Perfluoroisobutene: Poisonous Choking Gas

Patočka, Jiří

doi:10.31482/mmsl.2019.006

Cited by 6 publications

(4 citation statements)

References 40 publications

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“…First, the conditions always cogenerate a range of perfluoroalkenes (e.g. Scheme ), many of which are volatile and toxic . Second, the kinetics of reactions mediated by NaI can undergo acute and unpredictable autoacceleration (e.g.…”

Section: Discussionmentioning

confidence: 99%

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Difluorocarbene Generation from TMSCF₃: Kinetics and Mechanism of NaI-Mediated and Si-Induced Anionic Chain Reactions

et al. 2020

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The mechanism of CF2-transfer from TMSCF3 (1), mediated by TBAT (2-12 mol%) or by NaI (5-20 mol%), has been investigated by in situ / stopped-flow 19 F NMR spectroscopic analysis of the kinetics of alkene difluorocyclopropanation, and competing TFE / c-C3F6 / homologous perfluoroanion generation, 13 C/ 2 H KIEs, LFERs, CF2-transfer efficiency and selectivity, the effect of inhibitors, and density functional theory (DFT) calculations. The reactions evolve with profoundly different kinetics, undergoing auto-inhibition (TBAT) or stochastic auto-acceleration (NaI), and co-generating perfluoroalkene side products. An overarching mechanism involving direct and indirect fluoride transfer from a CF3-anionoid to TMSCF3 (1) has been elucidated. It allows rationalization of why the NaI-mediated process is more effective for less-reactive alkenes and alkynes, why a large excess of TMSCF3 ( 1) is required in all cases, and why slow-addition protocols can be of benefit. Issues relating to exothermicity, toxicity, and scale-up are also noted.a Relative rates (krel) are for competitive first-order CF2 capture by the alkene/yne, not to overall rates of reaction. b Values in parenthesis by DFT. 26 See sections S3.7, S3.8 and S6.2 in the SI. Singlet CF2 as the ReactiveIntermediate. We began by studying the reaction of TMSCF3 (1) with alkenes 3i, and E/Z-4 and alkyne 5, Table 1. All underwent difluorocyclopropanation, to varying degrees of conversion, in the presence of TMSCF3 (1, 1.5 M) and 1-5 mol % TBAT, or NaI. Reactions of E/Z-4 proceeded stereospecifically, and with >98 % retention. The difluorocyclopropene 8, generated in low yield (12%) from alkyne 5, under the TBATmediated conditions, underwent partial decomposition to unidentified products. In contrast, 8 was quantitatively-generated, and stable, under NaI-mediated conditions, see section S3.3 in the SI. The same difluorocyclopropane products (6, 7) were obtained from 3i and E/Z-4 on thermalization with the zwitterionic CF2-source Ph3PCF2CO2. 22 The relative reactivities (krel) of alkenes 3i, E-4, and Z-4, and the LFER correlation for a-methylstyrenes (3i-vii, r + = -0.6), 23 were independent of the reagent (1 / Ph3PCF2CO2), and initiator (TBAT / NaI), Table 1, 24 within experimental error. Scheme 3. Experimental a and calculated b KIEs for rapid addition of transient singlet CF2 to 3i, at 300 K. 25 a Experimental (exp.) values in THF; and in PhCl, as solvent. 25 b Calculated (calc.) values by DFT, at the M06/6-31+G* level in Gauss-ian09 employing IEF-PCM single points to account for solvation, and goodvibes, kinisot and PyQuiver to compute free energy corrections and KIEs, see sections S1.6 and S6.2 in the SI. 26Kinetic isotope effects for the reaction of p-F-a-methylstyrene 3i with TMSCF3 (1) initiated by TBAT were obtained by a series of competitions of 13 C-and 2 H-labelled a-methylstyrenes 3i against aryl-D4-3i, monitored by 19 F NMR spectroscopy (aryl-DdF = 0.5 ppm). 25 The resulting primary and secondary kinetic isotope effects, Scheme 3, were consistent with thos...

