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Protonation of Very Strong Bases by Phenols in Non-aqueousSolutions

 

作者: Bogumil Brzeziński,  

 

期刊: Journal of Chemical Research, Synopses  (RSC Available online 1997)
卷期: Volume 0, issue 5  

页码: 151-151

 

ISSN:0308-2342

 

年代: 1997

 

DOI:10.1039/a607619j

 

出版商: RSC

 

数据来源: RSC

 

摘要:

CH2 CH2 N N Me Me Me Me CH2 CH2 N N Me Me Me Me N N N Me Et N P N Me2N Me2N P NMe2 NMe2 NMe2 1 DMAMN 3 MTBD 2 DMAMB 4 P2Et J. CHEM. RESEARCH (S), 1997 151 J. Chem. Research (S), 1997, 151 J. Chem. Research (M), 1997, 1021–1040 Protonation of Very Strong Bases by Phenols in Nonaqueous Solutions Bogumil/ Brzezi�nski,a Eugeniusz Grech,b Zbigniew Malarski,c Maria Rospenk,c Grzegorz Schroedera and Lucjan Sobczyk*c aFaculty of Chemistry, A. Mickiewicz University, 60-780 Pozna�n, Poland bInstitute of Fundamental Chemistry, Technical University, 71-065 Szczecin, Poland cFaculty of Chemistry, University of Wrocl/aw, 50-383 Wrocl/aw, Poland The interactions between the very strong proton sponge bases 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD) and Phosphazene Base, P2Et, and phenols of varying strength were studied in non-aqueous solutions using UV–VIS and IR spectroscopy.Whilst the interaction of proton sponges 1 and 2 with various proton donors has been the subject of numerous studies,8 there is little known about the complexation of very strong bases 3 and 4 in non-aqueous solvents.14 Consequently IR and UV–VIS studies of these bases with phenols were undertaken.Phenols can be considered as model proton donors15 as, by the introducing of various substituents, one can regulate their acidity over a broad pKa range. Their UV spectra are a sensitive indicator of the interaction strength and particularly of the degree of proton transfer.On the other hand, the IR spectra of the phenol complexes with bases provide important information on the features of hydrogen bonds formed between OH groups and the basic centres. 4-Methylphenol, 4-chlorophenol, 4-cyanophenol, 2,4,6-trichlorophenol and pentachlorophenol were used in CCl4, CHCl3, CH2Cl2 and MeCN. A variety of situations were found to be present depending on the solvent and phenol used. For weaker phenols in non-polar CCl4 complexation equilibria without proton transfer were observed whereas in the case of stronger phenols in MeCN complete complexation and the creation of strongly polar8 proton transfer states take place. Various intermediate states were found for medium strong phenols in weakly polar solvents.In many cases the ion pairs are characterized by extended charge separation. The UV band shifts upwards very long wave lengths, Fig. 1. The IR spectra reflect the complicated situation which appears in the intermediate states, Fig. 2. For 1:1 complexes only a weak band assigned to the ‘free’ N+–H group occurs which is characteristic of a tetrachloroaureate salt and a ‘continuum’ characteristic of hydrogen bridges with double minimum or with a broad asymmetrical single minimum potential. 18 For the 2:1 complexes the intensity of the continuum reaches high values that correspond to the formation of (OHO)µ bridges. Simultaneously the intensity of the +N–H bands indicates a full proton transfer to the MTBD molecule.The financial support from the Committee for Scientific Research (KBN grant 3 T09A 059 10) is acknowledged. Techniques used: IR, UV–VIS References: 31 Table 1: pKa values of N-bases in acetonitrile Table 2: Complexation and proton transfer equilibrium constants for systems phenols-strong bases in various solvents with positions of phenolic band in the UV region Figs. 1–9: UV and IR spectra of various phenol-N-base systems in non-aqueous solvents Received, 8th November 1996; Accepted, 22nd January 1997 Paper E/6/07619J References cited in this synopsis 8 B.Brzezi�nski, A. Jarczewski, J. Olejnik and G. Schroeder, J. Chem. Soc., Perkin Trans. 2, 1992, 2257; G. Schroeder, B. Brzezi �nski and A. Jarczewski, J. Mol. Struct., 1992, 274, 83; G. Schroeder, B. Brzezi�nski, Z. Malarski and L. Sobczyk, Pol. J. Chem., 1994, 68, 261. 14 B. Brzezi�nski, P. Radzijewski and G. Zundel, J. Chem. Soc., Faraday Trans., 1995, 91, 3141. 15 Th. Zeegers-Huyskens and P. Huyskens, Proton Transfer and Ion Transfer Complexes in Molecular Interactions, eds. H. Ratajczak and W. J. Orville-Thomas, Wiley, New York, 1980, vol. 2. 18 G. Zundel, Trends Phys. Chem., 1992, 3, 129. *To receive any correspondence. Fig. 1 UV spectra of 2,4,6-trichlorophenol–MTBD systems in MeCN: (1) phenol; (2) 1:1 system; (3) phenol in CCl4 with added KOH in ethanol; (4) phenol in water with KOH Fig. 2 IR spectra of 4-cyanophenol–MTBD systems in MeCN: (1) 1:1 system; (2) 2:1 system; (3) MTBD.HAuCl4 salt

 



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