As a rule of thumb, it is known that a pKa difference between an organic acid and the protonated base exceeding 3 ie, ΔpKa = pKa(baseH + ) -pKa(acid) > 3 favours the formation of salt while ΔpKa < 1-2 leads to a co-crystal formation. A large-body of experimental data has confirmed this empirical observation. Nevertheless, there have been several reports particularly for ΔpKa ~ 2-3 where the state of the crystal lies intermediate between a co-crystal and salt. It is also worthwhile to mention that the ΔpKa rule must be strictly limited to equimolar mixtures of acids and bases. For example, in the case of the 1:4 pyridine-formic acid mixture, a salt-like crystal is formed. Steed and co -workers have reported that pressure produces a salt for the 1:2 pyridine-formic acid at ~ 10 kbar. Recent progress in experimental high-pressure chemistry in solids have provided an access to understanding the behaviour of matter under compressions. Crystals can be subjected to pressures as high as 100 GPa within specifically designed pressure transmission media within diamond anvil cells. At the same time significant development in the field of computational crystal structure predictions (CSP) under pressure has provided exciting new properties for materials which were otherwise unknown. Ashcroft and co -workers have shown that benzene transforms into a saturated polymeric network at 100 GPa. Similarly, the molecular crystals of ferrocene get polymerized in one-dimensional metallic chains at 220 GPa. Rahm et al. have found that the electronic configuration of elements change significantly under compression. Recently, we have shown under at a mild compression Fe(CO)4 planarizes into a square-planar complex and the electronic configuration resembles Pt(II) due to facile double-excited [Ar]3d 6 4s 2 (S=2) → [Ar]3d 8 4s 0 (S=0) transition. Under pressure, change in electronic configuration of atoms are reflected in their electronegativity. Rahm et al. have shown that ionic disproportionation of various molecular phases are preferred under compression. For example in case of ammonia-water mixture (NH3…H2O = 1:1) ionic phase NH4 + …OH -stabilizes over NH3…H2O at ~ 6 GPa. Hermann et al. also theoretically predicted that in ammonia hemihydrate (NH3…H2O = 2:1) the fully ionic deprotonated water phases, O 2-…(NH4 + )2 are stable at very high pressure of 65 GPa. For ammonia dihydrate (NH3…H2O = 1:2) case, calculation predicted that unusual ionic phases are stabilized above 11.81 GPa. In this article, we critically explore the effect of compression on the salt -co-crystal duality for acid-base complexes of organic solids. The co-crystal of the 1:1 adduct of pyridine-formic acid forms a pyridinium formate salt at 3 GPa as a consequence of the complete transfer of proton from the acid to the base. Formation of a salt under pressure notwithstanding ΔpKa = 1.46 indicates a violation of the ΔpKa rule. The probability for salt-formation is shown to be strongly correlated with the magnitude of compression. Pressure stabilizes the ionic configurations produced during the salt-formation. The remarkable ability of pressure to stabilize salts of otherwise co-crystal forming adducts is verified for pyrazine…formic acid and pyridazine…formic acid adducts as well.