Kinetics and Mechanism of the Reaction between Mercury(II) and a Series of Macrocyclic Organochromium Cations

Kinetic data are presented for the reaction of alkylchromium complexes (H2O)([14]aneN4)CrR2+ ([14]aneN4 = 1,4,8,11-tetraazacyclo-tetradecane) with Hg2+ via electrophilic substitution. The rate constants decrease in the order CH3 (1.1 × 106 mol-1 dm3 s-1) > C2H5 (7.7 × 102) > C3H7 (59) > 2-C3H7 (0.12) > CH2C(CH3)3 (0.0086). A series of meta and para substituted benzyl complexes obey a Ham-mett relationship with the reaction constant ρ = -1.66, consistent with electrophilic substitution at α-carbon

1,3-Transposition of Allylic Alcohols Catalyzed by Methyltrioxorhenium

Methyltrioxorhenium (MTO) catalyzes the 1,3-transposition of allylic alcohols to generate the more stable isomer at equilibrium. The direction of the equilibrium is largely decided by the nature of the OH group, i.e., whether it is primary, secondary, or tertiary. In the case of aliphatic allylic alcohols, tertiary is preferred to secondary which is preferred to primary. For aromatic allyl alcohols, the more conjugated isomer predominates largely at equilibrium. Oxygen-18 labeling showed that the OH groups of the parent and product are the same. The reaction is first order with respect to both allyl alcohol and MTO but strongly inhibited by traces of water. Theoretical calculations suggest the same results in the case of aliphatic allyl alcohols, although aromatic allyl alcohols do not follow the predictions. Studies of deuterium-labeled substrates show a large equilibrium isotope effect (K = 1.20 ± 0.02). For isomeric allyl alcohols differing in the position of deuterium only, the isomer with the deuterium at the sp3center predominates at equilibrium. The effect of conjugation from a phenyl group appears to be less important since calculations suggest that the phenyl group is forced out of plane of the allylic π system

Experimental and Theoretical Study of Oxygen Insertion into Trialkylsilanes by Methyltrioxorhenium Catalyst

Among the reactions of hydrogen peroxide that are catalyzed by methyltrioxorhenium, the oxidation of alkylsilanes is unique. It is not a reaction in which an oxygen atom is added to a substrate, but one featuring a net insertion, R3Si−H + H2O2 → R3Si−OH + H2O. Kinetics studies were carried out on 10 compounds. Rate constant were determined for the bimolecular reaction of the silane with the peroxo compound CH3Re(O)(η2-O2)2(H2O). The variation of rate constant with the alkyl groups R follows two trends:  the values of log(k) are linear functions of (a) the stretching frequency of the Si−H group and (b) the total Taft constant for these substituents. The reactions of (n-Bu)3Si−H and (n-Bu)3Si−D exhibit a kinetic isotope effect of 2.1 at 0 °C. From these data, a model for the transition state was formulated in which O−H and Si−O bond making accompany Si−H bond breaking. Quantum mechanical calculations have been carried out on the gas-phase reaction between Et3SiH and CH3Re(O)2(η2-O2). These results support this structure, calculating a structure and energy that are in agreement. The theoretical activation energy is 28.5 kcal mol-1, twice the experimental value in aqueous acetonitrile, 12.4 kcal mol-1. The difference can be attributed to the solvation of the polar transition state in this medium

Unstationary film model for the determination of absolute gas-liquid kinetic rate constants: ozonation of Acid Red 27, Acid Orange 7, and Acid Blue 129

