Nucleophilicities and Lewis basicities of imidazoles, benzimidazoles, and benzotriazoles

Transcription

1 This journal is The Royal Society of Chemistry 21 Electronic Supporting Information (ESI) Nucleophilicities and Lewis basicities of imidazoles, benzimidazoles, and benzotriazoles Mahiuddin Baidya, Fran Brotzel and Herbert Mayr* Department Chemie Ludwig-Maximilians-Universität München (LMU) Butenandtstraße 5-13 (Haus F) München (Germany) S1

2 This journal is The Royal Society of Chemistry 21 Table of Contents Page Materials S3 Product studies S3 Determination of equilibrium constants S6 Kinetics for the reactions of amines 1 3 with benzhydrylium ions (Ar 2 CH + ) in CH 3 CN and DMSO Kinetics for the reactions of imidazoles 1 with benzhydrylium ions in H 2 O S15 S49 References S58 S2

3 This journal is The Royal Society of Chemistry 21 Materials Commercially available CH 3 CN (VWR, Prolabo, HPLC-gradient grade) and DMSO (>99.8%, Acros extra dry) were used as received. The benzhydrylium tetrafluoroborates Ar 2 CH + BF 4 were prepared as described before. [S1] All imidazoles, benzimidazoles, and benzotriazoles were purchased from commercial sources and (if necessary) purified by crystallizations or distillation prior to use. Product studies 1 H NMR chemical shifts are reported in ppm relative to the deuterated solvent as internal standard (δ H = 7.24 for CDCl 3 ). The 13 C NMR chemical shifts refer to the solvent as internal standard (δ C = for CDCl 3 ). Product studies with imidazoles (1) General procedure: The blue CH 3 CN solution of (dma) 2 CH + BF 4 (1. equiv.) was added drop by drop to a solution of an appropriate imidazole 1 (1. eqiv.) in dry CH 3 CN (1 ml) under nitrogen at room temperature. After the disappearance of the blue color of the solution, solid K 2 CO 3 (1.2 equiv.) was added, and the reaction mixture was allowed to stir for a few more minutes. Then the solvent was removed in vacuum and the residue was directly transferred to the column (neutral alumina [S2] ). Purification by column chromatography (EtOAc/isohexane, 1:1 as eluent) gave the desired product. Reaction of imidazole (1a) with (dma) 2 CH + BF 4 : Imidazole 1a (2 mg, 2.94 mmol) and (dma) 2 CH + BF 4 (1 mg,.294 mmol) gave a light brown gummy solid (82. mg,.256 mmol, 87 %). N N N N δ H (3 MHz, CDCl 3 ) 2.92 (s, 12 H), 6.32 (s, 1 H), 6.65 (d, J 8.8 Hz, 4 H), (m, 1 H), 6.95 (d, J 8.8 Hz, 4 H), 7.4 (m, 1 H) and 7.38 (s, 1 H); δ C (75.5 MHz, CDCl 3 ) 4.7, 64.5, 112.5, 119.6, 127.6, 128.9, 129., and S3

4 This journal is The Royal Society of Chemistry 21 Reaction of 4-methylimidazole (1e) with (dma) 2 CH + BF 4 : 4-Methylimidazole 1e (242 mg, 2.95 mmol) and (dma) 2 CH + BF 4 (1 mg,.294 mmol) gave a 1. :.4 mixture of two regioisomers as a yellow oil (8.8 mg,.242 mmol, 82 %). N N N N Major isomer: δ H (3 MHz, CDCl 3 ) 2.18 (s, 3 H), 2.92 (s, 12 H), 6.24 (s, 1 H), 6.54 (s, 1 H), 6.65 (d, 4 H, J 9. Hz), 6.95 (d, 4 H, J 9. Hz) and (m, 1 H); δ C (75.5 MHz, CDCl 3 ) 14., 4.7, 64.3, 112.4, 116., 127.8, 129., 136.6, and Product studies with benzimidazoles (2) General procedure: The blue DMSO solution of (dma) 2 CH + BF 4 (1. equiv.) was added drop by drop to a solution of an appropriate benzimidazole 2 (3. equiv.) in dry DMSO (12 ml) under nitrogen at room temperature. After the disappearance of the blue color of the solution, solid K 2 CO 3 (1.2 equiv.) was added, and reaction mixture was allowed to stir for a few more minutes. Then, the mixture was diluted with H 2 O and extracted with ethyl acetate. The extract was washed several times with water and then dried (MgSO 4 ). The solvent was removed in vacuum, and the gummy residue was purified by column chromatography (neutral alumina, EtOAc/isohexane, 1:2 as eluent) to give pure product. Reaction of benzimidazole (2a) with (dma) 2 CH + BF 4 : Benzimidazole 2a (14 mg,.88 mmol) and (dma) 2 CH + BF 4 (1 mg,.294 mmol) gave a gummy oil (82.3 mg,.222 mmol, 76 %). N N N N δ H (4 MHz, CDCl 3 ) 3. (s, 12 H), 6.65 (s, 1 H), 6.73 (d, J 8.8 Hz, 4 H), 7.6 (d, J 8.8 Hz, 4 H), (m, 3 H), 7.71 (s, 1 H) and 7.88 (d, J 8. Hz, 1 H); δ C (11 MHz, CDCl 3 ) 4.6, 63.1, 111.4, 112.5, 12.2, 122.3, 122.8, 126.4, 129.1, 134.2, 143., and S4

