Use of Novel Non-Toxic Bismuth Catalyst for the Preparation of Flexible Polyurethane Foam

Foam products are one of the largest markets for polyurethane (PU) and are heavily used in many sectors. However, current PU formulations use highly toxic and environmentally unfriendly production processes. Meanwhile, the increasing environmental concerns and regulations are intensifying the research into green and non-toxic products. In this study, we synthesized flexible polyurethane foam (PUF) using different weight percentages (0.025%, 0.05% and 0.1%) of a non-toxic bismuth catalyst. The bismuth-catalyzed foams presented a well evolved cellular structure with an open cell morphology. The properties of the bismuth-catalyzed flexible PUF, such as the mechanical, morphological, kinetic and thermal behaviors, were optimized and compared with a conventional tin-catalyzed PUF. The bismuth-catalyst revealed a higher isocyanate conversion efficiency than the stannous octoate catalyst. When comparing samples with similar densities, the bismuth-catalyzed foams present better mechanical behavior than the tin-catalyzed sample with similar thermal stability. The high solubility of bismuth triflate in water, together with its high Lewis acidity, have been shown to benefit the production of PU foams.

Sustainable catalytic rearrangement of terpene-derived epoxides: towards bio-based biscarbonyl monomers

Seeking a sustainable and selective approach for terpene modification, a catalyst deconvolution approach was applied to the Meinwald rearrangement of (+)-limonene oxide as a model substrate to yield dihydrocarvone. In order to identify the most suitable catalyst and reaction conditions, different Lewis acids were evaluated. Bismuth triflate proved to be the most active catalyst under mild reaction conditions, with a low catalyst loading (1 mol%) and a relatively short reaction time (3 h). The optimized reaction conditions were subsequently transferred to other terpene-based epoxides, yielding different bio-based biscarbonyl structures, which constitute interesting and valuable substances, e.g. for polymer synthesis or as fragrances. Monoepoxides derived from ( R )-(−)-carvone and (+)-dihydrocarvone rearranged to the desired products with high selectivities and yields. γ-Terpinene dioxide could be transformed in a double rearrangement to the respective biscarbonyl in moderate yields. A better result was achieved for limonene dioxide after further adjustment of the protocol to reach acceptable yields with a low catalyst loading of 0.1 mol% using 2-methyl tetrahydrofuran as a sustainable solvent. Compared to many procedures described in the literature, this procedure represents a step towards an increased sustainability in terpene modification by considering several principles of Green Chemistry, such as renewable resources, catalysis and mild reaction conditions for elementary chemical transformations. This article is part of a discussion meeting issue ‘Science to enable the circular economy’.

Convenient Synthesis of 2-(1-Adamantyl)furans

A simple method of obtaining 2-(1-adamantyl)furans using a smaller amount of catalyst, providing a higher yield of the target products, as well as the possibility of varying the substituents in the furan ring was developed. The result wasachieved by the adamantylation of furans with 1-adamantanol in a nitromethane medium in the presence of a Lewis acid, for which aluminum or bismuth triflate was used in an amount of 10 mol%.

Liquid-Crystalline Properties of Thioesters

An extension of a new method for forming thioesters with mesomorphic properties has been described, whereby the treatment of aryl tert-butylthioethers with long-chain acid chlorides in the presence of bismuth triflate afforded simple derivatives in good yields. This method in the case of 1-cyanoazulenes was, however, complicated by a competitive Friedel–Crafts-type acylation side reaction at the 3-position. Long-chain derivatives of cyanobiphenyl attached through a thioester linkage exhibited mesophases comparable with their ester analogues. The use of shorter chains to decorate the cyanobiphenyl moiety did not produce mesophasic behaviour, unlike their ester analogues. The cyanobiphenyl derivatives showing mesophasic behaviour were studied by small-angle X-ray diffraction, showing alignment for molecules possessing a smectic A phase. It was found that the layer spacing in the smectic A phase was ~1.5 times the length of the molecule, owing to antiparallel pairing arising from π-stacking between neighbouring units. Calculations suggest these derivatives should exhibit large dielectric anisotropy; however, instability made an exact value difficult to determine. For potential use in a liquid crystal display (LCD), the thioester holds some promise, although this may be limited by the relative stability of the thioester functionality.

Studies in Cyclization of Aromatic Epoxy-acyclicpolyprenes: Lewis Superacids and Titanocene Chloride

Two catalytic cascade cyclization methods (radical and cationic) to obtain aromatic polycyclic diterpenes hydroxylated at C3 starting from aromatic epoxypolyprenes were developed. The catalytic use of the Lewis superacid bismuth triflate produces a good yield of cyclized 2 from epoxypolyprene 3. This research may well direct future efforts to the synthesis of bioactive natural products.