A new K reagent and efficient enrichment agent for low-concn. K ion, 1,2,4,5-tetrahydroxybenzene-O,O',O'',O'''-tetraacetic acid (I), was synthesized. Its enrichment behavior for K ion in low-concn. solution and the chem. structure of the corresponding K complex salt was investigated. A mechanism for the uptake of K ion is suggested. The synthetic intermediate, 1,2,4,5-tetrahydroxybenzene, was obtained by Zn-HCl reduction of 2,5-dihydroxybenzoquinone with a yield of 72%. A phase-transfer catalyst is used in the synthesis of I (55% yield) under mild condition to avoid air oxidation K is recovered quant. by I from low-concn. solns. (0.03-0.005 mol.dm-3) via precipitation reaction. The enrichment behavior of I for K ion in natural seawater (K+: 380 ppm) and in Laizhou Bay underground brine (K+ 1260 ppm) was studied. The reagent forms a crystalline ppt. with K ion but not with Na, Mg, or Ca ions. The K recovery is almost quant.

Key words: PHENOL P, POTASSIUM, SEA WATER, SOLVENT EXTRACTION, POTASSIUM COMPOUNDS, CONCENTRATION, POTASSIUM CHLORIDE, BRINE, POLYHYDRIC PHENOL, ACETIC ACID P