The standard enthalpies of formation of citric and tartaric acids and their dissociation products in aqueous solutions

The energies of combustion of citric and tartaric acids in oxygen were determined by bomb calorimetry. The standard enthalpies of combustion and formation of crystalline citric and tartaric acids were calculated. The heat effects of solution of crystalline acids in water and aqueous potassium hydroxide were determined by direct calorimetry at 298.15 K. The standard enthalpies of formation of acids and their dissociation products in aqueous solution were calculated.     

Vacuum-UV-photolysis of aqueous solutions of citric and gallic acids

The vacuum-UV- (VUV-) photolysis of water is one of the advanced oxidation processes (AOP) based on the production of hydroxyl radicals (HO) that can be applied to the degradation of organic pollutants in aqueous systems. The kinetics of the VUV-photolyses of aqueous solutions of citric acid (1) or gallic acid (2) were investigated in the presence or absence of dissolved molecular oxygen (O₂) and under different pH conditions. In the case of 1, the rate of consumption of the substrate was faster at pH 3.4 than in alkaline solution (pH 11), whereas, in the case of 2, the variation of pH (2.5–7.5) did not affect the course of the reaction. Unexpectedly, the rates of depletion of both 1 and 2 decreased in the absence of O₂, this effect being much more pronounced in the case of 2. In order to explain these results, possible reaction pathways for the degradation of 1 and 2 are proposed, and the roles of the oxidizing (HO) and reducing (H and e_aq⁻) species produced by the VUV-photolysis of water are discussed.     

Synthesis and odor description of optically active cyclopropanated analogues of geraniol,nerol, nor-leaf alcohol,and matsutake alcohol

Both enantiomers of cyclopropanated analogues of geraniol, nerol, nor-leaf alcohol, and matsutake alcohol were synthesized and their odor properties evaluated. Odor characters in enantiomeric pairs were similar in the geraniol series. The (+)-(2R,3S)-nerol derivative showed various odor aspects. From the results of nor-leaf alcohol derivatives, an interaction between the (2-re,3-re)-face of nor-leaf alcohol and the human olfactory receptor was suggested. The odor of (3R)-matsutake alcohol derivative was superior to the enantiomer.     

Photoreactions of quinine in aqueous citric acid solution

Two novel compounds, 2′-(1,3-dicarboxy-2-hydroxyprop-2-yl)-quinine and the corresponding deoxyquinine derivative, have been identified together with deoxyquinine as major products of the irradiation of quinine in aqueous citric acid solution.     

Photoreactions of quinine in aqueous citric acid solution. part 2, some end-products

A novel spiro-compound derived from 2',4'-b1s-(1,3-dicarboxy-2-hydroxyprop-2-y1) -1',4'-dihydroquinine has been identified as a major end-product of the irradiation of quinine in aqueous citric acid solution. 7'-(1,3-Dicarboxy-2-hydroxyprop-2-yl)deoxyquinine and products arising from the cleavage of quinine at C-9 were also detected in the reaction mixture.     

Thermal behaviour of citric acid and isomeric aconitic acids

Thermal decomposition of citric acid, trans- and cis-aconitic acid has been studied using the TG-MS, TG-FTIR and DSC techniques. The measurements were carried out in an argon atmosphere over a temperature range of 293–673 K. The influence of the acid structures and configurational geometry on stability of the transition products and pathways of thermal transformations of the studied compounds studied is discussed.     

The reactions of aroylpyruvic acids and their derivatives witho-aminophenyldiphenylmethanol

Aroylpyruvic acids and their methyl esters react witho-aminophenyldiphenylmethanol to form 4-aryl-2-[2-(1-hydroxydiphenylmethyl)phenylamino]-4-oxobut-2-enoic acids and their esters. The α-enamino acids obtained undergo intramolecular heterocyclization in the presence of Ac₂O to affort substituted 4,5-dihydrobenzo[e][1,4]oxazepin-3(1H)-ones. The reaction of 5-arylfuran-2,3-diones witho-aminophenyldiphenylmethanol leads to products of decyclization, 2-(1-hydroxydiphenylmethyl)phenylamides of 4-aryl-2-hydroxy-4-oxobut-2-enoic acid, which upon heating in AcOH or Ac₂O yield 3-aroylacetyl-1,1-diphenyl-1H-benzo[d][1,3]oxazines. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2317–2319, November, 1998.     

