Cresol
Since 1965, when the recovery of cresols from coal tar and spent refinery caustics had become insufficient to meet the rising demand, these compounds
have been increasingly produced by synthesis. The processes now in use are
– Alkali fusion of toluenesulfonates
– Alkaline chlorotoluene hydrolysis
– Splitting of cymene hydroperoxide
– Methylation of phenol in the vapor phase
Alkali Fusion of Toluenesulfonates
Technical-grade m-cresol can also be produced by toluene sulfonation according to a process developed by the Honshu Chemical Industry Co. Steam at 165
◦C is introduced into
an toluenesulfonic acid mixture rich in m isomer obtained under thermodynamically controlled conditions as described above (isomerization for several
hours at 190 – 200 ◦C), whereupon
o- and p-toluenesulfonic acid are hydrolyzed back to sulfuric acid and toluene. The toluene is distilled with the steam; m-toluenesulfonic acid with a
purity above 90% remains, together with sulfuric acid. Side reactions during the isomerization and hydrolysis can be suppressed by adding sodium
sulfate (5 – 10 mol%, calculated on the basis of sulfuric acid) to the sulfonation batch. In this way, removal of the sulfuric acid that is formed
in the hydrolysis as a lower phase at ca. 140 – 150 ◦C is also possible. It is also possible to neutralize the hydrolysis mixture with
concentrated sodium hydroxide solution,filter off the resulting sodium sulfate at 80 ◦C, introduce the solution of sodium m-toluenesulfonate
into a sodium hydroxide melt, containing 10 – 15% potassium hydroxide to facilitate stirring,at an initial temperature of 330 ◦C, and tofuse
it at 340 ◦C.The distillation of the crude cresol phase obtained after acidification gives m-cresol with a purity of up to 98% in a yield of ca.
65%, calculated on the basis of reacted toluene .
Ullmann's Enc. of Industrial Chemistry2007
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