5 This journal is The Royal Society of Chemistry 21 Reaction of 5 methylbenzimidazole (2d) with (dma) 2 CH + BF 4 : 5-Methylbenzimidazole 2d (117 mg,.885 mmol) and (dma) 2 CH + BF 4 (1 mg,.294 mmol) gave 1 : 1 mixture of two regioisomers as a yellow gummy oil (83.1 mg,.216 mmol, 74 %). N N and N N N N N N δ H (4 MHz, CDCl 3 ) 2.39/2.44 (2 s, 2 3 H), 2.92/2.93 (2 s, 2 12 H), 6.54/6.55 (2 s, 2 1 H = 2 H), (m, 2 4 H = 8 H), (m, 2 6 H = 12 H), (m, 1 H + 2 H = 3 H), 7.68 (d, J = 8.2 Hz, 1 H); δ C (11 MHz, CDCl 3 ) 21.7/22. (2 C), 4.6 (2 C), 62.7/63.1 (2 C), 11.8/11.9 (2 C), (2 C), 119.8/12. (2 C), 123.9/124.2 (2 C), 126.6/126.7 (2 C), (2 C), 131.8/132.5/132.6/143.6 (4 C), 142.4/142.6/143./144.7 (4 C) and 15.1 (2 C). Reaction of 5,6-dimethylbenzimidazole (2f) with (dma) 2 CH + BF 4 : 5,6-Dimethylbenzimidazole 2f (129 mg,.882 mmol) and (dma) 2 CH + BF 4 (1 mg,.294 mmol) gave a colorless solid (98. mg,.246 mmol, 84 %); mp. 193 C. N N N N δ H (4 MHz, CDCl 3 ) 2.27 (s, 3 H), 2.33 (s, 3 H), 2.92 (s, 12 H), 6.52 (s, 1 H), 6.65 (d, J 8.8 Hz, 4 H), (m, 5 H), 7.51 (s, 1 H) and 7.54 (s, 1 H); δ C (11 MHz, CDCl 3 ) 2.5, 2.8, 4.6, 62.8, 111.2, 112.6, 12.3, 126.9, 129.1, 131., 131.8, 133.1, 142.4, 143. and S5

6 This journal is The Royal Society of Chemistry 21 Determination of equilibrium constants Equilibrium constants were measured by UV/Vis spectroscopy in acetonitrile as follows: To solutions of the benzhydrylium tetrafluoroborates in acetonitrile small volumes of stoc solutions of amines 1 3 were added and the decay of the absorptions was monitored. When the absorbance was constant, another portion of stoc solution was added. This procedure was repeated four to eight times for each benzhydrylium salt solution. Assuming a proportionality between the absorbances and the concentrations of the benzhydrylium ions, the equilibrium constants (K) can be expressed by the absorbances of the benzhydrylium ions before (A ) and after (A) the addition of amines 1 3 using the following equation. Ar 2 CH + + NR 3 K + Ar 2 CH-NR 3 CH 3 CN K = [Ar 2 CH-NR 3 + ] [Ar 2 CH + ] [NR 3 ] = A - A A [NR 3 ] Where [NR 3 ] = [NR 3 ] - [Ar 2 CH-NR 3 + ] The temperature of the solutions during all equilibrium studies was ept constant at 2 C using a circulating bath thermostat. Equilibrium constant for the reaction of 1-methylimidazole (1b) and (lil) 2 CH + BF 4 ε [(lil) 2 CH + BF 4 at 631 nm] = M 1 cm 1 and d =.5 cm Entry [1b] A [(lil) 2 CH + BF 4 ] eq K (L mol 1 ) S6

7 This journal is The Royal Society of Chemistry K av (2 C) = L mol 1 Equilibrium constant for the reaction of 1-methylimidazole (1b) and (jul) 2 CH + BF 4 ε [(jul) 2 CH + BF 4 at 635 nm] = M 1 cm 1 and d =.5 cm Entry [1b] A [(jul) 2 CH + BF 4 ] eq K (L mol 1 ) K av (2 C) = L mol 1 Equilibrium constant for the reaction of 1-methylimidazole (1b) and (ind) 2 CH + BF 4 ε [(ind) 2 CH + BF 4 at 616 nm] = M 1 cm 1 and d =.5 cm Entry [1b] A [(ind) 2 CH + BF 4 ] eq K (L mol 1 ) S7

8 This journal is The Royal Society of Chemistry K av (2 C) = L mol 1 Equilibrium constant for the reaction of 1-methylimidazole and (thq) 2 CH + BF 4 ε [(thq) 2 CH + BF 4 at 62 nm] = M 1 cm 1 and d =.5 cm Entry [1b] A [(thq) 2 CH + BF 4 ] eq K (L mol 1 ) K av (2 C) = L mol 1 Equilibrium constant for the reaction of 1-phenylimidazole (1c) and (ind) 2 CH + BF 4 ε [(ind) 2 CH + BF 4 at 616 nm] = M 1 cm 1 and d =.5 cm Entry [1c] A [(ind) 2 CH + BF 4 ] eq K (L mol 1 ) S8

