CH96185A - Process for the separation of ortho- and para-chlorotoluene from their mixtures. - Google Patents

Description

Process for the separation of ortho- and para-chlorotoluene from their mixtures. The action of chlorine on toluene, when cold, in the presence of appropriate catalysts, is exclusively on the nucleus and always provides a mixture of ortho- and para-chlorotoluene.

The separation of the mixtures thus obtained is not practicable by physical methods. In fact, the boiling points of the two isomers are too close to allow fractionation even by the most sophisticated apparatus, and separation by crystallization is practically impossible, given the very low melting point of Portho - chlorotoluene (-340). In the presence of these difficulties, o-chlorotoluene, which constitutes a raw material of very great importance, has always been manufactured industrially until now either by synthetic methods or by indirect methods. (See Erdmann & , Kirchhoff, Ann. Chem. t. 247 p. 368, and German patent no. 294638.) Seelig (Ann. Chem. t. 237 p. making use of both the sulfonating ability of o-chlorotoluene and also the easy crystallization of the salts of its sulfonated derivative, which allows them to be isolated in a pure state by fractional crystallization. Thus, by treating the monochlorotoluene mixture at boiling temperature with two parts highly concentrated sulfuric acid (D = 1.85) or one part fuming acid, he prepared impure para-chlorotoluene, while that by fractional crystallization he obtained sodium or calcium salts of o-chlorotoluene sulphonic in pure form; he does not however succeed in preparing pure para-chlorotoluene in this way with a satisfactory yield and he says - expressly (Ann. Chem. t. 237 p. 155): "that a complete purification by the sulfuric acid seems problematic and that in any way it does not seem applicable with advantage".

However, the meticulous study of the sulfonation of ortho- and para-chlorotoluene has shown the inventors that it is possible to arrive more easily at a separation of ortho- and para-monochlorotoluene from their mixtures, if the mixture of the two monochlorotoluenes 6 is subjected, the partial srlffonation is subjected to temperatures considerably below the boiling point of the monochlorotoluenes.

This partial sulphonation can be interrupted before all of the ortho derivative has been attacked and the ortho-chlorotoluene sulphonic acid separated from the mass can be transformed back into ortho-chlorotoluene by simple hydrolysis. Alternatively, the partial sulfonation can be interrupted when all of the ortho derivative as well as a small proportion of the para derivative have been transformed into sulfonic acids, the unaltered para-chlorotoluene which remains being subsequently separated from the mass.

Example r: 40 Parts of a mixture of monochlorotoluines containing 60% ortho derivative and 40% para derivative are heated in an apparatus equipped with a stirrer with 75 Parts of ordinary sulfuric acid at 93-93.5% of SO4H at a temperature of 114-11511 for about 2'/-" hours. At this moment, an stops the operation and separates the supernatant oil by a current of steam. Parts of a mixture of monochlorotoluene boiling at 158-160 0 crystallizing at -41, and having the following analytical composition: 4.2 Parts or 21% of o-chlorotoluene 15.8 Parts or 79% of p-chlorotoluene The sulphonation therefore focused only on the ortho isomer, since more than 98% of the para derivative contained in the original mixture is thus recovered.

The sulfuric solution, which remains after steam stripping, contains the sulfonic acid of ortho-chlorotoluane

was compiled by Wynne (Chern. Soc. t. 61 p. 1072, 1892). This solution is concerrtree to bring its poirrt burrllitiorr to 175 ä. 1850. At this time, the sulphonic acid undergoes hydrolysis and it is sufficient to pass a current of heated water to drag the ortho-chlorotolu6ne with an excellent yield.

Example <I>2:</I> 50 parts of a mixture of monochlorotoluene containing 22% o-chlorotoluene and 78% para-chlorotoluene are heated with 40 parts ordinary sulfuric acid to 93-93, "u 0/0 h 114-115 0% For approximately 3 hours, and the supernatant oil is separated by a stream of steam. 38 Parts of a product boiled at 15-1610 crystallizing at -4.5 0; it constitutes para-chlorotolubne titrating approximately 97 RTI ID="0002.0273" WI="5" HE="4" LX="1451" LY="1077">%, that is That is to say that nearly 95% of the p-chlorotoluene contained in the original household was separated in this way.

Hydrolysis of the remaining sulfuric solution yields a small amount of a mixture of the two monochlorotoluenes which is added in a subsequent operation.

Claims (2)

CLAIM Process for separating ortho- and para-chlorotoluene from their mixtures, characterized in that the mixture of ortho- and para-chlorotoluene is subjected to partial sulfonation 6, at temperatures significantly below the boiling point of monochlorotoluenes. SUB-CLAIMS 1 ProG6d6 according to claim, characterized in that the sulphonation is interrupted before all of the ortho-chlorotoluene has been attacked, that orr separates the mass of the ortho-chlorotoluene sulphonic acid and that it is regenerated to ortho-chlorotoluhe by hydrolysis. 2 Process according to claim, characterized in that the sulphonation is interrupted when all of the ortho-chlorotoluene and a small proportion of the para-chlorotoluene have been converted into sulphonic acid and the mass is separated from the para-chloro-toluene remains unchanged.