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Acids and BasesSolvent Effects on Acid-Base Strength$

Brian G. Cox

Print publication date: 2013

Print ISBN-13: 9780199670512

Published to Oxford Scholarship Online: May 2013

DOI: 10.1093/acprof:oso/9780199670512.001.0001

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Appendices: Dissociation Constants in Methanol and Aprotic Solvents

Appendices: Dissociation Constants in Methanol and Aprotic Solvents

Chapter:
(p.130) 9 Appendices: Dissociation Constants in Methanol and Aprotic Solvents
Source:
Acids and Bases
Author(s):

Brian G. Cox

Publisher:
Oxford University Press
DOI:10.1093/acprof:oso/9780199670512.003.0009

Abstract and Keywords

Tables of dissociation constants are given for a wide range of substrates in the most extensively studied non-aqueous solvents, including methanol, dimethylsulphoxide, dimethylformamide, acetonitrile, and tetrahydrofuran. Equations representing correlations among the solvents and with water are also included.

Keywords:   dissociation constants, methanol, dimethylsulphoxide, dimethylformamide, acetonitrile, tetrahydrofuran

9.1 Methanol

The most comprehensive review of data is: Rived, F., Rosés, M., Bosch, E. Anal. Chim. Acta, 1998, 374, 309. Dissociation constants reported below are from this reference unless otherwise stated.

9.1.1 Carboxylic acids and phenols

Acid

pKa

Acid

pKa

Acid

pKa

Carboxylic acid:

Benzoic

2-methoxy

9.26

Aliphatic

2,6-dinitro

6.30

2-methoxy

9.30

CHCl2CO2H

6.38

2,4-dinitro

6.45

4-methoxy

9.79

CH(CN)CO2H

7.50

3,5-dinitro

7.38

2-methyl

9.24

CH2ClCO2H

7.88

3,4-dinitro

7.44

3-methyl

9.39

CH3CHClCO2H

8.06

4-chloro,3-nitro

8.10

4-methyl

9.51

CH2FCO2H

7.99

2,6-dichloro

7.05

3-hydroxy

9.58

CH2BrCO2H

8.06

3,5-dichloro

8.26

4-hydroxy

9.99

CH2ICO2H

8.38

3,4-dichloro

8.53

4-amino

10.25

CH2(OH)CO2H

8.68

2-nitro

7.64

PhCH2CO2H

9.34

3-nitro

8.32

Phenol:

CH3CO2H

9.63

4-nitro

8.34

2,4,6-trinitro

3.55

CH3CH2CO2H

9.71

2-fluoro

8.41

2,6-dinitro

7.64

CH3(CH2)2CO2H

9.69

3-fluoro

8.87

2,4-dinitro

7.83

oxalic:a

pKa1

6.10

4-fluoro

9.23

2,5-dinitro

8.94

pKa2

10.7

2-chloro

8.31

3,5-dinitro

10.29

maleic:b

pKa1

5.7

3-chloro

8.83

3.5-dichloro

12.11

pKa2

12.8

4-chloro

9.09

2-nitro

11.53

malonic:a

pKa1

7.50

2-bromo

8.19

3-nitro

12.41

pKa2

12.4

3-bromo

8.80

2-chloro

12.97

fumaric:b

pKa1

7.9

4-bromo

8.93

3-chloro

13.10

pKa2

10.3

2-iodo

8.24

4-chloro

13.59

succinic:a

pKa1

9.10

3-iodo

8.89

3-bromo

13.30

pKa2

11.5

4-iodo

9.04

4-bromo

13.63

glutamic:a

pKa1

9.40

3-methylsulphonyl

8.43

H

14.33

pKa2

11.5

3-cyano

8.53

2-methoxy

14.48

Adipic:a

pKa1

9.45

4-cyano

8.42

2-methyl

14.86

pKa2

11.1

3-acetyl

8.87

3-methyl

14.43

4-acetyl

8.72

4-methyl

14.54

1-H

9.30

4-t-butyl

14.52

(a) Chantooni, M. K.; Kolthoff, I. M. J. Phys. Chem., 1975, 79, 1176;

