Kinetics and mechanism of base-catalyzed cyclization of substituted amides and nitriles of hydantoic acid

1987 ◽  
Vol 52 (1) ◽  
pp. 140-155 ◽  
Author(s):  
Vladimír Macháček ◽  
Gabriela Svobodová ◽  
Vojeslav Štěrba
Keyword(s):  
Rate Constant ◽  
Acid Amide ◽  
Phenyl Group ◽  
Reaction Rate Constant ◽  
Amide Group ◽  
Cyclization Reaction ◽  
Hydrolysis Rate ◽  
Cyclization Reactions ◽  
Hydrolysis Of ◽  
Derivatives Of

Rates of base-catalyzed cyclizations of 8 substituted derivatives of hydantoic acid amide type R3-NH(5)-CO(4)-NR2(3)-CH2(2)-CO(1)-NHR1 and 9 nitriles type R3-NH(5)-CO(4)-NR2(3)-CHR1(2)-CN have been measured in aqueous and methanolic media. The cyclization of the amides in aqueous medium is also accompanied by hydrolysis of the hydantoins formed. In some cases the hydrolysis rate constant is greater than the corresponding cyclization reaction rate constant. With the least reactive amides, the cyclization is also accompanied by hydrolysis of the amide group. The rate of the cyclization reactions in water is higher than that in methanol (at the same concentration of the lyate ions) by the factor of 10-100. Substitution of hydrogen at 3 and 5 positions by methyl or phenyl groups causes an acceleration of the cyclization reaction, whereas a substitution in the amide group causes a considerable retardation. The greatest acceleration of the cyclization (by as much as 4 orders) is caused by introduction of phenyl group to the N(5) position, which is due to a substantial increase of concentration of the reactive anion.

THE HYDROLYSIS OF p-ACETOXYPHENYLETHYLAMINES BY INSECT CHOLINESTERASE

1958 ◽  
Vol 36 (1) ◽  
pp. 145-152
Author(s):  
L. S. Wolfe ◽  
G. D. Thorn
Keyword(s):  
Human Serum ◽  
Carbonyl Oxygen ◽  
Rectus Abdominis ◽  
Hydrolysis Rate ◽  
Rectus Abdominis Muscle ◽  
Oxygen Separation ◽  
Bovine Erythrocyte ◽  
Acetyl Group ◽  
Hydrolysis Of ◽  
Derivatives Of

The synthesis of the acetyl derivatives of tyramine and hordenine is described. The O-monoacetyl derivatives are hydrolyzed at significant rates by bovine erythrocyte cholinesterase, human serum, and fly head cholinesterase despite a nitrogen to carbonyl oxygen separation approximately twice that of acetylcholine. The pS-activity relationships, when O-acetyltyramine and acetylcholine were substrates for fly head cholinesterase, were similar, but the hydrolysis rate of O-acetyltyramine was much higher than that of acetylcholine. N-Acetylation of the O-acetyl compounds reduced the hydrolysis rate. None of the cholinesterases removed the acetyl group attached to nitrogen. The pI-activity relationships with the inhibitors Nu-683, Nu-1250, TEPP, and eserine showed that the hydrolysis of p-acetoxyphenylethylamine derivatives and acetylcholine by fly head preparations was accomplished by the same cholinesterase and not by aromatic or aliesterases. O-Acetylation of hordenine methiodide destroyed its nicotinelike action on frog rectus abdominis muscle.

The mechanisms of hydrolysis of alkyl N-alkylthioncarbamate esters at 100 °C

2005 ◽  
Vol 83 (9) ◽  
pp. 1483-1491 ◽  
Author(s):  
Eduardo Humeres ◽  
Maria de Nazaré M. Sanchez ◽  
Conceição ML Lobato ◽  
Nito A Debacher ◽  
Eduardo P. de Souza
Keyword(s):  
Rate Constant ◽  
Order Rate Constant ◽  
Base Catalysis ◽  
Hydrolysis Rate ◽  
Negative Slope ◽  
General Base ◽  
Order Rate ◽  
Basic Hydrolysis ◽  
Rate Profile ◽  
Hydrolysis Of

