Flame oxide

While no 1,2-alkyl shifts have been observed in solution, the cool flame oxidation of Me3CH (in the gas phase at 480°) is found to... 

Gluing is difficult, needing pre-treatments such as, for example, chemical etching (sulfo-chromic acid etching), flame oxidation or hot-air (500°C) treatment, corona discharge, plasma or UV treatments. The exposure must be brief and superficial and the original and aged properties must be tested. 

A photoanode comprised of flame oxidized carbon doped n-Ti02 films have been reported to perform water splitting with high photoconversion efficiencies [65]. While chemically modified n-Ti02 can be prepared by the controlled combustion of Ti metal in a natural gas flame the authors, in investigating this technique [66], have found reproducibility to be a challenge. Various authors [67,68,69] have discussed in considerable depth issues surrounding the stated photoconversion efficiencies of [65]. 

This scheme (in which the reversible arrows are not meant to imply that equilibrium is attained) provides an excellent qualitative, and reasonably semiquantitative, description of the formation of products during the cool-flame oxidation at 523° to 580°K. of 2-methylpentane (24). Also, because of the different energy requirements for the various modes of Reactions 4 and 5, the scheme is capable of explaining, at least in principle, the complex dependence of rate on temperature during cool-flame oxidation (24, 51). 

The modification of the chemical composition of polymer surfaces, and thus their wettability with chemical substances, can be realized in different ways electric discharges more commonly called Corona effect, oxidation by a flame, plasma treatment, UV irradiation and also UV irradiation under ozone atmosphere. Numerous studies have been devoted to the effects of these different treatments. More recently, Strobel et al. [204] compared the effects of these treatments on polypropylene and polyethylene terephthalate using analytical methods such as E.S.C.A., F.T.I.R., and contact angle measurements. They demonstrated that a flame oxidizes polymers only superficially (2-3 nm) whereas treatment realized by plasma effect or Corona effect permits one to work deeply in the polymer (10 nm). The combination of UV irradiation with ozone flux modifies the chemical composition of the polymers to a depth much greater than 10 nm, introducing oxygenated functions into the core of the polymer. 

CSPE have excellent combinations of properties that include total resistance to ozone excellent resistance to abrasion, weather resistance even in light colors, heat, flame, oxidizing chemical, solvents, crack growth, and dielectric properties. Also provide low moisture absorption, resistance to oil similar to neoprene, low temperature flexibility is fair at -40C (-40F), low gas permeability for an elastomer and good adhesion to substrates. Can be made into a wide range of colors. Use includes hoses, roll covers, tank liners, wire and cable covers, footware, and building products (flash, sealing, etc.). 

SAFETY PROFILE Very low toxicity by several routes. A skin irritant. See also ESTERS. Dangerously flammable reacts vigorously with heat, flame, oxidizing materials. To fight fire, use foam, CO2, dry chemical. 

SAFETY PROFILE A dangerous fire hazard when exposed to heat, flame, oxidizers, or... 

SAFETY PROFILE Poison by ingestion and intraperitoneal routes. Moderately toxic by skin contact. Mildly toxic by inhalation. A severe skin and eye irritant. Flammable liquid when exposed to heat, flames, oxidizers. To fight fire, use alcohol foam. When heated to decomposition it emits... 

COMPOUNDS OF CARBON AND HYDROGEN — ILLUMINATING GAS —FLAMES —OXIDATION AND REDUCTION. 

Cool flames are observed at pressures lower than those necessary for two-stage ignition. These non-isothermal events occur at intervals of time during an otherwise almost isothermal reaction. The majority of workers consider cool-flame propagation to be the central part of reaction during which the bulk of the fuel is incompletely oxidized. Shtern, however, considers the cool flame to be a minor process which plays little part in the overall reaction, since the cool-flame oxidation and the slow oxidation are very similar in their chemical nature. Indeed, the pressure--time curves Shtern obtained for the cool-flame oxidation of propane have the same S-shape as those for the slow oxidation if the non-isothermal events are ignored, as can be seen in Fig. 3. 

Fig. 3. The variation of pressure change with time during the cool-flame oxidation of propane. Initial temperature = 280 °C initial pressure of propane = 210 torr initial pressure of oxygen = 210 torr. (From ref. 2.)...

The importance of alkylperoxy radicals as intermediates had long been realized (see Sect. 2) and their subsequent reaction to yield the alkyl-hydroperoxide or decomposition products such as aldehydes and alcohols had been reasonably successful in describing the mechanism of the autocatalytic oxidation of alkanes. However, even though 0-heterocycles (which cannot be derived from intermediate aldehydes) had been found in the products of the oxidation of n-pentane as early as 1935 [66], the true extent of alkylperoxy radical isomerization reactions has been recognized only recently. Bailey and Norrish [67] first formulated the production of O-heterocycles in terms of alkylperoxy radical isomerization and subsequent cyclization in order to explain the formation of 2,5-dimethyl-tetrahydrofuran during the cool-flame oxidation of n-hexane. Their mechanism was a one-step process which involved direct elimination of OH. However, it is now generally formulated as shown in reactions (147) and(I67)... 