(b) Kolthoff, I. M., Chantooni, M. K. Anal. Chem., 1978, 50, 1440; Garrido, G.; de Nogales, V.; Ràfols, C, Bosch, E. Talanta, 2007, 73, 115

(p.131)

9.1.2 Protonated nitrogen bases

Base

pKa

Base

pKa

Base

pKa

Amine:

3-fluoro

4.60

2-bromo

1.0

hydroxylamine

6.29

2-chloro

3.71

3-bromo

2.90

ammonia

10.78

3-chloro

4.52

3-cyano

1.4

ethanolamine

10.88

4-chloro

4.95

4-cyano

1.9

methylamine

11.00

2-bromo

3.46

2-acetyl

3.54

dimethylamine

11.20

3-bromo

4.42

3-acetyl

3.73

trimethylamine

9.80

4-bromo

4.84

2-hydroxy

2.79

ethylamine

11.00

H

6.05

3-hydroxy

5.74

triethylamine

10.78

2-methyl

5.95

H

5.44

butylamine

11.48

3-methyl

6.09

2-methyl

6.18

cyclohexylamine

11.68

4-methyl

6.57

3-methyl

6.04

piperidine

11.07

3-methoxy

6.04

4-methyl

6.40

NMe4-guanidine

13.20

4-methoxy

6.89

3,5-dimethyl

6.43

3.4-dimethyl

6.83

Aniline:

Pyridine:a

2,6-dimethyl

6.86

2-nitro

0.20

2-chloro

1.0

4-dimethylamino

10.10

4-nitro

1.55

3-chloro

2.83

4-amino

10.37

(a) Augustin-Nowacka, D., Malowski, M.; Chmurzynski, L. Anal. Chim. Acta, 2000, 418, 233

Additional dissociation constants for neutral acids and cationic acids in methanol may be estimated from correlations with those in water, as follows:

pK a ( MeOH ) = m pK a ( H 2 O ) + c

The best-fit values of m and c for the different acid types are:

Acid type

m

c

Carboxylic acids

1.02

4.98a

Phenols

1.08

3.66

Protonated nitrogen basesb

1.02

0.72

(a) For the second pKa of dicarboxylic acids, c = 6.2;

(b) a correlation based on anilines alone gives m = 1.21 and c = 0.38

(p.132) 9.2 Dimethylsulphoxide

Data comes from Bordwell, F.G. Acc. Chem. Res., 1988, 21, 456, and references therein, unless otherwise indicated. A comprehensive listing is given on the Web, Bordwell pKa Table (Acidity in DMSO), © 2001-20011 Hans J. Reich.

9.2.1 Carboxylic acids, alcohols, phenols

Acid

pKa

Acid

pKa

Acid

pKa

Carboxylic acid:

3, 4−Cl2

11.0

3−NO2

14.4

Aliphatic a

2-Cl

11.2

4 NMe 3 +

14.7

CHCl2CO2H

6.4

3-Br

11.3

2-CN

12.1

CH2ClCO2H

8.9

4-Cl

11.5

4-CN

13.2

CH3CO2H

12.6

4-Br

11.6

3-CN

14.8

CH3(CH2)2CO2H

12.9

H

12.4

4−SO2Me

13.6

oxalic: b

pKa1

6.2

3-Me

12.4

4−CF3

15.3

pKa2

14.9

3-OH

12.5

3−CF3

15.6

malonic:b

pKa1

6.9

4-Me

12.6

3-Cl

15.8

pKa2

18.5

3, 4−Me2

13.0

4-Cl

16.7

succinic:b

pKa1

9.5

4−NH2

14.0

2-F

15.6

pKa2

16.5

4-F

18.0

glutaric:b

pKa1

10.9

Alcohol:

