Dielectric relaxation studies of some aliphatic alcohols and their mixtures in benzene solutions

Dielectric absorption of four aliphatic alcohols, viz., methyl alcohol, ethyl alcohol, n-propyl alcohol, tert-butyl alcohol and their binary mixtures, mixtures of these alcohols with dimethyl formamide and 2-fluoroaniline has been studied in the 3 cm microwave region at a temperature of 30°C in benzene. In alcohols and their mixtures the tan σ - concentration curve shows a marked increase in the concentration range 0.02 – 0.05 weight fraction. This behaviour has been explained as due to the formation of complex via self and hetero-association. The alcohols + DMF systems show complex formation at a very low concentration range. The study of systems alcohols + 2 - fluoroaniline indicate that the 2-fluoroaniline produces dissociating effects in these alcohols.     

微波介电谱应用于低碳醇化合物的分析

研究了甲醇、乙醇等低碳醇类化合物在微波传输过程中对传输散射参数(又称S参数)的影响,利用微波透射法测定了S参数,根据其变化探讨了微波介电谱应用于低碳醇化合物分析的可能性,建立了一种基于散射参数的微波介电化学分析法。实验数据表明,微波的S参数与甲醇、乙醇等低碳醇化合物的浓度在一定范围内呈现良好的线性关系。     

Raman spectroscopic analysis and fast identification of several saturated monohydroxy alcohols

The Raman spectra of nine monohydroxy alcohols have been obtained by confocal Raman spectrometer at room temperature. Based on the Raman spectra, the density functional theory was used to analyze the characteristic Raman bands of monohydric alcohols. Through the discussion of the characteristic Raman bands and their corresponding assignment, four major Raman bands were selected to identify nine monohydric alcohols using principal component analysis and Euclidean distance. Finally, nine saturated monohydroxy alcohols can be distinguished exactly, and the recognition rate is 100%.     

Corona Discharge Ion Mobility Spectrometry of Ten Alcohols

利用电晕放电离子源离子迁移谱装置对十种醇类有机物的迁移谱进行了研究. 在质子化的水合氢离子为反应离子和纯净空气为迁移气体的条件下,各种醇类有机物在其离子迁移谱中都获得了不同的产物离子峰. 利用指数稀释法得到各种样品的检测限在几个pmol/L量级. 利用所得到的离子迁移谱,以硬球碰撞为模型,得到了大气压下离子-分子相互作用的多个化学物理参数,包括离子分子碰撞、扩散系数、碰撞速率常数和离子半径.     

Structure–reactivity relationship for alcohol oxidations via hydride transfer to a carbocationic oxidizing agent

Second‐order rate constants were determined for the oxidation of 27 alcohols (R¹R²CHOH) by a carbocationic oxidizing agent, 9‐phenylxanthylium ion, in acetontrile at 60 °C. Alcohols include open‐chain alkyl, cycloalkyl, and unsaturated alcohols. Kinetic isotope effects for the reaction of 1‐phenylethanol were determined at three H/D positions of the alcohol (KIE_α‐D = 3.9, KIE_β‐D3 = 1.03, KIE_OD = 1.10). These KIE results are consistent with those we previously reported for the 2‐propanol reaction, suggesting that these reactions follow a hydride‐proton sequential transfer mechanism that involves a rate‐limiting formation of the α‐hydroxy carbocation intermediate. Structure–reactivity relationship for alcohol oxidations was deeply discussed on the basis of the observed structural effects on the formation of the carbocationic transition state (C^δ+? OH). Efficiencies of alcohol oxidations are largely dependent upon the alcohol structures. Steric hindrance effect and ring strain relief effect win over the electronic effect in determining the rates of the oxidations of open‐chain alkyl and cycloalkyl alcohols. Unhindered secondary alkyl alcohols would be selectively oxidized in the presence of primary and hindered secondary alkyl alcohols. Strained C₇? C₁₁ cycloalkyl alcohols react faster than cyclohexyl alcohol, whereas the strained C₅ and C₁₂ alcohols react slower. Aromatic alcohols would be efficiently and selectively oxidized in the presence of aliphatic alcohols of comparable steric requirements. This structure–reactivity relationship for alcohol oxidations via hydride‐transfer mechanism is hoped to provide a useful guidance for the selective oxidation of certain alcohol functional groups in organic synthesis. Copyright © 2011 John Wiley & Sons, Ltd.     

