Hydrogen-carbon bonds osmium tetroxide

Further chemistry of alkenes and alkynes is described in this chapter, with emphasis on addition reactions that lead to reduction and oxidation of carbon-carbon multiple bonds. First we explain what is meant by the terms reduction and oxidation as applied to carbon compounds. Then we emphasize hydrogenation, which is reduction through addition of hydrogen, and oxidative addition reactions with reagents such as ozone, peroxides, permanganate, and osmium tetroxide. We conclude with a section on the special nature of 1-alkynes— their acidic behavior and how the conjugate bases of alkynes can be used in synthesis to form carbon-carbon bonds. 

Osmylation and Epoxidation With osmium tetroxide, carbon nanotubes react as expected for a compound containing double bonds. The osmylation adduct with the respective double bond being replaced by two C-O-bonds is formed as shown in Figure 3.78. However, the process is normally conducted in a photochemical way here. The intermediates thus obtained can be transformed into hydroxylated nanotubes by hydrolysis. In doing so, it is advisable to effect a reoxidation of the resultant osmium(Vl) by hydrogen peroxide in order to minimize the consumption of osmium. The osmylation of carbon nanotubes is reversible so the process may also be employed for purification or separation steps. Contrary to an ozonoly-sis with subsequent reductive work-up, the osmylation does not give rise to holes in the side wall. Hence the electronic structure is less affected. 

In several of the reactions in previous sections, one heteroatom (halogen, oxygen) was added to one side of a 7i-bond and a hydrogen or another heteroatom to the other side. There is another type of reaction in which heteroatoms are incorporated on both carbons of a 71-bond. A specific example incorporates two hydroxyl (OH) units. In one experiment, cyclohexene is treated with OSO4 (osmium tetroxide) in anhydrous er -butyl alcohol (2-methyl-2-propa-nol) at 0°C. After standing overnight, a 45% yield of cis-l,2-cyclohexanediol (124) was obtained.Analysis of this reaction shows that two OH units added and that both oxygen atoms were derived from osmium tetroxide. This reaction is termed a dihydroxylation. Furthermore, the two OH units have a cis relationship. 

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