The hydrolysis of ethyl N-ethylthioncarbamate (ETE) at 100 °C was studied in the range of 7 mol/L HCl to 4 mol/L NaOH. The pH–rate profile showed that the hydrolysis occurred through specific acid catalysis at pH < 2, spontaneous hydrolysis at pH 2–6.5, and specific basic catalysis at pH > 6.5. The Hammett acidity plot and the excess acidity plot against X were linear. The Bunnett–Olsen plot gave a negative slope indicating that the conjugate acid was less hydrated than the neutral substrate. It was concluded that the acid hydrolysis occurred by an A1 mechanism. The neutral species hydrolyzed with general base catalysis shown by the Brønsted plot with β = 0.48 ± 0.04. Water acted as a general base catalyst with (pseudo-)first-order rate constant, kN = 3.06 × 10–7 s–1. At pH > 6.5 the rate constants increased, reaching a plateau at high basicity. The basic hydrolysis rate constant of ethyl N,N-diethylthioncarbamate, which must react by a BAc2 mechanism, increased linearly at 1–3 mol/L NaOH with a second-order rate constant, k2 = 2.3 × 10–4 (mol/L)–1 s–1, which was 10 times slower than that expected for ETE. Experiments of ETE in 0.6 mol/L NaOH with an excess of ethylamine led to the formation of diethyl thiourea, presenting strong evidence that the basic hydrolysis occurred by the E1cb mechanism. In the rate-determining step, the E1cb mechanism involved the elimination of ethoxide ion from the thioncarbamate anion, producing an isothiocyanate intermediate that decomposed rapidly to form ethylamine, ethanol, and COS.Key words: alkylthioncarbamate esters, ethyl N-ethylthioncarbamate, ethyl N,N-diethylthioncarbamate, hydrolysis, mechanism.

scholarly journals KINETIKA REAKSI FERMENTASI ALKOHOL DARI BUAH SALAK

2013 ◽  
Vol 2 (2) ◽  
pp. 16-20
Author(s):  
Fatimah ◽  
Febrina Lia G ◽  
Lina Rahmasari G
Keyword(s):  
Rate Constant ◽  
Reaction Rate ◽  
Alcoholic Fermentation ◽  
Reaction Kinetic ◽  
Reaction Rate Constant ◽  
Hydrolysis Reaction ◽  
Diffusion Reaction ◽  
Bioethanol Production ◽  
Film Diffusion ◽  
Hydrolysis Of

Research about bioethanol production from salak that are not marketable has been done. Salak containing 16.07% starch and 32.96% glucose, so that salak is potential to be converted into bioethanol by fermentation. This research aimed to study reaction kinetic of alcoholic fermentation that are the reaction kinetic of the hydrolysis of starch to glucose and fermentation of glucose to alcohol from salak by using Saccharomyces cereviseae. Hydrolysis of starch reaction containing two reaction rate controls that are chemical reaction and film diffusion. The results obtained for the hydrolysis reaction that the reacion rate constant is 1,41 x 10-11 and the film diffusion coefficient constant is 0,47 x 10-11 so the rate of the hydrolysis reaction is controlled by the film diffusion. Reaction rate constant for fermentation is 169,88. During the process of fermentation, the concentration of starch and glucose tended to decreased by time of fermentation and bioethanol concentration tended to increase by time of fermentation.

Angiotensin-converting enzyme preferentially hydrolyzes trans isomer of proline-containing substrate

1993 ◽  
Vol 75 (4) ◽  
pp. 1519-1524 ◽  
Author(s):  
M. P. Merker ◽  
C. A. Dawson ◽  
R. D. Bongard ◽  
D. L. Roerig ◽  
S. T. Haworth ◽  
...  
Keyword(s):  
Angiotensin Converting Enzyme ◽  
Trans Isomer ◽  
Rate Constant ◽  
Time Course ◽  
Enzyme Concentration ◽  
Hydrolysis Rate ◽  
Converting Enzyme ◽  
Trans Form ◽  
Hydrolysis Of

