Seven two ring chiral benzoates with different terminal substituents being isotropic liquids or low temperature monotropic compounds were tested as dopants inducing ferroelectricity in non-chiral S-c mixtures composed from esters. It was found that some of them strongly enhance the stability of smectic C in four component ester mixture up to the concentration of 30 wt.%. The spontaneous polarization Ps, the tilt angle theta, and both parts of complex dielectric permitivity of the doped mixtures upon dopant concentration and temperature were investigated.