Alkyl Benzoates Research Articles

Participation of Cluster Species in the Solvation Mechanism of a Weak Polar Solute in a Methanol/Water Mixture over a 0.2−0.7 Water Fraction Range: High-Performance Liquid Chromatography Study

It is known that a methanol/water mixture has a quaternary organization consisting of free water W, free methanol M, and two types of methanol/water clusters. A 1:1 methanol/water cluster has been observed at a high methanol concentration, and a 5:1 cluster has been observed at a low methanol concentration. In the water fraction range used in this paper, 0.2-0.7, the number of MW(5) clusters was always inferior to the number of MW clusters. When a weak polar solute is introduced into such a mixture, it is preferentially solvated by free methanol and the MW water clusters. Using this mixture as the mobile phase, a novel mathematical theory is presented to describe, in this water fraction range, the variations of the retention factor k' of alkyl benzoate esters and benzodiazepines in reversed-phase liquid chromatography. Excellent predictions of k' versus free methanol and methanol/water fractions were obtained. For the first time, using this model, enthalpy, entropy, and the Gibbs free energy of the two solute solvation processes were evaluated. Enthalpy-entropy compensation revealed that the main parameters determining retention in the range of the water fraction (0.2-0.7) increased as follows: free methanol ↔ solute solvation > methanol/water cluster ↔ solute solvation > RP18 stationary phase ↔ solute interaction. These results agree well with values obtained when ACN was used instead of methanol.

Thermal and induced decompositions of N-alkoxycarbonyldihydropyridines: end product analysis and EPR spectra of azacyclohexadienyl radicals

Hydrogen abstraction from N-alkoxycarbonyldihydropyridines generated azacyclohexadienyl radicals (pyridinyl radicals) which are characterised by EPR spectroscopy. In the presence of peroxide initiators, N-alkoxycarbonyl-1,2-dihydropyridines decomposed with production of pyridine, the corresponding alkyl formate, alkyl benzoate and alkanol being formed as the major products. Absence of cyclised products in experiments with substrates containing hex-5-enyl, pent-4-enyloxy etc. units demonstrates that radical production must be minor and that N-alkoxycarbonylazacyclohexadienyl radicals do not readily undergo β-scission of the exocyclic N–C bond. The most probable mechanism is a direct 1,2-elimination of formate. The alcohols which accompanied the other products are probably formed by hydrolysis of the formates and benzoates. Analogous chemistry is displayed by N-alkoxycarbonyl-1,4-dihydropyridines at higher temperatures where 1,4-elimination of formate is too rapid for homolytic radical production to compete.

High-Pressure Raman Noncoincidence Effect and Conformation of Alkyl Side Chain in Alkyl Benzoates

The Raman noncoincidence effect has been used to investigate the changes in intermolecular interactions induced by applying high pressure to neat liquid alkyl benzoates. The noncoincidence of the carbonyl band of a homologous series of straight chain alkyl benzoates (methyl, ethyl, propyl, butyl, and hexyl benzoate) and a branched chain alkyl benzoate (2-ethylhexyl benzoate) was measured at 20 and 40 °C over the pressure range 1−5000 bar. The density was measured as a function of pressure for all molecules. A transition point dividing the noncoincidence behavior as a function of density into two regions was found, for all molecules except methyl benzoate. Below the transition point, at lower density, the noncoincidence value was relatively insensitive to changes in density, while above the transition point, the noncoincidence value dropped sharply with increasing density. The decrease in the value of noncoincidence above the transition point was interpreted as the change in intermolecular interactions resulting from the conformational change in favor of a “folded” form of the alkyl side chain shielding the carbonyl group. To examine the plausibility of the presence of energetically allowable conformations with a folded alkyl side chain, conformational searches based on molecular mechanics calculations have also been performed. The strain energy of some alkyl benzoate conformers with folded side chain was calculated to be within a few kcal/mol of the global minimum conformation. Both the experimental results and the conformational analysis suggest that the population of the folded conformer increases under high-pressure conditions owing to its compactness.

A new anionic cyclization reaction: Condensation of benzoate esters with nitriles to give 3-amino-2-inden-1-ones

A new type of anionic cyclization has been discovered in which the condensation of alkyl benzoates with simple nitriles, induced by an excess of LDA, leads directly to substituted-3-amino-2-inden-1-ones. The corresponding intermediate β-oxonitriles undergo cyclization to give, in most instances, superior yields of the same compounds. Acid hydrolysis of these indenones leads in high yield to the corresponding biologically active (anticoagulant) indandiones.

