Aluminium photo-oxidation

Protopine has been isolated from Bocconia frutescens,110 Fumaria judaica,111 F. schleicheri,112 and Papaver bracteatum,146 cryptopine from F. schleicheri,112 and allocryptopine from B. frutescens110 and Zanthoxylum nitidum.141 The protopine ring-system has been prepared from tetrahydrobenzindenoazepines (75) by photo-oxidation to the amides (76) followed by reduction with lithium aluminium hydride and re-oxidation with manganese dioxide.148-150 The tetrahydrobenzindenoazepines have been prepared from A-chloroacetyl-/ -phenylethylamines (73) by cyclization to the lactam (74) followed by reaction with a benzyl bromide and phosphorus oxychloride. -Protopine (77 R R2 — CH2)148 and fagarine II (77 R1 = R2 = Me)149 have been synthesized in this way. 

Polyurethane ether (PUR-ether) foams are thought to degrade primarily by oxidation, particularly in the presence of light, resulting in discolouration and a loss of mechanical properties. Polyurethanes synthesized from a polyether polyol and an aromatic diisocyanate such as diphenylmethane diisocyanate (MDI) are highly vulnerable to photo-oxidation, whereas polyester-based polyurethanes are more resistant to ultraviolet radiation (Kerr and Batcheller, 1993). Metal ions, particularly copper, aluminium and zinc, form chelates with some polyurethanes imparting increased sensitivity to photo-oxidation (Ranby and Rabek, 1975). 

In the first class of CPs nanocomposites, the oxides considered as secondary component are titanium dioxide (TiO ), zirconium dioxide (ZrOj), silicon dioxide (SiO ), aluminium oxide (Al O ), cadmium oxide (CdO) and zinc oxide (ZnO) [19, 27, 31, 48-52]. Titanium dioxide nanoparticles have excellent properties such as charge carrier, oxidising power, non-toxicity, chemical and photo stability. Conductive PANI/TiO nanocomposites combine the qualities of PANI and nanocrystalline TiO within a single material, thereby developing multifunctional materials with combined properties which have very strong potential applications. 

Figure 5.38. The photo shows natural aluminium oxide Al20g (corundum). Aluminium oxide is only surpassed in hardness by diamond. Artificially made aluminium oxide is widely used as an abrasive.

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