The dissociation constants of some alkyl and acyl hydroperoxides

Abstract

The dissociation constants of organic peracids have been determined by potentiometric titrations ; they lie in the range of pK 7-8. U.-v. absorption spectra of hydroperoxides were used to assess their (classical) dissociation constants, the logarithms of which lie between 11-5 and 12.8. These data agree with the structure generally ascribed to the peracids. In the peroxide series, however, methyl substitution has less effect than usual : the reasons for this are discussed in terms of Walsh's theory of the peroxide bond.

Sur Le Spectre Ultraviolet De l'ACIDE Peracéetique Et l'HYDROLYSE Des Peracétates

“…de soude (variant de 20 5 50y0) 2 1 cc. d'acide peracbtique A 10y0, l'hydrolyse [3] semblait compl6te en quelques minutes tandis que la dCcomposition du peroxyde d1hydrog6ne Ctait allkatoire. Leur conclusion Ctait bas& sur le fait que ces solutions ne libhraient pas d'iode lors de l'addition d'une solution acide de K I , rCaction conilue sous le ilom de Riesenfeld-Liebhafslcy (6).…”

“…1). Bieil plus, ilous avons trouvC que l'addition d'un grand exc6s de soude (6:l) B l'acide peracbtique n'augmente pas le coefficient d'absorption au delB de la courbe C alors que dans l'hypotl16se de l'hydrolyse [3] l'absorption devrait tendre vers celle de l'ion OzH-(courbe A). RCcemment, Partington et Fathallah (5) oilt prouvl: qu'un test de Riesenfeld-Liebhafslcy nigatif in'est pas valide d a m le cas des perborates et des percarboizates; nos rCsultats confirment bieil qu'il en est de mCme pour les peracktates.…”

The Structural Chemistry of Acyclic Organic Peroxides

“…The relevance of the cyclic hydrogen-bonded structure is noted in a lower acid strength of, e.g. peracetic acid (pK a = 8.2) in comparison to acetic acid (pK a = 4.75) 21,23 . Unlike their carboxylic acid derivatives, peracids exist in solution and in the gas phase preferentially as monomers (Figure 11a,b).…”

“…2,5-Dimethyl-2,5-dihydroperoxyhexane (23) Figure 12) exhibits in the solid state two larger and one smaller O−C−C angle…”

“…properties of the peroxide functionality by means of electronic and/or steric effects, hyperconjugation and hydrogen bonding, which is reflected in different bond dissociation energies (BDE) 8 , redox potentials 20 , pK a 21 or pK HB 22 values. The pK a values of compounds of the type ROOH, for example, gradually decrease with the electron-withdrawing property of R along the series (H 3 C) 3 COOH (1) (pK a = 12.8), H 2 O 2 (11.6), CH 3 OOH (2) (11.5), CF 3 OOH (3) (8.9) to CH 3 C(O)OOH (8.2) 23 .…”