Decarboxylation exothermic

Replacement of hydroxyl by fluorine converts perfluoroalkanecarboxylic acids toperfluoroalkanoylfluorides The short chain acids react exothermally with FAR added in a dropwise manner, whereas the longer chain acids require heating [78] (equation 49) Attempts to fluorinate pentafluorobenzoic acid with FAR leads to decarboxylation to give pentafluorobenzene [78]... 

Pyruvic acid is not stable at ambient temperature when it is stored for a long period of time. It can only be stored in a refrigerated room. A bottle of this acid was stored in a laboratory at 25°C and detonated, probably because of the overpressure created by the formation of carbon dioxide. Indeed, with diacids and complex acids the decomposition is made by decarboxylation. In this particular case, this decomposition should give rise to acetaldehyde. It could be asked whether, in the exothermic conditions of this decomposition, a polymerisation of this aldehyde (see Aldehydes-ketones on p.310) did not make the situation worse. 

An inhomogeneous mixture of the dry salt with a little water exploded violently after 30 min [1], This was probably owing to exothermic decarboxylation generating the ad-salt of nitromethane, which is explosively unstable. The decomposition of sodium nitroacetate proceeds exothermically above 80° C [2],... 

Succinic anhydride is dimerised to 1,6-dioxaspiro [4.4] nonane-2,7-dione by heating with sodium hydroxide. Modification of an existing procedure by adding further sodium hydroxide after the initial reaction led to a severe exothermic reaction after heating for some 30 h which fused the glass flask to the heating mantle, probably at a temperature approaching 550°C. The reason for this was not known [1], At elevated temperatures and under influence of alkali, succinic acid condenses decarboxylatively beyond the dimeric spiroacetal, sometimes explosively. Contamination of the anhydride with base is to be avoided [2],... 

When a solution of 1-aminopyridinium iodide (143) in DMF was treated with anhydrous potassium carbonate, the mixture developed the deep blue color characteristic of pyridine 1-imine (144) addition of EP caused an immediate exothermic reaction giving the pyrazolopyridine 145 in 48% yield311 hydrolysis and decarboxylation gave a high yield of pyrazolo[l,5-a]pyridine (146).311 Many reactions of this type have now been carried out,312 and the regioselectivity for the cydization of 3-substituted derivatives has been examined,313... 

Lower temperatures than those mentioned above inhibit the exothermic reaction and the reaction time is extended to approximately 24 hr. Less efficient cooling results in warming to 70-80°C, which causes decarboxylation of the Intermediate carboxylate and/or simple oxidation by potassium hypochlorite. 

When a carboxylic acid loses CO the reaction is called decarboxylation. Although the reaction is usually exothermic, the energy of activation is usually high, making the reaction difficult to carry out. The energy of activation is lowered when the flea r bon is a carbonyl because either the anion intermediate is stabilized by resonance or tire acid forms a more stable cyclic intermediate. (A carboxylic acid with a carbonyl p-carbon is called a fi-keto acui.)... 

After two minor dust explosions in an industrial adipic acid dryer, evidence was obtained that adipic acid forms an iron complex capable of both decarboxylation/ dehydration of adipic acid to cyclopentanone and of catalysing air oxidation, giving exotherms from as low as 135°C. 

This reaction is the most dangerous in the commercial synthesis since it requires at least 50 °C to start, and once the reaction starts it is very exothermic. This would increase the heat under adiabatic conditions still further until at 120 °C the carboxylic acid would decarboxylate in another exothermic reaction creating C02 gas thus increasing the pressure in the reactor. The research group at Pfizer designed the... 

This particular reaction model was chosen because the authors proposed that proton transfer should be concerted with decarboxylation. This model reaction is quite exothermic in the gas phase (— 61.9 kcal mol-1), but in an environment of low dielectric (s = 4), as might be expected in an enzyme active site,38 the AH is a reasonable 17.6 kcal mol-1. This barrier is —25 kcal mol-1 less than the AH calculated by these authors for the uncatalyzed decarboxylation of orotate in a water dielectric, which is almost identical to the magnitude of catalysis observed experimentally.1,6 The authors thus concluded that concerted decarboxylation and proton transfer to the 4-oxygen appears to be a viable catalytic pathway. This particular viewpoint has been challenged by Warshel et al., whose quantum mechanical studies argue against pre-protonation.61... 

Continuous processes have recently been described in two patents for the preparation of cyclopropylamine, 10, (Figure 13.11), an intermediate for both the pharmaceutical and agricultural industries. In the earlier patent a two-reactor train was used in a CSTR approach [20]. To the first flask were charged simultaneously a solution of 8 in H20 and an aqueous solution of NaOCl.The overflow from this reactor was collected in a second reactor which was charged with 45% aqueous NaOH at temperatures below 30 °C. The extended addition allowed for temperature control of the very exothermic hydrolysis and decarboxylation. Subsequently the basic mixture was transferred to a distillation apparatus, and 10 was isolated by distillation in yields as high as 96%. 

The driving force for a number of fragmentation reactions, which are often endothermic, is an increase in entropy. An example of such transformations is the decarbonylation reaction of acyl radicals [RC(=0) ], which is generally endothermic, but can proceed with reasonable rates (104-107s 1 at 25 °C). In addition to these reactions being exothermic, they are also favoured by entropy and both of these factors contribute to give a fast and irreversible decarboxylation reaction. 

Decarboxylation of an aliphatic acid to the hydrocarbon is best effected by the so-called salt degradation method. That method is to treat the silver or mercury salt of, preferably, an aliphatic or alicyclic carboxylic acid with bromine in an inert solvent a halogenated hydrocarbon is then formed, together with carbon dioxide and the metal bromide, usually in an exothermic reaction, and the bromine can then usually be readily removed either cata-lytically or by means of a Grignard reagent (the Hunsdiecker reaction) ... 

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