Carboxylic acids thermal decarboxylation

There are a number of reasons why derivatization of samples is necessary. First, the hydroxide and carboxylic moieties may form hydrogen-bonds in the gas phase, thus resulting in poor chromatography. Secondly, the compounds may sorb onto the chromatographic system, resulting in poor chromatography performance, peak shape, and in the case of very low concentrations, non-detection of the analytes. Furthermore, it is known that -tetrahydrocannabinol carboxylic acid thermally decarboxylates at temperatures above 110-120° C, and converts into A -tetrahydrocannabinol. While in some laboratories this is assumed to be quantitative, this may not always be the case. Derivatization will allow determination of both the A -tetrahydrocannabinol and its carboxylic acid. In addition, in the case of very low concentrations of analytes, derivatization will improve the limits of determination and quantification. 

A cyclopropyl to allyl radical rearrangement could also be induced in 20 % yield by the thermal decomposition (in carbon tetrachloride at 32 °C with sonication) of the A-hy-droxypyridine-2-thione ester of l-fluoro-2,2-diphenylcyclopropane-l-carboxylic acid (Barton decarboxylation reaction). ... 

The thermal decarboxylation of malonic acid derivatives is the last step m a multistep synthesis of carboxylic acids known as the malonic ester synthesis This synthetic method will be described m Section 21 7... 

The main feature of the reactivity of pyrrole-2-carboxylic acids is the ease with which the carboxyl group is removed. Thermal decarboxylation is a preparatively useful reaction. 

Benzoxepins require drastic conditions for the thermal rearrangement to naphthols. When 3-benzoxepin-2,4-dicarboxylic acid is heated to 300 C, a decarboxylation reaction takes place and 3-hydroxynaphthalene-2-carboxylic acid (10) is formed in 44% yield.91... 

Although Ce(IV) oxidation of carboxylic acids is slow and incomplete under similar reaction conditions , the rate is greatly enhanced on addition of perchloric acid. No kinetics were obtained but product analysis of the oxidations of -butyric, isobutyric, pivalic and acetic acids indicates an identical oxidative decarboxylation to take place. Photochemical decomposition of Ce(IV) carbo-xylates is highly efficient unity) and Cu(ll) diverts the course of reaction in the same way as in the thermal oxidation by Co(IIl). Direct spectroscopic evidence for the intermediate formation of alkyl radicals was obtained by Greatorex and Kemp ° who photoirradiated several Ce(IV) carboxylates in a degassed perchloric acid glass at 77 °K in the cavity of an electron spin resonance spectro-... 

A reaction mechanism with Fe304 as catalyst has been proposed [68], in agreement with previous work concerning decarboxylation of acids in the presence of a metal oxide [83]. After the transient formation of iron(II) and iron(III) carboxylates from the diacid and Fe304 (with elimination of water), the thermal decarboxylation of these salts should give the cyclic ketone and regeneration of the catalyst. 

Carboxylic acids are thermally stable. Decarboxylation of carboxylic acids is observed at 600 K and higher in the absence of dioxygen [4], At the same time, the decarboxylation of fatty acids in oxidized cumene was observed at 350 K [71]. The study of C02 production from oxidized acetic, butanoic, isobutanoic, pentanoic, and stearic acids labeled with 14C in the... 

Thermal decarboxylation of pyrimidylcarboxylic organotin esters is another means to prepare the corresponding stannylpyrimidines [33]. This method obviates the intermediacy of lithiated pyrimidine species that would undergo undesired reactions at higher temperatures. The decarboxylation occurs at the activated positions. Therefore, thermal decarboxylation of tributyltin carboxylate 62, derived from refluxing carboxylic acid 61 with bis(tributyltin) oxide, provided 4-stannylpyrimidine 63. Addition of certain Pd(II) complexes such as bis(acetonitrile)palladium(II) dichloride improved the yields, whereas AIBN and illumination failed to significantly affect the yield. 

Naphthenic acids, complex carboxylic acids that are believed to have a cyclopentane ring or cyclohexane ring in the molecule, occur in petroleum. They seem to be of little consequence enviromnentally since thermal decarboxylation can occur during the distillation process. During this process, the temperature of the crude oil in the distillation column can reach as high as 395°C (740°F). Hence decarboxylation is possible (Speight and Francisco, 1990) ... 

