An Investigation of the Pathways for Oxygen/Sulfur Scramblings during the Copolymerization of Carbon Disulfide and Oxetane

Abstract

The catalytic coupling of oxetane, the symmetric isomer of propylene oxide, with carbon disulfide has been investigated utilizing (salen)CrCl in the presence of various onium salts. Oxygen and sulfur atom exchange was observed in both the polymeric and cyclic carbonate products. The coupling of oxetane and CS 2 was selective for copolymer formation over a wide range of reaction conditions. Five different polymer linkages and two cyclic products were determined by 1 H and 13 C NMR spectroscopy, and these results were consistent with in situ infrared spectroscopic monitoring of the process. The major cyclic product produced in the coupling process was trimethylene trithiocarbonate, which was isolated and characterized by single crystal X-ray crystallography. Upon increasing the CS 2 /oxetane feed ratio, a decrease in the O/S scrambling occurred. The reaction temperature had the most significant effect on the O/S exchange process, increasing exchange with increasing temperature. The presence of the onium salt initiator both accelerated the coupling process and promoted O/S scrambling. COS (observed), and CO 2 intermediates are proposed in the reactions leading to various polymeric linkages.

An Investigation on the Production of Random Copolymer with Monothiocarbonate and Trithiocarbonate Units over Cyclic Thiocarbonate via Metal‐free Catalysis

“…PGE is initially ring‐opened by LPs followed with a facile CS 2 insertion. Actually, similar to the copolymerization process involving oxetane and CS 2 , this is still anticipated to be the rate determining step here . An alternative reaction pathway could involve anion attack at the carbon center of the −O(C=S)S− propagating unit to form a tetrahedral intermediate.…”

“…Reasonable speculation is that, oxygen‐rich intermediate COS and CO 2 were produced and excluded from the polymerization process . Rather than L3 , linkages of L1 and L2 were produced by the interaction of CS 2 and PGE through a tetrahedral intermediate . On the other hand, direct copolymerization of CS 2 with C3 would also result in the formation of L2 .…”

“…To figure out the mechanism of O‐S ER, we have investigated the pathways for O‐S ER process by using oxetane, a symmetric monomer, to copolymerize with CS 2 in the catalyzing of (salen)CrCl/(onium salts) binary system . As a result, five different polymer linkages and two cyclic products were revealed by 1 H and 13 C NMR spectroscopy, and a plausible mechanism on a tetrahedral intermediate was presented based on the result of in situ infrared spectroscopic monitoring of the polymerization process.…”

Precise synthesis of sulfur-containing polymers via cooperative dual organocatalysts with high activity

“…In contrast with the CO 2 /epoxide copolymerization that is often expected to attain fully alternating structure and no production of side cyclic carbonate (i.e., 100% polycarbonate) 19 – 24 , the chemistry of COS/epoxide copolymerization is more complicated 6 . One is the possible occurrence of oxygen/sulfur exchange reactions (O/S ERs), which cause the production of CO 2 , and thiirane intermediate, will produce randomly distributed dithiocarbonate and carbonate units in the final copolymer 8 , 25 – 27 . The other is that the copolymerization of structurally asymmetric COS with a terminated epoxide, will generate four consecutive monothiocarbonate diads, i.e.,: head-to-tail (H–T), tail-to-head (T–H), tail-to-tail (T–T), and head-to-head (H−H) diads 6 .…”

Anionic Copolymerization of Carbonyl Sulfide with Epoxides via Alkali Metal Alkoxides

“…Werner and coworkers [30] used lithium tert-butoxide (t-BuOLi) to generate poly(thiocarbonate)s from carbon disulfide (CS 2 ) and epoxides. Unfortunately, oxygen/sulfur exchange reaction (OS/ER) [31][32][33] produced trithiocarbonate, dithiocarbonate and carbonate units randomly distributed in the polymer chain. Since COS is an asymmetric CO 2 (CS 2 ) analogue and has higher reactivity than CO 2 and poorer ability of O/S ER than CS 2 , [16,[31][32][33] we envisioned that COS could copolymerize with epoxides in an anionic copolymerization process.…”