Phthalocyanine precursors; synthesis and investigation of phthalonitrile-alcohol adducts

Abstract

Phthalocyanines and related macrocycles have received widespread attention since their discovery over 100 years ago. Chapter 1 provides a brief overview of the structures, synthesis and properties, with a particular focus of the mechanism of phthalocyanine formation and the initial intermediates that are formed. Chapter 2 describes a synthetic study on the reaction of phthalonitrile with a series of alcohols and diols. The known reaction between phthalonitrile and methanol has been re-- investigated and it is found that a high yield of the dimethoxy-adduct can be isolated. Prolonged heating leads to phthalocyanine formation. The adducts are potentially useful intermediates in more complex syntheses so attempts were made to improve the stability of the intermediates by exchanging methanol with diols (ethane diol, propane diol and catechol). It was demonstrated that in solution the adduct formation is an equilibrium process, and high-yielding conditions were developed using toluene as solvent so that the adduct precipitated from the reaction solution. The optimised conditions did not lead to any observable reaction between phthalonitrile and catechol. The new products were fully characterised and the observed NMR spectra are discussed. The ED adduct was selected for preliminary investigation of relative stability. It is found to be significantly less reactive that the dimethoxy-adduct. When heated in toluene, phthalocyanine is produced as the main product. However, MALDI- MS evidence indicates that the self-condensation product might also be formed. This is an important observation because such dimers offer potential as advanced intermediates in complex phthalocyanine synthesis. Chapter 3 provides full experimental and characterisation details.