9 This journal is The Royal Society of Chemistry K av (2 C) = L mol 1 Equilibrium constant for the reaction of 1-phenylimidazole (1c) and (thq) 2 CH + BF 4 ε [(thq) 2 CH + BF 4 at 62 nm] = M 1 cm 1 and d =.5 cm Entry [1c] A [(thq) 2 CH + BF 4 ] eq K (L mol 1 ) K av (2 C) = L mol 1 Equilibrium constant for the reaction of 1 phenylimidazole (1c) and (pyr) 2 CH + BF 4 ε [(pyr) 2 CH + BF 4 at 612 nm] = M 1 cm 1 and d =.5 cm Entry [1Ph Imi] A [(pyr) 2 CH + BF 4 ] eq K (L mol 1 ) S9

10 This journal is The Royal Society of Chemistry K av (2 C) = L mol 1 Equilibrium constant for the reaction of 1-phenylimidazole and (dma) 2 CH + BF 4 ε [(dma) 2 CH + BF 4 ] at 65 nm] = M 1 cm 1 and d =.5 cm Entry [1c] A [(dma) 2 CH + BF 4 ] eq K (L mol 1 ) K av (2 C) = L mol 1 Equilibrium constant for the reaction of 1-methylbenzimidazole (2b) and (ind) 2 CH + BF 4 ε [(ind) 2 CH + BF 4 at 616 nm] = M 1 cm 1 and d =.5 cm Entry [2b] A [(ind) 2 CH + BF 4 ] eq K (L mol 1 ) S1

11 This journal is The Royal Society of Chemistry K av (2 C) = L mol 1 Equilibrium constant for the reaction of 1-methylbenzimidazole (2b) and (thq) 2 CH + BF 4 ε [(thq) 2 CH + BF 4 at 62 nm] = M 1 cm 1 and d =.5 cm Entry [2b] A [(thq) 2 CH + BF 4 ] eq K (L mol 1 ) K av (2 C) = L mol 1 S11

12 This journal is The Royal Society of Chemistry 21 Equilibrium constant for the reaction of 1-methylbenzimidazole (2b) and (pyr) 2 CH + BF 4 ε [(pyr) 2 CH + BF 4 at 612 nm] = M 1 cm 1 and d =.5 cm Entry [2b] A [(pyr) 2 CH + BF 4 ] eq K (L mol 1 ) K av (2 C) = L mol 1 Equilibrium constant for the reaction of 1-methylbenzimidazole (2b) and (dma) 2 CH + BF 4 ε [(dma) 2 CH + BF 4 at 65 nm] = M 1 cm 1 and d =.5 cm Entry [2b] A [(dma) 2 CH + BF 4 ] eq K (L mol 1 ) S12

13 This journal is The Royal Society of Chemistry K av (2 C) = L mol 1 Equilibrium constant for the reaction of 1-methylbenzotriazole (3b) and (mfa) 2 CH + BF 4 ε [(mfa) 2 CH + BF 4 at 586 nm] = M 1 cm 1 and d =.5 cm Entry [3b] A [(mfa) 2 CH + BF 4 ] eq K (L mol 1 ) K av (2 C) = L mol 1 Equilibrium constant for the reaction of 1-methylbenzotriazole (3b) and (pfa) 2 CH + BF 4 ε [(pfa) 2 CH + BF 4 at 592 nm] = M 1 cm 1 and d =.5 cm Entry [3b] A [(pfa) 2 CH + BF 4 ] eq K (L mol 1 ) S13

14 This journal is The Royal Society of Chemistry K av (2 C) = L mol 1 S14

15 This journal is The Royal Society of Chemistry 21 Kinetics for the reactions of amines 1 3 with benzhydrylium ions (Ar 2 CH + ) in CH 3 CN and DMSO at 2 C The reactions of imidazoles 1, benzimidazoles 2, and benzotriazoles 3 with the colored benzhydrylium tetrafluoroborates were followed photometrically at the vicinity of absorption maxima of Ar 2 CH + by UV-Vis spectrometry using stopped flow or J&M instrument as described previously. [S1] Al experiments were performed under pseudo-first-order conditions (excess of amines 1 3) at 2 C in dry CH 3 CN or in dry DMSO. First-order rate constants were obtained by least-square fitting of the absorbances to the mono exponential curve A t = A exp( t) + C. Because of = [amine], the second-order rate constants (L mol 1 s 1 ) were derived from the slope of the linear plot of vs. [amine]. Kinetics of the reactions of imidazole (1a) with (Ar) 2 CH + in CH 3 CN at 2 C [(ind) 2 CH + ] [1a] λ = 61 nm E E E E-1 y = x +.12.E+ R 2 = [(thq) 2 CH + ] [1a] λ = 61 nm y = x R 2 = S15

