Most reports claim catalyst recyclability; however, parameters such as selectivity drop, changes in reaction kinetics upon catalyst reuse, metal leaching, long-term productivity and the need for catalyst regeneration are not always evaluated quantitatively. Great potential for selectivity improvement may be provided by catalysis under continuous flow conditions, because of the possibility for a careful control of reaction conditions, namely contact time with the catalyst and homogeneous heating.
This would open up the possibility for process intensification via direct conversion of cellulose to target chemicals, while avoiding intermediate conventional mineral acid depolymerisation protocols. The efficiency of such catalysts is ruled by the fine tuning of diverse factors and their interplay: nature of metal, type and strength of acidic sites, balance of acid and metal loading, and site accessibility.
Actually, examples have already been reported for the direct upgrade of cellulose without isolation of intermediate streams, for instance in the case of isosorbide synthesis Section 4.
However, these systems underperform with respect to carbon balance, mostly due to the significant formation of cellulose acidic depolymerisation by-products humins, levulinates, oligomers and dehydration isomers. This is partially due to the mixtures of supported metals and soluble acid catalysts often used to this aim. Indeed, the conventional sulfonated resin catalysts used in the acid-catalysed depolymerisation steps suffer from limited thermal resistance.
This may be circumvented, for example, using inorganic niobia or polymeric perfluorosulfonic acids. This may be the case of unconventional, inorganic monoliths featuring interconnected dual porosities meso, macro. By contrast, lignin is a very complex polymer which results in a variety of chemicals by deconstruction, depending on the biomass source and the method, and hardly reducible to single platform molecules. As a consequence, despite the huge amount of lignin available, its potential for chemical synthesis is still underutilised.
Despite the recent remarkable advancements, e. Indeed, recent advancements, although significant, restrict to the adoption of zeolite or enzyme catalysts for the synthesis of diphenolic scaffolds from monolignol units.
Challenge one: development of improved technologies for the selective conversion of lignin to chemicals, economically and sustainably. These new solutions shall optimise the utilisation of heterogeneously composed raw materials, while enabling the large-scale production of bulk chemicals for the process industry. Challenge two: development of catalytic deconstruction technologies affording novel building blocks, other than monolignol-derived monomers, directly from lignin, i.
However, with the few notable exceptions outlined above, they are usually synthesized via conventional, sometimes uncatalysed, organic reactions. Typical is the case of C1-bridged bis-phenols obtained by formaldehyde coupling, using soluble mineral acids H 2 SO 4 and HCl and, often, noxious or unstable solvents see Tables 4—6.
Thus, inventive solutions are needed, which avoid use of toxic reagents and media and which comply with the principles of green and sustainable chemistry. Novel rigid scaffolds have to be designed, for instance mimicking natural molecules and built upon C0-linked phenols or fused rings. As emerged from the literature, several other BPA replacements may be produced from the catalytic conversion of other biomass sources.
Some specific challenges may be envisaged. Challenge one: to increase the scenario of available platforms and production of BPA replacements, featuring structure alternatives to monosaccharide or phenol-based ones. High-throughput screening methods are expected to be particularly useful to this aim. Herein, possibilities are plenty, provided that the amount of raw material is suitable for industrial use. From that, a second challenge is closely related: to improve the uptake of unconventional, non-edible biomass sources, such as algae, biorefinery side-streams and waste food, agricultural.
The role of catalysis will be crucial in developing flexible and sustainable conversion routes in this direction. In conclusion, the results reported in the recent literature describing catalysts and approaches for the synthesis of monomers from biomass that are proposed as BPA replacements and that are collected in the present review provide a large choice of potential candidates for substitution.
While quite advanced catalytic systems are available for the upgrade of cellulose-derived feeds, the conversion of platforms originating from lignin still needs significant improvements, mostly due to the inherent complexity of lignin materials. In addition, further studies should be performed aiming at a careful evaluation of compliance with the viability and effectiveness criteria of the proposed BPA replacements, whose extension to chemical substitution, in general, would contribute to a safer and more sustainable future.
