The SN1CB Mechanism in Non-Aqueous Solution

1988 ◽  
Vol 41 (9) ◽  
pp. 1369 ◽  
Author(s):  
WG Jackson ◽  
RL Angel
Keyword(s):  
Aqueous Solution ◽  
Dimethyl Sulfoxide ◽  
Primary Amines ◽  
Tertiary Amines ◽  
Pka Values ◽  
First Order ◽  
Rate Laws ◽  
General Base ◽  
First Order Kinetics ◽  
Conjugate Base

The reaction between (NH3)5Co-NCMe3+ and dimethyl sulfoxide (Me2SO) to produce (NH3)5Co-OSMe23+ and MeCN in Me2SO solvent is general base-catalysed. The rates and rate laws have been determined for 10 substituted amines. First-order kinetics are observed, and the rates show a dependence which is less than first order on base (B) concentration. These facts are rationalized in terms of a common, reactive conjugate base (NH3)4(NH2)CoNCMe2+, the solvolysis of which occurs at a rate competitive with its rate of reprotonation by BH+. Alternative mechanisms are considered. The measured rates, which span two orders of magnitude, do not correlate with base nucleophilicity, steric features of the amines, nor pKa values as measured for aqueous solution. Primary amines are very effective catalysts; secondary and especially tertiary amines are poorer catalysts. There appears to be no reaction at the bound nitrile function as there is in aqueous solution.

Mo3S4 Nanorod: An Effective Photocatalyst for the Degradation of Organic Dyes in Aqueous Solution

2019 ◽  
Vol 12 (1) ◽  
pp. 61-69
Author(s):  
Madima Ntakadzeni ◽  
William Wilson Anku ◽  
Penny Poomani Govender ◽  
Leelakrishna Reddy
Keyword(s):  
Aqueous Solution ◽  
Ethylenediaminetetraacetic Acid ◽  
Organic Dyes ◽  
Sodium Molybdate ◽  
Rhombohedral Phase ◽  
Molybdenum Sulfide ◽  
Energy Band Gap ◽  
Facile Hydrothermal Method ◽  
First Order ◽  
First Order Kinetics

Background: A molybdenum sulfide (Mo3S4) nanorod photocatalyst was synthesised through the facile hydrothermal method and applied in the degradation of Rhodamine B and Methyl Blue dyes under visible light irradiation. Methods: The Mo3s4 nanorod was synthesised using sodium molybdate, sodiumdiethyldithiolcarbonate and ethylenediaminetetraacetic acid as molybdenum and sulfur sources, and capping agent respectively. The photocatalyst was characterized by using XRD, FTIR, TEM, SEM, EDS and UV-Vis spectroscopies. Results: SEM result shows that the synthesised sample has a rod-like shape made up of several thin sheets. The XRD result revealed the Mo3S4 nanorod to exist in the Rhombohedral phase. The energy band gap of the sample was calculated to be 2.02 eV. The synthesised Mo3S4 nanorod showed great potential in the removal of both RhB and MB in aqueous solution. 85.46% and 99.78% removals of RhB and MB dyes respectively were achieved in 90 min. Conclusion: It was also observed that the photodegradation of both RhB and MB follows pseudo-first order kinetics, with apparent rate constants of 0.0089 min-1 and 0.0118 min-1 for RhB and MB respectively.

Aerobic oxidative N-dealkylation of secondary amines in aqueous solution catalyzed by rhodium porphyrins

2014 ◽  
Vol 18 (10n11) ◽  
pp. 937-943 ◽  
Author(s):  
Lin Yun ◽  
Ling Zhen ◽  
Zikuan Wang ◽  
Xuefeng Fu
Keyword(s):  
Aqueous Solution ◽  
Oxidation Reaction ◽  
Catalyst Deactivation ◽  
Secondary Amines ◽  
First Order ◽  
Rate Determining Step ◽  
First Order Kinetics ◽  
Biochemical Oxidation ◽  
Iminium Ion ◽  
Rhodium Porphyrins

