Solvent-free synthesis and assessment of substituent effects from IR & NMR spectra of some substituted benzylidene-5-ethyl-1,3,4-thiadiazole-2-amines

A series containing ten titled compounds were synthesized by SiO2:H3PO4 catalyzed solvent-free condensation of substituted benzaldehydes and 2-amino-5-ethyl-1,3,4-thiadiazole under microwave irradiation. The yields of prepared amines are more than 90 %. The synthesized amines were characterized by their physical constants and spectroscopic data reported in literature earlier for known compounds. The assigned spectral group frequencies such as infrared νC=N, C-S-C, N-N (cm-1) and NMR chemical shifts (δ, ppm) of CH, C=N have been correlated with Hammett substituent constants, F and R parameters using single and multi-linear regression analysis. From the results of statistical analyses, the effects of substituent on the above spectral data have been discussed.