Squeezing alcohols into sonoluminescing bubbles: the universal role of surfactants

We conduct an experimental study of the dependence of single bubble sonoluminescence intensity on the concentration of various alcohols. The light intensity is reduced by one-half at a molar fraction of ethanol of approximately 2.5x10(-5); butanol achieves the same reduction at a concentration 10 times smaller. We account for the results by a theoretical model in which the alcohols are assumed to be mechanically forced into the bubble at collapse, modifying the adiabatic exponent of the gas. The increasing hydrophobicities of the alcohols lead to decreasing effective adiabatic exponents, and thus to less heating and therefore less light. Support for this model is obtained by replotting the experimental light intensity values vs the calculated exponents, yielding a collapse of all data onto a universal curve.     

The radio frequency conductivity of some aliphatic alcohols at different temperatures

Activation energies for viscous flow and conductivity are computed from experimental values of RF conductivity (frequency 400 kHz) at different temperatures for eight polar liquids. It is observed that for aliphatic alcohols the activation energy for conductivity is greater than that for viscous flow. However, their ratio is slightly greater than unity and is different for different alcohols whereas for nonassociating polar liquids the ratio is almost equal to unity. The dependence of conductivity on viscosity for the liquid alcohols does not follow the Walden’s law but can be well represented by Adamczewskis relation.     

Comparison of solubility of gases and vapours in wet and dry alcohols,especially octan‐1‐ol

Equations for the solubility of gases and vapours into dry alcohols from methanol to decan‐1‐ol and into water‐saturated alcohols from butan‐1‐ol to decan‐1‐ol have been compared through the use of the Abraham solvation equation. It is shown that there are noticeable differences in solvation into the dry and wet alcohols, and that these differences become larger as the alcohols become smaller and take up more water. The two main factors that lead to the differences in solvation are the solute hydrogen‐bond basicity, B, and solute size, L. Increase in solute hydrogen‐bond basicity favours the wet alcohols and increase in solute size favours the dry alcohols. Solute hydrogen‐bond acidity plays no part, because the hydrogen‐bond basicity of water, wet alcohols and dry alcohols is almost the same. Copyright © 2008 John Wiley & Sons, Ltd.     

Ultrasound promoted protection of alcohols: an efficient solvent-free pathway for the preparation of silyl ethers in the presence of no additive

Various types of alcohols and phenols were rapidly protected by hexamethyldisilazane in good to excellent yields at room temperature using high-intensity ultrasound irradiation in the presence of no solvent or any additive. Good to excellent chemoselectivity was observed for competitive protection of hydroxyl groups in favor of sterically less hindered alcohols. Exclusive protection of phenols in the presence of aromatic amines was also demonstrated successfully.     

辛醇对LiBr水溶液汽液界面的影响

采用分子动力学方法分析303.15 K时,添加不同量异辛醇的水或溴化锂水溶液汽液界面的微观结构,发现;未吸收水蒸气时,当异辛醇较少时,醇分子在界面处分布不均匀;当异辛醇较多时,异辛醇在界面处均匀分布,但排列比较松散;随着异辛醇数目的继续增加,异辛醇在界面处形成双层结构。异辛醇亲水羟基中的氢与阴离子存在氢键作用,而阳离子与异辛醇的氧之间存在着较强的静电相互作用。在非平衡条件下,采用分子动力学方法对添加或未添加正辛醇的溴化锂水溶液吸收水蒸气的动态过程模拟0到100ps,发现;加有正辛醇的溴化锂水溶液与未添加正辛醇的溴化锂水溶液相比,吸收的水分子数目明显增多。     

A RAIRS study of methoxy and ethoxy on oxidised Cu(100)

The adsorption and reaction of methanol and ethanol on a preoxidised Cu(100) surface was studied with Reflection-Absorption Infra-Red Spectroscopy (RAIRS). Both alcohols reacted with the modified surface well below room temperature, undergoing OH bond scission to form alkoxide species. The alkoxides were stable up to 340–360 K at which stage they desorbed as aldehydes. Vibrational assignments of the observed modes were made with reference to the RAIRS spectra of the alcohols and their deuterium substituted analogues on Cu(100) together with literature values for the gaseous, liquid and solid alcohols. Application of the metal surface selection rule to the alkoxide spectra indicate that in both cases the C---O bond lies perpendicular to the surface. The methoxy species is therefore assigned to an upright C_3v configuration. Oxygen precoverage is found to govern the amount of alkoxide formation which passes through a maximum at a precoverage of about 150 L.     

