Action of Organoaluminum Reagents on Esters: Alkene Production and the Degradation of Synthetic Lubricants
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Reactions of methylaluminium reagents with ester-based luricating oils are mimicked through the reaction of trimethylaluminium (TMA) with tetraesters C(CH2OC(O)R)4 (R = C5H11 4Pent, Bn 4Bn). Using a 2:1 stoichiometry gave the adduct 4Pent(TMA)4. NMR spectroscopy on 1:1-12:1 TMA:4Pent systems suggested 4Pent gave dimethylated adduct C5H11CMe2OAlMe2(TMA) 2Pent(TMA). Similar combination of TMA with 4Bn at raised temperatures transformed 4Bn into C(CH2OAlMe2)4(2Bn)4 5(2Bn)4 by sequential reaction of each ester group. Doubly-reacted {BnC(O)OCH2}2C(CH2OAlMe2)2(2Bn)2 7Bn(2Bn)2 was isolated and characterized. A Mitsubishi molecule could also be isolated, its formation rationalised by the elimination of 2Bn and TMA from 5(2Bn)4. The action of MenAlCl3-n (n = 1, 1.5, 2) was studied initially on monoester BnC(O)OMe 1Bn. Combining excess Me2AlCl with 1Bn gave adduct 1Bn(Me2AlCl) and small amounts of dimethylated BnCMe2OAlMe2(Me2AlCl) 2Bn(Me2AlCl) and MeOAlCl2 10. 2Bn(Me2AlCl) was fully characterized and, in the presence of 10, acted as a source of 2Bn(MeAlCl2). From this species, a mixture of alkenes could be generated by formal elimination of Me3Al2(OH)Cl2 13, the decomposition of which was presumed to also explain MeH observation. Replacing Me2AlCl with aluminium sesquichloride or MeAlCl2 led to progressively more sluggish but similar reactions. Using MenAlCl3-n (n = 1, 1.5, 2) with tetraesters suggested similar reactivity to monoesters.
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1520-6041
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Engineering and Physical Sciences Research Council (EP/N509620/1)