It's not that the compounds he listed are dangerous or illegal per se, but they are highly unusual in traveler luggage. Therefore nobody knows whether these compounds (or their oxydation products, or random impurities) can trigger a false alarm in some explosive detector or whatever. And once that alarm has gone off ... well, that's been covered in this thread already. I get enough trouble with my RZ67 plus roll film every single time I fly anywhere.

Please also think that it may or may not be legal to mail/UPS/Fedex random chemistry across the globe, there's a chance you need a license to do that. Misrepresenting the contents of your parcel may open you to lots of other problems. If random white crystalline powder packages could be simply mailed internationally by anyone, northern Mexico would be in better shape.

In your situation I would either look for local vendors at the place you go to, or have some chem supplier ship it there. At least they know the regulations.