The reaction of OH with CO

Hydroxyl radicals were prepared from the photolysis of N₂O at 213.9 nm in the presence of excess H₂. The O(¹D) produced in the primary photolytic act reacts with H₂ to produce OH radicals. If CO is also present, then OH can react either with H₂ or CO: The competition between reactions (1) and (2) was measured by measuring the CO₂ yield at various values of the ratio [CO]/[H₂] at 217–298°K. At 298°K the ratio of the rate coefficients k₁/k₂ increased with pressure from a low-pressure limiting value of 14 to a high-pressure limiting value of 50. The low-pressure limiting value agrees well with the low-pressure values found by others. At lower temperatures our high-pressure values of k₁/k₂ were larger than deduced from the accepted low-pressure Arrhenius expression and could be fitted to the expression The mechanism which seems to fit the results best is with k₁° = k_ak_b/k_-a and k₁^∞ = k_a.     

The reaction of OH with NO

Mixtures of N₂O, CO, and NO in excess H₂ were photolyzed at 213.9 nm and 298°K. The initially formed O(¹D) atoms from the photolysis of N₂O abstract an H atom from H₂ permitting a study of the competition: From the CO₂ yield the relative rate coefficient k₁/k₂ is obtained. It is found to be slightly dependent on pressure for total pressures (mainly H₂) of 95.5 to 768 torr. However, the values are near the high-pressure limiting value which is found by extrapolation to give k₁^∞ = 1.2 × 10^?11 cm³/sec based on k₂^∞ = 3.55 × 10^?13 cm³/sec.     

A novel palladium-catalyzed intramolecular redox reaction

[reaction: see text] A new type of palladium-catalyzed redox reaction is described, forming enones from 2-(2-bromobenzyl)-ketones with an overall loss of HBr. The scope and limitations of the reaction are demonstrated by a series of cyclic and acyclic substrates. The mechanism most probably involves the formation of an intramolecular arylpalladium enolate and is related to the oxidation of silyl enol ethers with palladium acetate.     

A novel bicyclic ketal fragmentation reaction

Bicyclic ketals of the 6,8-dioxabicyclo[3.2.1]octane series are specifically cleaved to give δ, ε-unsaturated ketones by treatment of the ketal with acetyl iodide.     

Kinetics of the OH + HCNO reaction

The kinetics of the OH + HCNO reaction was studied. The total rate constant was measured by LIF detection of OH using two different OH precursors, both of which gave identical results. We obtain k = (2.69 +/- 0.41) x 10(-12) exp[(750.2 +/- 49.8)/T] cm(3) molecule(-1) s(-1) over the temperature range 298-386 K, with a value of k = (3.39 +/- 0.3) x 10(-11) cm(3) molecule(-1) s(-1) at 296 K. CO, H(2)CO, NO, and HNO products were detected using infrared laser absorption spectroscopy. On the basis of these measurements, we conclude that CO + H(2)NO and HNO + HCO are the major product channels, with a minor contribution from H(2)CO + NO.     

A shock tube study of the OH + OH → H2O + O reaction

The rate coefficient for the reaction has been determined in mixtures of nitric acid (HNO₃) and argon in incident shock wave experiments. Quantitative OH time-histories were obtained by cw narrow-linewidth uv laser absorption of the R₁(5) line of the A² σ⁺ ← X² Π_i (0,0) transition at 32606.56 cm^?1 (vacuum). The experiments were conducted over the temperature range 1050–2380 K and the pressure range 0.18–0.60 atm. The second-order rate coefficient was determined to be with overall uncertainties of +11%, ?16% at high temperatures and +25%, ?22% at low temperatures. By incorporating data from previous investigations in the temperature range 298–578 K, the following expression is determined for the temperature range 298–2380 K © 1994 John Wiley & Sons, Inc.     

A novel modified baylis-hillman reaction of propiolate

A new reaction of propiolates and aldehydes mediated by DABCO analogous to the Baylis-Hillman reaction is described. This reaction provided novel beta-functionalized Baylis-Hillman products and a new methodology for the generation of alkylidene carbene species.     

A novel facet of the halolactonisation reaction

Steric versus acidity-controlled change during lactonisation of monosubstituted maleic anhydride-cyclopentadiene adducts has been studied to eliminate some confusion in the literature arising from the use of limited information. The transannular lactonisation of proximately aligned, yet dissymmetric, dicarboxylic acid is controlled under acidic conditions by bulk effects and under basic conditions by pK_a, effects.     

A novel ring cleavage reaction of oxazolines

An oxazoline can be cleanly converted to the parent carboxylic acid by treatment with NaOCl, followed by mild basic hydrolysis of the intermediate ester product(s).     

A novel oxidative reaction of 2,4,5-triphenylpyrrole

The effect of phenyl groups on the oxidation of 2,4,5-triphenylpyrrole (I) has been investigated. By oxidation of 2,4,5-triphenylpyrrolemagnesium bromide (II) with oxygen and of 2,4,5-triphenylpyrrole (I) with potassium permanganate besides 2,4,5,2′,4′,5′-hexaphenyl-3,3′-bi-pyrrole (III) another product, which has been assigned the 1,6-dihydro-2,3,4,5,6a-pentaphenylbenzo[g]pyrrole[3,2-e]indole (IV) structure, was obtained. The behaviour of IV toward further oxidation and the spectroscopic data (ir, nmr, ms) were in good agreement with the assigned structures.     

Kinetics of the reaction of OH with HCl

The rate constant of the reaction OH + HCl → H₂O + Cl was measured in a flow tube over the temperature range 224 to 460°K using resonance fluorescence detection of OH. An Arrhenius expression k₁ = (2.0 ± 0.1) × 10^?12 exp [?(620 ± 20 cal/mole)/RT] was obtained. Stratospheric and reaction kinetic implications are discussed briefly.     