16 This journal is The Royal Society of Chemistry 21 [(pyr) 2 CH + ] [1a] λ = 61 nm y = x R 2 = [(dma) 2 CH + ] [1a] λ = 61 nm y = x R 2 = Reactivity parameters for imidazole (1a) in CH 3 CN Ar 2 CH + E (ind) CH N = (thq) 2 CH s =.79 (pyr) 2 CH (dma) 2 CH y =.7853x R 2 =.988 log E S16

17 This journal is The Royal Society of Chemistry 21 Kinetics of the reactions of imidazole (1a) with (Ar) 2 CH + in DMSO at 2 C [(ind) 2 CH + ] [1a] λ = 62 nm y = x R 2 = [Nu] mol / L -1 [(thq) 2 CH + ] [1a] λ = 62 nm y = 478x R 2 = [(pyr) 2 CH + ] [1a] λ = 62 nm y = 165.7x R 2 = [Nu] mol / L -1 S17

18 This journal is The Royal Society of Chemistry 21 [(dma) 2 CH + ] [1a] λ = 62 nm y = 387.4x R 2 = Reactivity parameters for imidazole (1a) in DMSO Ar 2 CH + E (ind) 2 CH N = (thq) 2 CH s =.79 (pyr) 2 CH (dma) 2 CH y =.7871x R 2 =.9635 log E S18

19 This journal is The Royal Society of Chemistry 21 Kinetics of the reactions of 1-methylimidazole (1b) with (Ar) 2 CH + in CH 3 CN at 2 C [(lil) 2 CH + ] [1b] λ = 614 nm y = 23.34x +.11 R 2 = [(ind) 2 CH + ] [1b] λ = 614 nm y = x R 2 = [(thq) 2 CH + ] [1b] λ = 614 nm y = 48.88x +.45 R 2 = S19

20 This journal is The Royal Society of Chemistry 21 [(pyr) 2 CH + ] [1b] λ = 614 nm y = 144.3x R 2 = [(dma) 2 CH + ] [1b] λ = 614 nm y = x R 2 = Reactivity parameters for 1-methylimidazole (1b) in CH 3 CN Ar 2 CH + E (lil) 2 CH N = 11.9 (ind) 2 CH s =.73 (thq) 2 CH (pyr) 2 CH (dma) 2 CH log y =.7336x R 2 = E S2

21 This journal is The Royal Society of Chemistry 21 Kinetics of the reactions of 1-phenylimidazole (1c) with (Ar) 2 CH + in CH 3 CN at 2 C [(thq) 2 CH + ] [1c] λ = 62 nm t 4.21 y = 9.437E+1x E-1 obs / s-1 1 R 2 = 1.E [Nu] / mol L-1 [(pyr) 2 CH + ] [1c] λ = 68 nm y = 2.638E+2x E R 2 = 1.E [(dma) 2 CH + ] [1c] λ = 68 nm y = 7.288E+2x E-2 R 2 = 1.E S21

22 This journal is The Royal Society of Chemistry 21 [(mpa) 2 CH + ] [1c] λ = 613 nm y = x R 2 = [(mor) 2 CH + ] [1c] λ = 613 nm y = 527.9x R 2 = [(mfa) 2 CH + ] [1c] λ = 59 nm y = 81375x R 2 = S22

23 This journal is The Royal Society of Chemistry 21 Reactivity parameters for 1-phenylimidazole (1c) in CH 3 CN Ar 2 CH + E (thq) 2 CH N = (pyr) 2 CH s =.67 (dma) 2 CH (mpa) 2 CH (mor) 2 CH y =.6655x (mfa) 2 CH R 2 =.9868 log E S23

24 This journal is The Royal Society of Chemistry 21 Kinetics of the reactions of 2-methylimidazole (1d) with (Ar) 2 CH + in CH 3 CN at 2 C [(lil) 2 CH + ] [1d] λ = 633 nm y = x R 2 = [(jul) 2 CH + ] [1d] λ = 636 nm y = x R 2 = [(ind) 2 CH + ] [1d] λ = 619 nm y = 172.4x R 2 = S24

25 This journal is The Royal Society of Chemistry 21 [(thq) 2 CH + ] [1d] λ = 622 nm y = 473.3x R 2 = [(pyr) 2 CH + ] [1d] λ = 68 nm y = 147.6x R 2 = [(dma) 2 CH + ] [1d] λ = 68 nm y = 3285x R 2 = S25

26 This journal is The Royal Society of Chemistry 21 Reactivity parameters for 2-methylimidazole (1d) in CH 3 CN Ar 2 CH + E (lil) CH N = (jul) 2 CH s =.76 (ind) 2 CH (thq) 2 CH (pyr) 2 CH (dma) 2 CH y =.7591x R 2 =.9961 log E S26

27 This journal is The Royal Society of Chemistry 21 Kinetics of the reactions of 4-methylimidazole (1e) with (Ar) 2 CH + in CH 3 CN at 2 C [(lil) 2 CH + ] [1e] λ = 614 nm y = x R 2 = [(jul) 2 CH + ] [1e] λ = 614 nm y = 64.12x R 2 = [(ind) 2 CH + ] [1e] λ = 614 nm y = 196.5x R 2 = S27

