Bonds In Saturated Hydrocarbons Research Articles

Direct acylation and alkynylation of hydrocarbons via synergistic decatungstate photo-HAT/nickel catalysis.

Herein, we describe a protocol for the direct and selective acylation and alkynylation of the C(sp3)-H bonds of saturated hydrocarbons by synergistic decatungstate photo-HAT and nickel catalysis. This method, using cheap and easy-to-synthesize TBADT as a HAT photocatalyst, exhibits excellent site selectivity. A wide variety of high-value ketones, amides, esters, and diverse alkynes can be efficiently constructed from abundant hydrocarbon feedstocks.

Ce1−xCrxO2−δ Nanocrystals as Efficient Catalysts for the Selective Oxidation of Cyclohexane to KA Oil at Low Temperature under Ambient Pressure

AbstractThe selective oxidation of C−H bonds in saturated hydrocarbons at low temperature with noble‐metal‐free heterogeneous catalysts is a profound challenge for the catalysis community. Here we report the facile synthesis of Ce1−xCrxO2−δ (x=0, 0.1, 0.2, 0.3, and 0.4) nanocrystals through a low‐temperature hydrothermal method. The catalytic activity of the as‐prepared catalysts was evaluated in the selective oxidation of cyclohexane to cyclohexanone/cyclohexanol using H2O2 as an oxidant at room temperature and 45 °C. The activity results were correlated with their phase structure, composition, surface areas, and surface element states with the help of X‐ray diffraction, N2 adsorption, transmission electron microscopy, X‐ray photoelectron spectroscopy, and UV/Vis spectroscopy. It was found that these Ce0.7Cr0.3O2−δ nanocrystals are highly active for the selective oxidation of cyclohexane to cyclohexanone/cyclohexanol using H2O2 as an oxidant at low temperature. In the presence of H2O2 at 45 °C for 5 h using Ce0.7Cr0.3O2−δ as a catalyst, the conversion of cyclohexane reaches 50.3 % and the total selectivity of cyclohexanol/cyclohexanone is 94.4 % with relative good reversibility for at least four cycles. Mechanistic investigation results show that the high activity can be attributed to the high Cr6+ content in the Ce1−xCrxO2−δ solid solutions and the formation of highly oxidative intermediates with H2O2.

Singlet oxygen-mediated selective C\u2013H bond hydroperoxidation of ethereal hydrocarbons

Singlet O2 is a key reactive oxygen species responsible for photodynamic therapy and is generally recognized to be chemically reactive towards C=C double bonds. Herein, we report the hydroperoxidation/lactonization of α-ethereal C–H bonds by singlet O2 (1Δg) under exceptionally mild conditions, i.e., room temperature and ambient pressure, with modest to high yields (38~90%) and excellent site selectivity. Singlet O2 has been known for > 90 years, but was never reported to be able to react with weakly activated C–H bonds in saturated hydrocarbons. Theoretical calculations indicate that singlet O2 directly inserts into the α-ethereal C–H bond in one step with conservation of steric configuration in products. The current discovery of chemical reaction of singlet oxygen with weakly activated solvent C–H bonds, in addition to physical relaxation pathway, provides an important clue to a 35-year-old unresolved mystery regarding huge variations of solvent dependent lifetime of singlet O2.

Nitrogen incorporation in saturated aliphatic C6-C8 hydrocarbons and ethanol in low-pressure nitrogen plasma generated by a hollow cathode discharge ion source.

Ion/molecule reactions of saturated hydrocarbons (n-hexane, cyclohexane, n-heptane, n-octane and isooctane) in 28-Torr N2 plasma generated by a hollow cathode discharge ion source were investigated using an Orbitrap mass spectrometer. It was found that the ions with [M+14](+) were observed as the major ions (M: sample molecule). The exact mass analysis revealed that the ions are nitrogenated molecules, [M+N](+) formed by the reactions of N3 (+) with M. The reaction, N3 (+) + M → [M+N](+) + N2 , were examined by the density functional theory calculations. It was found that N3 (+) abstracts the H atom from hydrocarbon molecules leading to the formation of protonated imines in the forms of R'R″CNH2 (+) (i.e. C-H bond nitrogenation). This result is in accord with the fact that elimination of NH3 is the major channel for MS/MS of [M+N](+) . That is, nitrogen is incorporated in the C-H bonds of saturated hydrocarbons. No nitrogenation was observed for benzene and acetone, which was ascribed to the formation of stable charge-transfer complexes benzene⋅⋅⋅⋅N3 (+) and acetone⋅⋅⋅⋅N3 (+) revealed by density functional theory calculations. Copyright © 2016 John Wiley & Sons, Ltd.

