SUSTAINABLE CHEMISTRY & FLOW PHOTOCHEMISTRY

 

A definition

"Sustainable chemistry is a scientific concept that seeks to improve the efficiency with which natural resources are used to meet human needs for chemical products and services. Sustainable chemistry encompasses the design, manufacture and use of efficient, effective, safe and more environmentally benign chemical products and processes."

Organisation for economic co-operation and development (accessed 2020-03-24)

 

Principle 6

Energy requirements of chemical processes should be recognized for their environmental and economic impacts and should be minimized. If possible, synthetic methods should be conducted at ambient temperature and pressure.

The green chemisTREE: 20 years after taking root with the 12 principles.
Green Chem., 2018, 20, 1929-1961

 

Light on sustainability

"Nature is the main inspiration for scientists when it comes to sustainability. In biology, plants use photosynthesis to convert raw materials (CO2 and water) into chemical energy (carbohydrates), exploiting the energy of solar photons. Photosynthesis is the quintessence of sustainable chemical reactivity, and the pinnacle that Green Chemistry aims to reach. [...] Along with its synthetic advantages, photoredox catalysis has clear benefits for sustainability, fulfilling several principles of Green Chemistry. Light radiation is its primary energy source. Light is free, non-hazardous, and environmentally friendly (energy efficiency). Photons provide enough energy to achieve the desired reactivity, without the high temperatures or harsh conditions often required by thermal activation. The light-absorbing species (photocatalysts) can be used in low catalytic amounts (use of catalytic reagents). By reaching an electronically excited state, they trigger single-electron transfer (SET) events to or from inactive/stable substrates. This generates highly reactive species in a mild and controlled manner. This has two positive impacts on sustainability. First, one can use less reactive low-energy reagents, allowing less hazardous and safer synthetic routes and easier disposal of less toxic or polluting by-products. Second, photoredox catalysis can activate generally poor reactive moieties within molecules (e.g. C–H bonds), while showing heightened functional group tolerance. This makes photoredox catalysis invaluable for designing shorter synthetic routes with enhanced atom economy, using renewable feedstock materials."

Chemistry glows green with photoredox catalysis.
G. Crisenza, P. Melchiorre, Nature Commun., 2020, 11, 803-806

 

Going to flow

"Synthetic organic photochemistry has been intensively carried out in the 20th century and paved the way to complex organic molecules, which were not yet accessible via thermal chemistry. Several photochemical synthesis routes have found their way into industrial applications for the production of everyday commodities, but photochemistry was still underutilised as a synthesis method in organic chemistry until recently. With the advent of novel photocatalytic and photophysical concepts for the use of high power visible light the research field of synthetic organic photochemistry has evolved to a vivid and highly recognized technique in the last years. Fortunately, continuous flow technology has become a more and more accepted tool as well and proved to be an excellent key player for the advancement of photochemistry in academic and industrial research."

Reactor technology concepts for flow photochemistry.
T. H. Rehm, ChemPhotoChem, 2020, 4, 235-254