We explored hydrogenation reaction with a para-spin isomer of a hydrogen molecule as a source of nuclear singlet state. As a product of this reaction, the state was populated between two protons of the methylene group. We have shown that, utilizing long-lived properties of such a nuclear spin state, a high nuclear spin polarization can be accumulated. To explain this effect we have given a kinetic model which could be potentially applied for similar schemes involving spin dynamics in chemistry.