Interaction of 2,2,6,6-tetramethylpiperidine-1-oxyl chloritewith alcohols

The kinetics of the oxidation of a series of alcohols (viz., ethanol, propan-2-ol, butan-1-ol, butan-2-ol, heptan-4-ol, decan-2-ol, propan-1,3-diol, butan-2,3-diol, cyclohexanol, benzyl alcohol, and borneol) with the oxoammonium salt 2,2,6,6-tetramethylpiperidine-1-oxyl chlorite in acetonitrile was studied by spectrophotometry. The products of oxidation of primary alcohols are the corresponding aldehydes and carboxylic acids, and the products of oxidation of secondary alcohols are ketones. The reaction rate is described by the second order equation. The rate constants and activation parameters were determined. The rate constant as a function of the alcohol nature is described by the one-parameter Taft equation.     

Fine Control of the Redox Reactivity of a Nonheme Iron(III)–Peroxo Complex by Binding Redox-Inactive Metal Ions

Redox-inactive metal ions are one of the most important co-factors involved in dioxygen activation and formation reactions by metalloenzymes. In this study, we have shown that the logarithm of the rate constants of electron-transfer and C−H bond activation reactions by nonheme iron(III)–peroxo complexes binding redox-inactive metal ions, [(TMC)Fe^III(O₂)]⁺-Mⁿ⁺ (Mⁿ⁺=Sc³⁺, Y³⁺, Lu³⁺, and La³⁺), increases linearly with the increase of the Lewis acidity of the redox-inactive metal ions (ΔE), which is determined from the g_zz values of EPR spectra of O₂^.−-Mⁿ⁺ complexes. In contrast, the logarithm of the rate constants of the [(TMC)Fe^III(O₂)]⁺-Mⁿ⁺ complexes in nucleophilic reactions with aldehydes decreases linearly as the ΔE value increases. Thus, the Lewis acidity of the redox-inactive metal ions bound to the mononuclear nonheme iron(III)–peroxo complex modulates the reactivity of the [(TMC)Fe^III(O₂)]⁺-Mⁿ⁺ complexes in electron-transfer, electrophilic, and nucleophilic reactions.     

Rate constants for the gas-phase reactions of ozone with unsaturated alcohols,esters, and carbonyls

The kinetics of the gas-phase reaction of ozone with unsaturated alcohols, carbonyls, and esters in air have been investigated at atmospheric pressure, ambient temperature (285–295 K), and in the presence of sufficient cyclohexane to scavenge the hydroxyl radical which forms as a product of the ozone-unsaturated compound reaction. The reaction rate constants, in units of 10^?18 cm³ molecule^?1 s^?1, are 0.26 ± 0.05 for acrolein, 1.07 ± 0.05 for 2-ethyl acrolein, 6.0 ± 0.4 for ethyl vinyl ketone, 4.9 ± 0.4 for 3-buten-1-ol, 14.4 ± 2.0 for allyl alcohol, 105 ± 7 for cis-3-hexen-1-ol, 7.5 ± 0.9 for methyl methacrylate, 2.9 ± 0.3 for vinyl acetate, 4.4 ± 0.3 for methyl crotonate, and 8.1 ± 0.3 for the 1,1-disubstituted alkene 2-ethyl-1-butene. Substituent effects on reactivity are discussed by comparison with alkenes and indicate that the reactivity of unsaturated alcohols is the same as that of alkene structural homologues and that the —C(O)OR, —C(O)R, and —CHO groups decrease the reactivity towards ozone as compared to alkyl groups. Estimates are made of the atmospheric persistence of these unsaturated compounds using the kinetic data obtained in this study as input to structure-reactivity and linear free-energy relationships. © 1993 John Wiley & Sons, Inc.     

Fine Control of the Redox Reactivity of a Nonheme Iron(III)–Peroxo Complex by Binding Redox‐Inactive Metal Ions

Redox‐inactive metal ions are one of the most important co‐factors involved in dioxygen activation and formation reactions by metalloenzymes. In this study, we have shown that the logarithm of the rate constants of electron‐transfer and C−H bond activation reactions by nonheme iron(III)–peroxo complexes binding redox‐inactive metal ions, [(TMC)Fe^III(O₂)]⁺‐M^{n +} (M^{n +}=Sc³⁺, Y³⁺, Lu³⁺, and La³⁺), increases linearly with the increase of the Lewis acidity of the redox‐inactive metal ions (ΔE ), which is determined from the g_zz values of EPR spectra of O₂^.−‐M^{n +} complexes. In contrast, the logarithm of the rate constants of the [(TMC)Fe^III(O₂)]⁺‐M^{n +} complexes in nucleophilic reactions with aldehydes decreases linearly as the ΔE value increases. Thus, the Lewis acidity of the redox‐inactive metal ions bound to the mononuclear nonheme iron(III)–peroxo complex modulates the reactivity of the [(TMC)Fe^III(O₂)]⁺‐M^{n +} complexes in electron‐transfer, electrophilic, and nucleophilic reactions.     

