Acetic Acid Route

In order to speed up the aqueous carbonahon process, the use of acetic acid for the extrachon of calcium from a calcium-rich feedstock has been suggested by Kakizawa et al. [50]. In principle, this process comprises two steps, as given in Equations 14.5 and 14.6 [50]  

Although, globally, the C02 sequestration potential for this option is small, for individual steel plants he method could provide significant economical benefits and noticeable reductions in emissions. 

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Figure 14.1 The precipitated calcium carbonate (PCC) production process A schematic representation, according to the acetic acid route [21, 51].

Ri =s R2 = Ph). 4-Aryl-l,2-dithiolium salts of type (36 R = Me or Ph, R = H) yield 1,2-dithiolylidene ketones (37) when heated in ethanol, but this reaction fails when the dithiolium salt has a 5-amino-substituent (36 R = NRa). The 5-amino-compounds have been found to give 1,3-dithiole derivatives on treatment with phosphorus pentasulphide in pyridine. The structure of one of the products (38) was established by conversion into the 6a-thiathiophthen (39), which was also prepared by sulphurization of the dithiolylidene ketone (37 R = Ar = Ph, R = MeaN) obtained by the triethylamine-acetic acid route. 

Despite its own valuable synthetic potential, the use of [ C2]acetylene as a starting material for various building blocks is of much higher relevance. Mercury(II)-catalyzed hydration, for example, gives [ C2]acetaldehyde (Figure 8.5, Route 1) The same reaction carried out in the presence of ammonium persulfate furnishes [ 2] acetic acid (Route 2). Trapping of its mono- or dianion with formaldehyde or carbon dioxide affords [2,3- C2]propynol, [2,3- C2]butyne-l,4-diol, [2,3- C2]propiolic acid " and [2,3- C2]acetylenedicarboxylic acid, respectively (Routes 3-6). UV irradiation of a mixture of HBr and [ C2]acetylene produces l,2-dibromo[ C2]ethane (Route 8) . Reduction with chromium(II) chloride followed by a two-step epoxidation of the initially formed [ C2]ethylene converts [ 2]acetylene into [ C2]ethylene oxide (Route 7) . Finally, catalytic homotrimerization or co-trimerization with other alkynes provides [ " C ]benzene or substituted [ " C ]benzenes, respectively, the central starting materials for the vast majority of substituted benzenoid aromatic compounds (Route 9). 

As another route, formation of 1,3,7-octatriene (7) proceeds at higher temperature in the absence of nucleophiles by Pd-catalyzed elimination of acetic acid or phenol via a 7r-allylpalladium complex from their telo-mers[l4,17]. 

The reduction of o-nitrophenyl acetic acids or esters leads to cyclization to oxindoles. Several routes to o-nitrophenylacetic acid derivatives arc available, including nitroarylation of carbanions with o-nitroaryl halides[2l,22] or trif-late[23] and acylation of o-nitrotoluenes with diethyl oxalate followed by oxidation of the resulting 3-(u-nitrophenyl)pyruvate[24 26]. 

This process comprises passing synthesis gas over 5% rhodium on Si02 at 300°C and 2.0 MPa (20 atm). Principal coproducts are acetaldehyde, 24% acetic acid, 20% and ethanol, 16%. Although interest in new routes to acetaldehyde has fallen as a result of the reduced demand for this chemical, one possible new route to both acetaldehyde and ethanol is the reductive carbonylation of methanol (85). 

Figure 3 shows the production of acetaldehyde in the years 1969 through 1987 as well as an estimate of 1989—1995 production. The year 1969 was a peak year for acetaldehyde with a reported production of 748,000 t. Acetaldehyde production is linked with the demand for acetic acid, acetic anhydride, cellulose acetate, vinyl acetate resins, acetate esters, pentaerythritol, synthetic pyridine derivatives, terephthaHc acid, and peracetic acid. In 1976 acetic acid production represented 60% of the acetaldehyde demand. That demand has diminished as a result of the rising cost of ethylene as feedstock and methanol carbonylation as the preferred route to acetic acid (qv). 

Acetylation of acetaldehyde to ethyUdene diacetate [542-10-9], a precursor of vinyl acetate, has long been known (7), but the condensation of formaldehyde [50-00-0] and acetic acid vapors to furnish acryflc acid [97-10-7] is more recent (30). These reactions consume relatively more energy than other routes for manufacturing vinyl acetate or acryflc acid, and thus are not likely to be further developed. Vapor-phase methanol—methyl acetate oxidation using simultaneous condensation to yield methyl acrylate is still being developed (28). A vanadium—titania phosphate catalyst is employed in that process. 

