Neat Alcohols Research Articles

The Role of Non-Covalent Interactions in the Reactions between Palladium Hydrido Complex with Amidoarylphosphine Pincer Ligand and Brønsted Acids

The interaction between (PNP)PdH (1); PNP = bis(2-diisopropylphosphino-4-methylphenyl)amide and different acids (CF3SO3H, HBF4∙Et2O, fluorinated alcohols and formic acid) was studied in benzene or toluene as well as in neat alcohols by IR and NMR spectroscopies. The structures of hydrogen-bonded complexes were also optimized at the DFT/ωB97-XD/def2-TZVP level. The nitrogen atom of the amidophosphine pincer ligand readily accepts proton not only from strong Brønsted acids but from relatively weak fluorinated alcohols. That suggests that binding to palladium(II) increases the diarylamine basicity, making it a strong base. Nevertheless, H+ can be taken from [(PN(H)P)PdH]+ (2) by pyridine or hexamethylphosphoramide (HMPA). These observations confirm the need for a shuttle base to form [(PN(H)P)PdH]+ (2) as the result of the heterolytic splitting of H2 by [(PNP)Pd]+. At that, a stoichiometric amount of formic acid protonates a hydride ligand yielding an unstable η2-H2 complex that rapidly converts into formate (PNP)Pd(OCHO), which loses CO2 to restore (PNP)PdH, whereas the relatively high acid excess hampers this reaction through competitive protonation at nitrogen atom.

Application of COSMO-RS-DARE as a Tool for Testing Consistency of Solubility Data: Case of Coumarin in Neat Alcohols.

Coumarin is a naturally occurring lactone-type benzopyrone with various applications in the pharmaceutical, food, perfume, and cosmetics industries. This hydrophobic compound is poorly soluble in water but dissolves well in protic organic solvents such as alcohols. Despite the extensive use of coumarin, there are only a few reports documenting its solubility in organic solvents, and some reported data are incongruent, which was the direct impulse for this study. To resolve this problem, a theoretical congruency test was formulated using COSMO-RS-DARE for the determination of intermolecular interaction parameters, which allowed for the identification of outliers as suspicious datasets. The perfect match between back-computed values of coumarin solubility and the experimental ones confirms the reliability of the formulated theoretical approach and its adequacy for testing solubility data consistency. As the final approval, the temperature-related coumarin solubility in seven neat alcohols was determined experimentally. Four solvents (methanol, ethanol, 1-propanol, and 2-propanol) were used for reproducibility purposes, and an additional three (1-butanol, 1-pentanol, and 1-octanol) were used to extend the information on the homologous series. The consistency of this extended solubility dataset is discussed in terms of the comparison of remeasured solubility values with the ones already published and within the series of structurally similar solvents. The proposed procedure extends the range of applicability of COSMO-RS-DARE and provides a real and useful tool for consistency tests of already published solubility data, allowing for the approval/disapproval of existing data and filling gaps in datasets. Linear regressions utilizing a 2D molecular descriptor, SpMin2_Bhm, or the distance between solute and solvent in the Hansen solubility space, Ra, were formulated for the estimation of COMSO-RS-DARE integration parameters.