Supported titanium catalysts based on magnesium dichloride?silicon tetraethoxide adduct for propylene polymerization

Anhydrous magnesium dichloride was reacted with silicon tetraethoxide to form a solid adduct. The adduct was treated with titanium tetrachloride and an internal Lewis base to prepare supported titanium catalysts. Alkyl benzoate (PhCOOR, R = Me, Et, n - Bu) or dialkyl phthalate [Ph(COOR) 2 , R = Me, Et, n - Bu] was used as an internal Lewis base. The prepared catalysts (MT) in combination with triethylaluminum as a cocatalyst polymerize propylene to yield polypropylene. The nature and concentration of internal Lewis base influence the composition, specific surface area, and performance of the catalysts. The addition of diphenyl dimethoxysilane into the MT/Et 3 Al catalyst system increases the isotactic index of polypropylene from 75 to 97 at a Si/Al mol ratio of 0.05. The overall results indicate that a dialkyl phthalate-incorporated catalyst shows better physical, chemical, and polymerization characteristics compared to a corresponding alkyl benzoate catalyst.

Alkyl radical generation using cyclohexa-1,4-diene-3-carboxylates and 2,5-dihydrofuran-2-carboxylates

3-Methylcyclohexa-1,4-diene-3-carboxylic acid and 2-methyl-2,5-dihydrofuran-2-carboxylic acid were prepared by Birch reduction and alkylation of benzoic and furoic acid respectively and converted to alkyl esters. Cyclohexadienyl and 2,5-dihydrofuranyl radicals were generated by hydrogen abstraction and characterised by EPR spectroscopy. The esters decomposed thermally in the presence of a radical initiator to generate alkyl radicals which could be trapped with moderate efficiency by halogen donors or alkenes. Loss of methyl to afford an alkyl benzoate was an important side reaction at higher temperatures. From the thermal reaction of hex-5-enyl 3-methylcyclohexa-1,4-diene-3-carboxylate the rate constant for hydrogen abstraction from the ester by hexenyl radicals was determined to be 0.82 × 105 dm3 mol-1 s-1 at 140 °C.

ACN Clusters in a Water/ACN Mixture, with Implications for the RPLC Weak Polar Solute Retention

Recently, a model was proposed to describe the existence of pockets of ACN called clusters in an ACN/water mixture. Using this mixture as a mobile phase, a novel mathematical theory is presented to describe the variation of the retention factor, k‘, of alkyl benzoate esters in reversed-phase liquid chromatography. For the first time, using this model, enthalpy, entropy and the Gibbs free energy were determined for two physicochemical processes: (i) the transfer of the alkyl benzoate ester from a pure aqueous mobile phase to the stationary phase and (ii) the alkyl benzoate ester solvation by the ACN clusters. These thermodynamic data indicate that the main parameter determining retention is distribution of the alkyl benzoate esters to clusters of ACN, while the interactions with the stationary phase play a minor role.

Ruthenium-Catalyzed Addition of Aromatic Esters at the ortho C–H Bonds to Olefins

Abstract A ruthenium complex, Ru(H)2(CO)(PPh3)3, can catalyze the addition of aromatic and heteroaromatic esters at the ortho carbon-hydrogen bonds to olefinic double bonds. While un-substituted alkyl benzoate did not react, those substituted with CF3 or F underwent smooth catalytic addition. A heteroaromatic ester and a benzo-δ-lactone also reacted.

CH-π Interaction as an Important Driving Force of Host–Guest Complexation. Further Evidence for the Selective Incorporation of Alkyl Groups in the Polyhydroxy Aromatic Cavity of Calix[4]resorcarene Host

Abstract The complexation of a calix[4]resorcarene host (2,8,14,20-tetraundecylcalix[4]arene-4,6,10,12,16,18,22,24-octol) with borneol in benzene or alkylbenzene was investigated by circular dichroism (CD) spectroscopy. The binding constants are dramatically solvent-dependent and decrease with respect to the substituents on the benzene ring in the order H > methyl > ethyl > propyl > butyl. The complexation of the same host with alkyl benzoates in limonene as a chiral hydrocarbon solvent was readily monitored by following their competitive inhibition effects on the CD intensities, reflecting the chiral host-solvent interaction. The binding constants for alkyl benzoates were again highly dependent on the alkyl groups, and changed in the order decyl < hexyl < methyl < propyl ≈ pentyl << butyl. There is thus an optimal chain length at butyl. These results provide further evidence for the selective incorporation of alkyl groups in the polyhydroxy aromatic cavity of the host.