Conversion of acetaldehyde is typically more than 90% and the selectivity to acetic acid is higher than 95%. Stainless steel must be used in constmcting the plant. This is an estabHshed process and most of the engineering is weU-understood. The problems that exist are related to more extensively automating control of the system, notably at start-up and shutdown, although even these matters have been largely solved. This route is the most rehable of acetic acid processes. 

Butane-Naphtha Catalytic Liquid-Phase Oxidation. Direct Hquid-phase oxidation ofbutane and/or naphtha [8030-30-6] was once the most favored worldwide route to acetic acid because of the low cost of these hydrocarbons. Butane [106-97-8] in the presence of metallic ions, eg, cobalt, chromium, or manganese, undergoes simple air oxidation in acetic acid solvent (48). The peroxidic intermediates are decomposed by high temperature, by mechanical agitation, and by action of the metallic catalysts, to form acetic acid and a comparatively small suite of other compounds (49). Ethyl acetate and butanone are produced, and the process can be altered to provide larger quantities of these valuable materials. Ethanol is thought to be an important intermediate (50) acetone forms through a minor pathway from isobutane present in the hydrocarbon feed. Formic acid, propionic acid, and minor quantities of butyric acid are also formed. 

Prospective Processes. There has been much effort invested in examining routes to acetic acid by olefin oxidation or from ethylene, butenes, or j -butyl acetate. No product from these sources is known to have reached the world market the cost of the raw materials is generally prohibitive. 

Acetic acid made by methanol carbonylation sometimes has traces of iodine or bromine if the acid comes from the high pressure route. 

Ketene can be obtained by reaction of carbon oxides with ethylene (53). Because ketene combines readily with acetic acid, forming anhydride, this route may have practical appHcations. Litde is known about the engineering possibiHties of these reactions. 

Acetic anhydtide is a mature commodity chemical ia the United States and its growth rate in the 1970s and 1980s was negative until 1988 when foreign demand neatly doubled the exports of 1986. This increase in exports was almost certainly attributable to the decline in the value of the U.S. doUar. Over four-fifths of all anhydtide production is utilized in cellulose acetate [9004-35-7] manufacture (see Cellulose esters). Many anhydtide plants are integrated with cellulose acetate production and thus employ the acetic acid pyrolysis route. About 1.25 kg acetic acid is pyrolyzed to produce 1.0 kg anhydtide. 

Acetyl chlotide was formerly manufactured by the action of thionyl chlotide [7719-09-7], CI2OS, on gray acetate of lime, but this route has been largely supplanted by the reaction of sodium acetate or acetic acid and phosphoms ttichlotide [7719-12-2] (24). A similar route apparently is stiU being used in the Soviet Union (25). Both pathways ate inherently costly. 

Other acetyl chloride preparations include the reaction of acetic acid and chlorinated ethylenes in the presence of ferric chloride [7705-08-0] (29) a combination of ben2yl chloride [100-44-7] and acetic acid at 85% yield (30) conversion of ethyUdene dichloride, in 91% yield (31) and decomposition of ethyl acetate [141-78-6] by the action of phosgene [75-44-5] producing also ethyl chloride [75-00-3] (32). The expense of raw material and capital cost of plant probably make this last route prohibitive. Chlorination of acetic acid to monochloroacetic acid [79-11-8] also generates acetyl chloride as a by-product (33). Because acetyl chloride is cosdy to recover, it is usually recycled to be converted into monochloroacetic acid. A salvage method in which the mixture of HCl and acetyl chloride is scmbbed with H2SO4 to form acetyl sulfate has been patented (33). 

Liquid- and vapor-phase processes have been described the latter appear to be advantageous. Supported cadmium, zinc, or mercury salts are used as catalysts. In 1963 it was estimated that 85% of U.S. vinyl acetate capacity was based on acetylene, but it has been completely replaced since about 1982 by newer technology using oxidative addition of acetic acid to ethylene (2) (see Vinyl polymers). In western Europe production of vinyl acetate from acetylene stiU remains a significant commercial route. 

