Surface Of Reaction Vessel Research Articles

Increased Reaction Vessel Surface Area Decreases the Overall Mortality Rate of Rana catesbeiana Larvae during Chemically Induced Metamorphosis

Stimulating precocious metamorphosis in anuran larvae is an important pedagogical tool for understanding vertebrate development. However, historically, artificially provoking metamorphosis by immersing tadpoles in exogenous inducing agents (e.g., thyroxine, and iodine) compromises the longevity of the experimental animals, resulting in up to 100% mortality within a week. In our undergraduate teaching lab, we house our experimental tadpoles in circular glass dishes having a surface area of 182 cm2. Over the past four academic years this lab was performed, we observed 100% mortality of experimental animals within 10, 12, or 15 days when treated with 10-5 M, 10-6 M, or 10-7 M thyroxine, respectively. Here, we investigated whether increasing the surface area to 413 cm2 using square glass dishes would reduce the mortality of the treated animals. Omnibus Kaplan-Meier survival analysis demonstrates a statistically significant decrease in mortality in tadpoles reared in the larger square dishes compared to those housed in the smaller round dishes (P < 0.05). However, increasing the surface area of our reaction vessels could not rescue survivability of those tadpoles immersed in thyroxine, but did increase survivability of control tadpoles maintained in pond water (P < 0.01), tadpoles subjected to iodine (P < 0.05) or treated with actinomycin D (P < 0.05). These data demonstrate that increasing available reaction vessel surface area reduces overall tadpole mortality during chemically modified metamorphosis in an undergraduate teaching lab setting.

Chain ignition of propane-air and pentane-air mixtures in a heated vessel

The spatial propagation of the chain ignition of propane-air and pentane-air mixtures with oxygen at a pressure of 1 atm and T = 600–800 K is studied. It is established that the features of the spatial propagation of chain ignition process are determined by the conditions of the reactor’s surface. It is shown that the site (or sites) of ignition are located on the surface of the reaction vessel; the flame front propagates from the site into the volume at a normal speed corresponding to the reactor temperature and the composition of the combustible mixture.

Effect of structure on the rate and mechanism of thermolysis of some 4-substituted 3-methylfuroxans

The gas-phase thermolysis of I proceeds as a unimolecular process and is independent of the initial vapor pressure of the substance (over 190 mm Hg) and of the ratio of the reaction vessel surface to its volume (S/V = 0.55–4.62 сm). In the melt and in solution in an inert solvent dibutylphtalate (DBP) the furazans decompose according to the first-order reaction law to the conversion level of 30–45 %. The substance content in the solution (1–10 %) does not affect the reaction rate.

Heterogeneous stages in the below-ignition-limit oxidation of hydrogen and carbon monoxide

It was demonstrated experimentally that, during the oxidation of hydrogen and carbon monoxide under stationary conditions (i.e., below the first ignition limit), the state of the reaction vessel surface experiences reversible changes, which, in turn, influence the kinetics of the gas-phase process. It was concluded that the reaction of molecular oxygen with hydrogen adatoms plays an important role in chain reactions below the first ignition limit.

Kinetics and Mechanism of the Thermal Rearrangement of [1.1.1]Propellane

The kinetics of the thermal rearrangement of [1.1.1]propellane (1) have been investigated by gas-phase pyrolysis in a stationary system. The unimolecular reaction leads to dimethylenecyclopropane (2) and its thermal isomerization product ethenylidenecyclopropane (5) with the following Arrhenius parameters: log(A/s-1) = 14.02 ± 0.23; EA/kcal mol-1 = 39.66 ± 0.52. Furthermore, it was shown that the minor product methylenecyclobutene (3) and its thermal isomerization product 1,2,4-pentatriene (6) result from a heterogeneous side reaction catalyzed by the reaction vessel surface. Ab initio and DFT calculations of the potential energy surface indicate that the isomerization follows an asynchronous reaction path in which two side bonds of the [1.1.1]propellane (1) are involved. The activation barrier at the CCSD(T)/6-311G(2d,p)//MP2/6-311G(2d,p) level of theory was calculated as 40.0 kcal/mol.

Deposition of polyaniline on glass and platinum by autocatalytic oxidation of aniline with dichromate

The oxidation of aniline with dichromate was studied by UV–Vis spectrometry, and was shown to proceed autocatalytically leading to colored oligomers and polymers of aniline. Chemical polymerization of aniline by dichromate is greatly accelerated by thin film of the reaction product polyaniline, present on an inner surface of reaction vessel. Polyaniline films were deposited by chemical polymerization onto quartz glass and platinum surfaces, and some redox and electrochemical properties of the resulting films were investigated.

