Alkenyl Calixpyrrole towards ring closing metathesis and perfluoroalkyl calixpyrrole for efficient removal of fluoride ion and perfluoro pollutants from water

Abstract

Calixpyrroles are widely used as a neutral receptor for anion recognition, extraction and transportation. They are also frequently used as a ligand for metal complexation in organometallic chemistry. Depending on specific application and nature of guest molecules, calixpyrrole was modified either at meso or β-pyrrole position. However modification is always cumbersome and causes poor yield of the product. An easily available common mesosubstituted calixpyrrole would be of great importance to achieve various customized structures for specific interactions with different guest molecules. Substitution of alkyl chains with a terminal double bond at the meso position of calixpyrrole would be a common precursor for various modifications, where post functionalization of the terminal double bonds will aid in synthesizing different calixlpyrrole with tunable cavities for specific interactions with different guest molecules. Chapter 1: Introduction General accounts of calixpyrrole is narrated in first chapter. The synthetic strategy and the modification of calixpyrrole for particular applications are described. In addition, the overview of anion binding and metal complexation study are described. Chapter 2: Perfluoroalkyl calix[4]pyrrole for extraction of fluoride ion from aqueous media Symmetrical alkenylcalix[4]pyrrole functions as common precursor for the synthesis of various calixpyrrole with good yield. Incorporation of perfluoroalkyl groups [CF3(CF2)n-1, abbreviated as Rfn] at the terminal double bond creates hydrophobic environment inside the calix[4]pyrrole cavity owing to the highly hydrophobic nature of perfluoroalkyl chains. Hofmeister biased anions like fluoride remain highly solvated in aqueous solutions, having a very high hydration energy. Once the hydrated F - interacts via hydrogen bonds in the calix cavity, the hydration shell is broken by the hydrophobic environment of perfluoroalkyl chains (Rfn). Then, the interaction between calix-NH and F - depends only on charge density of the anion without the hydration shell and overcomes the Hofmeister biasness and separates the perfluoroalkylcalixpyrrole-fluoride ion complex as droplets from aqueous media. Chapter 3: Dipyrromethane and calixpyrrole embedded perfluoro copolymer for rapid removal of perfluoro pollutants from water The perfluoro pollutants like perfluorooctanoic acid (CF3(CF2)6COOH; PFOA) and perfluoro octane sulfonate (PFOS) are generated from degradation of fluoropolymers and a diverse collection of consumer goods ranging from pizza boxes to stain-resistant carpets to teflon pans. Due to extensive use of perfluoro products, every year huge amount of perfluoro chemicals are disposed to the environment. We have reported dipyrromethane embedded perfluoro copolymer which reduced more than 80% PFOA in a short time span of h from the industrial disposal site relevant concentration with very high adsorption kinetics of 9.18×104 g mg-1 min-1. Chapter 4: Metal alkenylcalixpyrrole towards ring closing metathesis The peripheral olefin functionality of calixpyrrole could be activated by coordinating with metals. The olefin moieties from alternate meso-posiiton of calixpyrrole undergoes ring closing oolefin metathesis by [Ru(COD)Cl2]n. Ring closing olefin metathesis between olefin moieties from alternate meso-positions by ruthenium complex is possible if calix[4]pyrrole adopts puckered conformation. Puckering of calix[4]pyrrole is feasible if metal is incorporated inside the calix[4]pyrrole cavity. The ring closing olefin metathesis from alternate meso-position is unable if metal is inhibited to incorporate inside the calixpyrrole core. Chapter 5: Summary and future perspective Meso-substituted olefin and hydroxyl functionalized calixpyrroles were functionalized for desire applications. Perfluoroalkyl calixpyrrole has been used to extract fluoride ion from aqueous media. Dipyrro and perfluorocalixpyrrole embedded polymer has been employed to remove perfluorooctanoic acid, an emerging perfluoro pollutant from water. The synthesized calixpyrrole could be an effective ionophore in ion selective electrode (ISE). Additionally, metal coordinated alkenylcalixpyrrole has been used to construct new C-C bond via cross olefin metathesis.