The Racemization of Sulfonium Salts. III. The Racemization of Arylsulfonium Salts

1973 ◽  
Vol 51 (21) ◽  
pp. 3647-3648 ◽  
Author(s):  
David Darwish ◽  
Christopher E. Scott
Keyword(s):  
Rate Constants ◽  
Half Life ◽  
Steric Effect ◽  
Optically Active ◽  
Sulfonium Salts

The rate constants for racemization by inversion of a variety of monoaryl- and diarylsulfonium salts are reported. There is a marked steric effect upon the rate of the racemization reaction. An estimate is made of the half-life for racemization of acyclic optically active triarylsulfonium salts.

Ligand Activity in the Clearance of Metals from the Blood of the Crayfish (Austropotamobius Pallipes)

1984 ◽  
Vol 113 (1) ◽  
pp. 19-27
Author(s):  
R. LYON ◽  
MARINA TAYLOR ◽  
K. SIMKISS
Keyword(s):  
Rate Constants ◽  
Half Life ◽  
Donor Ligands ◽  
Binding Characteristics ◽  
Austropotamobius Pallipes ◽  
Protein Ligands ◽  
Class A ◽  
Class B ◽  
Oxygen Donors ◽  
Ligand Activity

1. The rate at which metal ions are cleared from the blood of the crayfish Austropotamobius pallipes can be described as the sum of fast and slow exponential processes. 2. The rate constants of these processes were determined and discussed in terms of ligand chemistry. 3. The half life (t½) of the fast component shows a typical Irving- Williams series for the various metals. This is interpreted as showing that the retention of metals in the blood is due to binding to protein ligands. 4. The concentrations of metals in the various tissues also reflect their binding characteristics. Class (a) metals (Ca and Sr) become associated with oxygen donors in the exoskeleton and stomach. Class (b) and borderline metals become bound to nitrogen and sulphur donor ligands in the hepatopancreas. The rapid disappearance of Cd2+ and Zn2+ from the blood can be attributed to specific ligands in the hepatopancreas.

Asymmetric alkylation of .beta.-keto esters with optically active sulfonium salts

1989 ◽  
Vol 54 (10) ◽  
pp. 2374-2383 ◽  
Author(s):  
Kazuyuki Umemura ◽  
Haruo Matsuyama ◽  
Nobuko Watanabe ◽  
Michio Kobayashi ◽  
Nobumasa Kamigata
Keyword(s):  
Optically Active ◽  
Sulfonium Salts ◽  
Asymmetric Alkylation ◽  
Keto Esters

Kinetics of hydrolyses of o-methylbenzylideneaniline and o-hydroxybenzylideneaniline

1968 ◽  
Vol 46 (9) ◽  
pp. 1589-1592 ◽  
Author(s):  
Alfred V. Willi ◽  
José F. Siman
Keyword(s):  
Hydrogen Bond ◽  
Schiff Base ◽  
Rate Constants ◽  
Experimental Error ◽  
Steric Effect ◽  
Hydrolysis Rate ◽  
Aqueous Methanol ◽  
Buffer Solutions ◽  
Acid Catalyzed ◽  
Kinetics Of

Rates of hydrolysis have been measured for o-methylbenzylideneaniline, o-hydroxybenzylideneaniline, and benzylideneaniline in various buffer solutions in 20% (by volume) aqueous methanol at 29.9 °C. Rate constants for the o-CH3 compound and the unsubstituted Schiff base agree within experimental error which indicates that there is no appreciable rate retarding steric effect. The o-OH group decreases the hydrolysis rate at pH = 5.6 – 6.6 by approximately one power of ten. This effect is caused by the hydrogen bond between the OH group and the azomethine N, which renders the Schiff base less accessible to acid-catalyzed hydrolysis.

scholarly journals Kinetics of the reaction of 5-substituted orotic acids with diazodiphenylmethane

2004 ◽  
Vol 69 (11) ◽  
pp. 949-953 ◽  
Author(s):  
Bratislav Jovanovic ◽  
Fathi Assaleh ◽  
Aleksandar Marinkovic
Keyword(s):  
Rate Constants ◽  
Steric Effect ◽  
Substituent Effects ◽  
Electrical Effect ◽  
Kinetics Of

Rate konstants for the reaction of eight 5-substituted orotic acids with diazodiphenylmethane (DDM) in dimethylformamide (DMF) were determined at 30 ?C by the known spectrophotometricmethod. The determined rate constants were correlated with the equations: logk2 = ??1+??R+h logk2 = ??1+??R+??+h to detect the presence and investigate the influence of both electrical and steric substituent effects. The obtained results show that the electrical effect (the localized ? field and delocalized ? resonance) is predominant and that the steric effect, althought present, is releatively small in this reaction.

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.

Kinetics and Mechanism of Acid Catalyzed Decomposition of 1-Phenyl-3,3-dialkyltriazenes

1994 ◽  
Vol 59 (2) ◽  
pp. 401-411 ◽  
Author(s):  
Miroslav Ludwig ◽  
Pavla Valášková ◽  
Oldřich Pytela
Keyword(s):  
Rate Constants ◽  
Steric Effect ◽  
Aqueous Ethanol ◽  
Pivalic Acid ◽  
Decomposition Kinetics ◽  
Methyl Ethyl ◽  
Rate Determining Step ◽  
Alkyl Groups ◽  
Acid Catalyzed ◽  
Catalytic Rate

Five model 1-phenyl-3,3-dialkyltriazenes (methyl, ethyl, 2-propyl, butyl, cyclohexyl) have been synthesized and their acid-catalyzed decomposition kinetics have been investigated spectrophotometrically in aqueous ethanol (40 vol.%) with pivalic acid as the catalyst. The results show that the rate-determining step is catalyzed by the proton. The decrease in the observed rate constant at higher concentrations of pivalic acid is explained by the formation of an unreactive complex of the nondissociated acid and respective triazene. The steric effect of alkyl groups on the catalytic rate constants is discussed.

scholarly journals Effect of Storage Temperature on Degradation of Methidathion in Fortified Orange and Peach Juices

2000 ◽  
Vol 83 (4) ◽  
pp. 967-970 ◽  
Author(s):  
Nikolaos B Kyriakidis ◽  
Panagiotis Athanasopoulos ◽  
Ioulia Georgitsanakou
Keyword(s):  
Experimental Data ◽  
Rate Constants ◽  
Half Life ◽  
Chromatographic Method ◽  
Storage Temperature ◽  
Activation Energies ◽  
Fruit Juices ◽  
Maximum Residue Limits ◽  
Life Values ◽  
Gas Chromatographic Method

Abstract The effect of storage temperature on methidathion degradation in orange and peach juices was studied. The insecticide was aseptically added to packed orange and peach juices, which were stored at 40, 15, and 0°C. Samples were taken at regular intervals and examined for residues of methidathion. Residues were determined with a simple gas chromatographic method; recoveries of methidathion from orange and peach juices ranged from 88.1 to 110% for both juices, and the limits of determination were 0.004 and 0.003 mg/kg, respectively. The experimental data were used to evaluate rate constants, half-lives, and times required to reach legal maximum residue limits, and activation energies for the decomposition of methidathion in orange and peach juices. Storage of fruit juices in refrigerated rooms greatly extended the half-life of methidathion beyond that of methidathion in samples stored at higher temperatures. Half-life values for methidathion in orange and peach juices, respectively, were 4.1 and 3.8 days for storage at 40°C, 115 and 113 days for storage at 15°C, and 330 and 385 days for storage at 0°C. Activation energies for methidathion degradation in orange and peach juices were 22.6 and 21.7 kcal/mol, respectively.

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