Minimizing Chemical Waste Using Recyclable Catalysts and Reusable Green Solvents

Abstract

Global chemical demand and costs significantly increase every year, particularly solvents. To address this, chemical recycling has become a popular approach among researchers including the Bergbreiter group. We have explored the use of recyclable safer chemicals and recyclable greener solvents to improve chemical processes with the end goal of minimizing and preventing chemical waste. Our previous work showed that poly(α-olefin)s (PAOs) can be used as a greener substitute for hexane and heptane due to their low toxicity, low vapor pressure, and low flammability. The first part of this thesis focuses on further studies where PAOs can be used as an alternative safer and recyclable solvent for organometallic chemistry. PAOs can be used to store and extend the stability of reactive organometallics such as triaryllithium reagents and polymer-supported diphenyllithium, these colored species are stable in PAOs for months. The flammability of organomagnesium in PAOs is much less intense than in heptane because PAO does not itself inflame. A PAO solution of dialkylmagnesium reagents behaves in reactions such as carbonation, nucleophilic addition, and reduction the same as they do in heptane. Furthermore, PAOs alone or coupled with a polyisobutylene (PIB) bound-LDA analog can be used as the recyclable solvent or/and reagent in hydroboration/oxidation and as equal alternatives to LDA in enolate chemistry. We also recently investigated the use of PIB as a selective phase anchor, allowing catalysts to dissolve in nonpolar media and as a tool to promote catalyst recyclability. This selective solubility has allowed PIB-bound catalysts to be easily isolated from polar products and readily recycled by simple separations. The second part of this work explores integrated systems in a variety of organocatalytic reactions where both catalysts and PAOs solvents can be recycled. Three examples of PIB-bound DMAP, PIB-bound chiral nucleophilic catalyst (BTM), and PIB-bound phosphine oxide are successfully prepared. The reactivity and selectivity of these catalysts are investigated in PAOs and compared with traditional solvents and small molecular weight catalysts. This PIB-bound catalyst/solvent system is efficiently reusable multiple times with good to excellent isolated product yield. The advantages and drawbacks of each example are also addressed.