H

18.0

15.3

HOH

31.4

2−NH2

18.2

adipic: b

pKa1

11.9

MeOH

29.0

2-OMe

17.8

pKa2

14.1

EtOH

29.8

4-OMe

19.1

o−phthalicb:

pKa1

5.9

i-PrOH

30.3

4-Me

18.9

pKa2

16.0

t-BuOH

32.2

4−NMe2

19.8

CF3CH2OH

23.5

Benzoica

(CF3)2CHOH

17.9

Thiophenol:

2, 6−(OH)2

3.1

(CF3)3COH

10.7

4−NO2

5.5

2, 4−(NO2)2

5.2

2-chloro

8.55

2-OH

8.2

Phenol:

3-chloro

8.57

3, 5−(NO2)2

8.8

2, 6−(NO2)2

6.2

4-bromo

8.98

2−NO2

9.9

2, 4−(NO2)2

6.3

H

10.3

4−Cl, 3−NO2

10.0

3−CF3, 4−NO2

10.4

3-Me

10.55

3, 5−Cl2

10.4

3, 5−(NO2)2

11.3

4-OMe

11.19

4−NO2

10.6

4−NO2

12.2

3−NO2

10.8

2−NO2

12.2

(a) Ref: Ritchie, C. D., Uschold, R. E. J. Am. Chem. Soc., 1967, 89, 1721; 1968, 90, 2821: Kolthoff, I. M.; Chantooni, M. K. J. Phys. Chem., 1971, 93, 3843; Pytela, O., Kuhlánek, J., Ludwig, M., Řiha, V. Collect. Czech. Chem., Commun., 1994, 59, 627; Pytela, O., Kulhánek, J. Collect. Czech. Chem. Commun. 1997, 62, 913;

(b) Chantooni, M. K., Kolthoff, I. M. J. Phys. Chem., 1975, 79, 1176

Further values may be estimated from aqueous data through correlations between dissociation constants in water and DMSO (Chapter 6) as follows.

Carboxylic acids

pKa(DMSO) = 1.57pKa(H2O) + 4.21

Phenols

pKa(DMSO) = 1.98pKa(H2O) − 2.40

Thiophenols

pKa(DMSO) = 2.55pKa(H2O) − 6.26

(p.133) 9.2.2 Inorganic acids and miscellaneous

Acid

pKa

Acid

pKa

Acid

pKa

HBr

0.9

HC3

7.9

HF

15

CH3SO3H

1.6

NH 4 +

10.5

NH2CN

16.9

HCl

1.8

HSO 4

12.6a

H2O

32

CF3CO2H

3.4

HCN

12.9

HNO2

7.5

(a) Kolthoff, I. M., Chantooni, M. K. J. Am. Chem. Soc., 1968, 90, 5961

9.2.3 Anilines, anilides, amides (N–H-ionization)

Acid

pKa

Acid

pKa

Acid

pKa

Anilinesa

4-Br

29.1

R = Me; R′ = Me

25.9

2, 4−(NO2)2

15.9

H

30.7

4−NO2

20.9

3-Me

31.0

2, 6−Cl2

24.8

Amidesb

Anilidesc

Appendices: Dissociation Constants in Methanol and Aprotic Solvents

Appendices: Dissociation Constants in Methanol and Aprotic Solvents

4−COCH3

25.3

R = CF3; R′ = H

17.2

X= Br; Y = CN

15.4

4-CN

25.3

R = 4−Py; R′ = H

21.6

X = Br; Y = Cl

17.0

2, 4−Cl2

26.3

R = 3−Py; R′ = H

22.0

X = Br; Y = H

18.0

3−CF3

28.5

R = Ph; R′ = H

23.3

X = H; Y = CN

19.0

3-Cl

28.5

R = H; R′ = H

23.5

X = H; Y = Cl

20.7

4-Cl

29.4

R = Me; R′ = H

25.5

X = H; Y = H

21.5

(a) Bordwell, F. G., Algrim, D. J. J. Am. Chem. Soc., 1988, 110, 2964;

(b) Hansen, M. M., Harkness, A. R., Coffey, D. S., Bordwell, F. G., Zhao, Y. Tett. Letters, 1995, 36, 8949;

