Oxidation, acetaldehyde carbon monoxide

Other possible chemical synthesis routes for lactic acid include base-cataly2ed degradation of sugars oxidation of propylene glycol reaction of acetaldehyde, carbon monoxide, and water at elevated temperatures and pressures hydrolysis of chloropropionic acid (prepared by chlorination of propionic acid) nitric acid oxidation of propylene etc. None of these routes has led to a technically and economically viable process (6). 

Gas-phase oxidation of propylene using oxygen in the presence of a molten nitrate salt such as sodium nitrate, potassium nitrate, or lithium nitrate and a co-catalyst such as sodium hydroxide results in propylene oxide selectivities greater than 50%. The principal by-products are acetaldehyde, carbon monoxide, carbon dioxide, and acrolein (206—207). This same catalyst system oxidizes propane to propylene oxide and a host of other by-products (208). 

What is the initial source of the free radicals that are so important for oxidant development Calvert and McC igg attempted to answer this question by evaluating the many proposed reactions with their detailed chemical model. Although the actual importance of any particular source will depend on the concentration of pollutants assumed and the time of irradiation they found for a typical mixture (nitric oxide nitrogen dioxide rra/is-2-butene, formaldehyde acetaldehyde carbon monoxide water and methane) that the following reactions were the most important radical sources ... 

Photolytic. Major products reported from the photooxidation of 2,3-dimethylbutane with nitrogen oxides are carbon monoxide and acetone. Minor products included formaldehyde, acetaldehyde and peroxyacyl nitrates (Altshuller, 1983). Synthetic air containing gaseous nitrous acid and exposed to artificial sunlight (A. = 300-450 nm) photooxidized 2,3-dimethylbutane into acetone, hexyl nitrate, peroxyacetal nitrate, and a nitro aromatic compound tentatively identified as a propyl nitrate (Cox et al., 1980). 

Fig. 34, Composition profile of the cool and second stage flames during acetaldehyde oxidation [56] (a) x, Acetaldehyde <, carbon monoxide o, methane , oxygen — temperature, (b) Carbon dioxide +, formaldehyde methanol.

The photo-oxidation of SOa to S03T in the presence of H20 and Oa or NaO has been monitored by e.s.r.841 The photo-oxidation of carbon monoxide by oxygen may be catalysed by illumination of a number of inorganic oxides,842 and in another study it has been shown that the catalytic activity of ZnO for this reaction depends on the contact time of the catalyst with the gases prior to irradiation.843 Flash illumination of TiOz initiates the dehydrogenation of methanol or ethanol to formaldehyde and acetaldehyde, respectively.844 The oxidation of paraffins and olefins to ketones takes place on irradiation of Ti02 in the presence of these... 

Two molecules of lactic acid can be dehydrated to lactide, a cyclic lactone. Then, polymerized to lactide to either heterotactic or syndiotac-tic polylactide, which is also called PLA. Lactic acid can be produced from chemical or biotechnological methods. Chemical synthesis can be based on the hydrolysis of lactonitrile by strong acids, or by base-catalyzed degradation of sugars, oxidation of propylene glycol, or by chemical reactions of acetaldehyde, carbon monoxide, and water at elevated temperatures (Mussatto et al. 2008). 

About half of the wodd production comes from methanol carbonylation and about one-third from acetaldehyde oxidation. Another tenth of the wodd capacity can be attributed to butane—naphtha Hquid-phase oxidation. Appreciable quantities of acetic acid are recovered from reactions involving peracetic acid. Precise statistics on acetic acid production are compHcated by recycling of acid from cellulose acetate and poly(vinyl alcohol) production. Acetic acid that is by-product from peracetic acid [79-21-0] is normally designated as virgin acid, yet acid from hydrolysis of cellulose acetate or poly(vinyl acetate) is designated recycle acid. Indeterrninate quantities of acetic acid are coproduced with acetic anhydride from coal-based carbon monoxide and unknown amounts are bartered or exchanged between corporations as a device to lessen transport costs. 

The reaction is very exothermic. The heat of reaction of propylene oxidation to acrolein is 340.8 kJ /mol (81.5 kcal/mol) the overall reactions generate approximately 837 kJ/mol (200 kcal/mol). The principal side reactions produce acryUc acid, acetaldehyde, acetic acid, carbon monoxide, and carbon dioxide. A variety of other aldehydes and acids are also formed in small amounts. Proprietary processes for acrolein manufacture have been described (25,26). 

