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 00:00:00 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]

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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), Vol. 93:13; ISSN 0022-3654
• Country of Publication: United States
• Language: English

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ACETIC ACID
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MEASURING INSTRUMENTS
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NUMERICAL DATA
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