Of acetone to ketene

Jeffreys, in a treatment of the design of an acetic anhydride manufacturing facility, states that one of the key steps is the vapor-phase cracking of acetone to ketene and methane ... 

For pyrolyses that require higher temperatures, a reaction flask such as that shown in Fig. l-6(b) is useful. The reactant is placed in the flask and the air is replaced with nitrogen. The reactant is brought to a gentle reflux and the electrical coils are then heated by passing current through them. The product (if sufficiently volatile) distills from the reactor, while the unpyrolyzed reactant returns to the reaction flask. A reactor of this design has been used for the conversion of cyclohexene to 1,3-butadiene and for the pyrolysis of acetone to ketene. 

Since both the radicals CH3CO and CH3COCO rapidly decompose, the experimental methods available at present are not adequate to decide between initiation steps (2) and (2 ). Reactions (3), or (3 ), (4) and (6) necessarily follow step (2), or (2 ), if chains are to occur. Since acetone is produced in about 10-15 % yield of the biacetyl decomposed, reaction (5) has to be assumed. Other alternatives for acetone formation, as for instance the recombination of CH3 and CH3CO radicals or the addition of CH3 to ketene, are not able to explain the high acetone yield around 500 The mechanism of reaction (5) is uncertain (see Section 7 in Part II). 

It is possible that the dehydrogenation of aldehyde to ketene, as in the well known case with acetone, and the subsequent reaction of ketene and aldehyde to give carbon dioxide and an unsaturated hydrocarbon is the explanation.70 The presence of acetic acid might also be accounted for by the interaction of ketene and water. No such reaction would be expected in the case of isopropanol since a temperature of 650° C. is required for the fonnation of ketene from acetone and only traces of carbon dioxide have been reported from this alcohol.81... 

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. 

Acetone cracks to ketene, and may then be converted to anhydride by reaction with acetic acid. This process consumes somewhat less energy and is a popular subject for chemical engineering problems (24,25). The cost of acetone works against widespread appHcation of this process, however. 

The production of ketene by this method has no significant environmental impact. The off-gases from the ketene furnace are either circulated to the furnace and burned to save energy or led to a flare system. The reaction can also be carried out at 350—550°C in the presence of alkaH-exchanged zeoHte catalysts (54). Small quantities of ketene are prepared by pyrolysis of acetone [67-64-1] at 500—700°C in a commercially available ketene lamp (55,56). 

Thermal Stability. The saturated C —C 2 ketones are thermally stable up to pyrolysis temperatures (500—700°C). At these high temperatures, decomposition can be controlled to produce useful ketene derivatives. Ketene itself is produced commercially by pyrolysis of acetone at temperatures just below 550°C (see Ketenes, ketene dil rs, and related substances). 

The industrial precursor to 2,4-pentanedione is isopropenyl acetate, produced from acetone and ketene (307,308). The diketone is formed by the high temperature isomerization of isopropenyl acetate over a metal catalyst (309—311). 

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 ... 

We have also observed competition between products resulting from C-C and C-H bond activation in reactions of Y with propene,138 propyne,143 2-butyric,143 four butene isomers,138 acetaldehyde,128 acetone,128 ketene,144 and two cyclohexadiene isomers,145 as well as for Zr, Nb, Mo, and Mo with 2-butyne.143 In this chapter, we use the term C-C activation to describe any reaction leading to C-C bond fission in which the hydrocarbon reactant is broken into two smaller hydrocarbon products, with one hydrocarbon bound to the metal. It is important to note, however, that C-C activation does not necessarily require true C-C insertion. As will be shown in this chapter, the reaction of Y, the simplest second-row transition metal atom, with propene leads to formation of YCH2 +C2H4. The mechanism involves addition to the C=C bond followed by H atom migration and C-C bond fission, rather than by true C-C insertion. 

An example of a reacting system with a network involving reactions in series is the decomposition of acetone (series with respect to ketene) (C)... 

Conversion data were obtained in a tubular flow reactor for the pyrolysis of acetone at 520 C and 1 atm to form ketene. The reactor was 3.3 cm ID and 80 cm long. Find a rate equation. 

