Metal-catalysed hydrocarbon oxidations

This brief review describes recent findings by the author and his co-workers in the field of catalytic systems for the oxidation of saturated and aromatic hydrocarbons with molecular oxygen (from air), hydrogen peroxide and some other compounds. These systems are based on metal complexes as catalysts and often include obligatory co-catalysts, such as amino acids, nitrogen-containing bases or weak carboxylic acids. Some of these reactions can be considered as biomimetic models of corresponding oxidation processes occurring in living cells. In some cases, aerobic oxidations considered here occur in some cases under the action of light. Some features of these reactions and their mechanisms are presented and discussed. To cite this article: G.B. Shul'pin, C. R. Chimie 6 (2003).     

Water/hydrocarbon interfaces: effect of hydrocarbon branching on single-molecule relaxation

Water/hydrocarbon interfaces are studied using molecular dynamics simulations in order to understand the effect of hydrocarbon branching on the dynamics of the system at and away from the interface. A recently proposed procedure for studying the intrinsic structure of the interface in such systems is utilized, and dynamics are probed in the usual laboratory frame as well as the intrinsic frame. The use of these two frames of reference leads to insight into the effect of capillary waves at the interface on dynamics. The systems were partitioned into zones with a width of 5 A, and a number of quantities of dynamical relevance, namely, the residence times, mean squared displacements, the velocity auto correlation functions, and orientational time correlations for molecules of both phases, were calculated in the laboratory and intrinsic frames at and away from the interface. For the aqueous phase, translational motion is found to be (a) diffusive at long times and not anomalous as in proteins or micelles, (b) faster at the interface than in the bulk, and (c) faster upon reduction of the effect of capillary waves. The rotational motion of water is (a) more anisotropic at the interface than in the bulk and (b) dependent on the orientation of the covalent O-H bond with respect to the plane of the interface. The effect of hydrocarbon branching on aqueous dynamics was found to be small, a result similar to the effect on the interfacial water structure. The hydrocarbon phase shows a larger variation for all dynamical probes, a trend consistent with their interfacial structure.     

Chemiluminescence of hydrocarbon polymers

The thermal oxidation of some hydrecarbon polymers differing by their degree of branching was studied simultaneously by chemiluminescence and infrared spectrophotometry. In the case of isotactic polypropylene, measurements were made at various temperatures ranging from 140 to 180°C. The other polymers—ethylene–propylene copolymer, low and high density polyethylene—were studied only at 160°C. In all cases, the induction times of chemiluminescence coincide with those of carbonyl growth. The previously proposed mechanisms of light emission are not consistent with the kinetic data or with the structure effects on luminescence, which seems directly related with the presence of tertiary hydrogens. A hypothetical mechanism based on the β scission of tertiary alkoxyls is proposed.     

Liquid-liquid equilibria for ternary acetonitrile-ethanol-saturated hydrocarbon and acetonitrile-1-propanol-saturated hydrocarbon mixtures

Isothermal vapour-liquid equilibrium data for acetonitrile-1-propanol at 45° C were measured by use of a recirculating still. The liquid-liquid equilibria of (acetonitrile-etha-nol)-(n-hexane or n-heptane or n-octane) and those of (acetonitrile-1-propanol)-(cyclohexane or n-hexane or n-heptane) were obtained from measurements of tie-lines. The experimental results were compared with those calculated from the UNIQUAC associated-solution model.     

Macrolactonization via hydrocarbon oxidation

A novel Pd/sulfoxide-catalyzed macrolactonization reaction of linear omega-alkenoic acids is reported that proceeds via serial ligand-catalyzed allylic C-H oxidation. The scope of this macrolactonization appears to be very broad. Aryl, alkyl, and (Z)-alpha,beta-unsaturated acids are all competent nucleophiles for this reaction, with the latter undergoing macrolactonization with no olefin isomerization. High functional group compatibility is observed that includes biologically and medicinally relevant functionality such as ortho-substituted salicylate esters, bis(indoyl)maleimides, and peptides. Evidence is provided to support the hypothesis that macrolactonization proceeds via inner-sphere functionalization from a templated pi-allylPd carboxylate intermediate.     

Hydrophobic encapsulation of hydrocarbon gases

[reaction: see text] Encapsulation data for hydrophobic hydrocarbon gases within a water-soluble hemicarcerand in aqueous solution are reported. It is concluded that hydrophobic interactions serve as the primary driving force for the encapsulation, which can be used for the design of gas-separating polymers with intrinsic inner cavities.     

Head-group-influenced mixed micellization of sodium deoxycholate with conventional hydrocarbon surfactants of identical hydrocarbon tails

Conductivity, viscosity, turbidity, and NMR measurements were performed over most of the mole fraction range for sodium deoxycholate (SDC) with hexadecyltrimethylammonium bromide (HTAB), hexadecylpyridinium bromide (HPyBr), and hexadecylpyridinium chloride (HPyCl). All studies demonstrate that the mixed-micelle formation is more favorable in SDC plus HTAB rather than SDC plus HPyBr or SDC plus HPyCl mixtures. The results showed that the bulky pyridinium head groups of HPyBr or HPyCl create steric incompatibility with rigid SDC monomers in the mixed state.     

Long term nonmethane hydrocarbon and halogenated hydrocarbon measurements at three West German sampling sites

Summary Results of a long time series of nonmethane hydrocarbons and halogenated hydrocarbons measurements at three differently polluted sites in the FRG are presented. The question discussed is to what extent the observed seasonal cycles can be explained by variations in sources and sinks.     

