0.087 g (0.444 millimole) of barium carbonate are suspended in 15 ml of methanol whereupon 0.11 g (0.91 millimole) of benzoic acid is added. The suspension thus obtained is heated to boiling until a clear solution is obtained. The clear and colorless solution is added to a suspension of 1.0 g (0.887 millimoles) of primycin sulfate and 80 ml of methanol and the reaction mixture is heated to boiling for 20 minutes under stirring. The hot solution is filtered through Celite and the filtrate is evaporated to dryness in vacuo. The residue is treated with ether, filtered and the solid is washed on the filter with 15 ml of a 2:1 mixture of acetone and water. Thus 0.98 g of primycin benzoate is obtained in the form of a white powder, yield 90.6%. Mp.: 170°-171° C., /α/D25 =+36.9°.
