Benzylidene picramates of zinc, cadmium and mercury have been prepared by treating the corresponding aqueous sulphate and chloride solutions with sodium salt of 4'-dimethylaminobenzylidence-2-hydroxy-3, 5-dinitroaniline. A metal: ligand ratio of 1:2 has been established in all these cases. I.R. spectral studies of metal benzylidene picramates show N-M coordination (where M is zinc, cadmium or mercury). Explosive properties of these benzylidene picramates have also been studied and it was found that the thermal stability increases as the atomic radius decreases or ionization potential increases

Agrawal, S. P.

Bhargava, H. N.

Srivastava, R. S.

English

Defence Science Journal

CHEMISTRY OF METAL (BENZYLIDENE) PICRAMATE-PART I11 BENZYLIDENE PICRAMATES OF ZINC, CADMIUM AND MERCURY M.G. Degree College, Gorakhpur Goralrhpur University, Gorakhpur (Received 15 June 1978; revised 12 Ocfaber 1978) Benzylidene picramstes of zinc, cadmium and mercury have been prepared by treating the oorresponding aqueous sulphate and chloride solutions with sodium salt of 4/-dirnethylaminobenzylidene-2-hydroxy-3, &din!- troaniline. A metal : ligand ratio of 1:2 has been established in all these cases. I.R. spectral studies of metal benzylidene picramates show N +M coordination (where M is zinc, cadmium or mercury). Explosive properties of these benzylidene picramatea have also been studied and i t  was found that the thermal stability increases as the atomic radius decreases or ionixation potential in~reases. A number of explosive properties of metal picrates and picramates have been studied by various war- kers 1-6. Little work, however, seems to have been carried out on benzylidene picramates of metals. The present communication deals with the chemistry and explosive properties of zinc, cadmium and mercury benzylidene picramates. All the chemicals used were of AnalaR grade (BDH). 4'-Dimethylaminoben~ylideqe-2-h~dr0~~-3, 5-dinitroaniline was prepared by refluxing picramic acid and @-dimethylamino-benzaldehyde at 1000 C in ethanol for 3-4 hours in 1 : 1 molar ratio. Sodium benzylidene picramate was prepared by suspending a known weight of 4'-dirnethylaminobenzylidene-2-hydroxy-3, 5-dinitroaniline in water and then treating it with an equivalent amount of sodium bicarbonate. The resulting mixture was digested on water bath to ensure complete reaction. After cooling, the product was filtered and washed with ice. cool water. Red crystals of sodium benzylidene picramate were obtained. The general method employed for the preparation of metal benzylidene picramate is similar to that employed for metal picramates. The benzylidene picramate in question is simply prepared by adding a solution of an appropriate salt of the metal to a solution of sodium benzylidene picramate. For =ample, the benzylidene picramates of zinc, cadmium and mercury was precipitated from zinc sulphate, cadmium chloride and mercury chloride respectively. After keeping the reaction mixture overnight, the precipitate was separated by filtration, washed with water and ethanol and dried in a vacuum desiccator to cons- tant weight and analysed for its constitvents. This simple procedure was employed in the preparation of all these compounds. Results of microanalyses are listed in Table 1. I Spectrophotometric (visible) measurements were carried out with the help of a Unicam SP 8000 recording Spectropho$ometer and a Unicam Spectrophotometer number 23704. (Job's continuous varia- tion method7). The pH measurements were carried out with a Leeds and Northrup Co. (Philadelphia, U.S.A.) @H meter. The electrical conductances of the solutions were measured with a Toshniwal's conductivity bridge (type CL01/02). Job's monovariation method7 was employed to determine the composition of these complexes. I.R. spectra of the complexes were recorded with the help of a Perkin- Elmer Infrared Spectrophotometer model 337 using KBr pellet technique in the range of 400-4000 ,-m-1. T.G. was carried out on a thermogravimetric analyser supplied by Planning and Development Division, Fertilizer Corporation of India, Sindri Bihar. The magnetic susceptibility measurements were carried out with the help of Gouy's method using a semirnicro balance and a field of 1000 gauss at room tern- pyature (303OK). 