Date of Award

2023

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Chemistry

Department

Chemistry

First Advisor

Matthew Kiesewetter

Abstract

Esters have applications that span food packaging, medicine and even pest control, in addition to the applications of naturally occurring esters. Before new molecules or materials can move to applications, synthetic chemists must first design methods for their production. As such, this dissertation examines the formation and breaking of esters as well as their applications.

(Thio)Urea H-Bonding catalysts are used for the highly controlled ROP of lactones. ROP is a thermodynamically driven process, therefore, equilibrium can be utilized to selectively transform polymer to monomer. Here a new method of additive, solvent, and metal free recycling (depolymerization) of polylactones is presented. Three polymers were used in this study: PCL and PVL respectively yield 85% and 95% monomer recovery via distillation from polymer melt, PLA yields 89% monomer recovery via sublimation from the polymer melt. PhCyU-Na was the most effective catalyst for all polymers. PhCyU-Na is beneficial for both its superior rates and low volatility at elevated temperatures. Monomer recovered via these methods have been repolymerized achieving target molecular weights and narrow dispersity.

A series of conformationally flexible bis(thio)urea H-bond donors plus base cocatalyst were applied to the ring-opening polymerization of lactones. The rate of Ring-Opening Polymerization (ROP) displays a strong dependence upon the length and identity of the chain tethering the (thio)urea moieties, where a circa five methylene-unit long tether exhibits the fastest ROP. Any restriction to conformational freedom is deleterious to catalytic activity. For valerolactone and caprolactone, the bisurea H-bond donors are more effective, but for lactide the bisthioureas are the better catalysts. The ROP reactions are rapid and controlled across a wide range of reaction conditions, including solvent-free. The active mechanism is highly dependent upon the identity of the base cocatalyst, and a mechanistic rationale for the observations is discussed. Implications for the design of future generation catalysts are discussed.

Ester containing pyrethroids are a broad class of synthetic pesticides inspired by a family of natural compounds, pyrethrins. Pyrethrins have been used for their pesticidal and pestifugal properties for over two millennia. Allethrin, the first pyrethroid to exhibit toxicity comparable to pyrethrins, was discovered in 1945; since then countless pyrethroids whose activity exceeds pyrethrins have been discovered. A review of Structure-Activity Relationships is presented. This review begins after the structural elucidation of pyrethrins and spans the development of ester containing pyrethroids in use today. Generally, pyrethroids contain 2 regions, acid and alcohol regions, connected via a central ester. Through the development of modern pyrethroids, the acid region has transformed from substituted cyclopropane carboxylates to phenyl- or anilino- isovalerates. Similarly, alcohols used in pyrethroids began as cyclopentenolones, in the natural products, to substituted furylmethanols and eventually substituted benzyl alcohols. Toxicity is the central focus of the structure-activity relationships, with additional discussion of metabolism and resistance. From the reviewed publications, several structural suggestions for the development of pyrethroids intended for use against Varroa destructor are presented.

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