Sources, aliphatic hydrogenation

A general synthesis of thioamides from nitriles which utilizes thioacetamide as the source of hydrogen sulfide under acidic conditions is reported by Taylor and Zoltewicz.1 The thioamides are formed in good yield and high purity and the method is equally applicable to aliphatic nitriles and to aromatic nitriles containing either electronreleasing, electron-withdrawing, or potentially reducible substituents. One equivalent of the nitrile is heated on a steam bath for 15-30 min. with 2 eq. of thioacetamide in s s... 

The above considerations are not limited to concepts of chemical modification because even when lignins are considered as additives in the preparation of polymer blends or composites, their hydroxyl functions represent a key structural element in terms of polar contributions and sources of hydrogen bonds which will affect the quality of the interfacial interactions of the ensuing materials, just as the less-polar (ether groups, aromatic rings, etc.) and non-polar (aliphatic sequences) moieties will, in terms of hydrophobic interactions. 

The ratio of aromatic to aliphatic hydrogen depends mainly on the source of the starting material. The hydrogen aromaticity (ratio of aromatic to total hydrogen atoms) varies... 

Lastly, we show in Scheme 18.2 what would be two logical reaction products of the alkyl radical which is produced. The hydrogen abstraction was already proposed [11, 25] by others on the basis of spectroscopic evidence for an aldehyde but it has not been confirmed that the species was an aliphatic aldehyde being produced as opposed to an aromatic one and so is ambiguous. Hydrolysis of the top product of this section of the scheme would produce formic acid, which has been reported [11], However, more reasonable sources of formic acid exist in Schemes 18.3 and 18.4 (see below). The other product that one would expect to see would result in trimellitic acid being observed in the hydrolysate of the degraded polyester. This has, to our knowledge, not been reported as yet. 

The overall course of reaction depends on the relative rate constants for the various secondary radical processes. Aliphatic ketones are often photoreduced to secondary alcohols (4.121, but although there are interesting features in the stereochemistry of the reduction, the method is not a worthwhile alternative to thermal reduction using hydride reagents, except in cases where the substrate is sensitive to basic conditions. Photoaddition of methanol is promoted in the presence of titaniurnfiv) chloride, both for acyclic and cyclic (4.33) ketones the titanium involvement probably starts in the early steps of the reaction, but the detailed mechanism is not known. Addition may also be a major pathway when cyclohexene is used as hydrogen source (4.341 unlike many other simple alkenes, cydohexene does not readily give oxetanes by photocycloaddition (see p. 126). 

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