• Title/Summary/Keyword: Chemical reaction kinetics

Search Result 739, Processing Time 0.026 seconds

Hydrolysis of p-Nitrophenyl Acetate and p-Nitrophenyldiphenyl Phosphate in Micellar Solution by N-Chloro Compounds : Involvement of Counter Ions in Micellar Catalysis

  • 박병덕;이윤식
    • Bulletin of the Korean Chemical Society
    • /
    • v.16 no.10
    • /
    • pp.938-945
    • /
    • 1995
  • Hydrolysis of p-nitrophenyl acetate (PNPA) and p-nitrophenyldiphenyl phosphate (PNPDPP) by N-chloro compounds in micellar solution were studied. N,N'-dichloroisocyanuric acid sodium salt (DCI) in cetyltrimethylammonium chloride (CTACl) micellar solution gave pseudo first-order kinetics. But, DCI in cetyltrimethylammonium bromide (CTABr) micellar solution showed typical series first-order kinetics - fast hydrolysis of the esters and concomitant slow decay of the hydrolyzed product, p-nitrophenolate. The hydrolysis rate was decreased as the hydrophobicity of N-chloro compounds was increased, which is the opposite trend to the usual bimolecular micellar reaction. This curious behavior of the N-chloro compounds in the catalytic hydrolysis of PNPA and PNPDPP in a cationic micellar system can be best explained by participation of counter ions of the surfactants during hydrolysis.

Nucleiphilic Substitution Reactions of Thiophenyl Dimethylacetates and Trimethylacetates wkth Benzylamines in Acetonitfile

  • O, Hyeok Geun;Park, Chi Yeol;Lee, Jae Mun;Lee, Ik Chun
    • Bulletin of the Korean Chemical Society
    • /
    • v.22 no.4
    • /
    • pp.383-387
    • /
    • 2001
  • The kinetics and mechanism of the reactions of thiophenyl dimethylacetates (TDA) and trimethylacetates (TTA) with benzylamines in acetonitrile are studied. The reactions are first order in both the amine and the substrate. Relatively large values of ${\beta}X(\betanuc$ = 1.1-1.5; TDA and 1.1-1.5; TTA) and ${\beta}Z({\beta}lg$ = -1.8~-2.0; DTA and -1.3~-1.6; TTA) for benzylamines, significantly large kH/kD values (=1.2-1.5; DTA and 1.2-1.5; TTA) involving deuterated benzylamines, and large ${\rho}XZ$ (=0.82; TDA and 1.05; TTA) values are interpreted to indicate stepwise acyl transfer mechanism, but with the hydrogen bonded four center type transition state for benzylamine. The relatively greater magnitudes of ${\rho}XZ$ and the secondary kinetic isotope effects involving deuterated nucleophiles are in line with the proposed mechanism.

Kinetic Study on Dephosphorylation of Myelin Basic Protein by Some Protein Phosphates

  • 황인성;김진한;최명운
    • Bulletin of the Korean Chemical Society
    • /
    • v.18 no.4
    • /
    • pp.428-432
    • /
    • 1997
  • The dephosphorylation specificity of protein phosphatase 2A (PP2A), calcineurin (PP2B) and protein phosphatase 2C (PP2C) were studied in vitro using myelin basic protein (MBP) as a model substrate which was fully phosphorylated at multiple sites by protein kinase C (PKC) or cyclic AMP-dependent protein kinase (PKA). In order to determine the site specificity of phosphates in myelin basic protein, the protein was digested with trypsin and the radioactive phosphopeptide fragments were isolated by high performance liquid chromatography (HPLC) on reversed-phase column. Subsequent analysis and/or sequential manual Edman degradation of the purified phosphopeptides revealed that Thr-65 and Ser-115 were most extensively phophorylated by PKA and Ser-55 by PKC. For the dephosphorylation kinetics, the phosphorylated MBP was treated with calcineurin or PP2C with various time intervals and the reaction was terminated by direct tryptic digest. Both Thr-65 and Ser-115 residues were dephosphorylated more rapidly than any other ones by phosphatases. However it can be differentiated further by first-order kinetics that the PP2B dephosphorylated both Thr-65 and Ser-115 with almost same manner, whereas PP2C dephosphorylated somewhat preferentially the Ser-115.

