Chemistry 2030: A Roadmap for a New Decade

Open- and Closed-Loop Recycling: Highly Active Zinc Bisguanidine Polymerization Catalyst for the Depolymerization of Polyesters

In this study, the aliphatic N,N-bisguanidine zinc complex [Zn(DMEG2ch)2](OTf)2 ⋅ THF is introduced as a promising candidate for the chemical recycling of (bio) polyesters. This catalyst is highly active in the ring-opening polymerization (ROP) of lactide (LA) and ϵ-caprolactone (CL). The combination of polymerization and depolymerization activity creates new pathways towards a sustainable circular economy. The catalytic activity of [Zn(DMEG2ch)2](OTf)2 ⋅ THF for the chemical recycling of polylactide (PLA) via alcoholysis was investigated by detailed kinetic and thermodynamic studies. It is shown that various high value-added alkyl lactates can be obtained efficiently under mild reaction conditions. Catalyst recycling was successfully tested using ethanol for the degradation of PLA. In addition, LA can be recovered directly from PLA, enabling either open- or closed-loop recycling. Selective PLA degradation from mixtures with polyethylene terephthalate (PET) and polymer blends are presented. For the first time, a cascade recycling reaction of a PLA/polycaprolactone (PCL) blend is tested with a zinc-based bisguanidine catalyst, whereby PLA is degraded selectively at first and subsequent modification of the reaction conditions leads to efficient degradation of the remaining PCL. The highly active, universally applicable benign zinc catalyst allows the implementation of a circular plastics economy and thus the reduction of plastic pollution in the environment.

Towards a Sustainable Future: Challenges and Opportunities for Early-Career Chemists

The concepts of sustainability and sustainable chemistry have attracted increasing attention in recent years, being of great importance to the younger generation. In this Viewpoint Article, we share how early-career chemists can contribute to the sustainable transformation of their discipline. We identify ways in which they can engage to catalyse action for change. This article does not attempt to answer questions about the most promising or pressing areas driving research and chemical innovation in the context of sustainability. Instead, we want to inspire and engage early-career chemists in pursuing sustainable actions by showcasing opportunities in education, outreach and policymaking, research culture and publishing, while highlighting existing challenges and the complexity of the topic. We want to empower early-career chemists by providing resources and ideas for engagement for a sustainable future globally. While the article focuses on students and early-career chemists, it provides insights to further stimulate the engagement of scientists from diverse backgrounds.

Ancestral terpene cyclases: From fundamental science to applications in biosynthesis

Terpenes constitute one of the largest family of natural products with potent applications as renewable platform chemicals and medicines. The low activity, selectivity and stability displayed by terpene biosynthetic machineries can constitute an obstacle towards achieving expedient biosynthesis of terpenoids in processes that adhere to the 12 principles of green chemistry. Accordingly, engineering of terpene synthase enzymes is a prerequisite for industrial biotechnology applications, but obstructed by their complex catalysis that depend on reactive carbocationic intermediates that are prone to undergo bifurcation mechanisms. Rational redesign of terpene synthases can be tedious and requires high-resolution structural information, which is not always available. Furthermore, it has proven difficult to link sequence space of terpene synthase enzymes to specific product profiles. Herein, the author shows how ancestral sequence reconstruction (ASR) can favorably be used as a protein engineering tool in the redesign of terpene synthases without the need of a structure, and without excessive screening. A detailed workflow of ASR is presented along with associated limitations, with a focus on applying this methodology on terpene synthases. From selected examples of both class I and II enzymes, the author advocates that ancestral terpene cyclases constitute valuable assets to shed light on terpene-synthase catalysis and in enabling accelerated biosynthesis.

