Solid State Dimerization of a Styryl Disperse Dye

During an investigation into structure-property relationships of a series of ethyl-α-cyano-4-aminocinnamate disperse dyes, the 4-(N-β-cyanoethyl-N-β-acetoxyethyl) amino derivative showed anomalous behaviour on attempts to purify it. This compound was shown to be susceptible to dimerization to a colourless cyclobutane derivative, the structure of which was established by nmr spectroscopy. The dimerization is interpreted in terms of ‘Topochemical’ factors. Typical nmr spectra characteristics of some monomeric styryl disperse dyes are also indicated.