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An easy way to perdeuterated pyrazoles by catalytic exchange reactions
Catalysis Communications 2 (2001) 125±128
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An easy way to perdeuterated pyrazoles by catalytic exchange reactions Piero Frediani a,*, Donella Rovai b, Maurizio Muniz-Miranda b, Antonella Salvini a, Maria Caporali a a
Department of Organic Chemistry, University of Florence, Via Gino Capponi, 9-I 50121 Firenze, Italy b Department of Chemistry, University of Florence, Via Gino Capponi, 9-I 50121 Firenze, Italy Received 16 February 2001; received in revised form 14 May 2001
Abstract The perdeuterated pyrazole has been obtained through a base catalysed exchange reaction in very mild conditions. The 3,5-dimethylpyrazole-1,4-d2 has been also synthesised in the same way, while the perdeuterated 3,5-dimethylpyrazole was obtained in two steps. In the ®rst step the perdeuterated 2,4-pentandione was prepared according to a base catalysed exchange reaction and in the following step this product was condensed with perdeuterated hydrazine. In all cases the deuterated products contain about 90% of deuterium. The residual hydrogens are mainly located on nitrogen. Ó 2001 Elsevier Science B.V. All rights reserved.
1. Communication Nitrogen containing ligands are extensively employed in transition metal chemistry [1,3] to modulate the characteristics of the metals. The complexes formed are mainly used as photosensitising agents [4±8], or catalysts in reactions such as the water gas shift reaction [9±12], the reduction or carbonylation of nitrobenzene [13,14], the carbon dioxide reduction [15], the hydrogenation [16] and the hydroformylation of ole®ns [17]. Among these nitrogen containing ligands, pyrazoles show a very important role because they behave as monodentate ligands [1±3] or they are used as bridging ligands in the synthesis of binuclear compounds,
* Corresponding author. Tel.: +39-055-2757-648; fax: +39055-2757-660. E-mail address: [email protected]®.it (P. Frediani).
in¯uencing the metal±metal distance [2,3]. Furthermore pyrazole derivatives are employed in the manufacture of nonlinear optical materials [18] and in the preparation of standards for stable isotope dilution mass spectrometry [19]. Isotopomeric compounds are also important to solve several problems such as the attribution of the IR bands or the NMR resonances, in the analyses involving isotopic dilution, for the syntheses of new magnetic materials and ®nally to modify the photosensitising activity of a pyrazole containing products. The change of the IR spectrum of pyrazoles, due to the deuterated compounds avoids some undesirable absorptions. The perdeuterated pyrazole may be synthesised from the hydrogenated compound by a base catalysed exchange reaction with deuterium oxide at high temperature (200°C) in the presence of a strong base (NaOD 40%) [20]. Due to the problems connected to carry out this reaction in a
1566-7367/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 1 5 6 6 - 7 3 6 7 ( 0 1 ) 0 0 0 1 9 - X
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P. Frediani et al. / Catalysis Communications 2 (2001) 125±128
laboratory, we have tested if the same reaction can be performed at lower temperature in the presence of a weak base. A D2 O solution (5 ml) containing pyrazole (1 g) and K2 CO3 (0.10 g) was heated at 120°C for 8 h in a glass vial inserted in a stainless steel autoclave. About 80% of the hydrogen of the pyrazole was exchanged in these conditions. Water was eliminated using the freezing-throw technique and the residue submitted to a new exchange reaction in the same conditions. After sublimation, pure pyrazole was obtained with a chemical yield of 95%. The GC-MS spectrum (Shimadzu mod. QP5050 instrument, electron impact ionisation), shows peaks at m=z: 72 (100) M , 71 64 C3 D3 HN2 , 70 19 C3 D3 N2 ; C3 D2 H2 N2 , 69 (16) C3 D2 HN2 ; C3 DH3 N2 ; 68 1 C3 DH2 N2 ; C3 H4 N2 . The product was largely deuterated (85%), the isotopomeric composition was evaluated taking into account the fragmentation of pure pyrazole [21] (Table 1). The residual hydrogens are mainly located in position 1 on nitrogen (75%). The spectroscopic data of pyrazole-d4 are in agreement with those reported in the literature [22,23]. The 1 H-NMR spectrum con®rmed the deuterium content. The same reaction was carried out on the 3,5dimethylpyrazole, but in this conditions only the hydrogens of the heterocyclic ring were substituted by deuterium {GC-MS spectrum shows peaks at m=z: 98 100 M , 97 (70) C5 DH7 N2 , 96
