The enol content of simple carbonyl compounds: a kinetic approach

1979 ◽  
Vol 57 (7) ◽  
pp. 797-802 ◽  
Author(s):  
J. Peter Guthrie
Keyword(s):  
Carbonyl Compound ◽  
Excellent Agreement ◽  
Rate Constants ◽  
Carbonyl Compounds ◽  
Methyl Ketone ◽  
Sufficient Data ◽  
Enol Ether ◽  
Thermochemical Method ◽  
Acid Catalyzed ◽  
Hydrolysis Of

Following a suggestion of Lienhard and Wang, we demonstrate that the enol content of simple carbonyl compounds can be estimated as the ratio of the rate constants for acid-catalyzed enolization of the carbonyl compound and acid-catalyzed hydrolysis of the corresponding methyl enol ether. Values so estimated are in excellent agreement with those determined by our thermochemical method. Sufficient data are available for the following; compound, pKEnol: acetaldehyde, 4.7; propionaldehyde, 4.2; isobutyraldehyde, 2.7; acetone, 7.0; cyclopentanone, 6.7; cyclohexanone, 5.3; cycloheptanone, 7.2; cyclooctanone, 6.6; p-nitroacetophenone, 4.9; p-bromoacetophenone, 6.2; acetophenone, 6.6; p-methylacetophenone, 7.0; p-methoxyacetophenone, 7.3; and by estimating the rate constants for enolization, the following; indanone, 7; 2-phenyl-2-propanone, 4; cyclopropyl methyl ketone, 8; chloroacetaldehyde, 2 (corrected for hydration); phenylacetaldehyde, 2.

A kinetic standard for precise calibration of spectrophotometer cell temperature.

1981 ◽  
Vol 27 (5) ◽  
pp. 753-755 ◽  
Author(s):  
P A Adams ◽  
M C Berman
Keyword(s):  
Temperature Dependence ◽  
Rate Constants ◽  
Cell Temperature ◽  
First Order ◽  
Order Rate ◽  
Acid Catalyzed ◽  
Pseudo First Order ◽  
Hydrolysis Of

Abstract We describe a simple, highly reproducible kinetic technique for precisely measuring temperature in spectrophotometric systems having reaction cells that are inaccessible to conventional temperature probes. The method is based on the temperature dependence of pseudo-first-order rate constants for the acid-catalyzed hydrolysis of N-o-tolyl-D-glucosylamine. Temperatures of reaction cuvette contents are measured with a precision of +/- 0.05 degrees C (1 SD).

Acid-catalyzed hydrolysis of 2-methylene-1,3-dithiolane. 2. Remarkable effects of β substitution on reversibility of the carbon protonation

1986 ◽  
Vol 64 (6) ◽  
pp. 1116-1123 ◽  
Author(s):  
Tadashi Okuyama ◽  
Masayoshi Toyoda ◽  
Takayuki Fueno
Keyword(s):  
Aqueous Solution ◽  
Rate Constants ◽  
Isotope Exchange ◽  
Relative Stabilities ◽  
The Third ◽  
Initial Carbon ◽  
Acid Catalyzed ◽  
The Individual ◽  
Individual Rate ◽  
Hydrolysis Of

Hydrolyses of 2-ethylidene-(1b), 2-isopropylidene-(1c), and 2-benzylidene-1,3-dithiolane (1d) were kinetically investigated in aqueous solution. All the individual rate constants involved in this three-step reaction were evaluated. Initial carbon protonation is only partially reversible (k2/k−1 = 1.33, 0.68, and 1.02 for 1b, 1c, and 1d, respectively) at higher pH, while the protonation becomes completely reversible below pH 2 where the third step is rate determining. Complete H–D isotope exchange at the β-carbon of 1b and 1d was observed in deuterium media before appreciable hydrolysis took place. It was demonstrated that reversion from the tetrahedral intermediate 3 to 1 occurs extensively during the reaction in the latter acidity range. Relative stabilities and reactivities of the olefinic substrates 1 are discussed.

