Fourier transform near-infrared absorption spectroscopic study of catalytic isomerization of quadricyclane to norbornadiene by copper(II) and tin(II) salts

By using Fourier transform near-infrared (NIR) absorption spectroscopy, we have investigated the catalytic conversion of quadricyclane to norbornadiene. Either CuSO4 in chloroform or SnCl, in benzene is used as catalyst. To avoid the effect of sample heterogeneity, the reaction mixture is kept still without stirring. The NIR light beam is guided to propagate through the solution right above the surface of metal salt. The NIR absorption spectra are acquired at 5-min intervals for a reaction period of 6 h. The related concentrations of quadricyclane and norbornadiene in the temporal evolution are determined with the method of partial least squares. A kinetic model for the pseudo-first-order reaction is derived considering the diffusion motion. Accordingly, the second-order rate constant for the isomerization catalyzed by CuSO4 and SnCl2, respectively, are determined to be (1.38 +/- 0.04) x 10(-3) and (4.62 +/- 0.09) x 10(-3) min(-1) g(-1). The norbornadiene is produced via a one-site coordination between the reactant and the catalyst. The product contribution from the intermediate of a two-site coordination is negligible in our system. The obtained result for CuSO4 is comparable with that detected by using Raman spectroscopy.