Propynes carbonylation process

Although propyne can be made available from naphtha crackers as chemical feedstock (in amounts varying between 0.2 and 1.0% on total intake of hydrocarbon feedstock), until recently there existed no prospect of a feasible propyne carbonylation process to provide a route to MMA via the reaction represented in eq. (2) - i.e., a reaction similar to eq. (1) ... 

Carbonylation of methanol to acetic acid is fully discussed in Chapter 9. Another carbonylation process using a phosphine ligand to control the course of the reaction is a highly atom efficient route to the widely used monomer methyl methacrylate (Scheme 4.19). In this process the catalyst is based on palladium acetate and the phosphine ligand, bisphenyl(6-methyl-2-pyridyl) phosphine. This catalyst is remarkably (>99.5%) selective for the 2-carbonylation of propyne under the relatively mild conditions of <100 °C and 60 bar pressure. 

A more complex carbonylation process is involved in the formation of bisbutenolides (bifurandiones) from cobalt carbonyl-catalyzed carbonylation of alkynes112 117 (Scheme 68). The trans derivative (53) is formed in good yield from acetylene,112 but yields from substituted acetylenes (e.g., propyne)... 

In this chapter we discuss the mechanistic and other details of a few industrial carbonylation processes. These are carbonylation of methanol to acetic acid, methyl acetate to acetic anhydride, propyne to methyl methacrylate, and benzyl chloride to phenyl acetic acid. Both Monsanto and BASF manufacture acetic acid by methanol carbonylation, Reaction 4.1. The BASF process is older than the Monsanto process. The catalysts and the reaction conditions for the two processes are also different and are compared in the next section. Carbonylation of methyl acetate to acetic anhydride, according to reaction 4.2, is a successful industrial process that has been developed by Eastman Kodak. The carbonylation of propyne (methyl acetylene) in methanol to give methyl methacrylate has recently been commercialized by Shell. The Montedison carbonylation process for the manufacture of phenyl acetic acid from benzyl chloride is noteworthy for the clever combination of phase-transfer and organometallic catalyses. Hoechst has recently reported a novel carbonylation process for the drug ibuprofen. 

The carbonylation of propyne (methyl acetylene) in methanol to give methyl methacrylate (MMA) was commercialized by Shell. There is also a carbonylation process for the manufacture of phenyl acetic acid from benzyl chloride. A novel carbonylation process, which reduces the E factor significantly, has been reported for the drug ibuprofen. 

MMA from Propyne. Advances in catalytic carbonylation technology by Shell researchers have led to the development of a single-step process for producing MMA from propyne [74-99-7] (methyl acetylene), carbon monoxide, and methanol (76—82). 

Propyne process C3H4, CO, CH3OH Catalytic carbonylation of propyne Shell... 

Figure 4.10 Shell process for the carbonylation of propyne (methyl acetylene) in methanol to give MMA. In 4.39 one PflN may act as a monodentate ligand, and the fourth co-ordination site may be occupied by weakly coordinating X. ...

A much shorter route is the Reppe carbonylation [83] of propyne. Propyne is, together with propadiene (allene), part of the C3 stream of the cracking process. The order of metal substrate binding strength is allenes>alkynes>alkenes. Thus the desired reaction can only proceed if the propadiene has been removed from the feed, since it is an inhibitor of the Pd catalyst. Equally important, the alkyne complex reacts much faster than the alkene complex. Thus the product is neither a substrate nor an inhibitor for the catalyst (Scheme 5.46). 

A further development of the Reppe acrylic acid synthesis is the reaction, described in recent literature, of the noble metal-catalyzed carbonylation of higher acetylenes to give the corresponding acrylic acid derivatives. Thus, for example, the Pd-catalyzed carbonylation of propyne (eq. (10)) in the presence of methanol leads directly to methyl methacrylate [23]. Based on this work. Shell has developed a new production process for methyl methacrylate [24]. The propyne required can be isolated from the product streams from crackers, (cf. Section 2.3.2.3). 

A new class of cationic palladium catalysts for the carbonylation of alkynes is described which, under mild conditions, shows unprecedented high activity and selectivity for the carbonylation of (higher) alkynes. As a particularly interesting application, the catalysts allow the development of a commercially attractive and environmentally friendly process for the carbonylation of propyne to methyl methacrylate. 

The reaction is carried out in aqueous tetrahydrofuran, if acrylic acid is the desired product, or in aqueous alcohol if the ester is required. Nickel is introduced as bromide or iodide and is converted into carbonyl complexes under the reaction conditions, typically 200°C/100atm. One catalytic cycle which has been postulated for this process is shown in Fig. 12.18. Selectivity in the formation of acrylic acid from acetylene is better than 90%. Even from propyne, where anti-Markovnikov addition of [Ni]—H competes with the desired pathway, selectiv-ities of over 80% to methyl methacrylate H2C=C(Me)C02Me are achieved. The major by-product is methyl crotonate, MeCH=CHC02Me. 

On the other hand, new processes are being researched, such as i) the named Alpha process via ethylene carbonylation to methyl propionate, very similar to the aforementioned BASF route ii) the one-step method of propyne catal3dic carbonylation and iii) direct oxidation of isobutane to methacrolein or methacrylic acid. The use of isobutyraldehyde and isobutyric acid as feedstocks has also been explored. Among all these methods, the one employing the alkane in a one-step reaction to form methacrylic acid is the most simple and interesting process from both... 

Deprotonation of l,3-bis(trimethylsilyl)propyne with Bu Li and subsequent addition of carbonyl compounds in the presence or absence of an additive such as MgBr2 has been reported to furnish the enyne products with moderate to good Z-selectivity (Scheme 2.84) [235, 236]. It has been reasonably postulated that the reaction proceeds via a kinetically controlled pericyclic process as illustrated by intermediate 134, where steric factors and the interaction between the counter ion and the oxygen atom play major roles. Other additives are also employed in Z-selective enyne formation reactions, such as Ti(OPr )4, B(OMe)3, and B-methoxy-9-borabicydo[3.3.1]nonane (B-MeO-9-BBN) [225, 226, 237-240]. 

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