Volatile formation

These authors proposed a reaction mechanism with P-carotene monoepoxides and diepoxides as intermediates for volatile formation. 

Mercke P, Kappers IF, Verstappen FWA, Vorst O, Dicke M, Bouwmeester HJ (2004) Combined transcript and metabohte analysis reveals genes involved in spider mite induced volatile formation in cucumber plants. Plant Physiol 135 2012-2024... 

Ealdt J, Arimura G, Gershenzon J, Takabayashi J, Bohlmann J (2003) Functional identification of AtTPSOS as ( )-P-ocimene synthase a monoterpene synthase catalyzing jasmonate- and wound-induced volatile formation in Arabidopsis thaliana. Planta 216 745-751... 

Ten aspects of the Maillard reaction will be considered in this chapter the effect on a,, on pH, on redox potential, on solubility, on texture, on foamability and foam stability, on emulsifying power, on volatile formation on storage, on binding of volatiles, and on other functionalities. The third of these has received by far the most attention and this is reflected here. 

Volatile formation has been used widely as a means of following deterioration on storage. A recent example is the following. 

Cotton Ammonium phosphates are the most effective FRs for cotton as first identified by Gay-Lussac in 1821 and still widely used. All phosphates on heating release phosphoric acid, which catalyses dehydration reactions of cellulose to yield char at the expense of volatiles formation reactions.50 However, ammonium phosphates like mono- or diammonium phosphates are water soluble, hence applicable as nondurable treatments only. Ammonium bromide can be used in combination with ammonium phosphates to provide some vapor-phase FR action. Other examples include borax and boric acid, ammonium sulfamate, and sulfates. These nondurable finishes are useful for disposable fabrics, insulation, wall boards, theatrical scenery, packaging material, paper, etc. Ammonium polyphosphates (APPs) are used in combination with urea to provide semidurable finishes and by curing at 160°C, when some phosphorylation can occur. Semidurable finishes are very useful for materials that may not need frequent washings, e.g., mattresses, drapes, upholstery, carpets, etc. Some commercial examples of semidurable finishes include Flammentin FMB (Thor Specialities), Pyrovatim PBS (Ciba, now marketed by Huntsman), etc.26... 

Several problems have been associated with the comparison of genotypes for their production of induced volatiles when other differences between the genotypes can not be controlled (23). For example, differences may exist in direct defense between genotypes that cause differences in developmental rate of herbivores that may lead to differences in volatile formation. To circumvent this problem, in addition to spider mite infestation, we used jasmonic acid treatment in a comparison between seven cucumber genotypes. Earlier research had shown that jasmonic acid treatment mimics the effect of spider mite infestation in several plant species. Different cucumber genotypes... 

Molecular weight decrease and volatile formation above 300°C... 

Degradation of polystyrene without volatile formation (below 300°C)... 

In order to obtain further evidence on the mechanism of thermal degradation of polystyrene, several workers have recently studied the decrease in molecular weight occurring below 300°C. In this temperature range, in fact, volatile formation is negligible and it was hoped that the degradation kinetics would be easier to interpret. 

Polyethylene oxide reactions were thoroughly investigated by Fisher etal. [376]. The G values for crosslinking, chain scission and volatile formation for electron irradiation at 14°C and a dose rate of 600 Mrad h 1 are given in Table 27. To account for these values, the mechanism proposed was... 

Isotactic polymethylmethacrylate has been shown to isomerize into the atectic form under the effect of electrons [404] or 7-rays [405]. The yield of isomerization is higher with ionizing radiation than with UV irradiation [405], as is the main-chain scission yield the G value for volatile formation, on the other hand, is lower for 7 than for UV irradiation. The isomerization has therefore been attributed to main-chain scission followed by recombination of the radicals in the cage. This isomerization is completely inhibited in the presence of ethyl mercaptan [406]. 

The main-chain scission yield was recently compared at room and liquid nitrogen temperatures [415] in the presence of a large number of additives known as radical, cation or electron scavengers. The results are given in Table 31. The protection index, in this case defined as 100(7V0 — N)/N where N0 and N are the number of scissions per chain in the absence and in the presence of additive, respectively, is nearly independent of the irradiation temperature marked protection is observed for all the additives studied with the exception of nitrous oxide. It must therefore be concluded that the mechanism of main-chain scission is identical at room and liquid nitrogen temperatures and that ions and radicals are involved in the radiolysis. A detailed study of the effect of ethyl mercaptan on main-chain scission and volatile formation was then undertaken [395]. About 75% protection of main-chain scission was obtained at 313 and at 77°K when the polymer contained 1.49 wt. % of ethyl mercaptan the protection index increases to 90% for concentrations of the order of 10 wt. %. The yield of volatile products was, however, unaltered by the presence of 1.5 wt. % ethyl mercaptan. 

A different mechanism can be proposed in agreement with the recent experimental results. Side- and main-chain scission are clearly related since a one-to-one ratio is observed at room temperature and at 77°K. Main-chain scission, however, is inhibited in the presence of ethyl mercaptan whereas volatile formation is unchanged. This means that side-chain scission precedes and induces main-chain scission. Negative and positive charges are involved since anions and cations of acridine [395,... 

Vazquez, P.A.L., Qian, M.C., and Torres, J.A. 2007. Kinetic analysis of volatile formation in milk subjected to pressure assisted thermal treatments. Journal of Food Science 72 E389-E398. 

The release of volatile compounds starts in the H2 plasma when the temperature of the coal particles reaches about 1220K(Beiersetal., 1985). This critical temperature of volatiles formation is almost independent of the plasma-gas temperature. The temperatme of the coal particles remains fixed during the intensive generation of volatile compounds, which prevents effective heat exchange between the particles and the plasma gas. Coal-to-carbon conversion, therefore, also remains almost fixed at different plasma-gas temperatures. While C2H2 is a major product of plasma coal pyrolysis in Ar and H2, conventional by-products are... 

Research described in this paper focuses on the second step of the gasification process, and details the effects of temperature and residence time on product gas formation. Cellulose is used as a feedstock for pyrolytic volatiles formation. Earlier papers (JS.M) have discussed the effect of steam on cellulose pyrolysis kinetics. Two recent papers (1, 1 6) presented early results on pelletized red alder wood pyrolysis/gasification in steam. Future papers will discuss results using other woody materials, crop residues, and manures (17,1 ). Research to date indicates that all biomass materials produce qualitatively similar results in the gasification reactor described in the following section of this paper. Effects of pressure on the heat of pyrolysis of cellulose are also discussed as a prelude to future papers detailing the more general effects of pressure on reaction rates and product slates. 

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