Alkanes: by reduction

Yamanaka, L, Hasegawa, S., and Otsuka, K. 2002. Partial oxidation of light alkanes by reductive activated oxygen over the (Pd-black + VO (acac) (2)/VGCF) cathode of H-2-O-2 cell system at 298 K. Applied Catalysis A General. 226, 305-315. 

Alkanenitriles can be converted to alkanes by reductive decyanation with metallic sodium or potassium and several useful procedures are available. Sodium in liquid ammonia and potassium in HMPA are efficient reagents for the decyanation of alkanenitriles (equation 82). Sodium in the presence of tn s(acetylacetonato)iron III is a good combination for the reductive decyanation of primary and secondary alkanenitriles (equation 83). Highly dispersed potassium over alumina, easily prepared by melting potassium over dried alumina, converts primary, secondary and tertiary alkanenitriles to corresponding alkanes in good yield (equation 84) Recently, it has... 

Many new methods for the preparation of alkanes by reductive removal of functional groups have been reported during the year. Barton and his co-workers have presented a new radical decarboxylation for the conversion of carboxylic acids into hydrocarbons. Following esterification with /ran5-9-hydroxy-10-phenylthio-(or -10-chloro-)9,10-dihydrophenanthrene, a primary, secondary, or tertiary carboxylic acid is smoothly reduced under neutral conditions by tri-n-butylstannane and a radical initiator (e.g. Scheme 1). Formation of phenanthrene... 

The coupling of alkyl Grignard reagents with alkyl iodides to afford alkanes by use of dppf as a ligand has been reported[449], but re-examination of the reaction has shown that only reduction takes place, and no coupling was observed[450]. 

Alkenes are reduced by addition of H2 in the presence of a catalyst such as platinum or palladium to yield alkanes, a process called catalytic hydrogenation. Alkenes are also oxidized by reaction with a peroxyacid to give epoxides, which can be converted into lTans-l,2-diols by acid-catalyzed epoxide hydrolysis. The corresponding cis-l,2-diols can be made directly from alkenes by hydroxylation with 0s04. Alkenes can also be cleaved to produce carbonyl compounds by reaction with ozone, followed by reduction with zinc metal. 

Alkynes can be reduced to yield alkenes and alkanes. Complete reduction of the triple bond over a palladium hydrogenation catalyst yields an alkane partial reduction by catalytic hydrogenation over a Lindlar catalyst yields a cis alkene. Reduction of (he alkyne with lithium in ammonia yields a trans alkene. 

Carboxylic acids can also be converted to alkanes, indirectly,by reduction of... 

Though the usual product of epoxide reductions is the alcohol (10-85), epoxides are reduced all the way to the alkane by titanocene dichloride and Et3SiH-BH3. ... 

Reduction of simple alkyl halides to alkanes by ethylenediamine complexes of Cr(II), denoted Cr"(en) occurs readily , e.g. for isopropyl chloride in aqueous dimethylformamide at 25 °C simple second-order behaviour is found with ki dependent on [en]/[Cr(II)] but reaching a limiting value of 1.6x 10 l.mole . sec . Competition studies between a mixture of two alkyl chlorides for Cr(II) was achieved by estimating alkane products by gas-liquid chromatography and... 

The most important contributions in this area, however, directly related to bond activation chemistry, and, undoubtedly triggered by theoretical considerations along the lines of Figure 1, were reported by Whitesides and coworkers in 1986 and 1988 [11]. It was shown that the bent, bisphosphine-coordinated platinum chelate complex [(dcpe)Pt(O)] (9) (dcpe = bis(dicyclohexylphosphino)ethane), which could be generated thermally as a "hot" reactive intermediate by reductive elimination of neopentane from its ris-neopentylhydride Pt(II) precursor at around 60-70°C in solution, was able to activate C-H bonds, even of unactivated alkanes. 

Various catalytic or stoichiometric asymmetric syntheses and resolutions offer excellent approaches to the chiral co-side chain. Among these methods, kinetic resolution by Sharpless epoxidation,14 amino alcohol-catalyzed organozinc alkylation of a vinylic aldehyde,15 lithium acetylide addition to an alkanal,16 reduction of the corresponding prochiral ketones,17 and BINAL-H reduction18 are all worth mentioning. 