N-dealkylation demonstrates an important biochemical oxidation reaction by cytochrome P450 and other monooxygenases. In this article, catalytic oxidative N-dealkylation of secondary amines was achieved using rhodium(III) tetra (p-sulfonato-phenyl) porphyrin (( TSPP ) Rh III ) in aqueous solution with oxygen as the sole oxidant. Addition of benzaldehyde to trap primary amine product inhibited catalyst deactivation and dramatically increased reaction turnover numbers (TONs). Substrate scope examination suggested the reaction was performed with a preference for bulkier secondary amines. Kinetic study exhibited first-order kinetics with regard of ( TSPP ) Rh III catalyst. Results from the Hammett study gave a ρ value of -1.38, suggesting formation of an iminium ion intermediate in the rate determining step.

scholarly journals Efficient degradation of naproxen by persulfate activated with zero-valent iron: performance, kinetic and degradation pathways

2020 ◽  
Vol 81 (10) ◽  
pp. 2078-2091
Author(s):  
Shuyu Dong ◽  
Xiaoxue Zhai ◽  
Ruobing Pi ◽  
Jinbao Wei ◽  
Yunpeng Wang ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Hydroxyl Radical ◽  
Rate Constants ◽  
Zero Valent Iron ◽  
Degradation Pathways ◽  
First Order ◽  
First Order Kinetics ◽  
Degradation Rates ◽  
Initial Ph ◽  
Pseudo First Order

Abstract Degradation of naproxen (NAP) by persulfate (PS) activated with zero-valent iron (ZVI) was investigated in our study. The NAP in aqueous solution was degraded effectively by the ZVI/PS system and the degradation exhibited a pseudo-first-order kinetics pattern. Both sulfate radical (SO4•−) and hydroxyl radical (HO•) participate in the NAP degradation. The second-order rate constants for NAP reacting with SO4•− and HO• were (5.64 ± 0.73) × 109 M−1 s−1 and (9.05 ± 0.51) × 109 M−1 s−1, respectively. Influence of key parameters (initial pH, PS dosage, ZVI dosage, and NAP dosage) on NAP degradation were evaluated systematically. Based on the detected intermediates, the pathways of NAP degradation in ZVI/PS system was proposed. It was found that the presence of ammonia accelerated the corrosion of ZVI and thus promoted the release of Fe2+, which induced the increased generation of sulfate radicals from PS and promoted the degradation of NAP. Compared to its counterpart without ammonia, the degradation rates of NAP by ZVI/PS were increased to 3.6–17.5 folds and 1.2–2.2 folds under pH 7 and pH 9, respectively.

Enhanced sonochemical degradation of tetracycline by sulfate radicals

2015 ◽  
Vol 73 (6) ◽  
pp. 1293-1300 ◽  
Author(s):  
Akbar Eslami ◽  
Hamideh Bahrami ◽  
Anvar Asadi ◽  
Abdolazim Alinejad
Keyword(s):  
Aqueous Solution ◽  
Advanced Oxidation Processes ◽  
Ultrasound Irradiation ◽  
Sulfate Radical ◽  
Growth Promoters ◽  
Operational Conditions ◽  
First Order ◽  
First Order Kinetics ◽  
Initial Ph ◽  
Refractory Organic Pollutants

Tetracyclines (TCs) are widely used antibiotics in human and veterinary medicine and as growth promoters in the world. Sulfate radical-based advanced oxidation processes have been of great interest due to the high oxidizing potential of sulfate radical to degrade refractory organic pollutants in aqueous solution. In this study, the degradation of antibiotic TC in aqueous solution by silver-activated persulfate (Na2S2O8) in the presence of ultrasound irradiation under various conditions has been investigated. The effects of several parameters such as Ag2SO4, Na2S2O8 concentration, temperature, ultrasonic (US) power, initial TC concentration and initial pH on the degradation of TC were investigated. More than 83% of TC removal was achieved within 120 min under optimal conditions. The optimum operational conditions were found to be as follows: Ag2SO4 dosage 3.5 mmol/L, Na2S2O8 concentration 70 mmol/L, reaction temperature 25 °C, US power 120 W, initial TC concentration 50 mg/L, pH 3.0 and contact time 120 min. The degradation of TC in the persulfate/Ag+/US process followed the pseudo-first-order kinetics.

