Ethyl transfer process

The Nenitzescu process is presumed to involve an internal oxidation-reduction sequence. Since electron transfer processes, characterized by deep burgundy colored reaction mixtures, may be an important mechanistic aspect, the outcome should be sensitive to the reaction medium. Many solvents have been employed in the Nenitzescu reaction including acetone, methanol, ethanol, benzene, methylene chloride, chloroform, and ethylene chloride however, acetic acid and nitromethane are the most effective solvents for the process. The utility of acetic acid is likely the result of its ability to isomerize the olefinic intermediate (9) to the isomeric (10) capable of providing 5-hydroxyindole derivatives. The reaction of benzoquinone 4 with ethyl 3-aminocinnamate 35 illustrates this effect. ... 

Mechanistic studies also indicate that 4-nitroveratrole (equation 20) and 4,5-dinitroveratrole (equation 21) undergo both singlet and triplet nucleophilic aromatic substitution with ethyl glycinate23. An electron transfer process competes against the nucleophilic aromatic photosubstitution for singlet excited 4-nitroveratrole, causing a decreased product yield in equation 20. 

Polymerization of butyl acrylate was also studied by us in ethyl acetate/water two phase systems (3) using potassium persulfate/quaternary ammonium salts as the initiator system. Under these conditions (a minimum amount of water was used to dissolve the persulfate), it was found that symmetrical quat salts were more efficient than surfactant type quat salts. Also, the more lipophilic quat salts were more efficient. These results prompted us to propose formation of an organic-soluble quaternary ammonium persulfate via typical phase transfer processes. 

It is possible that in the later stages of polymerization there may occur transfer processes involving more than one ethyl group per aluminum atom. 

From the above summarized data, it follows that, during the polymerization, in the presence of triethylaluminum, there is a consumption of A1 atoms and ethyl groups bound to the aluminum, because the triethylaluminum is involved in chain transfer processes without being regenerated. Therefore, the polymerization process is now thoroughly catalytic only with... 

When the alkylation was performed with ethyl allyl carbonate as the precursor of the it-allyl intermediate, only 32% ee was obtained, indicative of a subtle proton-transfer process involved in the catalytic process such as in Scheme 8E.39. The chiral rhodium catalyst was shown to be the primary source of the asymmetric induction because the same reaction in the absence of the rhodium catalyst generated a racemic product in 91% yield. It is interesting that the use of only half an equivalent of the chiral ligand together with half an equivalent of achiral ligand (dppb) with respect to [Pd + Rh] was sufficient to give a high enantioselectivity (93% ee). 

In another reaction, alkynyl groups were transferable in the presence of a catalytic amount of Me3Al (Equation (78)).279 Preference for the Ph group transfer has been well featured in the competitive alkyl transfer process leading to selective imine arylation (Equation (79)). Higher organic chains such as ethyl and butyl are... 

In contrast to the preceding atom-transfer reaction, the solvent-induced rate change for the reaction between l-ethyl-4-(methoxycarbonyl)pyridinyl and 4-(halomethyl)-nitrobenzenes is so large that a change in mechanism must be involved [215, 570]. In changing the solvent from 2-methyltetrahydrofuran to acetonitrile, the relative rate constant for 4-(bromomethyl)-nitrobenzene increases by a factor of up to 14800. This is of the order expected for a reaction in which an ion pair is created from a pair of neutral molecules [cf. for example, reaction (5-16)]. It has been confirmed therefore that, according to scheme (5-67), an electron-transfer process is involved [215, 570]. 

The photochemical reactions of ethyl phenylglyoxalate (217) in benzene have been re-examined. The three new products (218), (219) and (220) have been isolated from the reaction mixture. The quantum yields for the formation of the products are dependent on concentration. Irradiation of the phenylglyoxalate derivatives (221) results in conversion into the lactones (222) from (221, R = H) and (223) and (224) from (221, R = Me). The reactions are proposed to involve an intramolecular electron transfer process forming a zwitterionic biradical. This leads to activation of the methylenes adjacent to the sulfur atom. A similar effect is observed with the nitrogen analogue (225) which affords (226) as the... 

An examination of the behaviour in the solid state of guest molecules such as aliphatic ketones ( acetone and ethyl methyl ketone) and suromatic ketones (acetophenone and /7>Cl-acetophenone) in deoxycholic and apocholic acids has identified stereospecific addition of the guest molecules to the host by a hydrogen abstraction radical combination path. A flash photolytic study of fluorenone has shown that the triplet state reacts with electron rich alkenes in an electron transfer process. 

Z polarity scale. A solvent polarity scale proposed by Koso ver [Kosower 1958a, 1958b] based on the energy of the electronic transition of the 1 -ethyl-4-carbomethoxypyridinium iodide that is strongly solvent-dependent. This is a measure of an internal charge transfer process. The original set of Z values being quite small, it was successively extended by means of other indicators (Table L2). 

Reaction 9 shows that the major portion of the reacting ethylene ions interact with ethyl chloride by discrete transfer steps including H" transfer, H2" transfer, and possibly Cl" transfer. Also, as discussed later, the total cross section for reaction of ethylene ions in this system is quite large (> 100 sq. A.). This may be compared with the corresponding reaction of ethylene ions with ethane, for which extremely small cross-sections have been found (44). In the latter case, however, the H" transfer reaction is endothermic, and the H2" transfer process would not have been detected in the previous experiments. These facts may explain the low reactivity reported. With ethyl chloride, H" transfer to ethylene ions is also indicated to be endothermic by the usual calculations. This suggests that the reactant ethylene ions in this system may well be vibra-tionally excited. It would also account for the chloride ion transfer to this ion, mentioned above. The ratio of rate constants observed for C2H4+ reaction with ethyl chloride is kU2-/ku- = 1.4. In addition to the reactions just discussed, part of the ethylene ion reactant forms a complex intermediate with CoH5C1, and elimination of HC1 and DC1 from this intermediate occurs with about equal probability. 

For the parent ion reactions shown in Table I, the observed products appear to be formed entirely by specific transfer processes, and there is no evidence of the extensive isotopic mixing characteristic of reactions in which long-lived collision complexes are formed. It is also notable that no ion corresponding to such a complex—i.e., the dimer ion—was observed. This is quite different from the ethyl bromide and ethyl iodide systems where such persistent collision complexes have actually been observed (32). 

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