Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

SULPHONATION 197
and the aliphatic olefines ; in this case they behave essentially in the
same way. Ethylene indeed forms an addition compound, ethyl sulphuric
acid, with concentrated sulphuric acid at a low temperature
(about 50°). CH2=CH2 —> CH3.CH2.O.SO3H ,
hence the H28O4 molecule is here broken up in a different way. For
obvious reasons this reaction cannot take place with benzene, since it
must be very readily reversible. If, however, ethylene is subjected to
the action of fuming sulphuric acid, a sulphonation product, so-called
carbyl sulphate, is formed just as in the case of benzene. Carbyl sulphate
is derived from the alcohol sulphonic acid which is first formed
by esterification with sulphuric acid and subsequent elimination of water.
CH2=CH2 —> CH20H—CH2SO3H —> CH2— CH2.SO3H
CH^ ^-^2
> 0 SO2 (Carbyl sulphate).
0—SO3H
S02-0
In a quite analogous way ethylene reacts with nitric-sulphuric acid,
nitroethyl nitrate (p. 164) being produced. How are alkyl sulphonic
acids prepared ?
The ease with which the sulphonic group enters into aromatic compounds
depends on the nature of the substituents present, just as it does
in nitration. Benzene is rather difficult to sulphonate, toluene and
naphthalene are somewhat more easy, phenols and amines very easy.
The sulphonation of nitrobenzene or the further sulphonation of the
benzene sulphonic acids proceeds with more difficulty, and the action
of the sulphuric acid must here be intensified by increasing its SO3content.
Since N02 and SO3H are substituents of the second order, a second
substituent enters in the w-position. Oleum containing a high percentage
of sulphur trioxide finally converts benzene into benzene trisulphonic
acid. Chlorosulphonic acid condenses with aromatic hydrocarbons,
giving aryl sulphochlorides.
From naphthalene two monosulphonic acids are obtained, namely,
naphthalene-a- and -j8-sulphonic acids :
8O3H
a-Acid /3-Acid
Substitution reactions in the naphthalene ring take place, without
exception, in the a-position, which is characterised by its high reactivity.