Oxidation of acrolein and methacrolein

The liquid phase catalytic oxidation of acrolein and methacrolein has been the subject of various investigations [35—38]. Considering the natural tendency of reactants and products to become polymerized as well as the sensitivity of chain oxidations to inhibitors, it is not surprising that the findings of the different investigations are sometimes rather conflicting. Nevertheless, the primary oxidation products are exactly analogous to those of saturated aldehyde oxidation. Only the acid yields are affected, mainly as the result of the lack of acid stability. The overall scheme for the oxidation of acrolein can be written as 

The presence of the intermediate X has been shown [37] and its decomposition into acrylic acid has been examined. 

In the case of acrolein oxidation in the presence of cobalt acetyl-acetonate, Co(Acac)3, Table 5 gives the results obtained with different solvents [37]. The influence of solvents on both rate and selectivity may occur in a complex manner. Free acid selectivity depends in particular on the stability of this acid, because the oxidation of acrolein primarily produces acid almost quantitatively. Consequently, in a benzene—nitrobenzene mixture, acid is obtained with an 80% selectivity with conversions of 40% [39,40]. 

The influence of a catalyst on the rate of oxidation may occur in two ways, either by direct interaction with aldehyde or by the catalytic decomposition of peracid or X peroxide. Initiation by aldehyde—catalyst 

It is generally accepted that there is the intermediate formation of a coordination complex. Cooper and Waters [41] propose, for initiation by divalent cobalt, the steps 

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The oxidation of acrolein and methacrolein over 12-heteropoIymolybdates has been proposed to proceed by the reaction mechanism shown by Eq. (4). ... 

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 ... 

Methacrolein and Methacrylic Acid. A two-stage technology, essentially the same as the propylene oxidation process for the manufacture of acrolein and acrylic acid, was developed to oxidize isobutylene to methacrolein and methacrylic acid 949-951 Two different molybdenum-based multicomponent catalysts are used. In a typical procedure949 isobutylene is reacted with excess steam and air (5 30 65) at about 350°C to produce a mixture of methacrolein and methacrylic acid with 80-85% selectivity at a conversion of 98%. In the second stage this reaction mixture is oxidized at slightly above 300°C to yield methacrylic acid (80% selectivity at >90% conversion). 

Solid heteropoly compounds are suitable oxidation catalysts for various reactions such as dehydrogenation of O- and N-containing compounds (aldehydes, carboxylic acids, ketones, nitriles, and alcohols) as well as oxidation of aldehydes. Heteropoly catalysts are inferior to Mo-Bi oxide-based catalysts for the allylic oxidation of olefins, but they are much better than these for oxidation of methacrolein (5). Mo-V mixed-oxide catalysts used commercially for the oxidation of acrolein are not good catalysts for methacrolein oxidation. The presence of an a-methyl group in methacrolein makes the oxidation difficult (12). The oxidation of lower paraffins such as propane, butanes, and pentanes has been attempted (324). Typical oxidation reactions are listed in Table XXXI and described in more detail in the following sections. 

In the past, acrolein was produced by the gas phase condensation of acetaldehyde with formaldehyde on sodium silicate, until it was supplanted by the catalytic oxidation of propylene. Early catalysts based on cuprous oxide were only sufficiently selective at low conversions of propylene. The real breakthrough came with the discovery made by Sohio of bismuth molybdate catalysts, developed into formulations specifically optimized for the manufacture of acrylonitrile, acrolein, and methacrolein. 

To conclude this summary of findings concerning unsaturated aldehydes, a comparison can be made between the rates obtained under the same conditions for crotonaldehyde, acrolein, and methacrolein [35] (Table 8) it can be seen that the rates of oxidation are fairly similar. Under the same conditions, butyraldehyde proves to be much more oxidizable. 

The patent to Hearne and Adams (87) gives the results of oxidation of propylene and the butenes over cuprous oxide. Propylene forms mainly acrolein, and isobutene forms methacrolein, while the normal butenes give methyl vinyl ketone, as well as small amounts of other products. Table VIII shows products and selectivities obtained with... 

