Chemistry has a bit of background in ontologies, and ChemAxiom is certainly not the first (though I think it is rather promising…). Three years ago I gave a presentation at the CUBIC (now existing as LinkedIn Alumni Group), which is not so extensive, but does have a few interesting citations on the use of ontologies in chemistry on slide 16:

Image of the first slide with the title, name, and date

This post was originally posted as https://chem-bla-ics.blogspot.com/2009/07/knowledge-management-ontologies.html.