Aryl halide

Haloaromatics (also halogenoarenes or aryl halides ) are derived from the group of aromatic compounds or aromatic compounds, in which one or more hydrogen atoms by elements of Group 7 ( halogens ) - fluorine, chlorine, bromine and iodine - the periodic table have been replaced. Compounds of the radioactive element astatine are poorly understood due to the short half life of astatine.

Aromatic halogen compounds are sometimes highly toxic and are or have been used as insecticides or fungicides. Many of them are now prohibited.

Selected examples:

  • Chlorobenzene, an important solvent for oils, fats, resins, etc.,
  • 2 -chlorophenol, a disinfectant,
  • CS gas, tear gas,
  • DDT, a banned in most industrialized countries since the 1970s, insecticide,
  • Decabromodiphenyl ether and tetrabromobisphenol A are flame retardants,
  • Eosin, a red dye is obtained from coal tar,
  • Merbromin (INN ) is a similar to the eosin dye, which was sold in 2003, in Germany as an antiseptic (trade name Mercuchrom ).

Parent compounds

The simplest compounds are those substituted with a halogen atom benzenes; therefore they are the parent compounds of aromatic halogen compounds.

Representation

Chloro- and bromobenzene, can be represented by halogenation with chlorine or bromine in the presence of a Lewis acid.

Starting from aniline all four halogenated benzenes can be represented by diazotization. Chloro, bromo and iodobenzene are accessible via the Sandmeyer reaction of fluorobenzene is the Schiemann reaction application.

Properties

Physical Properties

The mono halobenzenes are colorless liquids. With increasing molar mass of the boiling points increase. The melting points, these differences are not as pronounced. From fluorine (-42 ° C ) for chlorobenzene ( -45.2 ° C) is even determine a fall in the value while then bromine (-31 ° C ) and iodine (-29 ° C) towards rise moderately.

Chemical Properties

A characteristic reaction of aromatic halogen compounds is the nucleophilic aromatic substitution. This reaction is usually off to the addition-elimination mechanism. Haloaromatics subject rarely nucleophilic substitutions, except in high-energy industrial processes.

Haloaromatics react with magnesium metal to Grignard reagents, which are considered to be " working " reagents.

Haloaromatics with two halogen

Substituting benzene with two halogens, the result is a total of ten combinations. In any combination are the ortho -, meta- and para- isomers.

Haloaromatics with other functional groups

Also known aromatic parent compounds, such as phenol, aniline, anisole, toluene, nitrobenzene, benzyl alcohol, benzaldehyde, benzoic acid, etc., it is halogen-substituted derivatives. The name of the parent compound does not change. The halogen substituent is darvorgesetzt as syllable ( prefix). Within each group there is ortho-, meta -and para- isomers.

The - I effect of the halogen substituent leads the halogen phenols and halobenzoic to a higher acidity compared to phenol or benzoic acid. The pKa values ​​are therefore correspondingly lower ( phenol: 9.99 / halophenols: 9.06 - benzoic acid: 4.20 / halobenzoic: 3.58 ).

Halogenated heteroaromatics

The group of aromatic halogen compounds include halogenated heteroaromatic compounds, such as 2-chloropyridine, 2,6- the insecticide chlorpyrifos or Dibromopyridine.

Half-life 2-Chlorophenol Andrew Streitwieser Clayton Heathcock Integrated Authority File
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