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Organic Catalysis by Clay-Supported Reagents
Published in Benny K.G. Theng, Clay Mineral Catalysis of Organic Reactions, 2018
The presence of (hydrated) zinc ions in its mesoporous structure (Figure 4.1) makes clayzic more polar than the parent montmorillonite. As a result, polar substrates are more easily accommodated into the clayzic structure as compared with their nonpolar counterparts. Thus, in a mixture of alkyl alcohol and alkyl halide, the former compound is the first to react although the alcohol is less reactive than the corresponding halide. Further, the activity of clayzic in the benzylation of arylhalides decreases in the sequence: bromobenzene > chlorobenzene > fluorobenzene paralleling the polarizability of the substrates whereas the reverse order is observed under homogeneous conditions. By promoting the partitioning of alkylbenzenes into mesopores, dehydration also increases the catalytic performance of clayzic (Clark and Macquarrie 1996).
Effect of the Substituents in the Alkyalation of Aromatics With Methanol Over HZSM- 5 Zeolite
Published in Mike G. Scaros, Michael L. Prunier, Catalysis of Organic Reactions, 2017
M. R. Goldwasser, L. García, G. Giannetto, M. Guisnet, P. Magnoux
Alkyiation of substituted aromatics with methanol. The surface area value obtained (390m2/g), together with the X ray diffraction analysis, show that the commercial HZSM-5 zeolite is a highly crystalline solid. The evolution of activity as a function of reaction time for the alkylation of phenol, fluorobenzene, chlorobenzene and bromobenzene is shown in Figure 1. The activity is expressed in mmole h−1.g−1 of phenoi and halobenzenes converted. In all cases, regardless of the substrate, an activity decrease due to catalyst deactivation is observed. The observed reactivity pattern PhOH ≥ F-Bz > CI-Bz > Br-Bz for the substituted benzenes are to be expected and can be explained by the electronic effect of the substituents.
Production of Phenols from Haloaromatics in the Presence of Copper-Exchanged Zeolites: Synthesis of the Catalyst and Mechanistic Study
Published in John R. Kosak, Thomas A. Johnson, Catalysis of Organic Reactions, 2020
G. Perot, Y. Pouilloux, M. Guisnet, M. Gubelmann
The reactivities for phenol formation of fluoro-, chloro- and bromo-benzene were compared under the same conditions on 2CuHZSM5. The reactivity sequence was ⊘C1 > ⊘Br > ⊘F (Figure 7) which was not the one expected for a classical SNAr mechanism. In this case, the reactivity sequence is usually ⊘F ≫ ⊘Cl > ⊘Br since the attack by the nucleophile is favored by the electronegativity of the leaving group [7]. Nor was the sequence we obtained in agreement with the one generally observed with an arynic mechanism. Consequently it can be supposed that chloro- and bromobenzene, on the one hand, and fluorobenzene, on the other, react by two different mechanisms: possibly SNAr for the former and arynic for the latter.
Assessment of soil contamination caused by underground fuel leakage from selected gas stations in Riyadh, Saudi Arabia
Published in Soil and Sediment Contamination: An International Journal, 2018
Badr Hadhidh Alharbi, Mohammad Jahangir Pasha, Abdulrahman Hussein Alhudhodi, Abdulilah Khalid Alduwais
Quality control was maintained by verifying the method several times with a check standard containing a four-component mix (fluorobenzene, chlorobenzene, 1,4 dichlorobenzene, and bromopentafluorobenzene) with known concentrations. The performance of the method was evaluated by analyzing spiked and laboratory blank samples. New clear EPA vials (40 ml) with 24 mm screw caps fixed with PTFE/silicon septa were used for each water sample to avoid cross-contamination.