High Temperature HCCI Critical Compression Ratio of the C1-C4 Alcohol Fuels

<div class="section abstract"><div class="htmlview paragraph">In this work, a high temperature (HT) homogeneous charge compression ignition (HCCI) critical compression ratio (cCR) was defined as the compression ratio which resulted in HCCI combustion with a crank angle location of 50% fuel burned (CA50) of 3.0 degrees after top dead center (aTDC) while operating at an equivalence ratio of 0.33 (λ = 3), an intake pressure of 1.0 bar (naturally aspirated), an intake temperature of 473 K (200°C), and an engine speed of 600 rpm. Using a Cooperative Fuel Research engine, the HT HCCI cCR of seven alcohol fuels were experimentally determined and found to be ordered as follows (ordered from least reactive to most reactive): isopropanol > sec-butanol > methanol ≈ ethanol ≈ n-propanol ≈ isobutanol > n-butanol. The HT HCCI cCR for the alcohol fuels correlated well with experimental HCCI data from a modern gasoline direct injection (GDI) engine architecture with a pent-roof head and a rebreathe valvetrain. The HT HCCI cCR was also correlated with available cetane number (CN), motor octane number (MON), and research octane number (RON) values found in the literature. The coefficient of determination (R<sup>2</sup>) for these correlations was 0.02, 0.95, and 0.69, respectively. When the RON values were modified to account for the high cooling potential of the alcohol fuels, the R<sup>2</sup> increased from 0.69 to 0.96. When a wider array of other fuels were considered, including pure components of different fuel classes, pure-component fuel blends, and gasoline fuel blends, the critical compression ratio no longer correlated well with MON or HOV-modified RON. It was concluded that when fuels of a similar fuel class are considered, such as neat C1-C4 alcohols, MON or an HOV-modified RON may be sufficient to compare the HCCI reactivity of the fuels at MON-like cylinder conditions. However, due to the complex nature of the octane number tests, the HCCI ignition propensity is not well predicted by the standard octane numbers when fuels of varying chemical characteristics and combustion chemistry attributes are considered. Therefore, a metric for characterizing gasoline-like fuels under compression ignition conditions is required, such as an HCCI test method on the CFR octane rating engine.</div></div>

Effect of dilution of nonpolar solvents (CCl4 and C6H6) on densities and excess molar volumes of methanol + 1-butanol mixtures over the temperature range 293.15–308.15 K

Methanol and 1-butanol have philicity to each other but their binary mixing features were very rarely discussed. Non-linear density-composition plots of methanol + 1-butanol (M-B) binary mixtures indicates non-ideal mixing of the two alcohols. Excess molar volume (VmE) remains positive over the entire composition range. The VmE isotherms in the temperature range from 293.15 K to 308.15 K are measured at 5 K intervals exhibit maxima at xmethanol ~ 0.6, indicating maximum no of H-Bonds among the solvents are formed at this composition. No change in maxima position indicate no significant structural change with temperature. Due to different sizes of alkyl groups “hydrophobic-like” interactions for methanol have been proposed to explain positive VmE. Neat 1-butanol when diluted with CCl4 or C6H6 (nonpolar diluents) exhibits positive VmE is an indication of segregation of its molecules due to their weak mutual interactions. On the other hand, negative VmE for methanol upon adding the diluents suggests oligomer formation in it. Also, the binary mixtures of the alcohol and the diluents addition to neat alcohols results in non-linear density isotherms for methanol and negative VmE while for butanol, linear density isotherms and positive VmE was observed. This behavior should suggest that M-B molecules do not tend to congregate with each other rather methanol-methanol (M-M) association is preferred.

Molecular Origin of the Prepeak in the Structure Factor of Alcohols.

Prepeak in the structure factor of alcohols is known for a half century and was attributed to one of two mechanisms (i) self-assembly in aggregates and (ii) existence of spatial heterogeneity. Although both explnations are often argued the molecular origin is yet unclear. In this work, molecular dynamics simulation of neat alcohols and their mixtures in the presence of an apolar liquid in bulk and in confined phases is performed to unveil and to clarify the origin of the prepeak at the molecular scale. Unambiguously, we show that the existence of the prepeak is the result of the self-assembly in clusters leading to long-range correlations rather than the spatial heterogeneity. We also establish that the confinement of neat liquids at the nanoscale does not erase the clustering and the prepeak but strongly reduce the spatial heterogeneity. Regarding the binary alcohol/toluene mixtures, we highlight the possibility to erase the clustering and the spatial heterogeneity from nanoconfinement inducing the formation of a core-shell structure. By tuning the interfacial chemistry and pore size, we shed light on the possibility to control the spatial heterogeneity, the self-assembly, and the microphase separation.

