Carbonaceous radicals

Further reactions occur, including processes catalyzed by the solid products, where the different organic anions give various carbonaceous radicals. The participation of acetate in malonate breakdown has already been discussed above. Decompositions of calcium carboxylates have been used as a method of ketone preparation in organic chemistry. 

Endo et al. investigated the reductive decomposition of various electrolytes on graphite anode materials by electron spin resonance (ESR). In all of the electrolyte compositions investigated, which included LiC104, LiBF4, and LiPFe as salts and PC, DMC, and other esters or ethers as solvents, the solvent-related radical species, which were considered to be the intermediates of reductive decomposition, were detected only after prolonged cathodic electrolysis. With the aid of molecular orbital calculation, they found that the reduction of salt anion species is very difficult, as indicated by their positive reduction enthalpy and that of free solvent (A/4 — 1 kcal mol ). However, the coordination of lithium ions with these solvents dramatically reduces the corresponding reduction enthalpy (A/ —10 kcal mol ) and renders the reaction thermodynamically favored. In other words, if no kinetic factors were to be considered, the SEI formed on carbonaceous anodes... 

Carbonaceous compounds can also form in the absence of a catalyst by free-radical, gas-phase condensation reactions. The formation of this pyrolytic carbon is known in steam-reforming reactors where it can be controlled to some extent by minimizing the free volume within the reactor chamber. This type of carbon does not form readily with methane but can be severe with larger hydrocarbons. The compounds formed by free-radical reactions tend to be quite different from the graphitic carbon formed by metal catalysts. For example, Lee et al. showed that the compounds formed by passing pure, undi-... 

The CsHe desorption was essentially inhibited in the presence of SO2 because sulfur species can react with Fe O radical to form a relatively stable Fe SOs Fe (see Eq. 23), resulting in a significant decline in the density of available adsorption sites for CsH . Simultaneously, the scarcity of a-02 surface species (Fe 02") due to a competitive SO2 adsorption (Eq. 22) leads to a decrease in both rates of propene oxidation and carbonaceous species (CO and CO2) formation. 

In addition to being oxidized by the hydroxyl radical, alkenes may react with the N03 radical as has been described by several investigators (52, 56, 66). Listed in Table I are some of the organic nitrates that have been predicted to be produced via reaction of OH and N03 with isoprene and pro-pene. Analogous compounds would be expected from other simple alkenes and from terpenes such as a- and (3-pinene. Other possible organic nitrates may be produced via the oxidation of aromatic compounds (53, 54) and the oxidation of carbonaceous aerosols (67). Quantitative determination of these species has not been made in the ambient atmosphere. 

Esteve W, Budzinski H, Villenave E (2006) Relative rate constants for the heterogeneous reactions of N02 and OH radicals with polycyclic aromatic hydrocarbons adsorbed on carbonaceous particles. Part 2 PAHs adsorbed on diesel particulate exhaust SRM 1650a. Atmos Environ 40 201-211... 

Various forms of molecular carbon, from ions to radicals, have been detected in the diffuse interstellar medium (ISM) using electronic, rotational, and vibrational spectroscopies (Henning and Salama 1998 Snow and Witt 1995). Discrete absorption and emission bands seen toward diffuse interstellar clouds indicate the presence of numerous two-atom molecules such as CO, CN and C2. In addition to these interstellar features, a large family of spectral bands observed from the far-UV to the far-IR still defies explanation. Currently, it is the general consensus that many of the unidentified spectral features are formed by a complex, carbonaceous species that show rich chemistry in interstellar dust clouds (Ehrenfreund... 

Chemical oxidation reactions and radical-induced hydrophobic-to-hydrophilic aging processes tend to increase the water solubility of OAs and, therefore, are thought to enhance the activity of atmospheric OAs as cloud condensation nuclei (CCN). As discussed by Gysel et al. (2004), at 75-90% of relative humidity (RH) the inorganic fraction dominates the water uptake (59-80%). Nevertheless, under the same conditions of RH, between 20% and 40% of total particulate water is associated with water-soluble organic matter. More data concerning the multiphase aerosol and cloud processes, as well as the chemical reactivity of carbonaceous aerosol components, have been compiled in the reviews of Jacobson et al. (2000), Kanakidou et al. (2005), and Poschl (2005) (and references therein). 

