Indian Journal of Pure & Appl ied Physics Vol. 4 1 , November 2003, pp. 844-848

Vibrational analysis of some pyrazole derivatives

T Chithambarathanu, V Umayorubaghan* & V Krishnakumar'

PG Department of Physics, ST Hindu College, Nagercoil 629 002

* PG Department of Chemistry, ST Hindu College, Nagercoi l 629 002 tpG Department of Physics, Nehru Memorial College, Puthanampatti, Trichy 62 1 007

Received 1 6 June 2003; accepted 3 September 2003

The compounds 1 ,3 ,5-triphenyl-4,5-dihydro pyrazole, 1 ,3-diphenyl-5(p-methoxy phenyl)-4,5-dihydro pyrazole and I ,3-diphenyl-5(p-methyl phenyl)-4,5-dihydro pyrazole were prepared. The FfIR and laser Raman spectra of the compounds are recorded and all the normal modes of vibrations are assigned.

[Keywords: Synthesis, FfIR, Laser Raman spectra, V ibrational assignments]

1 Introduction

Pyrazole and i ts derivatives are used in the synthesis of analgesic, anti-bacterial and antiinflammatory drugs designing. They are also used as dyes and sensitizing agents i n colour photography. Pyrazole and several N-unsubstituted pyrazoles are inhibitors and derivators of l iver alcohol dehydrogenase )'·. The anti-inflammatory acti vity of pyrazole is more potent than aspirinS.

1 -( 4-Fluorophenyl )-4-( 4-ch lorophenyl)-3-pyrazoly l acetic acid (pirazolac) has been recently reportedS to have anti -inflammatory activity and the advantageous relationship between activity and gastric tolerance led to detailed biological investigations. 3,5-dimethylpyrazole possesses hypoglycemic activity in glucose primed and diabetic rats because of i ts metabolism to the corresponding 5-carboxylic acid. The metabol ism product acts primari ly on adipose tissue by inh ibiting l ipolysis, promoting the conversion of glucose to triglyceride, and stimulating glycogenesisl . Salts of 5-methyl pyrazole-3-carboxyl ic acid with basically substituted adenine derivati ves have s ignificantly more l ipolysis inhibitory , than the free acid itself 6.

In addition to the biological and pharmaceutical activities, some pyrazole derivatives have found appl ications in the agro-chemical field, as i nsecticides. There are few examples of natural ly occurring pyrazoles. Withasomnine, 4-phenyl- I ,5-

trimethy lene pyrazole, was i solated from the roots of Indian medicinal p lants7•x.

Consideration of these factors led to synthesis 1 ,3 ,5-triphenyl-4,5-dihydro pyrazole (p)) , 1 ,3-diphenyl-5(p-methoxy phenyl )-4,5-dihydro pyrazole(P2) and 1 ,3-diphenyl-5(p-methyl phenyl)-4,5-d ihydro pyrazole (P3) compounds and the detailed vibrational analysi s have been carried out to understand the spectral activities of these compounds.

2 Preparation of Compounds

The compounds were prepared by the fol lowing method out l ined by Joshi et aU.

2.1 Preparation of 1,3,5-triphenyl-4,5-dihydro pyrazole (P1)

(a) Preparation of benzalacetophenone - Sodium hydroxide (4.5 g) dissolved in 20 ml of water was taken in c lean beaker of ,250 ml . EthylaIcohol ( 1 5 ml) was added to thi s solution and cooled i n an icebath. To this was added, a mixture of acetophenone ( 10 ml) and benzaldehyde (8 ml) with constant stirring. The stirring was continued for 90 min. The reaction mixture was kept overn ight. The crude product was washed with ice-cold alcohol . A portion was re-crystal l i zed from ethyl alcohol to give crystals of pure benzalacetophenone.

(b) Preparation of 1 , 3,5-triphenyl - 4, 5-dihydro pyrazole - To benzalacetophenone (2 g) taken in a 1 00 ml round bottom flask, added phenyl hydrazine

CHITHAMBARA THANU et al.: VIERA TIONAL ANALYSIS OF PYRAZOLE 845

hydrochloride (3 g) and N,N-dimethyl formamide (50 ml) and refluxed for 3 hr. Then the reaction mixture was kept undisturbed for 3 days. The crude product was separated out and filtered and washed with ice-cold alcohol. A portion was re-crystall ized from ethyl alcohol to give 1 ,3 ,5-triphenyl-4,5-dihydro pyrazole.

R46 INDIAN J PURE & APPL PHYS, VOL 4 1 , NOVEMBER 2003

2.3 Preparation of 1,3-diphenyl-5(p-methyl phenyl)-4,5-dihydro pyrazole (P3)

(a) Preparation of p-methyl benzalacetophenone The compound was prepared, fol lowing the procedure 2. I a, by taking tolualdehyde (4.4 ml) in place of benzaldehyde.