Experimentally it is difficult to distinguish between these modes of formation. However, it has been shown [70] that in the cool-flame oxidation of n-pentane the yields of Cs O-heterocycles and C5 alkenes vary with time in a similar manner, suggesting that they are formed from a common precursor, e.g. 

Cullis and co-workers [80,85,86] have shown that group shifts involving ethyl radicals may also take place. Thus the presence of small yields (ca. 2 %) of 4-methylhexan-3-one and heptan-3-one in the products of the cool-flame oxidation of 3-ethylpentane show that the 3-ethyl-3-... 

There is no direct experimental evidence for this complex decomposition and it may well occur by several steps [107]. However, substantial yields of unsaturated carbonyl compounds are formed particularly at high pressures [78] under initial reaction conditions where cool flames propagate. For example, the cool-flame oxidation of 2-methylpentane at 525 °C and 19.7 atm in a rapid compression machine [78] yields no less than 14 unsaturated carbonyl compounds viz acrolein, methacrolein, but-l-en-3-one, pent-2-enal, pent-l-en-3-one, pent-l-en-4-one, trans-pent-2-en-4r one, 2-methylbut-l-en-3-one, 2-methylpent-l-en-3-one, 4-methylpent-l-en-3-one, 2-methylpent-l-en-4-one, 2-methylpent-2-en-4-one, 2-methyl-pent-2-enal and 4-methylpent-2-enal. Spectroscopic studies of the preflame reactions [78] have shown that the unsaturated ketones account for ca. 90 % of the absorption which, occurs at 2600 A. At lower initial temperatures and pressures acrolein and crotonaldehyde are formed from n-pentane [69, 70] and n-heptane [82], and acrolein is also formed from isobutane [68]. 

Fig. 12. The variation with time of peroxide yield during the cool-flame oxidation of isobutane. Initial temperature = 310 C isobutane introduced = 1.44 x 10 mole. 1 isobutane oxygen = 1 2 volume of reaction vessel = 500 cm. A fcrf-butyl hydroperoxide x 10 , hydrogen peroxide. (From ref. 132).

Further support for the attainment of a critical concentration of hydroperoxide prior to the passage of a cool flame at temperatures corresponding to the Lq and L, lobes has been obtained by Taylor [131], and more recently by Pollard and co-workers [68,132], who determined the maximum concentrations of tert-butyl hydroperoxide found during the cool-flame oxidation of isobutane. Again, the concentration of hydroperoxide increased prior to the cool flame and it was almost entirely consumed during its passage (Fig. 12). Also, in common with other hydrocarbon + oxygen systems, (e.g. refs. 55, 65, 78,133) the induction period to the first cool flame (r,) was related to the initial reactant pressure (po) by the expression... 

Thus, in the case of 3-ethylpentane initial attack at a secondary C—H bond may always be followed by oxygen addition and 1 5 H-transfer involving another secondary C—H bond. Furthermore, since the initial attack is unselective during cool-flame oxidation a considerable proportion of primary alkylperoxy radicals will be formed from this alkane and these may all undergo the relatively easy isomerization involving 1 5-hydrogen transfer from a tertiary C—H bond... 

The foregoing discussion has shown, however, that the molecular structure of the parent alkane profoundly affects the distribution of the intermediate products of its cool-flame oxidation and clearly, there is a strong correlation between the distribution, the degree of branching of the carbon skeleton, the rate of formation of the hydroperoxyalkyl radicals and the Research Octane Number of the alkane. 

Fig. 32. The variation of the peak at M/E 60 (resulting from peracetic acid decomposition in the mass spectrometer) during the cool-flame oxidation of acetaldehyde [47]. ...

Fig. 35. The effect of ethane addition on the cool-flame oxidation of acetaldehyde in a static system [70]. (a) Pressure—time plot for the cool-flame oxidation of acetaldehyde. Total pressure of a 1 1 acetaldehyde—oxygen mixture = 73 torr. Temperature = 230 °C. (b) As for (a) but with 10.9 torr of ethane present.

An earlier study of the reduction with hydrogen of tin dioxide (made by the flame oxidation of stannic chloride) in the presence of 0.5 wt % Cu, Rh, Pd, Ag, Os, Ir, Pt, or Au added to the dioxide by impregnation with soluble salts gave the activity series Rh > Pt > Ir > Os > Pd Cu, Ag, and Au. The order is much more like that to be expected if the dissociative chemisorption of hydrogen is the slow step the low position of palladium may be due again to a deactivation by absorbed hydrogen. Copper is unexpectedly inactive (even inhibiting) in... 

P2 3.11% AI2O3 0-11% Si02 P3 2.99% AI2O3 2.56% Si02 flame oxidation of TiCU+AICI3 + PCI3... 

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