Mechanism of Reactions of Some N1-Substituted Biguanides with Chromium(VI) in Aqueous Sulphuric Acid Media

Article abstract of DOI:10.1039/DT9880001557

N¹-Phenylbiguanide RHN-C(=X)NH-C(=NH)NH2 (R=Ph, X=NH) reacts quantitatively in aqueous sulphuric acid media with Cr^VI and Ce^IV to produce 1,4-benzoquinone, carbamimidoylurea (R=H, X=O), and ammonium ion.N¹-(4-Methoxyphenyl)biguanide (R=4-MeOC6H4, X=NH) reacts similarly except that, instead of a quinone, more extensively oxidized products are produced.Phenylbiguanide (pbg) itself, in acid solution, undergoes slow hydrolysis, and anilinium ion is one of the products.The hydrolyzed solution reacts rapidly with Cr^VI and Ce^IV.None of the other six biguanides investigated and three other structurally related compounds reacts with Cr^VI under the experimental conditions.The kinetics of the reactions is in accord with the rate law (i).A typical <*> (i) value of k is (0.25 +/- 0.03)*10^-5 s^-1 at 20 deg C, =1.0 mol dm^-3, and / =2.0 mol dm^-3, and when determined from experiments with an excess of Cr^VI (first-order kinetics observed) agrees closely with that determined in the presence of an excess of pbg (zero-order kinetics) and also that determined for reactions with Ce^IV.These results have been interpreted in terms of a mechanism involving the acid-promoted hydrolysis of phenylbiguanide , the oxidant functioning as an analytical assay of the anilinium product.

Full text of DOI:10.1039/DT9880001557

View Article Online / Journal Homepage / Table of Contents for this issue

View Article Online

View Article Online

View Article Online