Oxidation isoprene

The first successful example of a catalytic ring-expansion carbonylation was reported by Aumann et al. in 1970s [20,21], Here, isoprene oxide was allowed to react with CO in the presence of [Rh(cod)Cl]2 to give an fi,y-unsaturated lactone (Scheme 2). Soon after their report, the carbonylation of styrene oxide to yield the corresponding /1-lactone was demonstrated by using RhCl(CO)(PPh3)2 [22], The scope of this method is, however, quite... 

The oxidation of isoprene, one of the most common biogenic hydrocarbons, is expected to lead to the formation of some MPAN. Thus, as treated earlier, one of the major products of isoprene oxidation is methacrolein. Its subsequent oxidation by OH is expected to form MPAN ... 

Biesenthal, T. A., and P. B. Shepson, Observations of Anthropogenic Inputs of the Isoprene Oxidation Products Methyl Vinyl Ketone and Methacrolein to the Atmosphere, Geophys. Res. Lett., 24, 1375-1378 (1997). 

Helmig, D., J. Greenberg, A. Guenther, P. Zimmerman, and C. Geron, Volatile Organic Compounds and Isoprene Oxidation Products at a Temperate Deciduous Forest Site, . 1. Geophys. Res., 103, 22397-22414 (1998b). 

Kleno, J. and Wolkoff, P. (2004) Changes in eye blink frequency as a measure of trigeminal stimulation by exposure to limonene oxidation products, isoprene oxidation products and nitrate radicals. International Archives of Occupational and Environmental Health, 77 (4), 235-43. 

FIGURE 10.2 Mechanistic diagram of OH-initiated isoprene oxidation detailed reaction pathways and major products. 

Recently, the explicit oxidation mechanism of isoprene initiated by OH, O3, NO3, and Cl, incorporating the most recent laboratory and theoretical studies, has been evaluated using a box model [69]. The updated mechanism provides explicit reaction steps and detailed intermediates for isoprene oxidation and facilitates more accurate modeling of isoprene photochemistry in the atmosphere. 

Studies have been made of the rearrangement of oxiranes containing an acetylenic side-chain, isoprene oxides, and 7,5-unsaturated oxiranes. ... 

Tricyclen-10-oic acid was oxidized (KMn04) to the 3-ketone, which was cleaved to 5-bromocamphan-2-one-10-oic acid 506 the tosylhydrazone of tricyclen-3-one (and also of isotricyclen-2-one) underwent Bamford-Stevens decomposition in ROH solvent to the 3- or 2-OR compounds 507 8-bromotricyclene was coupled (RLi) with isoprene oxide to give a sesquiterpene precursor.508 e/ido-3-Amino-... 

In this contribution the re-evaluated yields from the OH-radical initiated oxidation of benzene, toluene, p-xylene, and initial results of new simulation chamber experiments on prompt glyoxal formation from isoprene oxidation are presented. A detailed discussion of sources, sinks and their uncertainties to model atmospheric concentrations of glyoxal is presented, and exemplifies how basic research in environmental simulation chambers besides giving input for photochemical models also triggers advancements with measurement techniques for field observations. The integration of laboratory and field observations by models in turn will guide future research on atmospheric chemical processes. 

Chambers were also used in the research on heterogeneous reactions of isoprene and of other atmospheric trace compounds. As already discussed, Czoschke et al. (2003) studied the formation of SOA from products of isoprene oxidation in 500 dm Teflon-bag chambers at UNC. FoUcers et al. (2003a,b,c) studied the partitioning and influence of dicarboxylic acids on aerosol formation in Aerosol Chamber in Julich. Shantz et al. (2003) investigated the growth of aqueous organic particles and cloud condensation nuclei in the CALSPAN chamber, linuma et al. (2004 paper submitted to this book) studied the reaction of a-pinene with ozone on acidic particles in the Leipzig tent-chamber (9 m ). 

