PREPARATIONS 147 This oxidation proceeds readily if the methylene group is activated by linkage to (a) a carbonyl group, (b) an aromatic ring; (c) an olefine link also activates adjacent :CH 2 and -CH: groups. Examples. (^z)CH 1 COCH, -*- CH.COCHO Also cyclohexanone -> cyclohexan-i,2-dione (b) 0,H 5 CH 1 C 4 H 6-> C 4 H 8 COC 4 H 6 CeHjCH.CH.C.H, -» C.H ft CO-COC e H 5 (c) CH 1 CHiCH 1-> CH 1 COCHO. Compounds containing olefine links may be oxidised to i,2-diketones, as in C 4 H^CHiCHC 4 H 5-* C e H B CO-COC e H R . Anthracene is readily oxidised to anthraquinone, but phenanthrene is almost unaffected. In certain cases, selenium dioxide may act solely as a dehydrogenating agent, as in the examples: C 1 H 6 OOC-CH 1-CH 1 COOC 1 H 5-* C,H 6 OOOCH:CH-COOC,H 6 Diethyl succinate Diethyl fumarate CH 1 COCH 1-CH 1 COCH 8-» CH 8 COCHrCHCOCH, Acetonyl-acetone Diacetyl-ethylene («-Hexan-2,5-dione) (n-Hex-3-ene-2,s-dione) The following oxidation of camphor to camphor-quinone illustrates the oxidising action of selenium dioxide, and readily gives a crystalline product. CAUTION. The vapour of selenium dioxide is poisonous, and all operations
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