- Investigations on substituent and solvent effects on solvolysis reactions Part IX. The influence of polar substituents on the imidazole catalyzed hydrolysis of 2,4-dinitrophenyl acetates in water
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The imidazole catalyzed hydrolysis of polar substituted 2,4-dinitrophenyl acetates in water has been investigated at different temperatures. The observed rates correspond to the bimolecular nucleophilic addition of the imidazole at the carboxylic carbon atom followed by a very fast hydrolysis of the N-acetylimidazole in water. The influence of polar substituents in the acid moiety of the ester molecule on the hydrolysis reaction can be described by an electrostatic dipole-dipole interaction in the same way as the neutral hydrolysis of polar substituted ethyl acetates.
- Bittner,Schmeer
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- H6GeMo10V2O40·16H 2O nanoparticles prepared by hydrothermal method: A new and reusable heteropoly acid catalyst for highly efficient acetylation of alcohols and phenols under solvent-free conditions
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A new Keggin-type heteropoly acid, namely decamolybdodivanadogermanic acid (H6GeMo10V2O40·16H 2O), with nanosized particles (5-8 nm), has been synthesized by a hydrothermal method and characterized by elemental analysis, thermogravimetric analysis (TGA), powder X-ray diffractometry (XRD), Fourier-transform infrared spectroscopy (FTIR), UV-Visible spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and potentiometric titration. H6GeMo10V2O40·16H 2O revealed high catalytic activity for acetylation of various alcohols and phenols with acetic anhydride at room temperature (298 ± 2 K) and under solvent-free conditions. The catalyst can be easily recovered and used repeatedly for five cycles with a slight loss of activity. The catalytic activity of H6GeMo10V2O40· 16H2O was higher than that of other Keggin-type heteropoly acids, such as H3PW12O40, H3PMo 12O40 and H4SiW12O40.
- Farhadi, Saeid,Zareisahamieh, Reza,Zaidi, Masoumeh
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experimental part
p. 1323 - 1332
(2012/04/04)
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- Spinel-type zinc aluminate (ZnAl2O4) nanoparticles prepared by the co-precipitation method: A novel, green and recyclable heterogeneous catalyst for the acetylation of amines, alcohols and phenols under solvent-free conditions
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Zinc aluminate (ZnAl2O4) nanoparticles with an average particle size of about 8 nm were easily prepared by the co-precipitation method using aqueous ammonia solution as the precipitating agent. This nanosized spinel-type oxide was characterized by TGA, XRD, FT-IR, TEM, and surface area measurement and used as the heterogeneous catalyst for the acetylation reaction. Efficient acetylation of various amines, alcohols and phenols was carried out over ZnAl2O4 nanoparticles using acetic anhydride and/or acetyl chloride as the acetylating agents at room temperature without the use of a solvent. The method is highly selective, allowing the alcoholic hydroxyl group to be protected while the phenolic hydroxyl group remains intact, and the amine group can be acetylated in the presence of the hydroxyl group. This method is fast and has a high yield. It is also clean, safe, cost effective, compatible with substrates that have other functional groups and very suitable for practical organic synthesis. In addition, the catalyst can be reused without significant loss of activity. Indeed, the catalytic activity of the ZnAl2O4 nanoparticles is higher than that of bulk ZnAl2O4.
- Farhadi, Saeid,Panahandehjoo, Somayeh
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scheme or table
p. 293 - 302
(2010/09/04)
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- Simple and efficient method for acetylation of alcohols, phenols, amines, and thiols using anhydrous NiCl2 under solvent-free conditions
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Solvent-free acetylation of alcohols, phenols, amines, and thiols with acetic anhydride (Ac2O) in the presence of 0.1mol% (13mg) anhydrous NiCl2, an inexpensive and easily available catalyst, is described. Excellent yields, short reaction time, and mild reaction conditions are important features of this method.
- Meshram, Gangadhar,Patil, Vishvanath D.
