The pre-reaction will generally be carried out in an organic solvent, including ketones such as methyl ethyl ketone, acetone and methyl isobutyl ketone; aliphatic alcohols such as methanol, ethanol, propanol and butanol; amides such as dimethyl formamide and dimethyl acetamide; cyclic ethers such as dioxane and tetrahydrofuran; aromatic hydrocarbons such as benzene, toluene or xylene and mixtures