Inoue, Kida and Imoto [252] found that the oxidation of unsaturated aldehydes such as cinnamaldehyde and acrolein proceeded much more slowly than did oxidation of the saturated substrates in the presence of copper-iron-polyphthalocyanine. As in the case of the saturated acids the products were a mixture of the peracid and the corresponding carboxylic acid. Other groups have recently investigated the oxidation of unsaturated aldehydes in the presence of metal complexes [253-260]. Methacrylic acid and acetic acid were formed in the copper naphthenate catalyzed oxidation of methacrolein [255]. The oxidation of acrolein to acrylic acid was catalyzed by Co, Ni, Mn and Cu acetates [256]. It was found that at concentrations of acrolein in... 

The performance of many metal-ion catalysts can be enhanced by doping with cesium compounds. This is a result both of the low ionization potential of cesium and its abiUty to stabilize high oxidation states of transition-metal oxo anions (50). Catalyst doping is one of the principal commercial uses of cesium. Cesium is a more powerflil oxidant than potassium, which it can replace. The amount of replacement is often a matter of economic benefit. Cesium-doped catalysts are used for the production of styrene monomer from ethyl benzene at metal oxide contacts or from toluene and methanol as Cs-exchanged zeofltes ethylene oxide ammonoxidation, acrolein (methacrolein) acryflc acid (methacrylic acid) methyl methacrylate monomer methanol phthahc anhydride anthraquinone various olefins chlorinations in low pressure ammonia synthesis and in the conversion of SO2 to SO in sulfuric acid production. 

Monodentate dipolarophiles such as acrolein, methacrolein, and a-bromoacrolein could be successfully utilized in the l ,J -DBFOX/Ph-transition metal complex-catalyzed asymmetric nitrone cycloadditions [76]. The reactions of N-benzylideneani-line N-oxide with acrolein in the presence of the nickel(II) aqua complex R,R-DBF0X/Ph-Ni(C104)2 3H20 (10mol%) and MS 4 A produced a mixture of two regioisomers (5-formyl/4-formyl regioisomers ca 3 1). However, enantio-... 

Catalytic oxidation and ammoxidation of lower olefins to produce a,/3-unsaturated aldehyde or nitrile are widely industrialized as the fundamental unit process of petrochemistry. Propylene is oxidized to acrolein, most of which is further oxidized to acrylic acid. Recently, the reaction was extended to isobutylene to form methacrylic acid via methacrolein. Ammoxidation of propylene to produce acrylonitrile has also grown into a worldwide industry. 

The conversion of isobutene to methacrolein is closely related to the selective oxidation of propene to acrolein and demands similar catalysts. It has been verified that the same mechanism applies, involving a symmetrical allylic intermediate, viz. 

Methacrylic acid is produced by a number of different processes, one of which is based on the oxidation of isobutene (or of t-butyl alcohol) via the intermediate formation of methacrolein (Equation 32). The general features and the catalyst for the first-stage process are not dissimilar to those for acrolein production, whereas the oxidation of methacrolein to MMA differs in that it is catalyzed by... 

There is no direct experimental evidence for this complex decomposition and it may well occur by several steps [107]. However, substantial yields of unsaturated carbonyl compounds are formed particularly at high pressures [78] under initial reaction conditions where cool flames propagate. For example, the cool-flame oxidation of 2-methylpentane at 525 °C and 19.7 atm in a rapid compression machine [78] yields no less than 14 unsaturated carbonyl compounds viz acrolein, methacrolein, but-l-en-3-one, pent-2-enal, pent-l-en-3-one, pent-l-en-4-one, trans-pent-2-en-4r one, 2-methylbut-l-en-3-one, 2-methylpent-l-en-3-one, 4-methylpent-l-en-3-one, 2-methylpent-l-en-4-one, 2-methylpent-2-en-4-one, 2-methyl-pent-2-enal and 4-methylpent-2-enal. Spectroscopic studies of the preflame reactions [78] have shown that the unsaturated ketones account for ca. 90 % of the absorption which, occurs at 2600 A. At lower initial temperatures and pressures acrolein and crotonaldehyde are formed from n-pentane [69, 70] and n-heptane [82], and acrolein is also formed from isobutane [68]. 