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experimental part
p. 4384 - 4395
(2010/04/29)
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- Zinc oxide (ZnO) as a new, highly efficient, and reusable catalyst for acylation of alcohols, phenols and amines under solvent free conditions
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Zinc oxide (ZnO) is a highly efficient catalyst for the acylation of a variety of alcohols, phenols and amines with acid chlorides or acid anhydrides under solvent free conditions. Primary, secondary, tertiary, allylic and benzylic alcohols, diols and phenols with electron donating or withdrawing substituents can be easily acylated in good to excellent yield.
- Hosseini Sarvari, Mona,Sharghi, Hashem
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p. 10903 - 10907
(2007/10/03)
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- Ruthenium(III) chloride catalyzed acylation of alcohols, phenols, thiols, and amines
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Ruthenium(III) chloride catalyzes the acylation of a variety of phenols, alcohols, thiols, and amines under mild conditions. Some of the major advantages of this method are high yields, short reaction times, ease of operation, and compatibility with other protecting groups.
- Kanta De, Surya
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p. 2919 - 2922
(2007/10/03)
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- Copper(II) Tetrafluoroborate-Catalyzed Acetylation of Phenols, Thiols, Alcohols, and Amines
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Copper(II) tetrafluoroborate efficiently catalyzes acetylation of structurally diverse phenols, alcohols, thiols, and amines with stoichiometric amounts of Ac2O under solvent-free conditions at room temperature. Acid-sensitive alcohols are smoothly acetylated without competitive side reactions. The reaction is influenced by the steric and electronic factors associated with the substrate as well as the anhydride. Acetylation of a sterically hindered substrate requires excess of anhydride and longer time. Acylation with less electrophilic anhydrides affords poor to moderate yields.
- Chakraborti, Asit K.,Gulhane, Rajesh,Shivani
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p. 111 - 115
(2007/10/03)
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- Kinetics and Equilibria of Reactions between Acetic Anhydride and Substituted Phenolate Ions in Aqueous and Chlorobenzene Solutions
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Potassium acetate, solubilised in chlorobenzene by 18-crown-6, displaces the phenolate ion from substituted phenyl acetates by a second-order (kCl-2) process.Potassium phenolate ions, under similar conditions, react with acetic anhydride via a second order (kCl2) to yield the phenyl acetate.The concentration of the crown does not affect the reactivity unless it is not sufficient to solubilise the reactants.The rate constants correlate with the ionisation of the substituted phenols in water: log kCl2=1.60+/-0.23pKArOH(aq)a - 9.06+/-1.4 log kCl-2=-0.97+/-0.12pKArOH(aq)a + 4.78+/-0.78.The equilibrium constant for transfer of the acetyl group between phenolate ions and acetic anhydride in chlorobenzene has a Broensted βCleq of 2.6 measured against pKArOH(aq)a.The second-order rate constants (k2aq) have been measured for the reaction of substituted phenolate ions with acetic anhydride in water and they obey the Broensted equation: log (k2aq) = 0.56 +/- 0.06 pKArOH(aq)a - 2.52 +/- 0.51 Comparison of the value of the Broensted exponent for the equilibrium constant in chlorobenzene (β = 2.6) compared with that for aqueous solution (β = 1.7) indicates a greater development of effective charge consistent with the weaker solvating power of chlorobenzene.The reaction of substituted phenoxide ion with acetic anhydride has a Leffler α value of 0.33 and 0.62 for aqueous and chlorobenzene solutions, respectively, indicating a more advanced bond formation in the transition state of the reaction in the latter solvent even though the reactions in chlorobenzene are faster than in water.
