Zirconium oxide with carboxyl

Figure 1. Projected structures of the chelates/complexes of hydrous zirconium (IV) oxide with carboxyl, hydroxyl, and amino groups, respectively...

Cyclic orthoesters derived from gem-diols offer a further route to alkenes. As part of a three-step conversion, they may be ring opened with hydrobromic acid to give O-acyl bromodeoxy compounds that undergo reductive elimination with copper-zinc. In this way, unsaturated nucleosides have been made by way of mixed 2y3,-bromo-2y3,-deoxy-3,/2, carboxyl-ates.174 A more direct route to alkenes from cyclic orthoesters involves heating in acetic anhydride together with zirconium oxide.175... 

While carboxylated latexes are widely accepted as not needing a cure system, those described above for SBRs are applicable, as are melamine formaldehyde or other formaldehyde condensates. Multivalent metal compounds may also be used with carboxylated systems the most common of these is zinc oxide, but other materials such as zirconium ammonium carbonate may also be used. Some of these types of materials have the advantage that they are effective at room temperature. Some functional SBR latexes have their own cure system built into the polymer and are often referred to as self-crosslinking y or as heat-reactive in instances where heat is involved in the curing process. 

Addition of carbon monoxide and water to an alkene, i.e. hydrocarboxylation, is catalyzed by a variety of transition metal complexes, including [Ni(CO)4], [Co2(CO)s] and [HaPtClg]. Unfortunately this reaction usually leads to mixtures of products due to both metal-catalyzed alkene isomerization and the occurrence of Irath Markownikov and anti-Markownikov addition of the metal hydride intermediate to the alkene. The commercially available zirconium hydride [(C5Hs)2Zr(H)Cl] can be used as a stoichiometric reagent for conversion of alkenes to carboxylic acids under mild conditions (equation 23). In this case the reaction with linear alkenes gives exclusively terminal alkyl complexes even if the alkene double bond is internal. Insertion of CO followed by oxidative hydrolysis then leads to linear carboxylic acids in very good yield. 

Oxidation of waste plastics, such as polyethylene, polypropylene, polystyrene, poly (alkyl acrylates), and nylon 6,6, with NO/O2 for 16 h at 170°C, led to mixtures of carboxylic acids, for which uses would have to be developed if this method was applied to large volumes of waste plastics.180 Hydrogenation of polyethylene at 150C>C for 10 h over a sil-ica/alumina-supported zirconium hydride catalysts gave a 100% conversion to saturated oligomers.181 Polypropylene gave a 40% conversion to lower alkanes at 190°C for 15 h. It is not clear what use these materials would have, other than serving as a feedstock for a petroleum refinery. 

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