Degradation carboxylic acids

MIESCHER DEGRADATION. Adaptation of the Barbier-Wieland carboxylic acid degradation to pcrmil simultaneous elimination of three carbon atoms, as in degradation of the bile acid side chain to the methyl ketone stage. Conversion of the methyl ester of the bile acid to the tertiary alcohol, followed by dehydration, bromination. dehydrohalogenatinn, and oxidation of the diene yields die required degraded ketone. 

Figure 10.3. Degradationof noradrenaline. COMT,Catechol-0-MethyItransferase MAO, and monamine oxidase. MAO initially forms an aldehyde (not shown) that is either reduced to an alcohol or oxidized to a carboxylic acid. Degradation of other catecholamines is analogous.

The development of a normal-phase HPLC method was warranted due to the presence of phthalic anhydride, which is unstable in water. Analysis in organo-aqueous solvent systems that are used in RPLC would lead to an on-column reaction forming the respective carboxylic acid degradation product. Figure 5-5 shows the chromatogram obtained for the separation of 9,10-anthraquinone from the reactants and impurities on a silica column. The method was successfully applied to monitor the reaction conversion and also to determine the stability of 9,10-anthraquinone at the specified storage conditions. 

Figure 8-49. Effect of organic composition on the retention of carboxylic acid degradation product. Column Waters Sunfire C18, 3.5 pm, 150 x 4.6 mm. (A) 10 mM NELtOAc, pH 5.8. (B) Acetonitrile Flow, 1.5mL/min temperature, 35°C.

Barbier-Wieland degradation. Stepwise carboxylic acid degradation of aliphatic acids (particularly in sterol side chains) to the next lower homo log. The ester is converted to a tertiary alcohol that is dehydrated with acetic anhydride, and the olefin oxidized with chromic acid to a lower homologous carboxylic acid. 

Trifluoroacetic acid sodium nitrite trifiuoroacetic anhydride Nitriles from carboxylic acids Degradation with loss of 1 C-atom... 

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