Ketene from acetic acid

Ketene from acetic acid Reduced reacdon temperature, eliminadon of recovery of ketene 1,781 0.64 0.001... 

Uses. The lowest member of this class, ketene itself, is a powerful acetylating agent, reacting with compounds containing a labile hydrogen atom to give acetyl derivatives. This reaction is used only when the standard acetylation methods with acetic anhydride or acetyl chloride [75-36-5] do not work weU. Most of the ketene produced worldwide is used in the production of acetic anhydride. Acetic anhydride is prepared from the reaction of ketene and acetic acid. 

The production of acetic anhydride from acetic acid occurs via the intermediate formation of ketene where one mole of acetic acid loses one mole of water ... 

In the mid-l O s, it was found that acetic acid itself could be catalytically dehydrated to ketene, which when absorbed in fresh acid gave the anhydride. Soon after this process became commercially established, the older processes of making the anhydride were discontinued. By this time synthetic acetic acid was being made from acetylene via acetaldehyde oxidation, from synthetic ethyl alcohol also via acetaldehyde, and by the direct oxidation of fermentation ethyl alcohol. The ketene route to acetic anhydride, in addition to starting from acetic acid, later employed acetone as raw material. 

Figure 17.14. Some unusual reactor configurations, (a) Flame reactor for making ethylene and acetylene from liquid hydrocarbons [Patton et al., Pet Refin 37(li) 180, (1958)]. (b) Shallow bed reactor for oxidation of ammonia, using Pt-Rh gauze [Gillespie and Kenson, Chemtech, 625 (Oct. 1971)]. (c) Sdioenherr furnace for fixation of atmospheric nitrogen, (d) Production of acetic acid anhydride from acetic acid and gaseous ketene in a mixing pump, (e) Phillips reactor for low pressure polymerization of ethylene (closed loop tubular reactor), (f) Polymerization of ethylene at high pressure.

Presumably, 1-acetoxycyclopropanol (88) is the intermediate in this reaction as well as that between the hydrate and ketene. 80> Although 88 has not been isolated in the above cases, it may be prepared from acetic acid and cyclopropanone and reacts with ketene to give 87. 5>15>... 

Cyclization of halogenoaryl-substituted /3-lactams can be mediated by palladium(n) derivatives. The formation of the lactam from a ketene-imine addition and subsequent cyclization of the product can be carried out as a one-pot process. As an example, in situ generation of the ketene from the acid chloride and formation of the /3-lactam followed by addition of palladium(ll) acetate, triphenylphosphine, and thalium carbonate gave 495 in 54% yield (Equation 79) <1995TL9053>. 

Acetic Anhydride. Acetic anhydride is required as a process intermediate in acetylations. To obtain acetic anhydride from acetic acid, acetic acid is first pyrolyzed to ketene, which then reacts with recovered acetic acid to yield the anhydride. 

In the ketene process, acetic acid is thermally dehydrated at 750°C to ketene. The ketene is separated from byproduct water and reacted with another mole of acetic acid to produce acetic anhydride. Figure 10.16 is a schematic diagram of this process. 

Fig. 10.16. Acetic anhydride from acetic acid ketene process. (Chem Systems Report No. 97/98- 7. Copyright Nexant Chem Systems, Inc. and used by permission of the copyright owner.)...

A portion of the acetic acid, which is the major product, can be converted in a separate unit to acetic anhydride. Acetic anhydride may be produced from acetic acid, acetone, or acetaldehyde. With both acetic acid and acetone the initial product is ketene. The ketene is highly reactive and reacts readily... 

Acrolein and condensable by-products, mainly acrylic acid plus some acetic acid and acetaldehyde, are separated from nitrogen and carbon oxides in a water absorber. However in most industrial plants the product is not isolated for sale, but instead the acrolein-rich effluent is transferred to a second-stage reactor for oxidation to acrylic acid. In fact the volume of acrylic acid production ca. 4.2 Mt/a worldwide) is an order of magnitude larger than that of commercial acrolein. The propylene oxidation has supplanted earlier acrylic acid processes based on other feedstocks, such as the Reppe synthesis from acetylene, the ketene process from acetic acid and formaldehyde, or the hydrolysis of acrylonitrile or of ethylene cyanohydrin (from ethylene oxide). In addition to the (preferred) stepwise process, via acrolein (Equation 30), a... 

Single pulse, shock tube decomposition of acetic acid in argon inv olves the same pair of homogeneous, molecular first-order reactions as thermolysis (19). Platinum on grapliite catalyzes the decomposition at 500—800 K at low pressures (20). Ketene, methane, carbon oxides, and a variety of minor products are obtained. Photochemical decomposition yields methane and carbon dioxide and a number of free radicals, wliich have complicated pathways (21). Electron impact and gamma rays appear to generate these same products (22). Electron cyclotron resonance plasma made from acetic acid deposits a diamond [7782-40-3] film on suitable surfaces (23). The film, having a polycrystalline stmcture, is a useful electrical insulator (24) and widespread industrial exploitation of diamond films appears to be on the horizon (25). 

