supplementary materials

In the course of the authors' investigations on the chemical and electrochemical properties of aromatic dicarbonyl compounds (Zuman, 2004) the reactivity of phthalaldehyde with nucleophiles has been studied. The reaction between phthalaldehyde and nucleophiles is important because namely the reaction of phthalaldehyde with amino acids is used for the fluorimetric determination of the latter substances. The fluorescence is substantially enhanced if another, stronger nucleophile is added in excess to phthalaldehyde prior to its reaction with an amino acid (Roth, 1971). Despite of the practical application of this reaction the chemical mechanism of this a rather complex process is still not fully understood. In order to elucidate the reaction steps we started to study the reactions between phthalaldehyde and a stronger nucleophile [2-aminoethanol (kolamine)] before adding an amino acid.

The interaction between phthalaldehyde and a nucleophile seems to be crucial because it is strongly dependent on a medium, on the sequence of the added chemicals (kolamine prior to phthalaldehyde or vice versa) as well as on the way, e.g. its speed, of their mixing as follows from our preliminary studies (Urban et al., 2007a,b). The aim of this study is to investigate the reaction pathway by isolation of some intermediate products before adding an amino acid.

As the first studied nucleophile we have used 2-aminoethanol (kolamine). A previously applied procedure (Urban et al. 2007a,b) involving the addition reaction in non-aqueous acetonitrile when kolamine was added dropwise led to the isolation of two products. In contrast to these previous studies the reaction presented here proceeded in 0.1 M HCl and yielded the title compound that is different from those described by Urban et al. (2007a,b; see Fig. 5). The study that aims to explain this difference in the reactions paths in various evironments is under progress as well as the study of the detailed reaction pathway of the subsequent reaction with an amino acid.

The molecular structure of the title compound is shown in Fig. 1. In the crystal structure, the most important intermolecular interactions between the molecules are strong (Desiraju & Steiner, 1999) O—H···N and O—H···O hydrogen bonds (Table 1). The O3—H3···N2ⁱ [symmetry codes as in Table 1] hydrogen bonds are involved in the formation of dimers with the graph set motif R₂²(10) (Etter et al., 1990; Fig. 2, Fig. 3). These dimers are located on crystallographic inversion centers. Each such a dimer is interconnected to another one displaced by 0, 1/2, 1/2 via O—H···O hydrogen bond with the motif C(10) (Fig. 3). These chains together with the above mentioned dimers are interconnected by other symmetry-equivalent O—H···O hydrogen bonds and form a two- dimensional pattern (Fig. 4) that is parallel to (100). There are also week C—H···O hydrogen bonds and it is interesting that the carbonyl oxygen O1 is involved in a weak C—H···O hydrogen bonding.

There are also π–π stacking interactions between the aromatic rings of the title molecule as indicates their stacking along the b axes in the approximate distance b/2=3.57334 (3) Å. Specifically, the distances between the centroids of the pyrrole rings equal to 3.4220 (7) and 3.8779 (7) Å for the rings displaced by 1/2 - x, 3/2 - y, z and 1/2 - x,1/2 - y, z, respectively. The distances between the centroids of the pyrrole and benzene rings equal to 3.8705 (7) and 3.9616 (7) Å for the benzene rings displaced by 1/2 - x, 3/2 - y, z and 1/2 - x, 1/2 - y, z, respectively.

The attempts at crystallizations of other isolated compounds failed and therefore their molecular structures were assigned by ¹H and ¹³C NMR spectrometry (Fig. 5). The spectra were taken on the NMR spectrometer Varian 300 MHz at frequencies 229.970 and 75.434 MHz for ¹H and ¹³C, respectively.