Elimination, direction hydrogen

The fatty acids obtained from the process can be used directly or further manipulated for improved or modified performance and stabiUty. Hardening is an operation in which some fraction of the unsaturated bonds present in the fatty acids are eliminated through hydrogenation or the addition of H2 across a carbon—carbon double bond. This process was initially intended to improve the odor and color stabiUty of fatty acids through elimination of the polyunsaturated species. However, with the growth in the use of specialty fatty acids, hydrogenation is a commercially important process to modify the physical properties of the fatty acids. 

The most widely applied precursors for the synthesis of monocyclic NHPs are a-diimines which can be converted to the target heterocycles either in a two-step reaction sequence involving two-electron reduction of the diimine to an enediamide, enediamine, or a-aminoamine and subsequent condensation with PC13 [18-20] or a dichlorophosphine RPC12 [21], or via direct base-promoted reaction with PC13 [20, 22], The latter reaction involves addition of a P-Cl bond to each imine moiety followed by base-promoted elimination of hydrogen chloride leading to 2,4-dichloro-... 

VAN DER VLIET, A., HOEN, P. A., Wong, P. S., Bast, A., Cross, C. E., Formation of S-nitrosothiols via direct nucleophilic nitrosation of thiols by peroxynitrite with elimination of hydrogen peroxide, J. Biol. Chem. 273 (1998), p. 30255-30262... 

For example, in one pathway H-atom elimination reactions generate the enol intermediate, which eventually rearranges to 2-butanone. In a second competing reaction pathway, H-atom addition results in direct hydrogenation to the saturated alcohol 2-butanol. 

Whether the sulfur is eliminated as a metal sulfide, as shown in the section entitled Hydroforming Reaction and burned off during regeneration of the catalyst, or is eliminated directly as hydrogen sulfide is a function of the pressure and catalyst holding time. At high pressure the bulk of the sulfur is eliminated as hydrogen sulfide. 

These are not accessible from coordinated dinitrogen and the preparative routes involve alkylation (equation 172) or protonation (equation 173) of hydrazido(2—) precursors or direct use of the hydrazine with elimination of hydrogen halide (equation 174). 

Grigg et a/.472,473 reported the first examples of the elimination of hydrogen cyanide and nitriles in retrocycloaddition reactions. The oxazoles 4 (R = H or Me) with DMAD in cold ether led directly to the furan 6 and the appropriate nitrile the expected intermediate 5 could not be isolated. The less reactive oxazole 7 was converted by DMAD into the furan 8 (69%) and benzonitrile only in boiling toluene about 10%... 

By addition of bromine at low temperature methyl 2-siloxycyclopropanecarboxylates are regioselectively cleaved to give a-bromo-y-oxoesters 126 quantitatively. These can be isolated in singular cases, but usually they are directly transformed to oe,P-unsaturated y-oxoesters 127 by subsequent elimination of hydrogen bromide with triethylamine 80). Thereby -alkenes are obtained in good overall yields, which are interesting acceptor building blocks for further synthetic operations. 

The electron-deficient double bond in lH-pentafluoropropene reacts easily with nucleophiles such as azide anion to form primarily an addition product l-azido-l,2,3,3,3-pentafluoropropane. In the basic medium, unsaturated l-azido-2,3,3,3-tetrafluoropropene is also formed, either by elimination of hydrogen fluoride from the addition product, or by direct displacement of fluorine by SN2 mechanism [90]. 

The direct fluorination of substituted pyridines with elemental fluorine results in the selective substitution of a hydrogen in the 2-position to give 2-fluoropyridines 1. - This selectivity is explained through an addition-elimination mechanism, the first step in which is the formation of a complex of type 2 between the fluorine and the pyridine. Then there is attack of the fluoride ion at C2 to give a formal addition product 3, followed by elimination of hydrogen fluoride. The initial step in thus reaction is supported by the fact that a complex between pyridine and fluorine has been isolated and characterized at — 80 C. ... 

Oxygen or, particularly, nitrogen adjacent to a carbon-fluorine bond greatly increases reactivity towards nucleophiles. Hydrolysis of a,a-difluoro ethers occurs under acid conditions [39] (Figure 5.19). Orthoesters are produced by reaction with aUcoxides such reactions may, however, occur via initial elimination of hydrogen fluoride, rather than by direct nucleophilic displacement of fluoride [40] (Figure 5.20). 

The addition of iodine azide to primary allylic alcohols occurred with complete regio- and simple diastereoselectivity allowing the direct preparation of valuable 3-azido-1,2-epoxides, e.g., 12 and 13, by base-promoted elimination of hydrogen iodide from the intermediate 3-azido-2-iodo alcohols44. 

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