28 This journal is The Royal Society of Chemistry 21 [(thq) 2 CH + ] [1e] λ = 614 nm y = x R 2 = [(pyr) 2 CH + ] [1e] λ = 614 nm y = x obs / s-1 R 2 = [Nu] / mol L-1 [(dma) 2 CH + ] [1e] λ = 614 nm y = x R 2 = S28

29 This journal is The Royal Society of Chemistry 21 Reactivity parameters for 4-methylimidazole (1e) in CH 3 CN Ar 2 CH + E (lil) 2 CH N = (jul) 2 CH s =.77 (ind) 2 CH (thq) 2 CH (pyr) 2 CH y =.7719x (dma) 2 CH log. R 2 = E S29

30 This journal is The Royal Society of Chemistry 21 Kinetics of the reactions of 2,4-dimethylimidazole (1f) with (Ar) 2 CH + in CH 3 CN at 2 C [(jul) 2 CH + ] [1f] λ = 635 nm y = x -.66 R 2 = [(ind) 2 CH + ] [1f] λ = 612 nm y = x +.46 R 2 = [(thq) 2 CH + ] [1f] λ = 62 nm y = x R 2 = S3

31 This journal is The Royal Society of Chemistry 21 [(pyr) 2 CH + ] [1f] λ = 612 nm y = 26.5x R 2 = [(dma) 2 CH + ] [1f] λ = 65 nm y = 546.2x / s-1 7 R 2 = Reactivity parameters for 2,4-dimethylimidazole (1f) in CH 3 CN Ar 2 CH + E (jul) 2 CH N = (ind) 2 CH s =.84 (thq) 2 CH (pyr) 2 CH (dma) 2 CH y =.8434x R 2 =.992 log E S31

32 This journal is The Royal Society of Chemistry 21 Kinetics of the Reactions of 1-trimethylsilylimidazole (1g) with (Ar) 2 CH + in CH 3 CN at 2 C [(jul) 2 CH + ] [1g] λ = 635 nm y = x R 2 = [(ind) 2 CH + ] [1g] λ = 61 nm y = x R 2 = [(pyr) 2 CH + ] [1g] λ = 61 nm y = 131.5x R 2 = S32

33 This journal is The Royal Society of Chemistry 21 [(dma) 2 CH + ] [1g] λ = 61 nm y = x R 2 = [(mpa) 2 CH + ] [1g] λ = 61 nm y = 23355x -.55 R 2 = [Nu] mol / L -1 Reactivity parameters for 1-trimethylsilylimidazole (1g) in CH 3 CN Ar 2 CH + E (jul) 2 CH N = (ind) 2 CH s =.79 (pyr) 2 CH (dma) 2 CH (mpa) 2 CH y =.7876x R 2 =.9988 log E S33

34 This journal is The Royal Society of Chemistry 21 Kinetics of the reactions of benzimidazole (2a) with (Ar) 2 CH + in DMSO at 2 C [(jul) 2 CH + ] [2a] λ = 635 nm y = x +.6 R 2 = [(ind) 2 CH + ] [2a] λ = 62 nm y = x +.3 R 2 = [(thq) 2 CH + ] [2a] λ = 61 nm y = 65.52x R 2 = S34

35 This journal is The Royal Society of Chemistry 21 [(pyr) 2 CH + ] [2a] λ = 62 nm y = x R 2 = [(dma) 2 CH + ] [2a] λ = 613 nm y = x -.51 R 2 = Reactivity parameters for benzimidazole (2a) in DMSO Ar 2 CH + E (jul) 2 CH N = 1.5 (ind) 2 CH s =.79 (thq) 2 CH (pyr) 2 CH (dma) 2 CH y =.7894x log R 2 = E S35

36 This journal is The Royal Society of Chemistry 21 Kinetics of the reactions of 1-methylbenzimidazole (2b) with (Ar) 2 CH + in CH 3 CN at 2 C [(ind) 2 CH + ] [2b] λ = 61 nm y = 2.233x +.18 R 2 = [(thq) 2 CH + ] [2b] λ = 62 nm y = x R 2 = [(pyr) 2 CH + ] [2b] λ = 611 nm y = 16.45x R 2 = S36

37 This journal is The Royal Society of Chemistry 21 [(dma) 2 CH + ] [2b] λ = 61 nm y = x +.55 R 2 = [(mpa) 2 CH + ] [2b] λ = 61 nm y = x R 2 = Reactivity parameters for N-methylbenzimidazole (2b) in CH 3 CN Ar 2 CH + E (ind) 2 CH N = 1.37 (thq) 2 CH s =.82 (pyr) 2 CH (dma) 2 CH (mpa) 2 CH log 2 y =.8151x R 2 = E S37

38 This journal is The Royal Society of Chemistry 21 Kinetics of the reactions of 2-methylbenzimidazole (2c) with (Ar) 2 CH + in DMSO at 2 C [(jul) 2 CH + ] [2c] λ = 635 nm y = 2.892x +.2 R 2 = [(ind) 2 CH + ] [2c] λ = 62 nm y = 1.79x +.1 R 2 = [(thq) 2 CH + ] [2c] λ = 618 nm y = x R 2 = S38