Study of molecular interactions in the polar binary mixtures of N-methyl aniline and alcohols,using excess dielectric and thermodynamic parameters

Molecular interactions between the polar systems N-methyl aniline and alcohols (propan-1-ol/propan-2-ol) for various mole fractions at different temperatures are studied by determining the dielectric permittivity using LF impedance analyzer, Microwave bench and Abbe’s refractometer in radio, microwave and optic frequency regions respectively. The dipole moment, excess dipole moment, excess Helmholtz energy, excess permittivity, excess inverse relaxation time and excess thermodynamic values are calculated using experimental results. The optimized geometry, harmonic vibrational wave numbers and dipole moments of pure and equimolar binary mixtures have been calculated theoretically from the ab initio Hartree–Fock (HF) and Density Functional Theory (DFT – B3LYP) methods with 6-31+G¹ and 6-311+G⁷ basis sets using Spartan 08 modelling software. Conformational analysis of the formation of hydrogen bond in the equimolar binary mixture systems of N-methyl aniline and alcohols (propan-1-ol/propan-2-ol) is supported by experimental FT-IR spectra. The calculated wave numbers and dipole moments agree well with the experimental values. Further, the correlations among the parameters are discussed in detail.     

Chemiluminescence parameters of peroxynitrous acid in the presence of short-chain alcohols and Ru(bpy)<Stack><Subscript>3</Subscript><Superscript>2+</Superscript></Stack>

The chemiluminescence behaviour and mechanism of peroxynitrous acid and Ru(bpy)₃²⁺ were studied in the presence of short-chain alcohols (methanol, ethanol, propan-1-ol, propan-2-ol, butanol, 2-methylpropan-1-ol, pentanol). It was found that the chemiluminescence intensity of peroxynitrous acid and Ru(bpy)₃²⁺ system could be significantly enhanced by these seven short-chain alcohols. The maximum chemiluminescence wavelength of 608 nm of [Ru(bpy)₃²⁺]* in the excited state was attributed to the reaction between Ru(bpy)₃²⁺ and dihydroxyalkyl radicals which were generated during the redox course of peroxynitrous acid and alcohols. In addition, the chemiluminescence signals of the system presented depended largely on the solubility and branched-chain structure as well as the length of carbon chain. The analytical characteristics and parameters of the peroxynitrous acid/Ru(bpy)₃²⁺/alcohols chemiluminescence system were investigated under optimum conditions.     

Gas-phase reactivity of rare earth cations with phenol: Competitive activation of C-O, O-H, and C-H bonds

The gas-phase reactions of Sc⁺, Y⁺, and Ln⁺ (Ln=La-Lu, except Pm) ions with phenol were studied by Fourier transform ion cyclotron resonance mass spectrometry. All the ions except Yb⁺ were observed to react with the organic substrate, activating O-H, C-O, and/or C-H bonds, with formation of MO⁺, MOH⁺, and/or MOC₆H ₄ ⁺ ions as primary products. The product distributions and the reaction efficiencies obtained showed the existence of important differences in the relative reactivity of the rare earth metal cations, which are discussed in terms of factors like the electron configurations of the metal ions, their oxophilicity, and the second ionization energies of the metals. The primary product ions participated in subsequent reactions, yielding species such as M(OH)(OC₆H₅)⁺, which lead mainly to M(OC₆H₅)₂(HOC₆H₅) _n ⁺ ions, where n=0–2. Formation of M(OC₆H₅)(HOC₆H₅) _n ⁺ species was also observed in the case of the metals that have high stabilities of the formal oxidation state 2+, Sm and Eu.     

