Calcium fluoride for nucleophilic fluorination

Thesis

Chapter 1 (Introduction) summarises the origin and role of fluorochemicals used in our everyday lives, including the production and use of hydrogen fluoride (HF). An account of the development of fluorine chemistry, including nucleophilic fluorination and CaF₂ chemistry, is also provided. This chapter concludes with an outline of the work disclosed in this thesis.

Chapter 2 (Fluorochemicals from Fluorspar via a Phosphate-Enabled Mechanochemical Process that Bypasses HF) begins with a brief introduction to mechanochemistry, mechanochemical fluorination and powder X-ray diffraction. The development of an inorganic fluorinating reagent (Fmix) via the solid-state (mechanochemical) activation of acid-grade fluorspar (>97% CaF₂) using K₂HPO₄ is disclosed. Applications of Fmix for S-F and C-F bond formation is described, followed by a mechanistic study on the composition of Fmix and the discovery of novel fluorinating reagents [K₃(HPO₄)F] and K_2-xCa_y(PO₃F)_a(PO₄)_b.

Chapter 3 (Low-Temperature Activation of Fluorspar in Water via Brønsted and Lewis Acid Cooperativity) first provides an overview of the reported methods for CaF₂ activation using Brønsted acids, followed by a brief introduction to boron and silicon fluorides. The development of a method entailing activation of acid-grade fluorspar in water (solution-phase) using B(OH)₃ or SiO₂ in the presence of a Brønsted acid, optimally oxalic acid, is then disclosed. The application of this technology for preparing fluorinating reagents well-documented for aromatic fluorination is then presented. Finally, mechanistic studies for HF monitoring by ¹⁹F NMR spectroscopy, and a study comparing the efficacy of oxalic acid versus H₂SO₄ are reported.

Chapter 4 (Experimental) contains experimental details for the work disclosed in Chapters 2 and 3, including procedures and characterisation for synthesised compounds and supplementary mechanistic data.

Authors: Patel, C

• DOI: 10.5287/ora-qyd88bx07
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: fluorine chemistry; nucleophilic fluorination