Thermodynamic properties of the mixtures of some ionic liquids with alcohols using a simple equation of state

In the present work, we have used a simple equation of state called the GMA EoS to calculate the density of three ionic liquid mixtures including 1-butyl-3-methylimidazolum hexafluorophosphate, [BMIM] [PF₆] + methanol, 1-butyl-3-methylimidazolum tetrafluoroborate, [BMIM] [BF₄] + methanol, and [BMIM] [BF₄] + ethanol at different temperatures, pressures, and compositions. The isothermal compressibility, excess molar volumes, and excess Gibbs molar energy of these mixtures have been computed using this equation of state. The values of statistical parameters show that the GMA EoS can predict these thermodynamic properties very well within the experimental errors. The results show that isothermal compressibility of ionic liquids is lower than alcohols and the effect of temperature and pressure on the isothermal compressibility of ionic liquids is lower than alcohols. The excess molar volumes and excess molar Gibbs energy for these ionic liquid mixtures with alcohols are all negative at various temperatures and pressures over the whole composition range. The results have been interpreted in terms of intermolecular interactions and structural factors of the ionic liquids and alcohols.     

DNA melting induced by alcohols: Role of the solvent properties

Summary The isothermal denaturation of calf thymus DNA, induced by the presence of some monohydric alcohols in the solution, was investigated. Measurements were performed at a temperature (67.2°C) at which the denaturation, in the absence of alcohols, is about 20% and melting profiles at varying temperatures were also recorded. Results show that with increasing alcohol concentration and alkyl group size DNA denaturation first reaches a maximum and then falls back. This behaviour, ascribed to ?unusual? water properties as inferred also from compressibility measurements, indicates that hydrophobic and electrostatic effects are connected in a complex way. Partially supported by Consiglio Nazionale delle Ricerche, Italy.     

Water and alcohol(s): what's the difference? A proton NMR and DFT study of hetero‐association with pyridine

Hetero‐association of water and some simple aliphatic alcohols with pyridine in benzene has been studied by ¹H nuclear magnetic resonance (NMR) spectroscopy at very low donor concentration, where self‐association is negligible. Association constants for the formation of 1:1 and 2:1 pyridine:water complexes can then be determined without recourse to ad hoc computer programmes. That for association of a second pyridine with water is about 10 times lower than for the first. Reaction parameters for the first association with water are very similar to those for the alcohols, whereas the reaction enthalpy for the second association is somewhat smaller. The chemical shift of the OH protons and the H? C? O? H coupling constants for alcohols at high dilution in benzene are almost identical with gas‐phase data. The change in chemical shift upon association with pyridine correlates with the free energy of the reaction. Quantum mechanical calculations [BPE0 functional, 6‐311+G(d,p) basis set and a polarized continuum model of the solvent (IEFPCM)] have been run on complexes of pyridine with water, both 1:1 and 2:1, and with four alcohols. Calculated reaction enthalpies are in qualitative and, in some cases, almost quantitative agreement with the experimental data. The association constants for 1:1 complexation of pyridine with alcohols follow a rough Taft correlation in terms of polar substituent constants. Substituent size, even in the case of very bulky groups, seems to be unimportant. Copyright © 2008 John Wiley & Sons, Ltd.     

利用生物质合成气在钼基催化剂上制备混合醇

采用柠檬酸作络合剂的溶胶凝胶法制备了一系列的钼基催化剂,并应用到从生物质气化合成气有效合成低碳混合醇的实际过程中. 在钼基催化剂中,Cu₁Co₁Fe₁Mo₁Zn_0.5-6%K催化剂具有相对较高的混合醇时空产率. 通过实验发现, 反应温度在340 oC以下时,碳转化率随着反应温度的增加而不断上升,总醇的选择性却逐渐下降. 在试验测试的条件内,从生物质气化合成气合成的混合醇最大产率为494.8 g/(kg_catal·h),其中C2⁺醇(C2-C6高碳醇)占总醇含量的80.4%. 在不同的钼基催化剂上合成的混合醇,其醇分布除甲醇以外均符合Schulz-Flory方程. 在醇类产物中,C2以上的高级醇含量占总醇重量的百分比为70%-85%. 同时,利用X射线衍射和BET等表征手段对钼基催化剂的形态和结构进行了表征. 从生物质合成气生产的洁净生物质燃料混合醇具有较高的辛烷值,可以用作运输燃料或汽油的添加剂.     

