Acid anhydrides, pyrolysis

Hexafluorabenzene may also add to methylene Lnphenylphosphorane to form a new pentafluorophenyl-bearing yhde Treatment of tins ylide with an acid fluonde or acid anhydride followed by pyrolysis (shown in equation 58) forms the corresponding pentafluorophenylacetylene [66] (equation 58). 

Reactions lla-e add up to Reaction 10. Reactions lla-b have been shown above to be catalyzed by Rh/CH3l. Reaction 11c, i.e. acid-catalysed pyrolysis of EDA to acetaldehyde and acetic anhydride, is well documented (9). Both reaction lid, hydrogenation of aldehyde, and Reaction lie, carbonylation of alcohols, are of course well known. The reaction sequence is in agreement with the fact that EDA and AH, especially in short-duration experiments, are detected as by-products. Acetaldehyde is also observed in small quantities, but no ethanol is found. Possibly, Reactions lid and He occur concertedly. We have separately demonstrated that both EDA and AH are suitable feeds to produce propionic acid under homologation reactions conditions. We thus demonstrated... 

With the discovery of benzyne formation by pyrolysis of phthalic anhydride, a new field was opened for the investigation of aryne reactions at high temperatures. A first concern was to determine the generality of aryne formation from aromatic acid anhydrides. Such syntheses could be of considerable significance because of the enormous quantities of aromatic mono- and polyanhydrides available from petroleum aromatics by oxidation. 

A number of reactions of metal salts can be rationalized in terms of the formation of a carbanion adjacent to the carboxylate. Dibasic metals such as calcium bring two carboxylate units close to each other so that the carbanion formed adjacent to one carboxylate may attack the carbonyl of the other. Thus pyrolysis of calcium acetate affords propanone (acetone) (Scheme 3.62). A similar reaction is found in the pyrolytic cyclization of some dicarboxylic acid anhydrides. Heating Cg and dicarboxylic acids gives cyclopentanones and cyclohexanones... 

Another group of polymers with good heat resistance includes certain aryl-alicyclic compounds. They are generated from the polycondensation of 4,4 -diaminodiphenyl oxide with various anhydrides such as tricyclo[4,2,2,0 ]dec-9-ene-3,4,7,8-tetracarboxylic acid anhydride, 9-oxatricyclo[4.2,2,0 ]nonane-3.4,7,8-tetracarboxylic acid anhydride, cyclobutene-1,2,3,4-tetracarboxylic acid anhydride, and bicyclo[2,2,2]octane-23,5,6-tetracarboxylic acid anhydride. Thermal stability of these polymers is affected by the ring stability (strain) regardless the true chemical structure. Pyrolysis at 650° C generates some compounds that are the same in nature and some others that are characteristic for each polymer. The main decomposition paths, as indicated by the main pyrolysis products are shown below for each polymer (Ar = 4,4 -diphenylene oxide) ... 

Reaction between equimolar amounts of dialkyl chlorophosphites and acyclic acid anhydrides at 50°C has been reported to produce the corresponding dialkyl acylphosphonates in satisfactory yields (70-75%), but the general utility of this procedure remains to be demonstrated. On pyrolysis, diethyl 1-oxoethyIphosphonate produces ketene and diethyl phosphite. ... 

The condensation polymerization of IX and X yields oligomers only (see Table I). Condensation of IX gave dithioglycolide XI as a byproduct (4). XI was also obtained by pyrolysis of poly(thioglycolide) (7). The polymerization of S-carboxy-a-mercaptoacetic acid anhydride XII using bases as initiators has been studied in detail (4). It is similar in many respects to the well-known polymerization of N-carboxy- -amino acid anhydrides. 

Gas phase pyrolysis of quinoxaline-2,3-dicarboxylic acid anhydride (58) yields o-phthalonitrile (60) in 72% yield. The intermediacy of the quinox-alyne intermediate (59) is postulated." The anhydride undergoes... 

On acetylation of karakolidine with acetic anhydride and pyridine at room temperature, a diacetate derivative (109) was formed, while treatment with acetyl chloride yielded a tetraacetate derivative (110). Pyrolysis of compound 110 followed by alkaline hydrolysis yielded the normal pyrolysis product, pyrokarakolidine (111), and a rearranged product, iso-pyrokarakolidine (112). The latter compound was obtained from pyrokarakolidine (111) by treatment with methanolic hydrochloric acid. This pyrolysis reaction confirmed the presence of the C-8 acetoxyl and C-16 methoxyl groups in karakolidine. Oxidation of karakolidine with Kiliani... 

The oldest method for the formation of a ketene, used by Staudinger in his studies on diphenylketene, is the reduction of an a-haloacyl halide with activated zinc. Most often, the ketene components used in the Staudinger reaction are usually produced by either of two ways the elimination of an acyl chloride (or less frequently another activated carboxyl derivative) in the presence of a base, or the Wolff rearrangement of a-diazocarbonyl compounds.The ketene is usually generated in situ in the presence of the imine however, if the ketene is stable enough, it may be prepared separately and then introduced into reaction with the imine. Other methods to produce ketenes have been used less often in the Staudinger reaction due to incompatibility with the imine component or p-lactam product or due to the harsh conditions required, such as the high temperatures employed in the pyrolysis of acid anhydrides or ketone acylals. 

Attempts to generate a related didehydrospecies, the anhydride of acetylene dicarboxylic acid (23), ended in failure, although the authors were sufficiently optimistic to reserve future studies in this area to themselves. A few years later the intermediacy of 23, along with the four-membered cycloalkyne 24, was claimed during the pyrolysis of acetoxymaleic acid anhydride. 

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