brønsted acidity of neutral and cationic acids in k
TRANSCRIPT
Ivo Leito, Agnes Kütt, Ivari Kaljurand, Eva-Ingrid Rõõm, Toomas Rodima, Ilmar A. Koppel
Institute of Chemical Physics, University of Tartu2 Jakobi street, Tartu 51014, Estonia, Fax: 372- 737-5264, [email protected]
Self-consistent acidity scales have been created in
acetonitrile (MeCN), heptaneand 1,2-dichloroethane (DCE)
Self-consistent basicity scales have been created in
acetonitrile (MeCN) and tetrahydrofuran (THF).
No Acid pK a (MeCN) Directly measured ∆pK a value
1 9-C6F5-Fluorene 28.11
2 (4-Me-C6F4)(C6H5)CHCN 26.96
3 (4-NC5F4)(C6H5)NH 26.34
4 (C6H5)(C6F5)CHCN 26.14
5 (4-Me2N-C6F4)(C6F5)NH 25.12
6 (4-Me-C6F4)(C6F5)NH 24.94
7 Octafluorofluorene 24.49
8 Fluoradene 23.90
9 9-COOMe-Fluorene 23.53
10 Acetic acid 23.51
11 (C6F5)CH(COOEt)2 22.85
12 2-NO2-Phenol 22.85
13 (4-Me-C6F4)2CHCN 22.80
14 (4-Me-C6F4)(C6F5)CHCN 21.94
15 Benzoic acid 21.51
16 9-CN-Fluorene 21.36
17 (4-H-C6F4)(C6F5)CHCN 21.11
18 (C6F5)2CHCN 21.10
19 (CF3)3COH 20.55
20 (4-Cl-C6F4)(C6F5)CHCN 20.36
21 2,4,6-Br3-Phenol 20.35
22 (2,4,6-Cl3-C6F2)(C6F5)CHCN 20.13
23 2,3,5,6-F4-Phenol 20.12
24 2,3,4,5,6-F5-Phenol 20.11
25 (2-C10F7)(C6F5)CHCN 20.08
26 1-C10F7OH 19.72
27 2,4,6-(SO2F)3-Aniline 19.66
28 (2-C10F7)2CHCN 19.32
29 9-C6F5-Octafluorofluorene 18.88
30 2-C10F7OH 18.50
31 (4-CF3-C6F4)(C6F5)CHCN 18.14
32 4-C6F5-2,3,5,6-F4-Phenol 18.11
33 (4-H-C6F4)CH(CN)COOEt 18.08
34 2,3,4,5,6-Cl5-Phenol 18.02
35 2,3,4,5,6-Br5-Phenol 17.83
36 (C6F5)CH(CN)COOEt 17.75
37 4-Me-C6H4CH(CN)2 17.59
38 (2-C10F7)CH(CN)COOEt 17.50
39 (4-Cl-C6F4)CH(CN)COOEt 17.39
40 2,4-(NO2)2-Phenol 16.66
41 4-CF3-2,3,5,6-F4-Phenol 16.62
42 (4-NC5F4)(C6F5)CHCN 16.40
43 (4-CF3-C6F4)2CHCN 16.13
44 (4-CF3-C6F4)CH(CN)COOEt 16.08
45 (4-NC5F4)(2-C10F7)CHCN 16.02
46 4-NC5F4-OH 15.40
47 (4-NC5F4)CH(CN)COOEt 14.90
48 3-CF3-C6H4CH(CN)2 14.72
49 Saccharin 14.57
50 4-Me-C6F4CH(CN)2 13.87
51 (4-NC5F4)2CHCN 13.46
52 C6F5CH(CN)2 13.01
53 4-H-C6F4CH(CN)2 12.98
54 2-C10F7CH(CN)2 12.23
55 Tos2NH 11.97
56 4-NO2-C6H4CH(CN)2 11.61
57 4-MeO-C6H4C(=O)NHTf 11.60
58 4-Me-C6H4C(=O)NHTf 11.46
59 (C6H5SO2)2NH 11.34
60 4-Cl-C6H4SO2NHTos 11.10
61 C6H5C(=O)NHTf 11.06
62 Picric acid 11.00
63 4-F-C6H4C(=O)NHTf 10.65
64 4-Cl-C6H4C(=O)NHTf 10.36
65 (4-Cl-C6H4SO2)2NH 10.20
66 4-CF3-C6F4CH(CN)2 10.19
67 4-NO2-C6H4SO2NHTos 10.04