Kinetics of acid-catalyzed hydrolysis of fluorinated propanoates

1983 ◽  
Vol 48 (10) ◽  
pp. 2805-2811 ◽  
Author(s):  
Oldřich Paleta ◽  
Jaroslav Kvíčala ◽  
Václav Dědek
Keyword(s):  
Rate Constants ◽  
Relative Rate ◽  
Chloride Concentration ◽  
Activation Entropy ◽  
High Activation ◽  
Isokinetic Relationship ◽  
Relative Rate Constants ◽  
Acid Catalyzed ◽  
Kinetics Of ◽  
Hydrolysis Of

Rates of hydrolysis, kH+, of methyl 2-chloro-2,3,3,3-tetrafluoro-(III), 2,3-dichloro-2,3,3-trifluoro-(IV), 2,2,3-trichloro-3,3-difluoro-(V), 2,3,3,3-tetrafluoro-(VI) and 3-chloro-2,3,3-trifluoropropanoate (VII) were measured in 0.5M-HCl in aqueous methanol (80% vol; 76% wt) at 40, 50 and 60 °C. The relative rate constants, krel (50 °C), (for the propanoate III, kH+ = 4.3 . 10-5 l mol-1 s-1; krel = 100) are 311, 100, 38, 9.4, 44 and 15 for the esters II, III, IV, V, VI and VII, respectively (experimental error ±9%). It was found that krel = αβ where α and β are the following factors for groups in the position 2 and 3: CClF 10, CHF 4.2, CCl2 2.8, CF3 10 and CClF2 3.6. The rate constants obey the isokinetic relationship. For the ester III the dependence of log kobs on logarithm of hydrogen chloride concentration is linear at concentrations 0.08-2.4 mol l-1 which, together with high activation entropy ΔS≠ for the esters III-VII (-167 to -217 J mol-1 K-1), shows that the hydrolysis proceeds by an AAC2 mechanism.

The hydrolysis of some N-benzoylamino acids in dilute mineral acid

1967 ◽  
Vol 45 (17) ◽  
pp. 1921-1924 ◽  
Author(s):  
J. B. Capindale ◽  
H. S. Fan
Keyword(s):  
Carboxylic Acid ◽  
Hydrochloric Acid ◽  
Glutamic Acid ◽  
Rate Constants ◽  
Mineral Acid ◽  
Dilute Solution ◽  
Acid Catalyzed ◽  
Ph Range ◽  
Hydrolysis Of ◽  
Derivatives Of

The behavior of N-benzoylaspartic acid and N-benzoylglutamic acid has been investigated at 100° in dilute solution in water and aqueous hydrochloric acid within the pH range 3.1–0.5. Some data are presented concerning the hydrolysis of the N-benzoyl derivatives of alanine, β-alanine, leucine, glycine, serine, and β-ethanolamine in water, 0.1 N hydrochloric acid, and 2 N hydrochloric acid. Benzoylglutamic acid undergoes a pH-independent conversion into pyrrolid-2-one-5-carboxylic acid, which then hydrolyses in mineral acid to glutamic acid; however, N-benzoylaspartic acid, under similar conditions, hydrolyses much more rapidly by a route which does not involve the corresponding lactam as an intermediate. In anhydrous alcohols the solvolysis of N-benzoylaspartic acid gives mixtures of aspartic acid and the β ester.First-order rate constants have been obtained for the acid-catalyzed hydrolysis of pyrrolid-2-one-5-carboxylic acid (I) and azetidin-2-one-4-carboxylic acid (II) in water over this pH range.

