Potentiometric study of equilibrium acidities of some carbon acids in acetonitrile

Abstract

The pK a values for 30 C-acids of the type CH·R 1 ·R 2 ·R 3 -where the R 1 , R 2 , and R 3 substituents are H, alkyl, and aryl, and the most common electron withdrawing groups used in studies of proton-transfer reaction -are given herein. The pK a values have been measured potentiometrically in acetonitrile, using a glass electrode. These values were determined in a buffer solution consisting of a C-acid and its tetrabutylammonium salt, at constant ionic strength (0.001 M), at 25°C. The measurements were done under nitrogen, to prevent oxidation of the anion. The influence of water within the sample of the tetrabutylammonium hydroxide base was negligible. The lowest pK a value of 19.1 was found for bis(4-nitrophenyl)cyanomethane, while the largest pK a s that could be measured were limited by the basicity of the hydroxide ion, and did not exceed 28. A satisfactory agreement between spectrophotometric and potentiometric acidities was achieved.

The Essential Role of Bond Energetics in C–H Activation/Functionalization

“…The p K a value, usually measured in solution, is defined as the negative logarithm of the equilibrium constant of eq (solvent is omitted for simplicity) . Although in C–H activation attention is more directly paid to BDE rather than p K a , because BDEs of most varieties of substrates have been (or could be) derived by the solution BDE method described in section , where p K a is the key parameter, we here introduce a most widely used and highly reliable “indicator overlapping” p K a method as representative. − Many other schemes applied for studies of weak C–H acids, such as by kinetics, − calorimetry of deprotonation, potentiometric titration, , or NMR, , will not be discussed here. There are some excellent reviews and monographs − for readers who are interested to refer to.…”

On the Basicity of Organic Bases in Different Media

“…Me 3 N 75-50-3 9.76 [58] 8.4 [59] 17.61 [34] 12.7 ± 0.5 [f ] 219.4 Et 3 N 121-44-8 10.65 [58] 9.0 [60] 18.83 [33] [e] 12.5 [63] 227 Pr 3 N 102-69-2 10.65 [58] 10.7 [67] 18.26 [37] [e] 13.0 [37] 229.5 Bu 3 N 102-82-9 10.89 [58] 8.4 [60] 18.09 [34] 12.7 ± 0.5 [f ] 231.3 Bn 3 N 620-40-6 7.44 [68] 4.1 [69] 12.9 [70] 6.5 ± 1.8 [d] 230.4 [g] Ph 3 N 603-34-9 -3.91 [71] 1.28 [42] [e] 209.5 N,N-Dimethylaniline 121-69-7 5.06 [62] 2.70 [66] 11.47 [33] [e] 4.9 [63] 217.3 Me 2 EtN 598-56-1 9.99 [58] 8.5 ± 1.2 [d] 18.33 [37] [e] 12.6 [37] 222. [58] 11.1 ± 1.2 [d] 18.46 [34] 13.6 ± 1.8 [d] 218.1 NH 2 -(CH 2 ) 3 -NH 2 109-76-2 10.47 [34] 12.3 ± 1.2 [d] 19.76 [37] [e] 14.8 ± 1.8 [d] 224.7 NH 2 -(CH 2 ) 4 -NH 2 110-60-1 10.65 [34] 12.6 ± 1.2 [d] 20.12 [34] 15.2 ± 1.8 [d] 228.1 NH 2 -(CH 2 ) 5 -NH 2 462-94-2 10.85 [34] 11.7 ± 1.2 [d] 19.14 [34] 14.2 ± 1.8 [d] 226.1 Me 2 N-(CH 2 ) 2 -NMe 2 110-18-9 9.15…”

Scale-up Study of Benzoic Acid Alkylation in Flow: From Microflow Capillary Reactor to a Milliflow Reactor

“…Due to the larger quantities used in this study, we reorientated our process toward the use of cheaper bases (DBU, 1,1,3,3-tetramethylguanidine (TMG), 2- tert -butyl-1,1,3,3-tetramethylguanidine = Barton’s base) for which basicities (p K BH+(DMF) 14.7–16.8) , are in the same range than the one of TMGN and sufficiently basic to fully deprotonate benzoic acid (p K a(DMF) = 12.27) . We first studied conditions previously described by Mal in the presence of DBU in acetonitrile (Table , entry 1), and DMF (entry 2) was demonstrated to be a much better solvent. , This can be explained by higher polarity of DMF compared to CH 3 CN that avoids the formation of aggregates or strong ion pairs .…”