68 4-Cl-3-NO2-C6H3SO2NHTos 9.71
69 4-NO2-C6H4C(=O)NHTf 9.49
70 4-NO2-C6H4SO2NHSO2C6H4-4-Cl 9.17
71 TosOH 8.6
72 (4-NO2-C6H4SO2)2NH 8.32
73 1-C10H7SO3H 8.02
74 C6H5CHTf2 7.85
75 4-Cl-C6H4SO3H 7.3
76 3-NO2-C6H4SO3H 6.78
77 4-NO2-C6H4SO3H 6.73
78 4-MeO-C6H4C(=NTf)NHTf 6.54
79 4-Me-C6H4C(=NTf)NHTf 6.32
80 TosNHTf 6.30
81 C6H5C(=NTf)NHTf 6.17
82 C6H5SO2NHTf 6.02
83 4-F-C6H4C(=NTf)NHTf 5.79
84 4-Cl-C6H4C(=NTf)NHTf 5.69
85 2,4,6-(SO2F)3-Phenol 5.66
86 4-Cl-C6H4SO2NHTf 5.47
87 4-Cl-C6H4SO(=NTf)NHTos 5.27
88 4-NO2-C6H4C(=NTf)NHTf 5.13
89 2,4,6-Tf3-Phenol 4.93
90 4-NO2-C6H4SO2NHTf 4.52
91 4-Cl-C6H4SO(=NTf)NHSO2C6H4-4-Cl 4.47
92 2,3,5-tricyanocyclopentadiene 4.16
93 4-Cl-C6H4SO(=NTf)NHSO2C6H4-4-NO2 3.75
1.15
0.63 1.78
0.20 0.82
1.96
0.15
0.28
0.79
0.52
0.53
-0.01
0.36
0.62
0.74
0.03
0.45
0.40
0.71
0.82
0.60
0.23
1.38
0.89
0.84
1.05
0.26
0.79
0.14
0.87
0.04
0.13
1.21
0.48
1.89
0.46
0.91
1.43
1.06
0.60 0.98
0.10
0.03
0.19 0.14
0.49 0.57
0.07
0.87
0.54
1.15
0.56 0.15
0.73 1.20
1.21
0.51
0.77
0.41
0.05
0.31
0.50
0.38
0.36
0.53
0.54
0.19
0.44
0.83
0.53
1.10
0.51
1.04
0.23
0.56
0.74
0.75
1.25
1.73
0.87
0.50
0.62
2.3
1.1
1.28
1.3 0.25
1.15
1.25
0.71
1.37
1.64
0.64
0.59 0.26
0.47
0.16 0.35 0.5
0.05
0.23 0.23
1.11
0.42
1.20
0.59
0.59
1.49
1.32
0.06
0.36
0.38
0.44
1.12
0.32
0.06
0.22
0.75
1.19
0.19
0.77
1.35
0.60
1.10
0.08
0.19
0.46
0.79
1.43
0.54
1.15
0.04
0.73
0.85
1.92
0.92
0.41
0.69
0.70
0.05
0.27
0.27
0.10
0.26
1.51
0.37
0.72
0.88
0.28 0.63
1.59
1.46 1.70
1.03
0.17
0.42
0.40
0.96
0.45
1.20
0.34
0.43
0.82 0.81
0.64
0.58
0.48 1.02
1.75 1.21
0.53
0.00 0.03
0.03 0.06
0.01
1.02 1.02
1.03
0.29 0.25
0.26 0.21
1.01
0.60
0.04
0.67
0.76
-0.01
0.75
0.39
0.42
0.26 0.25
1.49
0.92
1.05
0.90
0.68
0.73 0.71
-0.01
0.80
No Acid pK ip(1,2-DCE) Directly measured ∆pK ip
1 7.7
2 7.1
3 6.9
4 6.7
5 6.0
6 4.8
7 4.8
8 4.1
9 2.8
10 2.7
11 2.3
12 2.0
13 1.5
14 0.3
15 0.0
NC
CN
CN
S NH
OSO
OCl
NTf
S NH
OSO
OClCl
NTf
OH
SO2F
SO2F
FO2S
OH
Tf
Tf
Tf
S NH
OSO
OCl
NTfNO2
FF
F
F F
Tf
Tf
NC
CN
CN
CN
S NHTfO
NTfO2N
S NHTfO
NTf
S NHTfO
NTfCl
CN
CN
CN
CNCN
NC
NH
CN
CN
CNCN
CN
NC
CN
CNCN
NC CN
CN
CNNC
NC
0.76
0.21
0.65
0.66
1.01
1.11 0.16
1.15
0.04
0.97
0.7
2.3
0.36
0.3
0.19
0.12
2.5
1.2
1.09
0.25
N
P NNN
N
PP NNN
N N
NN
PNN
NN
PNN
NNN
PNN
NNBr
PNN
NNO2N
PN
N P NN
N
NPN
N N
NPN
NN
N
PN
NPN
N N
NPN
NN
P NNN
NNMe2
NMe2