Nastainczyk W, Ahr HJ, Ullrich V. 1982b. The reductive metabolism of halogenated alkanes by liver microsomal cytochrome P450. Biochem Pharmacol 31 391-396. 

On the other hand, the use of [Rh(CO)2Cl]2 as a catalyst results in ring opening of the siloxycyclopropanes 13 to the silyl enol ethers 14 with high stereoselectivity [10]. The 2-siloxyrhodacyclobutane 15a is proposed to undergo j8-elimination to give jr-allylrhodium 16a followed by reductive elimination to the silyl enol ether 14a. 1-Trimethylsiloxybicyclo[n.l.0]alkanes serve as / -metallo-carbonyl compounds via desilylation with a variety of transition metals [11]. The palladium-catalyzed reaction of the siloxycyclopropanes 17 under carbon monoxide in chloroform provides a route to the 4-keto pimelates 18. In the presence of aryl triflates, the 1,4-dicarbonyl compounds 19 are... 

In organic chemistry, reduction is defined as a reaction in which a carbon atom forms fewer bonds to oxygen, O, or more bonds to hydrogen, H. Often, a C=0 bond or C=C bond is reduced to a single bond by reduction. A reduction that transforms double C=C or C=0 bonds to single bonds may also be classified as an addition reaction. Aldehydes, ketones, and carboxylic acids can be reduced to become alcohols. Alkenes and alkynes can be reduced by the addition of H2 to become alkanes. 

In a scheme complementary to the one just presented where thiols are removed by reductive desorption of thiols, molecules can also be removed during stripping of a UPD layer. This was demonstrated by Shimazu et al. [221] where an alkane thiol SAM was deposited onto a Au(l 11) that had been modified with Pb. Oxidative stripping of the lead also caused thiols to be removed. The empty sites were then subsequently filled with mercaptopropionic acid (MPA). A remarkable result is that the binary SAMs exhibit only one desorption peak. From this it was concluded that a well-mixed layer forms that is very different from the mixed SAM obtained by adsorption from solution containing both types of thiols. In this case the layer exhibits singlecomponent domains that are refiected by two desorption peaks. 

Alkynes may also be hydrogenated, initially to alkenes, and then further to alkanes. By suitable modification of the catalyst, it has proved possible to stop the reaction at the intermediate alkene. Typically, platinum or palladium catalysts partially deactivated (poisoned) with lead salts are fonnd to be suitable for reduction of alkynes to alkenes. Again, syn addition is observed. 

The carbon-nitrile bond in cyanoalkanes is cleaved by reduction at very negative potentials. This is the route for decomposition of acetonitrile at tlie limit for its use as an aprotic solvent in electrochemistry [114, 115]. Preparative scale reduction of cyanoalkanes is best carried out in anhydrous ethylamine containing lithium chloride as supporting electrolyte and gives 60-80 % yields of the alkane plus cyanide ion. 

Cyclohexane. It can be prepared with high purity by distillation of a mixture of alkanes fi om petroleum refining or by reduction of benzene. 

Alkanes can also be prepared from alkyl halides by reduction, directly with Zn and acetic acid (AcOH) (see Section 5.7.14) or via the Grignard reagent formation followed by hydrolytic work-up (see Section 5.7.15). The coupling reaction of alkyl halides with Gilman reagent (R 2CuLi, lithium organocuprates) also produces alkanes (see Section 5.5.2). 

Addition of hydrogen atoms in the presence of a metal catalyst to double or triple bonds is known as hydrogenation or catalytic hydrogenation. Alkenes and alkynes are reduced to alkanes by the treatment with H2 over a finely divided metal catalyst such as platinum (Pt—C), palladium (Pd—C) or Raney nickel (Ni). The platinum catalyst is also frequently used in the form of Pt02, which is known as Adams s catalyst. The catalytic hydrogenation reaction is a reduction reaction. 

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