Reactions of ethyl 2-alkyl-3-oxobutanoate with thiourea and methylthiourea

1983 ◽  
Vol 48 (7) ◽  
pp. 1872-1877 ◽  
Author(s):  
Jaromír Kaválek ◽  
Vladimír Macháček ◽  
Vojeslav Štěrba
Keyword(s):  
Reaction Mechanism ◽  
Dissociation Constants ◽  
Reaction Rates ◽  
Medium Effects ◽  
Alkyl Derivatives ◽  
Alkyl Groups ◽  
Independent Synthesis ◽  
Kinetics Of ◽  
Derivatives Of

The reaction of ethyl 3-oxobutanoate with N-methylthiourea in alkoxide medium gives a mixture (1 : 20) of 1,6-dimethyl-2-thiouracil and 3,6-dimethyl-2-thiouracil: the latter isomer has been isolated from the mixture and the former isomer has been prepared by independent synthesis. Dissociation constants of ethyl 2-alkyl-3-oxobutanoates (alkyl = methyl, butyl, or isopropyl) have been measured in methanol. Reaction of these esters with thiourea and N-methylthiourea gives the corresponding alkyl derivatives of 6-methyl-2-thiouracil. Kinetics of these reactions have been measured in methoxide medium. Effects of the alkyl groups on the reaction rates have been investigated, and a reaction mechanism is suggested.

scholarly journals Kinetics of saccharose fermentation by Kombucha

2014 ◽  
Vol 20 (3) ◽  
pp. 345-352 ◽  
Author(s):  
Eva Loncar ◽  
Katarina Kanuric ◽  
Radomir Malbasa ◽  
Mirjana Djuric ◽  
Spasenija Milanovic
Keyword(s):  
Empirical Model ◽  
Black Tea ◽  
Reaction Rates ◽  
Yeast Cells ◽  
Inoculum Concentration ◽  
Viable Cells ◽  
Rate Of Reaction ◽  
Kinetics Of ◽  
Derivatives Of ◽  
Very High

Kinetics of saccharose fermentation by Kombucha is not yet well defined due to lack of knowledge of reaction mechanisms taking place during this process. In this research kinetics of saccharose fermentation by Kombucha was analysed using the suggested empirical model. The data were obtained on 1.5 g L-1 of black tea, with 66.47 g L-1 of saccharose and using 10% (v/v) or 15% (v/v) of Kombucha. Total number of viable cells was as follows: approximately 5x105 of yeast cells per mL of the inoculum and approximately 2x106 of bacteria cells per mL of the inoculum. The samples were analysed after 0, 3, 4, 5, 6, 7 and 10 days. Their pH values and contents of saccharose, glucose, fructose, total acids and ethanol were determined. A saccharose concentration model was defined as sigmoidal function at 22oC and 30oC, and with 10% (v/v) and 15% (v/v) of inoculum quantity. Determination coefficients of the functions were very high (R2>0.99). Reaction rates were calculated as first derivatives of Boltzmann?s functions. No simple correlation between rate of reaction and independent variables (temperature and inoculum concentration) was found. Analysis of empirical model indicated that saccharose fermentation by Kombucha occurred according to very complex kinetics.

Contribution à l'étude des réactions d'alkylation et de polyalkylation de l'adamantane et de ses homologues

1987 ◽  
Vol 65 (10) ◽  
pp. 2428-2433 ◽  
Author(s):  
G. Molle ◽  
J. E. Dubois ◽  
P. Bauer
Keyword(s):  
Radical Mechanism ◽  
Cage Structure ◽  
Alkyl Derivatives ◽  
Alkyl Groups ◽  
Free Radical Mechanism ◽  
Grignard Reactions ◽  
Secondary Reactions ◽  
High Boiling Point ◽  
Derivatives Of ◽  
Better Than

A method for preparing alkyl derivatives of cage-structure compounds is proposed. It relies on the use of Grignard reactions with a high boiling point solvent. The reactions take place at atmospheric pressure. Methylation of adamantane, diamantane, and homoadamantane occurs with quantitative yield. With other primary alkyl groups, yields are better than 60%. Competition between alkylation and secondary reactions is discussed on the basis of a free radical mechanism.