The processes for the manufacture of acetic anhydride have included, initially, the distillation of wood pulp, which was followed by the ketene route from acetic acid or acetone and finally the ethylene based oxidation of acetaldehyde. The carbonylation of CH3OAC to acetic anhydride has in part replaced anhydride capacity from the more expensive processes. 

Lewis add complexes formed by the reactions of various aminoalcohols with Et2AlG [778, 824] or by the reaction of Et2Zn with a chiral sulfamide [806] have displayed a low efficiency in the asymmetric condensations of ketene and thioketene silyiacetals derived from acetic acid with aldehydes. Disappointing se-lectivities have also been observed with some binaphtol-titanium complexes [778]. However, Mikami and Matsukawa [1296] recently performed the enantioselective condensation of various aldehydes with acetic acid derivatives in the presence of a chiral binaphtol-titanium complex. Good selectivities were observed when the reaction was performed at 0°C in toluene (Figure 6.95). Quaternary ammonium fluorides derived from cinchona alkaloids have been proposed as catalysts to perform additions of enoxysilanes derived from ketones to PhCHO, but the observed selectivities are modest [1303],... 

Acetic acid is the main impurity in acetic anhydride, which is prepared industrially from acetaldehyde or from acetic acid and ketene. The acid can be removed by fractionation, and residual amounts thereof by prolonged boiling with magnesium turnings.33... 

Secondary fragments are formed from the primary ones by single or consecutive eliminations of formaldehyde (30), methanol (32), ketene (42), acetic acid (60), methyl acetate (74), methoxymethyl acetate (104), or acetoxymethyl acetate (132). Mechanisms for elimination of formaldehyde from the primary fragment m/e 89 have already been described (see Section IV,3 p. 57), as well as those for the elimination of acetic acid (60) and the subsequent elimination of ketene (42) (see Section IV,1 p. 53). 

While acetone would serve as a source of ketene in a number of locations, the acetic acid dehydration would predominate and the acetic acid based ketene process is still widely practiced at the start of the 2r century. While acetone had some attractive features, particularly the generation of an inert co-product (methane) rather than reactive water which can destroy ketene, there are some sound reasons the acetic acid process predominated. First, let s recall that during the period 1910-1920, representing the time these processes were introduced, acetone was still made from calcium acetate, so acetone was obtained, at the time, in a two step process from acetic acid. The choice of acetic acid skipped two steps and eliminated wastes. 

The preparation of acetic anhydride from acetic acid at a high temperature probably depends upon the primary formation of ketene and its reaction with acetic acid. 

Figure 14.8a shows a simplified flowsheet for the manufacture of acetic anhydride as presented by Jeffries. Acetone feed is cracked in a furnace to ketene and the byproduct methane. The methane is used as furnace fuel. A second reactor forms acetic anhydride by the reaction between ketene from the first reaction and acetic acid. 

Silyl enol ethers are other ketone or aldehyde enolate equivalents and react with allyl carbonate to give allyl ketones or aldehydes 13,300. The transme-tallation of the 7r-allylpalladium methoxide, formed from allyl alkyl carbonate, with the silyl enol ether 464 forms the palladium enolate 465, which undergoes reductive elimination to afford the allyl ketone or aldehyde 466. For this reaction, neither fluoride anion nor a Lewis acid is necessary for the activation of silyl enol ethers. The reaction also proceed.s with metallic Pd supported on silica by a special method[301j. The ketene silyl acetal 467 derived from esters or lactones also reacts with allyl carbonates, affording allylated esters or lactones by using dppe as a ligand[302]... 

First prepared by C. F. Gerhardt from ben2oyl chloride and carefully dried potassium acetate (1), acetic anhydride is a symmetrical iatermolecular anhydride of acetic acid the iatramolecular anhydride is ketene [463-51-4]. Benzoic acetic anhydride [2819-08-1] undergoes exchange upon distillation to yield benzoic anhydride [93-97-0] and acetic anhydride. 

The materials of constmction of the radiant coil are highly heat-resistant steel alloys, such as Sicromal containing 25% Cr, 20% Ni, and 2% Si. Triethyi phosphate [78-40-0] catalyst is injected into the acetic acid vapor. Ammonia [7664-41-7] is added to the gas mixture leaving the furnace to neutralize the catalyst and thus prevent ketene and water from recombining. The cmde ketene obtained from this process contains water, acetic acid, acetic anhydride, and 7 vol % other gases (mainly carbon monoxide [630-08-0][124-38-9] ethylene /74-< 3 -/7, and methane /74-< 2-<7/). The gas mixture is chilled to less than 100°C to remove water, unconverted acetic acid, and the acetic anhydride formed as a Hquid phase (52,53). 

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). 

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