Temperature Dependence of the Isobutane Chemical Ionization Mass Spectra of Open-chain and Cyclic Alcohols; Structural,Stereochemical and Molecular-Size Effects. A reevaluation of the isobutane chemical ionization of alcohols

The temperature dependence of the isobutane chemical ionization (CI.) mass spectra of 54 open-chain, cyclic and unsaturated C₅- to C₁₀-alcohols was studied at temperatures ranging from 60 to 250°, and enthalpy changes were calculated for the corresponding main reactions of typical alcohols. The CI. reactivity is controlled by the temperature and the substrate structure as usual, and in addition, by the molecular size. The combination of thermal, structural and substrate-size effects leads to the following main conclusions. At low-reactivity conditions, i.e. at 150° or less, the alcohols with less than 11 C-atoms give four distinct types of spectra, with (M – OH)⁺ usually as the base peak. The characteristic ions are MC₄H₉⁺ and (M – H)⁺ for primary, MH⁺ and (MC₄H₉ – H₂O)⁺ for secondary, (MC₄H₉ – H₂O)⁺ for tertiary and allyl-type alcohols. Configurational assignments of stereoisomeric alcohols are also possible, by means of steric compression and shielding effects. The MH⁺/(M – OH)⁺ ratio in the spectra of epimeric methylcyclohexanols is at least 3 to 4 times higher for the isomers with mainly axial OH-group conformation compared to the equatorial isomers. Stereospecific (M - H)⁺ ions are apparently formed from trans-2-methylcyclopentanol and endo-norbornan-2-ol by a favorable abstraction of the unshielded H(α)-atoms versus normal behavior of the other epimers. While the spectra recorded at 200° show almost exclusively (M – OH)⁺ ions, those at 250° give nevertheless some C-skeleton information through the temperature dependent decomposition of the (M – OH)⁺ ions.     

Spectroscopic Capture and Reactivity of a Low‐Spin Cobalt(IV)‐Oxo Complex Stabilized by Binding Redox‐Inactive Metal Ions

High‐valent cobalt‐oxo intermediates are proposed as reactive intermediates in a number of cobalt‐complex‐mediated oxidation reactions. Herein we report the spectroscopic capture of low‐spin (S=1/2) Co^IV‐oxo species in the presence of redox‐inactive metal ions, such as Sc³⁺, Ce³⁺, Y³⁺, and Zn²⁺, and the investigation of their reactivity in C? H bond activation and sulfoxidation reactions. Theoretical calculations predict that the binding of Lewis acidic metal ions to the cobalt‐oxo core increases the electrophilicity of the oxygen atom, resulting in the redox tautomerism of a highly unstable [(TAML)Co^III(O^.)]^2? species to a more stable [(TAML)Co^IV(O)(Mⁿ⁺)] core. The present report supports the proposed role of the redox‐inactive metal ions in facilitating the formation of high‐valent metal–oxo cores as a necessary step for oxygen evolution in chemistry and biology.     

Isobutane chemical ionization mass spectra of unsaturated alcohols

Analysis of the isobutane chemical ionization mass spectra of hexenols, cyclohexenols and various syn/anti pairs of bicyclic and tricyclic homoallylic alcohols shows that: (i) the spectra of the allylic alcohols are dominated by [M + H – H₂O]⁺ and [M + C₄H₉–H₂O]⁺ ions and contain traces of [M + H]⁺ ions; (ii) [M + H]⁺ ions are prominent in the spectra of acyclic and certain cyclic homoallylic alcohols; and (iii) [M + H]⁺ ions dominate the spectra of other acyclic unsaturated alcohols. The [M + H]⁺ ions may result from either: (a) protonation of the hydroxyl group, followed by a very rapid intramolecular proton transfer from the protonated hydroxyl group to the carbon–carbon double bond or internal solvation of the protonated hydroxyl group by the carbon–carbon double bond; and/or (b) direct protonation of the carbon–carbon double bond with significant internal solvation of the resulting carbocation by the hydroxyl group, which may lead to carbon–oxygen bond formation to give a protonated cyclic ether. The consequences of placing various geometric constraints on the possible intramolecular interactions between the hydroxyl group and the carbon–carbon double bond in unsaturated alcohols are explored.     

