Vanadium(V) Oxoanions in Basic Water Solution: a Simple Oxidative System for the One Pot Selective Conversion of L-Proline to Pyrroline- 2-Carboxylate

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1 Electronic Supplementary Material (ESI) for Dalton Transactions. This journal is The Royal Society of Chemistry 207 Vanadium(V) Oxoanions in Basic Water Solution: a Simple Oxidative System for the One Pot Selective Conversion of L-Proline to Pyrroline- 2-Carboxylate Lorenzo Biancalana, Giada Tuci, Fabio Piccinelli, Fabio Marchetti, Marco Bortoluzzi, and Guido Pampaloni SUPPORTING INFORMATION Page Table S. Selected standard reduction potentials for V(V), Cr(VI) and Mn(VII) ions in 2 aqueous solution. Figure S. X-ray powder diffraction pattern of the precipitate from L-proline/NH 4 VO 3 3 Determination of ph as a function of the NH 3 /V molar ratio in the NH 4 VO 3 /NH 3 system 4 Figure S2. Plot of ph as a function of NH 3 /V molar ratio. Table S2. Experimental optimization of L-pyrroline-2-carboxylate (P2C ) yield from the reaction of NH 4 VO 3 with L-Proline. Analysis of vanadate species in the reaction mixture by 5 V NMR spectroscopy Figure S3. 5 V NMR spectrum of a ph = 9.4 solution prepared with NH 4 VO 3 ([V] = 0. M) and NH 3 (NH 3 /V molar ratio =.0). Table S3 and Figure S4. Overlay of 5 V spectra at selected time intervals of the NH 4 VO 3 /l- Proline/NH 3 reaction system and corresponding ph and 3 C NMR yield of pyrroline-2- carboxylate. Calculation of a plausible reduction potential for the V(V)/V(IV) couple under the 8 experimental conditions used in the reactions Table S4. Thermodynamic data on [V 4 O 2 ] 4- and [V O ] 2- ions in aqueous solution. (aq) 4 9 (aq) Figure S5. DFT-optimized structure of intermediates C and C-is2 9 Figure S6. DFT-optimized structure of [V 4 O 0 (OH) 2 (sarcosinate) H 2 O] 3 0 Figure S7. Relative Gibbs energy values (kcal mol -, T = K) of possible intermediates involved in the oxidation of L-prolinate to pirrolidine-2-carboxylate.

2 Table S. Selected standard reduction potentials for V(V), Cr(VI) and Mn(VII) oxoions in aqueous solution. Reaction (acidic solution) E vs. SHE (298 K) Ref. Eq. (S) [VO 2 (aq) + 2 H (aq) + e [VO] (aq) + H 2 O +.00 V Eq. (S2) [Cr 2 O 7 (aq) + 4 H (aq) + 6 e 2 Cr (aq) + 7 H 2 O +.33 V 2 Eq. (S3) [MnO 4 (aq) + 8 H (aq) + 5 e Mn (aq) + 4 H 2 O +.5 V 2 Reaction (basic solution) E vs. SHE (298 K) Ref Eq. (S4) Eq. (S5) [VO 4 (aq) + 7 H (aq) + 2 e [HV 2 O 5 ] (aq) + 3 H 2 O V [VO 4 (aq) + 4 H 2 O + 2 e [HV 2 O 5 ] (aq) + 7 OH (aq) 0.70 V 3 Eq. (S6) 2- [CrO 4 (aq) + 4 H 2 O + 3 e Cr(OH) 3(s) + 5 OH (aq) 0.3 V 4 Eq. (S7) - [MnO 4 (aq) + 2 H 2 O + 3e MnO 2(s) + 4 OH (aq) +.23 V 2 K. Post, R. G. Robins, Electrochim. Acta, 976, 2, N. N. Greenwood, A. Earnshaw, Chemistry of the Elements (Second Edition), Butterworth-Heinemann, Oxford, Reduction potential calculated for Eq. (S4) at ph = 4 and formally corresponding to the standard reduction potential for Eq. (S5). 4 A. F. Holleman, E. Wiberg, N. Wiberg, Inorganic Chemistry, San Diego 200, Academic Press. 2

3 Figure S. X-ray powder diffraction pattern of the black precipitate obtained from L-proline/NH 4 VO 3 (black line), and calculated pattern of an equimolar mixture of (NH 4 ) 2 V 3 O 8 and NH 4 VO 3 (red line). 3

Determination of ph as a function of the NH 3 /V molar ratio A suspension of NH 4 VO 3 (229 mg,.96 mmol) in H 2 O (ca. 20 ml) was stirred at 70 C until a clear yellow solution was obtained ([V] 0.