Rotational Diffusion of Coumarins in Alcohols: A Dielectric Friction Study

The rotational dynamics of three structurally similar polar molecules viz., coumarin 440, coumarin 151 and coumarin 450 has been studied in alcohols at room temperature using steady-state fluorescence depolarization method and time correlated single photon counting technique. The observed reorientation times of all the three probes are found to be longer than those predicted by Stokes–Einstein–Debye (SED) hydrodynamic theory with stick boundary condition and a deviation towards super-stick behavior is noted. Dielectric friction theories of Nee–Zwanzig and van der Zwan–Hynes, which treat the solute as a point dipole, overestimate the dielectric friction contribution exhibited by all the three coumarins in alcohols. Results are discussed in the light of theoretical models and the possibility of hydrogen bonding between the amino group of the probe molecules and the hydroxyl group of the alcohols.     

Fatty acids methyl esters from vegetable oil by means of ultrasonic energy

The transesterification of vegetable oil with short-chain alcohols, in the presence of base-catalyst, by means of low frequency ultrasound (28 and 40 kHz) in order to obtain biodiesel fuel was studied. By using ultrasounds the reaction time is much shorter (10-40 min) than for mechanical stirring. The quantity of required catalyst is 2 or 3 times lower. The molar ratio of alcohol/oil used is only 6:1. Normal chain alcohols react fast, while secondary and tertiary alcohols show some or no conversion after 60 min of reaction. Surprisingly, 40 kHz ultrasounds are much more effective in the reduction of the reaction time (10-20 min). Twenty eight kilohertz give slightly better yields (98-99%), but longer reaction time, while higher frequencies are not useful at all for the transesterification of fatty acids.     

Estimation of ultrasound induced cavitation bubble temperatures in aqueous solutions

Mean acoustic cavitation bubble temperatures have been measured in a series of aqueous solutions containing C(1)-C(5) aliphatic alcohols, at 355 kHz. The method relies on the distribution of hydrocarbon product yields produced from the recombination of methyl radicals generated on the thermal decomposition of the alcohols. The mean bubble temperature was found to decrease with increasing concentration of alcohol with the effect being more pronounced the higher the molecular weight (the lower the vapour pressure) of the alcohol. It is shown that the decrease in the temperatures measured correlates very well with an increase in the surface excess of the alcohol, similar to that previously reported for the quenching of sonoluminescence in aqueous solutions containing alcohols [J. Phys. Chem. B 101 (1997) 10845; J. Phys. Chem. B 103 (1999) 9231]. The measured temperatures ranged from 4600+/-200 K at zero alcohol concentration to 2300+/-200 K at 0.5 M t-butanol. The validity of the method is discussed and it is concluded that even though a number of assumptions need to be applied the results appear to indicate that the method gives an accurate measure of the mean bubble temperature.     

光诱导呫吨酮电子转移和氢转移反应的激光闪光光解研究

用时间分辨激光闪光光解的方法研究了在乙腈溶剂中呫吨酮的激发三重态的性质，并得到了呫吨酮激发三重态和胺类、醇类以及酚类反应的瞬态吸收光谱和猝灭速率常数(kq)．除了苯胺和3-硝基苯胺被认为是能量转移外，呫吨酮和其余胺类的反应随着自由能变的减校lgkq逐渐增大，由此认为发生了电子转移反应．而对于二甲基-对甲苯胺、3,5,N,N-四甲基苯胺、N,N-二甲基苯胺、三乙胺来说，通过瞬态吸收光谱的变化可以知道既有电子转移反应又有氢转移反应发生．呫吨酮和醇类只发生氢转移反应，其猝灭速率常数和醇的?-C?H的键能有关．由     

Dielectric studies of alkyl acrylates with primary alcohols using time domain reflectometry

Binary polar–polar liquid mixtures of alkyl acrylates (methyl acrylate, ethyl acrylate and butyl acrylate) with primary alcohols (propan-1-ol, butan-1-ol and hexan-1-ol) were subjected to dielectric studies at 303?K for different concentrations using time domain reflectometry (TDR) over the frequency range from 10?MHz to 10?GHz. Static permittivity (ε₀) dielectric constant at high frequency (ε_∞) and relaxation time (τ) were found through dielectric measurements for different concentrations of each system. The Bruggeman dielectric factor, Kirkwood correlation factor and the excess inverse relaxation time were determined and discussed to yield information on the molecular interactions of the systems. Deviations from the linearity of various models suggest molecular association through hydrogen bonding between the ?OH group of alcohols and C=O group of esters. The results also show a dependence of dielectric parameters on the alkyl chain length of both the alcohols and esters.