Transition State Analysis of Acid-Catalyzed Hydrolysis of an Enol Ether, Enolpyruvylshikimate 3-Phosphate (EPSP)

2012 ◽  
Vol 134 (31) ◽  
pp. 12947-12957 ◽  
Author(s):  
Meiyan Lou ◽  
Meghann E. Gilpin ◽  
Steven K. Burger ◽  
Ayesha M. Malik ◽  
Vivian Gawuga ◽  
...  
Keyword(s):  
Transition State ◽  
Enol Ether ◽  
Acid Catalyzed ◽  
Hydrolysis Of ◽  
State Analysis

Hydrolysis of trioxaadamantane ortho esters. II. Kinetic analysis and the nature of the rate-determining step

1984 ◽  
Vol 62 (6) ◽  
pp. 1074-1080 ◽  
Author(s):  
Robert A. McClelland ◽  
Patrick W. K. Lam
Keyword(s):  
Rate Constants ◽  
Product Formation ◽  
Low Ph ◽  
Acid Solutions ◽  
Ortho Ester ◽  
Rate Determining Step ◽  
Acid Catalyzed ◽  
Cation Hydration ◽  
Ortho Esters ◽  
Hydrolysis Of

A detailed kinetic study of the hydrolysis of a series of 3-aryl-2,4,10-trioxaadamantanes is reported. These ortho esters equilibrate with the ring-opened dialkoxycarbocation, in a very rapid process which could be studied using temperature-jump spectroscopy for aryl = 2,4-dimethylphenyl. Relaxation rate constants are of the order of 104 s−1; these could be analyzed to provide the rate constants for both the ring opening and the ring closing. Product formation from this equilibrating mixture is much slower. In acid solutions (0.01 M H+ −50% H2SO4), first-order rate constants for product formation initially increase with increasing acidity, but a maximum is reached at 20–35% H2SO4 and the rate then falls. This behavior is explained by a counterbalancing of two factors. Increasing acidity increases the amount of the dialkoxycarbocation in the initial equilibrium, but, outside the pH region, it decreases the rate of hydrolysis of this cation through a medium effect. Rate constants over a range of pH have been measured for two trioxaadamantanes and for the cation DEt+ derived by treatment of the ortho ester with triethyloxonium tetraafluoroborate. The latter models the cation formed in the ortho ester hydrolysis but it cannot ring close. Rate–pH profiles obtained in these systems are more complex than expected on the basis of rate-determining cation hydration. An interpretation is proposed with a change in rate-determining step between high pH and low pH. Cation hydration is rate determining at high pH but at low pH hemiorthoester decomposition becomes rate determining. Under these conditions the hemiorthoester equilibrates with both the dialkoxycarbocation and with the trioxaadamantane. The change in rate-determining step occurs because acid-catalyzed reversion of the hemiorthoester to dialkoxycarbocation is a faster process than acid-catalyzed hemiorthoester decomposition. This makes the latter rate-determining in acid solutions. Additional pathways available to the decomposition, however, make it the faster process at higher pH. A kinetic analysis furnishes all of the rate and equilibrium constants for the system, and provides support for the mechanistic interpretation. A comparison of these numbers with those obtained for the three stages in the hydrolysis of a simple monocyclic ortho ester underlines the novelty of the trioxaadamantane system.

A FACILE SYNTHESIS AND REACTIONS OF AMINO SELENOLO[2,3-b]PYRIDINE CARBOXYLATE

2015 ◽  
Vol 12 (1) ◽  
pp. 3910-3918 ◽  
Author(s):  
Dr Remon M Zaki ◽  
Prof Adel M. Kamal El-Dean ◽  
Dr Nermin A Marzouk ◽  
Prof Jehan A Micky ◽  
Mrs Rasha H Ahmed
Keyword(s):  
Biological Activity ◽  
Carbonyl Compounds ◽  
Mass Spectra ◽  
The Other ◽  
Pyridine Derivatives ◽  
Facile Synthesis ◽  
High Biological Activity ◽  
Basic Hydrolysis ◽  
Pyridine Carboxylate ◽  
Hydrolysis Of

