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Recently I asked a question on the naming of polyhydroxy phenols. One of them was pyrogallol (1,2,3-Trihydroxybenzene) which is synthesized from gallic acid obtained from oak galls. (BEWARE- not a compound of gallium). enter image description here

But why "pyro"? Pyro is usen in naming inorganic acids like pyrosulfuric acid ($\ce{H2S2O7}$) or pyrophosphoric acid ($\ce{H4P2O7}$). It is also observed that the carboxylic acid derivative is gallic acid not pyrogallic acid and the hydroxy derivative is pyrogallol not gallol. Why is it so?

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    $\begingroup$ pyro- is not a part of systemtic naming, it is a prefix meaning 'fire' and is used with acids or salt preparable via route involving heating. Obviously, there is often more than one acid preparable such way, but only one usually ends with pyro- prefix. Thus, the prefix is not encourged. $\endgroup$
    – permeakra
    Commented Jan 19, 2016 at 16:35
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    $\begingroup$ @permeakra please consider submitting your comment as an answer, as this is precisely the reason.... The formation of that product comes from simply heating. The example in the question shows that nicely. A link to the IUPAC Gold Book may be useful. $\endgroup$
    – long
    Commented Jan 19, 2016 at 18:25
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    $\begingroup$ This question mainly applies to organic chemistry. For the use of the prefix “pyro-” in inorganic chemistry, see also the questions and answers here, here, and here. $\endgroup$
    – user7951
    Commented Jan 20, 2016 at 15:46

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So, as @long and @permeakra stated, the name pyrogallol came from the fact that it is obtained by heating gallic acid. The IUPAC goldbook clearly states that:-

"pyro" is used as a prefix designating compounds formed by heating a compound, usually with the elimination of water, carbon dioxide, or other simple molecule, e.g. pyroglutamic acid from glutamic acid.

So as per rule, it is pyrogallol and not gallol.

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