The refinery of the future

Fossil fuels-coal, oil and gas-supply most of the world's energy and also form the basis of many products essential for everyday life. Their use is the largest contributor to the carbon dioxide emissions that drive global climate change, prompting joint efforts to find renewable alternatives that might enable a carbon-neutral society by as early as 2050. There are clear paths for renewable electricity to replace fossil-fuel-based energy, but the transport fuels and chemicals produced in oil refineries will still be needed. We can attempt to close the carbon cycle associated with their use by electrifying refinery processes and by changing the raw materials that go into a refinery from fossils fuels to carbon dioxide for making hydrocarbon fuels and to agricultural and municipal waste for making chemicals and polymers. We argue that, with sufficient long-term commitment and support, the science and technology for such a completely fossil-free refinery, delivering the products required after 2050 (less fuels, more chemicals), could be developed. This future refinery will require substantially larger areas and greater mineral resources than is the case at present and critically depends on the capacity to generate large amounts of renewable energy for hydrogen production and carbon dioxide capture.

Connecting chemical worlds for a sustainable future

Chemistry plays a central role in science and is the basis of one of the major, more impactful, and diverse industries. However, to address the most pressing global challenges, we must learn to create connections in an effective and meaningful way, with other disciplines, industries, and society at large. Here, we present the IUPAC Top Ten Emerging Technologies in Chemistry as an example of an initiative that highlights the value of the most promising advances in chemistry and contributes to creating connections to accelerate sustainable solutions for our society and our planet.

Ultrasound and sonochemistry enhance education outcomes: From fundamentals and applied research to entrepreneurial potential

With this manuscript we aim to initiate a discussion specific to educational actions around ultrasonics sonochemistry. The importance of these actions does not just derive from a mere pedagogical significance, but they can be an exceptional tool for illustrating various concepts in other disciplines, such as process intensification and microfluidics. Sonochemistry is currently a far-reaching discipline extending across different scales of applicability, from the fundamental physics of tiny bubbles and molecules, up to process plants. This review is part of a special issue in Ultrasonics Sonochemistry, where several scholars have shared their experiences and highlighted opportunities regarding ultrasound as an education tool. The main outcome of our work is that teaching and mentorship in sonochemistry are highly needed, with a balanced technical and scientific knowledge to foster skills and implement safe protocols. Applied research typically features the use of ultrasound as ancillary, to merely enhance a given process and often leading to poorly conceived experiments and misunderstanding of the actual effects. Thus, our scientific community must build a consistent culture and monitor reproducible practices to rigorously generate new knowledge on sonochemistry. These practices can be implemented in teaching sonochemistry in classrooms and research laboratories. We highlight ways to collectively provide a potentially better training for scientists, invigorating academic and industry-oriented careers. A salient benefit for education efforts is that sonochemistry-based projects can serve multidisciplinary training, potentially gathering students from different disciplines, such as physics, chemistry and bioengineering. Herein, we discuss challenges, opportunities, and future avenues to assist in designing courses and research programs based on sonochemistry. Additionally, we suggest simple experiments suitable for teaching basic physicochemical principles at the undergraduatelevel. We also provide arguments and recommendations oriented towards graduate and postdoctoral students, in academia or industry to be more entrepreneurial. We have identified that sonochemistry is consistently seen as a 'green' or sustainable tool, which particular appeal to process intensification approaches, including microfluidics and materials science. We conclude that a globally aligned pedagogical initiative and constantly updated educational tools will help to sustain a virtuous cycle in STEM and industrial applications of sonochemistry.

Reshuffle Bonds by Ball Milling: A Mechanochemical Protocol for Charge-Accelerated Aza-Claisen Rearrangements

This study presents the development of a mechanochemical protocol for a charge-accelerated aza-Claisen rearrangement. The protocol waives the use of commonly applied transition metals, ligands, or pyrophoric Lewis acids, e.g., AlMe₃. Based on (heterocyclic) tertiary allylamines and acyl chlorides, the desired tertiary amides were prepared in yields ranging from 17% to 84%. Moreover, the same protocol was applied for a Belluš-Claisen-type rearrangement resulting in the synthesis of a 9-membered lactam without further optimization.

