Homologous Series Of N-alkanes Research Articles

Single carbon surface reactions of 1-octadecene and 2,3,6-trimethylphenol on activated carbon: Implications for methane formation in sediments

The reactions of a terminal alkene (1-octadecene) and a polymethyl phenol (2,3,6-trimethylphenol) on activated carbon have been investigated in closed system pyrolysis experiments in the temperature range 170–340 °C. The reaction products of 1-octadecene included methane, isomeric octadecenes, methyl substituted alkanes, alkyl aromatics and an homologous series of n-alkanes with carbon numbers indicative of progressive single carbon depletion of the reactant. The reaction products of 2,3,6-trimethylphenol also contained methane, as well as C 1–C 4 methyl phenols produced by demethylation and methyl transfer reactions. A carbon surface reaction involving the formation of a reactive single carbon intermediate (i.e. methylene/carbene) is proposed. This reaction accounts for the products observed from the pyrolysis experiments and also is consistent with liquid hydrocarbon distributions found in petroleum basins. Methane was the dominant (ca. 85% of C 1–C 4) gaseous hydrocarbon product of 2,3,6-trimethylphenol but accounted for only ca. 17% of the C 1–C 4 hydrocarbons from 1-octadecene. These findings suggest that single carbon surface reactions may play an important role in the geochemical formation of crude oil and natural gas and that the composition of the source material and therefore the type of organic compounds undergoing such reactions, influences the hydrocarbon gas composition in sedimentary basins.

Isothermal solubility of individual light fullerenes in the homologous series of n-alkanes, n-alkanols, n-alkylcarboxylic acids, and arenes

Available published data on isothermal solubility (at 20°C) of individual light fullerenes in a homologous series of n-alkanes, n-alkanols, n-alkylcarboxylic acids, and arenas were systematized. A correlation between the parameter of Hildebrand’s cohesion and the logarithm of the mole fraction of the fullerene in the saturated solution was revealed.

Fluoroalkylated Silicon-Containing Surfaces−Estimation of Solid-Surface Energy

The design of robust omniphobic surfaces, which are not wetted by low-surface-tension liquids such as octane (γlv=21.6 mN/m) and methanol (γlv=22.7 mN/m), requires an appropriately chosen surface micro/nanotexture in addition to a low solid-surface energy (γsv). 1H,1H,2H,2H-Heptadecafluorodecyl polyhedral oligomeric silsesquioxane (fluorodecyl POSS) offers one of the lowest solid-surface energy values ever reported (γsv≈10 mN/m) and has become the molecule of choice for coating textured surfaces. In this work, we synthesize and evaluate a series of related molecules that either retain the POSS cage and differ in fluoroalkyl chain length or that retain the fluorodecyl chains surrounding a linear or cyclic molecular structure. The solid-surface energy (γsv) of these molecules was estimated using contact angle measurements on flat spin-coated silicon wafer surfaces. Zisman analysis was performed using a homologous series of n-alkanes (15.5≤γlv≤27.5 mN/m), whereas Girifalco-Good analysis was performed using a set of polar and nonpolar liquids with a wider range of liquid surface tension (15.5≤γlv≤72.1 mN/m). The hydrogen-bond-donating, hydrogen-bond-accepting, polar, and nonpolar (dispersion) contributions to the solid-surface energy of each compound were determined by probing the surfaces using a set of three liquid droplets of either acetone, chloroform, and dodecane or diiodomethane, dimethyl sulfoxide, and water.

Comparative characterization of the distribution of biomarker hydrocarbons in the chemical transformation products of oxygen-containing precursors of petroleum

The distribution of biomarker hydrocarbons in the thermolysis and thermocatalysis products of oxygen-containing compounds (possible petroleum hydrocarbon precursors) was studied by gas chromatography-mass spectrometry. It was found that n-alkylcyclohexanes and steranes were generated in the course of thermolysis along with expected hydrocarbons—n-alkanes and isoprenes, which resulted from the loss of a functional group. In this case, the molecular-weight distributions of n-alkanes and n-alkylcyclohexanes correlated well with each other. In the course of thermocatalysis, the homologous series of n-alkanes and n-alkylcyclohexanes were also generated; however, an n-alkylcyclohexane distribution maximum had an even number of carbon atoms in the molecule (C18). It was experimentally found that the sterane fragments of oxygen-containing compounds formed upon thermolysis were thermodynamically unstable; this was supported by the formation of biological C27–C29 5α, 14α, 17α, 20S, and 20R and 5β, 14α, 17α, and 20R (coprostane) steranes as a result of thermolysis. Unlike thermolysis, all of the four epimers of regular C27–C29 (5α, 14α, 17α, 20S, and 20R and 5α, 14β, 17β, 20S, and 20R) steranes were formed as a result of thermocatalysis. It was found that the relative distribution of biomarker hydrocarbons in the thermolysis products of various oxygen-containing compounds largely reflected the structure of the parent organic substance, as compared with that upon thermocatalysis in the presence of active aluminosilicate.

