Understanding the Accelerating Effect of epsilon-Caprolactam on the Formation of Urethane Linkages

The accelerating role of -caprolactam on the formation of urethane linkages is studied in the case of the reaction between toluene 2,4-diisocyanate and n-propanol in carbon tetrachloride at room temperature. FT-IR spectroscopy is exploited to follow the consumption of the isocyanate groups. The comparison between the rate of the reactions carried out in the presence and absence of a catalytic amount of -caprolactam shows its accelerating effect. The acylurea-like derivative 1-methyl-2,4-[(2-oxoazepane- 1-carbonyl)amino]benzene has been prepared and identified as the real catalytic species formed in situ as a result of the reaction between toluene 2,4-diisocyanate and -caprolactam. A kinetic model is proposed to analyze the experimental data, and B3LYP/6-31+G* calculations are exploited to investigate the structure of 1-methyl-2,4-[(2-oxoazepane-1-carbonyl)amino]benzene and clarify the structural features leading the catalytic activity.