Experimental values and analysis of mixing heats of the binary mixtures formed by alkyl benzoates and n-alkanes

H E values for 28 binary mixtures of four alkyl (methyl, ethyl, propyl, and butyl) benzoates and seven odd n-alkanes (from pentane to heptadecane) were determined experimentally at 298.15 K. Data plots ( x, H E) revealed the endothermicity of the mixtures. For a given ester the endothermic effects increased regularly with n-alkane chain length and decreased regularly with the length of the alkylated chain of benzoate. The experimental values were analysed using two versions of the UNIFAC group contribution model. Using the new data, values were calculated for the specific interactions of the characteristic carboxyl group, COO, on the benzoates with other groups in the mixing process for these mixtures, namely, CH 2 COO and ACH COO . Using the new values the model produced good H E estimates, with an overall mean error of less than 5%.

Poly(alkyl benzoate)s: preparation, properties and conversion to polyphenylenes

Poly(alkyl benzoate)s were prepared by the coupling of alkyl dichlorobenzoates with zerovalent nickel generated in situ from nickel(II) bromide and characterized by 1H NMR spectroscopy. While the spectra of the substituted poly( p-phenylene)s were complicated by the irregular distribution of substituents and the flipping of the phenylene rings, the spectra of poly( m-phenylene) derivatives were simple. In the spectra of poly(dodecyl- p-phenylene), the relative positions of the two signals due to the α-methylene group, associated with head-to-tail and head-to-head bondings of the phenylene rings, were reversed upon the introduction of the methoxycarbonyl group. The poly(alkyl benzoate)s melted under microscopic observation and thermally decomposed in two stages. The decomposition temperature ranged from 380 to 460°C for the first stage and from 550 to 590°C for the second stage. These findings indicated that these polymers were soluble, fusible and thermally stable. The poly(alkyl benzoate)s were hydrolysed and decarboxylated to the corresponding polyphenylenes. Although the substituted poly( p-phenylene)s were easily converted to polyphenylenes, the poly( m-phenylene) homologues were resistant to hydrolysis.

Hydrogen-bonded network and enforced supramolecular cavities in molecular crystals: An orthogonal aromatic-triad strategy. Guest binding, molecular recognition, and molecular alignment properties of a bisresorcinol derivative of anthracene in the crystalline state

Abstract Crystallization of an orthogonal resorcinol-anthracene-resorcinol compound 1a (host) from an ester solvent such as alkyl benzoate (guest) affords a 1:2 host-guest adduct 1a·2(ester). An essential aspect of the crystal structures of ethyl, propyl, and isobutyl benzoate adducts (space group, P21/n) and also that of methyl benzoate adduct (C2/c) is an extensive hydrogen-bonded network of host 1a, leading to a molecular sheet composed of hydrogen-bonded polyresorcinol chains and anthracene columns. This network generates well-defined, cyclophane-like supramolecular cavities, which incorporate two alkyl benzoate molecules in a highly selective manner via a combination of essential host-guest hydrogen-bonding and what may be called the cavity-packing effect. The selectivity factor between methyl benzoate (the lowest-affinity guest) and isobutyl benzoate (the highest-affinity guest) is 1:70 under competitive conditions. The actual geometry of the cavity is somehow dependent on and hence induced-fit adju...

Excess thermodynamic properties of mixtures of alkyl benzoates withn-heptane

The paper reportshE values at 298.15 K andvE and δη values at various temperatures for binary mixtures of propyl or butyl benzoate andn-heptane. The excess Gibbs energy of viscous flow,Δg*E, and the thermodynamic activation properties were calculated from these values. The results are compared with those for similar mixtures and interpreted on the basis of the characteristic dipole-dipole interactions of alkyl esters.

ChemInform Abstract: Chemisorption and Cleavage of Alkyl Benzoates on Alumina Surface Studied by Inelastic Electron Tunneling Spectroscopy.

