Pyrocatechol dibenzoate

Also obtained by reaction of benzoyl chloride with pyrocatechol dibenzoate in the presence of zinc chloride, followed by saponification of the 3,4-di(benzoyloxy) benzophenone formed with a boiling ethanolic sodium hydroxide solution [146]. 

Reaction of pyrocatechol dichloromethylene acetaP (133) with dibenzothiophene in the presence of titanium tetrachloride yields o-hydroxjrphenyl-2-dibenzothiophenecarboxylate (134) (100%). This reaction is closely related to the Rieche formylation of dibenzothiophene (Section VI,F, 1) in which a mixture of 2- and 4-dibenzothiophene-carboxaldehyde was obtained. The complete absence of the 4-isomer in this reaction may be due to steric effects at the 4-position between the sulfur atom and the bulky reagent. Hydrolysis of 134 yields 2-dibenzo-thiophenecarboxylic acid (70%). 4-Methyl-3-dibenzothiophenecar-... 

Ion-associates of niobium anionic complexes with pyrocatechol [18], or oxalate [19], and quaternary ammonium ions have been used for separating Nb from other refractory metals (Ti, W, Mo, V). Niobium has been extracted from solutions containing Fe(III), Ti(IV), and V(IV) with the use of 4,5-dibromopyrocatechol [20]. The crown-ether dibenzo-18-crown-6 has also been used for the extraction of Nb [21]. Tantalum has been separated from V (in 6 M HCl) by extraction into triphenylphosphine oxide in toluene [22]. 

---