Conjugative oxidative

Conjugated dienes and polyenes lead to unique cases of conjugated oxidations, such as the formation of endoperoxide by singlet oxygen attack on the endo-diene, e.g. u-terpinene29. 

Fundamental notions and Shilov s classification of conjugated oxidation reaction types. 

Hitherto, we have only discussed Shilov s classic work in which using the example of conjugated oxidation reaction the general theory of conjugated processes was properly achieved. However, a series of subsequent works should be mentioned which developed investigations in the field of conjugated reactions. Without attempting a full treatment of the subject, let us concentrate on the most important results for scientific and applied purposes. 

In the study of conjugated processes, of special attention are works by Emanuel [5], who has considered conjugated chain reactions to be of great importance and promising directions of radical reactions. Emanuel et al. have implemented detailed studies in this area. In particular, they suggested an effective method of propylene and acetaldehyde conjugated oxidation [6] for a one-stage synthesis of propylene oxide and acetic acid [7],... 

Let us now trace how the active oxygen concept, which in due course had been invaluable in helping chemists interpret the oxidation mechanism, led them to make outstanding discoveries, for example, that of conjugated oxidation and many other reactions and how it transformed with time into a modem theory of molecular oxygen oxidation. 

To illustrate the application of the active oxygen theory to inorganic oxidation, let us consider several conjugated oxidation reactions. 

Conjugated reactions are the only ones in which the active oxygen theory preserves the meaning ascribed to it by Shilov. This fact is clearly illustrated by Shilov s examples [ 1 ], in which inorganic substances were subject to conjugated oxidation and the rules of the game were strictly obeyed, conjugated reaction separation conditions, in particular. 

Of special attention were conjugated oxidation reactions by hydrogen peroxide. The possibility of using the processes described for development and modernization of various processes in chemical technology was discussed. 

Shilov, N.A., On Conjugated Oxidation Reactions, Mamontov Publishers Moscow, 1905, 304 pp. (in Russian). 

Mitskevich, N.I. and Erofeev, B.V., Conjugated Oxidation and Decarboxylation of Carboxylic Acids, Nauka i Tekhnika, Minsk, 1970, 188 pp. (in Russian). 

Let us consider some examples, such as conjugated oxidative dehydration of acetic acid [7] 2CH3COOH(lq) (CH3C0)20(lq) + H20(lq), (3.11)... 

The author [6] has shown that the secondary process represents a new type of reaction— conjugated oxidative dehydrogenation, and contrary to usual thermal dehydrogenation [8], may be performed at lower temperatures and give higher yields and selectivity [9],... 

Some aspects of the questions arising are illustrated by the example of conjugated oxidation reactions by hydrogen peroxide. As mentioned before, thermal dissociation of H202 generates OH radicals to the system by the following reaction ... 

As mentioned in Chapter 2, there is the actual question about detection of a thermodynamic condition of conjugated oxidation of various substrates with hydrogen peroxide required for quantitative characterization of conjugation from the energy positions. For this purpose, let us show data on several non-spontaneous reactions, stimulated by chemical conjugation ... 

The above discussed were several aspects of ethylbenzene conjugated oxidation (dehydrogenation) with hydrogen peroxide. This reaction was studied in detail in many investigations... 

Conjugated oxidation of methane and methanol by 25% hydrogen peroxide... 

Of special attention is the single-stage method of olefm oxide production by their conjugated oxidation with another, more easily oxidizing compound (aldehyde, ketone, etc.) [134,139], For the epoxidation of an olefm, active oxygen of peroxy radicals is used in such a system ... 

As mentioned above, at gas-phase conjugated oxidation with hydrogen peroxide in a flow system with stationary mode H02 radical concentration is several orders of magnitude higher than "OH radical concentration. Based on this fact and literary data on olefm epoxidation... 

Figure 4.21 Temperature dependencies of selectivity (y) (1), yields (/ ) of propylene oxide (2), acrolein (3) and side products (4), and propylene consumption (a) (5) for conjugated oxidation with hydrogen peroxide, (a) 30% H202 vH q = 1.3ml/h vc jj = 150ml/h and (b) 10% H202 vh2Q2 = 3-78ml/h vc3H6 = 900ml/h- 2 2 3 6...

Basing on investigations carried out, it is shown that the conjugated oxidation of propylene is a controllable process and, with respect to particular conditions, secondary reaction may display three dominant propagation directions as follows ... 

Propylene thermal oxidation with hydrogen peroxide is implemented with formation of propylene oxide, acrolein and allene, and C3H6 present in the system plays the role of the active oxygen acceptor from 0—OH. To put it another way, the conjugated oxidation of propylene with hydrogen peroxide is also a H02-dependent reaction [31]. 

This example shows the extent to which conjugated reaction study is simplified, if scientists have data on general regularities of conjugated oxidation with hydrogen peroxide. 

The activation energy of free radical recombination approached zero. As a result of these investigations, the conditions for selective conjugated oxidation of methane to formaldehyde with hydrogen peroxide were determined and the process mechanism was suggested. The example is notable, because two types of free radicals (CH and H02) are reactive particles in it. 

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