Measurement of Raman χ(3) and theoretical estimation of DOVE four wave mixing of hydrogen peroxide

Study on Reaction Mechanism and Process Safety for Epoxidation

The reaction mechanism and process safety for epoxidation were investigated in this study. 1-(2-Chlorophenyl)-2-(4-fluorophenyl)-3-(1,2,4-triazole) propene (triazolene), a typical representative of high steric olefinic compounds, was chosen as the raw material. In addition, hydrogen peroxide was chosen as the oxygen source in the reaction. Online Raman spectroscopy combined with high-performance liquid chromatography (HPLC) was used for the process monitoring analysis. The results of this study indicated that the epoxidation process is exothermic, and the apparent reaction heat was 1340.0 kJ·kg-1 (measured by the mass of triazolene). The heat conversion rate was 39.7% immediately after hydrogen peroxide dosing to a triazolene and maleic anhydride mixture solution in chloroform. This result indicated that a considerable amount of heat is accumulated during the epoxidation reaction, which leads to a potential high safety concern. The study of the reaction mechanism showed that maleic anhydride reacts with hydrogen peroxide quickly to form maleic acid peroxide, which is controlled by hydrogen peroxide feeding, and the formed maleic acid peroxide further reacts with triazolenes slowly, which is a kinetically controlled reaction. Decomposition kinetics studies revealed that the temperatures corresponding to the time of maximum reaction rate for 8 and 24 h are TD24 = 89.9 °C and TD8 = 104.1 °C, respectively.

Second hyperpolarizability of C-H, C-D, and C≡N stretch vibrations determined from computational Raman activities and a comparison with experiments

We have recently demonstrated that the second hyperpolarizability γ of a selected vibrational mode of a molecule can be determined by using the computational Raman activity against an internal standard with a known Raman γ value. This approach provides a convenient way for prediction of the γ magnitude of DOVE four wave mixing spectroscopy, an optical analogue to two-dimensional (2D) NMR. Here, by using the Hartree-Fock (HF) method, the density functional theory (DFT) method, and the second-order Møller-Plesset perturbation theory (MP2) method, we extend our early work from the less anharmonic region <2000 cm(-1) into the more anharmonic region >2000 cm(-1) covering C-H, C-D, and C≡N stretching modes of benzene, deuterated benzene, acetonitrile, deuterated acetonitrile, and tetrahydrofuran. The computed Raman γ values of these vibrational modes have been determined by using either the 992 cm(-1) Raman band of benzene or the compound's own Raman band (C-C stretch) around 800-1000 cm(-1) as an internal standard. In this more anharmonic region, the HF method with a larger basis set provides the best outputs and the predicted Raman γ values agree well with experimental values for most of the vibrational modes studied. By choosing a suitable method and basis set, this facile approach could be applied to a broader spectral range for Raman γ estimation of various materials.

Raman second hyperpolarizability determination using computational Raman activities and a comparison with experiments

Doubly vibrationally enhanced (DOVE) four-wave mixing spectroscopy, an optical analogue to 2D NMR, involves two infrared transitions and a Raman transition. The magnitude of the DOVE second hyperpolarizability γ (or third-order susceptibility χ((3))) can be theoretically estimated if the values of the dipolar moments of the two infrared transitions and the γ of the Raman transition are known. The Raman γ can be measured by using the four-wave mixing interferometric method or conventional Raman spectroscopy in the presence of an internal standard. In this work, we examine if one can use the Raman activity computed from density functional theory calculation to determine the Raman γ of selected vibrational modes of several samples including deuterated benzene, acetonitrile, tetrahydrofuran, and sodium benzoate aqueous solution. The 992 cm(-1) Raman band of benzene serves as an internal standard for organic solvents, and the 880 cm(-1) Raman band of hydrogen peroxide is for the aqueous solution sample with known γ values. We have found that the predicted Raman γ values from the computational Raman activities match experimental data reasonably well, suggesting a facile approach to predict the Raman γ of interested systems.