15 C5 DH6 N2 ; C5 H8 N2 , 95 10 C5 H7 N2 }. The perdeuterated heterocycle may be synthesised as reported by Junk et al. [24] using deuterium oxide and NaOD at the supercritical conditions. However, these conditions are very hard (410°C, 500 bar, 8 h) to be easily carried out and we try to obtain the same compound in an easily aordable method (Scheme 1) following the procedure reported by Iranzo and Elguero [25] for the 3,5bis(trideuteromethyl)pyrazole or by Okazaki et al. [18] for the synthesis of 3,5-dimethyl-1-(4-nitrophenyl)pyrazole-d7 . In the ®rst step the perdeuterated 2,4-pentandione was obtained, according to Egan et al. method [26], through a base catalysed exchange reaction carried out in the conditions above reported for pyrazole. A D2 O (100 ml) solution containing 2,4-pentandione (10 ml) and K2 CO3 (1 g) was heated at 120°C for 12 h. The ketone was extracted with CH2 Cl2 (50 ml for 3 times) and the organic phase dried on MgSO4 . The solvent was evaporated, the GC-MS spectrum showed a 90% deuteration. The deuteration was repeated a second time in almost the same conditions (K2 CO3 , 0.5 g). The perdeuterated product was obtained after the above reported working up, as shown by its spectroscopic data {GC-MS spectrum shows peaks at m=z: 108 (45) M , 107 12 MAH , 106 (1) MA2H , 90 (74) MACD3 , 89 (20) 107-CD3 , 88 (2) 106-CD3 , 80 (7) C4 D8 O , 64 (6) C3 D6 O , 46
Table 1 Isotopomeric composition of deuterated pyrazole m=z (amu)
Abundance experimental
Composition
Calculated abundance of the various fragments
72 71 70
100 64 19
C3 D4 N2 C3 D3 HN2 C3 D3 N2 from C3 D4 N2 C3 D3 N2 from C3 D3 HN2 C3 D2 H2 N2
100 64 11.0 1.8 6.2
69
16
C3 D2 HN2 from C3 D3 HN2 C3 D2 HN2 from C3 D2 H2 N2 C3 DH3 N2
5.3 0.3 10.4
68
1
C3 DH2 N2 from C3 D2 H2 N2 C3 DH2 N2 from C3 DH3 N2 C3 H4 N2
0.3 0.3 0.2
67
0
C3 H3 N2
0
P. Frediani et al. / Catalysis Communications 2 (2001) 125±128
127
Scheme 1. Table 2 Isotopomeric composition of 3,5-dimethylpyrazole m=z (amu)
Abundance experimental
Composition
Calculated abundance of the various fragment
104 103 102
65 82 82
C5 D8 N2 C5 D7 HN2 C5 D7 N2 from C5 D8 N2 C5 D7 N2 from C5 D7 HN2 C5 D6 H2 N2
65.0 82.0 52.0 8.2 21.8
101
77
C5 D6 HN2 from C5 D7 HN2 C5 D6 HN2 from C5 D6 H2 N2 C5 D5 H3 N2
57.4 4.4 15.2
100
8
C5 D5 H2 N2 from C5 D6 H2 N2 C5 D5 H2 N2 from C5 D5 H3 N2 C5 D4 H4 N2
6.0 2.0 0
99 98
0 0
C5 D3 H5 N2 C5 D2 H6 N2
0 0
(100) CD3 CO }. A 97% deuteration was obtained and a quantitative chemical yield. For synthetic purpose the D2 O solution of 2,4-pentandione-d8 was treated with perdeuterated hydrazine at room temperature as reported by Vogel [28] obtaining the perdeuterated 3,5-dimethylpyrazole. No attempt was made to conserve the exchangeable proton in position 1 during the work up {GC MS spectrum shows peaks at m=z: 104 65 M , 103 (82) C5 D7 HN2 , 102 82 C5 D7 N2 ; C5 D6 H2 N2 , 101 (77) C5 D6 HN2 ; C5 D5 H3 N2 , 100 (8) C5 D5 H2 N2 ; C5 D4 H4 N2 }. The 3,5-dimethylpyrazole-d8 shows a 88% deuteration, the isotopomeric composition was evaluated taking into account the fragmentation of 3,5-dimethylpyrazole [27] (Table 2), that is only the ND (70%) was lost during the working up. The proton on nitrogen may be restored at the end of the process by D2 O exchange. The product was separated by extraction with diethyl ether and crystallised, a 70% chemical yield, with respect to 2,4-pentandione,
was obtained. The characteristics of the perdeuterated product are in agreement with those reported in the literature [24]. The 1 H-NMR spectrum con®rms the deuterium content.