Ignition analysis on neat alcohols and biodiesel blends propelled research compression ignition engine

ABSTRACT In this present study, the emissions and performance characteristics of four-stroke, single-cylinder, water-cooled, diesel engine fueled with different blends of Rice bran biodiesel and octanol blends i.e. RBD100, RBD90O10 (10% Volume of octanol dispersed in RBD100) and RBD80O20 (20% Volume of octanol dispersed in RBD100) at 1800 rpm for compression ratio 17.5:1 were investigated. The transesterification process was used for biodiesel production with the presence of the alkaline catalyst (KOH) and methanol. The optimum biodiesel yield was found to be 88%. The fuel properties of the blends were found to be within the ASTM limits. Experimental results revealed that BTE increased and BSFC decreased with octanol addition to rice bran biodiesel. Furthermore, the diesel engine fueled with octanol and biodiesel blends reduced the NOx, Smoke, HC, CO emission due to the higher latent heat of vaporization and improved chemical properties.

Palladium oxide nanoparticles intercalated mesoporous silica for solvent free acceptorless dehydrogenation reactions of alcohols

Abstract Aggregation-free well-dispersed palladium oxide nanoparticles intercalated into the walls of mesoporous silica (PdOMS) were prepared by using thioether groups during the sol-gel preparation of mesoporous silica. The PdOMS material was characterized by N2 adsorption-desorption, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and UV–Vis spectroscopy. The material retains mesoporous structure with narrow pore size distribution with an average pore diameter of 6.8 nm and possesses high surface area of 683 m2g–1. The PdOMS catalyst was employed as an efficient heterogeneous catalyst in the acceptor- and oxidant-free dehydrogenation of neat alcohols to corresponding carbonyl compounds in very good to excellent yields (72–95%) at 80 °C under inert atmosphere. The catalytic efficacy of PdOMS has also been evaluated for the acceptorless dehydrogenative coupling reactions of alcohols with o-diamino benzene and o-amino phenol to yield azole-based heterocycles. The stability of PdOMS was assessed by investigating its recyclability and reusability in the dehydrogenation of neat alcohol for up to five cycles.

Structures of binary mixtures of ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide with primary alcohols: The role of hydrogen-bonding

The structure of ionic liquids (ILs) with shorter alkyl tail(s) of the constituent ions is predominantly governed by strong electrostatic interactions which are, in most cases, accompanied by specific interactions such as hydrogen bonding. Neat 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide Im1,4+/NTf2− IL possesses both of these interactions. However, in many conventional solvents such as short tail length primary alcohols, the structure is primarily determined by hydrogen bonding interactions. In this study, we aim to understand how the structure of Im1,4+/NTf2− changes with the addition of different amount of alcohol by employing atomistic molecular dynamics simulations. Specifically, we have chosen Im1,4+/NTf2− + 1-propanol and Im1,4+/NTf2− + 1-butanol mixtures as the pure components of both the mixtures possess complex interactions, including hydrogen bonding. The mixtures' composition-dependent structures were examined through simulated X-ray scattering structure functions (S(q)s), their partial components along with radial and spatial distribution functions. It is observed that there is significant hydrogen bonding between the anion and alcohols along with strong electrostatic interactions between the cation head and anion. For the entire composition of the mixtures studied, while alcohol's hydroxyl group is found near the cation head and the anion's oxygen atoms, the nonpolar tail of alcohol molecules tend to align with the tails of either the cation or other alcohol molecules. It is interesting to note that on adding even small amount of the IL (10%) to alcohol, the low q peak observed for the neat alcohols disappears. The X-ray scattering S(q)s reveal that the long-range charge ordering structure of the Im1,4+/NTf2− IL begin to build up at xIL = 0.3 but at larger length scales. The transitional structural changes in the both the mixtures take place for 0.3 ≤ xIL ≤ 0.8. The neat IL structure is virtually regained at and above xIL = 0.8.

A "Universal" Spectroscopic Map for the OH Stretching Mode in Alcohols.