NMe2Me2N
Me2NNMe2
P NNNMe2
NMe2
PNN
N
NMe2Me2N
Me2NNMe2
N
N
N
PhP4(dma)
PhP3(dma)
PhP2(dma)
PhP1(dma)
DMA(N,N-Dimethylaniline)
4-NO2-C6H4-P1(pyrr)
PhP1(pyrr) PhP1(tmg)
PhP1(tmg)2dma
PhP1(tmg)dma2
4-Br-C6H4-P1(pyrr)
4-Me2N-C6H4-P1(pyrr)
27.0
23.5
19.9
15.3
4.9
24.3
21.6
18.4
16.1
17.3
15.4
13.3
Phosphazenes:
basicity change upon variation of the
structure
No Base Directly measured ∆pK ip values pK ip (THF) pK α (THF)
1 t -BuP1(tmg) 28.4 29.1
2 HP1(tmg) 27.9 28.6
3 4-MeO-C6H4P4(pyrr) 27.8 28.9
4 PhP4(pyrr) 27.1 28.1
5 4-MeO-C6H4P4(dma) 27.0 27.7
6 t -BuP1(tmg)2NEt2 26.4 26.8
7 PhP4(dma) 26.3 27.0
8 EtP2(pyrr) 25.9 26.6
9 4-Br-C6H4P4(pyrr) 25.8 26.9
10 2-Cl-C6H4P4(pyrr) 25.6 26.6
11 EtP2(dma) 24.9 25.3
12 4-MeO-C6H4P3(pyrr) 24.9 25.7
13 PhP3(pyrr) 24.2 25.1
14 PhP1(tmg) 23.7 24.3
15 4-MeO-C6H4P3(dma) 23.6 24.1
16 PhP3(dma) 23.0 23.5
17 4-CF3-C6H4P3(pyrr) 22.3 23.2
18 TBD 21.7 21.0
19 EtP1(pyrr) 21.8 21.8
20 4-CF3-C6H4P3(dma) 21.2 21.7
21 2-Cl-C6H4P3(pyrr)6NEt2 21.1 22.0
22 PhP1(tmg)2dma 21.1 21.6
23 4-MeOC6H4P2(pyrr) 20.9 21.5
24 HP1(pyrr) 20.9 20.9
25 MeP1(dma) 20.7 20.7
26 2-Cl-C6H4P3(dma)6NEt2 20.4 20.9
27 PhP2(pyrr) 20.3 20.9
28 t -ButP1(pyrr) 20.3 20.3
29 HP1(dma) 19.7 19.7
30 PhP2(dma) 19.4 19.9
31 2,5-Cl2-C6H3P3(pyrr)6NEt2 19.3 20.2
32 4-Br-C6H4P2(pyrr) 19.3 20.0
33 BEMP 19.3 19.0
34 t -ButP1(dma) 18.9 18.9
35 MTBD 18.7 18.0
36 t -OctP1(dma) 18.5 18.5
37 DBU 18.1 16.9
38 PhP1(dma)2tmg 18.1 18.4
39 4-Me2N-C6H4P1(pyrr) 17.3 17.3
40 TMG 17.0 15.5
41 2-Cl-C6H4P2(pyrr) 16.9 17.6
42 4-MeO-C6H4P1(pyrr) 16.8 16.8
43 TMGN 16.5 16.8
44 PhP1(pyrr) 16.1 16.1
45 2-Cl-C6H4P2(dma) 15.8 16.3
46 N -Me-DAP 15.8 15.2
47 N,N' -Me2-Bispidine 15.5 15.4
48 N,N' -Me2-DAPb 15.5 14.9
49 PhP1(dma)2Me 15.4 15.4
50 4-Br-C6H4P1(pyrr) 15.4 15.4
51 N,N -Me2-DAPb 15.3 14.7
52 Pyrrolidine 15.3 13.5
53 PhP1(dma) 15.2 15.3
54 Homopiperazine 15.1 14.4
55 Piperidine 15.0 14.3
56 PhTMG 15.0 14.0
57 N,N,N' -Me3-DAPb 14.9 14.3
58 Piperazine 14.9 14.2
59 PrNH2 14.7 13.8
60 Me-PrNH 14.6 13.7
61 i -Pr2NH 14.6 13.6
62 4-CF3-C6H4P1(pyrr) 14.6 14.6
63 (-) Sparteine 14.2 14.3
64 1-NaphtP1(pyrr) 14.2 14.2
65 Me-Piperazine 14.1 13.4
66 N,N,N',N', 2-Me5-DAPa 14.1 13.4
67 Et3N 14.0 12.5
68 N,N,N',N' -Me4-DAPa 13.6 13.0
69 Me-Piperidine 13.6 12.9
70 Et-Me2N 13.6 12.6
71 N,N,N',N' -Me4-DABa 13.4 13.1
72 Bu-Me2N 13.4 12.8
