phenolsulfonic acid
noun
phe·nol·sul·fon·ic acid
variants:
or chiefly British phenolsulphonic acid \ ˌsəl-ˈfän-ik, -ˈfōn- 
\
\
Medical Definition of phenolsulfonic acid
: a sulfonic acid derived from phenol
especially
: a crystalline acid C6H6O4S used chiefly as an intermediate for dyes and pharmaceuticals