(c) Bordwell, F. G., Gou-Zhen, J. J. Am. Chem. Soc., 1991, 113, 8398

9.2.4 Carbon acids: ketones, esters, nitroalkanes

Acida

pKa

Acida

pKa

Acida

pKa

Appendices: Dissociation Constants in Methanol and Aprotic Solvents

Appendices: Dissociation Constants in Methanol and Aprotic Solvents

Appendices: Dissociation Constants in Methanol and Aprotic Solvents

X = SO2Ph

12.5

X = 4-CN

22.0

X = NO2

9.1

X = COCH3

13.3

X = 4−CF3

22.7

X = CN

12.5

X = COPh

14.2

X = 3−CF3

22.8

X = COCH3

14.2

X = SOPh

15.1

X = 3-Cl

23.2

X = CO2Et

16.4

X = Ph

19.8

X = 4-Cl

23.8

X = Ph

22.7

X = Ha

26.5b

X = 4-Br

23.8

X = H

29.5

Appendices: Dissociation Constants in Methanol and Aprotic Solvents

X = 3-F

23.5

Nitroalkanes:

NO2CH2X

X = NO2

7.7

X = 4-F

24.5

X = NO2

6.6

X = CN

10.2

X = H

24.7

X = SO2Ph

7.1

X = SO2Ph

11.4

X = 3-OMe

24.5

X = COPh

7.7

X = COPh

13.4

X = 4-OMe

25.7

X = CO2Et

9.1

X = Ph

17.7

X = 3−NMe2

25.3

X = Ph

12.1

X = F

21.7

X = 4−NMe2

27.5

X = Et

17.0

X = Ome

22.9

X = Me

16.7

X = H

24.7

X = H

17.2

(a) Bordwell, F. G. Acc. Chem. Res., 1988, 21, 456; Bordwell, F. G., Harrelson, J. A. Can. J. Chem., 1990, 68, 1714; Zhang, X. M., Bordwell, F. G. J. Org. Chem., 1993, 59, 6456;

(b) pKa = 18.2 for acetone enol

(p.134) 9.2.5 Carbon acids: nitriles, sulphones

Acid

pKa

Acid

pKa

Acid

pKa

Nitriles:

CNCH2X

X = 3-CN

18.7

Appendices: Dissociation Constants in Methanol and Aprotic Solvents

X = COPh

10.2

X = 3-CF3

19.2

X = pClC6H4

3.1

X = CN

11.1

X = 3-Br

19.4

X = Ph

4.2

X = SO2Ph

12.0

X = 3-Cl

19.5

X = pOMeC6H4

5.6

X = CO2Et

13.1

X = 3-F

20.0

X = NMe2

12.2

X = H

31.3

X = 4-Cl

20.5

X = H

11.1

X = Me

32.5

X = 3-OMe

21.6

X = Me

12.4

Appendices: Dissociation Constants in Methanol and Aprotic Solvents

X = H

21.9

Sulphones:

X = 4-NO2

12.3

X = 4-F

22.2

PhSO2CH2CN

12.0

X = 4-CN

16.0

X = 4-Me

22.9

(MeSO2)2CH2

15.0

X = 3-NO2

18.1

X = 4-OMe

23.8

(EtSO2)2CHCH3

16.7

X = 3-SO2Ph

18.5

X = 4-Me2N

24.6

CH3SO2CH3

31.1

a Bordwell, F. G., Cheng, J-P., Bausch, M. J., Bares, J. E. J. Phys. Org. Chem., 1988, 1, 209

