The Chemistry of the Oxychlorination Catalyst: an In Situ, Time-Resolved XANES Study

Abstract

Almost all of the world production of vinyl chloride today is based on cracking of 1,2-dichloroethane. For many decades, this compound has been produced by catalytic oxychlorination of ethylene with hydrochloric acid and oxygen [Eq. (1)]. The reaction is performed at 490 ± 530 K and 5 ± 6 atm (1 atm % 1.01 Â 10 5 Pa) using both air and oxygen in fluid-or fixed-bed reactors. [1] C 2 H 4 2 HCl 1 ³2O 2 3 C 2 H 4 Cl 2 H 2 O(1) 24 h, then cooled to 0 8C, and quenched with aqueous hydrochloric acid (3 m, 5 mL). The resulting mixture was warmed to 23 8C and stirred for 30 min, at which point aqueous sodium hydroxide (3 m, 10 mL) was added. The mixture was stirred at 23 8C for 30 min and extracted with diethyl ether (3 Â 20 mL). The combined organic layers were dried over anhydrous sodium sulfate, filtered, and concentrated in vacuo. Column chromatography on silica gel eluting with 30 % diethyl ether in pentane afforded (R)-2-ethyl-2-methyl-2,3-dihydrocinnamyl alcohol 5 a (239 mg, 1.34 mmol, 96 %) as a colorless oil. 1 H NMR (CDCl 3 ): d 7.19 ± 7.31 (m, 5 H), 3.33 (s, 2 H), 2.61 (AB, 2 H, J 24.6 Hz), 1.58 (bs, 1 H), 1.27 ± 1.40 (m, 2 H), 0.93 (t, 3 H, J 7.5 Hz), 0.82 ppm (s, 3 H); 13 C NMR (CDCl 3 ): d 139.0, 130.8, 128.1, 126.2, 68.4, 42.8, 39.1, 29.1, 21.0, 8.3 ppm. High-resolution FAB-MS: m/z (MH): 179.14359 (C 12 H 19 O requires 179.14359).[a] 25 D À 5.9 (c 14.2, CH 2 Cl 2 ). The product was determined to have 94 % ee by HPLC (Chiralcel OD column, eluting with 1 % 2-propanol in hexanes at 0.7 mL min À1 ; R t 20.5 min (major enantiomer), 22.8 min (minor enantiomer)).[21] Greater than two equivalents of electrophile must be added, as the Sand C-alkylations occur at similar rates.[22] The reasons for this dichotomous behavior are unclear. We have been unable to detect significant E/Z isomerization under the reaction conditions. Other effects such as aggregation state and/or different reactive conformations of the E and Z enolates cannot be ruled out.[23] Alkylation of amide enolates with unactivated electrophiles often requires the addition of HMPA or LiCl for useful reaction rates to be observed. For examples see ref.[19] and a

Origin and Dynamics of Oxygen Storage/Release in a Pt/Ordered CeO2–ZrO2 Catalyst Studied by Time‐Resolved XAFS Analysis

“…Energy‐dispersive XAFS is an in situ characterization technique to monitor X‐ray intensities over the whole energy range simultaneously with subsecond time resolution 25. 26, 31–33 Time‐resolved energy dispersive XAFS spectra at the Ce L 3 edge and Zr K edge were measured by Bragg‐type polychromators at NW2 in PF (http://www.wiley-vch.de/contents/jc_2002/2007/z703085_s.pdf). The time‐resolved XAFS spectra for oxygen storage/release processes were recorded in a homemade in situ cell every 2 ms for Zr K‐edge XAFS and every 300 ms for Ce L 3 ‐edge energy‐dispersive XAFS under 12.4 kPa of O 2 or H 2 in the temperature range 573–773 K. The structural parameters were determined by a curve‐fitting procedure in R space by using the FEFFIT program with multiple scattering effects 34…”

“…To evaluate time profiles of the fractions of Ce 4+ and Ce 3+ , the energy‐dispersive XANES spectra were analyzed by a linear combination with the formula X obs = C 1 X 1 + C 2 X 2 , where X obs , X 1 , X 2 , C 1 and C 2 represent observed XANES, XANES spectra of Ce 2 Zr 2 O 8 (Ce 4+ ) and Ce 2 Zr 2 O 7 (Ce 3+ ), and fractions of Ce 4+ and Ce 3+ , respectively 25. 26 The sum of C 1 and C 2 was constant at unity. The fractions of Ce 3+ and Ce 4+ species in the oxygen storage/release processes were plotted as a function of exposure time to O 2 or H 2 at 573, 673, and 773 K (Figure 2).…”

Detailed Structure Analysis of Atomic Positions and Defects in Zirconium Metal–Organic Frameworks

“…Temperature programmed H2-reduction (TPR) was performed feeding the samples with a flow of 10 cm 3 min −1 of 3% H2 in He, hosted inside an ad hoc conceived cell allowing temperature control and in situ XAS measurements in flux. 128 In all TPR experiments, PMLS functionalized MOFs were used. The main goal of the TPR experiment was to provide the temperature dependence of both NN and NCl coordination numbers, and follow the expected formation of metallic Pt nanoparticles.…”

Synchrotron ultrafast techniques for photoactive transition metal complexes

“…The energy position of the absorption edge is sensitive to the oxidation state of the absorber [82,101,102] due to the charge-shielding effect on the ionization energy (practically, a higher oxidation number corresponds to an edge shift towards higher energies). In addition, the edge location is influenced by the coordination geometry, which ultimately is determined by the energy position of molecular orbitals [25].…”