Collision induced dissociation in a flowing afterglow-tandem mass spectrometer for the selective detection of C5 unsaturated alcohols and isoprene

A flowing afterglow-tandem mass spectrometer (FA-TMS) was used to study a series of C₅ unsaturated alcohols and isoprene. The analytical procedure was validated through collision induced dissociation (CID) experiments on proton hydrates. In the FA, reagent H₃O⁺ ions were used to chemically ionize the alcohols under study and isoprene. Chemical ionization (CI) by H₃O⁺ is widely used, especially in PTR-MS instruments, and produces a main peak at m/z 69 for all studied compounds, implying the impossibility to distinguish them by a simple quadrupole mass filter. The CID of these ions at m/z 69 resulted in daughter ions with the same masses but with different intensities depending on the organic compound, the collision energy and the Ar target gas pressure in the collision cell. From these observations, pentenols were easily distinguished from methylbutenols and 3-methyl-3-buten-1-ol from the other compounds. CID experiments were also performed on the protonated alcohol, which is only a stable ion for 1-penten-3-ol, 2-methyl-3-buten-2-ol and 3-methyl-3-buten-1-ol, showing different CID patterns as a function of the collision energy. The coupling between a FA reactor and a TMS has proven to be a valuable approach to identify C₅ unsaturated alcohols and isoprene.     

Light-mediated oxidation of alcohols and mandelate by flavin-metal complexes

New flavins with metal affinity, (1) and (2) were applied to photo-oxidation of alcohols and mandelate. (1) rapidly photo-oxidized alcohols in the presence of Mg(II) and Zn(II): the rate augmentation corresponds to 16–18 fold. (2) could photo-oxidize PhCH(OH)COO^?K⁺ but only slightly PhCH(OH)COO-NMe₄⁺: the rate difference amounts to 110-fold. Thus, the photo-oxidizability of these modified flavins can be markedly improved through complexation with metal ions.     

Activation of aromatic rings by early transition metal ions in the gas phase. Implications for the metal-catalyzed [2 + 2 + 2] cycloaddition of alkynes and nitriles

The reactions of a series of monocyclic and bicyclic arenes with early transition metal ions (Sc⁺, Y⁺, Nb⁺ and Ta⁺) and their oxides and dioxides were studied in a Fourier transform ion cyclotron resonance mass spectrometer. Ring cleavage of the nitrogen-containing heterocycles results in loss of HCN as the dominant pathway. Thermochemical considerations, secondary reactions and correlations with solution cyclotrimerization reactions indicate that the MC₄H₄⁺ product is a metallacyclopentadiene. Based on correspondence between the reactivities of a series of early metals with their valence electron counts, the reactivities of quinoline and isoquinoline and the decomposition behavior of the products, a metallacycloheptatriene intermediate is proposed for the heteroaromatic ring cleavage reaction. These results are compared to metal complexes in solution which catalyze the [2 + 2 + 2] cyclotrimerization of alkynes and nitriles.     

Kinetics and mechanism of oxidation of secondary alcohols by potassium bromate

The oxidation by Br(V) of propan-2-ol follows the rate law (?d[Br(V)]/dt) = k₄ [alcohol][Br(V)][H⁺]². The initial reaction is complicated by the presence of the product bromide ion. The reaction is composed of two second order reactions—the first, a comparatively slow one and the second stage, a faster reaction which is mainly bromine oxidation. The pure bromate oxidation can be followed by the initial addition of mercuric acetate which prevents the accumulation of bromine in the system under these conditions. The reaction rate does not depend on the nature and structure of the alcohol. A mechanism involving a slow rate-determining formation of an alkyl-bromate ester followed by a fast decomposition to the products is in accord with the observed results.     

Oxidation of alcohols by chlorine dioxide in organic solvents

The kinetics of oxidation of a series of alcohols (propan-2-ol, 2-methylpropan-1-ol, butan-1-ol, butan-2-ol, 3-methylpentan-1-ol, heptan-4-ol, decan-2-ol, cyclohexanol, borneol) by chlorine dioxide in organic solvents was studied using spectrophotometry. The reaction is described by the second-order rate equation w = k[ROH][ClO₂]. The rate constants were measured in the range of 10–60 °C, and the activation parameters of the processes were calculated. The products were identified, and the yields were determined.     

Enhancement of 1,2-dehydration of alcohols by alkali cations and protons: a model for dehydration of carbohydrates

We have used electronic structure calculations to investigate the 1,2-dehydration of alcohols as a model for water loss during the pyrolysis of carbohydrates found in biomass. Reaction enthalpies and energy barriers have been calculated for neat alcohols, protonated alcohols and alcohols complexed to alkali metal ions (Li⁺ and Na⁺). We have estimated pre-exponential A factors in order to obtain gas phase rate constants. For neat alcohols, the barrier to 1,2-dehydration is about 67 kcal mol⁻¹, which is consistent with the limited experimental data. Protonation and metal complexation significantly reduce this activation barrier and thus, facilitate more rapid reaction. With the addition of alkali metals, the rate of dehydration can increase by a factor of 10⁸ while addition of a proton can lead to an increase of a factor of 10²³.     

