽  
Raman Spectroscopic Study ◽  
Unit Cells ◽  
Xrd Patterns

Structures of the two M0.50SbFe(PO4)3 (M = Mg, Ni) phases, abbreviated as [Mg0.50] and [Ni0.50], were determined at room temperature from X-ray diffraction (XRD) powder data using the Rietveld analysis. Both compounds belong to the NASICON structural family. XRD patterns of [Mg0.50] and [Ni0.50] phases were easily indexed with a primitive hexagonal unit cell [P$\overline 3 $ space group, Z = 6] similar to that already obtained for La0.33Zr2(PO4)3. Obtained unit cells parameters are [a = 8.3443(1) Å, c = 22.3629(1) Å], and [a = 8.3384(1), c = 22.3456(1) Å], respectively, for [Mg0.50] and [Ni0.50] phosphates. In both samples, the [Sb(Fe)(PO4)3]− NASICON framework is preserved and a partially-ordered distribution of Sb5+ and Fe3+ ions is observed. Raman spectroscopic study was used to obtain further structural information about the nature of bonding in [Mg0.50] and [Ni0.50] phases.

Raman studies of cyanate: Fermi resonance, hydration and hydrolysis to urea

1993 ◽  
Vol 71 (10) ◽  
pp. 1764-1773 ◽  
Author(s):  
Murray H. Brooker ◽  
Nanping Wen
Keyword(s):  
Hydrogen Bond ◽  
Raman Spectra ◽  
Room Temperature ◽  
Solid Phase ◽  
Equilibrium Mixture ◽  
Fermi Resonance ◽  
Ambient Conditions ◽  
Parallel Reactions ◽  
Associated Pair ◽  
Hydrolysis Of

Raman spectra were measured for potassium cyanate in the solid phase and as aqueous solutions in H2O and D2O for freshly prepared and for aged solutions. The results indicated that the assignment of the Fermi doublet, ν1 and 2ν2, for solid potassium cyanate was reversed from the assignment for the aqueous solution. The Fermi doublet has an associated pair of hot bands at 1191 and 1315 cm−1 which originate from the 638 cm−1 ν2 state, 010. Assignment of the hot bands was confirmed by studies of solid potassium cyanate at liquid-N2 temperature, room temperature, and at 473 K. Raman spectra of aged aqueous potassium cyanate revealed that the cyanate ion hydrolyzed slowly and spontaneously at room temperature (even without added ammonium) to produce urea and a carbamate, carbonate equilibrium mixture in parallel reactions. Hydrolysis of cyanate in aqueous ammonium chloride solution resulted in almost total conversion of cyanate to urea. The reaction was not reversible under ambient conditions. Differences in peak frequencies and half-widths were observed for the cyanate dissolved in H2O compared to solutions in D2O. The results provide evidence for strong hydrogen bonding of cyanate to water and are consistent with greater structure in the D2O solution. Theoretical ab initio calculations indicated that the water molecules hydrogen bond well at both the oxygen and nitrogen atoms of cyanate although the hydrogen bond to nitrogen was found to be slightly stronger.

Structural and Electrical Investigations of Ferroelectric Lead Strontium Titanate Thin Films and Ceramics

2003 ◽  
Vol 784 ◽  
Author(s):  
M. Jain ◽  
P. Bhattacharya ◽  
Yu. I. Yuzyuk ◽  
R. S. Katiyar ◽  
A. S. Bhalla
Keyword(s):  
Thin Films ◽  
Strontium Titanate ◽  
Room Temperature ◽  
Powder Processing ◽  
Lattice Structure ◽  
Spectroscopic Studies ◽  
Cubic Phase ◽  
Raman Spectroscopic ◽  
Structure Changes ◽  
Ceramic Targets

ABSTRACTLead strontium titanate (PbxSr1-xTiO3) (x=0.3–1.0) ceramic targets were prepared by the conventional powder-processing method. Thin films of these compositions were deposited on platinized silicon substrates by pulsed laser deposition technique. X-ray diffraction studies of the ceramic targets showed that the lattice structure changes from tetragonal to cubic phase with the increase of Sr content in PbTiO3. Raman spectroscopic studies of PbxSr1-xTiO3(PST) ceramics and thin films showed that the soft mode decreases to lower frequency and finally disappear at around 60–70 at% Sr content, which confirms the tetragonal to cubic phase transition at room temperature. Dielectric constant measured for PST thin films was in the range of 900–1500 at 1 MHz, with maximum value obtained for PST30 thin film. The loss tangents at room temperature were in the range of 0.07–0.1 for PST thin films with different compositions.