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Single and double hydrogen atom migrations in substituted alkyl benzoates: a study on the substituent effect using MIKE spectrometry

The substituent effect on the single and double hydrogen atom migrations is ionized ortho-, meta-, and para-substituted isobutyl (XC 6H 4COOC 4H 9) and isopropyl (XC 6H 4COOC 3H 7) benzoates is investigated by mass-analyzed ion kinetic energy spectrometry. The observed product ion ratios [XC 6H 4COOH] + /[XC 6H 4COOH 2] + show a general tendency: the compounds with an electron-donating substituent favour the formation of [XC 6H 4COOH] + by single hydrogen atom migration (McLafferty rearrangement), while those with an electron-withdrawing substituent produce preferentially [XC 6H 4COOH 2] + through double hydrogen atom migration (McLaffery + 1 rearrangement). The thermochemical considerations combined with MO calculations show that the substituent effects observed are rationalized by the effects of substituent on the ionization energy (IE) and proton affinity (PA) of XC 6H 4COOH, i.e. the product ratios are determined by the difference of the product thermochemical stabilities which can be evaluated as IE(XC 6H 4COOH) + PA(XC 6H 4COOH).

Chemisorption and Cleavage of Alkyl Benzoates on Alumina Surface Studied by Inelastic Electron Tunneling Spectroscopy

The technique of inelastic electron tunneling spectra (IETS) has been used to study the surface reaction of ethyl, isobutyl, and tert-butyl benzoates on alumina. The ethyl and isobutyl benzoates decompose to the corresponding alcohols where the net reaction accounts for the hydrolysis of the benzoate, and the ultimate products of chemisorption on alumina surface are detected to be the corresponding alkoxide anions. In the case of tert-butyl benzoate, the chemisorbed species on the alumina surface is benzoic acid rather than tert-butyl alcohol. In both cases, the surface reactions are identified as the dissociative chemisorption of the hydrolysis products of the original benzoate molecule

Ion spray mass spectrometric detection for liquid chromatography: A concentration- or a mass-flow-sensitive device?

As the mass spectrometer becomes more accepted as a detector for HPLC, its characteristics should become better understood by those performing routine LC-MS experiments. In particular, the ion current response for quantitative analysis studies involving significant dynamic range in concentration for target analytes must be determined as well as other factors that affect MS response. This work describes the concentration-sensitive response for the ion spray (pneumatically-assisted electrospray) LC-MS interface from the chromatographer's perspective. A comparison of LC-MS ion current response in the isocratic mode resulting from studies of a synthetic mixture containing alkyl benzoates is presented. LC-MS total ion current chromatograms from three different column sizes (1 mm I.D., 2.1 mm I.D. and 4.6 mm I.D.) with and without a post-column split, and high-flow ion spray LC-MS without a post-column split illustrates that the former behaves as a concentration-sensitive detector whereas the latter behaves as a mass-flow-sensitive detector. The flexibility of ion spray to high-flow applications allows the use of HPLC eluent flow ranging from 0.001-2.0 ml/min. The use of solvent—buffer post-column addition also allows optimization for improved analyte ion current response.

Studies on densities and viscosities of binary mixtures of alkyl benzoates in n-heptane

Densities and viscosities have been determined for the two binary mixtures of methyl and ethyl benzoate in n-heptane at different concentrations and temperatures. The corresponding excess properties and the activation magnitudes were also calculated from the experimental data. All excess properties, including the excess Gibbs free energy of activation of flow, are negative over the entire range of compositions. The results for these binary mixtures are compared with those for methyl benzoate with n-nonane, the molecular interactions occurring in the mixtures being explained on the basis of the deviation from ideality of the magnitudes studied.

Chemisorbed Species of Alkyl Benzoates on Alumina Surface Studied by Inelastic Electron Tunneling Spectroscopy

Abstract Vibrational spectra of alkyl benzoates dissociatively adsorbed on the alumina surfaces have been measured by inelastic electron tunneling spectroscopy. The analyses of the spectra indicate that ethyl and tert-butyl benzoates are adsorbed as ethoxide or benzoate ions, respectively, by the acid-catalyzed reaction on alumina surfaces.

Comparison of the selectivity of di(methacryloyloxymethyl)-naphthalene—divinylbenzene copolymers in reversed-phase high-performance liquid chromatography

The influence of chemical composition of porous copolymers on chromatographic properties of high-performance liquid chromatography columns was studied. Columns were packed with three di(methacryloyloxymethyl)naphthalene-divinylbenzene copolymers of different molar ratio of monomers. The retention behaviour of five homologous series (alkylbenzenes, N-alkylanilines, alkyl aryl ethers, alkyl benzoates and alkyl aryl ketones) was investigated using different eluents. Using the alkyl aryl ketone scale, the retention indices of the homologues and column test compounds were calculated. Their values were used to compare the selectivities of the studied stationary phases.