Catalytic methanol carbonylation

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). 

Industry uses a multitude of homogenous catalysts in all kinds of reactions to produce chemicals. The catalytic carbonylation of methanol to acetic acid... 

Mechanistic Pathways in the Catalytic Carbonylation of Methanol by Rhodium and Iridium Complexes... 

Acetic Acid Synthesis by Catalytic Carbonylation of Methanol... 

Haynes, A. (2005) Acetic acid synthesis by catalytic carbonylation of methanol, in Topics in Organometallic Chemistry, Vol. 18 (ed. M. Beller), Springer-Verlag, Berlin, pp. 179-205. 

Pseudo-first-order rate constants for carbonylation of [MeIr(CO)2l3]" were obtained from the exponential decay of its high frequency y(CO) band. In PhCl, the reaction rate was found to be independent of CO pressure above a threshold of ca. 3.5 bar. Variable temperature kinetic data (80-122 °C) gave activation parameters AH 152 (+6) kj mol and AS 82 (+17) J mol K The acceleration on addition of methanol is dramatic (e. g. by an estimated factor of 10 at 33 °C for 1% MeOH) and the activation parameters (AH 33 ( 2) kJ mol" and AS -197 (+8) J mol" K at 25% MeOH) are very different. Added iodide salts cause substantial inhibition and the results are interpreted in terms of the mechanism shown in Scheme 3.6 where the alcohol aids dissociation of iodide from [MeIr(CO)2l3] . This enables coordination of CO to give the tricarbonyl, [MeIr(CO)3l2] which undergoes more facile methyl migration (see below). The behavior of the model reaction closely resembles the kinetics of the catalytic carbonylation system. Similar promotion by methanol has also been observed by HP IR for carbonylation of [MeIr(CO)2Cl3] [99]. In the same study it was reported that [MeIr(CO)2Cl3]" reductively eliminates MeCl ca. 30 times slower than elimination of Mel from [MeIr(CO)2l3] (at 93-132 °C in PhCl). 

Mechanistic Pathways for Ligand Substitution Processes in Metal Carbonyls, 21, 113 Mechanistic Pathways in the Catalytic Carbonylation of Methanol by Rhodium and Iridium Complexes, 17, 255... 

Haynes A (2006) Acetic Acid Synthesis by Catalytic Carbonylation of Methanol. 18 He Y, see Nicolaou KC (1998) 1 73-104... 

The catalytic activity of the methanol carbonylation is very dependent on the nature of the iodide promoter, and different chemistry appears to follow using HI or Nal in this regard (72). However, under otherwise identical conditions, the catalytic activity increased in the order Nal < CH3I < HI. Contrary to what is observed for the rhodium/iodide catalyst, Braca et al. did not consider CH3I to be directly involved in the catalytic carbonylation cycle (70-73). This conclusion is based on the observation that CH3I was not carbonylated under their reaction conditions. Instead, because of the necessity of a proton supplier and the promoting effect of Nal, these authors... 

Figure 3.27 Catalytic carbonylation of methanol (r.d.s. = rate-determining step)...

Today most of the world s production of acetic acid uses the catalytic carbonylation of methanol (Equation 10),... 

Commercial methanol carbonylation processes have employed each of the group 9 metals, cobalt, rhodium and iridium as catalysts. In each case acid and an iodide co-catalyst are required to activate the methanol by converting it into iodomethane (CH3OH + HI CH3I + H2O) catalytic carbonylation of iodomethane into acetyl iodide is followed by hydrolysis to acetic acid. A problem common to all these processes arises because the mixture of HI and acetic acid is highly corrosive this necessitates special techniques for plant construction involving the use of expensive steels. We discuss each catalyst system in turn below. 

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