Kinetics of Methylation of Methyl 5-Deoxy-α/β-D-xylofuranosides

2004 ◽  
Vol 69 (10) ◽  
pp. 1877-1888
Author(s):  
Mária Oščendová ◽  
Jitka Moravcová
Keyword(s):  
Sodium Hydroxide ◽  
Methyl Iodide ◽  
Rate Constants ◽  
Reaction Rate ◽  
Steric Effect ◽  
Order Reaction ◽  
Half Time ◽  
First Order ◽  
Consecutive Reactions ◽  
Kinetics Of

The kinetics of methylation of methyl 5-deoxy-α-D-xylofuranoside (1), methyl 5-deoxy-β-D-xylofuranoside (2) and their partly methylated derivatives with methyl iodide in the presence of sodium hydroxide in acetonitrile was studied. The reaction rate was independent of the base concentration during the first half-time only and the methylation proceeded as a first-order reaction. The rate constants of all side and consecutive reactions were calculated and the influence of both polar and steric effect is discussed. The methylation of 1 was highly regioselective giving almost exclusively 5-deoxy-2-O-methyl-α-D-xylofuranoside.

Effects of Carrageenan and Chitosan as Coating Materials on the Thermal Degradation of Microencapsulated Phycocyanin from Spirulina sp.

2019 ◽  
Vol 15 (5-6) ◽  
Author(s):  
H. Hadiyanto ◽  
Marcelinus Christwardana ◽  
Meiny Suzery ◽  
Heri Sutanto ◽  
Ayu Munti Nilamsari ◽  
...  
Keyword(s):  
Antioxidant Activity ◽  
Thermal Degradation ◽  
Rate Constants ◽  
Reaction Rate ◽  
Order Reaction ◽  
Coating Materials ◽  
First Order ◽  
Reaction Rate Constants ◽  
Kinetics Of

AbstractPhycocyanin is a natural substance that can be used as an antioxidant and food colorant. The quality of phycocyanin deteriorates when it is exposed to heat, and such deterioration is evidenced by decreases in its antioxidant activity and color. Encapsulation, which introduces a coating material over a substance of interest, has been applied to prevent changes in substance quality. The objective of the present research is to evaluate the kinetics of thermal degradation of phycocyanin coated with carrageenan or chitosan. Encapsulated phycocyanin samples were exposed to temperatures of 40, 50, or 60 °C for 90 min, and kinetics of the resulting degradation was evaluated to determine changes in sample quality. The results showed that the thermal degradation of encapsulated phycocyanin at 40–60 °C follows first-order reaction kinetics with reaction rate constants (k) of 4.67–9.17 × 10–5 s-1 and 3.83–7.67 × 10–5 s-1 for carrageenan and chitosan, respectively, and that the k of encapsulated phycocyanin is slower than that obtained from samples without the coating materials (control). Encapsulation efficiencies (EE) of 68.66 % and 76.45 %, as well as loading capacities of 45.28 % and 49.16 %, were, respectively, obtained for carrageenan and chitosan.

Kinetics of the reaction between hexamethylenediisocyanate and 1-pentanol

1983 ◽  
Vol 48 (11) ◽  
pp. 3279-3286
Author(s):  
Slavko Hudeček ◽  
Miloslav Bohdanecký ◽  
Ivana Hudečková ◽  
Pavel Špaček ◽  
Pavel Čefelín
Keyword(s):  
Liquid Chromatography ◽  
Rate Constants ◽  
Reversed Phase ◽  
Order Reaction ◽  
Second Order ◽  
Second Order Reaction ◽  
Reversed Phase Liquid Chromatography ◽  
Consecutive Reactions ◽  
Phase Liquid ◽  
Kinetics Of

The reaction between hexamethylenediisocyanate and 1-pentanol in toluene was studied by means of reversed-phase liquid chromatography. By employing this method, it was possible to determine all components of the reaction mixture including both products, i.e. N-(6-isocyanate hexyl)pentylcarbamate and N,N'-bis(pentyloxycarbonyl)hexamethylenediamine. Relations for the calculation of kinetic constants were derived assuming a competitive consecutive second-order reaction. It was demonstrated that the reaction involved in this case is indeed a second-order reaction, and the rate constants of the first and second consecutive reactions were determined.

scholarly journals The alcoholysis of 1,2,2-trimethylpropyl-methylfluorophosphonate

