Topochemistry Part XXXV. The Formation of Mixed Dimers from Solid Solutions of Trans‐Cinnamic Acids and Trans‐Cinnamides

Abstract

Irradiation (λ >300 nm) of eight two‐component solid solutions of β‐arylacrylamides, prepared by melting and crystallising equimolar quantities of the amides tr‐ArCH:CHCONE where Ar=C6H5, p‐MeOC6H4, p‐ClC6H4, p‐MeC6H4, and 2‐thienyl, which appeared in the α crystal form, gave three photoproducts for each system studied: two α‐truxillic homodimers, derived from the respective monomers, and an α‐truxillic heterodimer. No other isomers were found. Similarly, two‐component solid solutions were prepared by melting and crystallising ring‐substituted cinnamic acids (tr‐ArCH:CHCO2H, where Ar=C6H5 (α‐form), p—ClC6H4(β), p‐MeC6H4(α), p‐MeOC6H4(γ), o‐ClC6H4(β) and o‐CH3C6H4(γ)) and irradiated. A solid solution of two α‐type acids (each photodimerising in the solid to α‐truxillic acid) behaved like the amides, affording two α‐truxillic homodimers and an α‐truxillic heterodimer. A solid solution of an α‐type acid with a β‐type acid (photodimerising to β‐truxinic acids) gave six photoproducts: three α‐truxillic acid dimers and three β‐truxinic acid dimers (i.e., four homodimers and two heterodimers). Irradiation of a solution of a γ‐type acid (non‐photodimerising in the solid state) with an α‐type acid afforded α‐truxillic dimers (two homodimers and one heterodimer). The above results are consistent with mutual miscibility of the two components which gives rise to mixed crystal formation and subsequent photo‐behaviour within each crystal which is characteristic of the particular lattice type. However, irradiation of the mixed crystals from p‐methoxycinnamic acid (γ‐type) and p‐chlorocinnamic acid (β‐type), which afford two α‐truxillic dimers (methoxy‐homodimer and methoxy, chloro‐heterodimer) and two β‐truxinic dimers (chloro‐homodimer and methoxy, chloro‐heterodimer) indicates that new phases, unobserved for the pure compounds, can also be generated. The new dimers were all characterised by the NMR and mass spectra of their dimethyl ester derivatives and, when possible, by conversion to known compounds.

A new polymorph of ortho-ethoxy-trans-cinnamic acid: single-to-single-crystal phase transformation and mechanism

“…(i) that it be labelled the -polymorph since it is the fourth known polymorph of OETCA (a system that seems to be most in use today), or (ii) that the new polymorph be labelled as the H -polymorph, indicating that it is related to the -polymorph through a reversible phase transition. In addition, both these polymorphs yield the same centrosymmetric photochemical product (making it an -polymorph according to the Schmidt labelling method; Cohen & Schmidt, 1964;Cohen & Green, 1973) and have the shortest cell axes greater than 5.1 A Ê (making it an -polymorph according to the Hung labelling method; Hung et al, 1972).…”

Polymorphic phase transformations of 3-chloro-trans-cinnamic acid and its solid solution with 3-bromo-trans-cinnamic acid

“…The formation of solid solutions composed of mixtures of trans-cinnamic acid derivatives has been reported previously (Hung et al, 1972) and it has been shown (Khoj et al, 2017) that, for a given binary system, solid solutions with a range of diverse structures can be formed depending on the composition of the material. In the case of solid solutions containing 3-ClCA and 3-BrCA [such solid solutions are denoted 3-(Cl/Br)CA], two different -type structures and two different -type structures have been reported (Khoj et al, 2017).…”

Crystal-to-crystal photodimerization of trans-cinnamamides

“…trans-4-Chlorocinnamamide (II) and trans-cinnamamide (IV) were commercially available. trans-4-Methylcinnamamide (I) and trans-3-(2-thienyl)acrylamide (III) were prepared according to the method reported (Hung et al, 1972;Mason & Nord, 1951). The -type photodimer (V) was prepared by the solid-state reaction of (II).…”

“…Solid-state [2 + 2] photodimerization of trans-cinnamic acids was extensively investigated by Schmidt and coworkers to establish the topochemical principles . The crystal structures and hydrogen-bond networks of the trans-cinnamamide (IV) and the 4-chloro derivative (II) were also investigated (Rabinovich, 1969;Leiserowitz & Schmidt, 1969) as well as the [2 + 2] photoreaction of (I)±(III) (Hung et al, 1972). An exposure of a single-crystal of (IV) to sunlight deformed the X-ray diffraction peaks, suggesting lattice distortion owing to photoreaction (Osaki & Schmidt, 1972).…”