Pentane

Abstract: For petrochemical applications knowledge of the critical properties of the n‐alkanes is of interest even at temperatures where these molecules are thermally unstable. Computer simulations can determine the vapor–liquid coexistence curve of a large number of n‐alkanes ranging from pentane (C5) through octatetracontane (C48). We have compared the predicted phase diagrams of various models with experimental data. Models which give nearly identical properties of liquid alkanes at standard conditions may have critical temperatures that differ by more than 100 K. A new n‐alkane model has been developed by us that gives a good description of the phase behavior over a large temperature range. For modeling vapor–liquid coexistence a relatively simple united atom model was sufficient to obtain a very good agreement with experimental data; thus it appears not necessary to take the hydrogen atoms explicitly into account. The model developed in this work has been used to determine the critical properties of the long‐chain alkanes for which experiments turned out to be difficult and contradictory. We found that for the long‐chain alkanes (C8–C48) the critical density decreases as a function of the carbon number. These simulations were made possible by the use of a recently developed simulation technique, which is a combination of the Gibbs‐ensemble technique and the configurational‐bias Monte Carlo method. Compared with the conventional Gibbs‐ensemble technique, this method is several orders of magnitude more efficient for pentane and up to a hundred orders of magnitude for octatetracontane. This recent development makes it possible to perform routinely phase equilibrium calculations of complex molecules.

Abstract: Publisher Summary The skeletal rearrangements of hydrocarbons represent an important class of reactions catalyzed by metal surfaces, that have few counterparts in homogeneous catalysis. The first examples of skeletal rearrangements on metals were reported by the Soviet school of catalysis. A major step in hydrocarbon chemistry is the finding that platinum, unlike palladium and nickel, selectively catalyzes the hydrogenolysis of cyclopentane hydrocarbons. At about 300°C, on the classical Zelinskii platinum-charcoal catalyst, cyclopentane yields n -pentane as sole reaction product, while palladized charcoal is completely inactive and nickel-alumina produces all the possible acyclic hydrocarbons, from methane to pentane. The predominant precursor species in skeletal rearrangements are metallocyclobutanes and metallocarbenes, which can be further dehydrogenated to metallocarbynes, dicarbenes, or carbene-olefin complexes, and react like the analogous species in coordination chemistry. Metallocyclobutane dismutation and the reverse reaction, carbene-olefin addition, are the two major steps in olefin metathesis, and dicarbene recombination also has an analogue in organometallic reactions.

Abstract: A solid superacid catalyst with an acid strength of H0⩽–14.52 was obtained by impregnating Zr(OH)4 or amorphous ZrO2 with aqueous ammonium metatungstate followed by calcining in air at 800–850 °C (13 wt.% W); this catalyst was active for the isomerisations butane to isobutane at 50 °C, and pentane to isopentane at 30 °C.

Abstract: The transitional properties of three methylene-linked liquid crystal dimers are reported, namely, 1,5-bis(4-cyanoanilinebenzylidene-4′-yl)pentane (CN-5-CN), 1,5-bis(4-methoxyanilinebenzylidene-4′-yl)pentane (1O-5-O1), and 1,5-bis(4-ethoxyanilinebenzylidene-4′-yl)pentane (2O-5-O2). Each dimer exhibits two monotropic mesophases. The higher temperature mesophase is a normal nematic phase while the lower temperature phase is assigned as a twist-bend nematic phase. The assignment of the twist-bend nematic phase was based on the strong similarities in the optical textures observed to those reported recently for a structurally similar dimer. The complete miscibility of the mesophases exhibited by CN-5-CN and 1O-5-O1 has been established. The analogous hexamethylene-linked dimers exhibit only the normal nematic phase as do the corresponding ether-linked dimers. A review of the literature reveals another five methylene-linked odd-membered dimers that exhibit a nematic–nematic transition and, in each, the lower tem...