Page 122 - Academic Press Encyclopedia of Physical Science and Technology 3rd Organic Chemistry

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Encyclopedia of Physical Science and Technology EN002C-85 May 17, 2001 20:35

470 Catalysis, Homogeneous

FIGURE 35 Monsanto carbonylation of methanol.

concentrations of the two reactants. The process scheme acid replaces water, and methyl acetate replaces methanol
is presented in Fig. 36. (Fig. 35):
CH 3 COOCH 3 + HI CH 3 COOH + CH 3 I

2. Acetic Anhydride
CH 3 COI + CH 3 COOH CH 3 COOOCH 3 + HI

In many applications acetic acid is used as the anhydride
The first reaction generates methyl iodide for the oxidative
and the synthesis of the latter is therefore equally impor-
addition, and the second reaction converts the reductive
tant. In the 1970s Halcon (now Eastman) and Hoechst
elimination product acetyl iodide into the product and it
(now Celanese) have developed a process for the con-
regenerates hydrogen iodide. There are, however, a few
version of methyl acetate and carbon monoxide to acetic
distinct differences between the two processes. The ther-
anhydride. The process has been on stream since 1983
modynamics of the acetic anhydride formation are less
and several 100,000 are being produced annually together
favorable and the process is operated much closer to equi-
with some 10–20% acetic acid. The reaction is carried out
librium. Under standard conditions the G values are ap-
under similar conditions as the Monsanto process, and
proximately:
also uses methyl iodide as the “activator” for the methyl
group. The reaction scheme follows that of the Monsanto MeOAc + CO → Ac 2 O −2.5 kcal/mol
process except for the “organic” cycle, in which acetic
Two more differences are
1. in the Eastman process 5% of H 2 is added to the
carbon monoxide to accomplish reduction of trivalent
rhodium, and
+
2. the addition of cations such as Li or Na is
+
necessary.
D. Hydroformylation
1. Introduction
Functionalization of hydrocarbons from petroleum
sources is mainly concerned with the introduction of
oxygen into the molecule. Roughly speaking, two ways
are open: oxidation and carbonylation. Oxidation is the
preferred route inter alia for aromatic acids, acrolein,
FIGURE 36 Simplified flow-scheme of the Monsanto process for maleic anhydride, ethene oxide, propene oxide, and
acetic acid. acetaldehyde. Hydroformylation (older literature and