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Radial Tire Materials Technology and Rubber Compounding
Published in Brendan Rodgers, Tire Engineering, 2020
The mechanism of silane coupling agent reinforcement comprises two phases, namely i) the silanization reaction, in which coupling agent reacts with silica, and ii) the formation of crosslinks between the modified silica and the polymer. Silanization of the silica surface can occur quite readily, though, with TESPT systems, the reaction is generally carried out in situ at between 150 and 160°C in an internal mixer. Though an excess of silanol groups are present on the silica surface and reaction rates are fast, this high temperature is required because of the steric hindrance around the silylpropyl group in TESPT. Essentially, three types of functional silanol groups exist on the silica surface: isolated hydroxyl groups, geminal groups (two -OH groups on one Si atom), and vicinal groups. The silanization reaction is illustrated in Figure 6.13.
Oxyfunctionalization of Pharmaceuticals by Fungal Peroxygenases
Published in Peter Grunwald, Pharmaceutical Biocatalysis, 2019
Jan Kiebist, Martin Hofrichter, Ralf Zuhse, Katrin Scheibner
Recently, a remarkable cleavage reaction was reported for corticosteroids catalyzed by MroUPO and MweUPO (isolated from the basidiomycete Marasmius wettsteinii). Three model steroids, cortisone (77), Reichstein’s substance S and prednisone were stepwise oxygenated at the C17 side chain and finally C–C cleaved to obtain adrenosterone (78), androstendione and 1,4-androstadien-3,11,17-trione, respectively (Fig. 18.22). The sequential steroid oxidation started with the hydroxylation of the terminal carbon (C21) leading to a stable geminal alcohol (e.g., cortisone 21-gem-diol) and proceeded through a second oxygenation resulting in the corresponding α-ketocarboxylic acid (e.g., cortisone 21-oic acid). The latter decomposed under formation of adrenosterone (78) as well as of formic and carbonic acid (Ullrich et al., 2018). Besides the reported fatty acid chain shortening by MroUPO, the steroidal side chain removal represents a second example of a C–C cleavage reaction accomplished by UPOs. Side chain removal from cortisone (77) by MroUPO.
Analytic Methods fo the Bioactive Compounds in Waste
Published in Quan V. Vuong, Utilisation of Bioactive Compounds from Agricultural and Food Waste, 2017
In 1D proton spectra, a wide range of coupling is possible and visible depending on the surrounding scaffold of the organic compound. The most important coupling is 3-bond coupling to another hydrogen atom (vicinal coupling) represented by 3JCH, generally having values between 0–20 Hz, or two bond coupling to another hydrogen (geminal coupling) represented by 2JHaHb, generally having values between 0–25 Hz. Geminal coupling is far less common, as hydrogen’s connected to the same carbon atom need to be in different chemical environments. This is seen when the structure of a 3-D molecule is locked in a specific unsymmetrical conformation. Both coupling types and an example of structures containing each type are illustrated below in Fig. 18 (Blackman et al. 2008, Brown 2010, Monakhova et al. 2013, Williams and Fleming 1995).
Cryokinetics and spin quenching in the N2 adsorption onto rhodium cluster cations
Published in Molecular Physics, 2021
Amelie A. Ehrhard, Matthias P. Klein, Jennifer Mohrbach, Sebastian Dillinger, Gereon Niedner-Schatteburg
Case (b): The adsorption of N2 onto Rh13+ and Rh14+ is all spontaneous ( < 0) up to (13,14) and (14,15). This corresponds to a full loading with two geminal N2s, depending on taking into account an inner, non-accessible Rh atom. The surface atoms of larger clusters are higher next neighbour coordinated and therefore less reactive towards adsorbates [76]. Additional N2 molecules bind more loosely and likely form a second adsorbate shell. These loosely bound N2s can easily desorb or roam about the surface of the cluster adsorbate complex. These processes will manifest themselves in the observed reversibility for large m up to mmax. Other than in the cases i = 6,7, the higher next neighbour coordination of i = 13,14 enhances the effect of desorption on the cryo N2 adsorption kinetics. The mmax/i stoichiometries decrease (12/6, 13/7, 19/13, and 20/14) with number of metal atoms i. It is beyond doubt that large Rhi+ clusters (i > 10) establish an N2 adsorption–desorption equilibrium across multiple steps, a range of m values. In contrast, small rhodium clusters hold tight to their N2 adsorbates but for the very last one, an adsorption–desorption equilibrium at a single m value.
Selenium chlorides in the domino process of the regiospecific allyl chlorination of betulin and diacetylbetulin
Published in Journal of Sulfur Chemistry, 2020
I. V. Bodrikov, Yu. A. Kurskii, A. A. Chiyanov, A. Yu. Subbotin, A. S. Shavirin, N. V. Anderson
The hybrid state of the carbon atom C(20) in 5a, b and 6a, b, is closer to the sp2 state according to the dihedral angle and the length of the partial bond Se-C(20). A further decrease in the dihedral angle is accompanied by a sharp increase in the energy of the system due to the repulsive interaction of geminal substituents at the C(20) carbon atom. Such an extreme increase in the energy of the repulsive interaction of bulky geminal substituents in the bromonium cation was revealed by the results of quantum chemical calculations [22]. With such a significant interaction of geminal substituents in the asymmetric episelenurane, the implementation of a nonadditive process such as the elimination of the β-proton, becomes more advantageous. Elimination, in turn, provides an increase in the specified dihedral angle up to 180° and leads to a decrease in the repulsive interaction of geminal substituents at the C(20) atom.
Levoglucosenone-derived synthesis of bio-based solvents and polyesters
Published in Green Chemistry Letters and Reviews, 2023
Cicely M. Warne, Sami Fadlallah, Adrian C. Whitwood, James Sherwood, Louis M. M. Mouterde, Florent Allais, Georg M. Guebitz, Con R. McElroy, Alessandro Pellis
Using water as an anti-solvent gave a higher yield when compared to methanol. However, when the Mn and Mw are considered, although the polymers worked up in CHCl3/H2O have much higher molecular weights than the CHCl3/MeOH polymers, this trend reversed when the work-up was performed in (1). A possible explanation for this trend is that the addition of water to (1) forms a geminal diol through hydration of the ketone moiety (40), which increases the overall polarity of the mixture (41). In our system, the wt% of (1) is approx. 11%, and previous studies have found the majority of (1) to be converted into its geminal diol at this concentration (42). The (1)/H2O antisolvent system is therefore very different when compared to the (1)/MeOH one. When comparing the two solvent systems, a blend of Cyrene and water (in the appropriate ratio) assuming all Cyrene has been converted to the geminal diol has a δP of 38.7 compared to 21.4 for the Cyrene/MeOH system (Table S9). As the Cyrene/H2O system is much more polar, more polymer crashes out, including lower molecular weight oligomers. This both increases dispersity and decreases Mn and Mw for this system. Using a MeOH-based anti-solvent system resulted in higher Mw polymers, which can be seen in Figure 1(c and d), when comparing the Mw of reactions 9 and 11, and reactions 10 and 12. The ODO-based polymer worked-up in (1)/MeOH gave the highest Mn/Mw in this data set; 7.7/17.6 kDa respectively.