Getting rid of functional groups

The real gain over the Sn/HCl method is in the work-up. Instead of separating and disposing of voluminous toxic tin residues, a simple filtration to remove the catalyst, evaporation, and crystallization or distillation gives the amine. 

Littiium triethylborohydride is used here, but other powerful hydride reducing agents would do as well. 

A slightly more vigorous method, known as the Wolff-Kishner reduction, is driven by the elimination of nitrogen gas from a hydrazone. Hot concentrated sodium hydroxide solution deprotonates the hydrazone, which can then eliminate an alkyl anion—a reaction you would usually be wary of writing, but which is made possible by the thermodynamic stability of N2. 

The third method is the simplest to do, but has the most complicated mechanism. The Clemmensen reduction is also rather violent, and really reasonable only for compounds with j ust the one functional group. It uses zinc metal dissolving in hydrochloric acid. As the metal dissolves, it gives up two electrons—in the absence of something else to do, these electrons would reduce the H in the acid to H2, and give ZnCl2 and H2. But in the presence of a carbonyl compound, the electrons go to reduce the C-0 bond. 

The mechanism has a good deal in common with a whole class of reductions, of which the Clemmensen is a member, known as dissolving metal reductions. We shall now look at these as our third (after metal hydrides and catalytic hydrogenation) important class of reducing agents. 

Hydrogenolysis happens under similar conditions to alkene hydrogenation, but involves breakage of a C—O or C—N a bond rather than a C=C jc bond. It is particularly important for removing benzyl protecting groups, to which we will return later in the chapter. 

Alcohols can be got rid of either by elimination to alkenes and then hydrogenation or by tosylation and substitution using borohydride to provide a nucleophilic hydrogen atom. 

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You can now clearly see the similarity with our target molecule , grandisol, but there are several more steps to carry out yet. The nitrile needs to be got rid of completely—we showed you a few ways of getting rid of functional groups in the last chapter, and the one used here was the Wolff-Kishner reduction of an aldehyde. The aldehyde comes from reduction of the nitrile with DIBAL. 

Think, for a moment, about the principal role played by the central carbon of a functional group in forming C-C bonds. Then ask how many C-C bonds that particular carbon is capable of forming until it gets rid of all heteroatoms directly substituted on it as well as unsaturations. This number could be anything from a maximum of four, for stable species of carbon, to a minimum of zero in the case of nonactivated hydrocarbon methylenes and methane. Then give this number a name, say Functionality Number, abbreviated as FN. 

FTIR measurements can be used to identify and semi-quantitatively verify the surface functionalities/polar groups on diamond nanoparticles surface induced by plasma treatment. Nicolet 6700 FT-IR Spectrometer (Thermo Scientific Inc.) was used to take Fourier Transform Infrared Spectra (FTIR) of the untreated and plasma treated diamond nanoparticles. Well-ground mixtures of nanoparticle and KBr powders (IR grade) were kept in an oven and baked at 200 °C for 48 h to get rid of moisture before performing the FTIR measurements. 

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