Multiple pathways in the α-cyclodextrin catalysed reaction of iodide and substituted perbenzoic acids

Abstract

The kinetic rate equation for the title reaction in aqueous acetate buffer has both first-order and second-order terms with respect t o cyclodextrin concentration, due t o catalysis both by one and by two molecules of cyclodextrin. The stabilisation of the transition state of the iodide-peracid reaction by cyclodextrin is examined using the pseudoequilibrium constant approach of Tee, Carbohydr. Res., 1989, 192, 181. This approach indicates that, depending on the nature of the peracid, the predominant pathway catalysed b y one cyclodextrin molecule involves the reaction of either free iodide and a cyclodextrin-peracid complex or free peracid and a cyclodextrin-iodide complex. The latter two pathways are kinetically indistinguishable, but the corresponding terms in the rate equation are separated using the extrakinetic assumption of a Bronsted-type relationship. This assumption is reasonable since the uncatalysed reaction and that catalysed by two molecules of cyclodextrin show Bronsted-type relationships. The mechanism of catalysis is discussed in terms of the effect of cyclodextrin o n the nucleophilicity of the iodide and acid catalysis via the protonation of the benzoate leaving group.

The Stability of Cyclodextrin Complexes in Solution

“…326,368 Kuroda et al 359b make a correlation with a reorientation (correlation time) free energy of activation.…”

Large‐Scale Ultrathin 2D Wide‐Bandgap BiOBr Nanoflakes for Gate‐Controlled Deep‐Ultraviolet Phototransistors

“…Mater. 2020, 32,1908242 (Figure 5a). Figure 5b shows the spectral photoresponse curve from 200 to 600 nm at a drain-source voltage (V ds ) of −10 V with a light spot diameter of 3 mm to confirm the peaks of photoresponse wavelength.…”

“…Figure 2b shows the typical Raman spectra of transferred BiOBr nanoflakes from 50 to 200 cm −1 with A 1g 1 Bi-Br external stretching mode (≈56 cm −1 ), A 1g 2 Bi-Br internal stretching mode (107-111 cm −1 ), E g 1 external Bi-Br stretching mode (≈86 cm −1 ), and E g 2 internal Bi-Br stretching mode (≈158 cm −1 ), in conformity to the previous reports. [31,32] Obviously, Raman spectrum of the ultrathin BiOBr shows different stretching mode compared to that of the BiOBr with thickness above 20 nm. In detail, when the thickness decreased below 5 nm, external E g 1 mode near 86 cm −1 emerges.…”

Micellar behavior of aqueous solutions of dodecyldimethylethylammonium bromide, dodecyltrimethylammonium chloride and tetradecyltrimethylammonium chloride in the presence of α-, β-, HPβ- and γ-cyclodextrins

“…Accommodation of the guest molecule depends on its size and polarity and on the size of the particular cyclodextrin. CDs, as a result of their complexation ability and other versatile characteristics, are continuing to have different applications in different areas of drug delivery and pharmaceutical industry [1][2][3][4][5][6][7][8][9][10][11][12][13].…”