Synthesis, Characterization of some New 1, 3, 4-Oxadiazole derivatives based on 4- amino benzoic acid

In this research various of 2,5-disubstituted 1,3,4-oxadiazole (Schiff base, oxothiazolidine , and other compounds) were synthesized from 2,5-di(4,4′amino-1,3,4oxadiazole ) which use quently synthesized from mixture of 4-amino benzoic acid and hydrazine in the presence of polyphosphorus acid. The synthesized compounds were characterized by using some Spectral data (UV, FT-IR, and 1H-NMR).


Introduction:
Heterocyclic compounds are those cyclic compounds in which one or more of the ring carbons are replaced by another atom.Oxadiazole are aromatic rings with three hetero atoms, two nitrogen and one oxygen atoms, where N and O as donor atoms, and resemble to the triazole ring in that they belong to the same aromatic hetero-cyclic class.1,3,4-Oxadiazole is the most thermally stabilized isomer which has attracted special attention, this is primarily due to the large number of uses in many diverse areas, including drugs, scintillation materials, dyes [1] and surface active agents [2].It has been reported [3].Those hetero-cycles such as oxadiazoles are themselves important chemotherapeutic agents and exhibit antitubercular, bacteriostatic, hypoglycemic, antiviral, antifungal, antithyroid, carcinostatic and strong herbicidal activities when properly substituted in 2-and 5-pos-itions.Variously 2, 5-diaryl-2, 5-dialkyl-and 2alkyl-5-aryl-1,3, 4-oxadiazoles showed herbicidal effect especially against broad leafed weeds and grasses in crops such as rice and corn [4].

Materials and Methods:
The FT-IR spectra in the range (4000-200) cm-1 were recorded as KBR disc on a Shimadzu IR prestige -21 spectrophotometer ,UV-visible spectra in the range (200-1100) nm wererecorded on a using Shimadzu UVvis .160A.UItra-violet spectrophotometer.Melting points were recorded on a hot stage Gallen Kamp melting point apparatus.
1H-NMR spectra were recorded 400 MHZ operating at 400 MHZ with tetra methylsi-lane as internal standard in CDCI3 and DMSO-d6 as solvent measurements were made at Mangdil chemical and pharm-aceutical center Wuhan City China.All chemicals used were analytical analar and of highest purity available from BDH, Fluka and Aldrich companies.

Results and Discussion:
The synthesized of compounds (1-10) were shown in Scheme (1) and Scheme (3).The structure of the synthesized compound (1) has been characterized and confirmed by FT-IR spectrum besides UV/Vis spectrum.The FT-IR spectrum of compound (1) in Figure (1) shows the appe-arance absorption band in the range (3460-3363) cm -1 which could be attributed to asymmetric and symmetric stretching vibr-ation of the (NH 2 ),the (-C=N) stretching band at (1596) cm -1 of the oxadiazole ring.Other bands were also absorbed in FT-IR spectrum of this compound which are listed in Table (2).The Uv/Vis spectrum of compound (1) Figure (6) showed the absorption bands at (227nm) (208nm), due to (n → π ⃰ ) and (π → π ⃰ ) transition.
The structure of the synthesized compound (2) has been characterized and confirmed by FT-IR spectrum.The FT-IR spectrum of compound (2) in Figure (2) shows the (NH) band at (3213) cm -1 [11], the (C=S) band at (1176)cm -1 .Other bands were also absorbed in FT-IR spectrum of this compound are listed in Table (2).
Compound (3) was synthesized from the reaction between compound (2) and hydrazine anhydrate.The structure of the synthesized compound (3) has been charac-terized and confirmed by FT-IR spectrum besides Uv/vis spectrum.The FT-IR Spectrum of compound (3) in Figure (3 ) shows the appearance absorption band at (3417-3406)cm -1 due to the asymmetric and symmetric stretching vibration of the (NH 2 ) group and appearance the (NH) band at (3255)cm -1 and the (C=S) band at (1257cm -1 Other bands were also absorbed in FT-IR spectrum of this compound which are listed in Table (2).The Uv/Vis spectrum of compound (3) Figure (7) showed the absorption bands at (281nm) (258nm), due to(n→ π ⃰ ) and (π→ π * ), and (n→ δ ⃰ ) at (231 nm) transition.
The structure of the synthesized compound (4) has been characterized and confirmed by FT-IR spectrum .The FT-IR spectrum of compound (4) in Figure (4) shows the (NH) band at (3236)cm -1 ,the (C=S) band at (1176)cm - 1 , and(C-Cl) band at (771)cm -1 .Other bands were also absorbed in FT-IR spectrum of this compound are listed in Table (2 ).
The compounds (5-7), were synthesized from the reaction between compound (1) and several aldehydes in absolute ethanol and glacial acetic acid.The structure of the synthesized compounds (5-7) has been characterized and confirmed using FT-IR spectra besides Uv/vis spectrum and the 1 H.MR spectra.