Photodegradation of amoxicillin in aqueous solution under simulated irradiation: influencing factors and mechanisms

2013 ◽  
Vol 67 (7) ◽  
pp. 1605-1611 ◽  
Author(s):  
Qian Zhao ◽  
Li Feng ◽  
Xiang Cheng ◽  
Chao Chen ◽  
Liqiu Zhang
Keyword(s):  
Aqueous Solution ◽  
Singlet Oxygen ◽  
Natural Waters ◽  
Pure Water ◽  
Chemical Species ◽  
Xenon Lamp ◽  
First Order ◽  
First Order Kinetics ◽  
Photodegradation Rate ◽  
Pseudo First Order

This paper investigated the effects of selected common chemical species in natural waters (HCO3−, NO3− and humic acids (HA)) on the photodegradation of amoxicillin (AMO) under simulated irradiation using a 300 W xenon lamp. Quenching experiments were carried out to explore the mechanisms of AMO photodegradation. The results indicated that AMO photodegradation followed pseudo-first-order kinetics. Increasing AMO concentration from 100 to 1,000 μg L−1 led to the decrease in the photodegradation rate constant from 0.2411 to 0.1912 min−1. The presence of NO3− and HA obviously inhibited the photodegradation rate of AMO because they can compete for photons with AMO. Bicarbonate, as a hydroxyl radical (·OH) scavenger, also adversely affected AMO photodegradation. Quenching experiments in pure water suggested that AMO could undergo self-sensitized photooxidation via ·OH and singlet oxygen (1O2), accounting for AMO removal of 34.86 and 8.26%, respectively. In HA solutions, the indirect photodegradation of AMO was mostly attributed to the produced ·OH (22.37%), 1O2 (24.12%) and 3HA* (20.80%), whereas the contribution of direct photodegradation was to some extent decreased.

scholarly journals Photodegradation of lincomycin in aqueous solution

2006 ◽  
Vol 2006 ◽  
pp. 1-6 ◽  
Author(s):  
Agatino Di Paola ◽  
Maurizio Addamo ◽  
Vincenzo Augugliaro ◽  
Elisa García-López ◽  
Vittorio Loddo ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Aqueous Solutions ◽  
Uv Light ◽  
Heterogeneous Systems ◽  
Degradation Pathways ◽  
Direct Photolysis ◽  
First Order ◽  
First Order Kinetics ◽  
Pseudo First Order ◽  
Complete Mineralization

Aqueous solutions of lincomycin were irradiated with UV light in homogeneous and heterogeneous systems. Lincomycin disappeared in both systems but the presence ofTiO2noticeably accelerated the degradation of the antibiotic in comparison with direct photolysis. The rate of decomposition was dependent on the concentration of lincomycin and followed a pseudo-first-order kinetics. Photolysis involved only the oxidation of lincomycin without mineralization. Differently, the treatment withTiO2and UV light resulted in a complete mineralization of the antibiotic. The degradation pathways involved S- and N-demethylation and propyldealkylation. The mineralization of the molecule led to the formation of sulfate, ammonium, and nitrate ions.

scholarly journals Temperature and pH effects on the kinetics of 2-aminophenol auto-oxidation in aqueous solution

2003 ◽  
Vol 1 (3) ◽  
pp. 233-241 ◽  
Author(s):  
Dumitru Oancea ◽  
Mihaela Puiu
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Aqueous Solution ◽  
Ph Effects ◽  
Influence Of Temperature ◽  
First Order ◽  
Incremental Methods ◽  
First Order Kinetics ◽  
Ph Range ◽  
Kinetics Of

AbstractThe kinetics of the auto-oxidation of 2-aminophenol (OAP) to 2-amino-phenoxazin-3-one (APX) was followed in air-saturated aqueous solutions and the influence of temperature and pH on the auto-oxidation rate was studied. The kinetic analysis was based on a spectrophotometric method following the increase of the absorbance of APX. The process follows first order kinetics according to the rate law—d[OAP]/dt=k′[OAP]. The experimental data, within the pH range 4–9.85, were analyzed using both differential and incremental methods. The temperature variation of the overall rate constant was studied at pH=9.85 within the range 25–50°C and the corresponding activation energy was evaluated.

scholarly journals In situ chemichromic studies of interactions between a lutetium bis-octaalkyl-substituted phthalocyanine and selected biological cofactors

2011 ◽  
Vol 9 (66) ◽  
pp. 183-189 ◽  
Author(s):  
C. Pal ◽  
A. N. Cammidge ◽  
M. J. Cook ◽  
J. L. Sosa-Sanchez ◽  
A. K. Sharma ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Nicotinamide Adenine Dinucleotide ◽  
Reduction Rate ◽  
Lithium Perchlorate ◽  
Linear Increase ◽  
First Order ◽  
Glass Substrates ◽  
First Order Kinetics ◽  
Neutralization Process