Starch-coated maghemite nanoparticles functionalized by a novel cobalt Schiff base complex catalyzes selective aerobic benzylic C–H oxidation

The CoL2@SMNP nanocatalyst catalyzed heterogeneous aerobic oxidation of benzylic C–H bonds of saturated hydrocarbons and alcohols to the related carbonyl compounds.

Quantum‐chemical derivation of electro‐optical parameters for alkanes

AbstractAn approach for deriving the bond electro‐optical parameters (EOPs) of the bond polarizability model (BPM) from quantum‐chemical calculations is proposed. The approach was used to obtain the equilibrium and valence EOPs for the CH and CC bonds in saturated hydrocarbons from the results of the DFT calculations of small chain alkanes. The parameters derived are in the range of those found in the literature. The results of the study show that for this class of molecules the polarizability tensor can be constructed as the sum of the individual bond polarizability tensors thus indicating the validity of the BPM. The use of the parameters in the calculation of the Raman activity of the normal modes of 2‐methylbutane shows a good correlation between the data obtained in the DFT calculations and those with the BPM. Factors influencing the reliability and transferability of the parameters are discussed. Copyright © 2006 John Wiley & Sons, Ltd.

C—H Bond Activation of Hydrocarbons by an Imidozirconocene Complex.

AbstractFor Abstract see ChemInform Abstract in Full Text.

C-H bond activation of hydrocarbons by an imidozirconocene complex.

Monomeric imidozirconocene complexes of the type Cp2(L)Zr=NCMe3 (Cp = cyclopentadienyl, L = Lewis base) have been shown to activate the carbon-hydrogen bonds of benzene, but not the C-H bonds of saturated hydrocarbons. To our knowledge, this singularly important class of C-H activation reactions has heretofore not been observed in imidometallocene systems. The M=NR bond formed on heating the racemic ethylenebis(tetrahydro)indenyl methyl tert-butyl amide complex, however, cleanly and quantitatively activates a wide range of n-alkane, alkene, and arene C-H bonds. Mechanistic experiments support the proposal of intramolecular elimination of methane followed by a concerted addition of the hydrocarbon C-H bond. Products formed by activation of sp2 C-H bonds are generally more thermodynamically stable than those formed by activation of sp3 C-H bonds, and those resulting from reaction at primary C-H bonds are preferred over secondary sp3 C-H activation products. There is also evidence that thermodynamic selectivity among C-H bonds is sterically rather than electronically controlled.

CH bond activation in hydrocarbon oxidation on solid catalysts

The activation of CH bonds in saturated hydrocarbons is the crucial step in several different types of oxidation reaction on a variety of catalysts and could occur through homolytic or heterolytic mechanisms. From the available evidence it appears that the heterolytic mechanism, with the extraction of a proton, is the most likely process on oxide catalysts and this may also apply to metallic catalysts under typical (oxidising) reaction conditions. However, the state of oxidation of a metallic surface under reaction conditions is complex and the degree of oxidation will depend on the metal, the temperature, the oxygen partial pressure, the metal particle size, the support and the choice of hydrocarbon. The importance of coadsorbates in facilitating the dissociative adsorption of saturated hydrocarbons seems to be well established and could explain the unusual enhancement of activity observed for the oxidation of some saturated hydrocarbons when inorganic gases, such as SO 2, are added to the reaction mixture. The inhibition by products of the oxidation reaction (CO 2 and H 2O) can be quite severe, but H 2O has by far the greatest effect. This is interpreted in terms of an equilibrium involving the formation of surface hydroxide ions which are considered to be inactive for activation of CH bonds. As a consequence, it is possible, especially at low temperatures, that the rate determining step in CH bond activation could be the regeneration of the active sites, through desorption of H 2O, rather than CH bond activation as is commonly assumed. The activation of CH bonds by NO 2 is addressed in the context of selective reduction of NO x by hydrocarbons on various types of oxide catalyst and possible similarities with the promotion of the CH bond activation process by SO 2 are discussed.

