A colorimetric Study of the reaction between vanadyl sulphate and catechol

Abstract Vanadyl sulphate, when mixed with catechol, undergoes a colour change from blue to violet. The violet colour is unstable and it turns violet‐black after some time. A colorimetric study of the reaction by using JOB'S continuous variation method reveals that at first a 1:2 complex is formed between vanadyl sulphate and catechol. The complex is stable only for a short time and it takes up one more molecule of catechol to form a 1:3 complex.