Distribution of n-Alkanes in the Northern Italy Aerosols: Data Handling of GC-MS Signals for Homologous Series Characterization

The paper describes the characterization of n-alkane homologous series present in PM samples performed by gas chromatography-mass spectrometry analysis. The PM samples were collected in three locations in northern Italy: Milan, a large urban area, Oasi Bine, a rural site far from big city centers, and Alpe San Colombano, a remote, high altitude site in the Alps. They represent different particle sizes (PM(1), PM(2.5), PM(10)) and seasons (summer, fall, and winter). The analyzed samples were characterized in terms of PM total mass, total concentration of C(20)-C(32) n-alkanes and carbon preference index, CPI, to quantify the relative abundance of odd versus even n-alkanes. As alternative to the conventional method based on peak integration, a chemometric approach based on autocovariance function (EACVF) computation was found reliable to characterize the homologous series. In particular two parameters have proven useful chemical markers for tracking the biogenic and anthropogenic origins of n-alkanes: CPI(EACVF) and series %, estimating the % n-alkanes abundance relative to total alkane concentration. The investigated samples display a large variation in the n-alkanes relative abundance: the lowest values (series % = 1-14%) were found in summer and the highest (series % = 24-48%) in winter. In addition, a considerable seasonal variation of CPI(EACVF) values can be identified for all the sampling sites: the CPI(EACVF) values are close to 1 (CPI(EACVF) = 0.8-1.2) in the cold seasons, revealing a strong contribution from anthropogenic emissions, while spreader values (CPI(EACVF) = 0.9-3) were found in the warm season, that is, reflecting a variable contribution from biogenic sources in combination with anthropogenic emissions.

Phase equilibria, critical behavior and derivative properties of selected n-alkane/ n-alkane and n-alkane/1-alkanol mixtures by the crossover soft-SAFT equation of state

We present here results from the crossover soft-SAFT equation of state as applied to selected n-alkane/ n-alkane and n-alkane/1-alkanol mixtures. The molecular parameters needed to apply the equation to experimental systems were obtained as a function of the molecular weight of the compounds, from published correlations. The fact that the equation takes into account the long range density and composition fluctuations appearing near the critical point enables it to predict with equal accuracy the behavior of the systems far from and close to the critical region. We have found that, for most of the mixtures investigated here, one size binary interaction parameter, with a fixed value for all systems, is enough to quantitatively predict the rich phase behavior shown by these mixtures, while for the case of very asymmetric mixtures, a second binary parameter, also independent of the thermodynamic conditions, is needed to quantitatively describe experimental data. Crossover soft-SAFT accurately reproduces transitions from type I to type V for the critical behavior of the methane/ n-alkane and ethane/ n-alkane homologous series. The equation also predicts in a quantitative manner the subcritical and critical behavior of the 1-propanol/ n-hexane and ethanol/ n-butane binary mixtures. Finally, we report speed of sounds of the mixture methane/ n-butane and the heat capacities of the mixture 1-propanol/ n-decane, in close agreement with experimental data. Results presented here encourage the development of molecular-based equations of state with a term taking into account the singular behavior in the near critical region, especially if one is searching for quantitative predictions in this region for further applications.

Acetate esters of saturated and unsaturated alcohols (C 12–C 20) are major components in Dufour glands of Bracon cephi and Bracon lissogaster (Hymenoptera: Braconidae), parasitoids of the wheat stem sawfly, Cephus cinctus (Hymenoptera: Cephidae)

