Preparation of some azo compounds by diazotization and coupling of 2-amino -5 – thiol -1,3,4-thiadizaole

: 2-amino -5- thiol-1,3,4-thiadiazole (S 1 ) was prepared by cyclic locking of thiosemicarbazide in the presence of anhydrous sodium carbonate and CS 2 . diazotization of (S 1 ) compound gave diazonium salt (S 2 ) that reacts with different activated aromatic compounds to get the following azo compounds ,2 [(4-aminophenyl) diazenyl ] 1,3,4- thiazdiazole-5-thiol (S 3 ) ,2-[4-amino-1-naphthyl diazenyl] -1,3,4 – thiazdiazole-5-thiol (S 4 ) , 3-amino-4-[(5-mercapto -1,3,4-thiadiazole -2-yl) diazenyl ] phenol(S 5 ) ,1-[(5-mercapto-1,3,4-thiadiazole-2-yl) diazenyl] -2-naphthol (S 6 ) , 5-{[4-(dimethylamino) phenyl] diazenyl}-1,3,4-thiadiazole-2-thiol(S 7 ) ,5-{[4-(diethylamino) phenyl] diazenyl}- 1,3,4- thiadiazole-2-thiol(S 8 ) ,2- amino-5-[(5-mercapto-1,3,4-thiadiazole-2-yl) diazenyl] phenol(S 9 ) . All the prepared azo compounds have been characterized and identified through the study of their some physical, chemical and spectrometrical (U.V.I.R) properties.


Introduction:
The azo group (-N=N-) brings the two aromatic rings into conjugation and extends their electrons system (1).As a result, azo compounds revealed absorption in the U.V. absorb visible region of electromagnetic spectrum.The intense color and easy low cost preparation of azo compounds enhanced the utilizing of azo compounds as a fabric, as food coloring additives ,dyes(2)and as antibacterial -fungal (3,4).
Azo compounds could be prepared by oxidation of hydrazine derivatives, amines and urea by different reagents (5).In practice , the diazo coupling reactions occur with the activated aromatic ring at the Para position and take place at ortho if the para is blocked (1) .Two azo insomers are from each S 5 and S 9 groups are expected since -NH 2 , -OH are strongly directed to ortho/ Para positions

Results and discussion
Reaction of thiosemicarbazide with carbon disulphide in the presence of anh.Sodium carbonate gave 2-amino-5thiol-1,3,4-thiadiazol (S1) as a greenishyellow solid.The structure of S1 was approved by m.p. (230-232o)6.Tautomerisim give the probability that makes the structure of the compound (S1) as a hybrid between thione and thiol form (7). As mentioned before, diazo coupling reactions are carried out with different activated aromatic compounds to get the fowling azo compounds.

Fig -A -
All the prepared azo compounds are identified and characterized by I.R and U.V spectra (Table 1,2).I.R spectra showed a weak band at 1500-1595 cm -1 for all azo compounds indicating the presence of (-N=N-) group.U.V. spectra showed absorptions for n-  and -  transitions.A considerable differences were observed in the values of i.r. and u.v.absorptions of azo compounds due to the presence of chromophors and auxochromes that shifts the absorptions to longer wave length. (7,8)(Tables 1,2,3).

Experimental
All chemical used in this work were the highest analytical grade.Melting points were determined with a Gallen-Kamp apparatus.I.R., U.V. spectra were recorded on a Pye-Unicom Spectrophotometer.
in which the diazonium cation is the electrophile.
Diazotization mechanism of S1 involved a critical intermediate that is dinitrogen trioxide which furnishes a good leaving (NO2-) by the lewis basic nitrogen of amino group. ).