9.2.6 Carbon acids: fluorenes

Acid

pKa

Acid

pKa

Acid

pKa

Appendices: Dissociation Constants in Methanol and Aprotic Solvents

X = CONH2

14.8

X = Et

22.3

X = NO2

7.1

X = Ph

17.9

X = Me

22.3

X = CN

8.3

X = Cl

18.9

X = H

22.6

X = COPh

10.0

X = F

22.3

X = i-Pr

23.2

X = CO2Me

10.3

X = Pr

22.2

X = t-Bu

24.4

(p.135) 9.2.7 Cationic acids: anilinium, ammonium, pyridinium ions

Basea

pKa

Basea

pKa

Basea

pKa

ammonia

10.5

n-butylamine

11.12

4-OMe-aniline

5.08

methylamine

11.0

di-n-butylamine

10.0

4-Me-aniline

4.48

dimethylamine

10.3

tri-n-butylamine

8.4

aniline

3.82

trimethylamine

8.4

4-chloroaniline

2.86

ethylamine

10.7

Me4-guanidine

13.2

3-chloroaniline

2.34

diethylamine

10.5

piperidine

10.85

3-cyanoaniline

1.36

triethylamine

9.0

pyrrolidine

11.06

N-Me-aniline

2.76

n-propylamine

10.7

pyridine

3.4

N, N–Me2-aniline

2.51

(a) Kolthoff, I. M., Chantooni, M. K., Bhowmik, S. J. Am. Chem. Soc., 1968, 90, 23: Asghar, B. H. M., Crampton, M. R. Org Biomol. Chem., 2005, 3, 3971: Mucci, A., Domain, R.; Benoit, R. L. Can. J. Chem., 1980, 58, 953

9.3 N, N-Dimethylformamide

9.3.1 Neutral acids

pKa-values are summarized by Maran, F., Celadon, D.; Severin, M. G., Viannelo, E. J. Am. Chem. Soc., 1991, 113, 9320; the reference includes original data and literature values.

Acid

pKa

Acid

pKa

Acida

pKa

Carboxylic acid:

4−Cl, 3−NO2

8.6

3−NO2

15.4

Aliphatic:

3, 5−Cl2

8.8

4−NO2

12.6

CHCl2CO2H

7.6

3, 4−Cl2

9.2

3−CF3

15.7

CH2ClCO2H

10.2

2−NO2

8.2

3-Cl

16.3

PhCH2CO2H

13.5

3−NO2

9.2

4-Cl

16.8

CH3CO2H

13.5

4−NO2

9.0

H

18.9

oxalic:

pKa1

8.6

2-Cl

9.3

pKa2

16.6

4-Cl

10.1

thiophenol

10.7

malonic:

pKa1

7.9

3-Br

9.7

4−NO2-thiophenol

6.3

pKa2

19.3

4-Br

10.5

succinic:

pKa1

10.2

H

11.0

Appendices: Dissociation Constants in Methanol and Aprotic Solvents

pKa2

17.3

3-Me

11.0

X= Br;Y = CN

16.4

glutaric:

pKa1

11.3

3-OH

11.1

X = Br;Y = Cl

17.9

pKa2

15.6

4-Me

11.2

X = Br;Y = H

18.9

adipic:

pKa1

12.2

3, 4−Me2

11.4

X = H; Y = CN

19.8

pKa2

15.7

4−NH2

12.8

X = H; Y = Cl

21.4

o-phthalic:

pKa1

6.7

X = H; Y = H

22.3

pKa2

16.5

Phenol:

2, 6−(NO2)2

6.2

Amide:

Benzoic:

2, 4−(NO2)2

6.3

nicotinamide

22.5

2, 6−(OH)2

3.6

3−CF3, 4−NO2

10.4

benzamide

23.9

2, 4−(NO2)2

6.5

3, 5−(NO2)2

11.3

formamide

24.3

2-OH

6.8

2−NO2

12.2

2-pyrrolidinone

25.0

3, 5−(NO2)2

7.4

(p.136)

Additional dissociation constants for neutral acids in DMF, NMP and DMAC can be estimated from correlations with those in DMSO (Section 9.2) as follows:

pK a ( DMF ) = 0.96 pK a ( DMSO ) + 1.56 pK a ( NMP ) = 0.99 pK a ( DMSO ) + 1.08 pK a ( DMAC ) = 1.0 pK a ( DMSO ) + 0.1

