Acetaldehyde reactions atmosphere

There are two ways to produce acetaldehyde from ethanol oxidation and dehydrogenation. Oxidation of ethanol to acetaldehyde is carried out ia the vapor phase over a silver or copper catalyst (305). Conversion is slightly over 80% per pass at reaction temperatures of 450—500°C with air as an oxidant. Chloroplatinic acid selectively cataly2es the Uquid-phase oxidation of ethanol to acetaldehyde giving yields exceeding 95%. The reaction takes place ia the absence of free oxygen at 80°C and at atmospheric pressure (306). The kinetics of the vapor and Uquid-phase oxidation of ethanol have been described ia the Uterature (307,308). 

Transition metal oxides or their combinations with metal oxides from the lower row 5 a elements were found to be effective catalysts for the oxidation of propene to acrolein. Examples of commercially used catalysts are supported CuO (used in the Shell process) and Bi203/Mo03 (used in the Sohio process). In both processes, the reaction is carried out at temperature and pressure ranges of 300-360°C and 1-2 atmospheres. In the Sohio process, a mixture of propylene, air, and steam is introduced to the reactor. The hot effluent is quenched to cool the product mixture and to remove the gases. Acrylic acid, a by-product from the oxidation reaction, is separated in a stripping tower where the acrolein-acetaldehyde mixture enters as an overhead stream. Acrolein is then separated from acetaldehyde in a solvent extraction tower. Finally, acrolein is distilled and the solvent recycled. 

Non-catalyzed reactions have also been performed. For instance, the pyrolysis of glycerol in steam was studied in a laminar flow reactor in the temperature range 923-973 K. Acrolein is the principal product along with acetaldehyde and CO [21]. Reported yields were as high as 52% when pyrolysis was carried in steam at 923 K and atmospheric pressure. 

The OH radical-initiated photooxidation of 2-butanone in a smog chamber produced peroxyacetyl nitrate and acetaldehyde (Cox et al., 1981). Reported rate constants for the reaction of 2-butanone with OH radicals in the atmosphere and in water are 1.15 x lO and 1.50 x 10 cmVmolecule-sec, respectively (Wallington and Kurylo, 1987 Wallington et al, 1988a). The rate constant for the reaction of 2-butanone and OH radicals in the atmosphere at 300 K is 2.0 x 10 cmVmolecule-sec (Hendry and Kenley, 1979). Cox et al. (1981) reported a photooxidation half-life of 2.3 d for the reaction of 2-butanone and OH radicals in the atmosphere. 

Grosjean et al. (1996) investigated the atmospheric chemistry of cyclohexene with ozone and an ozone-nitrogen oxide mixture under ambient conditions. The reaction of cyclohexene and ozone in the dark yielded pentanal and cyclohexanone. The sunlight irradiation of cyclohexene with ozone-nitrogen oxide yielded the following carbonyls formaldehyde, acetaldehyde, acetone, propanal, butanal, pentanal, and a C4 carbonyl. 

Chemical/Physical. Atkinson et al. (2000) studied the kinetic and products of the gas-phase reaction of 2-heptanone with OH radicals in purified air at 25 °C and 740 mmHg. A relative rate constant of 1.17 x 10 " cmVmolecule Sec was calculated for this reaction. Reaction products identified by GO, FTIR, and atmospheric pressure ionization tandem mass spectroscopy were (with respective molar yields) formaldehyde, 0.38 acetaldehyde, L0.05 propanal, X0.05 butanal, 0.07 pentanal, 0.09 and molecular weight 175 organic nitrates. 

Photolytic. Anticipated products from the reaction of 2-nitropropane with ozone or OH radicals in the atmosphere are formaldehyde and acetaldehyde (Cupitt, 1980). 

Hydrogenation of acetic anhydride to acetaldehyde (equation 23) has been demonstrated utilizing cobalt carbonyl under one atmosphere of hydrogen. However, the cobalt complex is short lived. A more efficient cobalt catalyzed reaction with substantial catalyst longevity was realized at a temperature of 190 and 3000 psi pressure CO and hydrogen. The main products were equal amounts of EDA and acetic acid. Upon investigation, this reaction was found exceptionally efficient at a more reasonable 1500 psi pressure provided that the temperature was maintained... 

