Ketene production from acetone

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. 

Ketene, H,C = C = 0, has been obtained by the pyrolysis of many compounds containing the CHjCO—group. However, its preparation from acetone has been the most successful from the standpoint of the laboratory and is carried out by passing the vapors through a combustion furnace at 650° (30%) or over a hot Chromel A wire filament at 700-750° (90%). The product is contaminated with ethylene, carbon monoxide, and methane. It may be purified by dimerization followed by depolymerization (cf. method 246). More often than not, since ketene dimerizes readily, it is passed directly from the generator into a reaction vessel for immediate consumption. 

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). 

Wolff rearrangements were also observed when most of the same acylsi-lyldiazoalkanes were photolyzed in acetone instead of benzene.21 The ketenes 185 resulting from a 1,3-methyl migration of the silene were detected in addition to the expected ene product 186 derived from the reaction of the silene with acetone (or other enolizable ketones) (Eq. 58). When R = Ad, only the cyclic siloxatene 187 was formed under the same... 

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. 

The liquids from all three cylinders are combined and fractionally distilled (Note 4). Most of the acetone is removed at room temperature under a pressure of 20 mm the last small portion is removed under atmospheric pressure. When the distillation temperature reaches 120°, the system is evacuated to a pressure of 80-100 mm. (Note 5), and the ketene dimer is collected within the boiling range 67-69°/q2 mm. The yield of pure product is 42-46 g. (50-55 per cent of the theoretical amount) (Notes 6 and 7). 

Acetyl-4//-pyrido[ 1,2-a]pyrimidin-4-one 186 was formed in the reaction of ethyl iV-(2-pyridyl)formimidate 187 (R = H) and ketene in acetone at ambient temperature for 2 days in 12% yield (83H597). It was assumed that diketene formed first from ketene, then it reacted with the formimidate 187 (R = H). When excess ketene gas was passed over formimidates 187 (R = H and Me) at 75°C for 0.5-1.5 hours without solvent, 4//-pyrido[ 1,2-a]pyrimidin-4-ones 188 and 7V-(2-pyridyl)formamides were obtained in 25-85% and 0-45% yields, respectively. From the 5-methyl derivative of the formimidate 187 (R = 5-Me) only pyridopyrimidinone 188 (R = 7-Me) was obtained. It was proposed that both products were formed by 1,4-... 

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... 

The reaction starts from [4+1] cycloaddition of the isocyanide to the electron-deficient heterodiene moiety of acid 396 to form intermediate iminolactone 397 that loses acetone to give acyl ketene 398 which then reacts with pyrrole at the ketene carbonyl to form the second acyl ketene 399 (Scheme 86). Ring closure of this ketene leads to the final product 400. Similar reaction conditions as described above, were employed for indole and 2-methylindole (Equation 94). 

Acetic acid decomposed on the (114[-faceted of the TiOi (001) surface to produce ketene as well as acetone [44]. The acetone generated arose from bimolecular coupling of pairs of surface acetates at four-fold coordinate cations this is analogous to the production of formaldehyde from surface formate on identically prepared surfaces. The reaction of propionic acid corresponded directly to the reaction of acetic acid, producing methyl ketene and 3-pentanone [46]. 

Another method makes the urea through the intermediate acetoacetanilide (2.12) 44 The catalyst was reused five times with no loss in activity. The by-product acetone might be py-rolyzed to ketene which would dimerize to diketene that would react with more amine to form acetacetanilide. In another variant from Asahi Chemical, ethyl TV-phenylurethane... 

Photoexcited acetone has been used previously to generate aromatic compounds from dihydroaromatic compounds by hydrogen abstraction. Further studies14 have revealed the limitations of this procedure, and shown that other products are often formed from ketyl and hydroaromatic radical coupling. Only the conversion of indoline into indole occurs in reasonable yield (46%). Hydrogen abstraction by excited acetone also appears to be responsible for an unusual reaction on irradiation of friedelin (13) in ether-acetone.16 The known intramolecular reaction which occurs in the cyclohexanone ring gives a keten (Scheme 2), but this is followed by addition of a ketyl radical and subsequent reduction to produce an hydroxycarbonyl compound (14). 

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. 

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. 

Two competitive methods are developed for the production of ethyl acetoacetate, both based on the dimerization of ketene (Scheme 2.31). By the first method, ketene is produced by thermal breakdown of acetone at over 300 °C [22], while the second wet method uses strong bases as catalysts for the elimination of hydrogen chloride from acetyl chloride [23]. Spontaneous dimerization results in a relatively stable four-membered lactone, known as diketene on the market, which on alcoholysis affords ethyl acetoacetate [24]. 

---