A method for the determination of absolute kinetic rate constants is proposed using an unstationary film model. This methodology avoids the experimental determination of parameters like the enhancement factor or the Hatta number which are usually model-dependent. The mathematical model is general for gas-liquid systems with irreversible second order reactions. An optimization procedure based on artificial neural networks is used to estimate the initial guess of the parameters and the subsequent application of Gauss-Newton algorithm for the final nonlinear parameter estimation. The model is tested with the ozonation reaction of Acid Red 27, Acid Orange 7 and Acid Blue 129. The second-order kinetic rate constants for the direct reaction with O3 are 1615±93, 609±83, and 49±2M−1s−1, respectivelyJF acknowledges the support of the doctoral fellowship from the Universitat Politecnica de Valencia (UPV-PAID-FPI-2010-04).Ferre Aracil, J.; Cardona Navarrete, SC.; López Pérez, MF.; Abad Sempere, A.; Navarro-Laboulais, J. (2013). Unstationary film model for the determination of absolute gas-liquid kinetic rate constants: ozonation of Acid Red 27, Acid Orange 7, and Acid Blue 129. Ozone: Science and Engineering. 35(6):423-437. https://doi.org/10.1080/01919512.2013.815104S423437356Biń, A. K. (2006). Ozone Solubility in Liquids. Ozone: Science & Engineering, 28(2), 67-75. doi:10.1080/01919510600558635Cardona, S. C., López, F., Abad, A., & Navarro-Laboulais, J. (2010). On bubble column reactor design for the determination of kinetic rate constants in gas-liquid systems. The Canadian Journal of Chemical Engineering, 88(4), 491-502. doi:10.1002/cjce.20327Chang, C. S., & Rochelle, G. T. (1982). Mass transfer enhanced by equilibrium reactions. Industrial & Engineering Chemistry Fundamentals, 21(4), 379-385. doi:10.1021/i100008a011Dachipally, P., & Jonnalagadda, S. B. (2011). Kinetics of ozone-initiated oxidation of textile dye, Amaranth in aqueous systems. Journal of Environmental Science and Health, Part A, 46(8), 887-897. doi:10.1080/10934529.2011.580201Danckwerts, P. V., & Lannus, A. (1970). Gas-Liquid Reactions. Journal of The Electrochemical Society, 117(10), 369C. doi:10.1149/1.2407312Das, A. K., & Das, P. K. (2009). Bubble Evolution through a Submerged Orifice Using Smoothed Particle Hydrodynamics: Effect of Different Thermophysical Properties. Industrial & Engineering Chemistry Research, 48(18), 8726-8735. doi:10.1021/ie900350hFerrell, R. T., & Himmelblau, D. M. (1967). Diffusion coefficients of nitrogen and oxygen in water. Journal of Chemical & Engineering Data, 12(1), 111-115. doi:10.1021/je60032a036Gerlach, D., Alleborn, N., Buwa, V., & Durst, F. (2007). Numerical simulation of periodic bubble formation at a submerged orifice with constant gas flow rate. Chemical Engineering Science, 62(7), 2109-2125. doi:10.1016/j.ces.2006.12.061Glasscock, D. A., & Rochelle, G. T. (1989). Numerical simulation of theories for gas absorption with chemical reaction. AIChE Journal, 35(8), 1271-1281. doi:10.1002/aic.690350806Gomes, A. C., Nunes, J. C., & Simões, R. M. S. (2010). Determination of fast ozone oxidation rate for textile dyes by using a continuous quench-flow system. Journal of Hazardous Materials, 178(1-3), 57-65. doi:10.1016/j.jhazmat.2010.01.043Gupta, P., Al-Dahhan, M. H., Duduković, M. P., & Mills, P. L. (2000). A novel signal filtering methodology for obtaining liquid phase tracer responses from conductivity probes. Flow Measurement and Instrumentation, 11(2), 123-131. doi:10.1016/s0955-5986(99)00025-4Hoigné, J., & Bader, H. (1983). Rate constants of reactions of ozone with organic and inorganic compounds in water—I. Water Research, 17(2), 173-183. doi:10.1016/0043-1354(83)90098-2Jamialahmadi, M., Zehtaban, M. R., Müller-Steinhagen, H., Sarrafi, A., & Smith, J. M. (2001). Study of Bubble Formation Under Constant Flow Conditions. Chemical Engineering Research and Design, 79(5), 523-532. doi:10.1205/02638760152424299Johnson, P. N., & Davis, R. A. (1996). Diffusivity of Ozone in Water. Journal of Chemical & Engineering Data, 41(6), 1485-1487. doi:10.1021/je9602125King, C. J. (1966). Turbulent Liquid Phase Mass Transfer at Free Gas-Liquid Interface. Industrial & Engineering Chemistry Fundamentals, 5(1), 1-8. doi:10.1021/i160017a001Ledakowicz, S., Maciejewska, R., Perkowski, J., & Bin, A. (2001). Ozonation of Reactive Blue 81 in the bubble column. Water Science and Technology, 44(5), 47-52. doi:10.2166/wst.2001.0248Lewis, W. K., & Whitman, W. G. (1924). Principles of Gas Absorption. Industrial & Engineering Chemistry, 16(12), 1215-1220. doi:10.1021/ie50180a002Lopez, A., Benbelkacem, H., Pic, J. ‐S., & Debellefontaine, H. (2004). Oxidation pathways for ozonation of azo dyes in a semi‐batch reactor: A kinetic parameters approach. Environmental Technology, 25(3), 311-321. doi:10.1080/09593330409355465Meldon, J. H., Olawoyin, O. O., & Bonanno, D. (2007). Analysis of Mass Transfer with Reversible Chemical Reaction†. Industrial & Engineering Chemistry Research, 46(19), 6140-6146. doi:10.1021/ie0705397Navarro-Laboulais, J., Cardona, S. C., Torregrosa, J. I., Abad, A., & López, F. (2006). Structural identifiability analysis of the dynamic gas–liquid film model. AIChE Journal, 52(8), 2851-2863. doi:10.1002/aic.10901Navarro-Laboulais, J., Cardona, S. C., Torregrosa, J. I., Abad, A., & López, F. (2008). Practical identifiability analysis in dynamic gas–liquid reactors. Computers & Chemical Engineering, 32(10), 2382-2394. doi:10.1016/j.compchemeng.2007.12.004Rapp, T., & Wiesmann, U. (2007). Ozonation of C.I. Reactive Black 5 and Indigo. Ozone: Science & Engineering, 29(6), 493-502. doi:10.1080/01919510701617959Tanaka, M., Girard, G., Davis, R., Peuto, A., & Bignell, N. (2001). Recommended table for the density of water between 0  C and 40  C based on recent experimental reports. Metrologia, 38(4), 301-309. doi:10.1088/0026-1394/38/4/3Tizaoui, C., & Grima, N. (2011). Kinetics of the ozone oxidation of Reactive Orange 16 azo-dye in aqueous solution. Chemical Engineering Journal, 173(2), 463-473. doi:10.1016/j.cej.2011.08.014Von Gunten, U. (2003). Ozonation of drinking water: Part I. Oxidation kinetics and product formation. Water Research, 37(7), 1443-1467. doi:10.1016/s0043-1354(02)00457-