These ESR observations focus on carbon radicals, unpaired electrons in the carbonaceous matrix of the macerals associated with incomplete carbon bonds. In the macerals surveyed here, these radical densities span a substantial range of values from 4 x 1018 radical spins/g-carbon for some subbituminous... 

Le Bras, M., Bourbigot, S., Delporte, C., Siat C., and Le Tallec, Y. 1996. New intumescent formulations of fire retardant polypropylene Discussion about the free radicals mechanism of the formation of the carbonaceous protective material during the thermo-oxidative treatment of the additives. Fire Mater. 20 191-203. 

There are reports on the use of both NMR and ESR for the study of electrode materials [83-85] and bulk products of electrochemical processes [86,87], For instance, 7Li NMR may be found to be very useful for the study of Li intercalation into carbonaceous materials [88], A major advantage of these techniques is that they are applied in situ. The electrochemical cell is, in fact, an NMR tube in which the studied electrode is mounted so that it can be placed within the magnet s cavity. While NMR provides information on the environment of the element studied, within the electrode measured, ESR provides information on the formation and stability of radical ions when formed during the course of an electrochemical process. 

A review is given on the physical and chemical reactions that occur if atomic hydrogen, hydrocarbon radicals, and low-energy ions interact with carbonaceous surfaces. In a first set of experiments the surface loss probabilities of different hydrocarbon radicals are determined in low-temperature plasmas using the cavity technique. The following values were determined / (C2H) = 0.90 0.05, / (C2H3) = 0.35 0.15, and / (CH3, C2H5) < KT2. 

We let a beam of atomic hydrogen and a beam of methyl radicals interact with the film surface simultaneously. This can be considered the simplest of all multi-species experiments first, H and CH3 are the simplest radicalic hydrocarbon species. Second, by restricting ourselves to radicals, the interaction of the beams with the film is purely chemical and expected to be limited to the very surface. Third, the effect of each species separately is already known the previous section described the temperature dependent interaction of CH3 radicals with the a-C H surface. The interaction of atomic hydrogen with carbonaceous materials has been studied extensively in the past by various groups [53,56,57]. A rate equation model describing chemical erosion by atomic hydrogen is well-established [53,58]. 

The chemical dynamics, reactivity, and stability of carbon-centered radicals play an important role in understanding the formation of polycyclic aromatic hydrocarbons (PAHs), their hydrogen-dehcient precursor molecules, and carbonaceous nanostructures from the bottom up in extreme environments. These range from high-temperature combustion flames (up to a few 1000 K) and chemical vapor deposition of diamonds to more exotic, extraterrestrial settings such as low-temperature (30-200 K), hydrocarbon-rich atmospheres of planets and their moons such as Jupiter, Saturn, Uranus, Neptune, Pluto, and Titan, as well as cold molecular clouds holding temperatures as low as 10... 

Slobodin et al. [39] confirmed that thermal decomposition of EPR (equimolar ratio) began at 170 °C and ceased at 360 C. A total 93.66% condensate products, 5.2% gas and 1.14% carbonaceous residue were obtained, mainly at 235 °C. The composition of the gaseous portion, determined by GLC was ethane-ethylene 1.25%, propane 0.81%, propylene 0.98%, butane-butylene 0.99% and butadiene 0.99% by wt. of EPR. The liquid products were separated into five fractions with boiling ranges of 100 C, 100-150 C, 150-200 °C, 200-250 °C, and >250 °C. The fractionation yielded pentane, 1-pentene, 2-methylbutane, 2-methyl-l-butene, 2-methyl-2-butene, isoprene and piperylene of C5 hydrocarbon and hexane, 1-hexane, 2-methylpentane of Cg hydrocarbons. Based on these data, the thermal degradation was proposed to proceed via a free-radical mechanism. A free radical CH3... 

---