Methacrolein, atmosphere

Much like the oxidation of propylene, which produces acrolein and acrylic acid, the direct oxidation of isobutylene produces methacrolein and methacrylic acid. The catalyzed oxidation reaction occurs in two steps due to the different oxidation characteristics of isobutylene (an olefin) and methacrolein (an unsaturated aldehyde). In the first step, isobutylene is oxidized to methacrolein over a molybdenum oxide-based catalyst in a temperature range of 350-400°C. Pressures are a little above atmospheric ... 

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). 

The air oxidation of 2-methylpropene to methacrolein was investigated at atmospheric pressure and temperatures ranging between 200° and 460°C. over pumice-supported copper oxide catalyst in the presence of selenium dioxide in an integral isothermal flow reactor. The reaction products were analyzed quantitatively by gas chromatography, and the effects of several process variables on conversion and yield were determined. The experimental results are explained by the electron theory of catalysis on semiconductors, and a reaction mechanism is proposed. It is postulated that while at low selenium-copper ratios, the rate-determining step in the oxidation of 2-methylpropene to methacrolein is a p-type, it is n-type at higher ratios. 

In the present work a large set of actinic spectra recorded in the EUPHORE chamber under various atmospheric conditions has been obtained and used for the calculation of photolysis frequencies of 17 organic carbonyl compounds. From a statistical analysis of the photolysis frequencies calculated for the compounds an analytical form for Jfd) has been derived. For unsaturated compounds (methyl vinyl ketone, methacrolein, acrolein and crotonaldehyde) < ) g is negligible, although those cxompounds possess absorption spectra reaching the near visible. 

Pedersen and Sehested (2002) showed that the aqueous-phase reaction of isoprene with ozone was insignificant for the processing of isoprene in the atmosphere. They estimated the overall and individual lifetimes of isoprene due to reactions with ozone and the hydroxyl radical, at 25 "C and typical in-cloud conditions. The results (Table 3) indicate that clouds generally should not contribute much to the processing of isoprene in the atmosphere. Only in the aqueous phase, were the lifetimes of isoprene due to reactions with ozone and with OH radicals comparable. Similar conclusions were drawn for methyl vinyl ketone, while for methacrolein the clouds could reduce the overall atmospheric lifetime by 50 %. 

Polymer-supported catalysts were suspended in dry CH2CI2 in a Schlenk tube under an argon atmosphere and the dienophile was added. The suspension was shaken and periodically monitored by GC. Then, the polymer was filtered, washed with dry CH2CI2 and kept under an argon atmosphere to be reused. The solvent and, in its case, the non reacted methacrolein were evaporated under reduced pressure and the cycloadducts were separated and purified by means of column chromatography on silica gel. After separation, the enantiomeric composition was analyzed by NMR in the major endo or exo cycloadduct using Eu(hfc)3. 

Ethylene and synthesis gas are used to produce propionaldehyde and formaldehyde. These aldehydes then are reacted in the presence of a catalyst to form methacrolein. The methacrolein reacts with atmospheric oxygen to form meth-acrylic acid in a catalytic multitubular reactor. The methacrylic acid is separated from water (a byproduct) and purified it then reacts with methanol to form MMA. The byproducts are incinerated on-site to recover the energy in the process [41]. 

OH and NOx do not appear in the net reaction as they are regenerated in other reactions. Notably, atmospheric oxidation of RH (at sufficient NOx) results in the production of ozone and a carbonyl that can undergo further photochemistry. If RH is the slowly reacting methane (typical lifetime, about 8 y), the carbonyl product is formaldehyde (HCHO). If RH is the more reactive hydrocarbon isoprene (CH2=C(CH3)CH=CH2 typical lifetime, 1-2 h) the net reaction produces two carbonyl products formaldehyde and a 4-carbon carbonyl, either methacrolein (MAC CH2=C(CH3)CH0), or methylvinyl ketone (MVK CH2=CHC(0)CH3) depending on the site of OH attack. 

The oxidation of isoprene, CH2=CHC(CH3)=CH2, in the atmosphere has not yet been fully delineated and thus remains speculative. Hanst et al. (1980) have discussed some of several possibilities. The successive addition of OH and 02 to either of the two double bonds of isoprene may be modeled in analogy of that to propene and is expected to give formaldehyde and methacroleine or formaldehyde and methyl vinyl ketone as the products. The reaction of isoprene with ozone is expected to produce dioxirane and... 

