Oxidation of small unsaturated methyl and ethyl esters

The ignition delay times were measured behind reflected shock waves for temperatures from 1280 to 1930 K, pressures from of 7–9.65 atm, fuel concentrations of 0.4, 0.5, and 1%, and equivalence ratios equal to 0.25, 1.0, and 2.0 in the cases of four unsaturated esters: methyl crotonate, methyl acrylate, ethyl crotonate, and ethyl acrylate. Ignition delay times were measured using chemiluminescence emission from OH at 306 nm and piezoelectric pressure measurements made at the shock tube sidewall. No important difference of reactivity was observed between methyl and ethyl unsaturated esters, methyl and ethyl crotonate having the same reactivity as methyl butanoate. The reactivity of acrylates is greater than that of crotonates especially at the lowest investigated temperatures. Detailed mechanisms for the combustion of the four studied unsaturated esters have been automatically generated using the version of EXGAS software recently improved to take into account this class of oxygenated reactants. These mechanisms have been validated through satisfactory comparison of simulated and experimental results. The main reaction pathways have been derived from flow rate and sensitivity analyses. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 204–218, 2011     

Thermochemistry of methyl and ethyl esters from vegetable oils

This paper deals with the gas‐phase thermodynamic properties of methyl ester and ethyl ester of vegetable oils (fatty acid methyl esters and fatty acid ethyl esters respectively) present in biodiesel. The standard enthalpies of formation at 298.15 K, heat capacities, and entropies in the temperature range 300–5000 K are determined by means of quantum chemistry calculations along with a protocol developed for these compounds. The resultant data, currently not available in the literature for most of them, are critical to the modeling of combustion chemistry of the subject compounds. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 481–491, 2007     

Anisotropic aggregation and phase transition in Langmuir monolayers of methyl/ethyl esters of 2,3-dihydroxy fatty acids

We studied interfacial properties of a series of methyl and ethyl esters of enantioenriched syn-2,3-dihydroxy fatty acids with different chain lengths at the air-water interface, using a Langmuir type film balance and a Brewster angle microscope (BAM). After analyzing their surface pressure (Pi)-area (A) isotherms, we inferred that these molecules existed as an E conformation in the liquid-expanded (LE) phase of monolayers, and the E conformation of molecules changed into a Z conformation during the LE-LC transition in a monolayer. BAM images evidenced the formation of elongated LC aggregates. This is possibly induced by the intermolecular hydrogen bonds, leading to the anisotropic growth of LC domains, on the basis of the FT-IR spectroscopy data. The enthalpy change of the LE-LC phase transition is considered to result from the three types of intermolecular interactions at the air-water interface during compression of these amphiphiles. These findings are discussed in terms of various physical factors that influenced intermolecular interactions and macroscopic aggregations of these amphiphiles.     

Adsorption parameters in solutions of ethyl esters of aliphatic acids

Based on the regression analysis of electrocapillary curves (ECC) in solutions of ethyl esters of aliphatic acids (from acetic to valeric), it is shown that the adsorption of these compounds on a mercury electrode from aqueous solutions corresponds in the first approximation to the model of two parallel capacitors. Moreover, to describe experimental ECC, the knowledge of only five main parameters of this model is necessary. The dependence of the adsorption parameters found on the number of carbon atoms in an ester molecule is analyzed.__________Translated from Elektrokhimiya, Vol. 41, No. 4, 2005, pp. 406–411.Original Russian Text Copyright © 2005 by Damaskin.     

Monolayer phases of the fatty acids and their ethyl esters

The miscibility correspondence between water-surface monolayer phases of the fatty acids and their ethyl esters was determined. Ester phases were found corresponding to all the known phases of the acids, and vice versa, in similar relative positions of the π-T diagram. Evidence is presented for the existence of a ninth distinct miscibility category, represented by a phase in each of the pure materials, and a tenth found only in mixtures. We propose a tentative correspondence to bulk smectic miscibility categories.     

Photodissociation dynamics of hydroxybenzoic acids

Aromatic amino acids have large UV absorption cross-sections and low fluorescence quantum yields. Ultrafast internal conversion, which transforms electronic excitation energy to vibrational energy, was assumed to account for the photostability of amino acids. Recent theoretical and experimental investigations suggested that low fluorescence quantum yields of phenol (chromophore of tyrosine) are due to the dissociation from a repulsive excited state. Radicals generated from dissociation may undergo undesired reactions. It contradicts the observed photostability of amino acids. In this work, we explored the photodissociation dynamics of the tyrosine chromophores, 2-, 3- and 4-hydroxybenzoic acid in a molecular beam at 193 nm using multimass ion imaging techniques. We demonstrated that dissociation from the excited state is effectively quenched for the conformers of hydroxybenzoic acids with intramolecular hydrogen bonding. Ab initio calculations show that the excited state and the ground state potential energy surfaces change significantly for the conformers with intramolecular hydrogen bonding. It shows the importance of intramolecular hydrogen bond in the excited state dynamics and provides an alternative molecular mechanism for the photostability of aromatic amino acids upon irradiation of ultraviolet photons.     

Analysis of styrenated methyl esters of linseed oil fatty acids by molecular distillation

The distillation of the reaction product of methyl esters of linseed oil fatty acids and gaseous styrene at 280° C in a highly efficient molecular still is described. From the specific refractions of the fractions obtained it follows that styrene has combined chemically with the esters.     

Reactions of methyl esters of adamantane acids with acetonitrile

Russian Chemical Bulletin - Methyl adamantane-1-carboxylate and methyl (1-adamantyl)acetate react with acetonitrile in the presence of sodium hydride to give 3-(1-adamantyl)-3-oxopropanenitrile and...     

Asymmetric synthesis of monohydroxy tetradecanoic acids and their methyl esters

Methyl 3-, 6- and 13-oxo tetradecanoates were reduced by NaBH₄ in the presence of 1,2:5,6-di-O-isopropylidene-d-glucofuranose (DIPGH) and (−)-menthol together with isovaleric and pivalic acids in THF solution. The highest enantiomeric purity was found for the 13-hydroxy ester isomer of 96% ee. Enantiomeric excess (ee, %) was determined by chiral HPLC and ¹H NMR with shift reagent, Eu(tfc)₃.