Chemistry of Dufour glands associated with the venom complex in Bracon cephi (Gahan) and Bracon lissogaster Muesebeck (Hymenoptera; Braconidae), two parasitoids of the wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), was examined by solid phase micro-extraction (SPME) and gas chromatography/mass spectrometry. Homologous series of five chemical classes were detected in individual glands from each species. Major classes included: (1) acetate esters of saturated and unsaturated primary alcohols with parent chain lengths from C 12 to C 20. Hexadecanyl acetate, octadecanyl acetate, and octadecenyl acetate were major components in B. cephi. The composition of the acetate series in B. lissogaster was similar except that the octadecanyl acetate was only a minor component. (2) A homologous series of monoenes from C 23:1 to C 35:1 were detected in both species, with C 29:1, C 31:1 and C 33:1 being the major components. Dienes from C 31:2 to C 35:2 and trienes (C 33:3–C 35:3) were also detected in both species. (3) A homologous series of n-alkanes from C 19 to C 31 was detected in both species. n-Tricosane was the major component. Minor components in both species included homologous series of both mono- and dimethyl branched alkanes. The Dufour gland hydrocarbon components in both B. cephi and B. lissogaster have some similarities to the composition of cuticular hydrocarbons of their host C. cinctus, a species with a complex pheromonal signaling system.

Solid surface mapping by inverse gas chromatography

Inverse gas chromatography (IGC) at infinite dilution, is a technique for characterising solid surfaces. Current practice is the injection of n-alkane homologous series to obtain the free energy of adsorption of the CH 2 group, from which the London component of the solid surface free energy, γ S d , is calculated. A value around 40 mJ/m 2 is obtained for poly(ethylene), and 30 mJ/m 2 for a clean glass fibre, while the potential surface interactivity of a glass fibre is far greater than that of poly(ethylene). A specific component of the surface, in mJ/m 2, should be calculated in order to obtain significant parameters. As applied up to date, when calculating the specific component of the surface energy, the fact that W a sp energy values are in a totally different scale than AN or DN values is a major drawback. Consequently, Ka and Kb values obtained are in arbitrary energy units, different from those of the London component measured by injecting the n-alkane series. This paper proposes a method to obtain Ka and Kb values of the surface in the same energetic scale than the London component. The method enables us to correct the traditional London component of a solid, obtaining a new value, where the amount of W a C H 2 accounting for Debye interactions with polar sites, is excluded. As a result, an approach to surface mapping is performed in several different substrate materials. We show results obtained on different solid surfaces: poly(ethylene), clean glass fibre, glass beads, chemically modified glass beads and carbon fibre.

The effect of density on the properties of short chain fluids

We incorporate density dependence into continuum Born-Green-Yvon (BGY) theory through calculation of the end-to-end intramolecular correlation function. Whereas in previous studies we had only performed this calculation for the case of an isolated (zero-density) square-well chain of m segments (3</=m</=7), here we consider this single chain to have been placed in a square-well monomeric fluid of variable density. We find that the results obtained by this more sophisticated approach are in good agreement with the predictions of both other theories and simulation concerning the structural properties of short chains. Using a homologous series of n-alkanes as a test case, we also conclude that BGY theory, with the current modifications, is capable of describing fluid properties for heptane (n-C7) through nonadecane (n-C19).

Cuticular Wax Profiles of Leaves of Some Traditionally Used African Bignoniaceae

Bignoniaceae, Newbouldia laevis, Markhamia acuminata, Spathodea campanulata and Kigelia africana were analysed by GC-MS. The principal constituents were represented by a homologous series of n-alkanes (C23-C33), n-alcohols (C18-C30) and related carboxylic acids (C16-C36). For N. laevis and M. acuminata, ursolic and oleanolic acid were the most abundant wax components (52 and 60%, respectively), followed by the C29, the C31 and the C33 n-alkanes. The predominant components of S. campanulata were n-alcohols (35%), with octacosanol and triacontanol as the most abundant ones, while K. africana is distinguished from these three members by the conspicuous absence of triterpenoic acids and the predominance of n-alkanes (70%) with hentriacontane and tritriacontane as the main representatives. Other notable constituents were sterols, albeit present in trace amounts. The wax profiles are discussed in terms of taxonomic characters.

Application of SAFT–VRX to binary phase behaviour: alkanes

In previous work, we developed the crossover SAFT–VR equation of state (SAFT–VRX) for pure fluids by following the crossover approach proposed by Kiselev. The SAFT–VRX equation was shown to be very accurate in the prediction of PVT and phase behaviour for both non-associating and associating fluids. In particular, simple expressions for the potential model parameters for the n-alkane homologous series were developed, allowing the prediction of the thermodynamic properties without fitting to experimental data. In this work, we have applied the SAFT–VRX equation to binary mixtures of short-chain n-alkanes, using the prescriptions for the model parameters developed previously to determine the pure fluid parameters. The SAFT–VRX equation is found to accurately predict the gas–liquid critical locus and vapor–liquid equilibrium data for the systems studied without fitting to binary experimental mixture data.

