Monsanto process

Monsanto process is a process for the industrial preparation of acetic acid. The process takes place at a pressure of 30 to 60 and a temperature of 150 to 200 ° C instead of with a selectivity of over 99%. It was developed by BASF in 1960 and 1966 improved by Monsanto through the introduction of another catalyst system. Methanol is catalytically reacted with carbon monoxide to acetic acid. The total equation is:

Monsanto process has now been complemented by the Cativa process using an iridium catalyst with a similar reaction mechanism and which has been developed by the BP. Another way of representation of acetic acid provides the Tennessee Eastman process, with the formation of acetic anhydride.

As a biological equivalent of the reductive acetyl -CoA pathway comes closest.

The catalytic cycle

The catalytically active species is the anionic complex cis-[ Rh (CO) 2I2 ] - (1). The catalytic cycle consists of six steps, two of which do not expire with the participation of rhodium: the conversion of methanol to methyl iodide and hydrolysis of Acetyliodids in acetic acid. The first step is the oxidative addition of methyl iodide to the rhodium complex under formation of the complex [( CH 3) Rh (CO) 2I3 ] - (2). This complex accumulates quickly, with insertion of the carbonyl into the metal -methyl bond in the acetyl complex [( CH 3 CO ) Rh ( CO) I3 ] - (3 ) to. At these five-coordinate complex another carbon monoxide molecule superposed on. This complex decomposes by reductive elimination of Acetyliodids CH3COI, which decays by hydrolysis in acetic acid and HI and the formation of the starting compound. The reaction is first order with respect to the catalyst and methyl iodide. Therefore, it is believed that the rate determining step is the oxidative addition of methyl iodide to the catalyst.

The Cativa process of iridium complex [Ir ( CO) 2I2 ] - the catalytically active species. Iridium is both a cheaper catalyst metal, the process also requires less water in the reaction solution and thus saves drying stages in later process steps. The development of the process started in the 1990s, in November 1995, the first commercial plant was in Texas City, United States, put into operation.

Tennessee Eastman acetic anhydride process

The formation of the acetic anhydride is carried out by the carbonylation of methyl acetate in a process, which is based on the Monsanto process

As catalysts, rhodium iodide and lithium salts. In contrast to the above method, this method is carried out because of the sensitivity of the anhydride in the absence of water.