Synthesis functional group modifications, organic

The wide availability of various polysaccharides provides an important source of some of the monosaccharides. Such monosaccharides are now used in organic reactions as low-cost starting materials in the synthesis of a range of simpler optically pure compounds (e.g. Expt 5.77). These synthetic strategies have been made possible from earlier work on the development of numerous selective protection methods, on the application of new selective reagents for functional group modification within the monosaccharide molecule, and on the realisation of the role of conformation in the interpretation of a reaction course. The preparative examples in this section are illustrative of these developments. 

In Section 17.10, we saw that functional group modification plays an important role in organic synthesis. We can use the reactions we discussed in this chapter and in Chapter 19 to carry out the transformation shown below. 

BRIEF SYNTHETIC REVIEW Functional Group Modification in Organic Synthesis 20.U SPECTROSCOPY OF CARBOXYLIC ACIDS Infrared Spectroscopy... 

As an example, bulk modification by the organic reaction of unsaturated PHA with sodium permanganate resulted in the incorporation of dihydroxyl or carboxyl functional groups [106]. Due to the steric hindrance of the isotactic pendant chains, complete conversion could not be obtained. However, the solubility of the modified polymers was altered in such a way that they were now completely soluble in acetone/water and water/bicarbonate mixtures, respectively [106]. Solubility can play an important role in certain applications, for instance in hydrogels. Considering the biosynthetic pathways, the dihydroxyl or carboxyl functional groups are very difficult to incorporate by microbial synthesis and therefore organic chemistry actually has an added value to biochemistry. 

Figure 3.9 Co-condensation method (direct synthesis) employing TEOS and a terminal organotrialk-oxysilane (top) or TEOS and an organo-bridged silsesquioxane (bottom) as mixed precursors for the organic modification of mesoporous pure silica phases. R = organic functional group.

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