(b) Preparation of 1, 3-diphenyl-5(p-methyl phenyl)-

4, 5-dihydro pyrazole - The title compound (P,) was prepared by following the procedure outlined in 2. 1 b, by taking p-methyl benzalacetophenone (2.38 g) instead of benzalacetophenone.

3 Recording of Spectra

The FfIR spectra of 1 ,3,5-triphenyl-4,5-dihydro pyrazole, 1 ,3-diphenyl-5(p-methoxy phenyl)-4,5-dihydro pyrazole and 1 ,3-diphenyl-5(p-methyl phenyl)-4,S-dihydro pyrazole were recorded on BRUKER IPS 66v model 1 600 spectrophotometer, using KBr pellets in the region 400-4000 cm· l . The far FfIR spectra of the compounds were recorded on the same instrument, using polyethylene pellets in the region 1 00-500 em- I . The laser Raman spectra were recorded by Dilor Z-24 spectrophotometer, using Kr ion laser source of 200 mw power exciting at 647. 1 nm line. The FfIR and laser Raman of PI 'p2 and P, are shown in Figs l a- I e, 2a-2c and 3a-3c, respectively.

4 Results and Discussion

Vibrational assignments - The observed frequencies along with their intenslttes and vibrational frequency assignments are given in Table I . The assignments of observed bands for P" P2 and Pl were carried out in analogy with the assignments proposed by earlier investigators on some simi lar type of molecules. The general agreement between in-plane and out-of-plane bending vibrations are good. The appearance of multiple bands in the stretching and bending region explains the effect of hydrogen bonding on the vibrations of the molecules.

C-H Vibrations - The heterocyclic aromatic compounds and its derivatives are structurally very close to benezene. The C-H stretching vibrations of aromatic and hetero aromatic structures occur in the region 3000-3 1 00 cml . This permits the ready identification of the structure. Further, in this region, the bands are not much affected due to the nature and position of the substitutions I I). Hence, in the

present study, the FfIR bands observed at 3 1 54-2872 em' for PI , 3096-2867 em' for P2 and 3 1 24-2862 em' for P, have been assigned to C-H stretching modes of vibrations.

1000 400

(b)

�ooo

4000 S500 " !OOO floQ � 400 Wavenumber (em - 1)

Fig. 3 - (a) FTIR spectrum of 1 ,3-diphenyl-5 (p-methyl phenyl)-4,5-dihydro pyrazole; (b) FTIR spectrum of 1 ,3-diphenyl-5 (p-methyl phenyl)-4,5-dihydro pyrazole in the region 1 00-500 cm- ' ; (c) Laser Raman spectrum of 1 ,3-diphenyl-5 (p-methyl phenyl)-4,5-dihydro pyrazole

C=N Vibrations - The IR bands at 1 700 em' , 1 698 cm- ' for P, and P2 and the peaks observed at 1 7 1 4, 1 7 1 7 em' for P3 have been assigned to C=N stretching vibrations. These assignments are in good agreement with the l iterature l ' .

CHITHAMBARATHANU et al. :VIBRATIONAL ANALYSIS OF PYRAZOLE 847

Table I - V ibrational frequencies and assignment of I ,3,5-triphenyl-4,5-dihydro pyrazoIe, I ,3-diphenyl-5(p-methoxy phenyl)-4,5-dihydro pyrazole, I ,3-diphenyl-5(p-methyl phenyl)-4,5-dihydro pyrazole

1 ,3 ,5-triphenyl-4,5-dihydro 1 ,3-diphenyl-5(p-methoxy 1 ,3-diphenyl-5(p-methyl Assignments pyrazole phenyl)-4,5-dihydro pyrazole phenyl)-4,5-dihydro pyrazole

FfIR Laser Raman FfIR Laser Raman FfIR Laser Raman (in cm' l ) (in cm- I) (in cm'l) (in cm' l) (in cm' l) (in cm' l )

3 1 54 w C - H stretching 3 1 26 w 3 1 24 w C - H stretching

3 1 1 2 w 3 1 1 4 w C - H stretching 3096 w C - H stretching

3080 w 3085 w 3085 w 3089 w C - H stretching 3064 w 306 1 m 306 1 m 3069 w C - H stretching

3046 w 3040 m 3042 m C - H stretching 303 1 w 303 1 w 3028 w C - H stretching 2924 w 2932 w 2937 w 2924 w C - H stretching 29 1 5 w 2920 w 29 1 5 w 29 1 8 w 2924 w C - H stretching 2872 w 2867 w 2862 w C - H stretching 1 700 w 1 698 w 1 7 1 4 w 1 7 1 7 m C = N stretching 1 596 s 1 606 m 1 596 s 1 59 1 vs 1 598 m 1 59 1 vs C - N stretching 1 574 w 1 576 w 1 576 w 1 578 w C - C stretching 1 498 w 1 504 m 1 497 m 1 489 w C - C stretching 1 468 w 1 468 w 1 484 w C - C stretching 1 426 vs 1 439 m 1 442 m 1 447 w C - C stretching 1 379 m 1 369 w 1 389 s 1 385 w 1 393 m 1 39 1 w N - N stretching 1 345 s 1 349 s 1 358 w 1 335 m C - C stretching 1 322 s 1 3 1 8 m 1 320 m 1 326 w C - C stretching 1 292 w 1 298 m 1 284 w 1 290 w C - N stretching

