C8 Cycloalkanes Research Articles

Mechanisms and Kinetics of the Dehydrogenation of C6–C8 Cycloalkanes, Cycloalkenes, and Cyclodienes to Aromatics in H-MFI Zeolite Framework

This work employs periodic density functional theory to elucidate dehydrogenation mechanisms of C6–C8 cycloalkanes, cycloalkenes, and cyclodienes into aromatics during methanol-to-olefin (MTO) chemistries in H-MFI zeolites. Aromatic compounds act as co-catalysts that predominantly form ethylene over propylene products and lead to site-blocking polyaromatic compounds; thus, understanding the formation of aromatic compounds during MTO is critical to understanding its selectivity and catalyst stability. Ring dehydrogenation reactions occur via sequential hydride transfer followed by deprotonation. The rate-controlling hydride transfer reactions were investigated with surface-bound protons (Z–H) and alkyls (Z–CnH2n+1) as hydride-accepting species. Hydride transfers via proton-mediated routes occur with intrinsic free energy barriers (623 K) of 215 kJ mol–1 for C6H12, 164 kJ mol–1 for C6H10, and 141 kJ mol–1 for C6H8, whereas methyl-mediated counterparts occur with intrinsic free barriers of 101, 95, and 81 kJ mol–1, respectively. Transition states for hydride transfer reactions prefer channel intersections within MFI networks, and their activation barriers suggest that methyl-mediated routes are favored over proton-mediated counterparts during MTO. Methyl substituents on hydrocarbon rings generally increase activation barriers for hydride transfers that occur proximal to the −CH3, partly because of steric hindrances between the hydride acceptor and ring-bound −CH3. Rapid double-bond isomerization within cyclohexenes and cyclohexadienes allows hydride transfer reactions to occur away from sterically hindering methyl substituents in methylated and dimethylated C6 ring hydrocarbons. The impact of carbocation substitution in hydride-accepting species was explored by contrasting barriers of methyl (Z–CH3), ethyl (Z–C2H5), 2-propyl (Z–C3H7), and tert-butyl (Z–C4H9) surface-bound alkyls. Intrinsic activation barriers decrease with increasing substitution of the alkyl hydride acceptor, consistent with those alkyls forming more stable carbocations. However, when accounting for steric hindrances associated with the co-adsorption of hydrocarbon rings near surface-bound alkyls, apparent free barriers are larger for more-substituted alkyls. Taking these apparent barriers into account, we predict that methyl-mediated hydride transfer reactions are responsible for the aromatization of hydrocarbon rings during MTO, leading to the CH4 formed during MTO reactions as the aromatic pool is enriched.

Electrosynthesis of Mono- and Disulfides Based on C5–C8 Cycloalkanes, Hydrogen Sulfide, and Isomeric Dibutyl Disulfides

A method of synthesis of organic mono-, di-, and polysulfides based on electrochemical reactions of unsubstituted and alkyl–substituted cycloalkanes C5–C8 with di(n-butyl)disulfide (di(tert-butyl)disulfide) and hydrogen sulfide is developed. Three–component electrosynthesis is carried out in methylene chloride under atmospheric pressure, at the room temperature under the conditions of anodic H2S activation to a cation radical fragmented to a proton and a thiyl radical. The suggested approach with application of oxidative conversion initiation allows obtaining asymmetric mono-, disulfides and symmetric disulfides. The yield of biologically active organic sulfur derivatives depends on the electrosynthesis duration, structure of isomeric dibutyl sulfides, alicycle size and saturation degree.

Synthesis of gasoline and jet fuel range cycloalkanes and aromatics from poly(ethylene terephthalate) waste

Gasoline and jet fuel range C7–C8 cycloalkanes and aromatics were synthesized for the first time in high overall yield (∼95%) from poly(ethylene terephthalate) waste.

Self-assembly generation, structural features, and oxidation catalytic properties of new aqua-soluble copper(ii)-aminoalcohol derivatives

Multidentate aminoalcohols were applied as unexplored building blocks to generate two novel Cu(ii) coordination compounds that act as efficient catalysts for the mild and acid-promoter-free oxidation of C5–C8cycloalkanes.

