Oxidation methylmethacrylate production

In the petrochemical industry the introduction of unsaturations in hydrocarbons is mainly obtained by dehydrogenation. This kind of reaction is less suitable for the functionalization of fine chemicals, because the high temperature necessary for the endothermic reaction can lead to the decomposition of thermally unstable compounds. An alternative reaction consists in the oxidative dehydrogenation, that can be carried out at lower temperatiu es. An example of this kind of reaction is constituted by the synthesis of methacrylic add (MAA, intermediate of methylmethacrylate production) via the oxidative dehydrogenation of isobutyric add (IBA), itself obtained from isobutyraldehyde (by-product of the oxo synthesis of nbutyraldehyde from propylene). This process constitutes one of the economically most interesting routes, alternative to the acetone-cyanohydrin process, which nowadays is the predominant process for the MAA production. 

Figure 31 The radical initiator (47) based on the oxidation adduct of an alkyl-9-BBN used for the production of poly(methyhnethacrylate) (48) from methylmethacrylate monomer by the radical polymerization route. (Adapted from ref. 69.)...

Methyl methacrylate (MMA) is an important commodity since it is polymerized to give poly methylmethacrylate (PMMA), a strong, durable and transparent polymer sold under the trade-names Perspex and Plexiglas. Since the conventional routes to MMA involve either the reaction of acetone with HCN to give the cyanohydrin (which has environmental problems), or the oxidation of isobutene, alternative carbonylation routes to MMA are being developed. One of these is the Lucite Alpha process which is claimed to decrease production costs by ca. 40%. This first synthesizes methyl propionate by a methoxycarbonylation of ethylene (Equation 23), using a palladium catalyst with very high (99.8%) selectivity. In the second step, MMA is formed in 95% selectivity by the reaction of methyl propionate with formaldehyde (Equation 24). 

The current industrial production of methylmethacrylate by the acetone-cyanohydrin process suffers from a number of drawbacks, which make it environmentally unfriendly. In particular, it makes use of a very toxic reactant (HCN) and intermediate (acetone cyanohydrin), and coproduces large amounts of impure ammonium sulphate, contaminated with organic compounds. Among the several alternative synthetic routes which have been proposed, particularly interesting from both the practical and scientific points of view is the single-step oxidation of isobutane to methacrylic acid, intermediate in the synthesis of methylmethacrylate. Several industrial companies have studied this reaction (and the selective oxidation of propane to acrylic acid, as well), and it has been established that the most active and selective catalysts are those which are based on Keggin-type polyoxometalates (POM s), containing phosphorus and molybdenum as the main components [1-18]. 

Batch Di (3-pentyl) Malate Process Acetaldehyde from Acetic Acid Ethylene by Oxidative Dehydrogenation of Ethane Butadiene to n-Butyraldehyde and n-Butanol Methacrylic Acid to Methylmethacrylate Coproduction of Ethylene and Acetic Acid from Ethane Methylmethacrylate from Propyne Mixed-C4 Byproduct Upgrade Hydrogen Peroxide Manufacture Di-tem fljy-butyl-peroxide Manufacture Vinyl Acetate Process PM Acetate Manufacture Propoxylated Ethylenediamine Petroleum Products Fuel Additives for Cleaner Emissions Gas Manufacture... 

If large amounts of isobutyl alcohol are available as by-product of the Oxirane process for propylene oxide manufacture, it can also be obtained very easily form the isobutylene contained in Cl streams of steam cracking units. After the recovery of butadiene, the isobutylene of these streams is selectively hydrated to tertiary butyl alcohol. This process carried out in the liquid phase in the presence of a solid catalyst is certainly realized in fixed bed reactors. Very few details have been disclosed on this reaction which constitutes the first step of a new process to obtain methylmethacrylate from a spent butylene isobutylene feed (5 ). 

---