39 This journal is The Royal Society of Chemistry 21 [(pyr) 2 CH + ] [2c] λ = 62 nm y = x -.51 R 2 = [(dma) 2 CH + ] [2c] λ = 613 nm y = x R 2 = Reactivity parameters for 2-methylbenzimidazole (2c) in DMSO Ar 2 CH + E (jul) 2 CH N = 1.2 (ind) 2 CH s =.85 (thq) 2 CH (pyr) 2 CH (dma) 2 CH log 1 y =.852x R 2 = E S39

40 This journal is The Royal Society of Chemistry 21 Kinetics of the reactions of 5-methylbenzimidazole (2d) with (Ar) 2 CH + in DMSO at 2 C [(jul) 2 CH + ] [2d] λ = 645 nm y = 9.749x R 2 = [(ind) 2 CH + ] [2d] λ = 62 nm y = x -.1 R 2 = [(thq) 2 CH + ] [2d] λ = 618 nm y = x R 2 = S4

41 This journal is The Royal Society of Chemistry 21 [(pyr) 2 CH + ] [2d] λ = 62 nm y = x R 2 = [(dma) 2 CH + ] [2d] λ = 613 nm y = x R 2 = Reactivity parameters for 5-methylbenzimidazole (2d) in DMSO Ar 2 CH + E (jul) 2 CH N = 1.69 (ind) 2 CH s =.79 (thq) 2 CH (pyr) 2 CH (dma) 2 CH y =.7882x R 2 = log E S41

42 This journal is The Royal Society of Chemistry 21 Kinetics of the reactions of 2,5-dimethylbenzimidazole (2e) with (Ar) 2 CH + in DMSO at 2 C [(jul) 2 CH + ] [2e] λ = 645 nm y = 4.538x +.1 R 2 = [(ind) 2 CH + ] [2e] λ = 62 nm y = x R 2 = [(thq) 2 CH + ] [2e] λ = 618 nm y = x -.27 R 2 = S42

43 This journal is The Royal Society of Chemistry 21 [(pyr) 2 CH + ] [2e] λ = 62 nm y = x R 2 = [(dma) 2 CH + ] [2e] λ = 613 nm y = x R 2 = Reactivity parameters for 2,5-dimethylbenzimidazole (2e) in DMSO Ar 2 CH + E (jul) 2 CH N = 1.21 (ind) 2 CH s =.85 (thq) 2 CH (pyr) 2 CH (dma) 2 CH log 2 1 y =.8485x R 2 = E S43

44 This journal is The Royal Society of Chemistry 21 Kinetics of the reactions of 5,6-dimethylbenzimidazole (2f) with (Ar) 2 CH + in DMSO at 2 C [(lil) 2 CH + ] [2f] λ = 64 nm y = 5.871x -..5 R 2 = [(jul) 2 CH + ] [2f] λ = 645 nm y = 14.57x +.5 R 2 = [(ind) 2 CH + ] [2f] λ = 62 nm y = x - 2E-5 R 2 = S44

45 This journal is The Royal Society of Chemistry 21 [(thq) 2 CH + ] [2f] λ = 618 nm y = x R 2 = [(dma) 2 CH + ] [2f] λ = 613 nm y = 82.76x R 2 = Reactivity parameters for 5,6-dimethylbenzimidazole (2f) in DMSO Ar 2 CH + E (lil) 2 CH N = 11.8 (jul) 2 CH s =.71 (ind) 2 CH (thq) 2 CH (dma) 2 CH y =.7129x R 2 =.9962 log E S45

46 This journal is The Royal Society of Chemistry 21 Kinetics of the reactions of 5-methoxybenzimidazole (2g) with (Ar) 2 CH + in DMSO at 2 C [(lil) 2 CH + ] [2g] λ = 64 nm y = x +.2 R 2 = [(jul) 2 CH + ] [2g] λ = 645 nm y = 12.21x +.4 R 2 = Reactivity parameters for 5-methoxybenzimidazole (2g) in DMSO Ar 2 CH + E (lil) 2 CH N = 11. (jul) 2 CH s = log.8.5 y =.715x R 2 = E S46

47 This journal is The Royal Society of Chemistry 21 Kinetics of the reactions of benzotriazole (3a) with (Ar) 2 CH + in CH 3 CN at 2 C [(mor) 2 CH + ] [3a] λ = 613 nm y = x R 2 = [(mfa) 2 CH + ] [3a] λ = 586 nm y = x R 2 = Reactivity parameters for benzotriazole (3a) in CH 3 CN Ar 2 CH + E (mor) 2 CH N = 7.69 (mfa) 2 CH s =.76 3 log 2 1 y =.7639x R 2 = E S47

