Comparative amine-catalyzed thia-Michael reactions of primary and secondary thiols with maleic and itaconic anhydrides and esters

Authors: Bantchev, Grigor; Doll, Kenneth - Ken

Submitted to: ChemistrySelect
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/2/2022
Publication Date: 12/21/2022
Citation: Bantchev, G.B., Doll, K.M. 2022. Comparative amine-catalyzed thia-Michael reactions of primary and secondary thiols with maleic and itaconic anhydrides and esters. ChemistrySelect. 7(48). Article e202204138. https://doi.org/10.1002/slct.202204138.
DOI: https://doi.org/10.1002/slct.202204138

Interpretive Summary: Itaconic acid and its derivatives are one of the top 12 substances that can be made from biomass and can be used as an intermediate for biobased materials. The chemical structure of the itaconic acid derivative allows it to participate in many different reactions that have not been fully studied. A particularly versatile reaction is the thia-Michael reaction (a classic organic reaction), which is used in many industrial applications. ARS researchers in Peoria, Illinois, have subjected itaconic acid derivatives to the classic organic reaction in a comparative study with other commonly used petroleum-based chemicals. The results show that not only is the reaction possible with an itaconic derivative, but it even gives better yields, demonstrating that this biobased material can be used instead of a petroleum-based chemical. Different compounds containing sulfur and an itaconic derivative were tested together and found suitable for making an entire family of different biobased products. This research is a key step in using a biobased material to replace petroleum-based ones in the production of lubricant additives, dispersants, and polymer materials.

Technical Abstract: Experiments using two amine catalysts (triethylamine, TEA and triethylenediamine, DABCO®), two thiols (primary 1-octanethiol, OctSH, and secondary cyclohexanelthiol, cHexSH) and four Michael acceptors (maleic anhydride, MA, itaconic anhydride, IA, dimethyl maleate, DMM, and dimethyl itaconate, DMI) in thia-Michael reactions were performed to gain mechanistic insight into these important carbon-sulfur bond forming reactions . The TEA catalyst showed higher activity than DABCO®. IA gave a steady increase of product whereas MA initially displayed fast growth followed by decline of the product after 24 h. Both DMM and DMI displayed no product for the first three hours but significant amounts after 24 h. Among the thiols, OctSH gave more product than cHexSH in all cases. Overall, IA showed more final product than MA. In the opposite manner, DMM showed more product than DMI. Isomerization of the double bonds in IA, and to a lesser extent in DMM and DMI, was noticed. This led to formation of isomeric thia-Michael products from IA. Density-functional theory was used to calculate the 'G of the reactions. It showed that the 'G of the thia-Michael reaction with MA to be 2.1 ± 0.1 kcal/mol more favorable than the one with IA, and that 'G of the reactions with primary thiol to be 1.1 ± 1.0 kcal/mol less than with those using secondary thiols.