Acetic carbonylation

Currently, almost all acetic acid produced commercially comes from acetaldehyde oxidation, methanol or methyl acetate carbonylation, or light hydrocarbon Hquid-phase oxidation. Comparatively small amounts are generated by butane Hquid-phase oxidation, direct ethanol oxidation, and synthesis gas. Large amounts of acetic acid are recycled industrially in the production of cellulose acetate, poly(vinyl alcohol), and aspirin and in a broad array of other... 

The reaction mechanism and rates of methyl acetate carbonylation are not fully understood. In the nickel-cataly2ed reaction, rate constants for formation of methyl acetate from methanol, formation of dimethyl ether, and carbonylation of dimethyl ether have been reported, as well as their sensitivity to partial pressure of the reactants (32). For the rhodium chloride [10049-07-7] cataly2ed reaction, methyl acetate carbonylation is considered to go through formation of ethyUdene diacetate (33) ... 

The first anhydride plant in actual operation using methyl acetate carbonylation was at Kingsport, Tennessee (41). A general description has been given (42) indicating that about 900 tons of coal are processed daily in Texaco gasifiers. Carbon monoxide is used to make 227,000 t/yr of anhydride from 177,000 t/yr of methyl acetate 166,000 t/yr of methanol is generated. Infrared spectroscopy has been used to foUow the apparent reaction mechanism (43). 

Fig. 2. Flow sheet for methyl acetate carbonylation to anhydride. To convert kPa to psi multiply by 0.145.

Methyl acetate carbonylation demands only 0.59 kg acetic acid per kg anhydtide manufactured.)... 

Name Molecular formula Hydroxyl Value Acidity, % as acetic Carbonyl, wt % 0 Boiling range, °C Color, APHA Moisture, % Plash point, °C ... 

A related but distinct rhodium-catalyzed methyl acetate carbonylation to acetic anhydride (134) was commercialized by Eastman in 1983. Anhydrous conditions necessary to the Eastman acetic anhydride process require important modifications (24) to the process, including introduction of hydrogen to maintain the active [Rhl2(CO)2] catalyst and addition of lithium cation to activate the alkyl methyl group of methyl acetate toward nucleophilic attack by iodide. 

Variations in the composition of a copolymer can cause substantial differences in the properties of the copolymer. Compositional information about copolymers may be acquired using selective detectors. Figure 3.9 shows the separation of an ethylene-vinyl acetate (EVA) copolymer by FfPSEC using IR detectors. One IR detector monitors the vinyl acetate carbonyl at 5.75 /u,m, and the other IR detector monitors the total alkyl absorbance at 3.4 /cm. 

Those bioses in which the aldehydic (cyclo-acetal) carbonyl group is free have a reducing action (on Fehling s solution). 

There is one report of competitive nucleophilic attack at the amide carbonyl in an Ai-acyloxy-A-aUtoxyamide. Shtamburg and coworkers have reported that MeONa reacted with Ai-acetoxy-A-ethoxybenzamide (159) in DME giving methyl and ethyl benzoate (160 and 161) (Scheme 26) . They attributed the formation of methyl benzoate to the direct attack of methoxide ion at the amide carbonyl rather than at nitrogen. The formation of 161 was attributed to a HERON reaction. Though not mentioned by the authors, it seems likely that under these aprotic conditions, 162 could also have been formed by methoxide attack at the acetate carbonyl leading to an anion-induced HERON reaction, by analogy with the reaction of Ai-acyloxy-Ai-alkoxyamides and aqueous hydroxide discussed above (Section IV.C.3.c)... 

Reaction rates have first-order dependence on both metal and iodide concentrations. The rates increase linearly with increased iodide concentrations up to approximately an I/Pd ratio of 6 where they slope off. The reaction rate is also fractionally dependent on CO and hydrogen partial pressures. The oxidative addition of the alkyl iodide to the reduced metal complex is still likely to be the rate determining step (equation 8). Oxidative addition was also indicated as rate determining by studies of the similar reactions, methyl acetate carbonylation (13) and methanol carbonylation (14). The greater ease of oxidative addition for iodides contributes to the preference of their use rather than other halides. Also, a ratio of phosphorous promoter to palladium of 10 1 was found to provide maximal rates. No doubt, a complex equilibrium occurs with formation of the appropriate catalytic complex with possible coordination of phosphine, CO, iodide, and hydrogen. Such a pre-equilibrium would explain fractional rate dependencies. 

In addition to the successful reductive carbonylation systems utilizing the rhodium or palladium catalysts described above, a nonnoble metal system has been developed (27). When methyl acetate or dimethyl ether was treated with carbon monoxide and hydrogen in the presence of an iodide compound, a trivalent phosphorous or nitrogen promoter, and a nickel-molybdenum or nickel-tungsten catalyst, EDA was formed. The catalytst is generated in the reaction mixture by addition of appropriate metallic complexes, such as 5 1 combination of bis(triphenylphosphine)-nickel dicarbonyl to molybdenum carbonyl. These same catalyst systems have proven effective as a rhodium replacement in methyl acetate carbonylations (28). Though the rates of EDA formation are slower than with the noble metals, the major advantage is the relative inexpense of catalytic materials. Chemistry virtually identical to noble-metal catalysis probably occurs since reaction profiles are very similar by products include acetic anhydride, acetaldehyde, and methane, with ethanol in trace quantities. 

Figure 7 shows the results of methyl acetate carbonylation in the presence of water. Methanol and dimethyl ether were formed up to 250 C suggesting that hydrolysis of methyl acetate proceeded. With increasing reaction temperature, the yield of acetic acid increased remarkably, while those of methanol and dimethyl ether decreased gradually. Figure 8 shows the effects of partial pressures of methyl iodide, CO, and methyl acetate in the presence of water. The rate of acetic acid formation was 1.0 and 2.7 order with respect to methyl iodide and CO, respectively. Thus, the formation of acetic acid from methyl acetate is highly dependent on the partial pressure of CO. This suggests that acetic acid is formed by hydrolysis of acetic anhydride (Equation 6) which is formed from methyl acetate and CO rather than by direct hydrolysis of methyl acetate. 

At high temperatures with low catalyst concentration the formation of acetanilides is favored. Maleic anhydride and acetanilides may be formed directly from the mixed anhydride by an initial attack of the nitrogen on the acetate carbonyl, but this process would involve a seven membered ring transition state. Another possible route to the formation of maleic anhydride and the acetanilides is participation by neighboring carbonyl in loosening the amide carbon-nitrogen bond to the extent that the amine can be captured by acetic anhydride as shown in path D. 

Heterogeneous palladium catalysts proved to be active in the conversion of simple alkenes to the corresponding allylic acetates, carbonyl compounds, and carboxylic acids.694 704 Allyl acetate or acrylic acid from propylene was selectively produced on a palladium on charcoal catalyst depending on catalyst pretreatment and reaction conditions.694 Allylic oxidation with singlet oxygen to yield allylic hydroperoxides is discussed in Section 9.2.2. 

In other studies Allara (27) used FTIR reflection to study the interaction of the oxide film of aluminum with acetic acid in which th aluminum acetate carbonyl stretch peak was found at 1590 cm- > in excellent agreement with the 1589 cm-1 peak determined by inelastic electron tunnelling spectroscopy (IETS), another modern technique for vibrational spectra at metal interfaces. The spectra of acetic acid adsorbed on copper oxide or indium,oxide were about the same. 

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