Manganese-Catalyzed Selective Oxidation of Aliphatic C-H groups and Secondary Alcohols to Ketones with Hydrogen Peroxide

An efficient and simple method for selective oxidation of secondary alcohols and oxidation of alkanes to ketones is reported. An in situ prepared catalyst is employed based on manganese(II) salts, pyridine-2-carboxylic acid, and butanedione, which provides good-to-excellent conversions and yields with high turnover numbers (up to 10 000) with H2O2 as oxidant at ambient temperatures. In substrates bearing multiple alcohol groups, secondary alcohols are converted to ketones selectively and, in general, benzyl C-H oxidation proceeds in preference to aliphatic C-H oxidation.

Kinetic detection of osmium(VI) ester intermediates during the OsO4‐mediated aqueous dihydroxylation of chloroethylenes

The kinetics and mechanism of the cis dihydroxylation of cis‐1,2‐ dichloroethylene, trans‐1,2‐dichloroethylene, and trichloroethylene by osmium tetroxide was studied systematically in aqueous solution. The stoichiometry of the process was determined based on the principle of continuous variation of reactant ratios with spectrophotometric detection. The results always showed 1:1 stoichiometry, which is in agreement with dihydroxylation. All three reactions were found to proceed in two distinct steps. The first step occurred on a time scale of seconds and was associated with a minor change in absorbance and was identified as the formation of a 1:1 adduct between the two reagents, which is the osmium(VI) ester that plays a decisive role in catalytic applications. This species is formed in an equilibrium that is very much shifted toward the reactants, so the osmium(VI) complex is a short‐lived intermediate of the process, which is detected kinetically, but its concentration is never high enough for structural characterization. The second reaction is accompanied by major spectral changes; it involves the formation of the final products. Our results clearly show that it is possible to detect the intermediate of the process by careful kinetic studies. It is also possible that the same strategy might be successful in other OsO4‐dependent dihydroxylation processes