1 243 vs 1 240 m C - 0 stretching 1 236 w 1 232 w 1 230 m 1 236 w C - C stretching 1 2 1 5 w 1 209 m 1 205 w 1 204 w C - C stretching 1 1 60 w 1 1 67 m 1 1 70 s 1 1 77 w 1 1 80 w 1 1 77 w CH3 wagging 1 1 28 m 1 1 27 s 1 1 25 w 1 1 23 m 1 1 25 w CH3 rocking 1 080 w 1 080 w 1 082 m 1 066 m 1 067 m Ring breathing

1 033 s C - 0 stretching 1 005 w 990 w 994 m 983 ms 999 w 985 ms C - H in plane bending 978 w 972 w 978 w C - H in plane bending 9 1 8 w 9 1 6 w 9 1 5 w 928 w CH2 twisting 872 m 865 w 868 m 870 w 867 w 865 w C - N in plane bending 769 s 790 s 755 m CH2 rocking 747 m 740 m 744 m 742 w 742 m 745 w C - H out of plane bending 692 s 687 m 676 w 686 m 684 w C - H out of plane bending 653 w 648 m C - N out of plane bending

63 1 w C - 0 in plane bending 488 w 490 m 49 1 m 509 w 5 1 2 w 509 w ring torsion 457 w 455 w 453 w 453 w 449 w CH3 torsion 420 m 4 1 8 m 4 1 2 m 4 1 8 w 409 w 4 1 2 w C-C-C out of plane bending 308 w 308 m 3 1 8 w 308 w 3 1 3 w ring deformation

286 vw 278 m C - 0 out Jf plane bending 234 vw 235 vw 23 1 vw 223 w Phenyl group vibration 220 vw 2 1 6 m 2 1 5 w 205 vw Phenyl group vibration 1 85 vw 1 86 bw 1 86 vw Lattice vibration 1 6 1 vw 1 44 vw 1 45 'M Lattice vibration

1 20 vw Lattice vibration

vs-Very strong; ms- medium strong; s-strong; w-weak; vw-very weak

848 INDIAN J PURE & APPL PHYS, VOL 4 1 , NOVEMBER 2003

N-N Vibrations -. In the vibrational analysis of 2,4-dinitrophenyl hydrazine, Krishnakumar et al. '2, identified the N-N stretching mode at 1 37 1 cm-' in FTIR and 1 368 cm" in FT Raman spectra. Hence, in the present study, the FTIR bands observed at 1 379 cm" for P I , 1 389 cm' for P2 and 1 393 cm" for P3 are assigned to N-N stretching modes of vibrations . The Raman bands for thi s mode have been identified at 1 369, 1 385, 1 3 9 1 cm" for P" P2 and Po, respectively,

C-N Vibrations - The identification of C-N stretching frequency is a very difficult task since, the mixing of bands are possible in this region. The FTIR bands observed at 1 292, 1 284 and 1 290 cm-' for P I , P2 and P3 have been designated to C-N stretching modes of vibrations. These assignments are made in accordance with the assignments proposed by Roy et al. '3, and Sharma et al. '4,

C-O Vibrations - A great deal of structural information can be derived from the exact position of carbonyl stretching absorption peak. The interaction of carbonyl group with the other group present in the system does not produce such a drastic and characteristic changes in the frequency of C-O stretch as done by interaction of N-H stretch . Further, if a compound contains a carbonyl group, the absorption caused by C-O stretching is generally among the strongest present' � . Consideration of these factors lead to assign the very strong FTIR bands observed at 1 243 cm" and the corresponding laser Raman band at 1 240 cm- ' to C-O stretching vibrations for P2•

C-C Vibrations - The bands of variable intensities observed between 1 525- 1 470 cm- ' and 1 465- 1 430 cm- ' in substituted benzenes have been assigned to ring carbon-carbon stretching vibrations by Varsanyi ' fi. Accordingly, in the present study, the carbon-carbon vibrations of the respective compounds are observed both in FrIR and Raman spectra and presented in Table 1 .

Apart from these vibrations, the wagging, rocking, twisting and torsional modes of vibrations

arising from methyl and ethyl groups are also found in the observed spectra and they are presented in Table I , Acknowledgement

The authors express sincere thanks to RSIC, lIT, Chennai, for recording the spectra and also to the Management of ST Hindu College, Nagercoil, for the laboratory facilities,

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