Silane reactivity

Weak resonances corresponding to the expected para-substituted phenylsilyl end groups appeared, but the resonances corresponding to the potential vinyl end groups were not observed in the H NMR spectra of the poly(MMA)s within detectable limits. One may anticipate that the silane reactivity (which could be directly related to the hydrogen... 

In addition to the basic strength of catalysts the acceptor strength of chlorosilanes is important for the hydrogenation course. With the increasing number of methyl groups (instead of Cl atoms) the silane reactivity decreases (Table 2). This tendency seems to be associated with the decreasing Lewis-acid strength of methyl chlorosilanes. 

Organolithium compounds can also be used conveniently for the preparation of silanes. Reactivity of the lithium reagents is higher than the corresponding Grignard reagents, as demonstrated by the following example. The reaction of... 

In its simplest terms, the titanate function (1) mechanism may be classed as proton-reactive through solvolysis (monoalkoxy) or coordination (neoalkoxy) without the need of water of condensation, while the silane function (1) mechanism may be classed as hydroxyl-reactive through a silanol-sUoxane mechanism requiring water of condensation. The silane s silanol-siloxane water of condensation mechanism limits its reactions to temperatures below 100 °C, thereby reducing the possibility of in situ reaction in the thermoplastic or elastomer melt above 100 °C as is possible with titanates. In addition, a variety of particulate fillers such as carbonates, sulfates, nitrides, nitrates, carbon, boron and metal powders used in thermoplastics, thermosets, and cross-linked elastomers do not have surface silane-reactive hydroxyl groups, while almost all three-dimensional particulates and species have surface protons, thereby apparently making titanates universally more reactive. 

Subsequent work by Pirkle and co-workers demonstrated that highly chlorinated silanes are even more effective at inducing this transformation [202-204]. Recently, a systematic study of the reaction of carbamates with various chlorosdanes has been reported [205]. It was found that, in general, the silane reactivity increases in the order MesSiCl < Me2SiCl2 < MeSiCla < HSiCh. Moreover, steric hindrance at the reaction center slows down the reaction, and, with N-Boc carbamates, isocyanate production is quite sluggish. In the cases involving O-alkyl carbamates, the reactions normally need to be conducted between room temperature and 70 °C. 

Two levels of silane treatment on clay are compared in natural rubber in Table 5. Differences in silane reactivity as indicated by peel tests are accentuated by increasing the level of silane... 

Jeffrey C. PeUetier of Wyeth Research, Collegeville, PA has developed (Tetrahedron Lett. 2007, 48,7745) a easy work-up Mitsunobu procedure for the conversion of a primary alcohol such as 1 to the corresponding primary amine 2. Shlomo Rozen of Tel-Aviv University has taken advantage (J. Org. Chem. 2007, 72, 6500) of his own method for oxidation of aprimary amine to the nitro compound to effect net conversion of an amino ester 3 to the alkylated amino ester 5. Note that the free amine of 3 or 5 would react immediately with methyl iodide. Keith A. Woerpel of the University of California, Irvine has uncovered (J. Am. Chem. Soc. 2007,129,12602) a Cu catalyst that, with 7, effected direct conversion of sUyl ethers such as 6 to the aUyl silane 8. An Ag catalyst gave 9, which also shows arllyl silane reactivity. Biswanath Das of the Indian Institute of Chemical Technology, Hyderabad has established (Tetrahedron Lett. 2007, 48, 6681) a compact procedure for the direct conversion of an aromatic aldehyde such as 10 to the benzylic halide 11. This will be especially useful for directly generating benzyhc hahdes that are particularly reactive. 

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