Reactions of (Hydroxo)(tetrakis(3,5-dicarboxy)-and (Hydroxo)(tetrakis(4,5-dicarboxy)phthalocyaninato)aluminum(III) with Sulfuric Acid: Simulation and Kinetic Experiments

The interaction of the octacarboxy-substituted aluminum(III) phthalocyanines (hydroxo)(tetrakis(3,5-dicarboxy)- and (hydroxo)(tetrakis(4,5-dicarboxy)phthalocyaninato)aluminum(III) with sulfuric acid is reported. It has been demonstrated by computer simulation (PM3 method) and by studying the dependence of the electronic absorption spectra of the complexes in sulfuric acid on the acidity of the medium that ((OH)AlPc(4-COOH)₄(5-COOH)₄ has three protonated forms (mono-, di-, and trication) both in the gas phase and in concentrated sulfuric acid and (OH)AlPc(3-COOH)₄(5-COOH)₄ has three protonated forms in the gas phase and two ones in concentrated sulfuric acid. The destruction kinetics of the aluminum(III) phthalocyanines in hot sulfuric acid is investigated. A destruction mechanism is suggested in which the rate-limiting step is the dissociation of an Al-N bond and the transition state consists of one aluminum(III) phthalocyanine molecule and one hydronium ion. A stability series is established for a set of differently carboxy-substituted aluminum(III) phthalocyanines. The major factors in the stability of the complexes are the negative inductive effect and the number of carboxyl groups.     

“In situ”13C NMR study of ethyl alcohol interaction with sulfuric acid

“In situ” NMR study of ethyl alcohol interaction with sulfuric acid of various concentrations confirmed that in accordance with chemical experience the main reaction product in an excess of concentrated acid is the mono-ethyl sulfate. Only traces of diethyl sulfate are formed in a large excess of 95% acid. In addition, ethyloxonium ions and protonated esters, which rapidly exchange protons with solvating water molecules, are detected as the reaction intermediates. The¹³C chemical shifts of methylene fragments in protonated esters and ethyl oxonium ions are more than 10 ppm higher than in neutral molecules. The study of reaction products at different sulfuric acid concentrations indicated that similarly to dissociation of concentrated sulfuric acid, hydrolysis of mono-ethyl sulfate requires at least two water molecules. Dedicated to Professor Pál Tétényi on the occasion of his 70th birthday     

REACTIVITY OF HALIDE COMPLEXES OF TIN(II) I. The Reduction of Methyl Orange

Abstract

Halide ion is required for the reduction of methyl orange by Sn(II). Equilibrium data on the formation of SnCl^2-n _n and SnI^2-n _n combined with kinetic data indicate that SnCl₃ ^? and SnI₃ ^? form activated complexes with protonated methyl orange. The data also suggest pathways involving SnCl₄ ^? SnCl₅ ³, SnI₅ ³ and SnI₇ ^5-.     

Superactivity and dual reactivity of the system N-iodosuccinimide-H2SO4 in the iodination of deactivated arenes

Dissolution of N-iodosuccinimide in sulfuric acid gives rise to electrophilic iodine-containing species which are capable of successfully iodinating aromatic compounds with electron-withdrawing substituents in the temperature range from 0 to 20°C. The iodination in sulfuric acid is effected by both protonated N-iodosuccinimide and IOS(O)(OH⁺)OH intermediate.     

Carbon-13 kinetic isotope effects in the decarbonylations of lactic acid containing13C at the natural abundance level

