Semicarbazide Hydrochloride Synthesis Essay

Synthesis of 3-[5-(4-substituted) phenyl-1,3,4-oxadiazole-2yl]-2-styrylquinazoline-4(3H)-ones was carried out by following steps:
Step 1: Synthesis of 4- substituted benzaldehyde semicarbazon51(2)
Semicarbazide Hydrochloride (0.1M) and sodium acetate (0.2M) was added and dissolved in 15-20ml of distilled water placed in flat-bottomed flask. In a separate beaker containing required aromatic aldehyde (1) (0.1M) was dissolved in aldehyde free alcohol. This ethanolic aromatic aldehyde solution was added slowly to the solution of semicarbazide hydrochloride. The precipitate, which gets separated, was filtered, dried and recrystallised from 95% hot ethanol.

Table 1: Quantity of aldehydes taken
S. No. Aldehydes Molecular weight Quantity taken

CH3 175 83.06% 287-289ºC
4. -OCH3 191 86.03% 275-277ºC
5.

204 78.78% 295ºC

Step-3 Synthesis of 2-Methyl benzoxazin -4(3H)-one53 (4) Anthranilic acid (0.1M, 18g) was taken in acetic anhydride and refluxed under anhydrous conditions for 4 hrs. Excess of acetic anhydride was then distilled off under reduced pressure. Obtained product was immediately used for next step.
Step-4 Synthesis of 2-Methyl-3-[5-(4-substituted)phenyl-1,3,4- oxadiazole-2-yl]- quinazoline-4(3H)-ones53 (5)

To the mixture of benzoxazinone (4), 2-Amino-5-aryl -1,3,4-oxadiazole (0.1M) in 100ml of glacial acetic acid was added and refluxed under anhydrous condition for 4 hrs. After cooling it was poured into crushed ice. The solid separated out was filtered thoroughly washed with cold distilled water, dried and recrystallised from hot ethanol (95 %).

5

Table 5 : Quantity of Oxadiazoles taken for synthesis
S.No. Oxadiazoles Mol. Wt. Quantity taken in g
1 2-Amino-5-phenyl-1,3,4-oxadiazole 161 16.1
2 2-Amino-5-(4-chloro)phenyl-1,3,4-oxadiazole 195.5 19.55
3 2-Amino-5-(4-methyl)phenyl-1,3,4-oxadiazole 175 17.5
4 2-Amino-5-(4-methoxy)phenyl-1,3,4-oxadiazole 191 19.1
5 2-Amino-5-(4-dimethylamino)phenyl-1,3,4-oxadiazole 204