Reaction routes, and mechanism

Ravindranath and co-workers studied the electrochemical behavior of 5-amino-2-phenyl-4-arylazo-l,2-dihydro-3//-pyrazol-3-one (90UC864) and 5-methyl-4-arylazo-2-(pyridin-2-ylcarbonyl)-2,4-dihydro-3//-pyrazol-3-(Mie (90IJC895). Similar studies were undertaken by Jain and Damodharan of pyrazol-3-ones 408a-f (95CJC176) (Scheme 94). The underlying rationale for this study on the electrochemical reduction of these biologically important pyrazol-3-ones is that it can lead to information on the reaction routes and mechanisms of biological redox reactions. 

In conclusion therefore it is felt that electrochemistry does offer a valuable technique to study the electron-transfer reactions of biologically-impor-tant molecules. The mechanisms and products observed electrochemically do appear to be similar in many instances to those of the biological reactions. In cases where the biological products or mechanisms are not known electrochemical studies should prove useful in suggesting potential reaction routes and products. 

Horinti has introduced the concepts of "independent intermediates , "stoichiometric number , "reaction route and "independent reaction routes that have been extensively used in the steady-state reaction theory. Let us clarify them by a model izomerization reaction with a detailed mechanism... 

One major reason for the great interest in the processes of thin metal-containing films is that reactions on the surface of small metal clusters can be studied. Indeed, prior to the development of thin-film chemistry, reactions of similar particles were studied only in the gas phase at rather high temperatures. Under these conditions, most of the primary products are unstable and decompose in the course of further reaction, which is non-selective. As a result, the information obtained on the routes and mechanisms of reactions of disperse metals appears to be scarce, while the use of such reactions in synthesis is inexpedient. Conversely, low-temperature reactions in the films of co-condensates are very promising from the standpoint of determining the detailed reaction mechanism, as well as for synthesis of previously unknown complexes and organometallic compounds. It is important that atoms of only a few metals react with organic compounds immediately at the instant of their contact on the cooled substrate. Rather often, atoms and/or small (molecular) clusters are first stabilized in the film, and then their transformations are observed. 

We have reported a number of cyclization reactions. The one- and two-N containing five and six-membered, saturated and unsaturated heterocycles were synthesized from C to Cs aliphatics like alcohols, aldehydes, ketones, in presence of ammonia and other amines [11-33]. For example, 3,5-lutidine was synthesized from propionaldehyde or propanol, formaldehyde and ammonia over modified ZSM-5 catalysts. The yield of 3,5-lutidine was in the range of 40 to 65 wt% at 60-90% conversion of propionaldehyde over modified ZSM-5 catalysts at 400 C. In the reaction of ethanol, formaldehyde and ammonia over ZSM-5 catalyst pyridine and picolines were obtained. The reaction route or mechanism is shown in Fig. 2 and 3. In the reaction of acetaldehyde, formaldehyde and ammonia over ZSM-5 pyridine and 3-Picoline were obtained. On the other hand, 2- and 4-Picolines were obtained in the reaction of acetaldehyde and ammonia. 

Table 8,3. Reaction routes and kinetic equations for mechanism in eg. 8.122.

In the case of 4-terbutylphenol, when overall reactions are irreversible, the reaction mechanism can be described by 4 reaction routes and written as follows... 

Complex investigations on electrode materials and electrode kinetics were carried out with the aim to elaborate electrodes with high electrochemical activity. The route and mechanism of the electrode reactions, dependence of polarization on electrode materials and structure, gas atmosphere, and other factors were studied. As a result of this research the electrodes based on Ni, Co, Cu, manganite, and cobaltite having high working characteristics were elaborated. 

A side reaction of this oxygenate initiation is the production of CO2 from the added tracer alcohols. Its C-O-H group gets chemisorbed in the vicinity of an M=0 entity, which obtained its oxygen from the dissociation of CO. CO2 produced from l-[ C]-l-pentanol tracer was radioactive but it was inactive if 2-[ C]-l-hexanol was added. The complicated reaction sequence of FT is still not clarified in every detail. The role of reactor hold-up in determining the distribution of alkanes and alkenes in higher C-number products has been pointed out recently. Possible suggested reaction routes ( current mechanism and futuristic needs ) have been summarised by Davis. 

In this work, we address the problem of partitioning De Donder relations into contributions associated with different types of reactions from the point of view of the theory of reaction routes, or mechanisms. Thus, derivation of reduced routes allows reaction rate analysis in terms of the QSS, RDS and QE formalisms. 