9.3.2 Cationic acids

Aminea

pKa

Aminea

pKa

ammonia

9.45

tri-n-butylamine

8.57

dimethylamine

10.4

triethanolamine

7.6

diethylamine

10.4

pyridine

3.3

triethylamine

9.25

Me4-guanidine

13.65

(a) Kolthoff, I. M., Chantooni, M. K., Smagowski, H. Anal. Chem., 1970, 42, 1622; Izutsu, K.,Nakamura, T., Takizawa, K., Takeda, A. Bull. Chem. Soc. Japan, 1985, 58, 455; Roletto, E.,Vanni, A. Talanta, 1977, 24, 73

9.4 Acetonitrile

9.4.1 Neutral acids

Acida

pKa

Acida

pKa

Acida

pKa

Carboxylic acid:

2, 6−Cl2

18.2

3−NO2

24.6

Aliphatic:

3, 4−(NO2)2

18.0

4−NO2

21.7

CHCl2CO2H

16.4

2−NO2

18.8

4-CN

23.7

CH2ClCO2H

19.7

3−NO2

20.2

3.4−Cl2

25.1

CH3CO2H

23.5

4−NO2

20.7

3−CF3

25.6

oxalic:  pKa1

14.5

3-CN

20.0

3-Cl

26.1

pKa2

27.7

4-CN

19.9

4-Br

26.8

malonic:  pKa1

15.3

3-Cl

20.1

H

28.5

pKa2

30.5

4-Cl

20.9

succinic:  pKa1

17.6

3-Br

20.2

Appendices: Dissociation Constants in Methanol and Aprotic Solvents

pKa2

29.0

glutaric:  pKa1

19.2

4-Br

20.2

X = CO2Me

22.5

pKa2

28.0

3-OMe

21.3 X = CN

X = CN

21.4

adipic:  pKa1

20.4

H

21.5

pKa2

26.9

3-Me

21.5

Appendices: Dissociation Constants in Methanol and Aprotic Solvents

azealic:  pKa1

20.8

4-Me

21.9

X = 4−MeC6H4

17.6

pKa2

24.8

4-OH

21.6

X = 3−CF3C6H4

14.7

o-phthalic:  pKa1

14.2

X = 4−NO2C6H4

11.6

pKa2

29.8

Phenol:

2, 4, 6−(NO2)3

11.0

Sulphonic acid:

Benzoic:

2, 4−(NO2)2

16.4

4-chlorobenzene

7.3

2, 6−(NO2)2

16.2

3, 5−(NO2)2

21.3

3-nitrobenzene

6.8

2, 4−(NO2)2

16.6

2−NO2

22.9

4-nitrobenzene

6.7

3, 5−(NO2)2

17.7

(a) Coetzee, J. F., Padmanabhan, G. R. J. Phys. Chem., 1965, 69, 3193; Kolthoff, I. M., Chantooni, M.K. J. Am. Chem. Soc., 1965, 87, 4428; Kolthoff, I. M., Chantooni, M. K.; Bhowmik, S. J. Amer. Chem. Soc., 1966, 88, 5430; Kolthoff, I. M., Chantooni, M. K. J. Phys. Chem., 1966, 70, 856; Kolthoff, I. M., Chantooni, M. K. J. Am. Chem. Soc., 1969, 91, 4621; Chantooni, M. K., Kolthoff, I. M. J. Phys. Chem., 1975, 79, 1176; Chantooni, M. K., Kolthoff, I. M. J. Phys. Chem., 1976, 80, 1306; Kütt, A.; Leito, I.; Kaljurand, I.; Sooväli. L.; Vlasov, V.M.; Yagupolskii, L. M., Koppel, I. A. j.orgChem., 2006, 71, 2829

(p.137)

The dissociation constants show excellent correlations with those in water and DMSO:

  1. (a)

    Water:

    carboxylic acids:

    pKa(MeCN) = 1.6pKa(H2O) + 14.9

    phenols:

    pKa(MeCN) = 1.8pKa(H2O) + 9.6

  2. (b)

