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The funny thing is, the EXACT same question has been asked in a chemistry forum. 
It looks to me like a Nucleophilic Aromatic Substitution Reaction. (I could be wrong about the second step because I've no idea what the steps/intermediates look like.)It would be nice to know what steps you tried, since that says a lot about where the reaction is going or if there's something you overlooked.What I can say is that Thiophenol is an activating group so it stabilizes positive charges at the para and ortho positions. The Diazonium ion is reactive because it his highly nucleophilic. Unfortunately, the diazonium at the para-position is in a sense 'deactivated' leading to no further substitution by SH-. I have no idea how you get the quinone from this, but I suspect the HNO2 to be responsibleThe Meta Position is unaffected substantially by this and so reaction can go. (if you go draw the canonical structures)The Ortho Position I find interesting. The presence of such an electron-rich S atom (which is huge) and the bulky N2+ group in such close proximity makes me believe that there should be a lot of steric strain around this area. I would go so far as to think that an S-N bond will form but obviously that doesn't happen since we're supposed to get our 1,2. At this point I'm guessing. Electrons don't stabilize the 2-position and thus still allow for a nucleophilic attack at the point? The steps would really help in drawing mechanisms to see what might actually be going on.
The thing is he was able to get the ortho and the meta products, but it did not work for the para!!!
Too easy? You really think so? 
That is because I was the one who asked it on chemicalforums.com You can also find the same question on yahoo answers