Reactions of Saturated and Unsaturated Tertiary Alkyl Halides and Saturated Secondary Alkyl Iodides with Lithium Aluminum Deuteride. Convincing Evidence for a Single-Electron-Transfer Pathway

Reactions of saturated secondary and tertiary alkyl halides with LiAlH4 (LAH) and LiAlD4 (LAD) have been carried out, and convincing evidence for a single-electron-transfer (SET) pathway has been obtained. Reactions involving saturated alkyl halides with LAD provide a model system in which a halogen-atom radical chain process is not possible, and therefore, the observation of large quantities (in some cases >90%) of protium in the reduction product provides strong evidence for a radical intermediate and a SET pathway. Specifically, the reaction of 2-iodooctane (10) with LAD produced octane with a deuterium content as low as 21%. Also, the reaction of the tertiary halide 2-iodo-2-methylheptane (15) with LAD produced 2-methylheptane (16) with a deuterium content as low as 8%. The effect of stoichiometry, halogen type, and reaction vessel surface on these reactions was studied. Reaction of the unsaturated tertiary halide 6-iodo-6-methyl-1-heptene (25) with LAD was also studied and was found to proceed predom...

On the Mechanism of the Decomposition of Acidic O3 Solutions, Thermally or H2O2-Initiated

Thermal or hydrogen peroxide initiated decomposition of acidic aqueous ozone is described as a chain process propagated by OH and O2-/HO2 radicals. In the absence of H2O2 added, the chain is initiated by surface-catalyzed formation of H2O2. Surface-dependent formation of H2O2 is experimentally verified. Since homogeneous radical−radical reactions are much too inefficient to account for the termination, a heterogeneous chain termination is strongly suggested. Without addition of H2O2 no dependence of the decay on the surface-to-volume ratio could be observed. However, on initial addition of H2O2 in amounts sufficient for homogeneous initiation to prevail, the rate of O3 decay becomes proportional to the surface of the reaction vessel. These findings strongly suggest that the decomposition of acidic aqueous O3 is governed by initiation and termination processes occurring at the reaction-vessel surface, while its apparent appearance of a homogeneous solution-phase reaction results from the counteractive natu...

Evidence for Single-Electron Transfer in the Reactions of Unhindered Saturated Primary Alkyl Iodides with Lithium Aluminum Hydride. Reactions of 1-Halooctanes with Lithium Aluminum Deuteride

Evidence for single-electron transfer (SET) in the reactions of lithium aluminum hydride (LAH) with unhindered, saturated primary alkyl halides has not been available. In this study, experiments have been carried out that provide convincing evidence that the unhindered, saturated primary alkyl iodide 1-iodooctane reacts with lithium aluminum deuteride (LAD) in a 1:0.2 ratio to form 1-deuteriooctane with up to 38% incorporation of protium. Since the protium incorporation increased as the reaction proceeded, studies involving the reaction of 1-iodooctane with AlD3 (one of the byproducts in the reaction of LAD with alkyl halides) were carried out in order to determine the effect of AlD3. With AlD3, protium incorporations as high as 84% were observed, indicating that the reaction of AlD3 with 1-iodooctane proceeds via a pathway that involves at least 84% radical formation. The study also included the effect of reaction vessel surface, concentration, and leaving group on the course of the reaction. Factors pre...

The thermal degradation of 5α(H)-cholestane during closed-system pyrolysis

Involatile hydrocarbons were identified following the heating of 5α(H)-cholestane in water with reaction vessel walls composed of 316 grade stainless steel and borosilicate glass. These analyses were compared with the hydrocarbon product compositions from closed-system pyrolysis experiments with no added water. Unsaturated hydrocarbons dominate their saturated counterparts following hydrous pyrolysis in both stainless steel-316 and borosilicate glass. In the absence of added water the converse is true in that saturated components dominate the hydrocarbon mixture. Backbone rearrangement in the steroid nucleus leading to spirosterene formation was only observed under aqueous conditions in both borosilicate glass and stainless steel-316 vessels. These comparisons demonstrate that water, as opposed to reaction vessel surface catalytic effects, plays a central role in mediating hydrocarbon degradation during closed-system hydrous pyrolysis. 5α(H)-cholestane degradation under aqueous conditions is a complex composite of dissociative and rearrangement processes. These include (I) carbon-carbon bond cleavage in the sidechains as well as the ring system, (2) dehydrogenation, and (3) backbone rearrangement. These laboratory experiments provide a product description of the involatile hydrocarbons which will be the basis for a mechanistic study of 5α(H)-cholestane degradation in hot water.