Unsubstituted thieno[3,4-6]thiophene (3) (see Litvinov and Fraenkel ), was prepared by Cava and Pollack s method for benzo[c]-thiophene i.e., thermal decomposition of H, 3 -benzo[c]thiophene sulfoxide. By refluxing 4/f,6/f-thieno[3,4-ft]thiophene-2-carboxylic acid 5-oxide (91) with acetic anhydride (the synthesis of dihydrothieno-thiophenes will be described below), Wynberg et a/." obtained the mixed anhydride 92 in 95% yield. Hydrolysis gave thieno[3,4-6]-thiophene-2-carboxylic acid (93) (88%). Decarboxylation of the acid (93) gave thienothiophene 3, unstable at room temperature [Eq. (29)]. 

In an extensive study into the application of the decarboxylative approach to azomethine ylides, Giigg reported the construction of numerous, complex polycyclic systems via an intramolecular protocol. Thiazolidine-4-carboxylic acid (263) was shown to react with 264 in refluxing toluene to furnish a 2 1 mixture of 265 and 266 in 63% yield (81). The reaction is assumed to occur via condensation of the aldehyde and amino acid to generate the imine 267, followed by cyclization to 268. Subsequent thermal decarboxylation of the ester generates either a syn dipole leading to 265 from an exo transition state, or an anti dipole and endo transition state generating adduct 266 (Scheme 3.90). 

Some relevant substituents are displayed in Table XV. Hydrolysis of esters or nitriles followed by thermal decarboxylation of 2-, 5-, 6-, and 7-carboxylic acids is often used for degradation reactions (61CPB883, 61JCS3046 64UP1). 5-Amino-l,2,4-triazole-3-carboxylic acid is decarbox-ylated in situ by condensation to TP (83S44) TP-5-amideoxime is cyclized to the 5-( 1,2,4-oxadiazol-3-yl) derivative (90EGP282009). 

Research Focus Method of preparing 4-hydroxystyrene by de-carboxylation of 4-hydroxylcinnamic acid for use in preparing poly(4-glycidyloxystyrene). Originality While the thermal decarboxylation of cinnamic acid as a method of... 

Pyrrole-2-carboxylic acid easily loses the carboxylic group thermally. Pyrrole-3-carboxylic acid and furan-2- and -3-carboxylic acids also readily decarboxylate on heating to about 200°C. Thiophene-carboxylic acids require higher temperatures or a copper-quinoline catalyst. In furans, 2-carboxylic acid groups are lost more readily than 3-carboxylic acid groups (Scheme 64). 

SAMPLE SOLUTION (a) Thermal decarboxylation of malonic acid derivatives leads to the replacement of one of the carboxyl groups by a hydrogen. 

Thermal cyclization of the isopropylidene ester of the malonates (70) was accompanied by decarboxylation at position 3, whereby 4-oxo-4H-pyrido-[l,2-fl]pyrimidines (74 R1 = H) were obtained.79,142,143 When the cyclization was performed in phosphoryl chloride-polyphosphoric acid and the reaction mixture was treated with alcohol, 4-oxo-4H-pyrido[l,2-a]pyri-midine-3-carboxylic acid esters were isolated.151 Treatment of the reaction mixture with water gave carboxylic acids. 

Several examples of the synthesis of aryl alkyl ketones by the thermal decarboxylation of mixtures of carboxylic acids over heated metal salts are included under the preparation of aliphatic ketones (Expt 5.93). In this section the preparation of dibenzyl ketone (Expt 6.127) by the pyrolysis of the barium salt of phenylacetic acid, which proceeds in good yield, is included as a further example of this general type of synthesis. 

Dicarboxylic acids in which both carboxyl groups are attached to the same carbon undergo ready thermal decarboxylation to produce the enol form of an acid. 

The silver(I) salts of carboxylic acids react with halogens to give unstable intermediates which readily decarboxylate thermally to yield alkyl halides. The reaction is believed to involve homolysis of the C-C bond and a radical chain mechanism. 

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