73 N,N,N',N' -Me4-DAEa 13.4 12.8
74 4-NO2-C6H4P1(pyrr) 13.3 13.3
75 2-Cl-C6H4P1(pyrr) 13.2 13.2
76 N,N' -Me2-Piperazine 13.1 12.4
77 Pr3N 13.1 13.0
78 4-Me2N-Pyridine 13.0 11.2
79 2-Cl-C6H4P1(dma) 12.5 12.5
80 2,5-Cl2-C6H3P1(pyrr) 11.9 11.9
81 2,6-Cl2-C6H3P1(pyrr) 11.8 11.8
82 Proton Sponge 11.6 11.1
83 2-NO2-4-Cl-C6H3P1(pyrr) 10.8 10.8
84 2-NO2-5-Cl-C6H3P1(pyrr) 10.1 10.1
85 2,4,6-Me3-Pyridine 9.6 8.1
86 2-NO2-4-CF3-C6H3P1(pyrr) 9.5 9.5
87 4-MeO-Pyridine 9.1 7.3
88 2,6-Me2-Pyridine 8.8 7.2
89 4-MeO-Aniline 8.3 6.5
90 2-Me-Pyridine 8.1 6.3
91 2,4-(NO2)2-C6H3P1(pyrr) 8.0 8.0
92 2,6-Cl-4-NO2-C6H2P1(pyrr) 7.8 7.8
93 2,6-(NO2)2-C6H3P1(pyrr) 7.5 7.5
94 Pyridine 7.3 5.5
95 Aniline 7.0 5.2
96 2-Me-Aniline 6.9 5.1
97 N,N -Me2-Aniline 6.5 4.9
98 4-Br-Aniline 5.8 4.0
99 2-MeO-Pyridine 4.4 2.6
a Denotions: DAE - 1,2-diaminoethane, DAP - 1,3-diaminopropane, DAB -1,4-diaminobutane
2.38
1.14
1.5
1.36
1.61
1.1 1.2
0.98 1.05
0.88 0.14
0.91
1.07
0.9 0.88
1.58
0.8
1.3
0.45
0.38
0.17
0.90
0.01 0.15
0.80 0.09
0.25
0.60
1.2
0.54
0.7
1.1
0.05
1.05 0.16
1.54 0.87
1.2 0.45
0.55 0.97
0.45 0.79
0.31
1.01
0.71
0.45
0.24 0.32
0.07 0.29
0.57
0.71 0.30
0.49 0.13
0.34 0.43
1.10 0.46
0.52
1.40 2.1
1.10 1.08
1.25 1.15
1.6 0.4
0.83
0.55
0.2 0.53
0.10
1.3 1.1
1.44
0.2
0.97 0.27
0.62 0.98
1.48
0.36 0.66
0.88 0.22 0.57
0.64
1.01
1.70
0.28 0.36
0.51
0.9
0.45 0.07
0.51
0.96
0.09
0.03
0.42
1.25
1.85
0.58
0.05
0.29 0.07
0.3 0.33
0.48 0.60
0.64
1.03 1.0
1.7
1.88
0.5
0.98
0.95
0.35 0.28 0.30
0.14 0.04
0.04
0.3 0.47
0.52 0.59
0.88
0.6 0.07
0.85 0.75
1.50 0.08 0.70
0.67
1.17
0.77
0.02
0.35
1.05 0.27
0.97 0.64 0.77
1.46 0.08 0.68
0.66
0.52 0.61
1.88 0.11
0.70 0.57
1.28 0.74
1.30
0.50 0.60
1.20
1.38
1.5
0.60
0.59
0.92 0.15
0.10
0.26
0.92 0.49 0.34
0.40
0.90
0.23
0.13
0.63 0.70
0.5
1.17
1.35
1.10
0.03
0.85
1.7
0.49
0.97
0.36 0.07
0.13 0.17
0.76 0.43
1.0 1.5
0.55
1 10 0.58
No Base pK a (MeCN) Directly measured ∆pK a values a
1 4-MeO-C6H4P3(dma) 31.99
2 PhP3(dma) 31.48
3 PhP1(tmg) 31.4
4 2-Cl-C6H4P3(pyrr)6NEt2 31.19
5 4-CF3-C6H4P3(pyrr) 30.50
6 2-Cl-C6H4P3(dma)6NEt2 30.16
7 2,5-Cl2-C6H3P3(pyrr)6NEt2 29.16
8 4-CF3-C6H4P3(dma) 29.10
9 PhP1(tmg)2dma 29.07
10 EtP1(pyrr) 28.88
11 t -BuP1(pyrr) 28.42
12 4-MeO-C6H4P2(pyrr) 28.23
13 PhP2(pyrr) 27.55
14 MeP1(dma) 27.52
15 HP1(pyrr) 27.01
16 t -BuP1(dma) 26.98
17 PhP2(dma) 26.46
