Synthesis and Characterization of a Novel 2-Pyrazoline

Reaction of dibenzalacetone with hydrazine hydrate and formic acid yielded a novel 2-pyrazoline 1, characterized by ESI-MS, FT-IR, UV, HNMR and CNMR data and microanalysis.


Results and Discussion
The structure of the reaction product (Scheme 1) has been elucidated by UV, IR, 1 HNMR, 13 CNMR, ESI-MS spectroscopic techniques and the progress of reaction was monitored by TLC.The ESI mass spectrum indicated its molecular mass to be 276 (by protonated and pseudo molecular ions).The IR spectrum of compound 1 showed a strong band for the carbonyl group at 1640 cm -1 and a band at 1560 cm -1 for C=N.In the 1 HNMR spectra, an ABX pattern was observable, H A, H B and H X appear as doublet of doublets at δ 3.1, 3.6 and 5.5 ppm with J AB = 17.6 Hz, J AX = 4.8 Hz, J BX = 11.6 Hz.The protons of the aromatic ring were observed at δ 7.2-7.4ppm and the formyl proton occurred as a singlet at δ 8.9 ppm.A pair of the trans-olefinic proton doublets appears at 6.8 and 7.1 ppm with J value of 16.2 Hz.The electronic spectra of the 1-formylpyrazoline (studied in the UV region) in methanol showed three absorption bands at ~ 407, 337, 321 nm assignable to n-π*, π-π* and n-σ* transitions.
Substituted pyrazolines have strong fluorescence in different solvents.They also give excellent fluorescence properties in solid state because the conjugation system contains two nitrogen atoms and one carbon atom while the other carbon atoms are sp 3 hybridized.The fluorescence spectrum of compound 1 showed an intense emission with λ em = 398.3nm and 451.9 nm at 330 nm excitation in methanol.

Experimental
Reaction of dibenzalacetone, hydrazine hydrate and formic acid afforded a crude product which was recrystallized from chloroform to give 1.Progress of the reaction was monitored by TLC, using hexane: ethyl acetate (8:2) as mobile phase.All the starting materials were AR/GR quality of Merck.Fluorescence spectra were recorded on a Perkin-Elmer LS-55 spectrofluorimeter; for fluorescence, an excitation lamp (Xe, 150 W) interfaced with the computer was used. 1 HNMR Spectra were obtained in CDCl 3 on a Bruker Spectrospin DPX-300 spectrometer (300 MHz) using TMS as the internal standard.

Preparation of dibenzalacetone
30 mmol of benzaldehyde and 15 mmol of acetone were dissolved in methanol.The roundbottomed flask was placed in an ice bath and the mixture was stirred for 3 h with addition of 11% NaOH (cold solution) drop by drop.The resultant mixture was left to stand for 2 h.The yellow precipitate was crystallized from methanol to afford dibenzalacetone.Yield: 90%, m.p.112 °C [23][24][25][26].

Molbank 2009 M614 (Page 3 )
Melting points have been recorded in open capillary with Metzer apparatus and are uncorrected.IR spectra were recorded for KBr pellets on a Perkin-Elmer FT-IR-RX-01 spectrophotometer.UV Spectra were recorded on a Perkin-Elmer double beam UV-Visible spectrophotometer (λ-25) in methanol.