Kinetics of Reactions Between Silica and Carbon and the Formation of Silicon Carbide

1995 ◽  
Vol 410 ◽  
Author(s):  
Kjell Wiik ◽  
Ketil Motzfeldt
Keyword(s):  
Silicon Carbide ◽  
Reaction Mechanism ◽  
Partial Pressure ◽  
Diffusion Path ◽  
Reaction Rates ◽  
Coarse Grained ◽  
Continuous Formation ◽  
Thermogravimetric Investigation ◽  
Kinetics Of

ABSTRACTThe reactions taking place between coarse grained mixtures of silica (cristobalite) and carbon (graphite) at 1558°C in pure CO as well as mixtures of CO and Ar, have been subjected to a thermogravimetric investigation. A model is developed in the regime where the formation of SiC does not take place. The primary steps are assumed to be: Reaction betweefn SiO2 and CO to give SiO(g) and CO2 followed by the reaction between CO2 and C to give CO. The model predicts the prevailing partial pressure of SiO throughout the charge, and the correlation between observations and model strongly supports the above given reaction mechanism.Enhanced and accelerating reaction rates were observed when the formation of β-SiC took place. It is suggested that this is due to the continuous formation of stable SiC-nucleus on the Csurface and the subsequent shortening of the diffusion path for SiO.

Modeling Reaction Kinetics of Twin Polymerization via Differential Scanning Calorimetry

2018 ◽  
Vol 43 (4) ◽  
pp. 347-357
Author(s):  
Janett Prehl ◽  
Robin Masser ◽  
Peter Salamon ◽  
Karl Heinz Hoffmann
Keyword(s):  
Reaction Mechanism ◽  
Density Functional ◽  
Reaction Rate ◽  
Density Functional Theory Calculations ◽  
Scanning Calorimetry ◽  
Functional Theory ◽  
Reaction Rate Constants ◽  
Acid Catalyzed ◽  
Kinetics Of ◽  
Derivatives Of

Abstract We present a kinetic model for the reaction mechanism of acid-catalyzed twin polymerization. Our model characterizes the reaction mechanism not by the reactants, intermediate structures, and products, but via reaction-relevant moieties. We apply our model for three different derivatives of 2,2’-Spirobi[4H-1,3,2-benzodioxasiline] and determine activation energies, reaction enthalpies, and reaction rate constants for the reaction steps in our mechanism. We compare our findings to previously reported values obtained from density functional theory calculations. Furthermore, with this approach we are also able to follow the time development of the concentrations of the reaction-relevant moieties.

scholarly journals Kinetics and mechanism of As2S2 oxidation

2005 ◽  
Vol 70 (6) ◽  
pp. 869-877 ◽  
Author(s):  
Ivan Mihajlovic ◽  
Nada Strbac ◽  
Zivan Zivkovic ◽  
Ilija Ilic
Keyword(s):  
Activation Energy ◽  
Thermal Analysis ◽  
Reaction Mechanism ◽  
Kinetic Equation ◽  
Chemical Transformation ◽  
Chemical Reaction ◽  
Reaction Rates ◽  
Fast Reaction ◽  
Isothermal Conditions ◽  
Kinetics Of

The kinetics of realgar (As2S2) oxidation was studied under isothermal and non-isothermal conditions. The obtained values of the activation energy indicate that the process occurs in the kinetic domainwith the realgar particles being converted to As2O3 and As4O6 (g). The very fast reaction rates were limited by the chemical reaction. The kinetic equation was found to be: ?ln (1??) = 4.56 x 103 x e(?8780/T) x t. The proposed reaction mechanism and chemical transformation investigated by ICP?AES, EDXRF and thermal analysis are discussed.

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