Innovative green oxidation of amines to imines under atmospheric oxygen

In recent years, the development of environmentally benign molecular construction methods has been of great importance, and especially, resource recycling, high atomic efficiency, and low environmental impact are in high demand. From this point of view, attention has also been focused on the development of one-pot synthesis of pharmaceuticals and functional molecules. Imines are excellent synthetic intermediates of these useful molecules, and the environmentally friendly oxidative synthesis of imines from amines has been energetically developed using oxygen (or air), which is abundantly available on the Earth, as an oxidant. This review focuses on the latest innovative and green oxidation systems of amines to imines under atmospheric oxygen, and their application to one-pot/eco-friendly and sustainable synthesis of pharmaceuticals and functional molecules. In particular, catalytic systems that activate molecular oxygen are categorized and described in detail as transition metal catalytic systems, photoirradiated catalytic systems, and organocatalytic systems.

Metal-Free Synthesis of 2-Substituted Quinazolines via Green Oxidation of o-Aminobenzylamines: Practical Construction of N-Containing Heterocycles Based on a Salicylic Acid-Catalyzed Oxidation System

Conventional quinazoline synthesis methods involve a highly multistep reaction, and often require excess amounts of substrate to control the product selectivity, leading to significant resource wastage. Hence, in this study, from the viewpoint of green chemistry, we developed a novel metal-free synthetic method for 2-substituted quinazoline derivatives by the 4,6-dihydroxysalicylic acid-catalyzed oxidative condensation of o-aminobenzylamines and benzylamines using atmospheric oxygen. In this system, the use of a catalytic amount of BF₃‧Et₂O (10 mol%) as a Lewis acid successfully led to the efficient oxidative condensation and intramolecular cyclization of these amines, followed by aromatization to afford the corresponding 2-arylquinazolines in up to 81% yield with excellent atom economy and environmental factor. Furthermore, to expand this green oxidation method to gram-scale synthesis, we investigated the development of an oxidation process using salicylic acid itself as an organocatalyst, and established a method for the practical green synthesis of a series of nitrogen-containing heterocycles. We expect that the findings will contribute to the development of practical synthesis methods for pharmaceutical manufacturing and industrial applications, along with further advancements in green chemistry.

Polyolefin plastic waste hydroconversion to fuels, lubricants, and waxes: a comparative study

A direct comparison of the recent advancements in the hydrogenolysis and hydrocracking of polyolefins is lacking. This perspective aims to address this gap while providing insights from model alkane studies to guide future research.

Excellent Catalytic Performances of a Au/C-CuO Binary System in the Selective Oxidation of Benzylamines to Imines under Atmospheric Oxygen

A green method of the oxidation of benzylamines to imines was developed using a novel binary system of Au/C-CuO. This system was evaluated under atmospheric oxygen, and the corresponding imines were obtained in up to 100% yields by loading 0.006 mol % of Au/C and 1.25 mol % of CuO under mild conditions. This system was also successfully applied to the syntheses of N-containing functional molecules, as well as that of imines on the scale of several grams. Furthermore, the turnover number of the system (more than 8000 times on a gold basis) as well as its ability to be reused more than 10 times for benzylamine oxidation demonstrates the excellent durability and recyclability of the developed system.

Pinene-Based Oxidative Synthetic Toolbox for Scalable Polyester Synthesis

Generation of renewable polymers is a long-standing goal toward reaching a more sustainable society, but building blocks in biomass can be incompatible with desired polymerization type, hampering the full implementation potential of biomaterials. Herein, we show how conceptually simple oxidative transformations can be used to unlock the inherent reactivity of terpene synthons in generating polyesters by two different mechanisms starting from the same α-pinene substrate. In the first pathway, α-pinene was oxidized into the bicyclic verbanone-based lactone and subsequently polymerized into star-shaped polymers via ring-opening polymerization, resulting in a biobased semicrystalline polyester with tunable glass transition and melting temperatures. In a second pathway, polyesters were synthesized via polycondensation, utilizing the diol 1-(1'-hydroxyethyl)-3-(2'-hydroxy-ethyl)-2,2-dimethylcyclobutane (HHDC) synthesized by oxidative cleavage of the double bond of α-pinene, together with unsaturated biobased diesters such as dimethyl maleate (DMM) and dimethyl itaconate (DMI). The resulting families of terpene-based polyesters were thereafter successfully cross-linked by either transetherification, utilizing the terminal hydroxyl groups of the synthesized verbanone-based materials, or by UV irradiation, utilizing the unsaturation provided by the DMM or DMI moieties within the HHDC-based copolymers. This work highlights the potential to apply an oxidative toolbox to valorize inert terpene metabolites enabling generation of biosourced polyesters and coatings thereof by complementary mechanisms.

