In a solitary bubble trapped at the antinode of the standing acoustic field in water, the density increase of n-butanoic acid in the bubble quenched the sonoluminescence in consuming the acoustic energy by sonochemical reaction. In the bubbles filled with inert gases (He, Ar, and Xe), the quenching was obvious in Xe, but in He. These observations suggest that He locating at the bubble center reduces the sonochemical reactivity.