Alkaline Hydrolysis of Nonphenolic β-0-4 Lignin Models: Substituent Effect of the A-Ring on the Rate

Holzforschung ◽  
2002 ◽  
Vol 56 (6) ◽  
pp. 592-594 ◽  
Author(s):  
T. P. Schultz ◽  
T. H. Fisher
Keyword(s):  
Alkaline Hydrolysis ◽  
Substituent Effect ◽  
Hydrolysis Rate ◽  
Side Reactions ◽  
Hydrolysis Rates ◽  
Hydrolysis Of ◽  
Electron Withdrawing Substituents

Summary Six nonphenolic β-0-4 lignin models substituted on the phenyl A-ring [unsubstituted; 3,5-dimethoxyl; 3,4-dimethoxyl; 3-methoxyl; 4-methoxyl; and 4-methyl] were synthesized and the alkaline hydrolysis rates at 170°C determined. Electron-withdrawing substituents enhanced the hydrolysis rate, but this effect was relatively minor. Over 90% of the disappearance of the dimer could be accounted for by appearance of the B-ring phenolic product for all compounds, which suggests that minimal side reactions occurred.

Effect of the α- and γ-Hydroxyls on the Alkaline Hydrolysis Rate of Nonphenolic β-0-4 Lignin Diastereomers

Holzforschung ◽  
2002 ◽  
Vol 56 (1) ◽  
pp. 67-72 ◽  
Author(s):  
Dexter L. Criss ◽  
Thomas Elder ◽  
Thomas H. Fisher ◽  
Tor P. Schultz
Keyword(s):  
Computational Modeling ◽  
Alkaline Hydrolysis ◽  
Rate Ratio ◽  
Electronic Effect ◽  
Activation Parameters ◽  
Hydrolysis Rate ◽  
Significant Extent ◽  
Hydrolysis Rates ◽  
Lignin Model ◽  
Hydrolysis Of

Summary Nonphenolic β-0-4 erythro and threo lignin model diastereomers with various γ-groups (CH3, CH2-O-CH3, and CH2OH) and Cα-substituents (OH, OCH3) were synthesized, and the alkaline hydrolysis rates and activation parameters determined. In addition, two of the diastereomer pairs were computationally modeled and the thermodynamic values for the ionization of the α- or γ-hydroxyl, and subsequent displacement of the phenolate group to form an epoxide intermediate, were determined. The results suggest that the erythro γ-hydroxyl may participate in the hydrolysis to a significant extent, which results in a relatively high erythro/threo rate ratio for the α,γ-di-OH isomers. The influence of the erythro γ-hydroxyl on the hydrolysis rate may be due to the relatively favorable stability of the erythro γ-oxyanion. The electronic effect of the g-substituent appears to influence how fast the α-hydroxyl displaces the phenoxyl. We had previously suggested that the γ-substituent sterically inhibits hydrolysis of the threo isomer, and computational modeling confirmed this.

Kinetic Study of Hydrolysis of Benzoates. Part XXVI. Variation of the Substituent Effect with Solvent in Alkaline Hydrolysis of Substituted Alkyl Benzoates

2006 ◽  
Vol 71 (11-12) ◽  
pp. 1557-1570 ◽  
Author(s):  
Vilve Nummert ◽  
Mare Piirsalu ◽  
Ilmar A. Koppel
Keyword(s):  
Kinetic Study ◽  
Alkaline Hydrolysis ◽  
Rate Constants ◽  
Substituent Effect ◽  
Substituent Effects ◽  
Alkyl Substituent ◽  
Solvent Parameters ◽  
Substituent Constants ◽  
Hydrolysis Of ◽  
Main Factor

The second-order rate constants k2 (dm3 mol-1 s-1) for the alkaline hydrolysis of substituted alkyl benzoates C6H5CO2R have been measured spectrophotometrically in aqueous 0.5 M Bu4NBr at 50 and 25 °C (R = CH3, CH2Cl, CH2CN, CH2C≡CH, CH2C6H5, CH2CH2Cl, CH2CH2OCH3, CH2CH3) and in aqueous 5.3 M NaClO4 at 25 °C (R = CH3, CH2Cl, CH2CN, CH2C≡CH). The dependence of the alkyl substituent effects on different solvent parameters was studied using the following equations:      ∆ log k = c0 + c1σI + c2EsB + c3∆E + c4∆Y + c5∆P + c6∆EσI + c7∆YσI + c8∆PσI     ∆ log k = c0 + c1σ* + c2EsB + c3∆E + c4∆Y + c5∆P + c6∆Eσ* + c7∆Yσ* + c8∆Pσ* .  ∆ log k = log kR - log kCH3. σI and σ* are the Taft inductive and polar substituent constants. E, Y and P are the solvent electrophilicity, polarity and polarizability parameters, respectively. In the data treatment ∆E = ES - EH2O , ∆Y = YS - YH2O , ∆P = PS - PH2O were used. The solvent electrophilicity, E, was found to be the main factor responsible for changes in alkyl substituent effects with medium. When σI constants were used, variation of the polar term of alkyl substituents with the solvent electrophilicity E was found to be similar to that observed earlier for meta and para substituents, but twice less when σ* constants were used. The steric term for alkyl substituents was approximately independent of the solvent parameters.

