Comparison of the structural motifs of acetoacetanilides and related azo pigments

Abstract

The structures of three methyl-substituted acetoacetanilides and of an azo pigment derived from one of them are presented and discussed together with a review of related known crystal structures. By considering the position of any aromatic substituents it is possible to predict whether the simple acetoacetanilides adopt planar structures with intramolecular hydrogen bonding or twisted structures featuring intermolecular hydrogen bonding. However, we ®nd that the same crystal engineering rules cannot be applied to the related azo pigments: this is apparently due to the presence of an sp 2 atom which facilitates the adoption of planar conformations. The thermal properties of the acetoacetanilides were measured by DSC and are discussed with reference to their crystal structures.

Maize 1: A Trimorphic Azo Pigment

“…Form III was crystallized from a melt of form II by cooling from 175 to 50 °C at 1 °C/min. Molecules in all three forms are nearly planar and are in the keto-hydrazone tautomeric form (Figure ), consistent with Yellow 14 and studies on the solid-state chemistry of related azo pigments. ,− Furthermore, all three forms crystallize in P 1̄, and forms I and III pack with sheetlike structures similar to Yellow 14 3 Thermal ellipsoid plot of Maize 1. …”

“…Molecules in all three forms are nearly planar and are in the keto-hydrazone tautomeric form (Figure 2), consistent with Yellow 14 and studies on the solid-state chemistry of related azo pigments. 17,[21][22][23][24][25][26][27][28] Furthermore, all three forms crystallize in P1 h, and forms I and III pack with sheetlike structures similar to Yellow 14. 17 Form I has two equivalent molecules in the unit cell (Figure 4) and two intramolecular hydrogen bonds between N(1)-H‚‚‚O(1) and N(3)-H‚‚‚O(2) with lengths of 1.73 and 1.74 Å, respectively.…”

Structural motifs in acetoacetanilides: the effect of a fluorine substituent

“…Similar effects were observed in previous work on methylsubstituted analogues (Chisholm et al, 2000). Therein, we rationalized that a methyl substituent ortho to the NÐH group sterically disfavoured intermolecular interactions and forced the adoption of a sterically disfavoured planar conformation.…”

“…We recently compared the structures of some commercially important acetoacetanilides with those of the monoazo pigments derived from them (Chisholm et al, 2000). To expand further our knowledge of the packing motifs for such compounds, we have prepared the¯uorinated compounds 2 H -¯uoroacetoacetanilide, (II), 3 H -¯uoroacetoacetanilide, (III), and 4 H -¯uoroacetoacetanilide, (IV), and determined the single-crystal structure for each of them.…”