Comparison of lattice and continuum treatments of n-alkanes with experimental data

Using a homologous series of n-alkanes as a model system, we compare the predictions of a lattice Born-Green-Yvon (BGY) theory and a continuum BGY theory with experimental results. We find that both theories are capable of describing the fluid properties and critical points of alkanes ranging from heptamers (n-C7) to nonadecamers (n-C19). We probe the connection between the lattice and continuum BGY models and extend our discussion to include a sampling of other lattice and continuum treatments.

Application of Crossover Theory to the SAFT-VR Equation of State: SAFT-VRX for Pure Fluids

The molecular-based SAFT equation of state has proven to be very versatile in the prediction of fluid phase equilibria. However, in common with all analytic equations of state, SAFT exhibits classical behavior in the critical region rather than the nonanalytical, singular behavior seen in real fluids. As a result, accurate agreement over the whole phase diagram cannot be obtained and must be localized to either the critical or subcritical regions. To overcome this problem, we have combined the SAFT-VR equation of state with a crossover technique developed by Kiselev (Kiselev, S. B. Fluid Phase Equilib. 1998, 147, 7) to obtain the SAFT-VRX equation. We have applied SAFT-VRX to both associating and nonassociating pure fluids. Results are presented for n-alkanes, water, and carbon dioxide. Furthermore, by fitting to the phase diagram and PVT behavior for a small number of n-alkanes, we have developed simple expressions for the potential model parameters for the n-alkane homologous series. These prescriptions enable the accurate prediction of the thermodynamic properties, including the phase diagram, of n-alkanes without additional fitting to experimental data. Additionally, by combining density functional theory with SAFT-VRX we predict the surface tension of both low and high molecular weight n-alkanes.

On the stability of oil-in-water emulsions to freezing

Oil in water emulsions (40 wt%) were prepared from a homologous series of n-alkanes (C10–C18). The samples were temperature cycled in a differential scanning calorimeter (two cycles of 40 °C to −50 °C to 40 °C at 5 °C min −1) and in bulk (to −20 °C). The emulsions destabilized and phase-separated after freeze–thaw if the droplets were solid at the same time as the continuous phase and were more unstable if a small molecule (SDS or polyoxyethylene sorbitan monolaurate) rather than a protein (whey protein isolate or sodium caseinate) emulsifier was used. The unstable emulsions formed a self-supporting cryo-gel that persisted between the melting of the water and the melting of the hydrocarbon phase. Microscopy provides further evidence of a hydrocarbon continuous network formed during freezing by a mechanism related to partial coalescence which collapses during lipid melting to allow phase separation.

Carbon isotope analyses of n-alkanes in dust from the lower atmosphere over the central eastern Atlantic

Atmospheric dust samples collected along a transect off the West African coast have been investigated for their lipid content and compound-specific stable carbon isotope compositions. The saturated hydrocarbon fractions of the organic solvent extracts consist mainly of long-chain n-alkanes derived from epicuticular wax coatings of terrestrial plants. Backward trajectories for each sampling day and location were calculated using a global atmospheric circulation model. The main atmospheric transport took place in the low-level trade-wind layer, except in the southern region, where long-range transport in the mid-troposphere occurred. Changes in the chain length distributions of the n-alkane homologous series are probably related to aridity, rather than temperature or vegetation type. The carbon preference of the leaf-wax n-alkanes shows significant variation, attributed to a variable contribution of fossil fuel- or marine-derived lipids. The effect of this nonwax contribution on the δ 13C values of the two dominant n-alkanes in the aerosols, n-C 29 and n-C 31 alkane, is, however, insignificant. Their δ 13C values were translated into a percentage of C 4 vs. C 3 plant type contribution, using a two-component mixing equation with isotopic end-member values from the literature. The data indicate that only regions with a predominant C 4 type vegetation, i.e. the Sahara, the Sahel, and Gabon, supply C 4 plant-derived lipids to dust organic matter. The stable carbon isotopic compositions of leaf-wax lipids in aerosols mainly reflect the modern vegetation type along their transport pathway. Wind abrasion of wax particles from leaf surfaces, enhanced by a sandblasting effect, is most probably the dominant process of terrigenous lipid contribution to aerosols.

Cuticular lipids of the booklouse, Liposcelis bostrychophila: hydrocarbons, aldehydes, fatty acids, and fatty acid amides.