Free radical and atom activity at a pyrex glass surface as a source of sodium D line emissions during combustion reactions

Hydrogen plus oxygen mixtures are able to undergo oscillatory ignition in a stirred-flow reactor. The temperature approaches that of the adiabatic flame during each oscillation and high free radical and atom concentrations are attained. We have measured hydroxyl radical concentrations of 10{sup {minus}8} mol cm{sup {minus}3}. The oscillatory ignition originates in a kinetic interaction between chain branching and chain termination processes, with supplementary effects on the accompanying heat release. The investigation and interpretation of the oscillatory reaction has been reported in detail elsewhere. A visible light emission also pervades the gaseous volume during ignition that corresponds to the frequencies of the sodium D lines. The emission originates from sodium atoms that are released from the Pyrex glass of the reaction vessel surface. (Similar effects are observed when Pyrex glass is held in a Bunsen burner flame.) In this paper, the authors report experimental results obtained by emission spectroscopy that link the release of the sodium atoms and their associated emission to reactions at the vessel surface involving the atoms or free radicals formed during ignition. Experimental details of the stirred-flow experiments have been described previously. Here the authors summarize only the main features.

Low temperature ignition of acetaldehydeoxygen mixtures initiated by organic peroxides adsorbed on the surface of a reaction vessel

The phenomenon of low temperature (up to room temperature) ignition of acetaldehydeoxygen mixtures, initiated by the products of heterogeneous radical decomposition of peroxide compounds, adsorbed at low temperature on a surface of the reaction vessel, has been discovered and studied. It has been shown that the minimum ignition temperature strongly depends on the character of the reaction vessel surface, as well as the nature and the concentration of the peroxide (peracetic acid, t-butyl hydroperoxide, and di-t-butyl peroxide). It has been discovered, that a blue-colored flame propagates along the cold reaction vessel as a result of the adsorption of the peroxy compounds on the wall and the subsequent rapid heating. The speed of the propagation of the flame depends on the peroxy compound adsorbed.

Induced heterogeneity, a novel technique for the study of gas‐phase reactions. 2. Direct study of CC bond scission in ethane

AbstractDeliberate activation of the reaction vessel surface leads to the domination of chain termination in ethane pyrolysis by the reaction As a result, chains are dramatically reduced in length, methane yields are entirely primary and larger in proportion to other products, and values of k1 can be directly determined from methane yield data without ambiguity. Experiments carried out in the temperature range of 841–913K at initial ethane pressures of 1–20 torr, without and with added nitrogen, yield the infinite pressure Arrhenius equation It is shown that most previously published data can be combined with those of this study to yield Fall‐off curves for k1 as a function of pressure are in good agreement with those from other laboratories. From these the relevant data for k−1 can be extracted for use in other kinetic studies.

Pyrolysis and microwaves

The historic background, 1750–1950, of pyrolysis is sketched. At the end of this period the role of pressure, temperature and reaction vessel surface had been clarified. The use of a standard Stark-modulated microwave spectrometer (18–40 GHz) as the detector for polar products of pyrolysis at 0.001–0.01 mm Hg is described and examples given. The gap between theories for calculation of reaction rate constants and experimental results obtained by closed-vessel pyrolysis is still too large, presently leaving us with the production of new species as the most worthwhile results.

Memory Effects in the Production of Benzene for Radiocarbon Dating

The use of materials having high levels of 14C activity (up to 113 times the activity of modern carbon) enabled a quantitative analysis of the magnitude and sites of memory occurring in the routine synthesis of benzene, via lithium carbide, for radiocarbon dating. Memory may be expressed as the percentage or fractional contribution of carbon from sources other than the original sample in this synthesis. Although tritium and radon contamination have also been found, the major site of memory was the inner surface of the stainless steel reaction vessel used for lithium carbide production. Up to 1 percent memory has been found there under extreme conditions in the routine dating system at Harwell. Values of half to one-third this size were more usual, but even etching and scouring the inner surface of the reaction vessel reduced the memory only by a factor of four. This lower limit is believed to exist because of the carburization and decarburization of steel which occurs at the temperature required for the production of lithium carbide. The levels of memory found are of the same order as the levels of significance associated with present radiocarbon techniques. With the accuracy and extended chronologies expected from direct 14G measurement by accelerator techniques, these levels of memory become increasingly important in the preparation of acetylene and pyrolitic graphite (via lithium carbide) used as target materials. This effect, however, can be limited by lowering the temperature of the carbide reaction stage or by lining or impregnating the lithium carbide reaction vessel with some carbon-impermeable alloy or material.

