Oxidation of beta-blocking agents--VII. Periodate oxidation of labetalol

The oxidation of labetalol with sodium metaperiodate is described. In spite of the bulky substituent on the amino group of labetalol, glycol cleavage of the molecule occurred. Spectrometric methods verified that the aromatic aldehyde formed was 2-hydroxy-5-formylbenzamide and that the amine was 1-methyl-3-phenylpropylamine. The polarographic behaviour of the aldehyde was examined as well. The half-wave potential in Britton-Robinson buffer pH 5.68 was -1.24 V. Direct linearity (r = 0.9999) was observed between the diffusion current and the concentration of the aldehyde. Quantitation of labetalol was carried out polarographically by measuring the concentration of 2-hydroxy-5-formylbenzamide formed in the oxidation.