Calcium-based Catalysts

Sustainable Catalysis With Non-endangered Metals, Part 1 

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In an attempt to combine the syndioselectivity of half-sandwich titanium catalysts with the living characteristics of anionic polymerization initiators, the use of half-sandwich calcium-based catalysts has been described.363 364 In neat styrene complex (152) affords 76% rr triad PS. However, polydispersities are still quite high (Mw/Mn > 2.2)... 

Weerasooriya, U., Aeschbacher, C. L., Leach, B. E., Lin, J. and Robertson, D. T., Process for alkoxylation of esters and products produced therefrom using a calcium-based catalyst to react a lower alkyl oxide and a methyl ester of a fatty acid to obtain a product having a narrow weight distribution, US Patent 5220 046, to Vista Chemical Company (1993) Chem. Abstr., 120, 57218. 

FIGURE 16.2 Oxyethylation of (a) dodecanol and (b) methyl dodecanoate in the presence of calcium-based catalyst at 185°C. 

Lower reactivity of FAME and increased temperature may cause some hazardous problems with the initiation of the process connected with the dissolution of the calcium-based catalyst [37-39]. The reaction does not proceed rapidly after the first portions of EO are dosed, and some initiation period is observed (Figure 16.2). This period decreases when the tanperature is increased up to nS-lSS C. Induction period depends on the hydrophobe and is shorter for alcohols, but longer for oxyethylation of rapeseed FAME compared to methyl dodecanoate (MD). 

FIGURE 16.3 Comparison of homologue distribution in OD and OMD for NaOH and calcium-based catalyst (DC-L70) (average degree of oxyethylation is equal to 4). 

The reaction pathway carried out in the presence of calcium-based catalysts is not well explained. Cox and Weerasooriya [18] proposed the following reaction scheme for EAME oxyethylation, carried out in the presence of calcium alkoxylate ... 

The calcium-based catalyst probably contains the following components ... 

Leach, B., Shannon, M., Wharry, D. 1988. Alkoxylation process using calcium-based catalysts alkoxyl-ated alcohols, calcium compound and organoaluminum compound. U.S. Patent 4,775,653. 

Calcium-Based Catalyst Systems Polymerization in Suspensions and Synthesis of High-MW PEO 556... 

Calcium-based catalysts have also shown promise in hydrophosphination reactions (Scheme 4.299) [62]. Treatment of phenylacetylene with diphenylphosphine in the presence of a p-diketiminate-ligated calcium complex afforded an excellent yield of the vinylphosphine. Furthermore, the reaction was highly selective for the formation of the F-stereoisomer. This chemistry provided a transition metal-free route to the synthesis of these valuable targets. 

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