Acknowledgements The authors wish to thank the University of Florence and the Ministero della Ricerca Scienti®ca e Tecnologica (MURST), Programmi di Ricerca Scienti®ca di Notevole Interesse Nazionale, Co®nanziamento MURST 2000-01, for ®nancial support.
References [1] R.P. Hughes, in: G. Wilkinson, F.G.A. Stone, E.W. Abel (Eds.), Comprehensive Organometallic Chemistry, Pergamon, New York, 1982, Vol. 5, p. 292.
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P. Frediani et al. / Catalysis Communications 2 (2001) 125±128
[2] N.N. Gerasimchuk, K. Bowman-James, in: R.B. King (Ed.), Encyclopedia of Inorganic Chemistry, Wiley, Chichester (GB), 1994, Vol. 5, p. 2260. [3] D.A. House, in: R.B. King (Ed.), Encyclopedia of Inorganic Chemistry, Wiley, Chichester (GB), 1994, Vol. 1, p. 148. [4] A. Launikonis, P.A. Lay, A.W.H. Mau, A.M. Sargerson, W.H.F. Sasse, Aust. J. Chem. 39 (1986) 1053. [5] M. Inoue, R. Cedeno, Inorg. Chim. Acta 145 (1988) 117. [6] S.D. Ernst, W. Kaim, Inorg. Chem. 28 (1989) 1520. [7] W.R. Murphy Jr., K.J. Brewer, G. Gettlie, J.D. Petersen, Inorg. Chem. 28 (1989) 81. [8] C.D. Tait, R.J. Donohoe, M.K. de Armond, D.W. Wertz, Inorg. Chem. 26 (1987) 2754. [9] T. Venalainen, E. Iiskola, J. Pursianen, T.A. Pakkanen, T.T. Pakkanen, J. Mol. Catal. 34 (1986) 293. [10] T. Venalainen, E. Iiskola, T.A. Pakkanen, T.T. Pakkanen, J. Mol. Catal. 34 (1986) 305. [11] T. Venalainen, T.A. Pakkanen, T.T. Pakkanen, E. Iiskola, J. Organomet. Chem. 314 (1986) C49. [12] H. Ishida, K. Tanaka, M. Morimoto, T. Tanaka, Organometallics 5 (1986) 724. [13] E. Alessio, G. Clauti, G. Mestroni, J. Mol. Catal. 29 (1985) 77. [14] E. Alessio, G. Mestroni, J. Organomet. Chem. 291 (1985) 117. [15] H. Ishida, H. Tanaka, K. Tanaka, T. Tanaka, J. Chem. Soc., Chem. Commun. (1985) 131. [16] P. Frediani, M. Bianchi, A. Salvini, R. Guarducci, L.C. Carluccio, F. Piacenti, J. Organomet. Chem. 498 (1995) 187. [17] P. Frediani, M. Bianchi, A. Salvini, L.C. Carluccio, L. Rosi, J. Organomet. Chem. 547 (1997) 35.
