Acetic anhydride, production

The mechanism of acetaldehyde oxidation is relatively complex. Considering only molecular species, the main steps appear to be 

If the oxidation is carried out with a metal catalyst and a hydrocarbon diluent, and the mixture is separated rapidly, an appreciable proportion of the acetic anhydride can be recovered. Thus mixtures of acetic anhydride (50-70% w/w) and acid are obtained in a total selectivity of over 90%. 

An alternative commercial route is the cracking of acetic acid to ketene, in the presence of a phosphate ester at over 700 C. After separating the gaseous ketene from condensed water, it is absorbed into acetic acid. 

The selectivity in the cracking step is some 90%, giving an overall selectivity to anhydride based on acetic acid of about 95%. 

However, Halcon have now developed a process, catalysed by rhodium (or nickel) with iodine and other promoters, for the carbonylation of methyl acetate (or dimethyl ether) to acetic anhydride. Like the ketene route, this technology fits in well with acetylation processes. 

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This process is one of the three commercially practiced processes for the production of acetic anhydride. The other two are the oxidation of acetaldehyde [75-07-0] and the carbonylation of methyl acetate [79-20-9] in the presence of a rhodium catalyst (coal gasification technology, Halcon process) (77). The latter process was put into operation by Tennessee Eastman in 1983. In the United States the total acetic anhydride production has been reported to be in the order of 1000 metric tons. 

The high cost of coal handling and preparation and treatment of effluents, compounded by continuing low prices for cmde oil and natural gas, has precluded significant exploitation of coal as a feedstock for methanol. A small amount of methanol is made from coal in South Africa for local strategic reasons. Tennessee Eastman operates a 195,000-t/yr methanol plant in Tennessee based on the Texaco coal gasification process to make the methyl acetate intermediate for acetic anhydride production (15). 

Formation of the partially saturated nitro derivatives 60 and 61 was reported by a Russian team <1994KGS1129>. The two products were obtained under fairly complicated reaction conditions when aminotetrazole 42 was first treated with potassium amidosulfonate and formaldehyde at pH = 4 followed by addition of nitric acid, methylamine, and acetic anhydride, product 60 was obtained in 24% yield. The same reaction, however, carried out at pH = 6 gave rise to formation of the acetoxy compound 61 in 21% yield. 

Acetic acid, 7 115-136 5 27 70 596 72 44. See also Glacial acetic acid Vinegar acetic anhydride production from, 7 115, 133, 149-150... 

The main use of acetaldehyde is in acetic acid and acetic anhydride production (70%) other uses include pyridine bases (8%), pentaerythritol (7%), peracetic acid (6%), and 1,3-butylene glycol (2%). 

Methanol is an ideal starting material for the synthesis of many chemicals. It is the most important feedstock for the large-scale commercial production of acetic acid and formaldehyde. Additionally, a variety of other chemicals such as methyl esters, methyl halides and methyl ethers can be produced from it. Tenessee-Eastman s recent pioneering commercialization of a coal-based process for acetic anhydride production illustrates the growing importance of methanol as chemical feedstock. 

A block diagram of the Monsanto process for acetic acid production is shown in Fig. 4.13. The process flow sheet is simple since the reaction conditions are mild (180°C/30-40 bar) when compared to the BASF process (250°C/700 bar). More than 40% of world s acetic acid is made by the Monsanto process. One of the problems with this process is the continuous loss of iodine. A block diagram of the Eastman process for acetic anhydride production is shown in Fig. 4.14. The process generates minimum waste, and all process tars are destroyed to recover iodine and rhodium. 

Figure 4.14 Simplified block diagram of the methyl acetate carbonylation process for acetic anhydride production.

The temperature dependence follows the Arrhenius equation and the reaction is usually carried out below 200 °C. The ratio of methanol/methyl acetate affects the overall reaction rate. With an increasing proportion of methanol, the space-time yield (g/L-h) increases (Figure 7). Therefore, the variability of the process in continuous operation is limited to certain acetic acid/acetic anhydride production ratios. 

Starting Molecule 2-Nitro-4,5-dihydroxybenzatdehyde Reagents Nitromethane, acetic anhydride Product fJ 2-Dinitro-4,5-diacetoxystyrene Reference (Beer 1948 1951)... 

Starting Molecule 2-Nitro-protocatechuic aldehyde Reagents Nitroethane, acetic anhydride Product ll 2-Dinitro-4,5-dlacetoxy-S-methylstyrene Reference (Partington 1948)... 

Commercial petrochemical processes using syngas or carbon monoxide are based on four principal classes of reactions phosgenation, Reppe chemistry, hydroformylations, and Koch carbonylations. Phosgenation is a key step in the manufacture of polyurethanes, polycarbonates, and monoisocyanates. Reppe chemistry is the basis for acetic acid and acetic anhydride production as well as formic acid and methyl methacrylate synthesis. Hydroformylations utilize syngas in the oxo synthesis to make a wide variety of aldehydes and long-chain alcohols. The fourth class of reactions are Koch carbonylations. Koch carbonylations are used commercially to produce neo acids which are specialty products that serve markets similar to 0X0 alcohols. 

C-1. The product distribution was found to depend upon the amount of water present in the system, more 6-(bromomethylene)cyclodecanone being obtained with less water present. This observation was explained in terms of capture of the carbonium ion formed from (56 = 2). There would seem to be no examples yet where an intramolecular shift process competes with ring-opening of a cyclopropyl cation. Solvolysis of 10,10-dibromo[4,3,l]propellane in acetic acid-sodium acetate-acetic anhydride gave products formed via the strained bicyclic acetate (56 n = 1, R = Ac). In the absence of acetic anhydride products derived from the corresponding alcohol (56 n = 1, R — H) were obtained as well. Solvolyses of 10,10-dibromo[4,3,l]propell-3-ene in acetic acid-sodium acetate, in the presence and absence of acetic anhydride, and in acetic acid-silver perchlorate, were also reported. Most of the products may have been formed by reaction pathways similar to those observed for (55). ... 

Startg. imide treated at room temp, with coned. H2SO4 and excess acetic anhydride product. Y 58%. F. e. s. K.D. Pauli and C. C. Cheng, J. Heterocyclic Chem. 10, 137 (1973). 

Eastman recently expanded the plant to increase the acetic anhydride production capacity to 1.2 billion Ib/yr (20). The new facilities include a new acetic acid plant and an expansion of the methyl acetate plant. 

Diethylacetylene allowed to react with thallic acetate sesquihydrate in glacial acetic acid containing 4.5 moles acetic anhydride product. Y 87%. F. e. s. R. K. Sharma and N. H. Fellers, J. Organometal. Chem. 49, C 69 (1973). 

Startg. lactam ester treated with 5%-HCl-acetic acid, and the resulting intermediate heated with acetic anhydride product. Y 95%. Y. Tsuda et al., Chem. Commun. 1975, 933. 

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