Pure Alkanes Research Articles

Spin correlation in the geminate recombination of radical ions in hydrocarbons. Part 1.—Theory of the magnetic field effect

Geminate recombination of radical ions of aromatic hydrocarbons in alkanes produces excited molecules: the relative yields of singlets and triplets change with time as the spin correlation decays. At short times ([graphic omitted] 50 ns) the process is a coherent one resulting from the isotropic hyperfine interaction with hydrogen nuclei: its rate is field-dependent and, for mobile liquids, it can be calculated exactly from e.s.r. data: deuteration will have a large effect and oscillations may be observed. At longer times, the yields became constant (but different) at high and zero field, but an additional small decay is predicted for very low fields. At still longer times, random spin relaxation will eventually make the yields independent of field. The theory is extended to cover initial production of triplet ion pairs in addition to singlets, the effect of charge transfer and recombination in viscous liquids and solids. It is applied to excited state production in radiolysis and to the radiation chemistry of pure alkanes.

Phase equilibria and critical phenomena in fluid mixtures of carbon dioxide + 2,6,10,15,19,23-hexamethyltetracosane up to 423 K and 100 MPa

In an optical high-pressure cell with sapphire windows and magnetic stirring, phase equilibria in fluid binary mixtures of carbon dioxide + 2,6,10,15,19,23-hexamethyltetracosane (squalane) have been measured up to 423 K and 100 MPa. The critical curve of the mixture starts at the critical point of the pure alkane ( T c = 933 K, p c = 0.51 MPa (calculated values)). With decreasing temperatures the critical curve runs first through a pressure maximum at about 39 MPa and 473 K, then through a pressure minimum at p = (36.3 ± 0.2) MPa and T = (373 ± 2) K, and at last through a temperature minimum at T = (328.2 ± 0.5) K and p = (70.5 ± 2.0) MPa. Finally the critical curve rises steeply to higher pressures with increasing temperatures. The results are discussed from a phase-theoretical point of view and are compared with phase equilibrium data of other carbon dioxide + alkane mixtures. It follows from this discussion that there are continuous transitions between liquid + gas, liquid + liquid, and gas + gas equilibria in these systems.

Studies of the spontaneous ignition in air of binary hydrocarbon mixtures

Detailed investigations of the combustion in of binary mixtures of n-decane and 2,2,5-trimethylhexane have provided useful information about the way in which the separate fuel components are involved in the reactions leading to cool flames and two-stage ignition. The presence of up to 10 mol% of the branched alkane has little effect on the slow combustion/cool flame boundary but as n-decane is further replaced by the nonane isomer, there is a progressive increase in the limiting temperature and pressure required for spontaneous ignition and well-defined changes are observed in the fine structure of the ignition profiles. It is also found that increasing concentrations of 2,2,5-trimethylhexane in the fuel decrease the pressure change accompanying the first cool flame and increase, quite markedly, the proceding induction period. More detailed analysis of the results obtained throws light not only on the factors governing the ignition in air of the binary fuel mixtures but also on the mechanism of spontaneous ignition of the two pure constituent alkanes. Although it is concluded that, as with binary mixtures of lower molecular weight hydrocarbons, the ignition tendency of n-decane-2,2,5-trimethyhexane mixtures is controlled largely by the more readily ignitable component, the results show that the introduction of quite small amounts of the branched alkane nevertheless results in increased ignition delay and may thus sometimes prevent spontaneous ignition taking place in an unconfined system.

Solvated electrons in alcohol-alkane and alcohol-amine solutions

The absorption spectrum of the solvated electron formed by pulse radiolysis of solutions of ethanol in 3-methylpentane, 2,2-dimethylbutane, and neopentane is unaffected by the presence of these alkanes above a few mole per cent of ethanol at room temperature. Above about 20 mol% solvated electron yields per unit of absorbed energy increase in the same order as the radiolytic free-ion yields of the pure alkanes. Below about 10 mol% this order is reversed and the half-time for decay of the solvated electron at constant solution composition also decreases with increasing extent of chain branching in the alkane constituent. Similarly, the solvated electron yield in dilute solutions of methanol, ethanol, and cyclohexanol in neopentane decreases with increasing hydrocarbon character of the alcohol constituent. ln ethanol- ethylenediamine solutions the amine is, to the contrary, the dominant solvating agent. These observations are discussed in the context of preferential solvation of excess electrons by microscopic aggregates of alcohol molecules and destabilization of these aggregates by alkanes and ethylenediamine. (auth)