4 Determination of ph as a function of the NH 3 /V molar ratio A suspension of NH 4 VO 3 (229 mg,.96 mmol) in H 2 O (ca. 20 ml) was stirred at 70 C until a clear yellow solution was obtained ([V] 0. mol/l). Once cooled to room temperature, stepwise addition of NH 3 (.8 mol/l in H 2 O) was performed and ph values as a function of the NH 3 /V molar ratio were determined (see Figure S2). Some relevant values are: NH 3 /V = 0, ph = 7.0; NH 3 /V = 0., ph = 8.4; NH 3 /V =.0, ph = 9.4; NH 3 /V = 2., ph = 9.7; NH 3 /V > 4, ph = Figure S2. Plot of ph as a function of NH 3 /V molar ratio determined with titration of solution 0. mol/l in vanadium (from NH 4 VO 3 ) with.8 mol/l NH 3. Enlarged view of the molar ratio region is given below ph ph NH3/V molar ratio NH3/V molar ratio 4

5 Table S2. Experimental optimization of L-pyrroline-2-carboxylate (P2C ) yield from the reaction of NH 4 VO 3 with L-Proline. Exp. NH V 3 /V concentration [a] molar ratio (ph [a] ) V/L- Proline molar ratio Temp. Reac. Time # 0.84 mol/l 0. (8.4) C 55 h 0 P2C NMR yield # mol/l.0 (9.4) C 45 h 40% # mol/l 2. (9.7) C 42 h 20% 65 h 25% # mol/l 2.2 with NaOH C 55 h 0 # mol/l 4.3 with NaOH C 55 h 0 #6.6 mol/l.0 (9.4).0 70 C 8 h 0% #7.6 mol/l.0 (9.4) C 9 h 30% 40 h 30% #8.6 mol/l.0 (9.4) C 2 h 35% 3h 60% #9.6 mol/l.0 (9.4) C 8 h 30% 42 h 50% #0 0.6 mol/l.0 (9.4) C 25 h 40% 45 h 50% #.0 mol/l.0 (9.4) C 7 h 45% 25 h 55% #2.6 mol/l.0 (9.4) C 2 h 35% 3 h 60% #3 2.0 mol/l.0 (9.4) C 7 h 40% 25 h 50% #4.0 mol/l.0 (9.4) C #5.0 mol/l.0 (9.4) C h 7 h 25 h 46 h 67 h 20.5 h 44 h 0 45% 55% 60% < 40% 0 Notes No reaction, only L- Proline in solution No reaction, only L- Proline in solution No reaction, only L- Proline in solution Byproducts were detected after 67 h. Only L-Proline in solution, but reaction mixture darkened [a] Vanadium concentration and ph are only formal values as we are dealing with suspensions. The NH 3 /V titration curve for the evaluation of ph has been obtained at a lower V concentration (0. mol/l) when all the vanadate precursor was dissolved (see pag. S4). 5

6 Analysis of vanadate species in the reaction mixture by 5 V NMR spectroscopy The predominant V(V) species within the ph interval 9-0 for concentrated solutions ([V] > 0. mol/l) are [HVO 4 ], [HV 2 O 7 ] 3 and higher-nuclearity oxoanions (tetra- and penta-vanadate species). 2,5 As a matter of fact, a solution prepared with equimolar amounts of NH 3 and NH 4 VO 3 ([V] = 0. M, ph = 9.4) showed four 5 V NMR resonances (Figure S3): i) 539 ppm, typical of [HVO 4 ] 6,7 ii) 565 ppm, typical of [HV 2 O 7 ] 3 7,8 iii) 576 ppm. 5 V NMR signals within the range 574 to 578 ppm have been assigned to the cyclic tetravanadate ion [V 4 O 2 ] 4 7,9,0 or alternatively to linear V 4 species as [HV 4 O 3 ] 5 or [V 4 O 3 ] 6 5,6,8 iv) 584 ppm. 5 V NMR signals around 585 ppm have been assigned to the cyclic pentavanadate 5-7,8, ion [V 5 O 5 ] Figure S3. 5 V NMR spectrum of a ph = 9.4 solution prepared with NH 4 VO 3 ([V] = 0. M) and NH 3 (NH 3 /V molar ratio =.0) ppm N. McCann, M. Wagner, H. Hasse, Dalton Trans., 203, 42, E. Heath, O. W. Howarth, J. Chem. Soc., Dalton Trans., 98, D. Rehder, M. Casny, R. Grosse, Magn. Reson. Chem. 2004; 42: D. C. Crans, A. S. Tracey, The Chemistry of Vanadium in Aqueous and Nonaqueous Solution, ACS Symposium Series, 998, 7. 9 S. E. O'Donnell, M. T. Pope, J. Chem. Soc., Dalton Trans., 976, M. A. Habayeb, O. E. Hileman Jr., Can. J. Chem., 58, 980, A. M. Amado, M. Aureliano, P. J. A. Ribeiro-Claro, J. J. Teixeira-Dias, J. Raman Spectros., 993, 24,

