Reaction trimolecular

If ( i = Cii = I, i. e. if the solution be normal with respect to alkali and ester, and if the transformed materials be continuously replaced, times the quantity originally present would be saponified in a minute. The reaction is therefore a very rapid one. 

It should be noticed that the equation may be derived from kinetic considerations, since to bring about the change a collision of the two reacting molecules is necessary, and the number of collisions is therefore obviously proportional to the amount of reaction taking place. The number in unit of volume is, however, proportional to both the mass of alkali and of ester, C and (7n, and we get accordingly 

The restriction to dilute systems (solutions and gases) which follows from the connexion with the law of equilibrium (p. 187) holds for the kinetic deduction also, since proportionality between the number of collisions and Ci and Oil is only to be expected in the limiting case when the space taken up by the molecules themselves vanishes by comparison with the total space, which is only true for infinite dilution. Practically the necessary condition holds for tenth-normality and below. 

If three molecules are required to complete a reaction, three cases may be distinguished, according as the molecules are all alike, two alike, or all different. 

If all are alike the velocity maybe taken as proportional to (7, in the other cases to G Ou and Ci, (7n, Cm respectively. 

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Trimolecular reactions have also been discussed for molecular reactions postulating concerted reactions via cyclic intennediate complexes, for example... 

Bimolecular and Trimolecular Reactions of Dioxygen with the Double Bond of Olefin... 

Later, both reactions were proved experimentally by Cooper and Melville in 1951 [58] and Miller and Mayo in 1956 [54]. In addition, the trimolecular reaction 2 RH + 02 was predicted in 1960 and experimentally proved in 1961 [59,60]. 

In addition to the bimolecular reactions of organic compounds with dioxygen, free radicals are generated in an oxidized substrate in the liquid phase by the trimolecular reaction [3,8,9]... 

The trimolecular reaction of two dioxygen molecules with two C—H bonds of one hydrocarbon was observed in ethylbenzene oxidation [43]. 

Rate Constants and Activation Energies of the Trimolecular Reaction 2RH + 02 —> Free Radicals (Experimental Data)... 

Unsaturated compounds react with dioxygen by trimolecular reaction also [48]. It is very probable that this reaction proceeds via preliminary formation of a CTC. The formed complex reacts with another olefin molecule. 

TABLE 4.5 Rate Constants of the Trimolecular Reaction RCH=CH2 RCHCH2OOCH2CHR + o2 + ch2=chr ... 

The values of the rate constants of the trimolecular reactions 2RCH=CH2 + 02 are collected in Table 4.5. 

In alcohol undergoing oxidation in the absence of initiators, free radicals are formed by bimolecular and trimolecular reactions of alcohol with dioxygen [8,9] ... 

This shows that the free radical generation proceeds via the trimolecular reaction (see Chapter 2). 

The preference of the trimolecular reaction over bimolecular RH + 02 is the result of weak C—H bond in diacetals and a polar media (see Chapter 4). The last factor is important for the energy of formation of very polar TS of the trimolecular reaction. The rate constants of trimolecular reactions are presented in Table 7.14. 

Rate Constants of Radical Generation by Trimolecular Reaction of Dioxygen with Ethers [68]... 

The trimolecular reaction of dioxygen with the weakest C—H bonds of two nonsaturated esters. 

The trimolecular reaction of dioxygen with double bonds of two molecules of non-saturated esters. As in the case of a similar bimolecular reaction, this reaction seems to be preceded by CTC formation. 

Free radical formation in oxidized organic compounds occurs through a few reactions of oxygen bimolecular and trimolecular reactions with the weakest C—H bond and double bond (see Chapter 4). The study of free radical generation in polymers (PE, PP) proved that free radicals are produced by the reaction with dioxigen. The rate of initiation was found to be proportional to the partial pressure of oxygen [6,97]. This rate in a polymer solution is proportional to the product [PH] x [02]. The values of the apparent rate constants (/ti0) of free radical formation by the reaction of dioxygen (v 0 = k 0[PH][O2]) are collected in Table 13.8. 

The overwhelming majority of reactions are bimolecular. Some reactions are unimolecular and a mere handful of processes proceed as a trimolecular reactions. No quadrimolecular (or higher order) reactions are known. 

A concerted mechanism has also been discussed [29,30], involving either a 2+2+1 or 3+2 mechanism. To avoid trimolecular reactions this requires an interaction between Rh(I) and silanes prior to the reaction with a ketone. Interaction of silanes not leading to oxidative addition usually requires high-valent metals as we have seen in Chapter 2. The model is shown in Figure 18.16 it proved useful for the explanation of the enantiomers formed in different instances. The formation of a rhodium-carbon bond is included and thus formation of silyl enol ethers remains a viable side-path. 

Trimolecular reactions (also referred to as termolecular) involve elementary reactions where three distinct chemical entities combine to form an activated complex Trimolecular processes are usually third order, but the reverse relationship is not necessarily true. AU truly trior termolecular reactions studied so far have been gas-phase processes. Even so, these reactions are very rare in the gas-phase. They should be very unhkely in solution due, in part, to the relatively slow-rate of diffusion in solutions. See Molecularity Order Transition-State Theory Collision Theory Elementary Reactions... 

Although elementary reactions and overall reactions can only be distinguished in the laboratory, a few simple guidelines can be used to guess. If the number of particles of the reaction is 4 or more, it is an overall reaction. If the number of particles is 3, then most likely the reaction is an overall reaction because there are only a limited number of trimolecular reactions. Almost all elementary reactions have molecularities of 1 or 2. However, the reverse is not true. For example. Reaction 1-5, 203(gas) 302(gas), has a "molecularity" of 2 but is not an elementary reaction. 

For bimolecular second-order reactions and for trimolecular reactions, if the reaction rate is very high compared to the rate to bring particles together by diffusion (for gas-phase and liquid-phase reactions), or if diffusion is slow compared to the reaction rate (for homogenous reaction in a glass or mineral), or if the concentrations of the reactants are very low, then the reaction may be limited by diffusion, and is called an encounter-controlled reaction. 

Trimolecular reaction of chain generation RH + 02 + RH > R + H202 + R was predicted and experimentally evidenced... 

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