An analysis of the hydrolysis kinetics of the synthetic angiotensin-converting enzyme (ACE) substrate benzoyl-phenylalanyl-alanyl-proline (BPAP) in the intact lung suggested that 12–15% of the BPAP was in a form that could not be hydrolyzed by ACE in the time course of a single pass through the lungs [C. A. Dawson et al. Am. J. Physiol. 257 (Heart Circ. Physiol. 26): H853-H865, 1989]. BPAP has been found to exist as a mixture of cis and trans isomers in a ratio of approximately 14:86 in aqueous solution at equilibrium. Thus, one possible explanation for the incomplete hydrolysis of BPAP on passage through the intact lung is that the trans form is the preferred substrate for ACE. To examine this hypothesis, we measured BPAP hydrolysis by ACE in vitro over a range of ACE concentrations and in the presence and absence of the peptidyl-prolyl cis-trans isomerase cyclophilin. In the presence of a sufficient concentration of ACE and in the absence of cyclophilin, hydrolysis of [3H]BPAP by ACE followed biexponential progress curves, consistent with the hypothesis that the rate of hydrolysis of the majority (approximately 87%) of the substrate is proportional to ACE concentration, whereas the hydrolysis rate of the remaining substrate fraction is independent of enzyme concentration. The addition of cyclophilin resulted in an increase in the ACE-independent rate constant, an effect that was reversed by the cyclophilin inhibitor cyclosporin A. These results suggest that the enzyme-independent rate constant represents the rate of cis-trans isomerization and that the enzyme-dependent rate constant represents the hydrolysis of the trans isomer.(ABSTRACT TRUNCATED AT 250 WORDS)

Reactivity of Silicates 1. Kinetic Studies of the Hydrolysis of Linear and Cyclic Siloxanes as Models for Defect Structure in Silicates

1986 ◽  
Vol 73 ◽  
Author(s):  
Carol A. Balfe ◽  
Kenneth J. Ward ◽  
David R. Tallant ◽  
Sheryl L. Martinez
Keyword(s):  
Rate Constant ◽  
Kinetic Studies ◽  
Order Rate Constant ◽  
Hydrolysis Rate ◽  
Rate Data ◽  
Cyclic Siloxanes ◽  
Highly Strained ◽  
Kinetics Of ◽  
Hydrolysis Of ◽  
Tetrahydrofuran Solution

ABSTRACTThe kinetics of hydrolysis of hexamethylcyclotrisiloxane and di-t-butyldimesitylcyclodisiloxane in tetrahydrofuran solution have been determined and compared to hydrolysis rates of silica defects. In the presence of sufficient excess witer, the first-order rate constant of the cyclotrisiloxine, k= 3.8 × 10−3 min is similar to the rate constant, k = 5.2 × 10−1 min, of the disappearance of the D2 Raman silica defect band it has been proposed to model. Limited hydrolysis rate data for the cyclodisiloxane suggests that it hydrolyzes at least four times faster than does the cyclotrisiloxane. These data are consistent with rate data available for silica crack growth and support the assignment of highly strained siloxane bonds at the crack tip to cyclodisiloxanes. Infrared spectra determined for the cyclodisiloxanes lend further support to this model.

Solvent effect as a criterion of solvolysis mechanism. Solvolysis of 3-acyl-1,3-diphenyltriazenes

1981 ◽  
Vol 46 (9) ◽  
pp. 2091-2103 ◽  
Author(s):  
Oldřich Pytela ◽  
Petr Svoboda ◽  
Miroslav Večeřa
Keyword(s):  
Transition State ◽  
Solvent Effect ◽  
Mole Fraction ◽  
Rate Constant ◽  
Rate Constants ◽  
Proton Donor ◽  
Hydrolysis Rate ◽  
Solvent Mixtures ◽  
Solvent Dependence ◽  
Hydrolysis Of

Solvent dependence of hydrolysis rate constants of 3-acetyl-1,3-diphenyltriazene (I) and 3-(N-methylcarbamoyl)-1,3-diphenyltriazene (II) has been followed in the solvent mixtures ethanol-water, methanol-water, dioxane-water, and formamide-water within the mole fraction x = 0.0 to 0.5 at 25, 35 and 45 °C. A criterion has been suggested, based on sign of change of logarithm of the observed rate constant in dependence on change of the solvent composition, for evaluation of the reaction molecularity and, hence, participation of water in the hydrolysis mechanism. It has been found that water takes part as a proton donor in the transition state of hydrolysis of the substrates studied.