Ethane. Ethane VPO occurs at lower temperatures than methane oxidation but requires higher temperatures than the higher hydrocarbons (121). This is a transition case with mixed characteristics. Low temperature VPO, cool flames, oscillations, and a NTC region do occur. At low temperatures and pressures, the main products are formaldehyde, acetaldehyde (HCHOiCH CHO ca 5) (121—123), and carbon monoxide. These products arise mainly through ethylperoxy and ethoxy radicals (see eqs. 2 and 12—16 and Fig. 1). 

The changeover from ROO radicals to HOO radicals and the switch from organic peroxides to HOOH has been shown as temperature is increased in propane VPO (87,141). Tracer experiments have been used to explore product sequences in propane VPO (142—145). Propylene oxide comes exclusively from propylene. Ethylene, acetaldehyde, formaldehyde, methanol, carbon monoxide, and carbon dioxide come from both propane and propylene. Ethanol comes exclusively from propane. 

Acetic acid (qv) can be produced synthetically (methanol carbonylation, acetaldehyde oxidation, butane/naphtha oxidation) or from natural sources (5). Oxygen is added to propylene to make acrolein, which is further oxidized to acryHc acid (see Acrylic acid and derivatives). An alternative method adds carbon monoxide and/or water to acetylene (6). Benzoic acid (qv) is made by oxidizing toluene in the presence of a cobalt catalyst (7). 

Acetic acid is also produced hy the oxidation of acetaldehyde and the oxidation of n-hutane. However, acetic acid from the carhonylation route has an advantage over the other commercial processes because both methanol and carbon monoxide come from synthesis gas, and the process conditions are quite mild. 

The catalyst is similar to that of the Wacker reaction for ethylene oxidation to acetaldehyde, however, this reaction occurs in presence of carbon monoxide. 

Approximately 2.5 million tons of acetic acid is produced each year in the United States for a variety of purposes, including preparation of the vinyl acetate polymer used in paints and adhesives. About 20% of the acetic acid synthesized industrially is obtained by oxidation of acetaldehyde. Much of the remaining 80% is prepared by the rhodium-catalyzed reaction of methanol with carbon monoxide. 

Chemical/Physical. Oxidation in air yields acetic acid (Windholz et ah, 1983). In the presence of sulfuric, hydrochloric, or phosphoric acids, polymerizes explosively forming trimeric paraldehyde (Huntress and Mulliken, 1941 Patnaik, 1992). In an aqueous solution at 25 °C, acetaldehyde is partially hydrated, i.e., 0.60 expressed as a mole fraction, forming a gem-diol (Bell and McDougall, 1960). Acetaldehyde decomposes at temperatures greater than 400 °C, forming carbon monoxide and methane (Patnaik, 1992). 

Photolytic. Major products reported from the photooxidation of butane with nitrogen oxides under atmospheric conditions were acetaldehyde, formaldehyde, and 2-butanone. Minor products included peroxyacyl nitrates and methyl, ethyl and propyl nitrates, carbon monoxide, and carbon dioxide. Biacetyl, tert-butyl nitrate, ethanol, and acetone were reported as trace products (Altshuller, 1983 Bufalini et al, 1971). The amount of sec-butyl nitrate formed was about twice that of n-butyl nitrate. 2-Butanone was the major photooxidation product with a yield of 37% (Evmorfopoulos and Glavas, 1998). Irradiation of butane in the presence of chlorine yielded carbon monoxide, carbon dioxide, hydroperoxides, peroxyacid, and other carbonyl compounds (Hanst and Gay, 1983). Nitrous acid vapor and butane in a smog chamber were irradiated with UV light. Major oxidation products identified included 2-butanone, acetaldehyde, and butanal. Minor products included peroxyacetyl nitrate, methyl nitrate, and unidentified compounds (Cox et al., 1981). 

Irradiation of toluene in the presence of chlorine yielded benzyl hydroperoxide, benzaldehyde, peroxybenzoic acid, carbon monoxide, carbon dioxide, and other unidentified products (Hanst and Gay, 1983). The photooxidation of toluene in the presence of nitrogen oxides (NO and NO2) yielded small amounts of formaldehyde and traces of acetaldehyde or other low molecular weight carbonyls (Altshuller et al, 1970). Other photooxidation products not previously mentioned include phenol, phthalaldehydes, and benzoyl alcohol (Altshuller, 1983). A carbon dioxide yield of 8.4% was achieved when toluene adsorbed on silica gel was irradiated with light X >290 nm) for 17 h (Freitag et ah, 1985). 