    DMSO:

    carboxylic acids and phenols:

    pKa(MeCN) = 1.00pKa(DMSO) + 10.5

    carbon acids:

    pKa(MeCN) = 1.00pKa(DMSO) + 12.9

9.4.2 Inorganic acids and miscellaneous

Acida

pKa

Acida

pKa

Acida

pKa

HclO4

1.57

H2SO4

7.9

NH 4 +

16.5b

CF3SO3H

2.60

HCl

10.4

HSO 4

25.9c

FSO3H

3.38

HNO3

10.6

(a) Kolthoff, I. M., Chantooni, M. K. J. Chem.Eng Data., 1999, 44, 124;

(b) Section 9.4.3;

(c) Kolthoff, I. M., Chantooni, M. K. J. Am. Chem. Soc., 1968, 90, 5962

(p.138) 9.4.3 Cationic acids: ammonium, anilinium, pyridinium ions

Base

pKa

Base

pKa

Base

pKa

Amine:a

Aniline:b

2-hydroxy

8.3

ammonia

16.5

2−NO2

4.80

3-cyano

8.0

methylamine

18.4

2, 6−Cl2

6.06

4-cyano

8.5

ethylamine

18.4

2, 5−Cl2

6.21

2-acetylo

9.6

n-propylamine

18.2

4−NO2

6.22

3-bromo

9.5

n-butylamine

18.3

4−F−3−NO2

7.67

3-chloro

10.0

t-butylamine

18.1

3−NO2

7.68

3-acetylo

10.8

benzylamine

16.9

2-Cl

7.86

3-hydroxy

12.6

morpholine

16.6

4−CF3

8.03

H

12.6

piperidine

18.9

2, 4−F2

8.39

3-methyl

13.7

pyrrolidine

19.6

4-Br

9.43

2-methyl

13.9

dimethylamine

18.7

2−Me

10.50

4-methyl

14.5

diethylamine

18.8

H

10.82

3-amino

14.4

di-n-butylamine

18.3

4-OMe

11.86

2-amino

14.7

trimethlyamine

17.6

N, N−Me2

11.4

4-amino

18.4

triethylamine

18.5

tri-n-proplyamine

18.1

Pyridine b:

tri-n-butylamine

18.1

2-chloro

6.8

DBUc

24.3

2-bromo

7.0

(a) Coetzee, J. F., Padmanaban, G. R. J. Am. Chem. Soc., 1968, 87, 5005;

(b) Kaljurand, I., Kütt, A., Sooväli, L., Mäemets, V., Leito, I., Koppel, I.A. J. Org.. Chem., 2005, 70, 1019; AugustinNowacka, D., Makowski, M., Chmurzynski, L. Anal. Chim. Acta., 2000, 418, 233;

(c) DBU = diazabicycloundecane

9.4.4 Phosphazene bases

The phosphazene bases, the structures of which are listed below the Table, exhibit a wide range of pKa-values.

Basea ,b

pKa

Basea, b

pKa

Basea, b

pKa

4−OMeC6H4P3(dma)

32.0

HP1(pyrr)

27.0

2−ClC6H4P1(pyrr)

20.2

PhP3(dma)

31.5

t−BuP1(dma)

27.0

4−CF3C6H4P1(pyrr)

20.2

2−ClC6H4P3(pyrr)6Net3

31.2

PhP2(dma)

26.5

2−ClC6H4P1(dma)

18.6

4−CF3C6H4P3(pyrr)

30.5

2−ClC6H4P2(pyrr)

25.4

2, 6−Cl2C6H3P1(pyrr)

18.6

2−ClC6H4P3(dma)6Net3

30.2

4−Nme2P1(pyrr)

23.9

2, 5−Cl2C6H3P1(pyrr)

18.5

4−CF3C6H4P3(dma)

29.1

4−OmeP1(pyrr)

23.1

4−NO2C6H4P1(pyrr)

18.5

EtP1(pyrr)