48 This journal is The Royal Society of Chemistry 21 Kinetics of the reactions of 1-methylbenzotriazole (3b) with (Ar) 2 CH + in CH 3 CN at 2 C [(mfa) 2 CH + ] [3b] λ = 586 nm y = x R 2 = Reactivity parameters for 1-methylbenzotriazole (3b) in CH 3 CN As only one rate constant is available for 1-methylbenzotriazole (3b), its N parameter was calculated assuming s =.76 as for benzotriazole (3a). Thus, log ( ) =.76(N 3.85) and N = S48

49 This journal is The Royal Society of Chemistry 21 Kinetics for the reactions of imidazoles 1 with benzhydrylium ions in H 2 O at 2 C When an amine is dissolved in water, the concentration of hydroxide ion increases by protolysis. For that reason, competing reactions of the carbocations with hydroxide and water have to be considered because the observed pseudo-first-order rate constant reflects the sum of the reactions of the electrophile with free amine 1 ( 1Ψ,N ), with OH ( 1Ψ,OH ), with water ( w ) and the bac reaction ( ). Rearrangement of eq 1 yields eq 2 where 1Ψ is defined as the overall rate constant minus the contribution of hydroxide. = 1Ψ,N + 1Ψ,OH + w + = [1] effective + OH [OH ] + w + (1) OH [OH ] = [1] effective + w + = 1Ψ (2) Concentrations of free amines [amine] effective and of hydroxide ions [OH ] were calculated from the nown pk B of the amines [S3] as shown below (eq A to F). Combining calculated [OH ] with published OH values yielded 1Ψ,OH. [S4] Thus, second-order rate constants for the reactions of imidazoles with benzhydrylium ions in water could be derived from the slopes of the 1Ψ (= OH [OH ]) vs. [1] effective plots. R 3 N + H 2 O + R 3 NH + OH - (A) K B [ammonium] [OH ] = [amine] (B) effective [amine] = [amine] effective + [ammonium] = [amine] effective + [OH - ] (C) Combination of equation B and C yields 2 [OH ] K B = (D) [amine] [OH ] Solving of the quadratic equation (D) leads to one logic solution for [OH - ] with the + in the numerator (eq F). 2 B [ + + KB KB OH ] = 2 K 2 [amine] (F) S49

50 This journal is The Royal Society of Chemistry 21 However, pk ah of imidazoles 1 in H 2 O are close to 7 and, therefore, one will not expect formation of considerable amounts of hydroxide ions and protonated imidazoles during inetic experiments. As shown below, the second-order rate constants for the reactions of 2-methylimidazole (1d) with (ind) 2 CH + were determined with and without considering the contribution of hydroxide ions. Both methods yielded identical second-order rate constants. The reactions of benzhydrylium ions with water are very slow compared to the corresponding reactions with imidazoles and, thus, do not affect our inetic evaluations. Hence the secondorder rate constants for the reactions of 1a-b,d with benzhydrylium ions in water were determined without considering the contribution from hydroxide ions and water following the procedure as described for acetonitrile and DMSO solvents. Imidazoles 1 are usually used in high excess to achieve pseudo-first-order conditions and were obtained by fitting the decays of the benzhydrylium absorbances to mono-exponential functions as discussed before. Determination of second-order rate constants for the reaction of 2-methylimidazole (1d) with (ind) 2 CH + BF 4 - in H2 O without considering contribution from OH (at 2 C, cosolvent:.2 vol-% CH 3 CN): [(ind) 2 CH + ] [1d] λ = 614 nm (mol L -1 ) (mol L -1 ) (s -1 ) (M -1 s -1 ) y = x R 2 = S5

51 This journal is The Royal Society of Chemistry 21 Determination of second-order rate constants for the reaction of 2-methylimidazole (1d) with (ind) 2 CH + BF 4 - in H2 O considering the contribution from OH (at 2 C, cosolvent:.2 vol-% CH 3 CN, stopped-flow, detection at 614 nm): No. [(ind) 2 CH + ] [Nu] [Nu] eff [OH - ] [Nu] eff /[El] 1Ψ, ΟΗ 1Ψ (mol L -1 ) (mol L -1 ) (mol L -1 ) (mol L -1 ) (s -1 ) (s -1 ) (s -1 ) ccy ccy ccy ccy ccy = 1.9 M -1 s -1 OH = 1.8 M -1 s -1 pk B = y = 1.943x +.14 R 2 = S51

52 This journal is The Royal Society of Chemistry 21 Reaction of imidazole (1a) with (lil) 2 CH + BF 4 - in H2 O (at 2 C, cosolvent:.4 vol-% CH 3 CN) [(lil) 2 CH + ] [1a] λ = 63 nm (mol L -1 ) (mol L -1 ) (s -1 ) (M -1 s -1 ) y =.695x +.2 R 2 = Reaction of imidazole (1a) with (jul) 2 CH + BF 4 - in H2 O (at 2 C, cosolvent:.2 vol-% CH 3 CN) [(jul) 2 CH + ] [1a] λ = 634 nm (mol L -1 ) (mol L -1 ) (s -1 ) (M -1 s -1 ) y = x R 2 = Reaction of imidazole (1a) with (pyr) 2 CH + BF 4 - in H2 O (at 2 C, cosolvent:.2 vol-% CH 3 CN) [(pyr) 2 CH + ] [1a] λ = 61 nm (mol L -1 ) (mol L -1 ) (s -1 ) (M -1 s -1 ) y = x R 2 = S52

