A new iron-based, light-activated alkyd drier

 
As a result of (expected) relabeling of cobalt-based materials, cobalt-free alkyd driers (based on iron or manganese) have been developed. Although these new driers perform similar to cobalt in many aspects, particularly hardness development is decreased. As anti-skinning agent, oximes like methyl ethyl ketoxime (MEKO) or 2-pentanone oxime (2-PO) are commonly used, but their use is also under legislative pressure. We will present a new alkyd drier which could potentially overcome the legislative and performance challenges described above. This drier is based on an abundant and environmentally benign metal (iron) and does not require an anti-skinning agent. Oxidation of the complex CpFe(cyclohexadienyl) (Cp = cyclopentadienyl) yields the cationic CpFe(benzene), which is converted to the active alkyd drier after exposure to (visible) light. The complex is the first example of a cobalt-free alkyd drier that matches the performance of cobalt-based driers not only in drying speed, but also in hardness development. As the complex is only active in the light, no anti-skinning agent is required to suppress drying activity upon storage (as no light penetrates the paint can).