It forms a stable cyclic complex with polyhydroxy compounds like cis-glycerol, catechol, etc. This helps in the release of ${\mathrm{H}}^{+}\mathrm{a}\mathrm{s}\mathrm{ }{\mathrm{H}}_3{\mathrm{O}}^{+}$ therefore, boric acid acts as a strong acid and hence can be titrated with sodium hydroxide using phenolphthalein.