2000 ◽  
Vol 65 (12) ◽  
pp. 857-866
Author(s):  
Mladjen Micevic ◽  
Slobodan Petrovic
Keyword(s):  
Kinetic Data ◽  
Reaction Rate ◽  
Frequency Factor ◽  
Reaction Rate Constant ◽  
Order Reaction ◽  
Activation Entropy ◽  
Second Order Reaction ◽  
Third Order ◽  
First Order ◽  
Kinetics Of

The alcoholysis of 1,2,2-trimethylpropyl-methylfluorophosphonate (soman) was examined with a series of alkoxides and in corresponding alcohols: methanol, ethanol, 1-propanol, 2-propanol, 2-methoxyethanol and 2-ethoxyethanol. Soman reacts with the used alkoxides in a second order reaction, first order in each reactant. The kinetics of the reaction between 1,2,2-trimethylpropyl-methylfluorophosphonate and ethanol in the presence of diethylenetriamine was also examined. A third order reaction rate constant was calculated, first order in each reactant. The activation energy, frequency factor and activation entropy were determined on the basis of the kinetic data.

Kinetik der Reaktion von 2.4-Dinitrofluorbenzol mit Imidazol-, SH- und Imidazol-SH-Verbindungen / Kinetics of the Reaction of 2,4-dinitro-1-fluorobenzene with Imidazole-, SH- and Imidazole-SH-compounds

1971 ◽  
Vol 26 (10) ◽  
pp. 1010-1016 ◽  
Author(s):  
Renate Voigt ◽  
Helmut Wenck ◽  
Friedhelm Schneider
Keyword(s):  
Temperature Dependence ◽  
Rate Constants ◽  
Reaction Rate ◽  
Ph Dependence ◽  
First Order ◽  
Molecular Transfer ◽  
Thiolate Anion ◽  
Nucleophilic Reactivity ◽  
Kinetics Of ◽  
Lindley Equation

First order rate constants of the reaction of a series of SH-, imidazole- and imidazole/SH-compounds with FDNB as well as their pH- and temperature dependence were determined. Some of the tested imidazole/SH-compounds exhibit a higher nucleophilic reactivity as is expected on the basis of their pKSH-values. This enhanced reactivity is caused by an activation of the SH-groups by a neighbouring imidazole residue. The pH-independent rate constants were calculated using the Lindley equation.The kinetics of DNP-transfer from DNP-imidazole to SH-compounds were investigated. The pH-dependence of the reaction displays a maximum curve. Donor in this reaction is the DNP-imidazolecation and acceptor the thiolate anion.The reaction rate of FDNB with imidazole derivatives is two to three orders of magnitude slower than with SH-compounds.No inter- or intra-molecular transfer of the DNP-residue from sulfure to imidazole takes place.

Kinetics of the Ozonation of Tetrabromobisphenol-A in Wastewater

2011 ◽  
Vol 383-390 ◽  
pp. 2945-2950 ◽  
Author(s):  
Jie Zhang ◽  
Shi Long He ◽  
Mei Feng Hou ◽  
Li Ping Wang ◽  
Li Jiang Tian
Keyword(s):  
Rate Constants ◽  
Apparent Rate Constant ◽  
Reaction Rate ◽  
Batch Reactor ◽  
Kinetic Studies ◽  
Tetrabromobisphenol A ◽  
First Order ◽  
Reaction Rate Constants ◽  
Pseudo First Order ◽  
Kinetics Of

The kinetics of TBBPA degradation by ozonation in semi-batch reactor was studied. The reaction rate constants of TBBPA with O3 and •OH were measured by means of direct ozone attack and competition kinetics, and the values of which were 6.10 l/(mol•s), 4.8×109 l/(mol•s), respectively. Results of kinetic studies showed that TBBPA degradation by ozonation under the different conditions tested followed the pseudo-first-order. The values of apparent rate constant of TBBPA degradation increased with the increase of ozone dosage and pH, but decreased with the increase of initial TBBPA concentration.