18 TBD 26.03
19 HP1(dma) 25.85
20 MTBD 25.49
21 2-Cl-C6H4P2(pyrr) 25.42
22 PhP1(dma)2tmg 24.72
23 DBU 24.34
24 2-Cl-C6H4P2(dma) 24.25
25 4-NMe2-C6H4P1(pyrr) 23.88
26 4-MeO-C6H4P1(pyrr) 23.12
27 N ,N' -Me2-Bispidine 22.74
28 PhP1(pyrr) 22.34
29 (-)-Sparteine 21.66
30 Bispidine 21.55
31 N ,N' -Bn2-Bispidine 21.38
32 N ,N' -(CHMePh)2-Bispidine 21.25
33 PhP1(dma) 21.25
34 4-Br-C6H4P1(pyrr) 21.19
35 PhP1(dma)2Me 21.03
36 PhTMG 20.84
37 1-NaphtP1(pyrr) 20.61
38 N ,N' -Me2-1,3-Diaminopropane 20.39
39 2-Cl-C6H4P1(pyrr) 20.17
40 4-CF3-C6H4P1(pyrr) 20.16
41 N ,N ,N' ,N' -Me4-1,3-Diaminobutane 20.09
42 N -Me-1,3-Diaminopropane 20.04
43 N ,N ,N' ,-Me3-1,3-Diaminopropane 20.01
44 N ,N ,N' ,N' -Me4-1,4-Diaminobutane 19.93
45 1,3-Diaminopropane 19.70
46 2-Tol-1-BG 19.66
47 N ,N -Me2-1,3-Diaminopropane 19.57
48 Pyrrolidine 19.56
49 Piperidine 19.29
50 N ,N ,N' ,N' -Me4-1,3-Diaminopropane 19.27
51 Homopiperazine 19.10
52 2-Cl-C6H4P1(dma) 19.07
53 MePrNH 18.92
54 Et3N 18.82
55 i -Pr2NH 18.81
56 Piperazine 16.69
57 N ,N ,N' ,N' -Me4-1,2-Diaminoethane 18.68
58 Proton Sponge 18.62
59 2,6-Cl2-C6H3P1(pyrr) 18.56
60 2,5-Cl2-C6H3P1(pyrr) 18.52
61 4-NO2-C6H4P1(pyrr) 18.51
62 PrNH2 18.43
63 4-Pyrr-Pyridine 18.33
64 Me2EtN 13.33
65 Pr3N 18.25
66 N -Me-Piperidine 18.25
67 Me2BuN 18.24
68 N -Me-Piperazine 18.07
69 4-NMe2-Pyridine 17.95
70 N ,N' -(CHPh2)2-Bispidine 17.79
71 2-NO2-4-Cl-C6H3P1(pyrr) 17.68
72 4-NH2-Pyridine 17.62
73 9-O-1,5-Me2-N ,N' -Bn2-Bispidine 17.48
74 N ,N' -Me2-Piperazine 17.36
75 2-NO2-5-Cl-C6H3P1(pyrr) 17.27
76 9-O-N ,N' -Bn2-Bispidine 16.93
77 PhCH2NH2 16.91
78 2-NO2-4-CF3-C6H3P1(pyrr) 16.54
79 2-NH2-Acridine 16.39
80 2-NH2-1-Me-Benzimidazole 16.31
81 2-NH2-Benzimidazole 16.08
82 2,3-(NH2)2-Pyridine 15.24
83 2,4,6-Me3-Pyridine 14.98
84 2,4-(NO2)2-C6H3P1(pyrr) 14.88
85 2,6-(NH2)2-Pyridine 14.77
86 2-NH2-Pyridine 14.47
87 2,6-Cl2-4-NO2-C6H2P1(pyrr) 14.43
88 4-MeO-Pyridine 14.23
89 3-NH2-Pyridine 14.17
90 2,6-Me2-Pyridine 14.13
91 2,6-NO2-C6H3P1(pyrr) 14.12
92 N ,N' -Ph2-Bispidine 13.97
93 9-O-1,5-(COOMe)2-N ,N' -Bn2-Bispidine 13.81
94 9-O-1,5-N ,N' -(CHPh2)2-Bispidine 13.48
95 2-Me-Pyridine 13.32
96 Pyridine 12.53
97 OEP 12.37
98 4-MeO-Aniline 11.86
99 2-methylkinolin-8-amine 11.54
100 N ,N -Me2-Aniline 11.43
101 Aniline 10.62
102 2-Me-Aniline 10.50
103 TPP 10.41
