Ketene from acetone

Caution is necessary in work with ketene it is an extremely poisonous gas which about equals phosgene in toxicity and causes approximately the same symptoms (edema of the lungs). 

A number of cyclohexene derivatives can be cleaved thermally to an olefin and a diene, preferably by passage in the vapor phase over red-hot metal wires. This is the reverse of the Diels-Alder diene synthesis. The oldest example is the formation of isoprene from dipentene described by Harries and Gottlob 96 

They gave details of the apparatus, called an isoprene lamp and later used it for other purposes, in which dipentene vapors pass over an electrically heated platinum wire wound on a glass spindle in the same way as in old-fashioned metal wire lamps. 

According to Harries,97 butadiene can be obtained from cyclohexene98 in a very similar way  

Using an apparatus constructed on the same principles, Ott and Schmidt99 prepared carbon suboxide C302 by thermal decomposition of diacetyltartaric anhydride on a feebly glowing platinum catalyst — the nature of chemical reaction is obscure. 

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An apparatus for the preparation of small amounts of ketene from acetone is described. Biltz, Z. angew. Chem. 36, 232 (1923). 

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. 

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 ... 

Ketene may be generated conveniently from acetone by means of a ketene lamp. 1 This apparatus was used by submitters and checkers. Other apparatus (Org. Syn. Coll. Vol. 1, 324) might also be used. 

The thermal decomposition of ketene into carbon monoxide and ethylene is prevented, as far as possible, by the rapid removal of ketene from the hot tube, which is accomplished by the undccomposed acetone vapor. About half the acetone originally used should be collected unchanged as distillate by the vertical condenser. The yield of ketene will fall considerably if less distillate is formed. 

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-... 

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. 

Construction of the suitably substituted geranic acid for making the furan ring has been effected too. For example, Poulter et al. have prepared the substituted geranate 865 by reaction of 4-methyl-3-pentenylcopper with the acetylenic ester 866. The ester 865 then underwent cyclization in the presence of acid to the lactone 867, related to scobinolide (161), and the action of acid on the lactol produced from 867 with diisobutylaluminum hydride gave perillene (849). The lactone 867 has also been prepared by a slightly different method the C9 alcohol 868 was made (in poor yield) from isobutenol and prenyl chloride with butyllithium. The extra carbon atom was introduced by the action of sodium cyanide on the epoxide of 868, and hydrolysis of the cyano group followed by dehydration yielded the lactone 867. The dimethylthioacetal of 867 has been used to synthesize perillene (849). This thioacetal was made from the suitably substituted ketene thioacetal 869 and dimethylsulfonium methylide. Thus the ketene thioacetal 870 (readily prepared from acetone, carbon disulfide, and sodium amylate, followed by methylation °) can be prenylated with lithium... 

Enol acetates are obtained in moderate yield by means of acetic anhydride containing /7-toluenesulfonic acid703 or, better, bypassing ketene into the appropriate ketone containing 0.5 % of sulfoacetic acid at 60-80°.704 705 They are elegantly prepared by transesterification with isopropenyl acetate, CH2==CCH3(OCOCH3),706 which is obtained from acetone and ketene at 55°.704... 

Isopropenyl acetate, obtained from ketene and acetone, reacts as an activated ester of acetic acid and, like its generator ketene, acetylates amides highly exothermally at room temperature.784 Even 1-acetylimidazole, which is difficult to prepare in other ways, is thus obtained from imidazole in 94% yield.785... 

The rate equation for the ketene formation from acetone may therefore be written ... 

It is assumed that acetone at such high temperatures decomposes into methyl and acetyl radicals, and the latter further degrades into methyl radical and carbon monoxide. Then methyl radical abstracts one hydrogen atom from acetone to give methane and an acetyl-methyl radical that decomposes into ketene and another methyl radical. Displayed here is the reaction mechanism for the Schmidlin ketene synthesis. 

Acrylic acid, CH2=CHCOOH, can be produced by a series of processes direct oxidation of acrolein oxidation of ethylene to ethylene oxide, with further reaction with hydrogen cyanide to ethylene cyanhydrin, which is then saponified and dehydrated addition of carbon monoxide and water to acetylene and from acetone by pyrolysis to ketene and addition of formaldehyde to the ketene to produce jS-propiolactone. jS-Propiolactone polymerizes to the corresponding polyester, which depolymerizes at 150 C to acrylic acid ... 

In the laboratory preparation of diketene the mixture of ketene, unchanged acetone, and methane from a ketene generator is passed into a condensing system which is cooled initially in Dry Ice, and the condensate is allowed to warm to room temperature over a period of about twenty-four hours. The resulting mixture of acetone, diketene, and dehydracetic acid is separated by distillation under reduced pressure (50-55% of diketene). More exact control of the concentration and... 

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). 

Carbonyl Compounds. Cychc ketals and acetals (dioxolanes) are produced from reaction of propylene oxide with ketones and aldehydes, respectively. Suitable catalysts iaclude stannic chloride, quaternary ammonium salts, glycol sulphites, and molybdenum acetyl acetonate or naphthenate (89—91). Lactones come from Ph4Sbl-cataly2ed reaction with ketenes (92). 

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. 

Figure 5.6 Alcohols, aldehydes, ketones and acids 15, ethylene glycol 16, vinyl alcohol 17, acetaldehyde 18, formaldehyde 19, glyoxal 20, propionaldehyde 21, propionaldehyde 22, acetone 23, ketene 24, formic acid 25, acetic acid 26, methyl formate. (Reproduced from Guillemin et at. 2004 by permission of Elsevier)...

Highly enantioselective Mannich-type reactions of A-(2-hydroxyphenyl) aldi-mines with ketene trimethylsilyl acetals and of A-Boc-aldimines with acetyl acetone or furan are catalyzed by chiral phosphonic acids 9 derived from 3,3 -diaryl-(l )-BlNOL and POCI3 (Scheme 12.7). ... 

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. 

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