A combined experimental and theoretical study of the reaction between methylglyoxal and OH/OD radical: OH regeneration

Experimental studies have been conducted to determine the rate coefficient and mechanism of the reaction between methylglyoxal (CH(3)COCHO, MGLY) and the OH radical over a wide range of temperatures (233-500 K) and pressures (5-300 Torr). The rate coefficient is pressure independent with the following temperature dependence: k(3)(T) = (1.83 +/- 0.48) x 10(-12) exp((560 +/- 70)/T) cm(3) molecule(-1) s(-1) (95% uncertainties). Addition of O(2) to the system leads to recycling of OH. The mechanism was investigated by varying the experimental conditions ([O(2)], [MGLY], temperature and pressure), and by modelling based on a G3X potential energy surface, rovibrational prior distribution calculations and master equation RRKM calculations. The mechanism can be described as follows: Addition of oxygen to the system shows that process (4) is fast and that CH(3)COCO completely dissociates. The acetyl radical formed from reaction (4) reacts with oxygen to regenerate OH radicals (5a). However, a significant fraction of acetyl radical formed by reaction (R4) is sufficiently energised to dissociate further to CH(3) + CO (R4b). Little or no pressure quenching of reaction (R4b) was observed. The rate coefficient for OD + MGLY was measured as k(9)(T) = (9.4 +/- 2.4) x 10(-13) exp((780 +/- 70)/T) cm(3) molecule(-1) s(-1) over the temperature range 233-500 K. The reaction shows a noticeable inverse (k(H)/k(D) < 1) kinetic isotope effect below room temperature and a slight normal kinetic isotope effect (k(H)/k(D) > 1) at high temperature. The potential atmospheric implications of this work are discussed.     

Tunneling in the reaction of acetone with OH

Based on recent detailed quantum mechanical computations of the mechanism of the title reaction and, this paper presents kinetics analysis of the overall rate constant and its temperature dependence, for which ample experimental data are available for comparison. The analysis confirms that the principal channel is the formation of acetonyl radical + H(2)O, while the channel leading to acetic acid is of negligible importance. It is shown that the unusual temperature dependence of the overall rate constant, as observed experimentally, is well accounted for by standard RRKM treatment that includes tunneling. This treatment is applied at the microcanonical level, with chemically activated distribution of entrance species, i.e. using a stationary rather than a thermal distribution that incorporates collisional energy transfer and competition between the redissociation and exit channel. A similar procedure is applied to the isotopic reaction acetone-d6 + OH with equally satisfying results, so that the experimental temperature dependence of the KIE (kinetic isotope effect) is perfectly reproduced. This very good agreement between calculation and experiment is obtained without any fitting to experimental values and without any adjustment of the parameters of calculation.     

Dynamics of the CH3 + OH reaction

We study dynamics of the CH₃ + OH reaction over the temperature range of 300–2500 K using a quasiclassical method for the potential energy composed of explicit forms of short‐range and long‐range interactions. The explicit potential energy used in the study gives minimum energy paths on potential energy surfaces showing barrier heights, channel energies, and van der Waals well, which are consistent with ab initio calculations. Approximately, 20% of CH₃ + OH collisions undergo OH dissociation in a direct‐mode mechanism on a subpicosecond scale (<50 fs) with the rate coefficient as high as ～10^?10 cm³ molecule^?1 s^?1. Less than 10% leads to the formation of excited intermediates CH₃OH? with excess vibrational energies in CO and OH bonds. CH₃OH? stabilizes to CH₃OH, redissociates back to reactants, or forms one of various products after intramolecular energy redistribution via bond dissociation and formation on the time scale of 50–200 fs. The principal product is ¹CH₂ (k being ～10^?11), whereas ks for CH₂OH, CH₂O, and CH₃O are ～10^?12. The minor products are HCOH and CH₄ (k～10^?13). The total rate coefficient for CH₃ + OH → CH₃OH? → products is ～10^?11 and is weakly dependent on temperature. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 455–466, 2011     

The reaction of OH radicals with dimethyl sulfide

The kinetics of the gas phase reaction of OH radicals with dimethyl sulfide (CH₃SCH₃) have been studied at various temperatures and total pressures using two relative rate methods and a flash photolysis technique. For the relative rate methods, rate constants were measured at 296 ± 2 K as a function of the O₂ pressure at a total pressure of ca. 740 torr. Data from these three experimental techniques were not in agreement. It is concluded that the relative rate techniques are subject to secondary reactions, possibly involving CH₃S radicals. A rate constant of (2.5) × 10^?12 e^{(130 = 102)/T} cm³ molecule^?1 s^?1 obtained using the flash photolysis-resonance fluorescence data in the absence of O₂, and which is in agreement with the lower range of values previously reported in the literature, is recommended.     

A novel isocyanide based three component reaction

A three component reaction involving an isocyanide, a carboxylic acid and an epoxide or aziridine is described.     

A novel flocculant of Al(OH)3-polyacrylamide ionic hybrid

A novel flocculant based on hybrid Al(OH)(3)-polyacrylamide (HAPAM) has been synthesized using a redox initiation system ((NH(4))(2)S(2)O(8)-NaHSO(3)) at 40 degrees C in aqueous medium. The HAPAM was characterized by viscometry, IR spectroscopy, TEM, conductivity, and TGA. The flocculation behavior for 0.25 wt% kaolin suspension was evaluated by spectrophotometry and phase contrast microscopy. It was found that an ionic bond exists between Al(OH)(3) colloid and polyacrylamide (PAM) chains in the HAPAM and the flocculation efficiency of HAPAM is much better than that of commercial polyacrylamide (PAM) and PAM/AlCl(3) blend.