28.9

PhP1(pyrr)

22.3

2−NO2, 4−ClC6H3P1ClC6H3P1(pyrr)

17.7

t-BuP1(pyrr)

28.4

PhP1(dma)

21.3

2−NO2, 5−ClC6H3P1(pyrr)

17.3

4−OmeC6H4P2(pyrr)

28.2

4-BrC6H4P1(pyrr)

21.2

2, 4−(NO2)2C6H3P1(pyrr)

14.9

PhP2(pyrr)

27.6

PhP1(dma)2Me

21.0

2, 6−(NO2)2C6H3P1(pyrr)

14.1

MeP1(dma)

27.5

1−NapthP1(pyrr)

20.6

(a) Kaljurand, I., Kütt, A., Sooväli, L., Rodima, T., Mäemets, V., Leito, I., Koppel, I. A. J. Org Chem., 2005, 70, 1019;

(b) The structures of the phosphazene bases are listed below

(p.139)

Phosphazene base structures: Appendices: Dissociation Constants in Methanol and Aprotic Solvents

(p.140) 9.5 Tetrahydrofuran

9.5.1 Neutral acids

Benzoic acida

pKa

Phenolb

pKa

2,4-dinitro

18.64

2,4,6-trinitro

11.84

3,5-dinitro

18.99

2,4-dinitro

16.94

2-nitro

21.10

4-nitro

21.13

4-nitro

21.16

2,4,6-trichloro

22.98

3,5-dichloro

21.64

3,5-dichloro

23.16

3-nitro

21.77

2,4-dichloro

23.50

2,6-dichloro

22.22

3-nitro

23.76

3-bromo

23.23

2-nitro

24.41

2-chloro

23.44

2,6-dichloro

25.10

4-chloro

23.88

2-chloro

26.30

H

25.11

4-chloro

26.80

3-methyl

25.34

4-bromo

27.30

2-methyl

25.39

H

29.23

(a) Barbosa, J., Barrón, D., Bosch, E., Rosés, M. Anal. Chim. Acta, 1992, 265, 157;

(b) Barrón, D., Barbosa, J. Anal. Chim. Acta, 2000, 403, 339

9.5.2 Cationic acids

Basea

pKa

Basea

pKa

Basea

pKa

N−EtP1(tmg)b

32.6

Amine:

2-Cl

5.98

t−BuP1(tmg)b

32.0

DBUd

19.1

3−NO2

5.81

4−OMe−C6H4P3(pyrr)

31.7

TMGe

17.8

3, 4−Cl2

5.33

4−OMe−C6H4P3(dma)

30.5

pyrrolidone

15.6

2−NO2

5.12

PhP4(dma)c

29.8

triethylamine

13.7

4−NO2

4.82

4−Br−C6H4P4(pyrr)

29.7

propylamine

14.7

4−(NO2)2

4.61

EtP2(pyrr)

29.4

5−Cl2

4.47

EtP2(dma)

28.1

Aniline:

PhP3(pyrr)

26.8

4-OMe

8.8

Pyridine:

PhP3(dma)

26.2

4-t-butyl

8.73

4−NMe2

14.1

EtP1(pyrr)

24.2

H

7.97

4-OMe

9.6

PhP2(dma)

22.2

4-Cl

6.97

2-Me

8.6

PhP1(dma)

17.8

3-Cl

6.38

H

8.25

4−NO2C6H4P1(pyrr)

15.8

4-Br

6.2

(a) Garrido, G., Koort, E., Ràfols, C., Bosch, E., Rodima, T., Leito, I., Rosés, M. J. Org Chem., 2006, 71, 9062: reference includes a more comprehensive set of phosphazene bases (structures are illustrated in Section 9.3.3);

(b) tmg denotes N, N, N′, N′tetramethylguanidine radical;

(c) P4 denotes R3P = N − P(= NR′)(= NR3)N = PR3;

(d) DBU = diazabicycloundecane;

(e) TMG = N, N, N′, N′-tetramethylguanidine