A method employed by Remsen and Fahlberg (Am. Ch. Jour. Vol. 1.
p __ ) for getting the sulphonic acid group in the ortho position to
methyl was; (a) treat toluene with fuming H_{2}SO_{4} forming thus
ortho- and para- toluene sulphonic acids, (b) make the calcium salt
of the sulphonic acids thus formed and from this the potassium
salt. (c) treat this mixture of potassium toluene sulphonates
with phosphorous penta-chloride forming the corresponding
sulphonchlorides. One of these (para) being a solid and the other
(ortho) an oily liquid a nearly complete separation could be
effected. The difficulty with this method is however that the larger
part of the product is the para and only a comparatively small
proportion of the ortho compound is formed.