Ketene acetic anhydride from

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. 

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). 

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. 

Acylation. Reaction conditions employed to acylate an aminophenol (using acetic anhydride in alkaU or pyridine, acetyl chloride and pyridine in toluene, or ketene in ethanol) usually lead to involvement of the amino function. If an excess of reagent is used, however, especially with 2-aminophenol, 0,A/-diacylated products are formed. Aminophenol carboxylates (0-acylated aminophenols) normally are prepared by the reduction of the corresponding nitrophenyl carboxylates, which is of particular importance with the 4-aminophenol derivatives. A migration of the acyl group from the O to the N position is known to occur for some 2- and 4-aminophenol acylated products. Whereas ethyl 4-aminophenyl carbonate is relatively stable in dilute acid, the 2-derivative has been shown to rearrange slowly to give ethyl 2-hydroxyphenyl carbamate [35580-89-3] (26). 

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). 

The filtrate from this first batch will comprise a solution of 180 to 270 kg of unprecipitated acetylsalicylic acid (1.0 to 1.5 mols), 510 kg of acetic anhydrice (5.0 mols), 600 kg of acetic acid (10.0 mols) (obtained as a by-product in the acetylation step) and 1,200 kg of the diluent toluene. Into this filtrate, at a temperature of 15° to 25°C, ketene gas is now passed through a sparger tube or diffuser plate, with good agitation, until a weight increase of 420.5 kg of ketene (10 mols) occurs. The reaction mixture wiil now contain 180-270 kg of unprecipitated acetylsalicylic acid (1.0-1.5 mols) and 1,532 kg of acetic anhydride (15 mols) in 1,200 kg of toluene. This mother liquor is recycled to the first step of the process for reaction with another batch of 1,382 kg of salicylic acid. On recirculating the mother liquor, the yield of pure acetylsalicylic acid is 1,780 to 1,795 kg per batch. 

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 ... 

Acetic anhydride is to be produced from acetone and acetic acid. In the first stage of the process, acetone is decomposed at 700°C and 1.013 bar to ketene via the reaction ... 

Since reaction of wood with acetic anhydride leads to the formation of acetic acid by-product, which must be removed from the wood, there has been some interest in the use of ketene gas for acetylation (Figure 4.4a). Ketene, for reaction with wood, is produced by pyrolysis of diketene. Provided that the wood contains no moisture, no acetic acid by-product is produced. However, ketene presents handling problems it is very toxic and explosive, and it also has a tendency to dimerize. A comprehensive series of studies of ketene-based acetylation has been performed in Latvia and this work has been reviewed by Morozovs etal. (2003). Hardwoods have been found to be more reactive to ketene than softwoods and the optimal temperature for reaction has been determined as 47 °C. Application of vacuum and treatment of wood with ammonia solution has been used to remove the excess ketene. The reaction of wood with liquid diketene was also studied, with a WPG of 35 % being obtained after reaction for 3 hours at 52 °C. 

Four different methods (vapour-phase acetylation using acetic anhydride, acetylation using ketene gas, liquid phase acetylation using acetic anhydride/xylene, or neat acetic anhydride) were used to acetylate pine wood chips to a variety of WPGs for the production of MUF-bonded particleboards (Nilsson etal., 1988). Composite boards were exposed to unsterile soil in fungal cellar tests. Boards made from ketene acetylated chips were not found to be resistant to decay at the maximum WPG level achieved (17 %) with a liquid acetic anhydride modification, no decay was recorded at a WPG level of c. 18 % after 12 months exposure, whereas with a vapour-phase treatment at the same WPG, evidence for decay was found. 