DOI: Abstract Bisphenol A is an oil-derived, large market volume chemical with a wide spectrum of applications in plastics, adhesives and thermal papers. Scheme 2 Representative structures of some BPA-based polymers.
Scheme 4 Structures of H, G and S monolignol subunits of lignin. Scheme 5 Simplified reaction pathways for the catalytic conversion chain of cellulose to isosorbide and furanic diols. Scheme 6 Structures and epimerization of isosorbide, isomannide and isoidide. Scheme 7 Pathways of acid-catalyzed dehydration of mannitol to isomannide. Table 1 Summary of recent catalytic systems for proposed BPA monomeric replacements from isohexides a.
Catalyst Biomass-derived substrate Product Reaction conditions Conv. Sorbitol dehydration. Isosorbide is a monomer for several bioplastics, including poly- ethylene- co -isosorbide terephthalate PEIT , poly isosorbide carbonate PIC and poly isosorbide oxalate. The isosorbide volume demand for PEIT production was around 3 ktons in , while the global isosorbide market is expected to reach million Euros by The latter steps are slowed down in the presence of water, thus requiring much higher reaction temperatures.
Scheme 9 One-pot synthesis of isosorbide via sorbitol ketalization. Scheme 10 Mechanism of sorbitol dehydration in dimethyl carbonate under basic conditions. Adapted with permission from ref. Tundo, Beilstein J. Glucose conversion. The effect of the reaction temperature on the reaction products, at fixed time and H 2 pressure, is reported in Fig.
Copyright , Royal Society of Chemistry. Cellulose conversion. Methods for the direct, catalytic conversion of aqueous lignocellulosic biomass to isosorbide Scheme 5 are receiving increasing attention, though only a few articles describe real improvements in terms of yields and catalyst reusability.
Selectivity in such processes is an usual drawback, as several poisoning by-products may form and the carbon balance of the final products is often moderate. This was ascribed to the oxidative treatment of the catalyst, which increased the amount of carboxylic acid groups on the carbon support and reduced the adsorption of oligomer by-products e.
Scheme 11 Simplified network of hydrogenation products originating from HMF. Table 2 Summary of recent catalytic systems for proposed BPA monomeric replacements from furanic diols a. Gray and blue balls represent carbon and nitrogen atoms, respectively. The palladium nanoparticles are golden in color. Reprinted with permission from ref. BPA was created from a condensation reaction of phenol and acetone with hydrogen chloride, an acid catalyst, and a promoter such as methyl mercaptan.
Once formed by this reaction, BPA is washed with water, neutralized with calcium hydroxide and distilled under vacuum. BPA can also be purified further by distillation and extractive crystallisation.
Skip to main content Skip to navigation. No comments. In this issue: bisphenol A BPA. Why is this chemical important? How is bisphenol A made? And polycarbonate? Source: Jupiterimages. No comments yet. You're not signed in. Only registered users can comment on this article. While morphological differences between treated and control animals were not noted at this age, biochemical differences were already apparent at 10 days old.
Within the epithelium of the mammary gland, DNA synthesis was suppressed. Both treatment groups had lower rates of DNA synthesis compared to controls. In the mammary gland stroma, however, DNA synthesis rates decreased compared to controls at age 10 days but increased compared to controls at 6 months age.
Morphological differences accumulated between 1 month and 6 months age. Typically, untreated mice experience significant development of the mammary gland during this period, with growth of a "ductal tree that comprises terminal ducts, terminal endbuds Quesada et al.
Both research groups investigated the nongenomic effects of Bisphenol A. This suggests that while estradiol has a weak activating effect of traditional estradiol receptors, it is also operating through non-tradional estradiol receptors. The cAMP pathway is a G-protein coupled receptor mechanism.
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