Fluorocarbon Refrigerants and their Syntheses: Past to Present

Abstract

This Review chronicles the progress made in the field of small fluorocarbon synthesis since their invention in the early 1930s by Thomas Midgley, Jr., and his coworkers, with special focus on their application as refrigerants, foam expansion agents, aerosol propellants, and precision solvents. Divided into four generations of C1–C4 halocarbons from CFCs through HCFCs, HFCs, and HFOs, the merits and challenges of each will be discussed in the context of market demands, as well as the evolution of industrial manufacturing methods. Vital transformations, such as exchange (Swarts) fluorination, hydrodehalogenation, dehydrohalogenation, and additions (Kharasch or Prins) will feature prominently and will be discussed in detail, as well as catalysts therefor. Of the myriad of fluorocarbons described herein, the models which have reached particular commercial significance (such as chlorodifluoromethane and 1,1,1,2-tetrafluoroethane) are given special consideration as flag-bearers for the generation to which they belong. Regulatory constraints to which this industry is bound will be outlined in brief, as well as an introduction to safety designations and nomenclature put forth by the American Society for Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE). This Review includes predominantly works which can only be found in the patent literature, but should be of equal interest to both academic and industrial practitioners of the art as it centers on fundamentals of organofluorine chemistry, which could equally be applied to the synthesis of larger molecules and building blocks for other applications.

Recent Advances in Synthesis of Difluoromethylene Phosphonates for Biological Applications

“…Chlorodifluoromethane (refrigerant Freon 22, HCFC‐22, R‐22), the precursor for HCF 2 P(O)(OAlk) 2 reagents, is a class II ozone‐depleting substance (ODS) in the Montreal Protocol and its amendments. Phaseout of class II ODSs is an ongoing process scheduled for completion in 2030, but the EU countries have banned HCF 2 Cl during the 2010s and the US virtually banned it last year [224] . Although this chemical is and likely will remain available for specialized purposes including laboratory needs, in practice, its applications will be restricted to very niche scenarios due to environmental concerns and regulatory hassle; think of the once ubiquitous solvent CCl 4 .…”

The Reactivity of α‐Fluoroketones with PLP Dependent Enzymes: Transaminases as Hydrodefluorinases

“…This is due to its capacity to modify molecular properties such as lipophilicity, metabolic stability or acidity, among others, [2] but also because of its role as a fundamental constituent of pollutants such chlorofluorocarbons (CFCs). [3] The special properties that fluorine confers to organic molecules is to a large extent due to the small size of this atom and the strength of the CÀ F bonds. Thus, the increasing interest around this halogen has gone in hand with the development of very efficient and selective synthetic pathways to obtain fluorinated compounds.…”

“…[4] Due to the inert nature of fluorinated compounds, many efforts have focused on their degradation, but since oxidative methods or incineration can produce toxic wastes, reductive alternatives are envisaged as safer methodologies. Among them, the cleavage of a CÀ X into a CÀ H bond, i. e. hydrodehalogenation [3,5] (hydrodefluorination, when X=F), [6,7] is one of the most promising chemical approaches to degrade these compounds. When dealing with fluorinated derivatives, most of these transformations rely on the application of transition metal complexes under harsh conditions on fluoroarene substrates.…”

Synthesis of Bioactive Fluoropyrrolidines via Copper(I)-Catalyzed Asymmetric 1,3-Dipolar Cycloaddition of Azomethine Ylides

“…Due to the special properties, introduction of fluorine containing groups into compounds often affect their biological activity a lot (Figure 1) and thus has always been regarded as a powerful tactics in agrochemicals and pharmaceuticals creation. [5][6][7][8][9][10][11][12][13][14] Accounting to recent survey, about half of newly developed pesticides and 35% of new drug candidates in phase II-III clinical trials contain distinct kinds of fluorine-substituted moieties. [15][16][17] During the past decades, the remarkable success and huge requirement of fluorine compounds in various fields have provided infinite vitality for organic chemists to explore methods for the construction of fluorinated molecules.…”