 Incorporating selenium metal bonded to the pyridine nucleus was achieved by the reaction of selenium metal with 2-chloropyridine carbonitrile 1 in the presence of sodium borohydride as reducing agent. The resulting non isolated selanyl sodium salt was subjected to react with various α-halogenated carbonyl compounds to afford the selenyl pyridine derivatives 3a-f  which compounds 3a-d underwent Thorpe-Ziegler cyclization to give 1-amino-2-substitutedselenolo[2,3-b]pyridine compounds 4a-d, while the other compounds 3e,f failed to be cyclized. Basic hydrolysis of amino selenolo[2,3-b]pyridine carboxylate 4a followed by decarboxylation furnished the corresponding amino selenolopyridine compound 6 which was used as a versatile precursor for synthesis of other heterocyclic compound 7-16. All the newly synthesized compounds were established by elemental and spectral analysis (IR, 1H NMR) in addition to mass spectra for some of them hoping these compounds afforded high biological activity.

The effect of polymeric and model imidazolium halides on the rate of hydrolysis of 4-acetoxy-3-nitrobenzoic acid

1985 ◽  
Vol 50 (4) ◽  
pp. 845-853 ◽  
Author(s):  
Miloslav Šorm ◽  
Miloslav Procházka ◽  
Jaroslav Kálal
Keyword(s):  
Catalyst Concentration ◽  
Low Molecular Weight ◽  
Imidazolium Chloride ◽  
First Order ◽  
Nitrobenzoic Acid ◽  
Rate Of Hydrolysis ◽  
Acid Catalyzed ◽  
Hydrolysis Of ◽  
Ethanol In Water ◽  
Direct Attack

The course of hydrolysis of an ester, 4-acetoxy-3-nitrobenzoic acid catalyzed with poly(1-methyl-3-allylimidazolium bromide) (IIa), poly[l-methyl-3-(2-propinyl)imidazolium chloride] (IIb) and poly[l-methyl-3-(2-methacryloyloxyethyl)imidazolium bromide] (IIc) in a 28.5% aqueous ethanol was investigated as a function of pH and compared with low-molecular weight models, viz., l-methyl-3-alkylimidazolium bromides (the alkyl group being methyl, propyl, and hexyl, resp). Polymers IIb, IIc possessed a higher activity at pH above 9, while the models were more active at a lower pH with a maximum at pH 7.67. The catalytic activity at the higher pH is attributed to an attack by the OH- group, while at the lower pH it is assigned to a direct attack of water on the substrate. The rate of hydrolysis of 4-acetoxy-3-nitrobenzoic acid is proportional to the catalyst concentration [IIc] and proceeds as a first-order reaction. The hydrolysis depends on the composition of the solvent and was highest at 28.5% (vol.) of ethanol in water. The hydrolysis of a neutral ester, 4-nitrophenyl acetate, was not accelerated by IIc.

Kinetics of hydrolysis of peroxodisulphate ions in acidic medium to peroxomonosulphuric acid

1981 ◽  
Vol 46 (5) ◽  
pp. 1229-1236 ◽  
Author(s):  
Jan Balej ◽  
Milada Thumová
Keyword(s):  
Ionic Strength ◽  
Rate Constants ◽  
Acidic Medium ◽  
Measured Data ◽  
Molar Ratios ◽  
Starting Solution ◽  
Kinetics Of Hydrolysis ◽  
Rate Of Hydrolysis ◽  
Kinetics Of ◽  
Hydrolysis Of

The rate of hydrolysis of S2O82- ions in acidic medium to peroxomonosulphuric acid was measured at 20 and 30 °C. The composition of the starting solution corresponded to the anolyte flowing out from an electrolyser for production of this acid or its ammonium salt at various degrees of conversion and starting molar ratios of sulphuric acid to ammonium sulphate. The measured data served to calculate the rate constants at both temperatures on the basis of the earlier proposed mechanism of the hydrolysis, and their dependence on the ionic strength was studied.

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