THE HYDROLYSIS OF p-ACETOXYPHENYLETHYLAMINES BY INSECT CHOLINESTERASE

1958 ◽  
Vol 36 (1) ◽  
pp. 145-152 ◽  
Author(s):  
L. S. Wolfe ◽  
G. D. Thorn
Keyword(s):  
Human Serum ◽  
Carbonyl Oxygen ◽  
Rectus Abdominis ◽  
Hydrolysis Rate ◽  
Rectus Abdominis Muscle ◽  
Oxygen Separation ◽  
Bovine Erythrocyte ◽  
Acetyl Group ◽  
Hydrolysis Of ◽  
Derivatives Of

The synthesis of the acetyl derivatives of tyramine and hordenine is described. The O-monoacetyl derivatives are hydrolyzed at significant rates by bovine erythrocyte cholinesterase, human serum, and fly head cholinesterase despite a nitrogen to carbonyl oxygen separation approximately twice that of acetylcholine. The pS-activity relationships, when O-acetyltyramine and acetylcholine were substrates for fly head cholinesterase, were similar, but the hydrolysis rate of O-acetyltyramine was much higher than that of acetylcholine. N-Acetylation of the O-acetyl compounds reduced the hydrolysis rate. None of the cholinesterases removed the acetyl group attached to nitrogen. The pI-activity relationships with the inhibitors Nu-683, Nu-1250, TEPP, and eserine showed that the hydrolysis of p-acetoxyphenylethylamine derivatives and acetylcholine by fly head preparations was accomplished by the same cholinesterase and not by aromatic or aliesterases. O-Acetylation of hordenine methiodide destroyed its nicotinelike action on frog rectus abdominis muscle.

scholarly journals RATE CONSTANT OF SOME AMINO DERIVATIVES DISSOCIATION

2021 ◽  
Vol 13 (1) ◽  
pp. 148-166
Author(s):  
Anud M. A. Efhema1 ◽  
Keyword(s):  
Dissociation Constant ◽  
Rate Constant ◽  
Phthalic Anhydride ◽  
Hplc Analysis ◽  
Sulfonyl Chloride ◽  
Hydrolysis Rate ◽  
Type Reaction ◽  
Amino Glycoside ◽  
Amino Derivatives ◽  
Hydrolysis Of

Amino glycoside derivation including, Neomycin, Streptomycin, Kanamycin and Gentamycin with special reagents, which are benzoylchloride; benzene sulfonyl chloride and phthalic anhydride were made to enhance Uv-detectability for HPLC analysis. But there are many problems facing pre column derivation and in order to solve this, the conductivity of antibiotic derivatives were used to calculate the dissociation constant and the hydrolysis rate which determined concern type reaction. In addition the characteristics those controlling the hydrolysis of antibiotic-derivatives were investigated.

scholarly journals Kinetika Reaksi Hidrolisis Virgin Coconut Oil dengan Katalis Asam Klorida / Reaction Kinetics of the Hydrolysis of Virgin Coconut Oil using Hydrochloride Acid as Catalyst

Buletin Palma ◽  
2017 ◽  
Vol 17 (1) ◽  
pp. 51
Author(s):  
Linda Trivana ◽  
Steivie Karouw
Keyword(s):  
Fatty Acid ◽  
Free Fatty Acid ◽  
Reaction Kinetics ◽  
Rate Constant ◽  
Reaction Rate ◽  
Fatty Acid Content ◽  
Coconut Oil ◽  
Reaction Rate Constant ◽  
Virgin Coconut Oil ◽  
Hydrolysis Of