1. E X P L O S * I V E  P R O P E R T I E S  The compounds used for the measurements of explosive properties were dried at 373-383OK for 2-3 hours to constant weight. DEE SUI. J., VOL. 29, A ~ I L  1979 The explosive properties like explosion delay, explosion temperature, activation energy and explosion pressure were measured in a manner similar to that reported in an earlier communication6. For measuring explosion delay ( DE ), approximately 20 milligrams of the prepared compound was taken in a small pyrex tybe (diameter 0.96 cm and thickness 0.14  cm) at the room temperature. The tube was then suddenly plunged into a paraffin liquid bath maintained at 595' K. The interval between the time of insertion and the moment of explosion was noted with the help of a stop watch. A mean of three reading was taken as the final reading in each case. Values of DE re given in Table 2. To measure explosion temperature (TE ), the above experiment was carried out at various tempra- tures in potassium hydrogen sulphate bath (instead of liquid paraffin) and DE was plotted against the tem- perature of the bath. Explosion temperature was read off from this plot as the temperature necessary to cause explosion in exactly 10-seconds. Results are recorded in Table 2. / Thermal setisitivity of an explosive is related to the activation energy controlling* DE E log DE = - 4.57 T S B ( T  is the absolute temperature of the bath in which the experiment is carried out). Curves obtained by plotting DE against 1/T are given in Fig. 1.  Fig. log DE with reciprocal of absolute temperature. A=Zinc benzylidene benzylidene picram.ate and C=mercury benzylidene picramate. Explosion pressurt was measured in a manner similar to that employed by Yoffe9 for studying thermal decomposition of azides. Instead of silicone oil potassium hydrogen sulphate was used in the bath in which explosion was carried out. The results obtained are listed in Table 4. R E S U L T S  A N D  D I S C U S S I O N  I Result are recorded in Tables 1-5 : Plots of DE against 1 / T  are given in Fig. 1 (valses of E obtained by these straight line curves are given in Table 3)" SRIVASTAVA, et at. : Chemistry of Bletal Benzylideae Picramate .-.--- Complex* M N Ha0 (%I (%) (%) Zn[C,H,(NO,)sNO.N(CH,)B (HaO)la . 9 .O 15 .o 4 -9 (8 (14.7) (4.7) *Setisfactory 0 , H  analysas were obtained for all complexes. Calculated values are given in parentheses. EXPLOSION DELAY AND EXFLOSION TEMPERATURE FOB THE METAL BENZYLIDENE P ~ R A B U T E S  I Complex Explosion Explosion temp. for delay a t  593% explosion delay of (mc.1 10 seo (K) Zin c benzylidene picramate 60 a 3  694f 2 pdmium benzylidene picramate 35 .4 646k2 Mercury benzylidene picramate 9 .I 5829 VALUES o r  E BOB D ~ F E R E N T  COMPOUNDS - Com~lex Activation energy (KJImde) *. 78 -50 Zino benzylidene pioramate Cadmium benzylidene picramate 62.22 Mercury benzylidene picramate 51 ~70 EXPLOSION PRESSURE FOR DIFERENT COYPOUNDS DENSITY OW XEROUBY =13 '595 glml; GRAVITATIONAL ACCELERATION (g) =980e665 om Seca) Complex Height (m) Explosion pressure* (bath temp. 623&2OK) (lllnlllna x 109 Zino benzylidene picramate 0 .lo60 14 -00 Cadmium benzylidene picramate 0 4890 11 -87 Mercury benzylidene picramate 0 ~0830 11 -06 I *The Explosion pressure was obtained by taking 10 mg of the explosive material. Compound Characteristic absorption frequencies (am-1) r ' .  -- Metal-Nitrogen Coordinated water - 8 1 ~ ~  p-Dimethylamino benzylidene picramic acid - - 1630 Zn- (11) p-dimethylamino benzylidene picramate 495 700 1618 Cd-.(II) p-dimethylltmiso benzylidene picramate ' 478 730 1616 Hg-(11) p-dimethylamino beneglidene picramate 490 680 I606 In all the cases, the spectrophotometric (visible), potentiometric and conductometric studies and micro-analysis point to the formation of complex in the metal : ligand ratio of 1 :2. The general formula may be expressed as where M stands for zinc (II), Cadmium (11) or mercury (11). Table 5 give some characteristic absorption frequencies in the Schiff base and its metal derivatives in the IR region. Absorption. associated with -N=C deformation mode is expected to appear near 1640 cm-1'10-12 In Schiff base a band appears at 1630 cm-1 while in the metal complexes it is found in the region 1620-1600 cm-1. The lowering in the -N=C frequency in the complexes is due to the coordination of-N=C with the metals 11J3. Other bands appear in the region 1600-1300 cm-1 and are due to ring deformation modes. Coordinated water gives bands in the range 880-650 cm-1. 