[18] M. Okazaki, N. Uchino, N. Nozaki, K. Kazumi, Bull. Chem. Soc. Jpn. 68 (1995) 1024. [19] W.J. Catallo, T. Junk, Biodegradation of Toxic Chemicals from Petroleum and Produced Water in Brackish Mash Sediments: Pathway Studies Using Deuterated Tracers, Final Report, Louisiana Oil Spill Research Program, State of Louisiana, Oce of the Governor/Oil Spill Coordinator, 1995. [20] J. Elguero, R. Jacquier, V. Pellegrin, V. Tabacick, Bull. Soc. Chem. France (1970) 1974. [21] MS spectrum of pyrazole shows peaks at m/z: 68 (100) M , 69 (11) M±H , in: S.R. Heller, G.W.A. Milne (Eds.), EPA/NIH mass spectra data base, U.S. Department of Commerce, National Bureau of Standards, 1978, p. 13. [22] M. Majoube, J. Phys. Chem. 92 (1988) 2407. [23] V. Tabacick, V. Pellegrin, Hs.H. Gunthard, Spectrochim. Acta Part A 35 (1979) 1055. [24] T. Junk, W.J. Catallo, J. Elguero, Tetrahedron Lett. 38 (1997) 6309. [25] G.Y. Iranzo, J. Elguero, J. Labelled Compd. Radiopharm. 28 (1990) 967. [26] W. Egan, G. Gunnarsson, T.E. Bull, S. Forsen, J. Am. Chem. Soc. 99 (1977) 4568. [27] MS spectrum of 3,5-dimethylpyrazole shows peaks at m/z: 96 (100) M , 95 (80) MAH , in: S.R. Heller, G.W.A. Milne (Eds.), EPA/NIH mass spectra data base, U.S. Department of Commerce, National Bureau of Standards, 1978, p. 63. [28] A. Vogel, in: Vogel's Textbook of Practical Organic Chemistry, Longman, London, 1978, p. 881.
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An easy way to perdeuterated pyrazoles by catalytic exchange reactions Piero Frediani a,*, Donella Rovai b, Maurizio Muniz-Miranda b, Antonella Salvini a, Maria Caporali a a
Department of Organic Chemistry, University of Florence, Via Gino Capponi, 9-I 50121 Firenze, Italy b Department of Chemistry, University of Florence, Via Gino Capponi, 9-I 50121 Firenze, Italy Received 16 February 2001; received in revised form 14 May 2001
Abstract The perdeuterated pyrazole has been obtained through a base catalysed exchange reaction in very mild conditions. The 3,5-dimethylpyrazole-1,4-d2 has been also synthesised in the same way, while the perdeuterated 3,5-dimethylpyrazole was obtained in two steps. In the ®rst step the perdeuterated 2,4-pentandione was prepared according to a base catalysed exchange reaction and in the following step this product was condensed with perdeuterated hydrazine. In all cases the deuterated products contain about 90% of deuterium. The residual hydrogens are mainly located on nitrogen. Ó 2001 Elsevier Science B.V. All rights reserved.
1. Communication Nitrogen containing ligands are extensively employed in transition metal chemistry [1,3] to modulate the characteristics of the metals. The complexes formed are mainly used as photosensitising agents [4±8], or catalysts in reactions such as the water gas shift reaction [9±12], the reduction or carbonylation of nitrobenzene [13,14], the carbon dioxide reduction [15], the hydrogenation [16] and the hydroformylation of ole®ns [17]. Among these nitrogen containing ligands, pyrazoles show a very important role because they behave as monodentate ligands [1±3] or they are used as bridging ligands in the synthesis of binuclear compounds,
* Corresponding author. Tel.: +39-055-2757-648; fax: +39055-2757-660. E-mail address: [email protected]®.it (P. Frediani).