Luminescence in High-Energy-Irradiated Alkanes at Low Temperature

Abstract High-energy bombardment is well-known to produce luminescence in condensed systems which contain suitable scintillators. Such light emission has been observed for weak scintillators like benzene in sufficiently dilute solutions in aliphatic hydrocarbons and, more recently, even in pure liquid benzene. It is not observed in pure liquid alkanes. However, when suitable alkanesare reduced to sufficiently low temperature (e.g., 77 °K), irradiation with 60Co gammas produces a persistent luminescence, the decay curves of which show peculiar behavior characteristics. This report reviews the decay characteristics and spectra of glassy 2-methylpentane and 3-methylpentane as well as of glassy and crystalline i-pentane, reexamines the kinetics and the mechanism of the luminescence process, interprets the applicability of the decay law Io/I = 1 + αt, demonstrates that an excited state of the system (probably a charge-separated state) and not of an individual molecule is involved, presents evidence that the number of available (A and B type) luminescence sites is limited and depends on the history of the system and suggests that the nature of the emitting state may change with temperature. An important aspect of the theoretical considerations is that they suggest that at sufficiently low temperatures such luminescence can be observed even for hydrocarbons as simple as methane. The most recent work of Janssen, Lang, Hebert, and the authors shows that, although luminescence can be induced in hydrogen and the lower alkanes by irradiation of polycrystalline material at sufficiently low temperature, it appears only when the temperature is raised to certain definite temperatures characteristics of each of the alkanes. Some of these temperatures correspond to know transition points; others may correspond to other solid-state changes.

Propriétés thermodynamiques des mélanges binaires. Volume et énergie interne de formation des solutions de l'hexadécane dans les isomères de l'hexane

AbstractThe volumes of mixing of hexadecane and each of the isomers of hexane have been measured for the equimolar mixtures at 20°C. The results have been used together with previously measured values of ΔH to obtain ΔUv.A very good correlation is found between the energy of mixing and the properties of the pure alkanes.

Luminescence Phenomena in Gamma-Irradiated Pure Alkanes at 77°K

Previous reports from this laboratory described the characteristic luminescence of γ-irradiated, pure 3-methylpentane glass and the influence of preirradiation standing time at 77°K on the luminescence intensity (annealing effect: decrease in intensity). In this paper it is shown: (a) that cracks in the annealed glasses are not necessarily required for the annealing effect to be observed, although they apparently accelerate the glass relaxation markedly, and (b) that the luminescence spectra of isopentane are different for the glassy and polycrystalline states. It is also shown, using a simple model, that the lowest charge-separated state can be stationary and lower in energy than the first excited state of the molecule; consequently, the charge-separated state can be the luminescent state for pure alkanes.

Luminescence Phenomena in Gamma-Irradiated Pure Alkane Glasses: Relaxation Mechanisms

It has been shown previously that gamma-irradiated pure 3-methylpentane glass at 77°K emits a characteristic luminescence according to a law which can be expressed as the sum of three first-order decays. In this new work on both 2-methylpentane and 3-methylpentane, it is shown: (1) that the two pentanes emit at 77°K, as nearly as can be established, in precisely the same fashion; (2) that the intensity of luminescence is decreased and the decay curve is flattened by permitting the glassy sample to relax at 77°K between vitrification and gamma irradiation; (3) that the decay law at both 77°K and 90°K is the sum of three first-order decay laws; (4) that the activation energies, as established by fixed-temperature measurements at those two temperatures, are all near 0.04 (±0.01) eV, but that the characteristic frequencies of the three laws vary by a factor of ∼102; (5) that, in addition to light which appears isothermally at 77°K and which is stimulated also by infrared irradiation, there is a glow portion which begins to appear only at temperatures near 100°K; (6) that while the long-wavelength portion of the luminescence spectrum is unaffected by the treatment to which the sample is subjected, there are significant changes in the shorter wavelength region on prolonged irradiation; (7) that at least two different kinds of electron traps are involved; (8) that chemical products are involved in the luminescence; and (9) that in gamma-sensitized luminescence as well as in radiation chemistry, radiolytic products play an important role in determination of the elementary processes responsible for the effects observed.

DITERMINAL OXIDATION OF LONG-CHAIN ALKANES BY BACTERIA.

Kester, A. S. (The University of Texas, Austin) and J. W. Foster. Diterminal oxidation of long-chain alkanes by bacteria. J. Bacteriol. 85:859-869. 1963.-A corynebacterial organism capable of growing in mineral salts with individual pure alkanes as carbon sources produces a series of acids from the C(10)-C(14) alkanes. They have been isolated in pure form and identified as monoic, omega-hydroxy monoic, and dioic acids containing the same number of carbon atoms as the substrate alkane. Oxidation took place at both terminal methyl groups-"diterminal oxidation." Appropriate labeling experiments indicate that omega oxidation of fatty acids occurs in this organism and that an oxygenation with O(2) occurs.

Radiolysis of Liquid Acetone : Effect of Dose-rate and Linear Energy Transfer

THE effect of the linear energy transfer parameter of the radiation and of dose-rate on the radiolysis of aqueous solutions can be understood in terms of interactions between spurs along a track and between spurs on adjacent tracks1. In contrast the radiolysis of organic liquids shows: (1) no effect of linear energy transfer on pure alkane liquids2, although a slight effect has been found with solutions containing iodine3, and a pronounced effect with aromatic liquids4 (see also ref. 5); (2) effects at much lower values of dose-rate than in the case of aqueous solutions6.