Abstract
AbstractElectrochemical fluorination reactions of organic compounds frequently employ hydrogen fluoride reagents that are corrosive. The corrosive nature of these reagents necessitates either the construction or purchase of cells that are stable to hydrogen fluoride, which require high‐cost materials, machining time and expertise. Herein, we offer an alternative solution using 3D printing, which is an inexpensive and rapid manufacturing technique. We have designed, printed and shared four different cell types in polypropylene and tested them in an electrochemical alkene difluorination reaction in the presence of triethylamine ⋅ 3HF and pyridinium poly ⋅ (HF).
Highlights
Electrochemical fluorination reactions of organic compounds frequently employ hydrogen fluoride reagents that are corrosive
While aqueous and anhydrous forms of Hydrogen fluoride (HF) have significant and prohibitive safety concerns associated with them,[15] commercially available organic sources of HF, such as triethylamine · 3HF and pyridinium poly(HF) (‘Olah’s reagent’, which is a mixture of 70 % HF in pyridine), are highly versatile fluoride reagents and frequently employed for electrochemical fluorination reactions
The combination of anodic oxidation and hydrogen fluoride has been used for the fluorination of alkenes,[7,17,18,19,20,21,22,23,24,25] alkynes,[18] aromatic rings,[26,27,28,29] esters,[30,31,32] ketones[16,33] and thioketals,[34,35,36,37,38] among others, Figure 1A
Summary
For alkene substrates with oxidation potential greater than 1.8 V (vs Fc/Fc+), an undivided cell can be used for the vicinal difluorination. The reported cell for reaction of 1 to 2 was constructed from a commercially available HDPE vial and an upturned septum that served as a lid to secure the electrode wires. Using this set-up, a 19F NMR yield of 90 % was achieved, Scheme 1. We have repeated this reaction using a glass (type III soda lime glass) vial instead of the HDPE vial, and a dramatic drop in yield to 17 % was observed. When the difluorination of alkenes 1 a and 1 b was conducted in this PP cell, the NMR and isolated yields were consistent with those conducted in the reported HDPE cell, Scheme 1. No leaks were observed, and the yield of 2 b from 1 b remained consistent after each successive run, signifying the reusability of these vessels
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