The reaction of alkynes with nitric acid or mixed acid is generally not synthetically useful. An exception is the reaction of acetylene with mixed acid or fuming nitric acid which leads to the formation of tetranitromethane. A modification to this reaction uses a mixture of anhydrous nitric acid and mercuric nitrate to form trinitromethane (nitroform) from acetylene. Nitroform is produced industrially via this method in a continuous process in 74 % yield. " The reaction of ethylene with 95-100 % nitric acid is also reported to yield nitroform (and 2-nitroethanol). The nitration of ketene with fuming nitric acid is reported to yield tetranitromethane. Tetranitromethane is conveniently synthesized in the laboratory by leaving a mixture of fuming nitric acid and acetic anhydride to stand at room temperature for several days. ... 

Acetic anhydride may be produced by three different methods. The first procedure involves the in situ production from acetaldehyde of peracetic acid, which in turn reacts with more acetaldehyde to yield the anhydride. In the preferred process, acetic acid (or acetone) is pyrolyzed to ketene, which reacts with acetic acid to form acetic anhydride. A new process to make acetic anhydride involves CO insertion into methyl acetate. This may be the process of the future. 

Treatment of chromium (III) acetylacetonate with acetic anhydride and boron trifluoride etherate yielded a complex mixture of acetylated chelates but very little starting material. Fractional crystallization and chromatographic purification of this mixture afforded the triacetylated chromium chelate (XVI), which was also prepared from pure triacetylmethane by a nonaqueous chelation reaction (8, 11). The enolic triacetylmethane was prepared by treating acetylacetone with ketene. The sharp contrast between the chemical properties of the coordinated and uncoordinated ligand is illustrated by the fact that chromium acetylacetonate does not react with ketene. 

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. 

Acetic anhydride is prepared from distilled acetic acid by the ketene method with ethyl phosphate as a catalyst. The water from the first cyclonite wash on the vacuum filter contains on an average 20% of acetic acid which is recovered by extraction with ethyl acetate. 

The consumption of ethyl acetate amounts to 1 kg per 100 kg of cyclonite. From the recovered concentrated acetic acid 85% acetic anhydride is produced by the ketene method. 

The resulting mixture is transferred to an apparatus for fractional distillation, and carefully fractionated, an oil bath being used for heating (Note 3). A low-boiling fraction, consisting of acetone containing some ketene, acetic acid, and a small quantity of acetic anhydride, is removed at atmospheric pressure. As the distillation progresses the temperature of the oil bath is raised to 220° over a period of about an hour and held there until three hours have elapsed from the time distillation started (Note 4). 

These results prompted them to attempt the stereoselective synthesis of the IV-phenylsulfonyl substituted spiro- (3-lactams 150, 151 (Scheme 36) from the N-(phenylmethyIe ne )be n ze nesulfonamide and the ketene valence tautomer of the bicyclic mesoionic compounds such as (2 S,4/ )-4-acetyloxy or benzoyloxy-IV-acyl-prolines 149 in the presence of acetic anhydride [109]. The presence of the stereocenter in position 4 of the cyclic amino acid 149 was found to be sufficient to ensure complete stereoselectivity on the spiranic C-4. 

Notes. (I) Keten is a poisonous gas having a toxicity comparable with phosgene leaks from the apparatus, which must be contained in a fume cupboard, are recognised by a pungent odour resembling acetic anhydride. For this reason it is customary to attach a second receiver flask containing a compound which readily reacts with keten, e.g. aniline, to the other arm of the three-way stopcock. In this way when the reaction in the main flask is complete the keten gas may be diverted to the second receiver flask while the apparatus is switched off and allowed to cool. Escape to the atmosphere of keten is thereby avoided. 

Some reactions of munchnones occur via acylamino ketenes, the covalent valence tautomers of the betaines. The ketenes are intermediates in the thermolysis (see Scheme 22) and in the formation of azetidinones from imines (equation 69) they are thought to be involved in the aminolysis of the mesoionic compounds, which results in amides of a-acylamino acids, and in the formation of the benzodioxin (247) by the combined action of acetic anhydride and tetrachloro-o-benzoquinone on Af-benzoylalanine (equation 70). 

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... 

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