I ron oxide

Plate 15.1 I ron oxide ooids in a silty matrix from an iron oolite -a thin section. Fula, Sudan (Schwarz, 1992 Courtesy T. Schwarz). 

Plate 15.11 I ron oxide formation by atmospheric weathering of a pyrite vein in a limestone (photo courtesy, Ph. Jaesche). 

Plate 15.111 I ron oxide bands in sandy-gravelly Pleistocene sediments, South Australia (Art object by Nicolaus Lang, courtesy H. Stanjek). 

Plate 19.1 I ron oxide coloured mask, Ekoi, Nigeria (Courtesy, R. Miehler)... 

Another example is the preparation of l,2-di(methoxycarbonyl)-4-cyclopentanone. This compound has been prepare from dimethylmaleate as a mixture of its cis- and /rons-isomers (yield 45-55%) . A second approach starts with the Diels-Alder adduct of 1,3-butadiene and maleic anhydride and leads to the tronj-diacid (yield 40 %) The oldest preparation of 1,2-di(methoxycarbonyl)-4-cyclopentanone stems from Auwers in 1893 Now, the tranj-isomer is available from methylenecyclopropane and dialkylfumerate in an overall yield of 85%, whereas the pure ciy-isomer ran be obtained from methylenecyclopropane and dialkylmaleate in 53 % yield. With dimethylmaleate, the Pd(0) catalyzed codimerization leads to a cis/trans-mi t ire of 4-methylene-l,2-cyclopentane-dimethylcarboxylate in the ratio 8 2 under optimal conditions (see Table 11) after oxidation, the pure cis-cyclopentanone derivative can be isolated by simple crystallization from pentane i 3.i95)... 

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