Synthesis of several aromatic aldazines

JOURNAL OF SCIENCE OF HNUE Chemical and Biological Sci., 2012, Vol. 57, No. 8, pp. 16-21 This paper is available online at SYNTHESIS OF SEVERAL AROMATIC ALDAZINES Le Van Co1, Nguyen Dang Dat2 and Nguyen Huu Dinh2 1Faculty of Chemistry, Tay Nguyen University 2Faculty of Chemistry, Hanoi National University of Education Abstract. Ten aromatic aldazines: 4-nitrobenzal-, 3-nitrobenzal-, 2-nitrobenzal-, 4-dimethylaminobenzal-, 4-methoxybenzal-, 3-methoxybenzal-, 4-fluorobenzal-, 4-chlorobenzal-, 4-bromobenzaldazine and 7-carboxymethoxy-6-hydroxy-3-sulfoquinolin-5-carbaldazine, were synthesized by condensing two equivalents of an appropriate aldehyde with one equivalent of hydrazine hydrate. The structure of the received aldazines was determined by IR, 1H-NMR and ESI MS spectra. Keywords: Aldazines, synthesis, IR, 1H-NMR and ESI MS spectra. 1. Introduction Aldazines are functional organic compounds which are formed by a condensation reaction of two equivalents of an aldehyde with one equivalent of hydrazine [1]. Aldazines have been used for preparation of hydrazones [2, 3] and diazo compounds [4, 5]. They have been also used as sources for hydrazine produced in situ, for example, in the production of herbicide precursor 1,2,4-triazole [6]. Symmetrical and unsymmetrical aldazines are efficiently converted to 2,5-disubstituted-1,3,4-oxadiazoles by oxidation with bis(trifluoroacetoxy)iodobenzene (BTI) [7]: Received July 17, 2012. Accepted September 24, 2012. Chemistry Subject Classification: 10401. Contact Nguyen Huu Dinh, e-mail address: nguyenhuusp@yahoo.com 16 Synthesis of several aromatic aldazines Aldazines readily participate in some pericyclic reaction variants [8] and react with isocyanate in a double [3 + 2] cycloaddition involving both C=N bonds to form triazolotriazoles [8]: In view of the above mentioned findings, herein we report the synthesis of some substituted benzaldazines and polysubstituted quinoline-5-carbaldazine as precursors to the triazolotriazoles. 2. Content 2.1. Experiment The aldazines (1 - 10) were synthesized according to the following procedure: A solution of 2 mmol aromatic aldehyde and 1 mmol hydrazine hydrate in dry ethanol was refluxed for 3 - 4 h. The reaction mixture was then allowed to stand at room temperature for one hour. The resulting precipitate was collected and recrystallized. Some physical characteristics of the obtained compounds are presented in Table 1. Table 1. Some physical characteristics of the synthesized aldazines Ar−CH=N−N=CH−Ar Compound Ar Form Solvent for recrystal Mp (oC) 1 Small yellow crystals DMSO/EtOH 1:4 259 2 Small yellow crystals DMSO/EtOH 1:4 243-4 3 Small yellow crystals DMSO/EtOH 1:4 233-4 4 Small rose crystals EtOH 249-50 17 Le Van Co, Nguyen Dang Dat and Nguyen Huu Dinh 5 Needle yellow crystals DMSO/EtOH 1:5 227-9 6 Small yellow crystals DMSO/EtOH 1:4 194-5 7 Needle white crystals EtOH 198-9 8 Thin light yellow crystals DMSO/EtOH 1:5 217-8 9 Thin light yellow crystals DMSO/EtOH 1:4 234-5 10 Small yellow crystals DMSO/EtOH 1:3 Decom. IR spectra were recorded using an IMPACT-410 NICOLET spectrometer with KBr discs at 400 - 4000 cm−1. ESI mass spectra were recorded using an Agilent LC-MSD-Trap-SL series 1100 spectrometer. NMR spectra were recorded with the use of a Bruker AVANCE 500 MHz spectrometer, d6-DMSO with TMS being the internal standard. 