53 This journal is The Royal Society of Chemistry 21 Reaction of imidazole (1a) with (dma) 2 CH + BF 4 - in H2 O (at 2 C, cosolvent:.5 vol-% CH 3 CN) [(dma) 2 CH + ] [Nu] λ = 61 nm (mol L -1 ) (mol L -1 ) (s -1 ) (M -1 s -1 ) y = 32.24x R 2 = Reactivity parameters for imidazole (1a) in H 2 O Ar 2 CH + E (lil) 2 CH N = 9.63 (jul) 2 CH s =.57 (pyr) 2 CH (dma) 2 CH log y =.5695x R 2 = E S53

54 This journal is The Royal Society of Chemistry 21 Reaction of 1-methylimidazole (1b) with (lil) 2 CH + BF 4 - in H2 O (at 2 C, cosolvent:.4 vol- % CH 3 CN) [(lil) 2 CH + ] [1b] λ = 63 nm (mol L -1 ) (mol L -1 ) (s -1 ) (M -1 s -1 ) y =.9436x R 2 = Reaction of 1-methylimidazole (1b) with (ind) 2 CH + BF 4 - in H2 O (at 2 C, cosolvent:.2 vol- % CH 3 CN) [(ind) 2 CH + ] [1b] λ = 62 nm (mol L -1 ) (mol L -1 ) (s -1 ) (M -1 s -1 ) y = x R 2 = Reaction of 1-methylimidazole (1b) with (thq) 2 CH + BF 4 - in H2 O (at 2 C, cosolvent: 1. vol- % CH 3 CN) [(thq) 2 CH + ] [1b] λ = 62 nm (mol L -1 ) (mol L -1 ) (s -1 ) (M -1 s -1 ) y = 8.135x +.72 R 2 = S54

55 This journal is The Royal Society of Chemistry 21 Reaction of 1-methylimidazole (1b) with (pyr) 2 CH + BF 4 - in H2 O (at 2 C, cosolvent:.5 vol- % CH 3 CN) [(pyr) 2 CH + ] [1b] λ = 62 nm (mol L -1 ) (mol L -1 ) (s -1 ) (M -1 s -1 ) y = x R 2 = Reaction of 1-methylimidazole (1b) with (dma) 2 CH + BF 4 - in H2 O (at 2 C, cosolvent:.5 vol-% CH 3 CN) [(dma) 2 CH + ] [1b] λ = 61 nm (mol L -1 ) (mol L -1 ) (s -1 ) (M -1 s -1 ) y = x R 2 = Reactivity parameters for N-methylimidazole (1b) in H 2 O Ar 2 CH + E (lil) 2 CH N = 9.91 (ind) 2 CH s =.55 (thq) 2 CH (pyr) 2 CH (dma) 2 CH log y =.5539x R 2 = E S55

56 This journal is The Royal Society of Chemistry 21 Reaction of 2-methylimidazole (1d) with (lil) 2 CH + BF 4 - in H2 O (at 2 C, cosolvent:.4 vol- % CH 3 CN) [(lil) 2 CH + ] [1d] λ = 63 nm (mol L -1 ) (mol L -1 ) (s -1 ) (M -1 s -1 ) y =.538x R 2 = Reaction of 2-methylimidazole (1d) with (ind) 2 CH + BF 4 - in H2 O (at 2 C, cosolvent:.2 vol- % CH 3 CN) [(ind) 2 CH + ] [1d] λ = 614 nm (mol L -1 ) (mol L -1 ) (s -1 ) (M -1 s -1 ) y = x R 2 = Reaction of 2-methylimidazole (1d) with (thq) 2 CH + BF 4 - in H2 O (at 2 C, cosolvent:.4 vol- % CH 3 CN) [(thq) 2 CH + ] [1d] λ = 618 nm (mol L -1 ) (mol L -1 ) (s -1 ) (M -1 s -1 ) y = 4.667x R 2 = S56

57 This journal is The Royal Society of Chemistry 21 Reaction of 2-methylimidazole with (pyr) 2 CH + BF 4 - in H2 O (at 2 C, cosolvent:.2 vol-% CH 3 CN) [(pyr) 2 CH + ] [Nu] λ = 61 nm (mol L -1 ) (mol L -1 ) (s -1 ) (M -1 s -1 ) y = x R 2 = Reaction of 2-methylimidazole with (dma) 2 CH + BF 4 - (at 2 C, cosolvent:.5 vol-% CH3 CN, stopped-flow, detection at 61 nm) [(dma) 2 CH + ] [Nu] λ = 61 nm (mol L -1 ) (mol L -1 ) (s -1 ) (M -1 s -1 ) y = 22.95x R 2 = Reactivity parameters for 2-methylimidazole (1d) in H 2 O Ar 2 CH + E (lil) 2 CH N = 9.45 (ind) 2 CH s =.54 (thq) 2 CH (pyr) 2 CH (dma) 2 CH log y =.538x R 2 = E S57