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Experiment 5.78 HEXANEDIAL
trans-Cyclohexane-l,2-diol (232mg, Expt 5.48) and sodium metaperiodate supported on silica gel (6.1 g 10% loading. Section 4.2.55, p. 455) are stirred in dichloromethane (15ml) (1) for 3 hours at 20~C. The solids are then filtered off and washed with dichloromethane (2 x 10 ml). Evaporation of the solvent from the combined filtrate and washings gives a clear oil (185mg 80%) which is pure dial.
Note. (1) The dichloromethane is distilled from phosphorus pentoxide and stored over molecular sieves.
5.7.3 THE OZONOLYSIS OF SUITABLY SUBSTITUTED ALKENES
Oxidation of alkenes with ozone followed by cleavage of the resulting ozonides to carbonyl compounds is widely used for the determination of structure of unsaturated compounds. The ozonolysis technique is described in detail in Section 2.17.4, p. 103.
For-preparative purposes the cleavage of the ozonide is best carried out by catalytic hydrogenation over palladium hydroxide:on-calcium carbonate a catalyst system which does not hydrogenate the aldehydic products; the yield of the latter are usually fairly good. An alternative procedure for the decomposi-tion of the ozonide is treatment with dimethylsulphide in methanol; the use of the less obnoxious thiourea is a good alternative
Two examples of preparative ozonolysis are given (Expt 5.79). In the first cyclohexene is subjected to ozonolysis in ethyl acetate to provide a convenient synthesis of theα,ω-dicarbonyl compound, adipaldehyde. In the second, the substrate is oleic acid, which yields two aldehydic fragments, non and azelaic hemialdehyde.
