文档介绍：CHAPTER IV
POUNDS
AROMATIC HYDROCARBONS
Aromatic hydrocarbons may be prepared by the following methods :—
1. Wurtz - Fittig reaction. The interaction of an aryl halide, alkyl
halide and sodium gives a reasonable yield of an alkyl aryl hydrocarbon, for
example :
C6H6Br + 2Na + BrCH2CH2CH2CH3 —* C6H6CH2CH2CH2CH3
Bromobenzene n-Butyl bromide n-Butylbenzene (. 182°)
The by-products are C4H9«—C4Hf* = n-C8H18, n-octane (. 125°) and
C6H6—C6H6, diphenyl (. 254°), and can be readily separated by distillation.
Two mechanisms have been proposed for the Wurtz reaction (compare Section
111,7) and for the Wurtz-Fittig reaction. According to one, sodium reacts
with the alkyl halide to produce a sodium halide and a free radical, which
subsequently undergoes coupling, disproportion a tion, etc. :
C4H9«Br + Na > C4H,a. + NaBr
C6H6Br + Na > C6H5. + NaBr
C6H5.+C4H9«. * C6H6-C4H9«
C6H5. + C6H6 •> C6H6—C6H6
C4H9«. + C4H9«. > C4H9a—C4H9a
2CH3CHJJCH2CH2. > CH3CH2CH = CH2 + CH3CHaCH2CH3
The other mechanism involves the intermediate formation anosodium
compounds :
R—X + 2Na > R~Na+ + NaX
The products from a mixture of alkyl and aryl halides may be represented by
the following scheme :
zj*2Na _ + ""~~~ ArAr—— X
Ar—X * Ar Na ». Ar—Ar
The fact that n-butylbenzene can be prepared in reasonable yield by the
action of sodium upon a mixture of bromobenzene and n-butyl bromide can be
partly explained on the assumption that n-butyl bromide reacts with phenyl-
sodium more rapidly than does bromobenzene. It is interesting to note that
n-butylbenzene can be prepared either from benzylsodium and n-propyl
bromide or from phenylsodium and n-butyl bromide (Section VI,29).
2. Friedel and Crafts reaction. An alkyl halide condenses with an
aromatic hydrocarbon in the presence of anhydrous aluminium chloride to
yield, in the first instance, a hydrocarbon in accordance with the following
scheme : —
A1C1,
ArH -I- RX -- » ArR + HX