in¯uencing the metal±metal distance [2,3]. Furthermore pyrazole derivatives are employed in the manufacture of nonlinear optical materials [18] and in the preparation of standards for stable isotope dilution mass spectrometry [19]. Isotopomeric compounds are also important to solve several problems such as the attribution of the IR bands or the NMR resonances, in the analyses involving isotopic dilution, for the syntheses of new magnetic materials and ®nally to modify the photosensitising activity of a pyrazole containing products. The change of the IR spectrum of pyrazoles, due to the deuterated compounds avoids some undesirable absorptions. The perdeuterated pyrazole may be synthesised from the hydrogenated compound by a base catalysed exchange reaction with deuterium oxide at high temperature (200°C) in the presence of a strong base (NaOD 40%) [20]. Due to the problems connected to carry out this reaction in a
1566-7367/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 1 5 6 6 - 7 3 6 7 ( 0 1 ) 0 0 0 1 9 - X
126
P. Frediani et al. / Catalysis Communications 2 (2001) 125±128
laboratory, we have tested if the same reaction can be performed at lower temperature in the presence of a weak base. A D2 O solution (5 ml) containing pyrazole (1 g) and K2 CO3 (0.10 g) was heated at 120°C for 8 h in a glass vial inserted in a stainless steel autoclave. About 80% of the hydrogen of the pyrazole was exchanged in these conditions. Water was eliminated using the freezing-throw technique and the residue submitted to a new exchange reaction in the same conditions. After sublimation, pure pyrazole was obtained with a chemical yield of 95%. The GC-MS spectrum (Shimadzu mod. QP5050 instrument, electron impact ionisation), shows peaks at m=z: 72 (100) M , 71 64 C3 D3 HN2 , 70 19 C3 D3 N2 ; C3 D2 H2 N2 , 69 (16) C3 D2 HN2 ; C3 DH3 N2 ; 68 1 C3 DH2 N2 ; C3 H4 N2 . The product was largely deuterated (85%), the isotopomeric composition was evaluated taking into account the fragmentation of pure pyrazole [21] (Table 1). The residual hydrogens are mainly located in position 1 on nitrogen (75%). The spectroscopic data of pyrazole-d4 are in agreement with those reported in the literature [22,23]. The 1 H-NMR spectrum con®rmed the deuterium content. The same reaction was carried out on the 3,5dimethylpyrazole, but in this conditions only the hydrogens of the heterocyclic ring were substituted by deuterium {GC-MS spectrum shows peaks at m=z: 98 100 M , 97 (70) C5 DH7 N2 , 96
15 C5 DH6 N2 ; C5 H8 N2 , 95 10 C5 H7 N2 }. The perdeuterated heterocycle may be synthesised as reported by Junk et al. [24] using deuterium oxide and NaOD at the supercritical conditions. However, these conditions are very hard (410°C, 500 bar, 8 h) to be easily carried out and we try to obtain the same compound in an easily aordable method (Scheme 1) following the procedure reported by Iranzo and Elguero [25] for the 3,5bis(trideuteromethyl)pyrazole or by Okazaki et al. [18] for the synthesis of 3,5-dimethyl-1-(4-nitrophenyl)pyrazole-d7 . In the ®rst step the perdeuterated 2,4-pentandione was obtained, according to Egan et al. method [26], through a base catalysed exchange reaction carried out in the conditions above reported