Talk Session 3

Let’s flow towards a sustainable morrow…

Have we ever imagined life without chemistry? Right from the toothbrush we pick up the first thing every morning to the switch of the bed-lamp we put off the last - chemistry surrounds us as much as air does!

However, as chemists ourselves, what could be more bothering than poor yield, reaction inefficiency and poor process scalability? The synthesis of controlled-morphology nanomaterials has continually remained a challenge for chemists till date. Though tremendously applicable in chemical catalysis, electrochemistry, drug delivery, and energy storage; the negative side of the list is unfortunately long as well - time-consuming synthesis, poor morphological control, poor scalability, low reaction efficiency, poor yield, large safety hazards, poor sustainability and low process economy. Though these issues do not seem too overwhelming on a laboratory scale, how about visualizing the big picture? What will happen if the environment remediation industry runs out of a crucial toxic gas-absorbing material tomorrow due to poor reaction yield and process scalability; or a drug company stops producing an anticancer medicine owing to poor reaction efficiency? It is no surprise that this very fear has started propelling chemical industries to focus on improving process sustainability and green efficiency.

Thankfully, with the era of continuous flow synthesis slowly but steadily overtaking conventional batch chemistry by virtue of its phenomenal advantages; this quest is speedily inching towards a permanent solution in the chemical manufacturing industry.

My research focusses on the concept of process intensification through continuous flow. In simplified terms; a way to make reactions easier, safer and more efficient; building sustainability in every step. As demonstration of the scalability and high-throughput nature of this technology, we have synthesized two materials; viz. KCC-1 (fibrous silica nanospheres) and Polyaniline (conjugated polymeric nanofiber) through continuous flow. The results obtained were not just superior in quality but quicker (involving less than half the amount of time needed through traditional batch techniques), scalable and high yielding as well. For instance, KCC-1 could be produced within 30 minutes through flow when the traditional batch techniques needed 1-12 hours; and PANI within 5 minutes and a throughput of 17-30 g/h through continuous flow as compared to 24 hours with a maximum throughput of only 3 g/h. These studies prove how continuous flow synthesis can provide a controlled and scalable solution for synthesizing crucial catalytic materials. Further, PolyHIPEs (polymeric emulsion foams) have been synthesized through conventional techniques for employment in scalable and high throughput dynamically stirred continuous flow reactors; which will be a boon for various industrially important processes like Heck and Suzuki coupling; which act as the synthetic base for a plethora of pharmaceutical and commercially important molecules.

Thanks to the miniaturized continuous flow reactor designs that are being actively developed since the last decade, there has been a bloom witnessed in the development of inherently sustainable, greener, safer, and efficient processes. It is time we flow towards a sustainable morrow!

A Direct Route to Six and Seven Membered Lactones via g-C(sp3)-H Activation: A Simple Protocol to Build Molecular Complexity

Lactones comprise a class of valuable compounds having biological as well as industrial importance. In particular, six and seven membered lactones are flavor and aroma constituent in many natural products Development of methodology to synthesize such molecules directly from readily available starting materials such as aliphatic carboxylic acid is highly desirable. We have developed the one step methodology to synthesize d-lactones and e-lactones via selective g-C(sp3)-H activation without using any directing group. The g-CH bond containing aliphatic carboxylic acids provides six or seven membered lactones depending on the olefin partner in presence of a palladium catalyst. Mechanistic investigation suggests that C-H activation is the rate-determining step. Further transformations of the lactones have been carried out to showcase the applicability of the present strategy.

Quest for Efficient and Sustainable Synthesis Ends with Photocatalysis

In a quest to develop facile metal-free sulfonylations via insertion of sulfur dioxide. We developed a standard protocol to efficiently generate sulfonyl radicals from aryldiazonium salts and DABSO. Wherein DABSO plays a dual role, acting as a benign and easy to handle source of sulfur dioxide as well as a redox mediator under mild conditions bypassing the use of stoichiometric radical initiators. Traditionally, the formation of these radicals require stoichiometric excess of radical initiators at high temperature. The effortlessly generated sulfonyl radicals were then employed to carry out a variety of transformations like a) coupling with photocatalytically generated sulfenyl radical to furnish thiosulfonates, b) spirocyclization with N-arylpropynamides and N-arylacrylamides, c) cascade cyclization with alkyne tethered cyclohexadienones and d) C-2 sulfonylation of pyrroles. All these reactions proceed under metal free, mild conditions, display broad functional group tolerance and furnish excellent yields of the corresponding products.