Kinetic Study of Hydrolysis of Benzoates. Part XXV. Ortho Substituent Effect in Alkaline Hydrolysis of Phenyl Esters of Substituted Benzoic Acids in Water

2006 ◽  
Vol 71 (1) ◽  
pp. 107-128 ◽  
Author(s):  
Vilve Nummert ◽  
Mare Piirsalu ◽  
Vahur Mäemets ◽  
Ilmar Koppel
Keyword(s):  
Acid Hydrolysis ◽  
Alkaline Hydrolysis ◽  
Substituent Effect ◽  
Ethyl Esters ◽  
Benzoic Acids ◽  
Neat Water ◽  
Substituted Benzoic Acids ◽  
Hydrolysis Of Esters ◽  
Hydrolysis Of

The second-order rate constants k2 for alkaline hydrolysis of phenyl esters of meta-, para- and ortho-substituted benzoic acids, X-C6H4CO2C6H5 (X = H, 3-Cl, 3-NO2, 3-CH3, 4-NO2, 4-Cl, 4-F, 4-CH3, 4-OCH3, 4-NH2, 2-NO2, 2-CN, 2-F, 2-Cl, 2-Br, 2-I, 2-CH3, 2-OCH3, 2-CF3, 2-NH2), and of substituted phenyl esters of benzoic acid, C6H5CO2C6H4-X (X = 2-I, 2-CF3, 2-C(CH3)3, 4-Cl, 4-CH3, 4-OCH3, 4-NH2), have been measured spectrophotometrically in water at 25 °C. The substituent effect in alkaline hydrolysis of phenyl esters of para-substituted benzoic acids, similar to that for ethyl esters of para-substituted benzoic acids, was found to be precisely described by the Hammett relationship (ρ = 1.7 in water). The log k value for alkaline hydrolysis of phenyl and ethyl esters of meta-, para- and ortho-substituted benzoic acids, X-C6H4CO2R, was nicely correlated with log km,p,ortho = log ko + (ρ)m,pσ + (ρI)orthoσI + (ρ°R)orthoσ°R + δorthoEsB where σ, σI, σ°R are the Hammett polar, Taft inductive and Taft resonance (σ°R = σ° - σI) substituent constants, respectively. EsB is the steric scale for ortho substituents calculated on the basis of the log k values for the acid hydrolysis of ortho- substituted phenyl benzoates in water owing to the ortho substituent in the phenyl of phenyl benzoates. In water, the main factors responsible for changes in the ortho substituent effect in alkaline hydrolysis of phenyl and ethyl esters of ortho-substituted benzoic acids, X-C6H4CO2R, were found to be the inductive and steric factors while the role of the resonance term was negligible ((ρ°R)ortho ca. 0.3). In alkaline hydrolysis of substituted benzoates in neat water, the ortho inductive effect appeared to be 1.5 times and steric influence 2.7 times higher than the corresponding influences from the ortho position in the phenyl of phenyl benzoates. The contributions of the steric effects in alkaline hydrolysis of esters of ortho-substituted benzoic acids was found to be approximately the same as in acid hydrolysis of esters of ortho-substituted benzoic and acid esterification of ortho-substituted benzoic acids.

scholarly journals Prediction of ortho substituent effect in alkaline hydrolysis of phenyl esters of substituted benzoic acids in aqueous acetonitrile

2013 ◽  
Vol 11 (12) ◽  
pp. 1964-1975 ◽  
Author(s):  
Vilve Nummert ◽  
Mare Piirsalu ◽  
Ilmar Koppel
Keyword(s):  
Alkaline Hydrolysis ◽  
Rate Constants ◽  
Substituent Effect ◽  
Substituent Effects ◽  
Benzoic Acids ◽  
Aqueous Acetonitrile ◽  
Substituent Constants ◽  
Substituted Benzoic Acids ◽  
Hydrolysis Of ◽  
Ortho Substituent

AbstractThe second-order rate constants k for the alkaline hydrolysis of phenyl esters of meta-, para- and ortho-substituted benzoic acids, X-C6H4CO2C6H5, in aqueous 50.9% acetonitrile have been measured spectrophotometrically at 25°C. The log k values for meta and para derivatives correlated well with the Hammett σm,p substituent constants. The log k values for ortho-substituted phenyl benzoates showed good correlations with the Charton equation, containing the inductive, σI, resonance, σ○ R, and steric, E s B, and Charton υ substituent constants. For ortho derivatives the predicted (log k X)calc values were calculated with equation (log k ortho)calc = (log k H AN)exp + 0.059 + 2.19σI + 0.304σ○ R + 2.79E s B − 0.0164ΔEσI — 0.0854ΔEσ○ R, where DE is the solvent electrophilicity, ΔE = E AN — E H20 = −5.84 for aqueous 50.9% acetonitrile. The predicted (log k X)calc values for phenyl ortho-, meta- and para-substituted benzoates in aqueous 50.9% acetonitrile at 25°C precisely coincided with the experimental log k values determined in the present work.The substituent effects from the benzoyl moiety and aryl moiety were compared by correlating the log k values for the alkaline hydrolysis of phenyl esters of substituted benzoic acids, X-C6H4CO2C6H5, in various media with the corresponding log k values for substituted phenyl benzoates, C6H5CO2C6H4-X.

