Simple Aliphatic Hydrocarbons Research Articles

Wood solubilization and depolymerization by supercritical methanol. Part 2: Analysis of methanol soluble compounds

Abstract Methanol treatment of ponderosa pine wood was performed in a batch reactor at temperatures close to and above the critical points of methanol (238°C and 8.3 MPa) to induce wood degradation into its monomeric and oligomeric components. The resultant methanol soluble and insoluble residues and gases were collected. The volatile components of the liquid and gaseous fractions were analyzed by GC-MS. The gases consisted mostly of carbon dioxide and simple aliphatic hydrocarbons. The non-volatile methanol soluble components were analyzed by HPLC and size exclusion chromatography. The mixture was found to be promising as a source of raw materials for fuel and chemical manufacturing. It consists of a blend of carbohydrate and lignin derived compounds and extractives in varying concentrations depending on the reaction conditions. More extractive compounds were found in the subcritical runs. In mild supercritical conditions the yield of lignin monomers and oligomers was increased, while under severe supercritical treatment, lignin and carbohydrate derived compounds were prevalent.

Ion–molecule reactions of ArN+2 with simple aliphatic hydrocarbons at thermal energy

The product ion distributions and rate constants are determined for ion–molecule reactions of ArN+2 with C2Hn (n=2,4,6) and C3Hn (n=6,8) by using a thermal ion–beam apparatus. Although charge-transfer channels leading to parent ions and/or fragment ions are found, no displacement reaction leading to ArCmH+n and N2CmH+n is detected. A comparison of the product ion distributions with breakdown patterns of the parent ions suggests that fragment ions, formed through cleavage of C–H and/or C–C bonds, are produced via near-resonant ionic states in the 13.1–13.4 eV range. The branching ratios of parent ions for C2H4 (68%) and C3H6 (20%) are larger than those for C2H6 (5%) and C3H8 (5%). The large branching ratios of the parent ions for the unsaturated hydrocarbons are explained as due to a strong interaction of a vacant orbital of ArN+2 with the highest occupied πC=C orbital of the unsaturated hydrocarbons which induces nonresonant charge transfer. The total rate constant for C2H2 is 6.8×10−10 cm3 s−1, while those for C2Hn (n=4,6) and C3Hn (n=6,8) are in the range (8.5–9.8)×10−10 cm3 s−1. The former and the latter values correspond to 69% and 77%–90% of the calculated values from Langevin or average dipole orientation (ADO) theory. The smaller kobs/kcalc ratio for C2H2 is attributed to the lack of near-resonant ionic states with favorable Franck–Condon factors for ionization.

Ion/molecule reactions of CO 2+ with simple aliphatic hydrocarbons at thermal energy

A thermal ion-beam apparatus has been used for studying ion/molecule reactions of CO 2 + with CH 4, C 2H n ( n = 2, 4, 6), and C 3H n ( n = 6, 8). The product ion distributions and rate constants are determined. Both hydrogen-atom transfer and charge transfer are observed as product channels for CH 4 with branching ratios of CO 2H + (72 ± 1%) and CH 4 + (28 ± 1%), whereas only charge-transfer channels leading to parent ion and/or fragment ions are found for C 2H n ( n = 2, 4, 6) and C 3H n ( n = 6, 8). A comparison of the product ion distributions with breakdown patterns of the parent ions leads us to conclude that charge-transfer products are predominantly formed through near-resonant (pre)dissociative states, which are 0.2–0.5 eV below the resonant states. The formation of a small amount of parent ion due to non-resonant charge transfer is found for unsaturated hydrocarbons (C 2H 4 and C 3H 6). This is explained as being due to a strong interaction between a vacant orbital of CO 2 + and the highest occupied π C=C orbital of the reagent molecule. The total rate constant for C 2H 2 is 0.56 × 10 −9 cm 3 s −1, while those for CH 4, C 2H n ( n = 4, 6), and C 3H n ( n = 6, 8) are in the range (0.78–0.99) × 10 −9 cm 3 s −1. The former and the latter values correspond to 51% and 60–87% respectively of the calculated values from Langevin theory. The smaller k obs/ k calc ratio for C 2H 2 is attributed to the lack of near-resonant ionic states with favorable Franck—Condon factors for ionization.

Dissociative charge-transfer reactions of Ar+ with simple aliphatic hydrocarbons at thermal energy

A flowing-afterglow apparatus coupled with a low pressure chamber has been used to measure product ion distributions and rate constants in the charge-transfer reactions of Ar+ with CH4, C2Hn(n=2,4,6), and C3Hn(n=6,8) at thermal energy. Only parent cation is formed for C2H2 due to energy restriction. Major product channels are dissociative charge transfer followed by cleavage of C–H bond(s) for CH4, C2H4, C2H6, and C3H6, while by cleavage of a C–C bond for C3H8. A comparison of the product ion distributions with the photoelectron–photoion coincidence data for CH4, C2H4, and C2H6 leads us to conclude that the mean energies of precursor (pre)dissociative states are 15.3–15.5 eV, which are 0.3–0.5 eV below the resonance states. Thus the fractions of available energy deposited into internal modes of precursor parent ions at the instant of charge transfer are estimated to be 85%–95%, indicating that most of the CT reactions occurs without significant momentum transfer. The total rate constants for CH4, C2Hn(n=4,6), and C3Hn(n=6,8) are (0.78–1.1)×10−9 cm3 s−1, corresponding to 60%–92% of the calculated values from the Langevin theory. The rate constant for C2H2, 4.2×10−10 cm3 s−1, amounts to 38% of the kcalcd value. The small kobsd/kcalcd ratio is attributed to the lack of ionic states with favorable Franck–Condon factors for ionization.

