Hydrogen scavenger, addition

Silylations of aromatic analogs including heteroarenes are known, although in some instances a small amount of non-directed product is formed. The addition of a hydrogen scavenger was found to increase the yield of product (Equations (98) and (99)).93... 

The cathode formulations further employ metallic catalysts to promote the recombination of hydrogen gas generated within the zinc anode at very low (0.025 %) or zero mercury content [41,42,43]. The hydrogen scavenger can form a discrete auxiliary electrode in electronic contact with the cathode or can be introduced simply as a cathode additive in a ratio of 30/70 in the cathode preparation process. A very reliable catalytic material even at elevated temperatures (65°C) is Ag20. The auxiliary electrode may be an annulus or a disk of similar... 

H" atom can both abstract hydrogen atoms and add to the double bonds. However it was found that the predominant reaction is the addition to the double bond. From the absorption of the cyclohexadienyl radical (formed by H abstraction) in acidic solution containing t-butanol (to scavenge the OH radicals) it was concluded14 that only 22% and 7% of the H atoms abstract hydrogen from 1,4- and 1,3-cyclohexadiene, respectively. 

Hydrogenation reactions with LiAlH4 and addition of acidic compounds XH, afford good derivatizing and scavenging schemes for compounds like 66 (see Table 6), which are very reactive149. For example, compounds 29, 30 (Table 4), 40 and 41 (Table 5) are derived in such a manner. 

For reasons which will become apparent in section 1.8.2, it is assumed that each electron-ion pair eventually produces one molecule of hydrogen. In an earlier section (p. 160) it was seen that in HC1 an additional 0.20+0.2 hydrogen atoms per ion pair should come from dissociative ionisation and charge transfer processes. In the absence of hydrogen atom scavengers they will undergo the reaction... 

An additional contributing factor to the mechanism of the present grafting reaction is the role of radiolytically produced hydrogen atoms. In the radiolysis of binary mixtures of aromatic and aliphatic compounds such as styrene-methanol, the concentration of aromatic strongly influences the G(H2) obtained from the methanol. In the most extensively studied binary mixtures of benzene-methanol (11) and pyridine-methanol (10), it is found that the yield of H atoms is important in determining product yields and types. Small additions (5%) of benzene and pyridine significantly reduce G(H2) from the methanol by scavenging H atoms. Above 5% additive, G(H2) is reduced further, but at a slower rate. These data for benzene-methanol and pyridine-methanol can be extrapolated... 

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