Kinetics analysis of energetic material using isothermal DSC (등온 DSC를 이용한 고에너지 물질의 정밀 반응 모델 기법 개발)

  • Kim, Yoocheon;Park, Jungsu;Kwon, Kuktae;Yoh, Jai-ick
    • 한국연소학회:학술대회논문집
    • /
    • 2015.12a
    • /
    • pp.219-222
    • /
    • 2015
  • The kinetic analysis of energetic materials using Differential Scanning Calorimetry (DSC) is proposed. Friedman Isoconversional method is applied to DSC experiment data and AKTS software is used for analysis. The frequency factor and activation energy are extracted as a function of product mass fraction. The extracted kinetic scheme does not assume multiple chemical steps to describe the response of energetic materials; instead, multiple set of Arrhenius factors are used in describing a single global step. The proposed kinetic scheme has considerable advantage over the standard method based on One-Dimenaionl Time to Explosion (ODTX). Reaction rate and product mass fraction simulation are conducted to validate extracted kinetic scheme. Also a slow cook-off simulation is implemented for validating the applicability of the extracted kinetics scheme to a practical thermal experiment.

  • PDF

Indole Derivatives I, The Kinetics and Mechanism of the Nucleopilic Addition of Thiourea to 1-Benzylindole-3-Acetophenone (인돌유도체 I, 1-Benzylindole-3-acetophenone유도체에 대한 Thiourea의 친핵성 첨가반응 메카니즘과 그 반응속도론적 연구)

  • Lee, Ki-Chang;Hwang, Sung-Kwu;Ryu, Jung-Wook;Hwang, Young-Hyun;Sung, Ki-Chun
    • Journal of the Korean Applied Science and Technology
    • /
    • v.8 no.2
    • /
    • pp.175-181
    • /
    • 1991
  • The kinetics of the addition of 1-benzylindole-3-(p-substituted) acetophenone derivatives was investigated by ultraviolet spectrophotometery in 30% dioxane -$H_2O\;at\;25^{\circ}C$. A rate equation which can be applied over wide pH range was obtained. The Substituent effects on 1-benzylindole-3-(p-substituted) acetophenone derivatives were studied, and addition were facilitated by electron attracting groups. On the base of the rate equation, substituent effect, and general base effect the plausible addition mechanism was proposed : Below pH 3.0, only neutral thiourea molecule was added to the carbon-carbon double bond, and in the range of pH 0.0${\sim}$14.0, netural thiourea molecule and thiourea anion competitively attacted the double bond. By contrast, above pH 10.0, the reaction was dependent upon only the addition of thiourea anion.

Biosorption of Methylene Blue from Aqueous Solution using Dried Rhodotorula glutinis Biomass

  • Dae Haeng Cho;Jaesung Lee;Eui Yong Kim
    • Korean Chemical Engineering Research
    • /
    • v.61 no.2
    • /
    • pp.273-277
    • /
    • 2023
  • The biosorption of methylene blue (MB) from aqueous solution was investigated using dried Rhodotorula glutinis as the biosorbent. The effects of pH, initial dye concentration, biosorbent dosage, and kinetic studies were determined to obtain valuable information for biosorption. Results indicated that most of the adsorbed MB bound within 30 minutes of contact and the MB adsorption capacity increased from 21.1 to 101.8 mg/g with the initial MB concentration increased from 50 to 300 mg/L. Additionally, the MB adsorption capacity gradually increased from pH 4.0 to 9.0, reaching its peak at an initial pH of 9.0. As the biomass load was increased from 0.25 to 4.0 g/L, the MB removal efficiency increased from 14.1 to 84.5%. The Langmuir model provided the best fit throughout the concentration range, and the maximum adsorption capacity (qmax) and Langmuir constant (b) were determined to be 135.14 mg/g and 0.026 l/mg, respectively. Furthermore, the biosorbent process of R. glutinis was found to follow pseudo-second-order kinetics and the calculated qeq,cal value showed good agreement with the experimental qeq value. Overall, the biosorption of MB by R. glutinis can be characterized as a monolayer, single site type phenomenon, and the rate-limiting step was determined to be the chemical reaction between the adsorbent and the adsorbate.