Montzka, S. A., Trainer, M., Goldan, P. D., Kuster, W. C., and Fehsenfeld, F. C. (1993) Isoprene and its oxidation products, methyl vinyl ketone and methacrolein, in the rural atmosphere, J. Geophvs. 

Attack of NO3 on isoprene apparently proceeds in much the same manner, but there is considerable controversy about the precise reaction pathway because of the variety of peroxy radicals that can be formed. The products, such as 4-nitroxy-2-methyl-l-butan-3-one and methacrolein, are consistent with the initial addition of NO3 to the terminal carbon atoms to form nitro-oxy-peroxy radicals in the presence of oxygen apparently the NO3 adds preferentially to position 1 (Fig. 12). 3-methyl-4-nitroxy-2-butenal was found as the main product in these experiments. The nitro-oxy-peroxy radicals can react with NO2, in the presence of O2, to yield thermally unstable nitroxy-peroxynitrate compounds. One particularly important feature of the addition of NO3 is the extent to which the initial adduct, which might eliminate NO2 to form an epoxide, is actually converted to the nitro-oxy-peroxy radicals in the atmosphere. 

Warneke, C, Holzinger, R., Hansel, A., Jordan, A., Lindinger, W., Poschl, LF., Williams, J., Hoor, P, Fischer, H., Crutzen, P.J., Scheeren, H.A., Lelieveld, J. (2001) Isoprene and its oxidation products methyl vinyl ketone, methacrolein, and isoprene related peroxides measured online over the tropical rain forest of Surinam in March 1998. Journal of Atmospheric Chemistry, 38,167-185. 

Photooxidation of isoprene in the atmosphere was thought to yield only lighter and more volatile products such as formaldehyde, methacrolein, and methyl vinyl ketone. Evidence that the formation of hygroscopic polar products such as 115 can give rise to aerosols by gas-to-particle formation processes has opened a new panorama for the role of isoprene in the atmosphere. Under simulated atmospheric conditions, photooxidation of isoprene by ozone was shown to be relatively slow and to occur mainly by reaction with OH radicals [65]. Furthermore, when the OH -initiated... 

Crounse JD, Knap HC, 0ms0 KB, J0rgensen S, Paulot F, Kjaerdaard HG, Wennberg PO (2012) Atmospheric fate of methacrolein 1 peroxy radical isomerization following addition of OH and O2. J Phys Chem A 116(24) 5756-5762... 

Recently, it has been reported that mechanical-phase mixtures of a phosphomolybdic cesium salt containing V and Te as counter-cations and a-La2Mo209 (LM) or fl-La2Moi,9Vo,i08.95 (LMV) have been studied as catalysts for the partial oxidation of isobutane into MAA and methacrolein. The catalysts with 50 wt.% of LMV in the phase mixture appeared to be the most efficient, with selectivity and yield into MAA of 71% and 12%, respectively, at 360°C and atmospheric pressure. ... 

The only available experimental data concerning the atmospheric chemistry of 4-heptanol come from the relative rate study by Chew et al. (1998) of the kinetics of the reaction with NO3 radicals at 298 K. Methacrolein was used as the reference compound with (NO3 methacrolein) = 3.4 x 10" cm molecule" s (Atkinson et al., 2006). Recognizing possible interferences associated with reaction of 4-heptanol with N2O5 (gas-phase or heterogeneous) to form nitrates, gives an upper limit of kiNOs 4-heptanol) < (6.2 2.1) x 10" cm molecule" s". See table II-B-37. 

The reaction of 3-methyl-3-buten-2-one with OH likely plays an important role in the atmospheric oxidation of this species. A lifetime of about 2 h is predicted, using the rate coefficient estimated in this section. By analogy to the stmcturally similar methacrolein, hydroxyacetone is anticipated as a major end product, with CO2 and CH2O as important co-products. Reaction with NO3 may also play a minor role in polluted nighttime conditions (lifetime of about 10 h for [NO3] 3 x 10 molecule cm ). Lifetimes for... 

Unsaturated organic acids(e.g., acrylic acid, CH2=CHC(0)0H and its derivatives) are produced as minor products in the ozonolysis of dienes, and from the OH-initiated oxidation of unsaturated aldehydes. The most important examples in the atmosphere involve the formation of methacrylic and acrylic acids from the ozonolysis of isoprene (Orzechowska and Paulson, 2005a) and the formation of methacrylic acid from the oxidation of methacrolein, itself a by-product of isoprene oxidation ... 

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