for pyrazole. A D2 O (100 ml) solution containing 2,4-pentandione (10 ml) and K2 CO3 (1 g) was heated at 120°C for 12 h. The ketone was extracted with CH2 Cl2 (50 ml for 3 times) and the organic phase dried on MgSO4 . The solvent was evaporated, the GC-MS spectrum showed a 90% deuteration. The deuteration was repeated a second time in almost the same conditions (K2 CO3 , 0.5 g). The perdeuterated product was obtained after the above reported working up, as shown by its spectroscopic data {GC-MS spectrum shows peaks at m=z: 108 (45) M , 107 12 MAH , 106 (1) MA2H , 90 (74) MACD3 , 89 (20) 107-CD3 , 88 (2) 106-CD3 , 80 (7) C4 D8 O , 64 (6) C3 D6 O , 46
Table 1 Isotopomeric composition of deuterated pyrazole m=z (amu)
Abundance experimental
Composition
Calculated abundance of the various fragments
72 71 70
100 64 19
C3 D4 N2 C3 D3 HN2 C3 D3 N2 from C3 D4 N2 C3 D3 N2 from C3 D3 HN2 C3 D2 H2 N2
100 64 11.0 1.8 6.2
69
16
C3 D2 HN2 from C3 D3 HN2 C3 D2 HN2 from C3 D2 H2 N2 C3 DH3 N2
5.3 0.3 10.4
68
1
C3 DH2 N2 from C3 D2 H2 N2 C3 DH2 N2 from C3 DH3 N2 C3 H4 N2
0.3 0.3 0.2
67
0
C3 H3 N2
0
P. Frediani et al. / Catalysis Communications 2 (2001) 125±128
127
Scheme 1. Table 2 Isotopomeric composition of 3,5-dimethylpyrazole m=z (amu)
Abundance experimental
Composition
Calculated abundance of the various fragment
104 103 102
65 82 82
C5 D8 N2 C5 D7 HN2 C5 D7 N2 from C5 D8 N2 C5 D7 N2 from C5 D7 HN2 C5 D6 H2 N2
65.0 82.0 52.0 8.2 21.8
101
77
C5 D6 HN2 from C5 D7 HN2 C5 D6 HN2 from C5 D6 H2 N2 C5 D5 H3 N2
57.4 4.4 15.2
100
8
C5 D5 H2 N2 from C5 D6 H2 N2 C5 D5 H2 N2 from C5 D5 H3 N2 C5 D4 H4 N2
6.0 2.0 0
99 98
0 0
C5 D3 H5 N2 C5 D2 H6 N2
0 0
(100) CD3 CO }. A 97% deuteration was obtained and a quantitative chemical yield. For synthetic purpose the D2 O solution of 2,4-pentandione-d8 was treated with perdeuterated hydrazine at room temperature as reported by Vogel [28] obtaining the perdeuterated 3,5-dimethylpyrazole. No attempt was made to conserve the exchangeable proton in position 1 during the work up {GC MS spectrum shows peaks at m=z: 104 65 M , 103 (82) C5 D7 HN2 , 102 82 C5 D7 N2 ; C5 D6 H2 N2 , 101 (77) C5 D6 HN2 ; C5 D5 H3 N2 , 100 (8) C5 D5 H2 N2 ; C5 D4 H4 N2 }. The 3,5-dimethylpyrazole-d8 shows a 88% deuteration, the isotopomeric composition was evaluated taking into account the fragmentation of 3,5-dimethylpyrazole [27] (Table 2), that is only the ND (70%) was lost during the working up. The proton on nitrogen may be restored at the end of the process by D2 O exchange. The product was separated by extraction with diethyl ether and crystallised, a 70% chemical yield, with respect to 2,4-pentandione,
was obtained. The characteristics of the perdeuterated product are in agreement with those reported in the literature [24]. The 1 H-NMR spectrum con®rms the deuterium content.
Acknowledgements The authors wish to thank the University of Florence and the Ministero della Ricerca Scienti®ca e Tecnologica (MURST), Programmi di Ricerca Scienti®ca di Notevole Interesse Nazionale, Co®nanziamento MURST 2000-01, for ®nancial support.
References [1] R.P. Hughes, in: G. Wilkinson, F.G.A. Stone, E.W. Abel (Eds.), Comprehensive Organometallic Chemistry, Pergamon, New York, 1982, Vol. 5, p. 292.