The¹³C kinetic isotope fractionation in the decarbonylation of lactic acid of natural isotopic composition by sulfuric acid has been studied in the temperature range of 20–80°C. The¹³C₍₁₎ isotope separation in the decarbonylation of lactic acid by concentrated sulfuric acid depends strongly on the temperature above 40°C. Below this temperature the¹³C isotope effect in the decarbonylation of lactic acid by concentrated sulfuric acid is normal similarly as has been found inthe decarbonylation of lactic [1-¹⁴C] acid. The experimental values of k(¹²C)/k(¹³C) ratios of isotopic rate constants for¹²C and¹³C are close to, but slightly higher than theoretical¹³C-kinetic isotope effects calculated (neglecting tunneling) under the asumption that the C₍₁₎-OH bond is broken in the rate-controlling step of the dehydration reaction. Dilution of concentrated sulfuric acid with water up to 1.4 molar (H₂O)/(H₂SO₄) ratio caused the increase of the¹³C isotope fractionation from 1.0273 found in concentrated sulfuric acid at 80.5°C to 1.0536±0.0008 (at 80.6°C). A discussion of the abnormally high temperature dependence of¹⁴C and¹³C isotope fractionation in this reaction and the discussion of the problem of relative¹⁴C/¹³C kinetic isotope effects is given.     

On the Beckmann rearrangement of ketoximes: A kinetic study in trifluoromethanesulfonic acid

The formation and the destruction of an intermediate involved in the Beckmann rearrangement of 2,4,6‐trimethylacetophenone oxime have been studied in concentrated trifluoromethanesulfonic acid by kinetic and spectroscopic measurements. Observed (k_obs) and thermodynamic rate constants (k^o) have been estimated and the values compared with the ones obtained in perchloric, sulfuric, and methanesulfonic acids. In the range 80–100 wt% of sulfuric acid, combined analysis of k_obs and k^o rates shows a specific catalysis due to [H₂SO₄] species. In trifluoromethanesulfonic acid, lower rate constants, compared to the values in sulfuric acid, have been observed which differ at 99 wt% by a factor of 10³ ca. The catalytic effect of different strong acids, the structure of the intermediate inferred from Raman and NMR spectra, and the role of the ion‐pairs involved in the reaction are discussed. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 417–426, 2004     

An unusual reaction polymerization in nitric acid medium

We are investigating an unusual reaction that occurs when methyl methacrylate (MMA) is kept in contact with concentrated nitric acid¹ (65% HNO₃, sp. gr. 1.41). Polymer of high molecular weight is formed, showing about one unit of methacrylic acid (MAA) per unit of MMA, when equilibrium is reached. The reaction depends on the temperature, the molar ratio MMA:HNO₃, and the reaction time. Although we also found polymer at temperatures in the range 50–70°C,² in this paper we only report the results when the temperature was kept between 25 and 40°C. Methacrylic acid (MAA) was found to homopolymerize under those mild conditions; its behavior was investigated. Although we also observed that polymer is formed with sulfuric acid (96%) and that acrylic acid polymerizes with both nitric and sulfuric acid at 20–30°C, we are limiting this article to the observed polymerizing action of nitric acid on methyl methacrylate and on methacrylic acid. Work proceeds on this matter in this laboratory.     

Transformations of methyl orange dimers in aqueous–acid solutions,according to UV–Vis spectroscopy data

The effect acidity has on the UV–Vis absorption spectra of azo dye methyl orange (MOD) in aqueous solutions of hydrochloric acid in the pH range of 1.7 to 7 and sulfuric acid in the 0.24 to 18 mol/L range of concentrations is investigated. The spectral transformations of MOD solutions are compared to the corresponding spectral transformations of solutions of dimethylaminoazobenzene (DAB), which is an azo dye akin to MOD. A close resemblance between the spectral transformations of MOD and dimers DAB₂ is revealed. It is concluded that the ground state of MOD, like the ground state of DAB, consists of not individual molecules but of supramolecular dimers MOD₂. It is found that dimers MOD₂ in aqueous low-acidic solutions are reversibly protonated with the formation of di- and triprotonated forms, which reversibly dissociate into diprotonated monomers upon an increase in acidity. The structural formulas of the chromogenic groups responsible for the spectral transformations, and the mechanisms of their reversible transformations, are given.     