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Section: Discussionmentioning

confidence: 99%

“…Scheme 6), many of which are volatile and toxic. 52 Second, the kinetics of reactions mediated by NaI can undergo acute and unpredictable autoacceleration (e.g. Figure 1B), resulting in rapid generation of TMSF (bp 19 °C) 53 and highly exothermic capture of CF 2 (eqs 8 and 9).…”

Section: ■ Conclusionmentioning

confidence: 99%

Difluorocarbene Generation from TMSCF₃: Kinetics and Mechanism of NaI-Mediated and Si-Induced Anionic Chain Reactions

et al. 2020

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“…The anionic chain processes inherently generate superstoichiometric TMSF (bp 19 °C), and with some substrates, the rate of TMSF generation in stage III accelerates considerably, potentially leading to uncontrolled exothermic events. Reactions involving anionic initiation of TMSCF 3 ( 1 ) invariably cogenerate a complex range of perfluoroalkenes, C n F 2 n , some of which are volatile and toxic . For all of the above reasons, caution should be exercised in the use of these processes, especially on scale-up.…”

Section: Safety Considerationsmentioning

confidence: 99%

“…Reactions involving anionic initiation of TMSCF 3 ( 1 ) invariably cogenerate a complex range of perfluoroalkenes, C n F 2 n , some of which are volatile and toxic. 19 For all of the above reasons, caution should be exercised in the use of these processes, especially on scale-up.…”

Section: Safety Considerationsmentioning

confidence: 99%

TMSCF₃-Mediated Conversion of Salicylates into α,α-Difluoro-3-coumaranones: Chain Kinetics, Anion-Speciation, and Mechanism

Minshull,

Lloyd-Jones

2023

J. Org. Chem.

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As reported by Zhao, the TBAT ([Ph 3 SiF 2 ] − [Bu 4 N] + )-initiated reaction of ethyl salicylate with TMSCF 3 in THF generates α,α-difluoro-3-coumaranones via the corresponding O -silylated ethoxy ketals. The mechanism has been investigated by in situ 19 F and 29 Si NMR spectroscopy, CF 2 -trapping, competition, titration, and comparison of the kinetics with the 3-, 4-, 5-, and 6-fluoro ethyl salicylate analogues and their O -silylated derivatives. The process evolves in five distinct stages, each arising from a discrete array of anion speciations that modulate a sequence of silyl-transfer chain reactions. The deconvolution of coupled equilibria between salicylate, [CF 3 ] − , and siliconate [Me 3 Si(CF 3 ) 2 ] − anions allowed the development of a kinetic model that accounts for the first three stages. The model provides valuable practical insights. For example, it explains how the initial concentrations of the TMSCF 3 and salicylate and the location of electron-withdrawing salicylate ring substituents profoundly impact the overall viability of the process, how stoichiometric CF 3 H generation can be bypassed by using the O -silylated salicylate, and how the very slow liberation of the α,α-difluoro-3-coumaranone can be rapidly accelerated by evaporative or aqueous workup.

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Chemical warfare agents: an outlook on past and present technologies

Mphuthi

Jijana

Mhlanga

et al. 2023

Sensing of Deadly Toxic Chemical Warfare Agents, Nerve Agent Simulants, and Their Toxicological Aspects

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Perfluoroisobutene: Poisonous Choking Gas

Cited by 6 publications

References 40 publications

Difluorocarbene Generation from TMSCF₃: Kinetics and Mechanism of NaI-Mediated and Si-Induced Anionic Chain Reactions

Difluorocarbene Generation from TMSCF₃: Kinetics and Mechanism of NaI-Mediated and Si-Induced Anionic Chain Reactions

TMSCF₃-Mediated Conversion of Salicylates into α,α-Difluoro-3-coumaranones: Chain Kinetics, Anion-Speciation, and Mechanism

Chemical warfare agents: an outlook on past and present technologies

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Perfluoroisobutene: Poisonous Choking Gas

Cited by 6 publications

References 40 publications

Difluorocarbene Generation from TMSCF3: Kinetics and Mechanism of NaI-Mediated and Si-Induced Anionic Chain Reactions

Difluorocarbene Generation from TMSCF3: Kinetics and Mechanism of NaI-Mediated and Si-Induced Anionic Chain Reactions

TMSCF3-Mediated Conversion of Salicylates into α,α-Difluoro-3-coumaranones: Chain Kinetics, Anion-Speciation, and Mechanism

Chemical warfare agents: an outlook on past and present technologies

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Difluorocarbene Generation from TMSCF₃: Kinetics and Mechanism of NaI-Mediated and Si-Induced Anionic Chain Reactions

Difluorocarbene Generation from TMSCF₃: Kinetics and Mechanism of NaI-Mediated and Si-Induced Anionic Chain Reactions

TMSCF₃-Mediated Conversion of Salicylates into α,α-Difluoro-3-coumaranones: Chain Kinetics, Anion-Speciation, and Mechanism