In this paper we exemplify a biased synthesis that can be relevant in primitive scenarios. We perform experiments simulating a possible prebiotic environment, in which an organic compound is adsorbed in soil and exposed to an energy source. To this end, carboxylic acids were adsorbed in a clay mineral and the systems were exposed to radiation. We observed that radiation decomposition in solution changes drastically if the system contains a clay mineral. Both solid surfaces and radiation play an important role.