Direct conversion of 1-deoxy-1-nitroalditols to methyl glycofuranosides

Treatment of the sodium nitronate forms of 1-deoxy-1-nitrohexitols with methanolic sulfuric or hydrochloric acid at −30 °C leads to their regiospecific conversion to the corresponding methyl glycofuranosides. The reaction exhibits more pronounced stereoselectivity for 1-deoxy-1-nitroalditols with the 2,3-erythro configuration than with the 2,3-threo substrates and cis methyl glycofuranosides are the major products. The observed stereoselectivity indicates the lysis of the protonated aci-nitro form which is a two-step process consisting of nucleophilic addition to the protonated carbon-nitrogen double bond followed by the bimolecular nucleophilic substitution of the nitrogen-containing residue.     

Enhanced positive secondary ion emission from substituted polynuclear aromatic hydrocarbon/sulfuric acid solutions

Secondary ion mass spectra of singly substituted aromatic hydrocarbon/H₂SO₄ solutions showed intense aromatic molecular ion and protonated aromatic molecule peaks characteristic of dissolved aromatic compounds from a number of aromatic compound classes, including acids, aldehydes, ketones, nitriles and nitrogen heterocycles. The presence of simultaneously abundant peaks for molecular ions and protonated molecules in secondary ion mass spectra of each aromatic compound/sulfuric acid solution is consistent with known or expected gas-phase proton transfer chemistry. The ratio of intensities, M⁺˙:[M + H]⁺, appears to be determined by sulfuric acid solution chemistry of the compound. Spectra obtained from 1–2 μl samples were relatively free from chemical noise and persisted for up to 20 min. Detection limits for some substituted aromatic compounds are estimated to be 10^?12.     

Chemistry of sulfonyl isocyanates and sulfonyl isothiocyanates. X. Possible routes to substituted imidazolidinethiones and hexahydropyrimidinethiones

4-Toluenesulfonyl isocyanate (I) reacted with 2-aminoethanol and 3-amino-l-propanol to give 2:1 isocyanate/amino alcohol addition products. 1-Amino-2-propanol and I gave 1:1 and 2:1 adducts while 2-amino-2-methyl-l-propanol afforded only a 1:1 adduct. 4-Toluenesulfonyl isothio-cyanate (III) gave 1:1 adducts with 2-aminoethanol, l-amino-2-propanol and 3-amino-l-propanol, the first two of which were cyclized by concentrated sulfuric acid to 1-(4-toluenesulfonyl)-imidazoline-2-thiones and the third to 1-(4-toluenesulfonyl)hexahydropyrimidine-2-thione. A 1:2 adduct was obtained from III and 2-amino-2-methyl-l-propanol. Amino acids reacted with I and with 4-chlorobenzenesulfonyl isocyanate (II) to give N-(arylsulfonyl)-N¹-(carboxylic acid)-ureas. N-(4-Toluenesulfonyl)-N¹-(acetic acid)-urea (XVI) was converted to the methyl ester (XIX) by concentrated sulfuric acid and methanol and to water-soluble unrecoverable products by sulfuric acid alone. Glycine and III gave N-(4-toluenesulfonyl)-N¹-(acetic acid)-thiourea (XX) which was converted to the methyl ester (XXII) by concentrated sulfuric acid/methanol and to the cyclic 1-(4-toluenesulfonyl)imidazolin-5-one-2-thione (XXI) by sulfuric acid alone.     

Spectrophotometric determination of formaldehyde with chromotropic acid in phosphoric acid medium assisted by microwave oven

In the present study, a spectrophotometric method for the determination of formaldehyde by using chromotropic acid was devised, in which the use of potentially hazardous and corrosive concentrated sulfuric acid was eliminated and advantageously replaced by a mixture of H₃PO₄ and H₂O₂. The reaction between formaldehyde and chromotropic acid (CA) in a concentrated phosphoric acid medium was accelerate by irradiating the mixture with microwave energy for 35 s (1100 W), producing a violet-red compound (λ_max=570 nm). Beer's Law is obeyed in a concentration range of 0.8-4.8 mg l⁻¹ of formaldehyde with a good correlation coefficient (r=0.9968). The proposed method was applied in the analysis of formaldehyde in commercial disinfectants. Recoveries were within 98.0-100.4%, with standard deviations ranging from 0.03 to 0.13%.     