104 5-NO2-Benzimidazole 10.39
105 TMP 10.15
106 MePh2P 9.96
107 TCPP 9.94
108 2-MeO-Pyridine 9.93
109 1-Naphthylamine 9.77
110 3-Cl-Pyridine 9.55
111 4-Br-Aniline 9.43
112 2,4-F2-Aniline 8.39
113 9-O-1,5-(COOMe)2-N ,N' -Ph2-Bispidine 8.13
114 4-CF3-Aniline 8.03
115 2-Cl-Aniline 7.86
116 3-NO2-Aniline 7.68
117 4-F-3-NO2-Aniline 7.67
118 2,6-(MeO)2-Pyridine 7.64
119 Ph3P 7.61
120 2-Cl-Pyridine 6.79
121 4-NO2-Aniline 6.22
122 2,5-Cl2-Aniline 6.21
123 Ph2NH 5.97
124 2,6-Cl2-Aniline 5.06
125 2-NO2-Aniline 4.80
126 4-Cl-2-NO2-Aniline 3.80
a Some of the measurements have been omitted for clarity
0.80
0.51 0.58
0.15 0.98
0.93
1.05
0.64
0.60
0.55
0.64
1.03
1.21 0.02
1.70
0.61
0.10
0.69
0.08
0.46
0.99
0.86
0.17 0.86
0.08
1.36
1.35
0.61
0.55
1.59
0.01
1.6
1.01
0.70
0.32
0.45 1.20
0.74
1.77
2.54
0.63
0.06
0.77
1.05
1.57
1.55
1.09
0.10
0.44
0.42
0.03 0.08
0.23
1.01
0.43
0.11 0.21
0.36
0.63
0.42
0.60
0.41
0.39
0.68
0.59 0.50
1.62
1.11
0.46
1.59 0.59 1.69
0.26
0.23
0.46
0.48
2.10
1.07
0.6
0.46
0.44
0.50
0.73 0.62 0.80
0.40 0.40
0.26
0.15
0.40
0.04
0.19 0.25
0.90
0.54
0.45
0.48
0.65
0.25
1.43
0.85
0.17 0.11
0.96
0.04 0.09 0.10
0.19
0.60
1.00
0.77
0.04
0.90
0.17
1.67
0.76
0.52
0.25
0.60
0.08
1.04
0.57
1.01
0.85
0.40
2.20
1.52
0.93
1.44
0.06
0.65
0.21
0.68
1.29
0.02
0.91
0.39
0.34
0.76
0.96
0.19
0.47 0.46
0.19
0.59
0.17
1.17
0.10
0.27 0.45
0.80
0.59
0.26 0.19
0.04
0.10
1.31
0.84
0.27
0.75
0.77
1.72
0.06
1.07
0.22
0.73
0.34
1.96
0.22
0.05
0.51
0.34
0.74
0.35
0.13
0.36
1.55
1.10
0.09 0.21
0.45
1.13
0.65
0.95
0.35
0.62
0.95
0.44 0.17
0.47
0.90
0.15 0.66
0.31 0.83
1.01
0.07
0.77 0.95
0.22
1.15
0.43
0.08
0.16
0.24 0.33
0.23
0.47
1.58
1.07
0.74 0.85 0.56
0.03
0.38
0.85
0.32
0.90
0.60
0.11
1.06
0.35
0.17
0.20
0.01
0.05
0.04
1.40
0.01
0.25
0.91
0.25
0.97 1.30
1.16
1.18
0.25
1.43
0.57
0.88
0.35
0.04
0.35
0.07 0.07
0.17
0.75
1.40 1.51
0.71
1.57
1.37
1.40
0.85
1.77
0.12
1.38
0.48 0.42
0.44
MeCN
THF
MeCN
DCE
0
0.15
0.3
0.45
0.6
200 295 390 485
wavelength (nm)
absorpion (AU)
H CN FF
FF
F
neutral
anionic
The method is based on UV-Vis spectrophotometric titration of a solution containing simultaneouslytwo acids (bases) with a nonabsorbing base (acid). From the different degree of ionization of thecompounds in titration points theirrelative acidity – the difference of their pKa values (∆pKa) – is obtained.