Magnetic and spectroscopic studies on nickel(II) and copper(II) complexes of some neutral tridentate ONS ligands

1980 ◽  
Vol 58 (7) ◽  
pp. 727-732 ◽  
Author(s):  
M. Akbar Ali
Keyword(s):  
Schiff Base ◽  
Schiff Bases ◽  
Elemental Analysis ◽  
Room Temperature ◽  
Chelating Agents ◽  
Spectroscopic Studies ◽  
Chloro Complex ◽  
Octahedral Structure ◽  
Schiff Base Ligands ◽  
Hydrolysis Of

New Schiff base ligands formed from 2-methoxybenzaldehyde and 2,4-dimethoxybenzaldehyde with N-methyl-S-alkyldithiocarbazates and their nickel(II) and copper(II) complexes have been prepared and characterised by elemental analysis and magnetic and spectroscopic measurements. The Schiff bases behave as neutral tridentate chelating agents forming stable nickel(II) complexes of stoichiometry NiLX2•xC2H5OH (L = 2-methoxy- or 2,4-dimethoxybenzaldehyde Schiff bases of N-methyl-S-methyldithiocarbazate; X = I−, SCN−; x = 0, 1). Conductivity, magnetic, and spectral data support an octahedral structure for the nickel(II) complexes. The CuLCl2 complexes were also isolated. Magnetic and spectral evidence are in accord with a chloro-bridged dimeric structure. The chloro-complex of copper(II) with the 2-methoxybenzaldehyde Schiff base displays a room-temperature magnetic moment of 1.81 BM, which remains virtually constant over the temperature range 343–123 K.Hydrated copper(II) chloride promotes complete hydrolysis of the 2,4-dimethoxybenzaldehyde and 2-methoxybenzaldehyde Schiff bases of N-methyl-S-benzyldithiocarbazate with the concomitant formation of copper(II) complexes of the parent N-methyl-S-benzyldithiocarbazate of general formula, Cu(N—SR)Cl2 (R = C6H5CH2—).

Lattice imaging and pore structure of β ferric oxyhydroxide

1978 ◽  
Vol 36 (1) ◽  
pp. 264-265
Author(s):  
T. Baird ◽  
J.R. Fryer ◽  
S.T. Galbraith
Keyword(s):  
Electron Microscopy ◽  
Room Temperature ◽  
Bulk Material ◽  
Model Structure ◽  
Bulk Crystals ◽  
Lattice Imaging ◽  
Thin Sections ◽  
Ferric Oxyhydroxide ◽  
Resolution Electron ◽  
Hydrolysis Of

Introduction Previously we had suggested (l) that the striations observed in the pod shaped crystals of β FeOOH were an artefact of imaging in the electron microscope. Contrary to this adsorption measurements on bulk material had indicated the presence of some porosity and Gallagher (2) had proposed a model structure - based on the hollandite structure - showing the hollandite rods forming the sides of 30Å pores running the length of the crystal. Low resolution electron microscopy by Watson (3) on sectioned crystals embedded in methylmethacrylate had tended to support the existence of such pores.We have applied modern high resolution techniques to the bulk crystals and thin sections of them without confirming these earlier postulatesExperimental β FeOOH was prepared by room temperature hydrolysis of 0.01M solutions of FeCl3.6H2O, The precipitate was washed, dried in air, and embedded in Scandiplast resin. The sections were out on an LKB III Ultramicrotome to a thickness of about 500Å.

