A 1:1 Co-Crystal of (Z,Z)- and (E,Z)-Dimethyl 3,3′-Thiodiacrylate

Methyl propiolate is known to react with a variety of sulfur compounds to give variable mixtures of the (Z,Z), (E,Z) and (E,E) isomers of dimethyl 3,3′-thiodiacrylate. From the reaction of methyl propiolate and thiourea in methanol, we have obtained the (Z,Z) and (E,Z) isomers in an approximate 1:1 ratio as determined by 1H NMR spectroscopy. We report here the surprising discovery that a crystal of this material consists of a 1:1 co-crystal with alternating layers of the two isomers as determined by X-ray diffraction.