Methyl acetate carbonylation, chromium

The catalyst system for the modem methyl acetate carbonylation process involves rhodium chloride trihydrate [13569-65-8]y methyl iodide [74-88-4], chromium metal powder, and an alumina support or a nickel carbonyl complex with triphenylphosphine, methyl iodide, and chromium hexacarbonyl (34). The use of nitrogen-heterocyclic complexes and rhodium chloride is disclosed in one European patent (35). In another, the alumina catalyst support is treated with an organosilicon compound having either a terminal organophosphine or similar ligands and rhodium or a similar noble metal (36). Such a catalyst enabled methyl acetate carbonylation at 200°C under about 20 MPa (2900 psi) carbon monoxide, with a space-time yield of 140 g anhydride per g rhodium per hour. Conversion was 42.8% with 97.5% selectivity. A homogeneous catalyst system for methyl acetate carbonylation has also been disclosed (37). A description of another synthesis is given where anhydride conversion is about 30%, with 95% selectivity. The reaction occurs at 445 K under 11 MPa partial pressure of carbon monoxide (37). A process based on a montmorillonite support with nickel chloride coordinated with imidazole has been developed (38). Other related processes for carbonylation to yield anhydride are also available (39,40). 

Eastman-Halcon A process for making acetic anhydride from syngas. The basic process is the carbonylation of methyl acetate. Methanol is made directly from the carbon monoxide and hydrogen of syngas. Acetic acid is a byproduct of the cellulose acetate manufacture for which the acetic anhydride is needed. The carbonylation is catalyzed by rhodium chloride and chromium hexacarbonyl. 

In the presence of RhCU -xHzO, Mel, an organic base and chromium compounds, methyl acetate is carbonylated to acetic anhydride. The rate is first order in rhodium, Mel, and, at low concentrations, the base chromium compounds have less influence on the rate but reduce the induction period remarkably. " Catalytic carbonylation of nitrocompounds has been reviewed. " ... 

C, Carbide iron complex, 26 246 ruthenium cluster complexes, 26 281-284 CHF,02, Acetic acid, trifluoro-tungsten complex, 26 222 CHFjOjS, Methanesulfonic acid, trifluoro-iridium, manganese, and rhenium complexes, 26 114, 115, 120 platinum complex, 26 126 CH2O2, Formic acid rhenium complex, 26 112 CH, Methyl iridium complex, 26 118 manganese complex, 26 156 rhenium complexes, 26 107 CHjO, Methanol platinum complexes, 26 135 tungsten complex, 26 45 CNajOuRusCn, Ruthenate(2- )ns-carbido-tetradecacarbonyl-disodium, 26 284 CO, Carbonyls chromium, 26 32, 34, 35 chromium, molybdenum, and tungsten, 26 343... 

C,Hj, Acetic acid palladium complex, 26 208 tungsten complex, 26 224 02CiH(, 2-Propenoic acid, methyl ester platinum ester, 26 138 02C4Hu, Ethane, 1,2-dimethoxy-solvates of chromium, molybdenum, and tungsten carbonyl cyclopentadienyl complexes, 26 343 tungsten complex, 26 50 ytterbium complex, 26 22 02C4Hi, -NaCsHs, Ethane, 1,2-dimethoxy-compd with cyclopentadienylsodium(l l), 26 341... 

Usually decarboxylation is accomplished by heating the acids above their melting points, often in the presence of a copper-chromium catalyst. Imidazole-4,5-dicarboxylic acid can be monodecarboxylated by heating its monoanilide imidazole- and benzimidazole-2-carboxylic acids decarboxylate very readily indeed, so readily that the carboxyl function makes a useful blocking group in metallation procedures (see Scheme 7.2.1) [3-5]. A potentially useful method of preparation of imidazole-4-carboxylic acid derivatives heats the 4,5-dicarboxylic acid (2) with acetic anhydride to form (1), which is essentially an azolide and very prone to nucleophilic attack which cleaves the nitrogen-carbonyl bond (Scheme 8.3.1). With methanol the methyl ester (3) is formed with hydrazines the 4-hydrazides (4) result [6]. 

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