14315. In the Schiff base a band is present near 3475 cm-1. This could be assigned to the phenolic group which normally absorbs in the region 3600-3500 cm-1. The shift in the absorption peak is due to the intramole- cular hydrogen bond present between the hydrogen of the phenolic group and the oxygen of the nitro group ortho to each other12,16,17. However, a band in the region 3600-3400 cm-I could also be due to the presence of water moleculesl8 and is not influenced by coordination. But, hydrogen-bonding in the complexes is expected to disappear completely due to ionization of the labile hydrogen and coordination of the negative oxygen with the metal concerned. Thus, benzylidene picramic acid has two centres of coordination, viz. the nitrogen of the -N=C group and the oxygen of the phenolic group. In addition to these frequencies a frequency is observed between 500-300 cmml. This may be assigned to the metal-nitrogen stretching modes similar to the metal-nitrogen stretching modes ie metal glycine complexes assigned by Nakamuralg. The metal-oxygen stretching frequency has been reported at 360-260 cm-1.20,21. However, Lane e t .  al. 22 assumed that metal-oxygen vibration appears below 200 cm-1 because metal-oxygen band is highly ionic. The magnetic susceptibility measurementsFarried out by us show that these benzylidene picramatea are diamagnetic. This is also what we would expect for dl0 ions14. A gravimetric estimation of coordinated water mo!ecules show that two molecules are present in each of these complexes. The fact that a bidentate ligand is involved and two water molecules are coordinated to it points to an octahedral geometry for these complexes which can be represented as shown in Fig. 2. 5 0 10 I 100 200 300 1 SOD. TEMPERATURE (*c Wg. 2--Structural formula of metal (benzylidene) picramatea [va atan& for Zw (II), Cd (11) or Hg (II)]. Fig. 3-Thermogravimetrir analysis of metal-benzylidene picramates (A=Zinc bezylidene picramate, B=Cad- mium benzylidene picramate & C=%ercurg benzyli- dene picramate. SRIVA~TAVA, el al. : Chemistry of Metal Benzyliderne Picramate From the T.G. study (Fig. 3) it has been observed that the zinc and cadmium benzylidene picramates explode at 553°K and 513OK respectively while mercury benzylidene picramate does not explode even up to 673OK. As obvious from the T.G. curve in the case of mercury complex, the loss in weight is accompanied by elimination of water molecules. A change in curve between 473-513OK clearly indicates that the com- plex is decomposed into mercury oxide. After 513QK a nearly constant weight is obtained which indicates that the complex is completely decomposed into mercury oxide between 473-513°K. On the basis of the above discussion it may be concluded that the zinc benzylidene picramate is thermally more stable than the analogous complexes formed by cadmium and mercury. These conclusions are further supported by the data on explosive properties viz. explosion delay, explosion temperature and activation energy. For example, the ex losion temperature, (YE) follows the order: TE (Zn complex) TE (Cd complex) TE (Hg complex), w 1 ich is the same as that observed in T.G. Studies. I t  may be con- cluded that the thermal stability increases as the ionic radius decreases or ionization potential increases. This has also been established by various other workers 23-25. On the basis of the value of bond dissociation of different linkages present in the metal benzylidene picramates, it may be suggested that the initial stage in the explosion reaction is the breaking of the N - 0  linkage 228329 of the -NO2 group directly linked to the benzene nucleus. This then enables the oxygen which was linked wholly to nitrogen to be consumed for the complete oxidation of carbon and hydrogen obtained from the ring rupture and thus produces a huge amount of heat. A C K N O W L E D G E M E N T  The authors express their sincere thanks to Professor R.P. Rastogi, Head, Department of Chemistry Gorakh~ur University for constant encouragement and for laboratory facilities. Thanks are also due to the Director, Central Drug Research Institute, Lucknow for spectral (I.R. and visible) and elemental analyses. R E E ' E R E N C E S  1. QLOWAK, B., Chemia Stosowasa, 5 (1961), 575. 2. AURAWAL, S. P. & AGRAWAL, J. P., Indian J .  Chem., 7 (1969), 1264. 3. AURAW~L, S. 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Chemistry of Metal (Benzylidene) Picramate-Part III Benzylidene Picramates of Zinc Cadmium and Mercury

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Chemistry of Metal (Benzylidene) Picramate-Part III Benzylidene Picramates of Zinc Cadmium and Mercury

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