Methacrylic acid hydroformylation

Propylene-Based Routes. The strong acid-catalyzed carbonylation of propylene [115-07-1] to isobutyric acid (Koch reaction) followed by oxidative dehydration to methacrylic acid has been extensively studied since the 1960s. The principal side reaction in the Koch reaction is the formation of oligomers of propylene. Increasing yields of methacrylic acid in the oxydehydration step is the current focus of research. Isobutyric acid may also be obtained via the oxidation of isobutyraldehyde, which is available from the hydroformylation of propylene. The -butyraldehyde isomer that is formed in the hydroformylation must be separated. 

A third homogeneously catalyzed process, on the basis of formaldehyde condensation with propanal to give methacrolein and subsequent oxidation to methacrylic acid, was commercialized in 1990 by BASF. Application of this process is limited by the availability of cheap propanal, produced by large-scale ethylene hydroformylation (cf. Section 2.1.1). 

Other technologies, already commercially applied or under development, are summarized in Figure 2.63b. Alternative routes of synthesis include (i) ethene hydroformylation to propionaldehyde, which then forms methacrolein by condensation with formaldehyde methacrolein is then oxidized to methacrylic acid (BASF process) (ii) isobuthyraldehyde conversion into isobutyric acid and then oxidative dehydrogenation to methacrylic add (Mitsubishi Kasei/Asahi process) and (iii) oxidation of terf-butyl alcohol to methacrolein followed by oxidation to methacrylic acid and esterification. 

Commercial petrochemical processes using syngas or carbon monoxide are based on four principal classes of reactions phosgenation, Reppe chemistry, hydroformylations, and Koch carbonylations. Phosgenation is a key step in the manufacture of polyurethanes, polycarbonates, and monoisocyanates. Reppe chemistry is the basis for acetic acid and acetic anhydride production as well as formic acid and methyl methacrylate synthesis. Hydroformylations utilize syngas in the oxo synthesis to make a wide variety of aldehydes and long-chain alcohols. The fourth class of reactions are Koch carbonylations. Koch carbonylations are used commercially to produce neo acids which are specialty products that serve markets similar to 0X0 alcohols. 

The first step is the hydroformylation of ethylene to yield propionalde-hyde to which formaldehyde is added to give methacrolein. This can then readily be oxidised to give methacrylic acid. 

The major product obtained (Scheme 150) is formylpropionic acids, which are precursors of methacrylate monomers and can be used for a number of important pharmaceuticals. A number of other applications of hydroformylation have been reviewed. ... 

Scheme 4.31 Hydroformylation of a-substituted methacrylates under various conditions and first steps in the total synthesis of a,a-branched p-amino acids.

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