Kinetic analysis of new multi-component reaction for the formation of Z-N-(3-(naphthalene-2-yl)-4-oxothiazolidine-2-ylidene) benzamide

A new three-component reaction was studied kinetically among benzoyl isothiocyanate (1), 1-naphthylamine (2), and methyl bromoacetate (3) in the presence of triethylamine (4) as a catalyst, to yield Z-N-(3-(naphthalene-2-yl)-4-oxothiazolidine-2-ylidene) benzamide (5). The overall reaction is a combination of two reactions; 1) reaction a, between (1) and (2) forming 1-benzoyl-3-(naphthalen-1-yl) thiourea (P₁); 2) reaction b, between (P₁), (3) and (4) to form the product (5). The rate of reaction a, ($k_{obs}^a=66.49 M-1 min-1$) was more than the reaction b ($k_{obs}^b=2.9 M-1 min-1)$, in acetonitrile solvent at 25 °C. A mechanism was proposed involving step₁ ($k_{obs}^a$), step₂ (k₂ ), step₃ (k₃ ) and step₄ (k₄ ). Substituent effects with electron-withdrawing groups on para-position of benzoyl isothiocyanate (1) increased the rate constants of $k_{obs}^a$ and k₂ . The large negative entropy, ΔS^‡, values in reactions a, and b are in agreement with step₁ ($k_{obs}^a$) and step₂ (k ₂), an associative mechanism with a negative ΔS^‡. The sum of these observations proved that the rate-determining step (RDS) is step₂. It seems that the most important steps in the reaction mechanism are step₁ ($k_{obs}^a$) and step₂ (k₂ ), which strongly control the reaction process. The kinetics and mechanism of these reactions were assessed by UV–vis spectrophotometry.