The pK sub a value of the O sub 2 CH sub 2 CO sub 2 H radical: The Taft. sigma. * constant of the minus CH sub 2 O sub 2 group

Journal Article · Thu Jun 29 04:00:00 EDT 1989 · Journal of Physical Chemistry; (USA)

DOI:https://doi.org/10.1021/j100350a055· OSTI ID:7071071

Schuchmann, M N; Schuchmann, H; von Sonntag, C ^[1]

---

1. Max-Planck-Institut fuer Strahlenchemie, Ruhr (West Germany)

The pulse radiolysis of oxygen-containing dilute aqueous acetic acid solutions of different pH has been investigated through conductivity detection. It has been shown that the acetic acid peroxyl radical {center dot}O{sub 2}CH{sub 2}CO{sub 2}H is considerably more acidic than acetic acid itself (pK{sub a}({center dot}O{sub 2}CH{sub 2}CO{sub 2}H) = 2.1 {plus minus} 0.2 vs 4.76 for acetic acid). This pK{sub a} value corresponds to a Taft {sigma}* value of 1.55 {plus minus}0.12 for the {minus}CH{sub 2}O{sub 2}{center dot} group. As a check by means of optical detection, the malonic acid peroxyl radical {center dot}O{sub 2}CH(CO{sub 2}{sup {minus}}){sub 2} ({epsilon}(340 nm) = 750 dm{sup 3} mol{sup {minus}1} cm{sup {minus}1}; the protonated form(s) absorbs considerably less) was observed likewise to be more acidic (second pK{sub a} at about 3) than its parent compound (second pK{sub a} at 5.7). The bimolecular decay of the acetic acid peroxyl radical occurs via an intermediate tetraoxide (self-termination) and via the corresponding hydrotetraoxide (termination with the hydroperoxyl radical). Some of these decay routes lead to formaldehyde. Its yield is pH-dependent, reflecting the fact that the intermediate tetraoxides are carboxylic acids that can exist in various states of dissociation.

• OSTI ID: 7071071
• Journal Information: Journal of Physical Chemistry; (USA), Journal Name: Journal of Physical Chemistry; (USA) Vol. 93:13; ISSN JPCHA; ISSN 0022-3654
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
54 ENVIRONMENTAL SCIENCES
540110
550000 -- Biomedical Sciences
Basic Studies
59 BASIC BIOLOGICAL SCIENCES
ACETIC ACID
CARBOXYLIC ACIDS
CHEMICAL RADIATION EFFECTS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHEMISTRY
DATA
DATA ANALYSIS
DECOMPOSITION
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
EXPERIMENTAL DATA
INFORMATION
IONIC CONDUCTIVITY
KINETICS
MEASURING INSTRUMENTS
MEASURING METHODS
MONOCARBOXYLIC ACIDS
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
OZONE
PEROXY RADICALS
PHYSICAL PROPERTIES
RADIATION CHEMISTRY
RADIATION EFFECTS
RADICALS
RADIOLYSIS
REACTION KINETICS