This extensive data set showed good agreement with a Master Chemical Mechanism for isoprene oxidation. In addition, one of the predictions of the mechanism is that at low NOx levels, like those seen in Surinam, isoprene hydroperoxides (six isomers, e.g. HOCH2C(OOH)(CH3)CH=CH2) will accumulate. It was noted that correlations between isoprene and other VOCs (different times of day and altitude) were greatest with MlOl ", which could be indicative of isoprene hydroperoxides. This result is an example where PTR-MS analysis can detect previously unmeasured VOCs, although as mentioned above, verification of the identity of unknown positive ions requires complementary methods (e.g. GC-MS). 

Reactions of alkyl-lithiums with isoprene oxide (186) yield (3,7-disubstituted allylic alcohols of Z configuration. The proportion of Z-isomer can be increased by using a base thus the formation of (187) from (186) and Bu Li is improved fron an isomer yield of 88% in hexane at 0°C (76% overall yield of allylic alcohols) to an isomer yield of 97% (73% overall) in the presence of Bu"OLi. 

Identification of (a) products of isoprene oxidation, (b) products of toluene/NOx chamber experiments... 

In addition to the important role biogenic terpenes play in gas-hase chemistry, their impact also extends to heterogeneous air chemistry. Although Went (1960) linked the formation of the blue haze over coniferous forests to the biogenic emission of 20 monoterpenes over 40 years ago, it was not until recently that terpenes received their due attention with respect to their role in secondary organic aerosol (SOA) formation. O Dowd et al. (2002) reported that nucleation events over a boreal forest were driven by the condensation of terpene oxidation products. Formaldehyde (HCHO) is a high-yield product of isoprene oxidation. The short photochemical lifetime of HCHO allows the observation of this trace gas to help constrain isoprene emissions (Shim et al. 2005). 

Outstanding progress has been made in RO2 chemistry, both in terms of reactivity and reaction mechanisms. The data have been compiled and reviewed [1], and further progress in defining structure-reactivity aspects for more complex VOCs is documented in this Final Report. For example, the mechanism of isoprene oxidation involving six different RO2 radicals, for low NOx and high NOx conditions, has recently been validated against observations. 

The products of the reaction with OH, especially in the absence of NOx, and of the reaction with O3 have been investigated. In addition rate coefficients for the reactions with OH and O3 were measured for some recently identified products of the isoprene oxidation. The concentrations of the reactants were in the low ppm range (usually 1-10 ppm). OH radicals were generated either by continuous UV photolysis of H2O2 (254 nm) with or without NO present, or by photolysis of CH3ONO. 

Kinetics of reactions of isoprene oxidation products with OH and O3... 

This high reactivity towards the important atmospheric photo-oxidants, probably valid also for similar isoprene oxidation products like unsaturated hydroxy carbonyls, hydroxy nitrates or hydroxy hydroperoxides, is an indication that these reactions need more consideration in laboratory experiments as well as photooxidation models. 

The production of formaldehyde in appreciable yield is an important feature of isoprene oxidation. Large amounts of isoprene are naturally emitted from trees, making formaldehyde a prominent by-product. In addition, HCHO photolysis provides a significant source of HOj radicals that are necessary for hydrocarbon oxidation. The other products, glycolaldehyde, methylglyoxal, and hydroxyacetone, react with OH radicals and can partly undergo photolysis, but the reaction products and their relative yields are not fully known. 

Similarly, the isomeric isoprene oxidation products, methyl vinyl ketone and methacrolein, could also be distinguished by adjusting CID voltage in the PTR-LIT-MS. Their limits of detection are about 100 ppt. 

Keywords Hydroxyl radical Isoprene oxidation Field measurements Box model Biogenic emissions... 

Experimental Indication for OH Formation During Isoprene Oxidation. 63... 

In this chapter we examine the mechanism for the OH initiated oxidation of isoprene under low NO levels (NO < 50 ppt). At higher NO levels, although it is likely that there are still processes that are missing within atmospheric models (e.g. [3]), isoprene oxidation chemistry is simplified somewhat by the loss of the isoprene-derived peroxy radicals being dominated by reaction with NO. Under low NO c conditions the fate of these peroxy radicals is much less certain. New insights into the isoprene mechanism have been derived using a combinatirHi of ... 

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