Richard L. Powell

Free radical chemistry. Part 5. [1] A new approach to the synthesis of perfluorinated ethers

Abstract Fluorinations of the free-radical adducts of fluorinated alkenes, to ethers, over cobalt trifluoride are described and perfluorinated ethers are obtained at temperatures in excess of 400°C. The effect of structure on the formation of perfluoroethers is outlined.

The reactions of xenon difluoride with ‘inert’ solvents

Abstract The reactions of XeF2 with a variety of organic solvents are described. XeF2 is foundto undergo both hydrogen- and chlorine-fluorine exchange over a relatively short timescalewith chloroform, dichloromethane and dibromomethane. XeF2 reacts very slowly withtetrachloromethane and fluorotrichloromethane, although the addition of a catalytic amountof HF increases the rate of reaction considerably. XeF2 dissolves in acetonitrile withnegligible reaction to the extent of 2.25 mol kg−1.

SELECTIVE FLUORINATION OF DICHLOROMETHANE BY HIGHEST OXIDATION STATE TRANSITION-METAL OXIDE FLUORIDES

Abstract In contrast to the reactivity of high oxidation state binary transition-metal fluorides with organic solvents, many transition-metal oxide fluorides do not react with CH2Cl2. Only the highest oxidation state species react, at temperatures below room temperature, via Cl-F exchange with > 90% selectivity, affording unstable high oxidation state chloro complexes which decompose to chlorine and lower oxidation state species.

Cycloaddition reactions of furan derivatives with trifluoroethene

Abstract The cycloaddition reaction of trifluoroethene with furan and a number of derivatives to give the unreported 1,1,2-trifluoro-7-oxa-bicyclo[2.2.1]hept-4-ene, and derivatives has been investigated. Reactions were carried out in stainless steel autoclaves at 200°C under autogenous pressure using an excess of trifluoroethene. Reactions were found to proceed with furan and derivatives with methyl groups in the 2 and/or 5 positions. Electron-withdrawing substituents in these positions prevented reaction however. Attempted dehydrofluorination of 1,1,2-trifluoro-7-oxa-bicyclo[2.2.1]hept-4-ene using a variety of bases gave no reaction, however use of LDA led to the preparation in 25% yield of 2,3-difluoro phenol.

Substituent chemical shifts (SCS) in NMR. Part 5. Mono- and di-fluoro SCS in rigid molecules

The complete assignment of the proton, carbon and fluorine NMR spectra of fluorocyclohexane (axial and equatorial conformers), 4-methyl-1,1-difluorocyclohexane, 4-tert-butyl-1,1-difluorocyclohexane, 3-methyl-1,1-difluorocyclohexane and 2,2-difluoronorbornane is reported and the proton substituent chemical shifts obtained. The fluorocyclohexane substituent chemical shifts (SCSs) are in close agreement with monofluoro SCS data obtained from steroids, the SCS of the 2ax- and 2eq-H being independent of the orientation of the fluorine. The SCS obtained from fluorocyclohexane are not applicable to the difluorocyclohexane systems and this non-additivity is shown to be general for CF2 and CF3 groups. The proton chemical shift calculation scheme previously given for hydrocarbons can now be extended to include fluoroalkanes using the data presented here. It is shown that the proton chemical shifts of a variety of fluoroalkanes can be well predicted on this scheme.

The transition-metal fluorides and oxide fluorides as selective fluorinating agents for hydrohalogenoalkanes

Abstract The reactions of the transition-metal fluorides, ReF 7 , ReF 6 , OsF 6 , IrF 6 , UF 6 , RuF 5 , VF 5 and CrF 5 , and the transition-metal oxide fluorides, VOF 3 , MoOF 4 , WOF 4 , ReOF 4 , ReOF 5 , OsO 3 F 2 , OsO 2 F 3 , OsOF 5 and OsOF 4 , with a variety of hydrohalogenoalkanes have been studied. Some of the transition-metal compounds exhibit remarkable specificity in their reactions. For example, in the reaction of CH 2 Cl 2 with ReF 6 , 85% of available fluorine is used to yield CH 2 ClF whereas, with UF 6 , all of the available fluorine is utilised to give CHCl 2 F; like ReF 6 , ReOF 4 produces efficient halogen exchange, some 98% of the available fluorine yielding CH 2 ClF. The selectivity and reactivity will be discussed in terms of the oxidation state and coordination geometry of the transition metal fluorinating agents.

Reactions involving fluoride ion. Part 21 [1]. Nucleophilic substitution reactions of perfluorocyclobutene oligomers

Abstract Reaction of perfluorocyclobutene oligomers, (1) - (4), with some simple nucleophiles gives products arising from S N 2′ displacement [N.B. this term is used here to describe the overall process of addition of a nucleophile to an alkene and elimination of an allylic fluorine and is not meant to imply that the reaction is concerted] or vinylic substitution of fluorine, or a mixture of both processes. The reactivity of the dimers, (1) and (2), is much greater than that of acyclic analogues and this can be attributed to the ring strain present in these compounds.

Free-radical chemistry: Part XII: Radical reactions of trifluoroethene

Abstract Free-radical chemistry of trifluoroethene (3FE) is explored. Chain-shortening by telomerisation with acetone occurs and the product is successfully fluorinated to a corresponding perfluorinated material. Other telomerisation reactions involving alcohols, ethers and amines are described and the importance of polar effects on radical reactivity is highlighted. Reactions of alcohol derived telomers with base yields oxetanes and oxiranes which are polymerised to corresponding fluorinated polyethers. Further reactions of telomers are discussed.

High oxidation state binary transition metal fluorides as selective fluorinating agents

High oxidation state transition metal fluorides are selective fluorinating agents for dichloromethane; those with d0; electronic configurations undergo hydrogen–fluorine exchange and metal reduction, while dn species undergo chlorine–fluorine exchange.

Polyhalogenoheterocyclic compounds. Part 35. Reactions of fluorinated alkenes and cycloalkenes with enolate anions

Reactions of compounds that are oligomers of tetrafluoroethylene, with enolate anions derived from ethyl acetoacetate and acetylacetone, give fluorinated pyran derivatives whereas an uncyclised product is obtained from diethyl malonate. Similar reactions with perfluoro-but-2-ene, -cyclohexene, and -cyclopentene give furan or pyran derivatives. The different behaviour of these systems is rationalised.