- The effect of 4-halogenobenzoate ligands on luminescent and structural properties of lanthanide complexes: Experimental and theoretical approaches
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The ligands 4-fluorobenzoate (4-fba), 4-chlorobenzoate (4-cba), 4-bromobenzoate (4-bba) and 4-iodobenzoate (4-iba) were chosen in order to synthesize europium(iii), gadolinium(iii) and terbium(iii) complexes and compare the effect of halogens on their phy
- Monteiro, Jorge H. S. K.,De Bettencourt-Dias, Ana,Mazali, Italo O.,Sigoli, Fernando A.
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p. 1883 - 1891
(2015/03/18)
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- Electronic and steric effects: How do they work in ionic liquids? the case of benzoic acid dissociation
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(Figure Presented) The need to have a measure of the strength of some substituted benzoic acids in ionic liquid solution led us to use the protonation equilibrium of sodium p-nitrophenolate as a probe reaction, which was studied by means of spectrophotometric titration at 298 K. In order to evaluate the importance of electronic effect of the substituents present on the aromatic ring, both electron-withdrawing and -donor substituents were taken into account. Furthermore, to have a measure of the importance of the steric effect of the substituents both para- and ortho-substituted benzoic acids were analyzed. The probe reaction was studied in two ionic liquids differing for the ability of the cation to give hydrogen bond and π-π interactions, namely [bm 2im][NTf2] and [bmpyrr][NTf2]. Data collected show that benzoic acids are less dissociated in ionic liquid than in water solution. Furthermore, the equilibrium constant values seem to be significantly affected by both the nature of ionic liquid cation and the structure of the acid. In particular, the ortho-steric effect seems to operate differently in water and in the aromatic ionic liquid, determining in this solvent medium a particular behavior for ortho-substituted benzoic acids.
- D'Anna, Francesca,Marullo, Salvatore,Vitale, Paola,Noto, Renato
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experimental part
p. 4828 - 4834
(2010/10/04)
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- Kinetics and mechanism of alkaline hydrolysis of hydroxamic acids
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Kinetics and mechanism of the alkaline hydrolysis of N-p-tolylbenzohydroxamic acid (p-X-C6H4(C=O)N(OH)C6H4-CH 3; X = H, CH3, Cl) and its para-substituted methyl and chloro derivatives have been studied in 10% (v/v) aqueous dioxane at 65°. Two cases of hydrolysis applicable to two different ranges of NaOH concentrations are recognized. The relative reactivity, temperature, salt, solvent and solvent isotope effects have also been examined.
- Ghosh, Kallol K.,Thakur, Santosh S.
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- Effect of solvents on the kinetics and mechanism of the acidic and alkaline hydrolysis of hydroxamic acids
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The acid catalyzed hydrolysis of N-phenylbenzohydroxamic acid (PBHA) C6H5C(=0)N(OH)C6H5 has been studied in aq. dioxane, acetone, dimethylsulphoxide, dimethylformamide, methanol, ethanol and 2-propanol mixtures. Dioxane and methanol have a rate enhancing effect but DMF, acetone, ethanol and 2-propanol exert a rate decreasing effect. In DMSO an increase is followed by a decrease i.e. a rate maximum is observed. An attempt has also been made to study the alkaline hydrolysis of PBHA and two of its derivatives (X-C6H4C(=0)N(OH)C6H5; X=4-NO2, 4-Cl) in aq. dioxane. In all case the pseudo first order rate constant increase with increasing dioxane content. The activation parameters ΔH(+), Δ(+), and ΔGH(+) have been calculated. An attempt has been made to correlate rate data for acidic hydrolysis in terms of solvatochromic parameters and linear free energy relationships.
- Ghosh, Kallol K.,Krishnani, Kishore K.,Ghosh, Sharmistha
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p. 337 - 342
(2007/10/03)
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- CLEAVAGE OF THE PHENACYL ESTERS OF CARBOXYLIC AND THIOCARBOXYLIC ACIDS BY METAL ALKOXIDES
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During the cleavage of phenacyl esters with general formula XC6H4COCH2OCOR by metal alkoxides in alcohols and in ether-alcohol solutions the acids, esters, and ethers are formed as a result of cleavage of the C-C bond.The solvent participates in the formation of the ether and gives rise to transesterification of RCOOCH3 with catalytic participation of the metal alkoxide.The reactivity of the phenacyl esters of the thio acids is much higher.Before dissociation the esters of substituted benzoins C6H5COCH(OCOCH3).C6H4X-4 undergo irreversible rearrangement with the formation of isomeric products.
- Morozov, A. A.
