Abstract
The selective catalytic synthesis of limonene‐derived monofunctional cyclic carbonates and their subsequent functionalisation via thiol–ene addition and amine ring‐opening is reported. A phosphotungstate polyoxometalate catalyst used for limonene epoxidation in the 1,2‐position is shown to also be active in cyclic carbonate synthesis, allowing a two‐step, one‐pot synthesis without intermittent epoxide isolation. When used in conjunction with a classical halide catalyst, the polyoxometalate increased the rate of carbonation in a synergistic double‐activation of both substrates. The cis isomer is shown to be responsible for incomplete conversion and by‐product formation in commercial mixtures of 1,2‐limomene oxide. Carbonation of 8,9‐limonene epoxide furnished the 8,9‐limonene carbonate for the first time. Both cyclic carbonates underwent thiol–ene addition reactions to yield linked di‐monocarbonates, which can be used in linear non‐isocyanate polyurethanes synthesis, as shown by their facile ring‐opening with N‐hexylamine. Thus, the selective catalytic route to monofunctional limonene carbonates gives straightforward access to monomers for novel bio‐based polymers.
Highlights
Terpenes are a large and diverse class of hydrocarbons naturally occurring in the oils of plants[1] and fruits that have been used for flavour and fragrance manufacturing since antiquity.[2]
Polyoxometalates such as those originally reported by Ishii and Venturello, [phase transfer catalyst (PTC)]3[PW4O24] (PTC = methyl tricapryl ammonium) (A) are excellent catalytic systems for the epoxidation of a vari
Integrated epoxidation and carbonation of 1,2-limonene cyclic carbonate With an efficient catalyst system in hand, we explored the possibility of using A in a direct epoxidation–carboxylation sequence starting from terpenes
Summary
A wide range of catalysts for the synthesis of cyclic carbonates from epoxides has been described in literature, including metal complexes, metal organic frameworks, quaternary ammonium salts, imidazolium halide salts and supported ionic liquid phase catalysts.[25,26,27,28,29,30,31,32] After formation of cyclic carbonates such as 1,2,8,9-limonene carbonate, the ability to further modify the monomer or carry out post-polymerization functionalisation is an important factor With their multiple sites of unsaturation, terpenes can be ideally exploited in this way; examples such as 1,2,8,9-limonene carbonate can only be tuned through the linking co-monomer. Both chiral cyclic carbonates are shown to undergo radical coupling with 1,3-propanedithiol and react with N-hexylamine to result in novel hydroxyurethanes as a demonstration of their utility in the synthesis of bio-based NIPUs
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