7 During 5 V NMR monitoring of the NH 4 VO 3 /L-Proline/NH 3 reaction system (see Experimental), we observed three signals, corresponding to [HVO 4 ], [HV 2 O 7 ] 3 and tetravanadate (Table S3 and Figure S4). The signal due to tetravanadate species was absent at the beginning of the reaction (yellow line in Fig. S2) while becoming the major species during the course of the reaction. Table S3 and Figure S4. Overlay of 5 V spectra at selected time intervals of the NH 4 VO 3 /L- Proline/NH 3 reaction system and corresponding ph and 3 C NMR yield of pyrroline-2-carboxylate. Reaction time ph P2C yield ( 3 C NMR) [a] 5 V NMR Line colour h % Yellow 2.5 h % green 24 h cyan 26.5 h % blue 33.5 h violet 48 h % red [a] Yields taken from Entry #4 in Table S2 at comparable reaction times. 7

8 Calculation of a plausible reduction potential for the V(V)/V(IV) couple under the experimental conditions used in the reactions It is difficult to provide a meaningful reduction potential for the V(V)/V(IV) couple under conditions relevant to the oxidation of L-Proline, since V(V) species with different nuclearity and protonation state are present in solution (see Pag S7) and can be involved in the redox reaction. The reaction mechanism proposed by DFT calculations considered the transformation of the V(V) cyclic tetravanadate [H 2 V 4 O 2 ] 2 to the mixed valence V(V)/V(IV) compound [H 4 V 4 O 2 ] 2 of the same nuclearity. On the other hand, thermodynamic data available in the literature for tetranuclear V(V) and V(IV) species, compiled in Table S4, are related to [V 4 O 2 ] 4 and [V 4 O 9 ] 2. These ions are the conjugate base of [H 2 V 4 O 2 ] 2 and the fully reduced (and deprotonated) counterpart of [H 4 V 4 O 2 ] 2, respectively, which have been used in DFT calculations. Table S4. Thermodynamic data on [V 4 O 2 ] 4- and [V O ] 2- ions in aqueous solution. (aq) 4 9 (aq) Reaction G (298 K) Ref. Eq. (S8) [VO 4 ] 3 (aq) + 2 H + [H VO ] (aq) 2 4 (aq) Eq. (S9) 4 [H 2 VO 4 ] (aq) [V 4 O 2 ] H O (aq) 2 Eq. (S0) 4 [VO 4 ] 3 (aq) + 4 H e [V O ] H O (aq) 4 9 (aq) 2 22 kj/mol 80 kj/mol 846 kj/mol 5 Using these data, a standard reduction potential of E = V (corresponding to G = 278 kj/mol) can be calculated for the V 4 (V) V 4 (IV) transformation reported in Eq. (S) at 298 K. (S) [V 4 O 2 ] H e - [V O ] H O (aq) (aq) 4 9 (aq) 2 Therefore, on considering the variation of the potential with ph as E = E - 6 of E at different ph were calculated: ph, values For ph = 4, E = 0.52 V, corresponding to the standard reduction potential for Eq. (S2). (S2) [V4O2] 4 (aq) + 4 e [V4O9] 2 (aq) + 6 OH (aq) For ph = 0 E = 0.7 V For ph = 9 E = 0.08 V 8

9 Figure S5. DFT-optimized structure of intermediates C and C-is2 and Gibbs energy difference (kcal mol -, T = K). C-PCM/ B97X calculations, water as continuous medium. Colour map: light grey, hydrogen; dark grey, carbon; red, oxygen; blue, nitrogen; green, vanadium; light blue, spin density surface (isovalue = 0.0 a.u.). 9

10 Figure S6. DFT-optimized structure of [V 4 O 0 (OH) 2 (sarcosinate) H 2 O] 3. C-PCM/ B97X calculations, water as continuous medium. Colour map: light grey, hydrogen; dark grey, carbon; red, oxygen; blue, nitrogen; green, vanadium. Selected computed bond lengths: V O carboxylate Å, O carboxylate ---H,.558 Å, O H(---O carboxylate ).008 Å. Cartesian coordinates are collected in a separated. xyz file. 0

11 Figure S7. Relative Gibbs energy values (kcal mol -, T = K) of possible intermediates involved in the oxidation of L-prolinate to pirrolidine-2-carboxylate. C-PCM/ B97X calculations, water as continuous medium. Black line: isotope H for all hydrogen atoms. Blue line: isotope 2 H for the N- and O-bonded hydrogen atoms.

Supporting Information

Supporting Information Electronic Supplementary Material (ESI) for RSC Advances. This journal is The Royal Society of Chemistry 2017 The Reactions of α-amino Acids and α-amino Esters with High Valent Transition Metal Halides: