75203-70-2Relevant academic research and scientific papers
A systematic entropy relationship for the general-base catalysis of the deprotonation of a carbon acid. A quantitative probe of transition-state solvation
Bunting, John W.,Stefanidis, Dimitrios
, p. 779 - 786 (2007/10/02)
The general-base-catalyzed deprotonation of a carbon acid, the l-methyl-4-(phenylacetyl)pyridinium cation (pKa = 9.02 at 25 °C), has been investigated for 32 general-base catalysts (25 amines and seven phenoxide ions) in aqueous solution. Amines give a generally scattered Bronsted plot; ring-substituted benzylamines have ?= 0.52, and ring-substituted phenoxides have ?= 0.60, with the phenoxides being more reactive than amines of similar basicity. The temperature dependences of the general-base-catalyzed deprotonation of this carbon acid have been measured over the range 15-45 °C for 12 base catalysts (eight primary, secondary, and tertiary amines; 4-(dimethylamino)pyridine; two phenoxide ions; hydroxide ion). The entropies of activation for these deprotonations show a clean curvilinear dependence upon the entropies of protonation of these base species, with the hydroxide ion being the only significant deviant from this relationship. This observation quantitatively establishes the importance of solvation effects as the major source of deviations that are commonly observed in Bronsted relationships for general-base-catalyzed processes.
Copper(II) and nickel(II) chelates of the dihydrogen nitrilotriacetate(1-) ion: Crystal and molecular structure of bis(N,N-bis(carboxymethyl)glycinato)copper(II) dihydrate
Dung, Nguyen-Huy,Viossat,Busnot,González Pérez,González García,Niclós Gutiérrez
, p. 1227 - 1231 (2008/10/08)
Bis(dihydrogen nitrilotriacetato) chelates of copper(II) and nickel(II) have been obtained as dihydrates, [M(H2NTA)2]· 2H2O (M = Cu, Ni; H3NTA = nitrilotriacetic acid or N,N-bis(carboxymethyl)glycine). The potentiometric and conductometric titration curves, TG-DTA analysis, spectral properties (IR, reflectance, ESR), and magnetic susceptibility data of these sparingly soluble in water compounds are discussed, taking in view the crystal structure of the copper complex [Cu(H2NTA)2]·2H2O, which crystallizes in the monoclinic system, space group P21/c (a = 6.845 (1) A?, b = 14.095 (4) A?, c = 9.427 (3) A?, β = 91.95 (2)°, Z = 2, V = 909.1 A?3, dmeasd = 1.73 (2) g·cm-3, dexptl = 1.75 g·cm-3, μ = 1.631 mm-1 (Mo Kα)). Final R = 0.032 and Rw = 0.033 for 1416 independent observed reflections. The copper atom lies in the center of symmetry. Two dihydrogen nitrilotriacetate(1-) or N,N-bis(carboxymethy)glycinate(1-) ions, H2NTA-, act as tridentate chelating agents, making up an all-trans elongated octahedral coordination around the same copper atom (Cu-N = 2.062 (3) A?, Cu-O(3) = 1.954 (2) A?, Cu-O(13) = 2.321 (2) A?) where each ligand remains with a free carboxylic group of one of the two acetic or N-carboxymethyl arms. Two interesting structural features of this solid are (1) the very short trans-apical Cu-O(13) and Cu-O(13i) bonds (symmetry code i: 1 - x, 1 - y, 1 - z), as compared with the un-ionized carboxyl-to-copper(II) coordination bonds in related compounds (2.467-2.518 A?), and (2) the formation of hydrogen bonds O(14)-H?OW (2.598 (4) A?; 164°) involving one water oxygen atom and the carboxylic group of each ligand bonded to copper.