Empirical maps are presented for the OH stretching vibrations in neat alcohols in which the relevant spectroscopic quantities are expressed in terms of the electric field exerted on the hydrogen atom by the surrounding liquid. It is found, by examination of the four lowest linear alcohols, methanol, ethanol, n-propanol, and n-butanol, that a single map can be used for alcohols with different alkyl groups. This "universal" map is in very good agreement with maps optimized for the individual alcohols but differs from those previously developed for water. This suggests that one map can be used for all alcohols, perhaps even those not examined in the present study. The universal map gives IR lineshapes in good agreement with measured spectra for isotopically dilute methanol and ethanol, while the two-dimensional IR photon echo spectra give results that differ from experiments. The role of non-Condon effects, reorientation dynamics, hydrogen bonding, and spectral diffusion is discussed.

Microwave Promoted Oxidative Addition Reactions of Os3(CO)12: Efficient Syntheses of Triosmium Clusters of the Type Os3(μ-X)2(CO)10 and Os3(μ-H)(μ-OR)(CO)10

Microwave heating allows for the high-yield, one-step synthesis of the known triosmium complexes Os3(μ-Br)2(CO)10 (1), Os3(μ-I)2(CO)10 (2), and Os3(μ-H)(μ-OR)(CO)10 with R = methyl (3), ethyl (4), isopropyl (5), n-butyl (6), and phenyl (7). In addition, the new clusters Os3(μ-H)(μ-OR)(CO)10 with R = n-propyl (8), sec-butyl (9), isobutyl (10), and tert-butyl (11) are synthesized in a microwave reactor. The preparation of these complexes is easily accomplished without the need to first prepare an activated derivative of Os3(CO)12, and without the need to exclude air from the reaction vessel. The syntheses of complexes 1 and 2 are carried out in less than 15 min by heating stoichiometric mixtures of Os3(CO)12 and the appropriate halogen in cyclohexane. Clusters 3–6 and 8–10 are prepared by the microwave irradiation of Os3(CO)12 in neat alcohols, while clusters 7 and 11 are prepared from mixtures of Os3(CO)12, alcohol and 1,2-dichlorobenzene. Structural characterization of clusters 2, 4, and 5 was carried out by X-ray crystallographic analysis. High resolution X-ray crystal structures of two other oxidative addition products, Os3(CO)12I2 (12) and Os3(μ-H)(μ-O2CC6H5)(CO)10 (13), are also presented.

A simple lattice model for the microstructure of neat alcohols: Application to liquid methanol

Simple lattice model for self-associating molecules such as methanol or tert-butanol is proposed and studied in mean-field (MF) approximation in the case of methanol. In addition to the isotropic van der Waals interaction, the hydrogen bonding is present in this model when the neighboring alcohol molecules are in appropriate orientations. The orientation of the polar molecule is given by the unit vector n parallel to the vector connecting the center of the tail group with the center of the head group of the molecule. Stability region of the uniform fluid phase against gas-liquid separation and order-disorder transition is obtained for neat methanol in MF approximation. In order to describe the self-association patterns in the liquid, we consider the grand-canonical ensemble average of the scalar product of the orientations of the molecules <n(x) * n(x + Delta x)> as a function of the vector Delta x describing the separation between the centers of the molecules. For methanol we find in MF oscillatory decay of <n(x) * n(x + Delta x)> for Delta x perpendicular n(x) and for Delta x parallel n(x); the wavelength is somewhat less than two molecular diameters in both cases, and the decay length is larger in the perpendicular direction. This indicates that on average alternating antiparallel and parallel orientations of the second molecule are found for increasing separation from the first molecule in both directions. Such local orientational ordering of the molecules is consistent with association into zigzag chainlike clusters found in recent spectroscopic measurements and computer simulations. In Fourier representation the above structure function assumes maximum for the wave number that coincides with the prepeak position for site-site correlations found in simulations. We argue that <n(x) * n(x + Delta x)> can provide a useful tool for discriminating between different local arrangements of any polar molecules.