Mild homogeneous oxidation and hydrocarboxylation of cycloalkanes catalyzed by novel dicopper(II) aminoalcohol-driven cores

N-benzylethanolamine (Hbea) and triisopropanolamine (H3tipa) were applied as unexplored aminoalcohol N,O-building blocks for the self-assembly generation of two novel dicopper(II) compounds, [Cu2(μ-bea)2(Hbea)2](NO3)2 (1) and [Cu2(H3tipa)2(μ-pma)]·7H2O (2) {H4pma=pyromellitic acid}. These were isolated as stable and aqua-soluble microcrystalline products and were fully characterized by IR spectroscopy, ESI–MS(±), and single-crystal X-ray diffraction, the latter revealing distinct Cu2 cores containing the five-coordinate copper(II) centers with the {CuN2O3} or {CuNO4} environments. Compounds 1 and 2 were used as homogeneous catalysts for the mild oxidation of C5–C8 cycloalkanes to give the corresponding cyclic alcohols and ketones in up to 23% overall yields based on cycloalkane. The reactions proceed in aqueous acetonitrile medium at 50°C using H2O2 as an oxidant. The effects of different reaction conditions were studied, including the type and loading of catalyst, amount and kind of acid promoter, and water concentration. Despite the fact that different acids (HNO3, H2SO4, HCl, or CF3COOH) promote the oxidation of alkanes, the reaction is exceptionally fast in the presence of a catalytic amount of HCl, resulting in the TOF values of up to 430h−1. Although water typically strongly inhibits alkane oxidations due to the reduction of H2O2 concentration and lowering of the alkane solubility, in the systems comprising 1 and 2 we observed a significant growth (up to 5-fold) of an initial reaction rate in the cyclohexane oxidation on increasing the amount of H2O in the reaction mixture. The bond-, regio- and stereo-selectivity parameters were investigated in oxidation of different linear, branched, and cyclic alkane substrates. Both compounds 1 and 2 also catalyze the hydrocarboxylation of C5–C8 cycloalkanes, by CO, K2S2O8, and H2O in a water/acetonitrile medium at 60°C, to give the corresponding cycloalkanecarboxylic acids in up to 38% yields based on cycloalkanes.

Aquasoluble iron(III)-arylhydrazone-β-diketone complexes: Structure and catalytic activity for the peroxidative oxidation of C5–C8 cycloalkanes

The aquasoluble FeIII complexes [Fe(H2O)3(L1)]∙4H2O (3) and [Fe(H2O)3(L2)]∙3H2O (4), bearing the basic forms of 5-chloro-3-(2-(4,4-dimethyl-2,6-dioxocyclohexylidene)hydrazinyl)-2-hydroxy-benzenesulfonic acid (H3L1, 1) and 3-(2-(2,4-dioxopentan-3-ylidene)hydrazinyl)-2-hydroxy-5-nitrobenzenesulfonic acid (H3L2, 2), were synthesized and fully characterized including by X-ray crystal structural analysis. In the channels of the water-soluble 3D networks of 3 and 4, the uncoordinated water molecules are held by oxygen atoms of the carbonyl and sulfonyl groups, and by the water ligands. The FeIII coordination environment resembles that in the active sites of some mononuclear non-heme iron-containing enzymes. The complexes show a high catalytic activity for the peroxidative oxidation (with aqueous H2O2) of C5–C8 cycloalkanes to the corresponding alcohols and ketones under mild conditions. The effects of various factors, such as amounts of oxidant, catalyst and HNO3 additive, were investigated allowing to reach overall yields of ca. 25% and turnover numbers (TONs) up to 290. The catalytic reactions proceed via both oxygen- and carbon-radicals as shown by radical trap experiments.

Carbonylation of C7C8 cycloalkanes leading to individual tertiary carbonyl-containing compounds

Carbonylation of cycloheptane, methylcyclohexane, cyclooctane and ethylcyclohexane by CO in the presence of CBr4·2AlBr3 at −40°C and 1 atm was performed with good yields and selectivities. Individual esters of tertiary carboxylic acids of the cyclohexane series were the products of these cycloalkane carbonylations.

Isomerization of saturated hydrocarbons Communication 3. Isomerizations of cycloalkanes

1. The isomerization of C6–C9 cycloalkanes was carried out in presence of a multifunctional catalyst and of hydrogen under pressure. 2. The compositions of the isomerization products from C7 and C8 cycloalkanes were in good agreement with the calculated thermodynamic values. 3. A mechanism was proposed for the isomerization of cycloalkanes. It is considered that, as in the case of the isomerization of paraffins, the first stage of the reaction is the formation of unsaturated hydrocarbons. 4. The effects of pressure and temperature on the course of the reactions of cycloalkanes in presence of multifunctional catalysts were demonstrated.