The procedure is technically feasible, but high recovery of unconverted raw materials is required for the route to be practical. Its development depends on the improvement of catalysts and separation methods and on the avaHabiUty of low cost acetic acid and formaldehyde. Both raw materials are dependent on ample supply of low cost methanol. 

This reaction is rapidly replacing the former ethylene-based acetaldehyde oxidation route to acetic acid. The Monsanto process employs rhodium and methyl iodide, but soluble cobalt and iridium catalysts also have been found to be effective in the presence of iodide promoters. 

Liquid-phase oxidation of lower hydrocarbons has for many years been an important route to acetic acid [64-19-7]. In the United States, butane has been the preferred feedstock, whereas ia Europe naphtha has been used. Formic acid is a coproduct of such processes. Between 0.05 and 0.25 tons of formic acid are produced for every ton of acetic acid. The reaction product is a highly complex mixture, and a number of distillation steps are required to isolate the products and to recycle the iatermediates. The purification of the formic acid requires the use of a2eotropiag agents (24). Siace the early 1980s hydrocarbon oxidation routes to acetic acid have decliaed somewhat ia importance owiag to the development of the rhodium-cataly2ed route from CO and methanol (see Acetic acid). 

Synthesis Gas Chemicals. Hydrocarbons are used to generate synthesis gas, a mixture of carbon monoxide and hydrogen, for conversion to other chemicals. The primary chemical made from synthesis gas is methanol, though acetic acid and acetic anhydride are also made by this route. Carbon monoxide (qv) is produced by partial oxidation of hydrocarbons or by the catalytic steam reforming of natural gas. About 96% of synthesis gas is made by steam reforming, followed by the water gas shift reaction to give the desired H2 /CO ratio. 

Liquid-Phase Oxidation. Liquid-phase catalytic oxidation of / -butane is a minor production route for acetic acid manufacture. Formic acid (qv) also is produced commercially by Hquid-phase oxidation of / -butane (18) (see HYDROCARBON OXIDATION). 

MEK is also produced as a by-product in the Hquid-phase oxidation of / -butane to acetic acid (31—33). This route was once the most favored route to acetic acid, however, since the early 1980s the acetic acid technology of choice has become methanol carbonylation, and MEK growth by this path is doubtflil. 

Production is by the acetylation of 4-aminophenol. This can be achieved with acetic acid and acetic anhydride at 80°C (191), with acetic acid anhydride in pyridine at 100°C (192), with acetyl chloride and pyridine in toluene at 60°C (193), or by the action of ketene in alcohoHc suspension. 4-Hydroxyacetanihde also may be synthesized directiy from 4-nitrophenol The available reduction—acetylation systems include tin with acetic acid, hydrogenation over Pd—C in acetic anhydride, and hydrogenation over platinum in acetic acid (194,195). Other routes include rearrangement of 4-hydroxyacetophenone hydrazone with sodium nitrite in sulfuric acid and the electrolytic hydroxylation of acetanilide [103-84-4] (196). 

In contrast with the well-known Embden-Meyerhof-Pamass glycolysis pathway for the conversion of hexose sugars to alcohol, the steps in conversion of ethanol to acetic acid remain in some doubt. Likely, ethanol is first oxidized to acetaldehyde and water (39). For further oxidation, two alternative routes are proposed more likely, hydration of the acetaldehyde gives CH2CH(OH)2, which is oxidized to acetic acid. An alternative is the Cannizzaro-type disproportionation of two molecules of acetaldehyde to one molecule of ethanol and one molecule of acetic acid. Jicetobacter... 

Acetic Acid. Manufacture of acetic acid [64-19-7] by homogeneous catalytic methanol carbonylation has become the leading commercial route to acetic acid (eq. 8) (34,35). 

Other Rea.ctlons, The anhydride of neopentanoic acid, neopentanoyl anhydride [1538-75-6] can be made by the reaction of neopentanoic acid with acetic anhydride (25). The reaction of neopentanoic acid with acetone using various catalysts, such as titanium dioxide (26) or 2irconium oxide (27), gives 3,3-dimethyl-2-butanone [75-97-8] commonly referred to as pinacolone. Other routes to pinacolone include the reaction of pivaloyl chloride [3282-30-2] with Grignard reagents (28) and the condensation of neopentanoic acid with acetic acid using a rare-earth oxide catalyst (29). Amides of neopentanoic acid can be prepared direcdy from the acid, from the acid chloride, or from esters, using primary or secondary amines. 

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