The determination of the core structure and core surfactant interface in overbased detergents
Overbased detergents are oil additives, which are included in oil to neutralise the acids that are generated as by-products during the combustion process within an engine. These overbased detergents have been investigated on an atomic scale by the preparation and characterisation of pure model complexes with relevant metal ions and ligands. Group 2 metal ion complexes have been prepared with sulfurised alkylphenol ligands from a range of conditions. The complexes prepared from methanol have shown that calcium cations and strontium cations give isostructural complexes and that the alkyl chain has a minimal effect on the structures of the complexes. In the solid state, the complexes all have the formula M₂L₂.6MeOH. Calixarene complexes have been prepared, including a mixed metal ion complex with an ion-channel structure. Three calcium cation complexes have been prepared with calixarene ligands, where two of the complexes are mimics for the precursors for overbased detergents as they contain calcium hydroxide cores. One of the complexes has a tetranuclear Ca₄(OH)₄ core and has shown that the conversion of the calcium hydroxide core to the calcium carbonate core in an overbased detergent is a facile reaction. The second precursor mimic contains a decanuclear calcium cation core and has the formula (Ca²+)₁₀(BC8⁵¯)₂ (OH)₈(OMe¯)₂(DMF)₁₀.5DMF. An unusual monodentate carboxylic acid complex with calcium has been prepared which utilised ligand design to achieve the desired monodentate coordination. Finally, a novel complex containing calcium cations and carbonate anions has been prepared, which has the formula Ca₁₀(M2²)₈ (CO₃²¯)₂(DMPD)₄(MeOH)₄.8acetone. This complex contains µ₆-CO₃²¯ anions and can be considered to be a model for overbased detergents.