Reactions of O(3P) with secondary C-H bonds of saturated hydrocarbons in nonequilibrium plasmas

The functionalization of three n-alkanes by means of a low-pressure oxygen plasma has been achieved. The plasma was generated by applying a low-Frequency high-voltage glow discharge through an oxygen flow. bit, activated species so produced have been allowed to interact with the surface of each one of the liquid compounds at a time. The hydrocarbon has been cooled down to a temperature low enough so that its vapor pressure is about 20–100 times lower than the O2 pressure, this heing of the order of 0.1–0.4 torr. Under these conditions the main products of the reactions have been the alcohols, except for the primary ones, and the corresponding ketones. A remarkable result we have arrived at is that for the first time secondary carbon hydrogen bonds have shown to possess different reactivities withO(3P). The latter has proved to he the most relevant active species of the plasma. A discussion is given to explain this novel result under two theoretical bases recently published: (i) a conformational analysis of the hydrocarbons according to molecular mechanics calculations, and (ii) an analysis of properties of the molecules based on calculations with charge distributions derived from 6–31G* wave functions.

Oxidation of saturated hydrocarbons by hydrogen peroxide in pyridine solution catalysed by copper and iron perchlorates

Oxidation of secondary C–H bonds of saturated hydrocarbons (C6H12, 2-methylbutane) by H2O2 in the presence of copper or iron perchlorates in pyridine solution yields the ketone and alcohol with alkyl radicals not being intermediates.

Activation of C–H bonds in saturated hydrocarbons. H–D exchange between methane and benzene catalysed by a soluble iridium polyhydride system

The soluble iridium pentahydride (Pri3P)2IrH5(activated by But-CHCH2) catalyses H–D exchange between C6D6 and CH4 under mild conditions.

Activation of C-H bonds in saturated hydrocarbons. The selective, catalytic functionalisation of methyl groups by means of a soluble iridium polyhydride system

The selective, catalytic conversion of methylcyclohexane into methylenecyclohexane at 100°C, and of n-hexene into 1-hexene at 45°C, has been effected using bis(triisapropylphosphine)iridium pentahydride and an olefin (neohexene) as a hydrogen acceptor; with this system, approximate relative reactivities of C-H bonds in saturated hydrocarbons are: sec-alkyl-H, 1; iso-alkyl-H, 8; n-alkyl-H, > 60.

Activation of C-H bonds in saturated hydrocarbons. The formation of bis(triphenylphospine)(η-alkadiene)rhenium trihydrides from n-Alkanes, and their selective conversion into the corresponding 1-alkenes

n-Alkanes (C 6C 8) react at 70°C with bis(triphenylphosphine)-rhenium heptahydride and 3,3-dimethylbutene to afford equilibrium mixtures of the corresponding bis(triphenylphosphine) (η-conjugated-diene)-rhenium trihydrides; treatment of these mixtures with trimethylphosphite at 60°C converts them, in >95% yield and with >98% selectivity, into the corresponding 1-alkenes.

Activation of C-H bonds in saturated hydrocarbons. The catalytic functionalisation of cycloöctane by means of some soluble iridium and ruthenium polyhydride systems

Homogeneous catalytic dehydrogenation of cycloöctane into cycloöctene has been effected by means of a variety of iridium and ruthenium polyhydrides, at 150°C, in the presence of an olefin as the hydrogen acceptor; best results (45–70 catalytic turnovers) have been achieved with (iPr 3P) 2IrH 5, [( p -F-C 6H 4) 3P] 2IrH 5 and [( p -F-C 6H 4) 3P] 3RuH 4.

Activation of carbon-hydrogen bonds in saturated hydrocarbons on photolysis of (.eta.5-C5Me5)(PMe3)IrH2. Relative rates of reaction of the intermediate with different types of carbon-hydrogen bonds and functionalization of the metal-bound alkyl groups

Irradiation of (eta/sup 5/-pentamethylcyclopenta-dienyl)(trimethyl phosphine) dehydroiridium (eta/sup 5/-C/sub 5/Me/sub 5/)(PMe/sub 3/)IrH/sub 2/ in saturated hydrocarbons using a 500 W Oriel focused-beam mercury lamp leads to extrusion of hydrogen and production of the hydrido alkyl iridium complexes (----HRIr). Competition experiments were used to measure relative rates at which the intermediate formed on hydrogen loss reacts with different types of C-H bonds. Relative to cyclohexane (1), these rates are: benzene (4), cyclopropane (2.65), cyclopentane (1.6), neopentane (1.14), cyclodecane (.23), and cyclooctane (.09). Reductive elimination of hydrocarbon occurs at elevated temperature, regenerating the intermediate, which may then react with another hydrocarbon acting as solvent. The factors which presumed to influence the rates of reaction of transition-metal complexes with saturated C-H bonds are discussed.

