SYNTHESIS AND PROPERTIES OF 3-SUBSTITUTED , 4-SUBSTITUTED AND 5-SUBSTITUTED 2-PYRIDINECARBALDEHYDE 5-NITRO-2-PYRIDYLHYDRAZONES AND CHARACTERIZATION OF THEIR METAL-COMPLEXES

Eight new hydrazones derived from 2-pyridinecarbaldehyde 5-nitro-2-pyr idylhydrazone (PA-5-NPH) were synthesized. Their properties, reactivit ies with metal ions and extractabilities of the complexes have been in vestigated and compared. It has been found that (1) the introduction o f a nitro group to the 3-, 4- and/or 5-position of the pyridine ring i n the aldehyde moiety of PA-5-NPH lowers the pK(a) values and causes r emarkable bathochromic shifts in the absorption spectra of the hydrazo ne and its metal complexes, (2) the introduction of a nitro group to t he 5-position of the pyridine ring brings about increases in molar abs orptivities of the metal complexes, whereas introduction to the 4-posi tion causes them to decrease, and (3) the introduction of electron-rel easing groups to the 4-position of the pyridine ring, on the contrary, brings about increases in molar absorptivities of the metal complexes . Furthermore, considering the results reported already, it is conclud ed that the introduction of a nitro group to the 5-position of the pyr idine ring in both the hydrazine and aldehyde moiety of 2-pyridinecarb aldehyde 2-pyridylhydrazone (PAPH) is very effective for increasing th e molar absorptivity of the metal complexes.