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p. 1138 - 1143
(2007/10/02)
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- Preparation of anhydrous organic acid salts
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One-step process for preparing anhydrous, organic acid alkali or alkaline earth metal salts by contacting and reacting an organic or polymeric acid fluoride, anhydride or ester and an organic alkali or alkaline earth metal silanolate.
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- Mechanistic Studies on the Basic Hydrolysis of 2,2,2-Trichloro-1-arylethanones
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The basic hydrolysis of 2,2,2-trichloro-1-phenylethanone (1a), 2,2,2-trichloro-1-(p-methoxyphenyl)ethanone (1b), and 2,2,2-trichloro-1-(p-chlorophenyl)ethanone (1c) has been studied in the pH range 5.5-13.2.In all cases the reaction products were chloroform and the corresponding benzoate.The reaction is first order toward both the ethanone and hydroxide ion and proceeds via an addition-elimination-type mechanism.The initial addition step forms the corresponding ethanone hydrates, which, depending on the pH, will form the mono- and dianionic intermediates, the elimination of CCl3 from the mono- and/or dianionic species being the rate-limiting step of the reaction.
- Zucco, Cesar,Lima, Claudio F.,Rezende, Marcos C.,Vianna, Jose F.,Nome, Faruk
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p. 5356 - 5359
(2007/10/02)
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- Substituent Constants of the Pyrazol, 1,2,3-Triazol, Benzotriazol, and Naphthotriazol Group
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The synthesis of benzoic acids with the title substituents in p- and m-position (15, 13, 11, 9) and their ethyl and methyl esters is described.The ?p and ?m values of the substituents obtained by alkaline hydrolysis of the esters in ethanol/water and methylcellosolve/water demonstrate an inductive electron withdrawing and a mesomer electron donating effect of these groups which are important for dye chemistry.
- Sachweh, Volker,Langhals, Heinz
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p. 1627 - 1639
(2007/10/02)
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- METAL SILANOLATES: ORGANIC SOLUBLE EQUIVALENTS FOR O-2
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Alkali metal trimethylsilanolates, M+ -OSiMe3, convert carboxylic acid derivatives into their corresponding anhydrous acid salts under mild non-aqueous conditions.
- Langanis, E. D.,Chenard, B. L.
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p. 5831 - 5834
(2007/10/02)
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- Studies of the Borderline between Concerted and Stepwise Mechanisms of Elimination : E1cB Elimination of Fluoren-9-ylmethyl Carboxylate Esters
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Rates of β-elimination of carboxylate leaving groups from fluoren-9-ylmethyl carboxylate esters in methanolic sodium methoxide at 25 deg C are reported.An E1cB mechanism with rate-determining formation of a carbanion intermediate is assigned on the basis of near identity of measured elimination rates and rates of carbanion formation predicted from a Taft correlation, and the similarity with elimination of 1-(1-acetoxy-1-methylethyl)indene for which the mechanism has been established by Ahlberg and Thibblin.Values of ρ=0.42 and βlg=0.27 measured for substituted benzoate leaving groups are a little larger than expected (ca. 0.24 and 0.18, respectively) and the discrepancy is tentatively ascribed to conformational enhancement of remote substituent effects, rather than to a contribution of E2 elimination.The effects of alkyl and aryl substitution α to the leaving group are discussed, especially in relation to the borderline between concerted and stepwise mechanisms.The measurements fail to confirm an earlier inference that the borderline shows a discontinuity in transition-state structure at the point of mechanistic change.
- O'Ferrall, Rory A. More,Larkin, Finbar,Walsh, Peter
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p. 1573 - 1580
(2007/10/02)
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- Kinetics and Mechanism of Ru(III)-catalysed Oxidation of Aromatic Aldehydes by Sodium Metaperiodate in Alkaline Medium: A Change in Mechanism from Hydride Loss in Acid Medium to Proton Loss in Alkaline Medium
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The title reactions are first order in the substrate and first order in the catalyst, the order with respect to periodate being zero.The dependence on alkali is unity.The reactivity order is p-nitro > m-nitro > m-bromo > m-methoxy > p-bromo > p-chloro- > H ca. p-methyl > p-methoxy.The pH-rate profile attains a minimim at neutral pH and the rate increases on either regions of this pH.The Hammett plot shows a fair linearity with a ρ-value of + 1.66 pointing to a rate-limiting proton loss.A mechanism involving the complexation of the monoanion of the aldehydes with the Ru(III) followed by rate-limiting proton loss is postulated.Activation parameters have been computed.
- Radhakrishnamurti, P. S.,Misra, P. C.
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p. 427 - 430
(2007/10/02)
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