scholarly journals Genetic control of the hydrolysis of aromatic esters by sheep plasma A-esterase

1966 ◽  
Vol 7 (3) ◽  
pp. 373-382 ◽  
Author(s):  
R. M. Lee
Keyword(s):  
Esterase Activity ◽  
Phosphate Esters ◽  
Hydrolysis Rate ◽  
Aromatic Esters ◽  
Hydrolysis Rates ◽  
Rate Of Hydrolysis ◽  
Hydrolysis Of ◽  
Naphthyl Acetate ◽  
Genetic Marking ◽  
Genetic Hypothesis

1. The rate of hydrolysis by sheep plasma of some carboxylic and phosphate esters has been determined for a random flock, and for a flock previously selected for its ability to hydrolyse di-(2-chloroethyl) aryl phosphates.2. A discontinuous variation in hydrolysis rate was found with all substrates tested and, using combinations of substrates, six types of plasma could be distinguished, each type having a different pattern of esterase activity.3. The most useful substrates for distinguishing between phenotypes were 1-naphthyl acetate and 4-ethoxycarbonylcoumarin-7-yl acetate. Three rates of hydrolysis were possible for each of these esters, and the highest rate for one was invariably combined with the lowest rate for the other, although the converse did not apply.4. To explain these results, and those of Lee (1964), it has been postulated that the quantitative production of esterase hydrolysing 1-naphthyl acetate is governed by the presence of an allele, termed Esa, at a particular gene locus. Similarly, the production of esterase hydrolysing 4-ethoxycarbonylcoumarin-7-yl acetate is determined by allele Esb, and where neither substrate is attacked the presence of a third allele, Esc, is proposed.5. The hydrolysis rates of haloxon, 1-naphthyl butyrate and 4-nitrophenyl butyrate varied in the same way as that of 1-naphthyl acetate, whereas the hydrolysis of indophenyl acetate followed the same pattern as that of 4-ethoxycarbonylcoumarin-7-yl acetate. The variation in hydrolysis rate of Coroxon could be explained by assuming that Esa and Esb are equal in this respect.6. A mating experiment produced results which were in accordance with the genetic hypothesis, but were too few in number to provide confirmation.7. The genetic marking of six types of sheep is possible, utilizing the variation in plasma A-esterase activity.

Alkaline Hydrolysis of Nonphenolic ß-O-4 Lignin Model Dimers: Further Studies of the Substituent Effect on the Leaving Phenoxide

Holzforschung ◽  
1996 ◽  
Vol 50 (5) ◽  
pp. 420-424 ◽  
Author(s):  
Willard E. Collier ◽  
Thomas H. Fisher ◽  
Leonard L. Jr. Ingram ◽  
Angela L. Harris ◽  
Tor P. Schultz
Keyword(s):  
Alkaline Hydrolysis ◽  
Substituent Effect ◽  
Lignin Model ◽  
Hydrolysis Of

Hydrolysis kinetics and mechanism of N'-(3-N-methylcarbamoyloxyphenyl)-N,N-dimethylformamidine

1980 ◽  
Vol 45 (4) ◽  
pp. 1065-1071 ◽  
Author(s):  
Alexandr Čegan ◽  
Jaroslav Šlosar ◽  
Miroslav Večeřa
Keyword(s):  
Reaction Mechanism ◽  
Paper Chromatography ◽  
Kinetics And Mechanism ◽  
Hydrolysis Rate ◽  
Hydrolysis Kinetics ◽  
Hydrolysis Products ◽  
Hydrolysis Rates ◽  
Ph Range ◽  
Hydrolysis Of

Hydrolysis of N' -(3-N-methylcarbamoyloxyphenyl)-N,N-dimethylformamidine (I) has been studied in mixture water-dioxane (4 : 1) at pH 1 to 13. The hydrolysis rates of methylcarbamoyl and dimethylformamidine groups are comparable within pH range 4 to 10, and they differ by as much as several orders of magnitude in pH ranges 1-3 and 11-13. The hydrolysis products of the whole pH range have been determined by paper chromatography, and reaction mechanism has been suggested on the basis of the measured hydrolysis rate constants.Effects of protonation and hydratation of dimethylformamidine group on the hydrolysis rate of the methylcarbamoyl group is discussed.

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