Halogen substituted benzoic acids were proposed for organic-organic heteroepitaxy in semiconductor industry for the many parameters, like hydrogen disorder or molecular polarizability, that could be varied in order to affect the crystallinity and orientation of the growing semiconductor. Neutron diffraction (ND) has recently evidenced that positional disorder on the hydrogen atoms site appears in IBA only above 100K, i.e. there is a temperature offset of about 100K in the energy necessary for the proton hopping, as compared to the hydrogen disorder in BA. Moreover, Anisotropic Displacement Parameters in IBA are consistent with a low frequency out-of-plane libration of the COOH group, not present in BA. This proposal aims at mapping the ND evidenced differences in the onset of the dynamic disorder in BA and IBA by comparing the anisotropy of proton momentum distributions in BA and IBA.