128
P. Frediani et al. / Catalysis Communications 2 (2001) 125±128
[2] N.N. Gerasimchuk, K. Bowman-James, in: R.B. King (Ed.), Encyclopedia of Inorganic Chemistry, Wiley, Chichester (GB), 1994, Vol. 5, p. 2260. [3] D.A. House, in: R.B. King (Ed.), Encyclopedia of Inorganic Chemistry, Wiley, Chichester (GB), 1994, Vol. 1, p. 148. [4] A. Launikonis, P.A. Lay, A.W.H. Mau, A.M. Sargerson, W.H.F. Sasse, Aust. J. Chem. 39 (1986) 1053. [5] M. Inoue, R. Cedeno, Inorg. Chim. Acta 145 (1988) 117. [6] S.D. Ernst, W. Kaim, Inorg. Chem. 28 (1989) 1520. [7] W.R. Murphy Jr., K.J. Brewer, G. Gettlie, J.D. Petersen, Inorg. Chem. 28 (1989) 81. [8] C.D. Tait, R.J. Donohoe, M.K. de Armond, D.W. Wertz, Inorg. Chem. 26 (1987) 2754. [9] T. Venalainen, E. Iiskola, J. Pursianen, T.A. Pakkanen, T.T. Pakkanen, J. Mol. Catal. 34 (1986) 293. [10] T. Venalainen, E. Iiskola, T.A. Pakkanen, T.T. Pakkanen, J. Mol. Catal. 34 (1986) 305. [11] T. Venalainen, T.A. Pakkanen, T.T. Pakkanen, E. Iiskola, J. Organomet. Chem. 314 (1986) C49. [12] H. Ishida, K. Tanaka, M. Morimoto, T. Tanaka, Organometallics 5 (1986) 724. [13] E. Alessio, G. Clauti, G. Mestroni, J. Mol. Catal. 29 (1985) 77. [14] E. Alessio, G. Mestroni, J. Organomet. Chem. 291 (1985) 117. [15] H. Ishida, H. Tanaka, K. Tanaka, T. Tanaka, J. Chem. Soc., Chem. Commun. (1985) 131. [16] P. Frediani, M. Bianchi, A. Salvini, R. Guarducci, L.C. Carluccio, F. Piacenti, J. Organomet. Chem. 498 (1995) 187. [17] P. Frediani, M. Bianchi, A. Salvini, L.C. Carluccio, L. Rosi, J. Organomet. Chem. 547 (1997) 35.
[18] M. Okazaki, N. Uchino, N. Nozaki, K. Kazumi, Bull. Chem. Soc. Jpn. 68 (1995) 1024. [19] W.J. Catallo, T. Junk, Biodegradation of Toxic Chemicals from Petroleum and Produced Water in Brackish Mash Sediments: Pathway Studies Using Deuterated Tracers, Final Report, Louisiana Oil Spill Research Program, State of Louisiana, Oce of the Governor/Oil Spill Coordinator, 1995. [20] J. Elguero, R. Jacquier, V. Pellegrin, V. Tabacick, Bull. Soc. Chem. France (1970) 1974. [21] MS spectrum of pyrazole shows peaks at m/z: 68 (100) M , 69 (11) M±H , in: S.R. Heller, G.W.A. Milne (Eds.), EPA/NIH mass spectra data base, U.S. Department of Commerce, National Bureau of Standards, 1978, p. 13. [22] M. Majoube, J. Phys. Chem. 92 (1988) 2407. [23] V. Tabacick, V. Pellegrin, Hs.H. Gunthard, Spectrochim. Acta Part A 35 (1979) 1055. [24] T. Junk, W.J. Catallo, J. Elguero, Tetrahedron Lett. 38 (1997) 6309. [25] G.Y. Iranzo, J. Elguero, J. Labelled Compd. Radiopharm. 28 (1990) 967. [26] W. Egan, G. Gunnarsson, T.E. Bull, S. Forsen, J. Am. Chem. Soc. 99 (1977) 4568. [27] MS spectrum of 3,5-dimethylpyrazole shows peaks at m/z: 96 (100) M , 95 (80) MAH , in: S.R. Heller, G.W.A. Milne (Eds.), EPA/NIH mass spectra data base, U.S. Department of Commerce, National Bureau of Standards, 1978, p. 63. [28] A. Vogel, in: Vogel's Textbook of Practical Organic Chemistry, Longman, London, 1978, p. 881.