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?

  • $\begingroup$ 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
  • $\begingroup$ 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
  • $\begingroup$ I had also watched a video on you tube claiming both option B and D check ques. 30 of uploaded link youtu.be/9J-SPkoPTno. $\endgroup$ – Harsh jain May 13 '19 at 13:37

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