Fluorocarbons, organic molecules with carbon skeletons and fluorine "skins", differ fundamentally from their hydrocarbon counterparts in interesting and useful ways. A selection of the myriad applications fluorocarbons and their derivatives have found in modern life is described and related to molecular properties. Salient aspects of the nature and reactivity of fluorocarbon compounds are highlighted by comparison with their more familiar hydrocarbon analogues.

Perspective on Fluorocarbon Chemistry

Enamines: recent advances in synthetic, spectroscopic, mechanistic, and stereochemical aspects—I

The preparation and properties of polyfluoro aromatic and heteroaromatic compounds

The chemistry of thiocyanic esters

The chemistry of azetidin-3-ones, oxetan-3-ones, and thietan-3-ones

The use of crown ethers in the synthesis of hexafluoropropene and tetrafluoroethylene oligomers

Controlled chlorination of 2,6-diaminopyridine (1) affords 2,6-diamino-3,5-dichloropyridine (2a) which is then bis(diazotised) to give 2,3,5,6-tetrachloropyridine (3a); similarly prepared are other 2,3,5,6-tetra(chloro/bromo)pyridines and 2,6-dichloro-3,5-bis(thiocyanato)pyridine (3h), from which 3,5-bis(alkylthio)pyridines are easily obtained.

A convenient synthesis of 2,3,5,6-tetrahalogenopyridines and of 3,5-bis(alkylthio)pyridines from 2,6-diaminopyridine

Perfluoro-2-methylpent-2-ene (1) reacts with aromatic amines to give high yields of 4-arylaminoquino-lines; aminopyridines react similarly to give the corresponding derivatives of either naphthyridine or pyridopyrimidine, whereas aromatic primary amines with substituents in the ortho-positions, or t-butylamine, give ketenimines, dialkylamines give enamines, and ammonia gives a dicyano-enamine.

Reaction of aromatic or heterocyclic amines and perfluoro-2-methylpent-2-ene to give fused pyridines, ketenimines, or enamines

1,4-Dichloro-1,4-diphenyl-2,3-diazabutadiene (1) reacts with potassium cyanate to give 5-phenyl-1,2,4-triazol-3(2H)-one (9), but with potassium thiocyanate it gives the 1-chloro-4-thiocyanato-2,3-diazabutadiene (3). The thiocyanate (3) is not isomerized by heat, but is hydrolysed by acid to a mixture of 2,5-diphenyl-1,3,4-oxadiazole and 2-amino-5-phenyl-1,3,4-thiadiazole. Sodium hydrosulphide, potassium ethylxanthate, and thiourea all convert the dichlorodiazabutadiene (1) into 2,5-dipheyl-1,3,4-thiadiazole, while 2-aminobenzenethiol converts it into 2-phenylbenzothiazole.

Unsaturated compounds containing nitrogen. Part 5. Reactions of 1,4-dichloro-1,4-diphenyl-2,3-diazabutadiene with nucleophiles

1-Chloro-1,4-diaryl-2,3-diazabutadienes (Ar1CClNNCHAr2), prepared by the reaction of thionyl chloride with aroylhydrazones (Ar1CONHNCHAr2), react with thiosemicarbazide or thiocarbohydrazide to give 2-arylidenehydrazino-5-aryl-1,3,4-thiadiazoles, and with potassium thiocyanate to give 1-thiocyanato-1,4-diaryl-2,3-diaza-butadienes which isomerize thermally to arylideneamino-5-aryl-1,3,4-thiadiazoles. 1-Chloro-1,4-diphenyl-2,3-diazabutadiene reacts with potassium ethylxanthate to give a 1-ethylxanthyl-2,3-diazabutadiene which on pyrolysis yields 2,5-diphenyl-1,3,4-thiadiazole.

William T. Flowers

Papers

The use of crown ethers in the synthesis of hexafluoropropene and tetrafluoroethylene oligomers

A convenient synthesis of 2,3,5,6-tetrahalogenopyridines and of 3,5-bis(alkylthio)pyridines from 2,6-diaminopyridine

Reaction of aromatic or heterocyclic amines and perfluoro-2-methylpent-2-ene to give fused pyridines, ketenimines, or enamines

Unsaturated compounds containing nitrogen. Part 5. Reactions of 1,4-dichloro-1,4-diphenyl-2,3-diazabutadiene with nucleophiles

Unsaturated compounds containing nitrogen. Part 4. Further reactions of 1-chloro-2,3-diazabutadienes with S-nucleophiles