Reactions of phenylium ions with gaseous hydrocarbons. 1. methane, ethane, and propane

The reaction of free tritiated phenylium ion, generated from nuclear decay of [l,4-T 2]-benzene in the presence of simple gaseous hydrocarbons RH (R = CH 3, C 2H 5, C 3H 7; partial pressure: 10-100 torr), yields predominantly the corresponding tritiated C 6H 5R products. The effects of gaseous nucleophilic acceptors (NuH = NH 3, CH 3OH) on the reaction with CH 4, were also investigated. Phenylium ion confirms its exceedingly high reactivity even toward pure σ- -type substrates, as well as its considerable site selectivity, demonstrated by the distinct preference for the C-H bonds of the substrate. The stability features of the ionic intermediates from addition of phenylium ion with RH have been evaluated, as well as their fragmentation and isomerization mechanisms. The behaviour of phenylium ion toward simple aliphatic hydrocarbons in the gas phase (10-100 torr) is discussed and compared with previous mechanistic hypotheses from ICR mass spectrometric studies, carried out at much lower pressures (10 -5 torr).

Mechanisms of the chlorine-38 for chlorine substitution in dichlorobenzene in the condensed phase

The /sup 38/Cl-for-Cl or -H substitution following the /sup 37/Cl(n,..gamma..)/sup 38/Cl nuclear reaction was studied in neat liquid dichlorobenzene isomers with and without I/sub 2/ present as radical scavenger as well as in highly diluted mixtures of these compounds with a variety of organic solvents, such as simple aliphatic hydrocarbons, aromatics, and perfluorinated aliphatics and aromatics. The results obtained in these systems suggest an interaction between the molecules making up the solvent cage with the intermediates forming the substituted product. This interaction consists most likely of a H abstraction by the Cl radical in the solvent cage, which competes with the reactions of thermal Cl leading to the /sup 38/Cl-substitution products, resulting in reduced yields of the latter compound. In the cases of unreactive wall molecules, e.g., perfluorinated hydrocarbons, such a reaction cannot take place, and the yields of the /sup 38/Cl-substitution products remain large. When the hot /sup 38/Cl-for-Cl substitution in solid dichlorobenzenes present in different crystal forms was studied, no effect of the crystal structure on the substitution process was observed.

The Dissociative Excitation and Dissociative Ionization of Simple Aliphatic Hydrocarbons by Controlled Electron Impact

Abstract Photoemissions from the following excited species were observed from simple aliphatic hydrocarbons (CH4, C2H2, C2H4, 1,3-C4H6) under controlled electron-impact excitation (0–400 eV) at wavelengths from 300 to 600 nm: H(Balmer), CH(A–X, B–X, C–X), CH+(A–X, B–A, b–a), C2(C–A, d–a; not from CH4), and C4H2+(A–X; not from CH4). All the excited species except for C4H2+ from C2H2 and C2H4 were confirmed to be primarily produced. The excitation function (0–400 eV) and the appearance potential of H, CH, and CH+ produced from CH4 and C2H2 were measured, and the corresponding processes of the fragmentation near the threshold were determined. The CH4+e→CH+(B)+H2(X)+H(n=1) and C2H2+e→CH+(B)+CH(X) processes were concluded to be responsible for the formation of CH+(B). The formation of ionic species, H+ and CH+, can be considered as the limiting case of the dissociative excitation for producing H and CH. A triplet excitation process may contribute to the formation of CH(A) from C2H2. The observed threshold energies indicated that superexcited states were involved in the formation of excited neutral fragment species.

Behaviour of simple aliphatic hydrocarbons in the region of high positive potential

Behaviour of simple aliphatic hydrocarbons in the region of high positive potential

Low-Energy Electron-Diffraction Studies of the Adsorption of Unsaturated Hydrocarbons and Carbon Monoxide on the Platinum (111) and (100) Single-Crystal Surfaces

The interaction of simple aliphatic hydrocarbons and carbon monoxide with Pt(111) and Pt(100) surfaces, at gas pressures ≤ 1 × 10−7 torr, has been studied using low-energy electron diffraction (LEED), mass spectrometry, flash desorption, and work-function (φ) measurements. The Pt(111) substrate was characterized by a (1 × 1) diffraction pattern while a (5 × 1) surface structure was visible on Pt(100). In contrast to the saturated hydrocarbons, all the other gases used (CO, C2H2, C2H4, C3H6, 1,3-butadiene and the isomeric butenes) were readily chemisorbed on both substrates. Relatively large decreases in φ resulted from the chemisorption of the unsaturated hydrocarbons while a small increase in φ was measured due to the adsorption of CO. A (2 × 2) surface structure was produced on the (111) face by all of the unsaturated hydrocarbons studied, with the exception of isobutylene which exhibited a larger unit mesh. Although C2H2 and C2H4 produced a C(2 × 2) structure on the (100) face of platinum, the adsorption of the other hydrocarbons was disordered. The necessity of close packing of the olefins appeared to be responsible for the presence of ordered structures on the Pt(111) surface and for their absence on Pt(100). The results of these structural studies indicate that the carbon atoms are sp2 hybridized in the adsorbed state. The chemisorption of CO resulted in the appearance of a C(4 × 2) structure on both (111) and (100) surfaces. This structure was transformed by electron-beam desorption into a (21/2 × 51/2)R45° structure on the Pt(100) surface. Three bonding states of CO were apparent on this substrate whilst only one was detected on Pt(111). A simple model can rationalize these differences.