[AJ]

I did a pracitical on Gas Chromatography to detect the presence m-,p- and o-xylene and and unknown in a commerical xylene. I need to identify the major component and why this may be so.
Based on the peaks, I have concluded that m-xylene is the major component as it appears(if I have read this correctly) to have the largest area. In order to explain why this is the largest component I imagine is to do with the stability of this isomer? I know I have to make reference to aromatic substitution but having never studied that before I am not sure what the mechansims or explanation for its stability is...I am reading about it in a book but unfortunatley it is making little sense to me.
any help with explaining this would be greatly appreciated!

[Kithairin]

Hi, I've never studied commercial xylene syntesis, so I can only guess why the meta isomer is the major component.

The reason should be that the xylene is synthethised form a benzene which undergoes two consecutive Friedel-Crafts acylations, and the two formyl groups (which will be reduced in the next step to methyl, probably a Clemmensen reduction) are mostly located in meta position because the acyl group is a meta-directing group, so the first formyl group directs the second formyl group mostly into the meta position.

[orgopete]

This is one of those air, fire, and water questions that doesn't have a normal introductory organic chemistry answer. Xylene comes from toluene.

From a Google search,

BACKGROUND OF THE INVENTION

Since the announcement of the first commercial installation of Octafining in Japan in June, 1958, this process has been widely installed for the supply of p-xylene. See "Advances in Petroleum Chemistry and Refining" volume 4 page 433 (Interscience Publishers, New York 1961). That demand for p-xylene has increased at remarkable rates, particularly because of the demand for terephthalic acid to be used in the manufacture of polyesters.

Typically, p-xylene is derived from mixtures of C 8 aromatics separated from such raw materials as petroleum naphthas, particularly reformates, usually by selective solvent extraction.

Principal sources are catalytically reformed naphthas and pyrolysis distillates. The C 8 aromatic fractions from these sources vary quite widely in composition but will usually be in the range 10 to 32 wt.% ethyl benzene with the balance, xylenes, being divided approximately 50 wt.% meta, and 25 wt.% each of para and ortho.

An increase in temperature of 50°F. will increase the equilibrium concentration of ethyl benzene by about 1 wt.%, ortho-xylene is not changed and para and meta xylenes are both decreased by about 0.5 wt.%.

Individual isomer products may be separated from the naturally occurring mixtures by appropriate physical methods. Ethyl benzene may be separated by fractional distillation although this is a costly operation. Ortho xylene may be separated by fractional distillation and is so produced commercially. Para xylene is separated from the mixed isomers by fractional crystallization.

As commercial use of para and ortho xylene has increased there has been interest in isomerizing the other C 8 aromatics toward an equilibrium mix and thus increasing yields of the desired xylenes.