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Chloride salts of diazonium cation, traditionally prepared from the aniline, sodium nitrite, and hydrochloric acid, are unstable at room temperature and are classically prepared at 0 – 5 °C. However, one can isolate diazonium compounds as tetrafluoroborate or tosylate salts, [ 8 ] which are stable solids at room temperature. [ 9 ]
The tetrafluoroborate can be obtained from crude benzenediazonium chloride by salt metathesis using tetrafluoroboric acid. [C 6 H 5 N 2]Cl + HBF 4 → [C 6 H 5 N 2]BF 4 + HCl. The tetrafluoroborate is more stable than the chloride. [2]
Phenylhydrazine was the first hydrazine derivative characterized, reported by Hermann Emil Fischer in 1875. [7] [8] He prepared it by reduction of a phenyl diazonium salt using sulfite salts.
These compounds are diazotized followed by treatment with cuprous chloride. [1] Industrially, the diazonium method is reserved for 3-chlorotoluene. The industrial route to 2- and 4-chlorotoluene entails direct reaction of toluene with chlorine. The more valuable 4-chlorotoluene is separated from 2-chlorotoluene by distillation.
Its melting point at -44 °C is lower than that of benzene. In contrast, the boiling points of PhF and benzene are very similar, differing by only 4 °C. It is considerably more polar than benzene, with a dielectric constant of 5.42 compared to 2.28 for benzene at 298 K. [ 4 ] Fluorobenzene is a relatively inert compound reflecting the strength ...
Chlorobenzene (abbreviated PhCl) is an aryl chloride and the simplest of the chlorobenzenes, consisting of a benzene ring substituted with one chlorine atom. Its chemical formula is C 6 H 5 Cl. This colorless, flammable liquid is a common solvent and a widely used intermediate in the manufacture of other chemicals.
It can also be prepared using diazonium salts. When aniline is treated with NaNO 2 +dilute HCl at 5°C, it yields benzene diazonium chloride. When this is further reacted with benzene, biphenyl is formed. This is known as the Gomberg–Bachmann reaction.
Difluorobenzenes can be prepared by the Balz-Schiemann reaction, which entails conversion of diazonium tetrafluoroborate salts to their fluorides. The synthesis of 1,2-difluorobenzene starts with 2-fluoroaniline: [3] C 6 H 4 F(NH 2) + HNO 2 + HBF 4 → [C 6 H 4 F(N 2)]BF 4 + 2 H 2 O [C 6 H 4 F(N 2)]BF 4 → C 6 H 4 F 2 + N 2 + BF 3