Acid-catalyzed isomerization of caryophyllene in the presence of SiO<Subscript>2</Subscript> and Al<Subscript>2</Subscript>O<Subscript>3</Subscript> impregnated with sulfuric acid

The conversion of caryophyllene upon contact with Al₂O₃ and SiO₂ impregnated with sulfuric acid was carried out, and the components of the resulting mixtures were identified. Having in hands such “standard” mixtures greatly facilitates identification of components of sesquiterpene fractions of essential oils and other mixtures of natural origin. The catalytic activity of silica gel impregnated with sulfuric acid (H⁺-SiO₂) in the acid-catalyzed isomerization of caryophyllene is significantly higher than that for H⁺-Al₂O₃ and is comparable with the activity of concentrated sulfuric acid.     

On the Dissociation of Methyl Orange: Spectrophotometric Investigation in Aqueous Solutions from 10 to 90 ∘C and Theoretical Evidence for Intramolecular Dihydrogen Bonding

The dissociation of methyl orange was investigated by spectrophotometry in aqueous solutions from 10 to 90 ^∘C and by quantum chemical calculations. Combined chemometric and thermodynamic analyses of the spectrophotometric data were used to simultaneously extract the thermodynamic stabilities and the spectrophotometric attributes of the dominant methyl orange species in solutions containing less than 20.00 mmol-kg⁻¹ perchloric acid and submillimolal concentrations of methyl orange. The analyses revealed the presence of only one monomeric deprotonated and one monomeric protonated species. The spectra did not reveal any evidence for the presence of tautomeric equilibria between the protonated azo and ammonium species in the experimental range studied. Thermodynamic analyses of the temperature-dependent dissociation constants showed the reactions to be endothermic and enthalpy driven with increasing acidity and increasing temperature. All molar absorption coefficients in the 275–375 nm range can be adequately reproduced in the 10–90 ^∘C range with a set of Gauss–Lorentz parameters and used to predict the absorption spectra for any desired condition. The dominant features of the spectrophotometric attributes of the methyl orange species could also be retrieved in Time Dependent–Density Functional Theory (TD–DFT) calculations. Topological analyses of the electron density also revealed the formation of a dihydrogen bond between the azo proton and an adjacent phenyl ring hydridic hydrogen which increases the stability of the azo molecules relative to the ammonium molecule.     

An electrochemical investigation of the redox properties of lumiflavin in acidic media

The electrochemistry of lumiflavin in acidic media (1% to 40% sulfuric acid) has been investigated using cyclic voltammetry and bulk electrolysis in conjunction with UV—Vis absorption spectroscopy. The observed stabilization of flavin radicals in strongly acidic media has been explained on the basis of differences in medium effects on fully reduced flavin cations (FH⁺₄) as compared with protonated oxidized (FH⁺₂) and radical (FH^∓+₃) species. The equilibrium constant for the comproportionation reaction between protonated lumiflavin species (FH⁺₂ + FH⁺₄ → 2 FH^∓+₃) has been determined. Acid dissociation constants for FH⁺₂ and FH⁺₄ have also been evaluated. These data are used in conjunction with the pK_a reported for FH^∓+₃ to estimate the value of the comproportionation constant for the neutral lumiflavin species.     

Density functional theory studies of N-protonation of the free base phthalocyanine

The structures and relative energies of twenty-two N-protonated species of the free base phthalocyanine (H₂Pc) have been systematically studied with the density functional theory at the B3LYP/6-31G(d) level of theory. The calculations demonstrated that the N-protonation tends to increase the N–C bonds and the C–N–C angles on the protonation sites. The inner protonation at the isoindole-nitrogen atoms causes significant out-of-plane deformation of the macrocycle, ascribed to the steric hindrance of the central cavity. The relative energies of various protonated species were calculated and compared to deduce the preferred sites for protonation. It was revealed that the outer protonation at the meso-nitrogen atoms is energetically more favorable than the inner protonation at the isoindole-nitrogen atoms. Among the studied twenty-two protonated species, the most stable one is H₆Pc⁴⁺(IS1), for which all the outer meso-nitrogen atoms are protonated. TDDFT calculations have been performed for selected species, and the results were used to analysis the UV–visible spectrum of the concentrated sulfuric acid solution of the free base phthalocyanine.     