Pyrolytic hydrocarbon growth from cyclopentadiene

Aromatic hydrocarbon growth from cyclopentadiene (CPD) was studied using a laminar flow reactor operating in the temperature range 550-950 °C without oxygen. Benzene, indene, and naphthalene were the major products, which is in agreement with the previous computational studies on the reaction pathways from CPD. A crossover of indene and naphthalene yields around 775 °C was also observed, which further supports the results of the computational studies. Although the specific intermediates in the proposed pathways from CPD were not detected, the high selectivity of products and the observation of other methylindene and dihydronaphthalene intermediates suggest that the recombination of two CPDs via radical-molecule and/or radical-radical pathways to form indene and naphthalene is the dominant formation pathway. In addition to the products from the CPD-CPD reactions, the products from the reactions of CPD with indene, naphthalene, and acenaphthylene were also observed, which demonstrate the importance of CPD in carbon growth.     

Attractive-dominant and repulsive-dominant hydrocarbon reactions

The difference between the expectation values of the total electronic kinetic energy operator (ΔE_K), and the operators accounting for the Coulombic interactions between the electrons and nuclei (ΔV_en), between all pairs of electrons (ΔV_ee), and between all pairs of nuclei (ΔV_nn) for the product and reactant species in a wide variety of hydrocarbon reactions are calculated using single determinant basis set data reported in the literature. Following Allen, their contributions to ΔE_T, the difference between the corresponding total molecular energies and thus the reaction heat, are grouped together as a repulsion energy term, ΔE_rep = ΔE_K + ΔV_ee + ΔV_nn, and an attraction energy term ΔE_attr = ΔV_en. For all but 2 of the 71 individual reactions considered in this paper, the experimental reaction heat at 0°K corrected for zero-point energy contributions, (ΔH)_zpe, is the result of near compensation between far larger ΔE_rep and ΔE_attr terms, in sharp contrast to the much smaller ΔE_rep and ΔE_attr terms which are characteristic of many molecular rotation processes. By matching the sign of (ΔH)_zpe with that of ΔE_rep or ΔE_attr, as the case may be, the reactions are classified as attractive-dominant or repulsive-dominant (46 in the former class and 23 in the latter), a property which is independent of the direction in which the reaction is written. The sign and magnitude of ΔV_ee, ΔV_nn, and ΔV_en and reaction category are discussed in relation to the various kinds of structural change involved in going from reactants to products. For the vast majority of reactions, the numerical relationship ΔV_ee ≈ ΔV_nn has been found to hold to within a few percent.     

Order parameters in hydrocarbon chains

Order in lipid bilayers is often described by order parameters S_CD, S_HH and S_chain which are rather directly obtained from deuterium NMR, proton NMR and ESR spectroscopy respectively. A relation is derived that makes one of these parameters redundant from purely geometrical reasons. Further, the effect of conformational disorder upon these order parameters is investigated theoretically using a trans—gauche model. Corrections from the finite of the trans—gauche wells and from non-fixed valence angles are shown to be negligible.     

Unexpected phenyl group rearrangement of Thiele’s hydrocarbon derivative under polycyclic aromatic hydrocarbon synthesis

An unexpected ketone was obtained in the synthesis of tetrabenzo[a,d,j,m]coronene having tert-butyl groups from Thiele’s hydrocarbon derivative. The structure of the product was confirmed by not only spectroscopic but also diffraction studies. This product was formed by the rearrangement reaction of one phenyl group and this reaction could be analogous to the pinacol-pinacolone rearrangement.     

Identification of gasolines with hydrocarbon markers

A procedure for the identification of gasoline samples containing hidden chemical markers based on the results of fuel analysis by gas-liquid chromatography with sample preevaporation is proposed. Tetracosane (C₂₄H₅₀) in a concentration of 2.0 × 10⁻³ wt % was used as a marker. The procedure allowed us to detect the presence of the marker in gasoline samples subjected to uncontrollable evaporation in storage or on fire.     

Modified calculations of hydrocarbon thermodynamic properties

A test set of 65 hydrocarbons was examined to elucidate theoretically their thermodynamic properties by performing the density-functional theory (DFT) and ab initio calculations. All the calculated data were modified using a three-parameter calibration equation and the least-squares approach, to determine accurately enthalpies of formation (DeltaH(f)), entropies (S), and heat capacities (C(p)). Calculation results demonstrated that the atomization energies of all compounds exhibited an average absolute relative error ranging between 0.11- 0.13%, and an DeltaH(f) of formation with a mean absolute absolute error (M.|A.E.|) ranging from only 5.7-6.8 kJ/mol (1.3-1.6 kcal/mol) (i.e., those results correlated with those of Dr. Herndon's 1.1 kcal/mol). Additionally, the entropy ranged from 3.5-4.2 J/mol K (0.8-1.0 cal/mol K) M.|A.E.|; a heat capacity between 2.3-2.9 J/mol K (0.5-0.7 cal/mol K) M.|A.E.| was obtained as well.     

The recognition of polyrex hydrocarbon radicals

Rapid topological tests for discerning radical benzenoids from nonradical ones are reviewed. These tests include HückelB matrix, Gordon-Davison, Hall-Tutte, path, and excised internal structure inspection methods. The potential magnetic properties of type 2 diradicals are pointed out.Received by the publisher 5 July 1988