The Kinetics and Mechanism of Nucleophilic Addition of Mercaptan to a ${\beta}$-Nitrostyrene in Acidic Media (I) (${\beta}$-Nitrostyrene에 대한 Mercaptan의 親核性 添加反應에 關한 硏究 (I))

  • Park, Ok-Hyun
    • Journal of the Korean Chemical Society
    • /
    • v.12 no.3
    • /
    • pp.106-113
    • /
    • 1968
  • The rate-constants of the nucleophilic addition reaction of n-butylmercaptan to 3,4-methylenedioxy-${\beta}$-nitrostyrene were determined at various acidic pH and a rate equation which can be applied over wide pH range was obtained. From this equation, one may conclude that this reaction is started by addition of mercaptan molecule below pH 3, while above pH 6, the overall rate of addition is almost only depend upon the concentration of nitrostyrene and the mercaptide ion. At pH 3∼6, the complex mechanism of this addition reaction can also be fully explained by the rate equation.

  • PDF

Cure Characteristics of Metal Particle Filled DGEBA/MDA/SN/ zeolite Composite System for EMI Shielding

  • Cho, Young-Shin;Lee, Hong-Ki;Shim, Mi-Ja;Kim, Sang-Wook
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
    • /
    • 1999.05a
    • /
    • pp.548-551
    • /
    • 1999
  • The cure characteristics of metal particle filled DGEBA/MDA/SN/ zeolite epoxy resin composite system for EMI shielding were investigated by dynamic DSC run method and FT-lR spectroscopy. As the heating rate increased, the peak temperature on dynamic DSC curve increased because of the rapid cure reaction. From the straight line of the Kissinger plot, the curing reaction activation energy and pre-exponential factor could be obtained. As the post-curing time at 15$0^{\circ}C$ increased, the glass increased the glass transition temperature or the thermal stability increased. When the post curing time is too long, the system filled with metallic Al particle can be thermally oxidized by the catalytic reaction of metal filler and the thermal stability of the composite for the EMI shielding application may be decreased.

  • PDF

Kinetics and Mechanism for the Reaction of 4-Nitrophenyl 2-Furoate with Secondary Alicyclic Amines

  • 이종팔;윤지회;엄익환
    • Bulletin of the Korean Chemical Society
    • /
    • v.20 no.7
    • /
    • pp.805-808
    • /
    • 1999
  • Second-order-rate constants (kN) have been measured spectrophotometrically for the reactions of 4-nitrophenyl 2-furoate (1) with a series of secondary alicyclic amines in H2O containing 20 mole % DMSO at 25.0℃. 1 is about 5-8 times more reactive than 4-nitrophenyl benzoate (2), although 1 is expected to be less reactive than 2 based on MO calculations and 13 C NMR study. The Brфnsted-type plots for the aminolysis reactions of 1 and 2 are linear with βnuc values of 0.78 and 0.85, respectively. The replacement of the CH=CH group by an O atom in the acyl moiety (2->1) does not cause any mechanism change. The reaction of piperidine with a series of substituted phenyl 2-furoates gives a linear Hammett plot with a large ρ- value (ρ- = 2.88) when σ- constants are used. The linear Brфnsted and Hammett plots with a large ρ- value suggest that the aminolysis reaction of 1 proceeds via rate-determining break-down of the addition intermediate to the porducts.

Photochemical C$_4$-Cycloadduct Formation between 5(E)-Styryl-1,3-dimethyluracil and Some Olefins-Via Photochemical Diels-Alder Type [4 + 2] Adduct

  • Shim, Sang-Chul;Shin, Eun-Ju
    • Bulletin of the Korean Chemical Society
    • /
    • v.8 no.5
    • /
    • pp.376-380
    • /
    • 1987
  • The cyclobutane forming photocycloaddition reaction of 5(E)-styryl-1,3-dimethyluracil with some olefins occurs on the 5,6-double bond of uracil ring rather than the expected central double bond via an intermediate, probably the photochemical Diels-Alder type adduct. This intermediate formed on short term irradiation of 5(E)-styryl-1,3-dimethyluracil and 2,3-dimethyl-2-butene solution is converted into the $C_4$-cycloadduct on the prolonged irradiation. Quantum yield of the intermediate formation is not linear with the concentration of 2,3-dimethyl-2-butene probably due to the secondary reaction accompanied with the complex reaction kinetics. The intermediate is formed from the lowest excited singlet state.