Ketene can be generated conveniently by pyrolysis of acetone in a hot tube or over a hot wire in a ketene lamp, or by pyrolysis of diketene in a hot tube. Other methods of preparation have been summarized. It has been shown that diketene cracks quite cleanly to ketene, although some allene and carbon dioxide are formed at the same time. ... 

The two most convenient procedures for preparing ketene are the present one and the pyrolysis of acetone over a hot wire. The latter procedure can give ketene at a faster rate (0.45 mole per hr. versus 0.2 mole per hr.), but it takes considerable adjustment to get optimum conditions, and trouble is sometimes caused by the wire getting coated with carbon. Furthermore, because the efl ciency of a given wire coil varies with time, passing throu a maximum, frequent calibration of the apparatus is necessary. The present method is more reliable and is the method of choice, when diketene is available. 

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. 

Malonyl chloride reacted with boiling acetone to give the bicyclic 2 1 adduct 210 comprising a pyranone and a l,3-dioxan-4-one moiety (Scheme 99). The modest yield was compensated for by the ease of its preparation. Compound 210 bears a chloride which is almost as reactive as an acyl chloride and which can be substituted by various nucleophiles in a Stille coupling in modest yields <1997SL895>. Treatment of malonyl chloride with ketene and acetone at low temperature afforded symmetric bis(l,3-dioxin-4-ones) in 60% yield although a different reaction pathway may be assumed (Scheme 99) <2000TL4959>. 

With conjugated dienes, photocycloaddition of carbonyl compounds occurs at one of the double bonds to give vinyloxetanes. An interesting example is the reaction of acetone with 2-methyl-l,3-butadiene, which gave the two oxetanes (60) and (61) in a ratio of 3 1 and a total yield of about 20% (72JA8761). Other alkenes which have been used for photosynthesis of oxetanes include enol ethers, ketene acetals, enamines, allenes and diketene, with the reaction of the last compound with benzaldehyde illustrated in equation (105) (75CPB365). 

Preparation of Ketene. Ketene was prepared by the pyrolysis of acetone using a generator identical to that described in the literature (3). The generator was calibrated for ketene yield by passing the effluent gas through standard sodium hydroxide. 

For some years acetone has been converted to ketene (CH2 CO) by high temperature decomposition. The ketene is reacted with acetic acid to give acetic anhydride. Since the mid-1930 s acetone has also been one of the basic raw materials for methacrylate plastics. The first step in this process involves the addition of hydrocyanic acid to acetone to produce acetone cyanohydrin (CH3)2CO + HCN(CHs)2C(OH)CN. The methacrylate ester monomers are then made by reacting with methanol or another alcohol in the presence of sulfuric acid or some other dehydrating agent. 

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. 

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). 

Three 300-cc. gas-washing cylinders (Note 1) are connected in series, and the second and third cylinders are charged with 150 cc. each of dry acetone. Each of the three cylinders is immersed, in a thermos bottle, in sufficient Dry Ice-acetone cooling mixture to cover half of the cylinder. Ketene gas, prepared by the pyrolysis of acetone (Note 2), is passed through the system (Note 3) until a quantity of 2 moles has been introduced. This... 

Pyrolysis of Meldrum s acid (2,2-dimethyl-l,3-dioxane-4,6-dione) 362 proceeds by loss of acetone and CO2 to give ketene. Because of the ready availability of the starting material and the ease with which it can be functionalized at the acidic 5-position, pyrolysis of Meldrum s acid derivatives has been widely studied. Pyrolysis of the 5-formyl and 5-acyl derivatives 363 gives formyl or acylketenes 364, which can be trapped in a number of ways170-171. in many cases, loss of acetone and CO2 is accompanied by loss of CO to give a carbene, and this is illustrated by FVP of 365 at 560 °C which affords the Q -diketone 368 by way of ketene 366 and carbene 367172. 

Mikami et al. also investigated the addition of ketene silyl acetals. They found that addition of the silyl enol ether of acetone and allylic silanes did not result in the synthesis of substituted l,2-dihydro[60]fullerenes [218a,220], In 1997, Mikami et al. [221] reported the photoaddition of allylic stannanes that leads to monoallylation of C6o (Scheme 13). 

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