In addition to the role of atmospheric reactions in the fate of airborne FLAPs, atmospheric chemistry also plays a role in the formation of some of them, most notably formaldehyde and acetaldehyde. Thus, the potential formation of such compounds from the oxidation of precursors in the atmosphere must also be taken into account in their risk assessments. 

The development of new models for the prediction of chemical effects in the environment has improved. An Eulerian photochemical air quality model for the prediction of the atmospheric transport and chemical reactions of gas-phase toxic organic air pollutants has been published. The organic compounds were drawn from a list of 189 species selected for control as hazardous air pollutants in the Clean Air Act Amendments of 1990. The species considered include benzene, various alkylbenzenes, phenol, cresols, 1,3-butadiene, acrolein, formaldehyde, acetaldehyde, and perchloroethyl-ene, among others. The finding that photochemical production can be a major contributor to the total concentrations of some toxic organic species implies that control programs for those species must consider more than just direct emissions (Harley and Cass, 1994). This further corroborates the present weakness in many atmospheric models. 

Current regulatory policies for HAPs target the sources of direct emissions. Over 40% of the HAPs being regulated under Title 111 of the CAAA have atmospheric lifetimes of less than one day. The transformation products of these HAPs with low atmospheric persistence are important for assessing risks to human health, especially for cases where the transformation products are more toxic than the HAP itself. Formaldehyde and acetaldehyde are produced by almost every hydrocarbon photo-oxidation reaction (Kao, 1994). 

The oxidation process is carried out in the temperature range 300— 450°C, and generally studied at atmospheric pressure. Excess air is usually applied (with some exceptions) and substantial amounts of water vapour may be added to the feed. High initial selectivities (>95%) are feasible, and, although some further oxidation (combustion) of the product is unavoidable, yields of 70—90% are reported in the patent literature. The main by-products are carbon oxides, in addition to minor amounts of acrylic acid, acetaldehyde and formaldehyde. Acrylic acid may be a main product depending on specific catalyst properties and reaction conditions, as described in more detail in Sect. 2.2.3. 

Onsager inverted snowball theory (Com.) relation to Smoluchowski equation in, 35 relaxation time by, 34 rotational diffusion and, 36 Ozone in the atmosphere, 108 alkene reactions with, 108 Crigee intermediate from, 108 molozonide from, 108 ethylene reaction with, 109 acetaldehyde effect on, 113 formic anhydride from, 110 sulfur dioxide effect on, 113 sulfuric acid aerosols from, 114 infrared detection of, 108 tetramethylethylene (TME) reaction with, 117... 

The most important synthetic processes are (1) the oxidation of acetaldehyde, and (2) the direct synthesis ftom methyl alcohol and carbon monoxide. The latter reaction must proceed under very high pressure (approximately 650 atmospheres) and at about 250 C. The reaction takes place 111 the liquid phase and dissolved cobaltous iodide... 

The reactions were conducted for the synthesis of dirithromycin according to the following procedure. 2-(2-Methoxyethoxy)acetaldehyde dimethyl acetal (12 g, 2.7 eq) was placed in a three-neck flask equipped with a mechanical stirrer and dissolved in 60 ml of acetonitrile containing 4% water, p-Toluenesulfonic acid (200 mg, 0.04 eq) was added and the mixture was stirred under a nitrogen atmosphere for 3 hours at 30°C, after which, the temperature was adjusted to 23°C. 