The results of pyrolysis of polypropylene in air depends on the pyrolysis heating rate because the pyrolysis process competes with the oxidation [108], By heating between 120° C and 280° C in air, polypropylene is reported to generate ethene, ethane, propene, propane, isobutene, butane, isobutane, pentadiene, 2-methyl-1-pentene, 2,4-dimethyl-1-pentene, 5-methyl-1-heptene, dimethylbenzene, methanol, ethanol, 2-methyl-2-propene-1-ol, 2-methylfuran, 2,5-dimethylfuran, formaldehyde, acetaldehyde, acrolein, propanal, methacrolein, 2-methylpropanal, butanal, 2-vinylcrotonaldehyde, 3-methylpentanal, 3-methylhexanal, octanal, nonanal, decanal, ethenone, acetone, 3-buten-2-one, 2-butanone, 1-hydroxy-2-propanone, 1-cyclopropylethanone, 3-methyl-2-buten-2-one, 3-penten-2-one, 2-pentanone, 2,3-butanedione [109]. 

Multitubular reactors are mainly used in gas-phase partial oxidation processes, such as the air oxidation of light olefins, paraffins, and aromatics. Examples of chemistries where these reactors are used include the partial oxidation of methanol to formaldehyde, ethylene to ethylene oxide, ethylene and acetic acid to vinyl acetate, propylene to acrolein and acrylic acid, butane to maleic anhydride, isobutylene to methacrolein and methacrylic acid, and o-xylene to phthalic anhydride. An overview of the multitubular reactor process for the partial oxidation of n-butane to maleic anhydride is given here. 

Cycloaddition The [2+3] cycloaddition of N-benzylidene N-oxide with a,f)-un-saturated carbonyl compounds has been promoted by catalytic amounts of ATPH (Scheme 6.55) [75]. ATPH was effective both in rate enhancement and in improving the regioselectivity. Cycloaddihon of N-benzylidene N-oxide and acrolein with 10 mol% ATPH proceeded at O fi to give cycloadducts 86 and 87 quantitatively in a ratio of >99 1. Methacrolein, crotonaldehyde, and 3-bulcn-2-onc undergo cycloaddition with similar effectiveness, but methyl acylate is not reactive when ATPH is used. 

In 1979, Koga and coworkers disclosed the first practical example of a catalytic enantioselective Diels-Alder reaction [44] promoted by a Lewis acidic complex, presumed to be menthoxyaluminum dichloride (1), derived from menthol and ethylaluminum di chloride, whose structure remains undefined [45]. This complex catalyzed the cycloaddition of cyclopentadiene with acrolein, methyl acrylate, and methacrolein with enantioselectivities as high as 72% ee. Oxidation of 2 (predominantly exo) followed by recrystallization actually lowered the ee ... 

Vapor-phase aerobic oxidations of lower olefins, e. g. propylene to acrolein or acrylic acid and isobutene to methacrolein or methacrylic acid, are well-established bulk chemical processes [1,2], They are usually performed over oxidic catalysts, such as bismuth molybdate or heteropoly compounds, although the scope of these allylic oxidations is limited to olefins that cannot form 1,3-dienes via oxidative dehydrogenation. Thus 1- and 2-butene are converted to butadiene, and methylbutenes to isoprene, and with higher olefins complex mixtures result from further oxidation. Hence, such methodologies are not relevant in the context of fine chemicals. 

Selective reduction of the carbonyl group of a,/S-unsaturated aldehydes and ketones has been achieved by a vapor-phase hydrogen transfer reaction using saturated primary and secondary alcohols as hydrogen donors. The preferred catalyst for the reaction, which is reversible, is magnesium oxide. Application to the reduction of acrolein to allyl alcohol, methacrolein to methallyl alcohol, crotonaldehyde to crotyl alcohol, and methyl isopropenyl ketone to 3-methyl-3-buten-2-ol is described. 

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