Interactions of some protonated α-amino acid methyl esters with hexaethyl p-tert-butylcalix[6]arene hexaacetate in nitrobenzene saturated with water

The exchange extraction constants corresponding to the general equilibrium C⁺(aq) + 1·Cs⁺(nb) ? 1·C⁺ (nb) + Cs⁺(aq) occurring in the two-phase water–nitrobenzene system (C⁺ = protonated α-amino acid methyl ester, 1 = hexaethyl p-tert-butylcalix[6]arene hexaacetate; aq = aqueous phase, nb = nitrobenzene phase) were evaluated on the basis of extraction experiments and γ-activity measurements. Further, the stability constants of the 1·C⁺ cationic complex species in nitrobenzene saturated with water were calculated; they were found to increase in the following cation order: protonated l-tryptophan methyl ester < protonated l-phenylalanine methyl ester < protonated l-leucine methyl ester < protonated l-methionine methyl ester < protonated l-valine methyl ester.     

Raman study of ratational diffusion in methyl iodide

The usefulness of Raman and NMR spin relaxation spectroscopic methods in probing the details of molecular motions in liquids is demonstrated in a study of methyl iodide. Analysis of the lineshape of the ν₃ Raman band of methyl iodide as a function of temperature yields values of the perpendicular component D_⊥ of the diffusion tensor D_i and an activation energy of reorientation perpendicular to the C₃ axis of the molecule of 2.1 kcal/mole. Coupling the Raman data with ²D NMR spin relaxation data yields values of D_| and an activation energy for reorientation about the C₃ axis of 0.4 kcal/mole indicating quasi-free rotation for this motion. Thus the reorientational motions of methyl iodide are shown to be highly anisotropic in the liquid state.     

Preparation of cellulose I nanowhiskers with a mildly acidic aqueous ionic liquid: reaction efficiency and whiskers attributes

Cellulose I nanowhiskers were prepared in relatively high yield (48 ± 2 %) by single-stage hydrolysis of microcrystalline cellulose with an aqueous solution of 1-butyl-3-methylimidazolium hydrogen sulfate ([Bmim]HSO₄). This reaction occurred under mildly acidic reaction conditions with an [H⁺]/[AGU] ratio of 0.24 mol/mol, i.e., 2 orders of magnitude lower than with concentrated sulfuric acid. The nanowhiskers exhibited small width and width distribution and also smaller length than nanowhiskers obtained with concentrated acid. With a relatively low content of sulfur they also exhibited higher thermal stability than whiskers obtained with concentrated sulfuric acid. The lower solvating power of the aqueous ionic liquid compared to that of concentrated sulfuric acid likely contributes to the greater hydrolysis efficiency in the present system.     

Syntheses of 2,6-Anhydro-3-Deoxy-D-Glycero-D-Galacto-Non-2-Enonic Acid (Kdn2En) and Its Hydrogenation Products 1

Abstract

Methyl 4,5,7,8,9-penta-O-acetyl-2,6-anhydro-3-deoxy-D-glycero-D-galacto-enonate (5) was synthesized from KDN methyl ester 2 with a catalytic amount of concentrated sulfuric acid in acetic anhydride, or from 2-chloro-KDN methyl ester 4 with DBU in good yield. Hydrogenation of 4 and 5 with 10% Pd-C gave 2-deoxy-2-H_ax-KDN 8 and 2-deoxy-2-H_eq-KDN derivative 11 in high yield, respectively. The structures of these compounds were elucidated from the MS, elemental analysis, ¹H NMR and ¹³C NMR data.