Fixation of Amine Copper Preservatives. Part 1. Reaction of Vanillin, a Lignin Model Compound with Monoethanolamine Copper Sulphate Solution

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Abstract
Summary: The fixation reaction of copper-ethanolamine preservatives in wood was studied using the reaction between vanillin, a lignin model compound, and ethanolamine-copper sulphate solution. The green compound precipitated after the reaction has been characterized spectroscopically as di(ethanolamine)-bis (vanillinato)dicopper(II); [Cu(vanillin) (ethanolamine)]2. Single crystal X-ray crystallographic studies showed that the crystals of [Cu(vanillin)(ethanolamine)]2 are triclinic with the space group P1 with a = 9.1271(7), b = 10.8723(9), c = 6.360(1) Å, α = 97.08(1), β = 100.63(1), and γ = 110.024(7)°. Z = 1. The binuclear molecule has crystallographic inversion symmetry. The ligand arrangement around the Cu(II) is a distorted square based pyramid, with a base plane made up of two oxygen atoms from the ethanolamine ligands, one oxygen atom from a hydroxyl group in vanillin and one nitrogen atom from ethanolamine. Two Cu-O [1.916(2) and 1.950(5) Å], one Cu-O (hydroxyl) [1.926(4) Å] and one Cu-N [1.999(3) Å] bonds form a plane with Cu-O (methoxyl) [2.303(2) Å] bond in an axial direction at an angle 77 ° to the plane. The result suggests that after treatment with copper-ethanolamine wood preservatives, stable copper-nitrogen-lignin complexes can be formed through reaction with guaiacyl units in lignin.
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