- Ba-Saif, Salem A.,Maude, Antony B.,Williams, Andrew
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p. 2395 - 2400
(2007/10/02)
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- Footprint Catalysis. IV. Structural Effects of Templates on Catalytic Behavior of Imprinted Footprint Cavities
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Footprint catalysts are silica(alumina)gel catalysts with tailored specificities.Their catalytic sites are "molecular footprint-like" cavities formed by a molecular imprinting procedure with templates, which are referred to as transition-state or reactive-intermediate analogs of the catalyzed reactions.To clarify the relationship between the structural feature of template molecules and catalytic behavior, seven footprint catalysts were prepared by imprinting with templates of several types closely related to the substrates, benzoic anhydride and acetic anhydride; their catalytic activity and thermodynamic parameters for 2,4-dinitrophenolysis were then estimted.Among these catalysts, a catalyst imprinted with N,N'-dibenzoylbenzenephosphonediamide, a tetrahedral intemediate analog for benzoic anhydride substrate, showed a 10-fold higher catalytic activity than did the other imprinted catalysts.
- Shimada, Toyoshi,Nakanishi, Kiyoko,Morihara, Kensaku
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p. 954 - 958
(2007/10/02)
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- An Open Transition State in Carbonyl Acyl Group Transfer in Aqueous Solution
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The second-order rate constants have been measured for the reaction of substituted phenolate ions with 2,4-dinitrophenyl acetate, 2,4-dinitrophenyl 4-methoxy-2,6-dimethylbenzoate and acetic anhydride in aqueous solution at 25 deg C.The data are over a wide range of phenolate ion basicity and obey good Broensted equations which have βnuc values of, respectively, 0.57 +/- 0.03, 0.15 +/- 0.07 and 0.59 +/- 0.05.The principal conclusion of this work is that the identity reaction of 2,4-dinitrophenolate ion with 2,4-dinitrophenyl 4-methoxy-2,6-dimethylbenzoate has anopen transition state, namely one with very weak bonds to entering and departing ligands.The transition state possesses a Kreevoy tightness parameter (τ) of 0.18.The open transition state arises from the stabilising effect of the acyl group substituents on the benzoylium ion and their destabilising effect on the putative tetrahedral intermediate as well as the weak basicities of the nucleophile and nucleofuge.This is the first example of an open transition state in an acyl group transfer which does not require the assistance of a negatively charged internal nucleophile.The data for 2,4-dinitrophenyl acetate may be employed to calculate an identity rate constant (kii) for the reaction of 2,4-dinitrophenolate ion with the ester.This data may be fitted to a theoretical Lewis-Kreevoy plot (log kii vs. pKi) possessing both positive and negative values of βii (slope of the line).Microscopic medium effects place a limit to the accuracy of predictions of rate constants, including kii, from linear free energy relationships.
- Ba-Saif, Salem A.,Colthurst, Matthew,Waring, Mark A.,Williams, Andrew
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p. 1901 - 1908
(2007/10/02)
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- A Kinetic Study of the Hydrolysis of Aryl Esters by the pH-Stat Method
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The rates of hydrolysis of a series of aryl acrylates and aryl acetates in water at 24 deg C have been monitored by the pH stat method.The second-order rate coefficients for base-induced reactions (kOH) determined by this method are consistent with literature values determined under buffered conditions and conform to the conventional BAC2 mechanism for ester hydrolysis.
- Marsh, Mary Rose,Gold, Victor,Hall, C. Dennis,Sghibartz, Christopher
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p. 1801 - 1814
(2007/10/02)
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- (Trimethylsilyl)ethoxyacetylene. An Effective Reagent for Mild Dehydrative Condensation of Carboxylic Acids and H-Acidic Materials
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(Trimethylsilyl)ethoxyacetylene, a stable and easy to handle dehydrating reagent, is quite effective for the title condensation to prepare ester-, lactone-, lactam-, and peptide-linkages under mild conditions.
- Kita, Yasuyuki,Akai, Shuji,Yamamoto, Miki,Taniguchi, Miyako,Tamura, Yasumitsu
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p. 334 - 337
(2007/10/02)
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- Activation volumes for ester hydrolysis via elimination-addition
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Esters that have an acidic proton α to the carbonyl group (or vinylogous situation) and a good leaving group may undergo hydrolysis by elimination to an intermediate ketene, which rapidly hydrates.Examples are found in p-hydroxybenzoate, malonate, and acetoacetate esters of nitrophenols.The evidence for this mechanism (E1 cb type) includes the independence of rate with pH in the region of dissociation of the acidic proton and, in particular, positive volumes of activation that contrast sharply with negative values typical of the more usual BAc2 mechanism of hydrolysis.