Standing on the Shoulders of Giants - Your Mentors and Role Models Will Shape Your Career

Choosing the right mentors and role models has a profound impact in both our lives and professional careers; however, most often, not enough time or thought is given to this important decision. Because of that, we may miss some great opportunities and limit the potential benefits. In this invited contribution, I share my personal experience on nurturing the relationship with mentors and on choosing role models with my same values and a strong sense of service.

An overview of young chemists’ expectations towards the sustainable development of the chemical sector. Opinions that matter

Young chemists play an important role in the transformation of the chemical sector in the next couple of years. They will have to do the heavy lifting and find the solutions needed for a sustainable tomorrow. Therefore, it is important to give them a voice in what their expectations are, how they believe they should be educated and prepared, and what opportunities they see for implementation levels in different areas to promote sustainable development. To shed light on these often under-represented opinions, young chemists across the globe were asked to express their views on the role and responsibilities of the chemical sector anonymously. The result is a snapshot of how young chemists perceive the future of chemistry and the immediate actions that need to be taken to get there. Throughout all answers, their hopes are expressed that the chemical sector will realize its great role and responsibility in leading and promoting sustainable development, thus limiting global warming, through cooperation with authorities, other sectors, and civil society. In this regard, young chemists do have numerous specific ideas about appropriate measures and are eager to take part in shaping a sustainable future.

Circular Aqueous Fmoc/t-Bu Solid-Phase Peptide Synthesis

Circular economy and aqueous synthesis are attractive concepts for sustainable chemistry. Here it is reported that the two can be combined in the universal method for peptide chemistry, fluorenylmethoxycarbonyl(Fmoc)/t-Bu solid-phase peptide synthesis (SPPS). It was demonstrated that Fmoc/t-Bu SPPS could be performed under aqueous conditions using standard Fmoc amino acids (AAs) employing TentaGel S as resin and 4 : 1 mixture of water with inexpensive green solvent PolarClean. This resin/solvent combination played a crucial dual role by virtue of improving resin swelling and solubility of starting materials. In a model coupling, TCFH and 2,4,6-collidine afforded a full conversion at only 1.3 equiv. AA, and these conditions were used in SPPS of Leu enkephaline amide affording the model peptide in 85 % yield and 86 % purity. A method to recycle the waste by filtration through a mixed ion exchange resin was developed, allowing reusing the waste without affecting quality of the peptide. The method herein obviates the use of unconventional or processed AAs in aqueous SPPS while using lower amounts of starting materials. By recycling/reusing SPPS waste the hazardous dipolar aprotic solvents used in SPPS were not only replaced with an aqueous medium, solvent use was also significantly reduced. This opens up a new direction in aqueous peptide chemistry in which efficient use of inexpensive starting materials and waste minimization is coupled with the universal Fmoc/t-Bu SPPS.

Chemophobia cured by chemists: chemists as children of the Sun

The success of chemists in the fight against COVID-19 provides us with a unique opportunity for strengthening the position of chemistry in society and suppressing chemophobia which has badly affected the image and development of chemistry over several decades. By highlighting the unique merits of chemistry in controlling infections and healing diseases, we propose developing a communication strategy "Chemists as children of the Sun". The time is ripe for chemists to take control of the story of chemistry. We believe that chemists must help the public to see chemistry in a whole new light. Only a positive perception of chemistry and the chemical profession will secure a sufficient supply of new talents, ideas, and also financial resources for the development of this unique and irreplaceable science for humanity.

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