Spin-coated films, approximately 100 nm thick, of a newly synthesized bis[octakis(octyl)phthalocyaninato] lutetium(III) complex on ultrasonically cleaned glass substrates exhibit pronounced chemichromic behaviour with potential application in healthcare. In situ kinetic optical absorption spectroscopic measurements show that the phthalocyanine Q-band is red shifted by 60 nm upon oxidation arising from exposure to bromine vapour. Recovery to the original state is achieved by the treatment of the oxidized films with nicotinamide adenine dinucleotide and l -ascorbic acid (vitamin C) in an aqueous solution containing 1.5 M lithium perchlorate. The neutralization process is found to be governed by first-order kinetics. The linear increase of the reduction rate with increasing concentration of cofactors provides a basis for calibration of analyte concentrations ranging from 3.5 mM down to 0.03 mM.

A Comparative Study on Photocatalytic Degradation of Pyridinium – Based Ionic Liquid by TiO2 and ZnO in Aqueous Solution

2019 ◽  
Vol 17 (9) ◽  
Author(s):  
Oualida Nour El Houda Kaabeche ◽  
Razika Zouaghi ◽  
Soraya Boukhedoua ◽  
Seyfeddine Bendjabeur ◽  
Tahar Sehili
Keyword(s):  
Aqueous Solution ◽  
Ionic Liquid ◽  
Photocatalytic Degradation ◽  
Alkaline Medium ◽  
Kinetics Study ◽  
No Adsorption ◽  
Experimental Conditions ◽  
First Order ◽  
First Order Kinetics ◽  
Carbonate Ions

Abstract The photocatalytic degradation of hexylpyridinium bromide (HPyBr) from an aqueous solution was studied by focusing on comparison of the photoactivity of ZnO and TiO2 P25. The process was carried out under different experimental conditions. The results showed that there is no adsorption of pollutant by both catalysts in the dark. The efficiency of P25 Degussa and ZnO photocatalysts were compared, and the photocatalytic kinetics study showed that ZnO is more efficient than TiO2 P25. The HPyBr photodegradation was found to follow a pseudo-first order kinetics, and the higher rates constants were obtained at the alkaline medium for ZnO (pH = 11, kapp = 9.61 × 10–2 min−1) and at acidic medium for TiO2 P25 (pH = 3, kapp = 1.28 × 10–2 min−1). The Langmuir–Hinshelwood model was found suitable to explain the rate constant data for the ionic liquid degradation by both catalysts. The presence of carbonate ions at alkaline medium was found to reduce the HPyBr degradation for ZnO and to enhance the HPyBr degradation for TiO2, this enhancement in TiO2/CO32-/UV system was confirmed by the addition of •OH and hvb+ scavengers. According to TOC and COD results, HPyBr mineralization was faster in ZnO/UV system than in TiO2/UV system.

Photocatalytic Degradation of 4-Chlorophenol with a Novel α-Ga2O3

2011 ◽  
Vol 356-360 ◽  
pp. 1319-1322
Author(s):  
Bao Xiu Zhao ◽  
Li Na Zheng ◽  
Yuan Wei ◽  
Fan Yang
Keyword(s):  
Aqueous Solution ◽  
Photocatalytic Degradation ◽  
Degradation Kinetics ◽  
Endocrine Disrupting Chemicals ◽  
Life Time ◽  
First Order ◽  
First Order Kinetics ◽  
Endocrine Disrupting ◽  
The Common ◽  
Main Factors

Chlorophenols is a kind of environmental endocrine disrupting chemicals (EDCs) and it is hard for the common methods to degrade or remove them, so how to decompose these pollutants has attracted researches’ attention. In this paper, a novel α-Ga2O3was used to degrade 4-chlorophenol via photocatalytic reaction and degradation kinetics was investigated. The effects of main factors, such as dosage of α-Ga2O3and pH of aqueous solution, on degradation were studied, and degradation kinetics was also established. Experimental results displayed that the optimal pH of aqueous solution was about 7.8 and almost 98% 4-chlorophenol was decomposed after 2 h, when the dosage of α-Ga2O3was 0.4 g and the initial concentration of 4-chlorophenol was 20 mg/L (V=200 ml). Photocatalytic degradation of 4-chlorophenol with α-Ga2O3abided by first-order kinetics and half-life time was 20.4 min.

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