- Isaacs, Neil S.,Najem, Tariq S.
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p. 1140 - 1144
(2007/10/02)
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- MECHANISM OF ESTER AMINOLYSIS IN APROTIC MEDIA AND SPECIFIC SOLVENT EFFECTS
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The n-butylaminolysis of nitro-substituted 4'-nitrophenyl benzoates and cinnamates as well as of phenylacetates in aprotic solvents is governed by a kinetic law implying higher order terms in nucleophile.It is shown that the attacking nucleophile forms a n-? type molecular complex with the substrate before reaching the transition state in the subsequent kinetic step.This molecular complex is a true reaction intermediate as evidenced by the observed negative activation enthalpy.Other nucleophile molecules intervene as general base catalysts.Tertiary amines also catalyse the reaction.Their catalytic activity is linearly related to their hydrogen bond forming ability and it is not a direct function of their proton basicity.By varying the nucleophile structure, an excellent Broensted relationship could be obtained for the first time in aprotic media, the β of which confirms that the catalytic collapse of tetrahedral intermediate is the rate determining step.The reaction of cinnamates turns out to be less sensitive to structural changes of the substrate than is the reaction of benzoates as shown by the corresponding Hammet ? values.The electronic effects of 2-nitro groups are strongly solvent dependent.Once more, it is established that whenever specific solvent effects (?-donor or n-donor ability) are present, they dominate the overall effect.A general reaction mechanism is proposed which not only explains the various roles played by the nucleophile but also accounts successfully for the great variety of kinetic schemes observed in aprotic media.
- Nagy, Otto B.,Reuliaux, Victor,Bertrand, Nicole,Mensbrugghe, Anne Van Der,Leseul, Jean,Nagy, Janos B.
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p. 1055 - 1074
(2007/10/02)
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- Kinetics and Some Equilibria of Transacylation between Oxy Anions in Aprotic Solvents
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β-Deuterium isotope effects (β-DIE) determined in acetonitrile for the following reactions are: CH3COO- + 4-NO2C6H4O2CCL3 (L = H, D) (PNPA-L3), 0.958 +/- 0.007 (5-45 deg C); CH3COO- + 2,4-(NO2)2C6H3O2CCL3 (DNPA-L3), 0.964 +/- 0.011 (5-20 deg C; OH(1-) + PNPA-L3, 0.972 +/- 0.028 (25 deg C); 4-NO2C6H4O- (PNP-) + CL3COOCOCL3, 1.00 +/- 0.02 (20 deg C); 4-NO-C6H4O- (PNOP-) + CL3COOCOCL3, 1.00 +/- 0.03 (20 deg C). β-DIEs in benzene for two of these reactions are: CH3COO- + PNPA-L3, 0.957 +/- 0.045 (10-20 deg C); CH3COO- + DNPA-L3, 0.985 +/- 0.050 (5-10 deg C).The fraction of tetrahedral character at the transition state (TS) deduced from β-DIEs for reactions of CH3COO- + PNPA is 0.32 in both CH3CN and benzene, of CH3COO- + DNPA is 0.28 in CH3CN and 0.12 in benzene, and of OH- + PNPA is 0.21 in CH3CN.These values are similar to what is found in water and indicate TSs of essentially trigonal geometry.Isotope effects (CH3)2/k(CD3)2> of unity for ester formation from CL3COOCOCL3 with phenoxides might be interpreted by two contributing factors to the observed effect; one of the usual hyperconjugation source and the other from electoststic effect of the label in the departing CL3COO-.An equilibrium isotope effect (CH3)2/K(CD3)2> of 1.03 in the direction of ester formation is calculated.A Hammett correlation of reactions of substituted phenoxides with CH3COOCOCH3 in CH3CN yielded ρ = -2.54.The reaction of CH3COO- in CH3CN could not be effected with phenyl acetate.The reaction was endergonic (ΔG0 = +2.59 kcal/mol)with PNPA and exergonic (ΔG0 = -7.61 kcal/mol) with DNPA.Activation enthalpies of these reactions decrease from H2O to CH3CN to benzene, whereas activation entropies increase in this order.