Sustainable Synthesis of Aldehydes, Ketones or Acids from Neat Alcohols Using Nitrogen Dioxide Gas, and Related Reactions

Benzylic alcohols are quantitatively oxidized by gaseous nitrogen dioxide to give pure aromatic aldehydes. The reaction gas mixtures are transformed to nitric acid, which renders the processes free of waste. The exothermic gas-liquid or gas-solid reactions profit from the solubility of nitrogen dioxide in the neat benzylic alcohols. The acid formed impedes further oxidation of the benzaldehydes. The neat isolated benzaldehydes and nitrogen dioxide quantitatively give the benzoic acids. Solid long-chain primary alcohols are directly and quantitatively oxidized with nitrogen dioxide gas to give the fatty acids in the solid state. The oxidations with ubiquitous nitrogen dioxide are extended to solid heterocyclic thioamides, which gives disulfides, and to diphenylamine, which gives tetraphenylhydrazine. These sustainable (green) specific oxidation procedures produce no dangerous residues from the oxidizing agent or from auxiliaries.

Correlated Volume Fluctuations in Binary Liquid Mixtures from Isothermal Compressions at 298.15 K

New fluctuation-related properties are introduced based on the link between the mean-squared fluctuation of the volume and the isothermal compressibility of binary liquid mixtures by applying the methods of chemical thermodynamics. Some weaknesses have been pointed out in previous similar attempts by other authors. A different result is obtained when Pfeiffer and Heremans' model for correlated volume fluctuations is worked out in terms of the PTN ensemble (i.e. at constant pressure and temperature). An expression is derived for estimating adjusted correlation coefficients in pairwise volume fluctuations from the knowledge of excess molar isothermal compressions, and it is shown that this expression predicts bounding values for the latter property in real mixtures. Ultrasound speeds in 31 aqueous mixtures of 2-(ethylamino)ethanol are reported at 298.15 K. The adjusted correlation coefficients for volume fluctuations are graphically depicted at several compositions of two nonaqueous mixtures and eleven aqueous amphiphile mixtures at 298.15 K. This procedure is shown to be an effective means of monitoring interactions between unlike molecules in binary liquid mixtures. A surprisingly high limiting adjusted correlation coefficient is found for water in neat amino alcohols and alcohols possessing a tertiary functional group.

Microstructure of neat alcohols: A molecular dynamics study

Neat methanol and tert-butanol are studied by molecular dynamics with the focus on the microstructure of these two alcohols. The site-site radial distribution functions, the corresponding structure factors, and an effective local one-body density function are shown to be the appropriate statistical quantities that point in a complementary manner towards the same microstructure for any given liquid. Methanol is found to be a weakly associated liquid forming various chainlike patterns (open and closed) while tert-butanol is almost entirely associated and forms micellelike primary pattern. The presence of stable local microheterogeneity within homogeneous disordered phase appears as a striking feature of these liquids. The absence of any such apparent clustering in water--a stronger hydrogen bonding liquid--through the same two statistical quantities is analyzed.

Microstructure of neat alcohols

Formation of microstructure in homogeneous associated liquids is analyzed through the density-density pair correlation functions, both in direct and reciprocal space, as well as an effective local one-body density function. This is illustrated through a molecular dynamics study of two neat alcohols, namely, methanol and tert-butanol, which have a rich microstructure: chainlike molecular association for the former and micellelike for the latter. The relation to hydrogen bonding interaction is demonstrated. The apparent failure to find microstructure in water--a stronger hydrogen bonding liquid--with the same tools is discussed.

Palladium-catalyzed oxidation of primary alcohols: Highly selective direct synthesis of acetals

Selective direct synthesis of acetals through a tandem oxidation–acetalization of primary alcohols, using a chloride-free Pd(OAc) 2 /Cu(OAc) 2 / p -TsOH system as an efficient bifunctional catalyst, has been developed. The reaction occurs in neat alcohols with no use of other solvent under mild aerobic conditions. p -Toluenesulfonic acid ( p -TsOH) and Cu(OAc) 2 exert a great synergetic effect on the reaction rate and selectivity for acetals. Selective direct synthesis of symmetric acetals through a tandem aerobic oxidation–acetalization of primary alcohols, using a chloride-free Pd(OAc) 2 /Cu(OAc) 2 / p -TsOH system as an efficient bifunctional catalyst, has been developed. The reactions occur in neat alcohols with no use of other solvent under mild conditions (50–80 °C, 1–10 atm). p -Toluenesulfonic acid exerts a great accelerative and catalyst stabilizing effect, showing a synergism with Cu(OAc) 2 . Bimetallic Pd–Cu catalysis is suggested in these reactions. Under similar conditions, a secondary alcohol, propanol-2, reacts more slowly giving mainly acetone. Conventional palladium catalytic systems, such as PdCl 2 /CuCl 2 , Pd(OAc) 2 /LiNO 3 , and Pd(OAc) 2 /pyridine, showed no or very low activity in the oxidation of neat n -butanol.