The booklouse, Liposcelis bostrychophila, is an increasingly common pest of stored food products worldwide. We report here the cuticular lipid composition of this pest (the first report of the hydrocarbons of any member of the Order Psocoptera and the first report of fatty acid amides as cuticular components for any insect). No unsaturated hydrocarbons were present. A homologous series of n-alkanes (C21-C34), monomethyl alkanes (3-, 4-, 5-, 7-, 9-, 11-, 12-, 13- and 15-methyl-) with a carbon chain range of C28-C42, and dimethyl alkanes (3, 7-; 9, 13-; 11, 15-; 13, 17-; 9, 21-; 11, 19-; and 13, 21-) with a carbon number range of C31-C41 were identified. The relative abundances of these hydrocarbons were low, comprising approximately 0.0125% of total biomass. The amides were a homologous series (C16-C22 in chain length), with the major amide being stearoyl amide. In addition to the amides, free fatty acids (C16:1, C16:0, C18:2, C18:1, and C18:0 in chain length) and three straight chain aldehydes (C15, C16, and C17:1 in chain length) also occurred as cuticular components. These findings are discussed in terms of the chemical and physiological ecology of this species.

Solution properties of poly(n-hexyl methacrylate) in homologous series of n-alkanes

Dilute solutions of poly(n-hexyl methacrylate) have been studied in the homologous series of alkanes at different temperatures using viscometry. Mark-Houwink relations in solvents widely differing in their thermodynamical quality were established together with the unperturbed dimensions and their temperature coefficient.

A New Intermolecular Potential Model for the n-Alkane Homologous Series

A new model for the n-alkane homologous series has been developed, parametrized to the vapor−liquid coexistence properties for a range of chain lengths. The model utilizes the Buckingham exponential-6 potential to describe the nonbonded interaction energy. Histogram reweighting grand canonical Monte Carlo methods were used to determine the model parameters. The new model reproduces the experimental saturated liquid and vapor densities and vapor pressures for ethane through octane to within average absolute deviations of 0.5%, 2.1%, and 2.2% respectively. Critical temperatures and densities were also found to be in good agreement with experiment. Critical pressures are slightly overestimated for longer chain lengths. Comparisons were made to the TraPPE [J. Phys. Chem. B 1998, 102, 2569.] and NERD [J. Chem. Phys. 1998, 108, 9905.] models. The two previous models reproduce the liquid properties with comparable accuracy to the proposed model; however, the new model was found to describe the vapor pressures mo...

Variation of the Surface Properties of Hematite upon Heat Treatment Evidenced by Inverse Gas Chromatography and Temperature Programmed Desorption Techniques: Influence of Surface Impurities and Surface Reconstruction

The influence of heat treatment on the surface properties of hematite samples of different origins was examined by inverse gas chromatography (IGC) and temperature programmed desorption (TPD) techniques. Comparison of the curve relating the evolution of the free energy of adsorption of a methylene group, ΔGa(CH2), measured by IGC using a homologous series ofn-alkanes, and the TPD curve reveals similarities. In particular, the increase either of the rate of departure of impurities (SO2from a polluted hematite sample) or the rate of water release upon heating a pure hematite sample is accompanied by a significant increase of ΔGa(CH2). Rehydration experiments of heat-treated hematite samples show that restoring the characteristics of the initial, nonheated oxide surface becomes quasi-impossible for samples treated at above 350°C. This points to reconstruction or relaxation of the surface layer upon heat treatment. Determination of the changes in nanomorphology and acid/base properties complements this study. A layer of oxyhydroxide possibly exists on hematite surfaces.

Intermolecular Interactions in Gas Chromatography on Carbon Black Coated with Monolayers of Hydrocarbons with Different Electronic Structures

The adsorption and chromatographic properties of surfaces obtained by the adsorptive modification of thermally graphitized carbon black (TGCB) with hydrocarbons differing in composition and electronic structure (n-dotriacontane and coronene) were studied by gas chromatography (GC). The contributions towards the retention of methylene groups in homologous series of n-alkanes, alkylbenzenes, ethers, esters and n-alcohols were estimated for TGCB coated with monolayers of the above-mentioned hydrocarbons. The thermodynamic characteristics of the adsorption process were also measured for molecules of the various classes of organic compounds described. In addition, differences in the mechanism of chromatographic retention on n-alkane monolayers, when the latter may exist as solid-like, transitional or liquid-like states, and on coronene monolayers were studied. The influence of the electronic configuration of the carbon atoms in the modifier molecules on the adsorption energy of the various organic compounds studied has been demonstrated. The possibility of employing GC methods for demonstrating phase transitions in long-chain alkane monolayers adsorbed on carbon black is discussed. Furthermore, the possibility of controlling the retention selectivity during GC by TGCB modification with adsorbed monolayers of hydrocarbons is presented.