Wolf is right. But the more trivial name tetrachloroguajacol is used in English too, in this, slightly different version. The reference is German, and is the only hit found in Google, but the non-chlorinated guajacol gives many hits. Trivial names like guajacol for the slightly longer, but more systematic o-methoxyphenol, are used often in English, more often than in many other languages, I'd say.