Darstellung substituierter p ‐Aminophenole aus p ‐Phenylendiaminen

A classical organic redox reaction is the conversion of an aromatic compound from its reduced form R to a semioxidized state S, and further to a totally oxidized (quinoid) species T. Complex redox systems are present in a reaction of quinoid and aromatic forms derived from different parent compounds. In this case, the exchange of one or two electrons in one step between T and R can be distinguished experimentally. These reactions were investigated in a stopped‐flow apparatus with optical detection. In the system N,N,N′,N′‐tetramethyl‐para‐phenylene‐diamine/N,N‐dimethyl‐para‐phenylene‐diamine the rate constants for all elementary reactions have been determined. Protonated, and unprotonated R were found to be reactive. In this system, as well as the others considered, no direct transfer of two electrons between T1 and R2 takes place. The essential steps of the mechanism have to be seen in a mixed symproportionation yielding S1 and S2, and a subsequent fast oxidation of S2 by surplus starting material T1. As a generalization, a tangent criterion has been derived to distinguish between one‐ and two‐electron steps in such mixed redox systems.

Section: Substances 221 Reduced Formsmentioning

confidence: 99%

An Investigation of Electron Transfer Reactions between Aromatic and Quinoid Systems

Goez

Jaenicke

Nickel

1988

“…It has been shown earlier that most oxidants can only react with the unprotonated p-phenylenediamines [9 -131. Therefore the protonation equilibria (4) and (5) Although the first oxidation product is a radical, it is stable, whereas the second oxidation product undergoes rapid deamination in alkaline [2,3] as well as in acid solution …”

Section: Introductionmentioning

confidence: 99%

Coupled Catalytic and Autocatalytic Oxidation Reactions Linked by a Feedback Reaction Part 1. The Mechanism of the Superadditive Oxidation of p‐Phenylenediamines by Iron(III)_aq and Hexacyanoferrate

Nickel

Zhou

Gulden

1985

Self Cite

Catalysis / Chemical Kinetics / Oxidation / Radicals / Superadditivity The 2-step oxidation of some organic compounds in homogeneous aqueous solution often occurs according to an autocatalytic mechanism, because by a feedback reaction the semi oxidized form is autocatalytically increased. In presence of two different oxidants additional homogeneous catalysis can sometimes be observed, yielding a complex redox system which often causes curious experimental curves. For example p-phenylenediamines are oxidized by iron(1IQaq irreversibly, but slowly, whereas hexacyanoferrate(II1) oxidizes rapidly, but reversibly. A mixture of both oxidants, however, oxidizes rapidly and irreversibly, even if the concentration of hexacyanoferrate is less than lo-' M.

“…It is required to distinguish clearly between the present additivity rule and the traditional one [4,5] before applying the former to see the anomaly of cycloalkanes. The important differences are as follows: (i) The well defined translational contribution to the partial molal volume is given by K T R T [1,9] in the present expression in contrast to the ambiguous definition in the traditional treatment.…”

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confidence: 99%

“…The important differences are as follows: (i) The well defined translational contribution to the partial molal volume is given by K T R T [1,9] in the present expression in contrast to the ambiguous definition in the traditional treatment. (2) and (3) makes useless the traditional concept "covolume" [4,5,10,11] which is based on the primitive assumption that all atoms or groups of the same kind make the contribution of the same increment in any molecules; thus the environmental differences which may cause different packing efficiencies have been ignored in the traditional treatment. (2) and (3) makes useless the traditional concept "covolume" [4,5,10,11] which is based on the primitive assumption that all atoms or groups of the same kind make the contribution of the same increment in any molecules; thus the environmental differences which may cause different packing efficiencies have been ignored in the traditional treatment.…”

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confidence: 99%

Additivity Rule of the Partial Molal Volume. 3. Anomaly of Cycloalkane Molecules and Volume Change for the Ring Formation Reaction

Yoshimura

Nakahara

1985

Liquids / Molal Volume 1 Solutions / ThermodynamicsThe semimicroscopic theory of the partial molal volume which takes account of the local molecular packing efficiency through the surface energy has been applied to the cycloalkane by using a simple molecular model to evaluate the core dimensions. The anomalous deviation of the partial molal volume of the cycloalkane from the additivity rule is successfully interpreted; the anomaly arises simply from the geometrical factor that the core dimensions of the cycloalkane are larger than those of the corresponding linear alkane. The semimicroscopic approach provides a new framework for the interpretation of the volume change accompanying the chemical reaction in solution; this is demonstrated in the case of the cycloaddition reaction. The present approach justifies the separation of the overall reaction volume into the components in the additive manner.