Kinetics and Mechanism of the Oxidation of Propan-1-ol and Propan-2-ol by Permanganate in the Absence and Presence of Tween-20 in Perchloric Acid Medium

The kinetics of the oxidation of propan-1-ol and propan-2-ol by KMnO₄ in HClO₄ medium has been studied in absence and presence of Tween-20. In the absence of Tween-20 the reaction is of first order with respect to each of permanganate and H⁺, but of complex order with respect to substrate. The active oxidant species HMnO₄ reacts with the alkanol molecule to form an intermediate complex, which decomposes in the rate-determining step to form the respective product and Mn^v. In the presence of Tween-20, both the oxidant and the substrate are distributed between the aqueous phase and the micellar pseudo-phase and then react. Different kinetic and thermodynamic parameters have been evaluated. Compensation between water structure destruction and substrate–micelle interaction plays an important role in the presence of the surfactant.     

The excess molar volumes and enthalpies of (N-methyl-2-pyrrolidinone + an alcohol) atT = 298.15 K and the application of the ERAS theory

Excess molar volumes V_m^EatT =  298.15 K and atmospheric pressure are reported for (N -methyl-2-pyrrolidinone  +  propan-2-ol, or butan-1-ol, or butan-2-ol, or 2-methylpropan-1-ol ). TheV_m^E have been calculated from measured values of density using the vibrating tube technique. The results are discussed in terms of the hydrogen bonding and other intermolecular association. Excess molar enthalpiesH_m^E at T =  298.15 K and atmospheric pressure are reported for (N -methyl-2-pyrrolidinone  +  propan-1-ol, or propan-2-ol, or butan-1-ol, or butan-2-ol, or 2-methylpropan-1-ol). The H_m^Ehave been obtained using flow calorimetry. The experimental results have been correlated and compared with the results from the Extended Real Associated Solution (ERAS) theory. The parameters adjusted to the mixtures properties are two cross association parameters and the interaction parameter responsible for the exchange energy of the van der Waals interactions. Self-association parameters of the alcohols and NMP are taken from the literature.     

A Complete Guide on the Influence of Metal Clusters in the Diels–Alder Regioselectivity of Ih‐C80 Endohedral Metallofullerenes

The chemical functionalization of endohedral metallofullerenes (EMFs) has aroused considerable interest due to the possibility of synthesizing new species with potential applications in materials science and medicine. Experimental and theoretical studies on the reactivity of endohedral metallofullerenes are scarce. To improve our understanding of the endohedral metallofullerene reactivity, we have systematically studied with DFT methods the Diels–Alder cycloaddition between s‐cis‐1,3‐butadiene and practically all X@I_h‐C₈₀ EMFs synthesized to date: X=Sc₃N, Lu₃N, Y₃N, La₂, Y₃, Sc₃C₂, Sc₄C₂, Sc₃CH, Sc₃NC, Sc₄O₂ and Sc₄O₃. We have studied both the thermodynamic and kinetic regioselectivity, taking into account the free rotation of the metallic cluster inside the fullerene. This systematic study has been made possible through the use of the frozen cage model (FCM), a computationally cheap approach to accurately predicting the exohedral regioselectivity of cycloaddition reactions in EMFs. Our results show that the EMFs are less reactive than the hollow I_h‐C₈₀ cage. Except for the Y₃ cluster, the additions occur predominantly at the [5,6] bond. In many cases, however, a mixture of the two possible regioisomers is predicted. In general, [6,6] addition is favored in EMFs that have a larger charge transfer from the metal cluster to the cage or a voluminous metal cluster inside. The present guide represents the first complete and exhaustive investigation of the reactivity of I_h‐C₈₀‐based EMFs.     

Stereoselectivity ratios in a simple Diels-Alder reaction in aqueous salt solutions of alcohols

This is the first exhaustive report on the variation of stereoselectivity ratios for a simple Diels-Alder reaction between cyclopentadiene and methyl acrylate. The reaction was carried out in aqueous mixtures of methanol, ethanol, propan-1-ol and butan-1-ol in presence of LiClO₄, LiCl, NaCl, KCl, CaCl₂ and MgCl₂. The endo stereoisomer decreases with the increase in carbon chain length of the alcohol. However, LiClO₄, a salting-in agent in water becomes salting-out in aqueous mixtures of alcohols. The solvent properties, thus can be attuned by adjusting the amount of solvents and salts.