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Supported organocatalysts and their applications in the upgrade of bioderived polyols: desymmetrisation of glycerol to obtain building blocks for fine and pharmaceutical chemicals prod

Periodic Reporting for period 1 - SOCUPols (Supported organocatalysts and their applications in the upgrade of bioderived polyols: desymmetrisation of glycerol to obtain building blocks for fine and pharmaceutical chemicals prod)

Reporting period: 2016-02-01 to 2018-01-31

Natural polyols are very interesting feedstock. Their chemical upgrading aims at obtaining lower oxygenated compounds to be used as building blocks for traditional, fossil based chemical productions. On the other hand, their molecular complexity and high oxygen content can be seen as part of the work already done by Mother Nature.
SOCUPols proposes a different approach consisting in the exploitation of the molecular complexity and high oxygen content of polyols to obtain valuable products and synthons for fine and pharmaceutical chemistry. The direct use of complex, highly oxygenated molecules is challenging but could allow to save time, energy and money.
SOCUPols project aims at preparing novel organo-catalysts based on supported IL-like fragments for the upgrading of biomass derived polyols such as diols and glycerol. These heterogeneous catalytic systems will be fully recyclable and suitable for continuous flow operation.
Due to the applied nature of this project the results could be of interest for the industrial sector.
Further, the use of supported catalysts for flow chemistry in combination with the use of green solvents and reactants are of very high interest in pharmaceutical chemistry but also in the energy and fuels sector.
The overall objectives can be listed as follows:
(a) the development of an easy technology for catalysts preparation and manipulation;
(b) their use for the transesterification of diols and glycerol;
(d) the use of carbon dioxide as reagent, attaining polyols upgrading and CO2 fixation;
(e) the development of new chemical processes for glycerol desymmetrisation using supported onium catalysts modified for asymmetric transformations;
(f) the implementation of the most successful protocols in continuous flow.
1. Design and synthesis of new supported organic onium catalysts.
1.1 Synthesis of new catalysts from available cationic structures.
Commercial anion exchange resins were tested to verify their activity as catalyst for well-known chemical transformations, in order to compare their properties and activities.
Preliminary tests confirmed that the available materials were completely inactive as catalysts. However they could be activated by simple anion exchange procedure.
1.2 Synthesis of new supported -onium catalysts.
We then focused on the preparation of new materials, in order to investigate the influence of different cationic functional groups and supporting matrices.
The obtained catalysts were obtained in very high yields using efficient and straightforward procedures. The processes were optimized in order to reduce as much as possible the impact on the environment reducing the amount and toxicity of reagents and solvents and proposing the recycle of the materials where possible.
In addition to these achiral organic salts, new synthetic pathways to asymmetric catalysts suitable for immobilization were designed and explored.
After designing the synthetic strategy during periodic meetings with the scientist in charge and other members of the research groups, the researcher tested step by step the preparation of the designed structures.
First we use available asymmetric catalysts and supported them on polystyrene in order to obtain asymmetric cations and then obtain a cooperative N/E catalyst via anion exchange procedure. These catalysts were tested in common organic reactions. Moderate activity was observed. Unfortunately unsatisfactory enantioselection was achieved.
New structure were also designed and preliminarly tested.
2. Application of supported onium salts in catalysis.
2.1. Transformation of diols
The prepared catalysts have been tested for transesterification reactions. Transesterification of simple diols was studied under different condition and optimised.
The catalysts based on polystyrene supported organic salts prepared by us proved extremely active. The reaction was faster than any other reported procedure.
In addition the catalysts were very easy to be recovered and recycled. Recyclability tests demonstrated that our catalysts could be reused up to 7 times with no loss of activity under optimised conditions.
Potential and limits of the catalysts developed by us were investigated and several diols were used as starting material evaluating the applicability of the process.
Besides organic carbonates, other green reactants like urea have been be taken into account. Unfortunately the lack of reactivity of urea did not allow any reaction.
Preliminary tests on the activation of CO2 show interesting potential of the cooperative N/E catalysis in this field. Insertion of CO2 in epoxides proceeded smoothly in the presence polymer supported organic salts.
2.2 Transformation of glycerol.
Glycerol was used as starting material and reacted with organic carbonates. The particular nature of glycerol prompted us selectivity issues.
2.2 Desymmetrisation of polyols.
Asymmetric catalysts based on binaphtol prepared by us were tested in the asymmetric desymmetrisation of diols using aldehydes. The selectivity proved promising, but unfortunately the activity was relatively low.
The immobilisation of an organic salt acting as cooperative N/E catalysts on a support is a remarkable step forward in the use of this kind of catalysts.
The fact that the catalyst is confined in the solid phase will allow an easy separation and recycling.
In addition, our studies on the use of the new catalysts allowed also a deeper comprehension of the mechanism of the so-called cooperative nucleophilic/electrophilic catalysis.
The latter result in particular represents not only a very interesting basis science achievement, but also a strong stimulus to the implementation of these systems for industrial applications.
Finding new applications as catalysts for a cheap and available material like polystyrene will represent a high impact result as it will open the possibility of a low investment to obtain high added value products.
The focus of SOCUPols on transformations that involve bio-derived material, further increase the impact of the obtained results. The use of catalysts that are cheap, robust, easily recoverable and suitable for continuous flow processing, will surely be of interest for the scientific community and beyond. The use of flow techniques to carry out asymmetric reactions is still in its infancy, but has great industrial potential. This is why the development of more active, robust and selective catalysts for a sustainable chemistry, is currently a crucial topic.
Among the bioderived chemicals the particular interest on the upgrading of glycerol increase the interest on the chemical processes investigated during the process, that allow to obtain useful chemical products from such a largely largely available starting material.
Remarkably, catalysts prepared by us showed the ability of activating CO2 efficiently. These results are very promising and will be surely exploited in future studies that will trigger collaboration between researchers in the host institution and other institutions.
In conclusion, the use supported catalysts for flow chemistry in combination with the use of green solvents and reactants are of very high interest in pharmaceutical chemistry, but also in the energy and fuels sector.
A collaboration between the group of Prof. Pericas at ICIQ and profs. Selva and Perosa at the Università Ca’ Foscari Venezia is being started to continue the work started during the project.