Kinetics and selectivity of oxidation of saturated hydrocarbons in sulphuric acid media containing anthracene and cyclohexane oligomers

o1.Solutions of anthracene and cyclohexene in 93% sulphuric acid are sources of fairly stable species, which oxidize tertiary and secondary C−H bonds of saturated hydrocarbons at 90°C. A study was made of kinetics and selectivity of the first stage of oxidation of paraffins in these systems.2.The selectivity, isotope effect and kinetics of oxidation of the anthracene-H2SO4 system and oligomers of cyclohexene-H2SO4 are similar and approximate to the oxidizing agent-sulphuric acid systems, previously examined.3.Based on this analogy a mechanism was proposed for the oxidative homolysis of C-H bonds for the first stage of oxidation of saturated hydrocarbons in anthracene-sulphuric acid and cyclohexene-sulphuric acid systems. Solutions of anthracene and cyclohexene in 93% sulphuric acid are sources of fairly stable species, which oxidize tertiary and secondary C−H bonds of saturated hydrocarbons at 90°C. A study was made of kinetics and selectivity of the first stage of oxidation of paraffins in these systems. The selectivity, isotope effect and kinetics of oxidation of the anthracene-H2SO4 system and oligomers of cyclohexene-H2SO4 are similar and approximate to the oxidizing agent-sulphuric acid systems, previously examined. Based on this analogy a mechanism was proposed for the oxidative homolysis of C-H bonds for the first stage of oxidation of saturated hydrocarbons in anthracene-sulphuric acid and cyclohexene-sulphuric acid systems.

Hydrogenolysis of hydrocarbons over supported catalysts derived from metal carbonyl clusters

A comparison between the activities of silica-supported ruthenium, rhodium and platinum catalysts prepared from metal cluster compounds and their conventional analogues towards the activation of saturated hydrocarbons has been made. Ruthenium cluster-derived catalysts display greatly enhanced activity for the complete hydrogenolysis of straight chain aliphatic hydrocarbons to methane and provide a temperature advantage of 150°C relative to conventionally prepared ruthenium catalysts where only moderate hydrocarbon conversions are noted. The increased activity superficially correlates with the smaller metal crystallite sizes (15–20 A) reproducibly obtainable using metal cluster compounds as catalyst precursors. The highly specific activity for the hydrogenolysis of C-C bonds in saturated hydrocarbons has been applied to the selective cleavage of the alkyl group in ethylbenzene, giving toluene and methane. Conversions of up to 30% ethylbenzene have been observed at 225°C and 1 atm using a Ru3(CO)12/SiO2-based catalyst. The xylenes, particularly o-xylene, are much less susceptible to hydrogenolysis and, at 225°C, relative hydrocarbon destruction rates of 30 : 1 and 7 : 1 have been observed using mixed feeds of ethylbenzene/o-xylene and ethylbenzene/p-xylene, respectively. Such a catalyst system can, in principle, therefore provide a means of separating ethylbenzene from its mixtures with xylenes.

Electron charges of bonds and spectroscopic characteristics of organic compounds

On the basis of the fact that the electronic shielding of the protons should be related to the value of the electronic charge at the corresponding C-H bond, the chemical shifts in the PMR spectra were compared with the electronic charges of the σ-bonds of CH in alkanes and cycloalkanes. In this case, the variation of the chemical shifts in structurally different bonds of saturated hydrocarbons and the unusual chemical shift of the protons of cyclopropane were explained.

Insertion reactions of trifluoromethylcarbene

Trifluoromethylcarbene, generated photolytically from 2,2,2-trifluorodiazoethane, reacts with the C–H bonds of saturated hydrocarbons in the liquid phase to give high yields of the corresponding insertion products. The primary and secondary C–H bonds in n-butane undergo insertion at essentially the same rate, but the tertiary C–H bond in isobutane is some 30% more reactive than the primary C–H. In the vapour phase very low yields of insertion product result, and 1,1,1-trifluoroethane and trifluoroethylene are also produced. Liquid-phase photolysis in trimethylsilane gives more rapid insertion into Si–H than into C–H bonds. The mechanistic implications of the results are discussed.