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My textbook says:

Boric acid is a weak monobasic acid but on addition of certain organic polyhydroxy compounds, such as mannitol, glycerol, dextrose or invert sugar, it is transformed into a relatively stronger acid. Ethylene glycol cannot give this test (reason is uncertain).

I do know that cis-diols form a boron-ether compound with the $\ce{[B(OH)4]-}$, leading to an increase in acidity. But is it true that ethylene glycol is exceptional? And is there any possible reason for it?

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  • $\begingroup$ Maybe it is about the molecular geometries. I can't run the necessary calculations until at least the weekend, though. Would be interesting to know how buta-2,3-diol would behave (but then again, maybe it does not dissolve in water). $\endgroup$ – TAR86 Mar 20 '19 at 15:17
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    $\begingroup$ But a question in iit jee advanced(2014) says that on addition of ethylene glycol too the acidity of orthoboric acid is increased. ques- The correct statement(s) for orthoboric acid is/are (A) It behaves as a weak acid in water due to self ionization. (B) Acidity of its aqueous solution increases upon addition of ethylene glycol. (C) It has a three dimensional structure due to hydrogen bonding. (D) It is a weak electrolyte in water. ans- B,D (official) i am also confused now beacuse its opposite is written in j d lee as per your question $\endgroup$ – Tanmay Singh Apr 20 '19 at 14:36
  • $\begingroup$ But in my institutes exercise book the question is marked as of jee 2014 but only D option is mentioned as an answer $\endgroup$ – Harsh jain May 13 '19 at 13:29
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    $\begingroup$ Yes it has been written in jd Lee that ethylene glycol don't give this test $\endgroup$ – Kuvcharu May 9 at 1:42
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    $\begingroup$ Will somebody please make a solution of boric acid, check its pH, then add some ethylene glycol to see if the pH decreases, and by how much? It would save time for so many people checking their textbooks. $\endgroup$ – James Gaidis May 9 at 13:54

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