Kinetic study of hydrolysis of benzoates. part xxvii. ortho substituent effect in alkaline hydrolysis of phenyl esters of substituted benzoic acids in aqueous Bu4NBr

2009 ◽  
Vol 74 (1) ◽  
pp. 29-42 ◽  
Author(s):  
Vilve Nummert ◽  
Mare Piirsalu ◽  
Signe Vahur ◽  
Oksana Travnikova ◽  
Ilmar A. Koppel
Keyword(s):  
Alkaline Hydrolysis ◽  
Rate Constants ◽  
Pure Water ◽  
Substituent Effects ◽  
Benzoic Acids ◽  
Resonance Effects ◽  
The Media ◽  
Substituted Benzoic Acids ◽  
Hydrolysis Of ◽  
Ortho Substituent

The second-order rate constants k (in dm3 mol–1 s–1) for alkaline hydrolysis of phenyl esters of meta-, para- and ortho-substituted benzoic acids, X-C6H4CO2C6H5, have been measured spectrophotometrically in aqueous 0.5 and 2.25 M Bu4NBr at 25 °C. The substituent effects for para and meta derivatives were described using the Hammett relationship. For the ortho derivatives the Charton equation was used. For ortho-substituted esters two steric scales were involved: the EsB and the Charton steric (υ) constants. When going from pure water to aqueous 0.5 and 2.25 M Bu4NBr, the meta and para polar effects, the ortho inductive and resonance effects in alkaline hydrolysis of phenyl esters of substituted benzoic acids, became stronger nearly to the same extent as found for alkaline hydrolysis of C6H5CO2C6H4-X. The steric term of ortho-substituted esters was almost independent of the media considered. The rate constants of alkaline hydrolysis of ortho-, meta- and para-substituted phenyl benzoates (X-C6H4CO2C6H5, C6H5CO2C6H4-X) and alkyl benzoates, C6H5CO2R, in water, 0.5 and 2.25 M Bu4NBr were correlated with the corresponding IR stretching frequencies of carbonyl group, (ΔνCO)X.

scholarly journals Kinetics and Mechanistic Study of Hydrolysis of Adenosine Monophosphate Disodium Salt (AMPNa2) in Acidic and Alkaline Media

2019 ◽  
Vol 17 (1) ◽  
pp. 544-556
Author(s):  
Yoke-Leng Sim ◽  
Beljit Kaur
Keyword(s):  
Rate Constant ◽  
Adenosine Monophosphate ◽  
Disodium Salt ◽  
Second Order ◽  
Information Storage ◽  
Alkaline Media ◽  
Basic Medium ◽  
Mechanistic Study ◽  
Phosphate Ester ◽  
Hydrolysis Of

AbstractPhosphate ester hydrolysis is essential in signal transduction, energy storage and production, information storage and DNA repair. In this investigation, hydrolysis of adenosine monophosphate disodium salt (AMPNa2) was carried out in acidic, neutral and alkaline conditions of pH ranging between 0.30-12.71 at 60°C. The reaction was monitored spectrophotometrically. The rate ranged between (1.20 ± 0.10) × 10-7 s-1 to (4.44 ± 0.05) × 10-6 s-1 at [NaOH] from 0.0008 M to 1.00M recorded a second-order base-catalyzed rate constant, kOH as 4.32 × 10-6 M-1 s-1. In acidic conditions, the rate ranged between (1.32 ± 0.06) × 10-7 s-1 to (1.67 ± 0.10) × 10-6 s-1 at [HCl] from 0.01 M to 1.00 M. Second-order acid-catalyzed rate constant, kH obtained was 1.62 × 10-6 M-1 s-1. Rate of reaction for neutral region, k0 was obtained from graphical method to be 10-7 s-1. Mechanisms were proposed to involve P-O bond cleavage in basic medium while competition between P-O bond and N-glycosidic cleavage was observed in acidic medium. In conclusion, this study has provided comprehensive information on the kinetic parameters and mechanism of cleavage of AMPNa2 which mimicked natural AMP cleavage and the action of enzymes that facilitate its cleavage.

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