Action of Organoaluminum Reagents on Esters: Alkene Production and the Degradation of Synthetic Lubricants

Abstract

Reactions of methylaluminum reagents with ester-based lubricating oils are mimicked through the reaction of trimethylaluminum (TMA) with tetraesters C­(CH2OC­(O)­R)4 (R = C5H11 4 Pent, Bn 4 Bn). Using a 2:1 stoichiometry gave adduct 4 Pent(TMA)4. NMR spectroscopy on 1:1–12:1 TMA/4 Pent systems suggested 4 Pent gave dimethylated adduct C5H11CMe2OAlMe2(TMA), 2 Pent(TMA). Similar combination of TMA with 4 Bn at raised temperatures transformed 4 Bn into C­(CH2OAlMe2)4(2 Bn)4 5(2 Bn)4 by sequential reaction of each ester group. Doubly reacted {BnC­(O)­OCH2}2C­(CH2OAlMe2)2(2 Bn)2 7 Bn(2 Bn)2 was isolated and characterized. A Mitsubishi molecule could also be isolated, its formation rationalized by the elimination of 2 Bn and TMA from 5(2 Bn)4. The action of Me n AlCl3–n (n = 1, 1.5, 2) was studied initially on monoester BnC­(O)­OMe 1 Bn. Combining excess Me2AlCl with 1 Bn gave adduct 1 Bn(Me2AlCl) and small amounts of dimethylated BnCMe2OAlMe2(Me2AlCl), 2 Bn(Me2AlCl), and MeOAlCl2 10. 2 Bn(Me2AlCl) was fully characterized and, in the presence of 10, acted as a source of 2 Bn(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 aluminum sesquichloride or MeAlCl2 led to progressively more sluggish but similar reactions. Using Me n AlCl3–n (n = 1, 1.5, 2) with tetraesters suggested similar reactivity to monoesters.

Influence of different ester side groups in polymers on the vapor phase infiltration with trimethyl aluminum

“…This indicates that either during sputtering in the XPS experiment the carbon is preferentially removed, or a second reaction of TMA with the polymer chain takes place which might be indicated by investigations of reactions of TMA with ester containing lubricants in toluene solution. 57,58 A third option would be that the time for excess TMA within the polymer was too short to diffuse off the polymer before it was trapped by reaction with water to form aluminum oxide during the water pulse. Of course, all three phenomena may occur at the same time.…”