Carbohydrates in alkaline systems. II. Kinetics of the transformation and degradation reactions of cellobiose, cellobiulose, and 4-O-β-D-glucopyranosyl-D-mannose in 1 M sodium hydroxide at 22 °C

1969 ◽  
Vol 47 (21) ◽  
pp. 3957-3964 ◽  
Author(s):  
Donald J. MacLaurin ◽  
John W. Green
Keyword(s):  
Sulfuric Acid ◽  
Sodium Hydroxide ◽  
Column Chromatography ◽  
Rate Constants ◽  
Reaction Rate ◽  
Reaction System ◽  
Reaction Rate Constants ◽  
Degradation Reactions ◽  
Fructose 2 ◽  
Kinetics Of

Rates of isomerization, epimerization, and degradation reactions were measured for cellobiose (7), cellobiulose (8), and 4-O-β-D-glucopyranosyl-D-mannose (9) at 0.001 M in 1 M NaOH under N2 in the dark at 22 °C. Reaction system resolution was by column chromatography on anion resins in the borate form. Assay for D-glucose (1), D-fructose (2), D-mannose (3), and 7,8, and 9 was by continuous automated colorimetry of column effluent with orcinol–sulfuric acid as reagent. Reaction rate constants (h−1) found: k78 0.078, k79 0.0005, k7,10 0.002, k87 0.022, k89 0.003 k81 0.065, k8,12 0.023, k97 0.002, k98 0.013, k9,11 0.006 where 10,11, and 12 are other products than 1,2,3,7,8, and 9. Details for preparation of 8 and 9 are given.

Kinetics and Mechanism of Oxidation of Selenium(IV) by Permanganate Ion in Aqueous Perchlorate Solutions

1993 ◽  
Vol 58 (3) ◽  
pp. 538-546 ◽  
Author(s):  
Refat M. Hassan ◽  
Sahr A. El-Gaiar ◽  
Abd El-Hady M. El-Summan
Keyword(s):  
Reaction Mechanism ◽  
Reaction Rate ◽  
Oxidation Process ◽  
Selenium Dioxide ◽  
Order Reaction ◽  
Acid Solutions ◽  
First Order ◽  
Acid Catalyzed ◽  
Mechanism Of Oxidation ◽  
Kinetics Of

The kinetics of permanganate oxidation of selenium dioxide in perchloric acid solutions at a constant ionic strength of 2.0 mol dm-3 has been investigated spectrophotometrically. A first-order reaction in [MnO4-] and fractional order with respect to selenium(IV) were observed. The reaction rate was found to be pH-independent at lower acid concentrations ([H+] < 0.5 mol dm-3) and was acid-catalyzed beyond this range. Addition of Mn2+ and F- ions leads to the prediction that MnO4- is the sole reactive species in the oxidation process. A tentative reaction mechanism consistent with the reaction kinetics has been proposed.

Partial methylation of methyl α-D- and β-D-threofuranoside

1990 ◽  
Vol 55 (7) ◽  
pp. 1777-1782 ◽  
Author(s):  
Jiří Jarý ◽  
Miroslav Marek ◽  
Ivan Raich
Keyword(s):  
Sodium Hydroxide ◽  
Methyl Iodide ◽  
Rate Constants ◽  
Relative Rate ◽  
Hydroxyl Groups ◽  
Partial Methylation ◽  
Methylation Rate ◽  
Consecutive Reactions ◽  
Relative Rate Constants ◽  
The Individual

The methylation rate of hydroxyl groups of the title glycosides I and II has been studied in their reaction with methyl iodide and sodium hydroxide in acetonitrile. From the relative rate constants determined for the side and consecutive reactions taking place the differences in methylation rate of the individual hydroxyl groups have been deduced and are discussed from the standpoint of possible steric and polar effects.

Pyrolysis of methylcyclohexane

1987 ◽  
Vol 52 (6) ◽  
pp. 1527-1544 ◽  
Author(s):  
Ulrika Králíková ◽  
Martin Bajus ◽  
Jozef Baxa
Keyword(s):  
Activation Energy ◽  
Coke Formation ◽  
Tubular Reactor ◽  
Frequency Factor ◽  
Order Reaction ◽  
The Other ◽  
First Order ◽  
Consecutive Reactions ◽  
Secondary Reactions ◽  
Kinetics Of

The kinetics of pyrolysis of methylcyclohexane was investigated from the viewpoint of coke formation in a steel tubular reactor (S/V = 6·65 cm-1) at 0·1 MPa, 700 to 820 °C and residence time 0·01 to 0·24 s. Decomposition of methylcyclohexane proceeds as a first order reaction with a frequency factor 6·31 . 1015 s-1 and activation energy 251·2 kJ mol-1. The course of secondary reactions associated with the formation of coke is discussed. Investigation of coke formation showed a greater tendency of methylcyclohexane to coking in comparison with heptane. A prominent role plays the course of dehydrogenation of cycloalkane radicals up to aromates, this being reflected by the overall conversion of methylcyclohexane, and, on the other hand the thus formed aromates enter the consecutive reactions leading to coke.

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