0
0.4
0.8
1.2
1.6
200 310 420 530
wavelength (nm)
absorpion (AU
)
pK a = 1.96
H CN FF
FF
F
F
FF
F
F
0
0.13
0.26
0.39
200 310 420 530
wavelength (nm)
absorpion (AU)
F
FF
F
F
anionic
neutral
CH acids giving anions with highly delocalized charges, e.g.
were particularly useful in constructing the scales:• no homo- or hetero-conjugation• weak ion-ion interactions• acidities insensitive to traces of water in the medium• favorable spectral properties
MeCN acidity scale [ref 3]:• 24 orders of magnitude (from pKa 3.7 to 28.1)• Consistency s = 0.03 pKa units• Practically all acid families included: alcohols, phenols, carboxylic acids, sulfonic acids, anilines, diphenylamines, disulfonimides, fluorenes, diphenylacetonitriles,phenylmalononitriles, ethyl aryl cyanoacetates,phenyl malononitriles
• Self-consistentbasicity scales in MeCN [ref 2, 5]and THF [ref 4, 6]• 82 bases are included in bothscales• Solid basis forfurther basicitystudies
Variation of1. Number of N=P subunits2. Number of tmg fragments
large basicity changes(3-4 orders of magnitude)
Variation of1. Amino fragments
2. Substituents in the ring“fine-tuning” of basicity
The heavy compression of the liquid phase scales, evident with bases, is
absent with acids
• pKa measurements are complemented with gas-phase basicity measurements of phosphazenes [ref 1]• The GB scale expanded by 20 kcal/mol towards superbasic region
pKa
H2O MeCN THFa GP
10.7
9.66
9.21
11.9411.77
13.6
18.82 12.5166.4 (227.0)
17.9518.56
20.84
23.3023.12
11.211.8
14.0
16.6170.2 (232.1)
176.2 (240.4)
194.0 (264.6) EtP2(dma)
172.1 (234.8)
189.6 (258.7)
15.3
13.9
13.3
11.52
27.0120.8
187.0 (255.1)
25.85
19.7
183.0 (249.6)
22.34 15.9
184.8 (252.0)
4.62
10.625.2
149.0 (203.3) NH2
5.36
11.43
4.9
159.3 (217.3)N
PNN
NN
PP NNN
N N
NN
200.9 (274.0)b PhP1(tmg)
31.4 24.3
202.4 (276.1)b HP1(tmg)
28.6
177.9 (242.7)
16.8
24.34
N
N
5.25 12.535.5
157.4 (214.7)
N
PNN
NNH
P NNN
NH
PNN
NN
NN
NH
NN
N
NN
N
11.96
21.66
14.3
178.4 (243.4)
9.38
22.74
15.4
176.5 (240.8)
N N
N N
N N
NH
NH2
172.5 (235.2)
166.6 (223.3)19.27 13.0
20.04
15.2
P NNN
NNMe2
NMe2NMe2Me2N
Me2NNMe2
H
P NNN
NNMe2
NMe2
NMe2Me2N
Me2NNMe2
a pKα valuesb Computational values (DFT B3LYP 6-311+G**)
t-BuP1(pyrr)
HP1(pyrr)
HP1(dma)
PhP1(pyrr)
AcOH vs 9-PhFl:• Gas phase: AcOH 4 orders weaker• MeCN: AcOH 8 orders stronger• H2O: AcOH 13 orders stronger!
Heavy compression of solvent scales comparedto the gas phase:• THF 2.8 times• MeCN 2.7 times• H2O 4.8 times!