Under an atmosphere of nitrogen, a solution of n-butyl lithium in hexane (321 ml, 15%) was added to a solution of diisopropylamine (48.6 g, 0.48 mole) in tetrahydrofuran (1000 ml) at -30°C and the mixture was stirred for one hour. The reaction mixture was then cooled to -72°C and methyl 3,3-dimethyl acrylate (55 g, 0.48 mole) was added to it. Stirring was continued at -65° to -75°C for 30 min. To the resulting mixture, a solution of p-ionylidene acetaldehyde (100 g, 0.458 mole, 9-trans content 80%) was added and the reaction mixture was stirred at -65° to -75°C for 1 h. The reaction mixture was then warmed to 40°C and stirred at this temperature for 3 h. Solvent was removed under vacuum and the reaction mixture was diluted with water (700 ml) and methanol (300 ml). Activated charcoal (4 g) was then added and the mixture was refluxed for 30 min. The heterogeneous mixture was filtered through hyflo and the hyflo bed was washed with methanol (300 ml) and water (150 ml). The aqueous methanolic layer was then extracted with hexanes (2 x 500 ml) and acidified with 10% sulfuric acid to pH 2.80.5. The desired product was then extracted with dichloromethane (2 x 500 ml). The combined dichloromethane layer was washed with water (2 x 300 ml) and concentrated in vacuo to afford the desired isotretinoin. Crystallization from methanol (200 ml) afforded isotretinoin (44 g) in greater than 99% HPLC purity. 

More than 140 different alkenes have been identified in the atmosphere [27]. The sources of alkenes are similar to those for the alkanes with combustion of fossil fuel being a major source. The presence of unsaturated bonds makes these compounds much more reactive than the alkanes. The most persistent member of this class of compounds (ethene) has an atmospheric lifetime of the order of a day, while more typically the lifetimes for alkenes are measured in hours. As a result of their short lifetimes the atmospheric concentrations of alkenes are highly variable and decrease dramatically away from their source locations. The mechanisms of atmospheric oxidation of alkenes have recently been reviewed [55]. As with the alkanes the reaction of OH radicals is an important loss mechanism. This reaction proceeds mainly via addition to the unsaturated bond as illustrated for ethene in Fig. 4. In one atmosphere of air at 298 K the dominant atmospheric fate of the alkoxy radical HOCH2CH2O is decomposition via C - C bond scission, while reaction with O2 makes a 20% contribution [56]. The fate of alkoxy radicals resulting from addition of OH to alkenes is generally decomposition via C - C bond scission [8]. Thus, the OH radical initiated oxidation of propene gives acetaldehyde and HCHO, oxida-... 

The oxidation of ethylene to acetaldehyde using PdCb and CuCb as catalysts undo- an oxygm atmosphere is well known as the Wacker process (Scheme 1), and is one of the most important industrial processes employing transition metal catalysts.This industrial oxidation reaction of ethylene involves the following three stoichiometric reactions. These sequential oxidation and reduction reactions constitute a catalytic cycle. 

In contrast to polymerisates, polycondensates can not be depolymerized under inert conditions. Decomposition usually leads to the destruction of the chemical structure and the monomers. The thermal decomposition of PET starts at about 300°C in an inert atmosphere [25]. Between 320 and 380°C the main products are acetaldehyde, terephthalic acid, and carbon oxides under liquefaction conditions. The amounts of benzene, benzoic acid, acetophenone, C1-C4 hydrocarbons, and carbon oxides increase with the temperature. This led to the conclusion that a P-CH hydrogen transfer takes place as shown in Eigure 25.8 [26]. Today the P-CH-hydrogen transfer is replaced as a main reaction in PET degradation by several analytic methods to be described in the following sections. The most important are thermogravimetry (TG) and differential scanning calorimetry (DSC) coupled with mass spectroscopy and infrared spectroscopy. 

This method finds commercial application in the production of acetaldehyde from acetylene. Mercuric salts in the presence of dilute sulfuric acid act as the catalyst. The reaction has been extended to higher alkylacetylenes, which are obtained in about 60% yield from sodium acetylide and alkyl halides. These compounds are readily hydrated in aqueous solutions of acetone, methanol, or acetic acid to give 80-90% yields of the corresponding methyl ketones, fot example, methyl butyl, methyl amyl, and methyl hexyl ketones. Hydration has been accomplished by passing the acetylenic hydrocarbon and steam over a phosphoric acid catalyst at 150-204° and atmospheric pressure. ... 

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