Nanotechnologies / Materials
Decomposition of environmental pollutants, Decomposition of PFAS

Development of the Hydrodefluorination reactionof perfluoroalkyl substances
Department of Applied Chemistry, Graduate School of Engineering
Assistant Professor Ryohei Doi
https://researchmap.jp/ryoheidoi?lang=en

Nanotechnologies / Materials

Abstract
The perfluoroalkyl substances are organofluorine compounds
having several continuous CF2 units. The perfluoroalkyl
substances
Figure1
are recently recognized as environmental pollutants due to theirhigh thermal and chemical stability. For example, we can frequently find newspaper issues about perfluorooctanoic acid (PFOS) andperfluorooctane sulfonic acid (PFOA). In this work, we developedhydrodefluorination reactions of perfluoroalkyl substances. In thepresence of a nickel catalyst, the treatment of perfluoroalkyl arenes
with hydrosilanes resulted in the conversion of all C-F bonds into
C-H bonds. Our detailed mechanistic studies revealed that fluoroalkene is a key intermediate, and nickel catalyst plays multiple
roles in the catalytic cycle.

expand the substrate scope and to use a cheaper reductant thanhydrosilane is underway to establish an effective disposal method
for perfluoroalkyl substances.
Figure 1. Research Background
Example of perfluoroalkyl substances• Chemical stability• Repellency• Thermal stability…etc• Persistent pollutant• Flame resistance

PTFE
Figure 2. This work: Hydrodefluorination reaction
Nickel catalyst
K3PO4▍ Background & Results
In recent years, environmental pollution caused by perfluoroalkylsubstances (PFAS) has become increasingly serious. When PFAS
are released into the environment, they do not decompose andbecome long-lasting environmental pollutants. Practical methods
for the decomposition of perfluoroalkyl substances are Figure2
still underdevelopment.
Our research group has focused on hydrodefluorination reactions. This reaction replaces C−F bonds in organofluorinecompounds with C−H bonds, thus converting perfluoroalkyl compounds into harmless hydrocarbons. While there have been numerous reports of defluorination reactions for the trifluoromethyl group(CF3), there have been few precedents for defluorination of longer
perfluoroalkyl chains.
Using a nickel catalyst and potassium phosphate (base), we
conducted a reaction of 1-(pentafluoroethyl)naphthalene andhydrosilane. This reaction proceeded at a relatively low temperature of 60 ℃, yielding 1-ethylnaphthalene with an 86% yield. In
this reaction, the combination of a carbene ligand called ICy with
Ni(cod)2 (cod = 1,5-cyclooctadiene) as a nickel source is essential.
When we investigated the reactions of longer 1-heptafluoropropyland 1-nonafluorobutyl naphthalenes, though higher temperature'(#$conditions were required, in both cases, small amountsof thecorresponding alkanes were observed. By quantifying the co-produced fluorosilane, roughly half of the fluorine was found to be removed.
A detailed analysis of the reaction mechanism of 1-pentafluoroethyl naphthalene revealed that the reaction progresses throughfive steps: (1) benzylic hydrodefluorination, (2) HF elimination by
the base, (3) hydrodefluorination of the fluoroalkene, (4) hydrosilylation of vinyl naphthalene, and (5) protonation of benzylsilane. The
nickel was found to catalyze all of these processes except for the
final protonation step.

PFOA

Pentafluoroethylnaphthalene

ProductThermally stable bond＝energetic driving force!!

Hydrosilane

Hydrodefluorination
Perfluoroalkyl substances

Hydrocarbon

n Thermal & chemical stability

n Burnable wasten Persistent pollutant

n Short environmental lifetimen Bioaccumulationn Biological degradation

Limitation of this work
Future perspectiven Broader scope(escape from naphthyl)
Requirement ofnaphthyl groupn Cheaper hydride source

Expensive hydrosilane! TVJIURVMKNMIOGPMQKRS! ZOVMXJIJ[\PI™´¨≠ÆØ∞"<º∫ ´ÆΩøPÃÆºæÕπ´∑´¡∫ØP¡ÆPß>!

=√´øPÃÆºæÕ—Æ¬∆∫ºP∏∫ºªπΩÆºÆ∂πæ≤π! ]WW[GXJIGKLMIKM[KL^VRMWVRN[UKRKJ[S\[M^RKUW±ß≤▍ Significance of the research and Future perspective
Our reaction enables the conversion of perfluoroalkyl substances
into hydrocarbons. Generally, hydrocarbon is easy to combust. Inaddition, the environmental effect of hydrocarbon is negligible due
to biological metabolism, which leads to a shorter lifetime than thatof perfluoroalkyl substances. Currently, our reaction is applicable
only to a specific perfluoroalkyl arenes. Further investigation to™Æ¬∂ªπΩÆºÆ¿Ω¡≤π¬∂∏√¡√∂π∫¬∫P a t e n tDoi, Ryohei; Yasuda, Masashi; Kajita, Naoki et al. Nickel-catalyzed exhaustive hydrodefluorination of perfluoroalkyl arenes. Journal of the American
Chemical Society. 2023, 145 (20), 11449–11456. doi: 10.1021/jacs.3c03471
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L http://www.chem.eng.osaka-u.ac.jp/~ogoshi-lab/en/index.html
K e y w o r d fluorine chemistry, nickel, PFAS
Tr e a t i s e