In the 1940 s, in addition to these operations, two other processes became important. Acetic acid was made by reacting methanol with carbon monoxide, and acetic anhydride was being made by the ethylidene diacetate process, which in effect is the dehydration of acetic acid to the anhydride by the use of acetylene. Fermentation ethyl alcohol was converted to acetic acid via acetaldehyde as well as by the direct oxidation of ethyl alcohol. A new operation on the Gulf Coast was also based on acetaldehyde. However, the acetaldehyde is made by the direct oxidation of liquefied petroleum gas. A further process for the production of these materials, in which acetaldehyde is oxidized in one step to a mixture of anhydride and acid, was also begun. 

In a separate investigation MargeHs and Roginekii1107 carried nut catalytic oxidation of ethylene at 350° over vanadium pentoxidc. reportedly similar to metallic silver in catalytic properties. TVv asoertainod that carbon dioxide was formed faster from, ethylene oxide, or from acetaldehyde under comparable conditions, than from ethylene itself. Further, they noted the formation of carbon monoxide, and determined that its rate of formation was considerably greater than that of carbon dioxide, increasing still more in the presence of adtk-d ethylene oxide. The addition of ethylene oxide also appeared to depro both ethylene oxide and acetaldehyde formation. They concluded that reactions leading to carbon dioxide and water did not proceed by wav of ethylene oxide, but by way of some other intermediates, and tlmt-this process could occur either on the catalyst surface or in the gas phase. 

Catalysts used to convert ethylene to vinyl acetate are closely related to those used to produce acetaldehyde from ethylene. Acetaldehyde was first produced industrially by the hydration of acetylene, but novel catalytic systems developed cooperatively by Farbwerke Hoechst and Wacker-Chemie have been used successfully to oxidize ethylene to acetaldehyde, and this process is now well established (7). However, since the largest use for acetaldehyde is as an intermediate in the production of acetic acid, the recent announcement of new processes for producing acetic acid from methanol and carbon monoxide leads one to speculate as to whether ethylene will continue to be the preferred raw material for acetaldehyde (and acetic acid). 

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... 

Few chemicals have experienced as long and as successful a career us acetic acid, Acetic acid reluins its importance in (he production of vinyl and cellulose acetates Acetic acid is made industrially by oxidation of acetaldehyde or butane in air, or from methanol and carbon monoxide. 

The recent dramatic increase in the price of petroleum feedstocks has made the search for high selectivities more urgent. Several new processes based on carbon monoxide sources are currently competing with older oxidation processes.103,104 The more straightforward synthesis of acetic acid from methanol carbonylation (Monsanto process) has made the Wacker process obsolete for the manufacture of acetaldehyde, which used to be one of the main acetic acid precursors. Several new methods for the synthesis of ethylene glycol have also recently emerged and will compete with the epoxidation of ethylene, which is not sufficiently selective. The direct synthesis of ethylene... 

Other oxidation products, in addition to those above, have been reported for the oxidation of DMS (I, 2, 16, 22, 23, 28, 35) formic acid, carbon dioxide, carbon monoxide, silanols (Si—OH), cyclic siloxanes, hydrogen, and methanol. Analogously, acetaldehyde and acetic acid are reported as the oxidation products from diethyl silicone at 160°—190° C. 

Reactions involving abstraction from acetaldehyde are just as likely in diethyl ketone oxidation as reactions involving abstraction from formaldehyde in acetone oxidation. The acetyl radical so produced will oxidize as in the oxidation of acetone to give mostly carbon dioxide (from the -carbon atom of diethyl ketone71), but a little decomposition seems to occur since some carbon monoxide does not come from the original carbonyl group of the ketone.71... 

The amounts of acetaldehyde produced approached a maximum with time and the amounts of nitrous oxide also decreased with the % conversion. Since carbon monoxide, carbon dioxide, and methanol increased with time, it seems likely that, parallel to the role of formaldehyde in azomethane oxidation, acetaldehyde was a reactive intermediate. Acetaldehyde removed by such a reaction as... 

Tlie mechanistic approach to the direct syntheses of oxalates is that which has been well established for the ethylene oxidation to acetaldehyde, the so called Wackcr process. We have, first of all, activation of the substrate by coordination, followed by an electron transfer to the metal (which in this case produces the formation of a carbon to carbon bond). The first important effect, therefore, is the activation of carbon monoxide by coordination to palladium. 

---