The gas‐phase thermal unimolecular elimination of 1,1‐dimethylketene from 7,7‐dimethylbicyclo[3.2.0]hept‐2‐en‐6‐one

AbstractThe gas‐phase thermal decomposition of 7,7‐dimethylbicyclo[3.2.0]hept‐2‐en‐6‐one (DBH) to yield cyclopentadiene and 1,1‐dimethylketene as primary products was studied in the temperature range of 470‐550 °K using a static reaction system. First‐order rate constants for the depletion of DBH based on the internal standard technique and gaschromatographic analyses were independent of the initial starting pressure (7‐68 torr) and of the conversion, ranging between 5% and 89%. (Throughout this paper, 1 torr = (101.325/760) kNm−2, and 1 cal = 4.184J). The reaction is essentially homogeneous, as the nature of the reaction vessel surface (Teflon or glass) had no effect on the observed rate constants which fit the Arrhenius relationship where θ = 2.303 RT. These activation parameters, when compared with those for similar reactions involving the molecules bicyclo[3.2.0]hept‐2‐en‐6‐one, bicyclo[3.2.0]heptan6‐one, and cyclobutanone, demonstrate a very small effect of the alkyl substituents bonded to the carbon atom adjacent to the carbonyl carbon. Accepting the previously discussed concerted and pronounced polar nature of the mechanism for these retro‐ketene addition reactions, the present data suggest that considerable changes in charge densities between the ground and transition state are only occurring on the two opposite centers of the molecule, with the negative charge residing essentially on the oxygen atom and the positive charge on the opposing bridgehead carbon atom. It then appears that the charge separation in the transition state is more appropriately described as being pseudo‐zwitterionic rather than quadrupolar in nature.

The mechanism of combustion of pentane in the gas phase between 250° and 400°C

The initial stages of the slow reaction between gaseous n-pentane and oxygen have been studied under static conditions between 250° and 400°C by analysis of the reaction products, using gas chromatography. The dependence of initial fractional yields on surface, mixture composition, and temperature has been established. The reaction has been proved to be propagated homogeneously by carrying out competitive experiments, from which the rate of radical attack on pentane relative to 2-methyl propane is 1.35±0.05. Nevertheless, the initial fractional yields of products depend strongly upon the nature of the reaction vessel surface, indicating that an important part of the reaction is heterogeneous. Trends in product yields with composition at 290°C indicate that RO2 radicals can: (a) abstract H from RH to give ROOH, which subsequently decomposes heterogeneously; (b) decompose homogeneously to pentenes and O-heterocycles; and (c) diffuse to the walls to give predominantly acetone. The rate constants which can be deduced for (a) and (b) on the basis of a calculated rate for (c) are in good agreement with those proposed elsewhere. At about 250°C, the entire product appears to arise from heterogeneous reactions of radicals, while above 350°C the major products arise from homogeneous pyrolysis of ROO radicals.

Kinetics and mechanism of the thermal decomposition of 1-bromo-2-chloroethane

The thermal decomposition of 1-bromo-2-chloroethane at 307–358° results in vinyl chloride and hydrogen bromide as the main products, with vinyl bromide and hydrogen chloride as minor products, the latter being formed mainly via a secondary reaction between the main products. Induction periods are evident below 327°, and propene has a marked inhibitory effect upon the decomposition. The rate of decomposition is sensitive to the nature and treatment of the reaction vessel surface and there is autocatalysis owing to hydrogen bromide. In vessels seasoned with the pyrolysis products of allyl bromide, the reaction catalysed by a sufficiently high proportion of hydrogen bromide is of the half-order in substrate and zero-order in catalyst. At 307–358° the rate coefficient is expressible as in equation (A). The catalysed reaction does not show induction periods, but the rate is decreased k0·5= 9·3 × 109 exp (–40,800/RT) mole–½ l.–½ sec.–1(A) slightly in packed vessels. The results are consistent with a radical-chain reaction, and possible mechanisms are discussed.

The Competitive Chlorination of Propane and Olefins

AbstractBy chlorinating mixtures of propane and olefins (ethylene, propene and isobutene) we have shown that there is a strong heterogeneous component in the chlorination of the olefins. The heterogeneous reaction can be somewhat reduced by choosing a suitable reaction vessel surface but cannot be completely eliminated. However in favourable cases it can be allowed for and the ratios of the rate constants for chlorine atom attack on propane and olefins can be determined. The absolute rate constants for addition of chlorine atoms to olefins can then be derived using the known value of the rate constant for Cl + C3H8 = C3H7 + HCl.

Dependence of Methane—Oxygen Low-Pressure Explosion Limit on Nature of Reaction Vessel Surface1

Dependence of Methane—Oxygen Low-Pressure Explosion Limit on Nature of Reaction Vessel Surface¹