Schiff Bases — A Primer

The amines used in the fragrance industry are methyl anthranilate and ethyl anthranilate, the former being used more commonly. Note that some materials are sold as Schiff bases of indole, a secondary amine, but these evidently are aminals, a different class. The aldehyde may be chosen from the usual suspects: alkyl or aromatic aldehydes, such as decanal and benzaldehyde; terpene aldehydes, such as hydroxycitronellal; or terpene-like aldehydes, such as lilial, triplal, and lyral. Methyl anthranilate generally gives Schiff bases that are yellow solids or viscous, yellow liquids. For easier handling, an excess of methyl anthranilate is sometimes employed in order to make the product more fluid, or, at least, lowermelting. The reaction is usually not driven to completion, for the same reason, and also to minimize undesirable darkening. Further, the product may be diluted with common solvents; for example, diethyl phthalate or dipropylene glycol. There are several available methods, but in my own personal experience at Vigon, we remove the by-product water under vacuum, instead of at higher temperature at atmospheric pressure, and use other, proprietary techniques to maintain light color while driving the reaction to a consistent, targeted degree of completion.