<p>An accurate kinetic data has been considered as main substance in hydrolysis reaction. This research was conducted at the laboratory of processing of Indonesian Palm Crops Research Institute (IPRI) during June-July 2015. The objective of the research was to obtain the optimum condition of hydrolysis of VCO and the data of reaction kinetics (the reaction rate constant (k), the activation energy (Ea), and the reaction kinetics equation). Virgin coconut oil hydrolysis was done in two stages, the first step was the determination of the ratio of VCO:water (1:3; 1:6; 1:9; 1:12), the second step was the evaluation of reaction temperatures (60°C, 70°C, and 80°C). The determination of the optimum condition was based on the result of free fatty acid content and the values of the reaction rate constant. The free fatty acid content was measured by acid-base titration, meanwhile the reaction rate constant was determined by the equation –ln(1-XA)=kt. The results showed that the hydrolysis of VCO using ratio of VCO:water 1:12 produced higher content of FFA (0.11%) compared than others. The ratio of VCO:water 1:12 was then used to obtain the optimum temperature of hydrolysis. The optimum temperature of hydrolysis was 80°C with 0.14% of FFA, the reaction conversion was 0.88, and the reaction rate constant was 0.27 hour-1. The water consentration and reaction temperature influenced the FFA content, reaction conversion, and the reaction rate constant. The best condition of VCO hydrolysis using 1% of hydrochloride acid catalyst was on ratio of VCO:water 1:12, reaction temperature 80°C for 8 hours. The relationship between the reaction rate constant and temperature, follow Arrhenius equation k = 1,62 x 1015 e -25831/RT. Free fatty acid and glycerol are extensively used as raw materials in the manufacture of products such as detergents, cosmetics, surfactants, and pharmaceuticals.</p><p align="center"><strong>ABSTRAK</strong></p><p>Hidrolisis dapat berjalan baik apabila menggunakan data kinetika yang tepat untuk mendapatkan produk yang diinginkan. Penelitian ini dilaksanakan di Laboratorium Pengolahan Hasil, Balai Penelitian Tanaman Palma pada bulan Juni-Juli 2015. Penelitian bertujuan menentukan kondisi optimum hidrolisis Virgin Coconut Oil (VCO) secara kimiawi dengan katalis HCl dan mendapatkan data kinetika reaksi, yaitu konstanta kecepatan reaksi (k), energi aktivasi (Ea), dan rumusan persamaan kinetika reaksi. Hidrolisis VCO dilakukan 2 tahap, yaitu tahap pertama penentuan rasio VCO:air (1:3; 1:6; 1:9; dan 1:12) dipilih yang menghasilkan kadar ALB terbesar, dilanjutkan pada tahap kedua, yaitu penentuan suhu reaksi (60°C, 70°C, dan 80°C). Penentuan kondisi optimum berdasarkan kadar asam lemak bebas yang dihasilkan dan nilai konstanta kecepatan reaksi. Kadar asam lemak bebas ditentukan dengan titrasi asam-basa, sedangkan konstanta kecepatan reaksi menggunakan rumus persamaan kecepatan reaksi -ln(1-XA)=kt. Hidrolisis VCO menggunakan rasio VCO:air (1:12) menghasilkan kadar asam lemak bebas (ALB) yang lebih tinggi (0,11%), selanjutnya digunakan untuk penentuan suhu optimum hidrolisis. Suhu hidrolisis optimum adalah 80°C dengan kadar ALB sebesar 0,14%, konversi reaksi 0,88 dan konstanta kecepatan reaksi 0,27 jam-1. Konsentrasi air dan suhu reaksi berpengaruh terhadap kadar ALB, konversi reaksi, dan konstanta kecepatan reaksi. Hidrolisis VCO dengan katalis HCl 1% terbaik pada rasio VCO:air 1:12, suhu reaksi 80°C selama 8 jam. Hubungan konstanta kecepatan reaksi dengan suhu reaksi mengikuti persamaan Arrhenius k = 1,62 x 1015 e -25831/RT. Asam lemak bebas dan gliserol hasil hidrolisis banyak digunakan sebagai bahan baku dalam industri deterjen, kosmetik, surfaktan, dan obat-obatan.</p><p> </p>

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