This substitution reaction provides a useful general route to alkyl halides. Because halide ions are good nucleophiles, we obtain mainly substitution products instead of dehydration. Once again, the reaction rate and mechanism depend on the class of alcohol (tertiary, secondary, or primary). 

Secondly, the existence of adsorbed hydrogen atoms on the surface makes possible alternative reaction routes, and two mechanisms are generally considered important, namely... 

To illustrate this point, let us discuss the following hypothetical mechanism with two reaction routes and when adsorption of multi-centered species occurs requiring a cluster of several metal surface sites ... 

Reaction routes, and are the complete and partial oxidation of the hexadecane, while N and N correspond to the reduction of NO. Routes N and N describe the complete and partial HC-SCR with the presence of reacting NO2. Routes N and N account for the basic mechanism for the formation of CO2 and NO2 and route deals with the isocyanate pathway. 

Structure and Mechanism of Formation. Thermal dimerization of unsaturated fatty acids has been explaiaed both by a Diels-Alder mechanism and by a free-radical route involving hydrogen transfer. The Diels-Alder reaction appears to apply to starting materials high ia linoleic acid content satisfactorily, but oleic acid oligomerization seems better rationalized by a free-radical reaction (8—10). 

Available information on the mechanism of cyclocondensation is rather contradictory. According to one hypothesis, both the condensation of aryl halides with copper acetylides and the cyclization occur in the same copper complex (63JOC2163 63JOC3313). An alternative two-stage reaction route has also been considered condensation followed by cyclization (66JOC4071 69JA6464). However, there is no clear evidence for this assumption in the literature and information on the reaction of acetylenyl-substituted acids in conditions of acetylide synthesis is absent. 

The sex hormone estrone has been synthesized by a route that involves the following step. Identify the pericyclic reactions involved, and propose a mechanism. 

Fig. 3.3.4 Reaction mechanism of the coelenterazine bioluminescence showing two possible routes of peroxide decomposition, the dioxetanone pathway (upper route) and linear decomposition pathway (lower route). The Oplopborus bioluminescence takes place via the dioxetanone pathway. The light emitter is considered to be the amide-anion of coelenteramide (see Section 5.4).

The photolysis of chlorinated aromatic compounds occurs by several processes which follow predictable routes 13). They frequently undergo photochemical loss of chlorine by dissociation of the excited molecule to free radicals or, alternatively, through a nucleophilic displacement reaction with a solvent or substrate molecule. Either mechanism is plausible, and the operation of one or the other may be influenced by the reaction medium and the presence of other reagents. 

Anthraquinone is widely use in the manufacture of a range of dyes. Two possible routes for manufacturing anthraquinone are (1) from the reaction of 1,4-naphthoquinone with butadiene and (2) reaction of benzene with phthalic anhydride. Describe mechanisms for both these reactions and identify likely reaction conditions and any other reagents required. Compare the atom economy of the two routes. Identify three factors for each route that may influence the commercial viability. 

Give an example of an SnI and an 8 2 reaction, explaining the mechanism and calculating the atom economy of the reaction. Suggest alternative synthetic routes to your products that are more atom economic. 

The results obtained by Candlin and Halpern are given in Table 13 in all cases, it is seen that AF is positive. These results strongly suggest that the Fe(II) reductions proceed by inner-sphere routes. However, to be convincing the method requires calibration by reactions of known mechanism. 

This reaction typifies the two possibilities of reaction routes for M-catalyzed addition of an S-X (or Se-X) bond to alkyne (a) oxidative addition of the S-X bond to M(0) to form 94, (b) insertion of alkyne into either the M-S or M-X bond to provide 95 or 96 (c) C-X or C-S bond-forming reductive elimination to give 97 (Scheme 7-21). Comparable reaction sequences are also discussed when the Chalk-Harrod mechanism is compared with the modified Chalk-Harrod mechanism in hydrosily-lations [1,3]. The palladium-catalyzed thioboratiori, that is, addition of an S-B bond to an alkyne was reported by Miyaura and Suzuki et al. to furnish the cis-adducts 98 with the sulfur bound to the internal carbon and the boron center to the terminal carbon (Eq. 7.61) [62]. 

A simplified scheme of the dual pathway electrochemical methanol oxidation on Pt resulting from recent advances in the understanding of the reaction mechanism [Cao et al., 2005 Housmans et al, 2006] is shown in Fig. 15.10. The term dual pathway encompasses two reaction routes one ( indirect ) occurring via the intermediate formation of COads. and the other ( direct ) proceeding through partial oxidation products such as formaldehyde. 

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