In this part of thescheme there is still a
lot of work to do!
pKa
H2O DMSO MeCN GP
~-8a
1.21.8
8.9
240.5 (328.1)
-1.8~0
2.0
10.5
11.61
11.0
23.90
222.0 (302.8)
219.6 (299.5)
213.3 (291.0)
238.2 (324.9)
10.0
4.75
9.50
18.0 29.1
250.7 (342)
12.3 23.51
250.1 (341.1)
7.95 229.0 (312.4)
~0
10.7
20.55
237.5 (324.0)
5.4
~-9a
0.9
5.5
233.4 (318.3)
~0.3
2.6
219.6 (299.5)
~-14a
2.3
OHCF3
CF3F3C
OHNO2
NO2
O2N
CN
CNO2N
CF3SO2
NHCF3SO2
3.2
~15a
268.0 (365.5)
194.6 (263.0)c
~0...2a
231.6 (315.9)b
14.57
1.8
4.0
SNH
O
O O
HF
HCl
HBr
a Approximate or estimated valuesb Computational values, DFT B3LYP 6-311+G**c Computational values, G3(MP2)
17.9
32a
246.0 (335.5)
17.6
4.7
17.75
229.8 (313.5)
5.8
CN
COOEtH
FF
F
F F
22.6
~36a
252.2 (344.0)
~22a
OH
CH3COOH
8.3
21.36
235.6 (321.4)
7.9
CN
21.10
CNFF
FF
FF
F
FF
F
CF3SO2OH
210.9 (287.6)b
-5.0
HNCCN
CN
195.4 (267.2)b
H
NC
NC
CNCN
CN
202.8 (276.6)b HPF6
C
HHH
H
H H
HH H H
HH
H+
-
~4a
Acidity scale in DCE is about to become the strongest equilibrium acidity scale in constant medium ever composed. Thestrongest acids currently on the scale are estimated to have pKa values in water around -10.
1. J. Phys. Chem. A. 2007, 111, 1245-1250.
2. J. Org. Chem. 2006, 71, 7155-7164.
3. J. Org. Chem. 2006, 71, 2829-2838.
4. J. Am. Chem. Soc. 2005, 127, 17656-17666.
5. J. Org. Chem. 2005, 70, 1019-1028.
6. J. Org. Chem. 2003, 68, 9988-9993.
7. J. Org. Chem. 2003, 68, 7795-7799.
CNFF
FF
FF
F
FF
F CN
CNO2N
CN
COOEtH
FF
F
F F
Brønsted Acidity of Neutral and Cationic Acids in Nonaqueous Solvents: Recent Developments
No pK ip(Heptane) Directly measured ∆pK ip value No
21 8.63
8.25 20
19 7.37
7.11 18
17 7.04
6.40 16
15 6.32
5.87 14
13 5.18
4.61 12
11 4.60
3.29 10
9 2.16
2.11 8
7 1.85
1.81 6
5 1.10
1.09 4
3 0.00
-0.68 2
1 -1.39
FF
F
FFF
F
FF
F
CNH
FF
CF3
FFF
F
FF
F
CNH
FF
Cl
FFF
F
FF
F
CNH
FF
CH3
FFF
F
FF
F
CNH
FF
CH3
FFF
F
CH3
FF
CNH
FF
FFF
F
FF
FF
FF
FF
CNH
ClF
Cl
FClF
F
FF
F
CNH
FF
F
FFF
F
FF
F
NH
FF
CF3
FFF
F
FF
F
NH
FF
Cl
FFF
F
FF
F
NH
FF
H
FFF
F
FF
F
NH
FF
CH3
FFF
F
FF
F
NH
FF
F
F F
NH
NO2
FF
FFF
F
FF
HF
FF
F
F
C2F5H
FF
F
FFF
F
FF
F
F
FF
F
F
FF
F
FFF
F
FF
F
Cl
ClCl
Cl
Cl
FF
Cl
FFF
F
FF
F
F
FF
F
F
FCl
F
ClFF
F
FF
F
F
FF
F
F
FF
FF
FF
F
FFF
FF
F
FF
F
F
0.32 1.3
0.82
0.22 0.37
0.06 0.7
0.76 0.75
0.07
0.46
1.72 0.65
1.3
0.54 1.9 0.05
1.31
1.13
1.47 0.04
0.28 0.4
0.24 0.02 0.03
0.73 0.82
1.8 0.82
0.73 1.7
1.2 1.15
0.67 1.4
0.69a
a
a
a
a
a a
a
a
Heptane
Heptane is the least polar solvent where an acidity scale has been built[ref 7]. Key to success: t-Bu-P4phosphazeneas the titrant:
• one of the strongest bases known• soluble in heptane• forms large cation with delocalizedcharge → weak interaction with anions
P NNN
NP
P
PNMe2
NMe2NMe2Me2N
Me2NNMe2
NMe2
NMe2
NMe2