- Kovach, Ildiko M.
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p. 2235 - 2241
(2007/10/02)
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- Reaction Progress at the Transition State for Nucleophilic Attack on Esters
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β-Deuterium isotope effects (kCH3/kCD3) at 25 deg C in aqueous solution for reaction of the following nucleophiles and substrate acetate esters are as follows: CH3CO2(-), 2,4-(NO2)2C6H3O2CCL3 (L = H,D), 0.950 +/-0.008; C6H5O(-), 4-NO2C6H4O2CCL3, 0.971 +/-0.020; C6H5O(-), 2,4-(NO2)2C6H4O2CCL3, 0.968 +/-0.009; HO(-), 4-NO2C6H4O2CCL3, 0.970 +/-0.009; HO(-), C6H5O2CCL3, 0.980 +/-0.009.These are consistent with fractions of reactant progress at the transition state of 0.37, 0.21, 0.22, 0.22, and 0.15, respectively.Agreement is reasonably good with fractions of reaction progress estimated from α-deuterium isotope effects in formate ester reactions, measured by Cordes et al.For the nucleophilic reaction of water with C6H5O2CCL3, protolytically catalyzed by CH3CO2(-), the β-D effect is 0.914 +/-0.023 (fraction of reaction progress 0.65).This corresponds well with fractions of reaction progress of 0.58-0.66 from α-D effects for carboxylate general catalysis of three formate ester hydrolyses, studied by Cordes et al.For very strong bases (pK > 12) reacting as nucleophiles, the value of βnuc(ca. 0.2) is similar to, or smaller than, the fraction of reaction progress estimated from the isotope effects (ca. 0.2-0.4).The value of βnuc for nucleophilic reactions of weaker bases (pK = ca. 8-11) is larger than the fractions of reaction progress calculated from isotope effects (0.2-0.4 while βnuc = ca. 0.7).This evidence is consistent with negative deviations both for aryloxide ions and for strongly basic nucleophiles such as alkoxide and hydroxide ions from a hypothetical line of βnuc greater than 0.2 but smaller than 0.7.The major reason for negative deviation of aryloxide ions is probably disproportionate loss of resonance energy and of alkoxide ions is disproportionate loss of solvation energy, upon nucleophilic binding at the transition state.These two factors may be linked and may not be entirely separable.
- Kovach, Ildiko M.,Elrod, James P.,Schowen, Richard L.
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p. 7530 - 7534
(2007/10/02)
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- Bronsted Plots in the Reactions of 2,4-Dinitrophenyl Acetate and Methyl Phenyl Carbonate with Substituted Pyridines
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Rate constants are reported for nucleophilic attack of a series of 3- or 4-substituted pyridines on 2,4-dinitrophenyl acetate and methyl phenyl carbonate at 25 deg C, and ionic strength 0.2 M.The Bronsted plot obtained is curved for the acetate and linear for the carbonate.The first shows two linear regions (at low and high pKa values with slopes 0.85 and 0.2, respectively) and a curvature in between.The Bronsted slope for the carbonate is 1.3.The Bronsted curve can be accounted for in terms of a tetrahedral intermediate in the reaction path and a change in the rate-determining step from breakdown of the intermediate to its formation, as the substituted pyridine becomes more basic.A semiempirical equation based on these assumptions fits the experimental data.From the shape of the curved Bronsted plot, an equal leaving ability from the tetrahedral intermediate for 2,4-dinitrophenolate and a (hypothetical) pyridine of pKa = 7.3 is deduced.The influence of the group that does not leave on the relative leaving abilities of phenolates and pyridines is discussed.
- Castro, Enrique A.,Freudenberg, Margarita
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p. 906 - 910
(2007/10/02)
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