2.2. Results and discussion The substituted benzaldehydes which were used were commercially available while 7-carboxymethoxy-6-hydroxy-3-sulfoquinolin-5-carbaldehyde was synthesized from eugenoxyacetic acid in the three successive reaction steps presented in the following scheme: The structure of the aldehyde was determined by analyzing its IR, 1D-NMR, 2D-NMR and MS spectra and making comparisons with some spectra of its quinoline 18 Synthesis of several aromatic aldazines precursor and two arylhydrazones derivatives [9]. Aromatic aldehydes readily react with hydrazine to produce hydrazones. In our experiment the intermediate hydrazones condensed with a second equivalent of aldehyde to form the aldazines: The absence of absorption bands for stretching vibrations of NH2 and C=O groups in IR spectra of the aldazines, as in Figure 1 for example, indicates that the above reaction does not stop at the hydrazone formation step. Figure 1. IR spectrum of aldazine 8 For compounds 2, 3, 8, 9 and 10, the absorption band of azine C=N group is present at 1620 - 1627 cm−1, but for the others this band and an absorption band of aromatic C=C groups overlap at ∼ 1600 cm−1 (Table 2). Table 2. The main absorption bands of aldazines 1 - 10, cm−1 1 2 3 4 5 6 7 8 9 10 νCH 3113 2934 2848 3091 2915 2850 3072 2923 2855 3080 2925 2860 3080 2945 2847 3050 2912 2850 3112 2934 2848 3053 2990 2945 3057 2936 2858 3050 2975 2850 νC=N , νC=C 1595 1522 1450 1627 1529 1440 1626 1552 1492 1599 1580 1518 1601 1504 1461 1603 1525 1500 1995 1519 1450 1621 1586 1480 1620 1583 1480 1621 1593 1472 1H-NMR spectra allow identification of the aldehyde moiety of the aldazines. For example, in the 1H-NMR spectrum of aldazine 7 (Figure 2) the two multiplets 7.35 ppm, 2H, JH,H ≈ JF,H ≈ 7Hz and 7.95 ppm, 2H, JH,H ≈ 7Hz, JF,H ≈ 5Hz indicate a presence of 19 Le Van Co, Nguyen Dang Dat and Nguyen Huu Dinh F in the para position of the phenyl group. The singlet at 8.72 ppm (lower than the signal of the CH=O proton ∼ 1ppm) shows the presence of the CH=N group in the aldazine. Figure 2. The 1H-NMR spectrum of aldazine 7 Table 3. 1H-NMR signals of the examined compounds: , δ (ppm), J (Hz) H1 H2 H3 H4 H5 H6 Others 1 8.85 s 8.16 d, J 9 8.36 d, J 9 - 8.36 d, J 9 8.16 d, J 9 - 2 8.91 s 8.71 t, J 2 - 8.37 dd, J 8; 2 7.83 t, J 8 8.32 d, J 8 - 3 8.96 s - 8.15 d, J 8 7.88 t, J 8 7.80 t, J 8 8.08 d, J 8 - 4 8.52 s 7.66 d, J 9 6.78 d, J 9 - 6.78 d, J 9 7.66 d, J 9 H7 (6H): 3.01 s 7 8.72 s 7.95 m, J 7; 5 7.35 m, J 7 - 7.35 m, J 7 7.95 m, J 7; 5 - 8 8.71 s 7.90 d, J 9 7.58 d, J 9 - 7.58 d, J 9 7.90 d, J 9 - 9 8.70 s 7.83 d, J 8.5 7.72 d, J 8.5 - 7.72 d, J 8.5 7.83 d, J 8.5 - 10 9.19 s 8.81 d, J 1.5 - 8.79 d J 1.5 - H7a (2H): 4.83 s H8: 7.36 s In the aldazines that were examined, there are two PhCH groups but they give rise 20 Synthesis of several aromatic aldazines to only one set of proton signals (Table 3). This is evidence of a symmetrical structure of the aldazines. The data in Table 3 are in accordance with the structure of the examined aldazines. In order to determine the final structure, ESI + MS of 7 as a presenter for the synthesized aldazines was recorded and analyzed. The pseudomolecular ion peak at m/z 245 corresponds to a molecular mass of 7 (244 au). 3. Conclusion Ten aromatic aldazines were synthesized by condensing two equivalents of an aromatic aldehyde with one equivalent of hydrazine hydrate. The structure of resulting aldazines was determined making use of IR, 1H-NMR and ESI MS spectra. Acknowledgment. This work was supported by the National Foundation for Science and Technology Development (NAFOSTED) of Vietnam. REFERENCES [1] G. P. Moss, P. A. S. Smith, D. Tavernier, 1995. IUPAC Recommendations. Pure Appl. Chem. 67 (8-9): 1307 - 75. [2] A. C. Day, M. C. Whiting, 1970. Org. Synth. Coll. Vol. 6: 10. [3] H. Staudinger, Gaule, Alice, 1916. Ber. Dtsch. Chem. Ges. 49 (2): pp. 1897-1918. [4] A. C. Day, P. Raymond, R. M. Southam, M. C. Whiting, 1966. J. Chem. Soc. pp. 467-69. [5] S. D. Andrews, Day, P. Raymond, M. C. Whiting, 1970. Org. Synth. 50: 27. [6] Nagata, Nobuhiro; Chiharu Nishizawa & Toshikiyo Kurai, 1999. US Patent 6002015, 12-14. [7] Zhenhua Shang, John Reiner, Junbiao Chang , Kang Zhao, 2005. Tetrahedron Letters, 46 (11) p. 2701. [8] Henri Ulrich, 2009. Cumulenes in Click Reactions. John Wiley & Sons. [9] Le Van Co, Tran Thi Thu Trang, Nguyen Minh Hai, Nguyen Huu Dinh, 2012. Journal of Chemistry, p. 50 (accepted). 21