Structure property correlations in alcohols through two-photon absorption cross-section measurements

Two-photon absorption (TPA) cross-sections of neat alcohols are shown to be a femtosecond laser measurable property with useful structure property correlations that are directly correlated to the self-phase modulation of the alcohol in question. The amount of self-phase modulation is shown to be a molecular structure dependent property. The real and the imaginary components of the second-order hyperpolarizability are thus shown to be interrelated. Such TPA measurements prove that it is not possible to predict two-photon absorption properties by simple doubling the wavelengths of one-photon absorption spectra.

Direct Synthesis of Esters and Amides from Unprotected Hydroxyaromatic and -aliphatic Carboxylic Acids

A facile method for the activation of hydroxy-substituted carboxylic acids using benzotriazole chemistry without prior protection of the hydroxy substituents is presented. The N-acylbenzotriazole intermediates 2a-g, 6a-d, and 9a-c have been used for high-yielding synthesis of both aliphatic (3a-l) and aromatic (7a-h, 10a-f) hydroxy carboxamides. High yields of aromatic hydroxy esters 12a-h and 13a-i were obtained using either neat alcohols in neutral microwave conditions or nucleophilic alkoxides and the intermediate N-(arylacyl)benzotriazoles. Moderate yields were obtained in the case of aliphatic hydroxy esters 11a,b and thiolesters 11e-g from the intermediates 2a-c.

Enantiomeric separation of mineralocorticoid receptor (hMR) antagonists using the Chiralcel® OJ‐H HPLC column with novel polar cosolvent eluent systems

This study demonstrates the increased versatility of the Chiralcel OJ-H stationary phase when using various alcohol/acetonitrile mobile phases. This chiral stationary phase has traditionally been employed in the normal phase mode and more recently with neat alcohols as eluents. Selected isomeric human mineralocorticoid receptor (hMR) antagonist pharmaceutical candidates and synthetic intermediates were separated using the Chiralcel OJ-H HPLC column with novel polar cosolvent eluent systems. The capacity factors, resolution, and selectivity of the chiral separations were assessed while varying the alcohol/acetonitrile composition and alcohol identity. The mixed polar eluents provide separations that are nearly always superior to both the traditional hexane-rich and single-alcohol "polar organic" eluents for the compounds tested in this article.

Aryl Cation and Carbene Intermediates in the Photodehalogenation of Chlorophenols

The photochemistry of 2,6-dimethyl-4-chlorophenol (6) has been studied in methanol and trifluoroethanol (TFE) through product studies and transient absorption spectroscopy. Chloride loss from triplet 6 gave triplet hydroxyphenyl cation 14, which equilibrated with triplet oxocyclohexadienylydene 15 within a few tens of nanoseconds; the cation can, however, be selectively trapped by allyltrimethylsilane (k(ad) = 10(8)-10(9) m(-1) s(-1)) to give a phenonium ion and the allylated phenol. In neat alcohols, 14 and 15 are reduced through different mechanisms, namely by hydrogen transfer through radical cation 17 and via phenoxyl radical 16, respectively. The mechanistic rationalization has been substantiated by the parallel study of an O-silylated derivative. The work shows that the chemistry of the highly (but selectively) reactive phenyl cation 14 can not only be discriminated from that of the likewise highly reactive carbene 15, but also exploited for synthetically useful reactions, as in this case with alkenes. Photolysis of electron-donating substituted halobenzenes may be the method of choice for the mild generation of some classes of phenyl cations.