Complexation of citric and tartaric acids with Na and K ions in aqueous solution

The formation of MTar^–, MCit^2– and M₂Cit^– complexes (M is Na⁺ or K⁺) was established in reactions of aqueous solutions of citric and tartaric acids with sodium or potassium chloride solutions; their stability constants were determined by potentiometric titration in aqueous solution at 298.15 K and ionic strength 0.1 and 0.3 mol/l with tetraethylammonium chloride (TEACl) as a supporting electrolyte. Heat effects of reactions between citric acid solutions and sodium or potassium chlorides were measured by calorimetric method at 288.15, 298.15, and 308.15 K and at the ionic strength 0.1, 0.2, and 0.3 M TEACl. The increasing ionic strength was found to decrease exothermic effect of complex formation processes, while the temperature produced the opposite effect. Extrapolation to zero ionic strength was used to find thermodynamic stability constants and standard heat effects of complex formation reactions in solutions of oxyacids. The changes in entropy and heat capacity were calculated as well as standard enthalpies of formation of Na and K complexes of the indicated oxyacids in aqueous solution at 298.15 K.__________Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 4, 2005, pp. 253–261.Original Russian Text Copyright © 2005 by Zelenina, Zelenin.     

Cyclization of α-terpenols and their acetates by fluorosulfonic acid

It has been shown that the superacid cyclization of α-terpenols and their acetates takes place with structural selectivity and chemo- and stereospecificity and leads to cyclic isoprenoids with higher yields than the cyclization of the corresponding β-terpenols and their acetates.     

A thermochemical study of acid-base interactions in aqueous solutions of citric acid

The heat effects of interaction of a solution of citric acid with HNO₃ and KOH were measured calorimetrically at 298.15 K and ionic strengths of 0.5, 1.0, and 1.5 (KNO₃). The heat effects of acid dissociation were calculated using the universal HEAT program. The standard thermodynamic characteristics of step dissociation of citric acid were determined.     

Perfluoro and polyfluoroalkanesulfonic acid: XVII. Difluoromethyl perfluoroalkanesulfonates and their reactions

In contrast to R_FSO₃CH₂R(1)(R=hydrogen, alkyl and perfluoroalkyl) and R_FSO₃CF₂R_F′ (2), the reactions of difluoromethyl perfluoroalkanesulfonates RFSO₃CF₂H (3) With nucleophiles are more complicated. Halide inos, X^? (X = F, Cl, I) and ethanol only attack the alkoxyl carbon atom, cleaving the C? O bond to give HCF₂X (4) and HCF₂OEt (5) respectively. Other reagents such as RCO₂^? (R=CH₃, CF₃), C₆H₅S^? etc. can either attack the carbon or sulfur atom of 3 to give the corresponding products of C? O and S? O bond cleavages. More basic nucleophiles RO^? (R = C₆H₅, Et) mainly abstract the proton of the HCF₂ moiety to produce difluorocarbene. Ether and benzene, which can be alkylated by methyl perfluoroalkanesulfonate, do not react with 3 under similar conditions. The reaction rate of 3 with KF is much slower than that of 1 (R = H). All these data seem to indicate that the shielding effect caused by the two fluorine atoms on the methyl carbon in 3 prevents to some extent the nucleophilic attack on this carbon, but not so completely as in 2 due to the presence of a hydrogen atom.     

Cleavage of alkylsilanes by strong acids : IV. The reactions of alkyldimethylfluorosilanes with fluorosulfonic acid

The kinetics of cleavage of alkyl groups and fluorine from five alkyldimethylfluorosilanes by fluorosulfonic acid dissolved in methylene chloride has been studied with proton magnetic resonance. Competitive cleavage of alkyl, methyl and fluoro occurs to form three products. A mechanism is proposed based on the third order kinetics which involves the formation of a pentacoordinate intermediate through nucleophilic attack of fluorosulfonic acid at silicon followed by electrophilic attack α to silicon.