Cation production

Ahphatic dihahdes, like ethylene dichloride [107-06-2] react with alkylene amines to form various polymeric, cross-linked, water soluble cationic products (19) or higher alkyleneamine products depending on the reactant ratio. 

On reaction with acid, 4-pvrone is protonated on the carbonyl-group oxygen to give a stable cationic product. Using resonance structures and the Hiickel 4n 4- 2 rule, explain why the protonated product is so stable. 

How- does this reaction take place Although it appears superficially similar to the SN1 and S 2 nucleophilic substitution reactions of alkyl halides discussed in Chapter 11, it must be different because aryl halides are inert to both SN1 and Sj 2 conditions. S l reactions don t occur wdth aryl halides because dissociation of the halide is energetically unfavorable due to tire instability of the potential aryl cation product. S]sj2 reactions don t occur with aryl halides because the halo-substituted carbon of the aromatic ring is sterically shielded from backside approach. For a nucleophile to react with an aryl halide, it would have to approach directly through the aromatic ring and invert the stereochemistry of the aromatic ring carbon—a geometric impossibility. 

Figure 2. Probability density plots of the ethyl cation product, (a) from the unlabeled reaction, (b) CH2CH3 from the labeled reaction, and (c) CD3CH2 from the labeled reaction. The backward scattered ethyl cation is more probable in (b), while the forward scattered ethyl cation is more probable in (c). Reprinted from [39] with permission from Elsevier.

Anionic and cationic products generally tend to interact with each other, usually diminishing the surface-active properties of both and often resulting in precipitation of the complex formed. Amphoteric compounds can also be incompatible with anionics in acid solution but are generally compatible with cationics and nonionics. Interaction between anionic and cationic agents can sometimes be prevented by addition of a nonionic. In some cases, if an ethoxylated sulphate or phosphate is used as the anionic component a cationic compound produces no obvious precipitation, since the oxyethylene chain acts as dispersant for any complex that may be formed. 

Most of the polymeric cationic products available [448] are based on the types described in Table 10.44. The ideal aftertreating agent must fulfil many requirements [448]. There is a high demand for ... 

There is a strong resemblance between the transition state and the cation product. 

Cationic polyelectrolytes, 20 469—472 Cationic polymerization, 19 835 20 409 living, 14 271-272 of cyclic siloxanes, 22 560 of higher olefin polymers, 20 425 Cationic polymers, 11 632 Cationic products, 9 193-194 Cationic PVA, 25 602... 

Shortly after Perkin had produced the first commercially successful dyestuff, a discovery was made which led to what is now the dominant chemical class of dyestuffs, the azo dyes. This development stemmed from the work of Peter Griess, who in 1858 passed nitrous fumes (which correspond to the formula N203) into a cold alcoholic solution of 2-aminO 4,6 dinitrophenol (picramic acid) and isolated a cationic product, the properties of which showed it to be a member of a new class of compounds [1]. Griess extended his investigations to other primary aromatic amines and showed his reaction to be generally applicable. He named the products diazo compounds and the reaction came to be known as the diazotisation reaction. This reaction can be represented most simply by Scheme 4.1, in which HX stands for a strong monobasic acid and Ar is any aromatic or heteroaromatic nucleus. 

This transition-state, 22, has a calculated energy only slightly higher (0.48 kcal/mol at B3LYP/6-31G ) than the transition-state for isomer 18, and the geometry is also slightly different, for example, a somewhat shorter H—H bond. Loss of dihydrogen from this transition-state will lead to a secondary cation intermediate, and after a 1,2-hydride shift, to the same 1-methylcyclohexyl cation product that is directly produced from the other route. 

It was assumed that, during an oxidation of these aromatic moieties, an electron would be removed from the aromatic ring at the location where the electron-donating methoxy is positioned. Whether this oxidation is reversible critically depends on the stability of the produced cationic product. On the... 

Many valuable reviews of the chemistry of these species are given in the new book Dicoordinated Carbocations An introduction by Grob " is followed by reviews of various theoretical studies of vinyl cations, their gas-phase chemistry, their generation by nuclear decay, and their NMR spectroscopic characterization. Vinyl cation production by addition to acetylenes and allenes, by solvolysis, and photolytically are covered, together with the chemistry of the species generated in these various ways. The next chapter deals with the synthetic applications of vinyl cations,and alkynyl and aryl cations are covered in the last chapter. A review of the NMR spectroscopic and quantum-chemical investigation of vinyl cations in superacid media (also of dienyl and 1-cyclopropylvinyl cations) is published separately,as is a review of alkynylcar-... 

Under much milder conditions, the same reaction occurs with 1,2,4-triazinone 164, resulting in the formation of a l,3,4-thiadiazolo[2,3-c][l,2,4]triazinium cation 165 (Scheme 64) (88H1935). Another cationic product is obtained upon conversion of dithiocarbazate to carbodiimide, which occurs via iminophosphorane formation and aza-Wittig reaction with... 

Methylbenzenes lose a proton from a methyl group to form a benzyl radical. In aqueous M-percbloric acid this reaction is fast with a rate constant in the range 10 lO s and the process is not reversible [24]. The process becomes slower as the number of methyl substituents increases, Hexaethylbenzene radical cation is relatively stable. When the benzyl radical is formed, further reactions lead to the development of a complex esr spectrum. Anodic oxidation of hexamethylbenzene in trifluoroacetic acid at concentrations greater than 1 O M yields the radical-cation I by the process shown in Scheme 6.1 [14], Preparative scale, anodic oxidation of methylbenzenes leads to the benzyl carbonium ion by oxidation of the benzyl radicals formed from the substrate radical-cation. Products isolated result from further reactions of this carbonium ion. 

Alkylation of hydroxyazines where reaction does not lead to quaternization is not considered. Molecules such as 4-pyridone usually exist largely as the carbonyl, but not as the 4-hydroxypyridine, tautomer in polar solvents8 [Eq. (1)]. Monoalkylation of the neutral species of such molecules can take place preferentially at either the annular nitrogen atom of the OH form or the oxygen atom of the N—H form in each case subsequent proton loss yields a neutral product. Dialkylation then gives rise to a cationic product, the second alkyl group being introduced at the other site. 

The processes of cation production by weathering or ion exchange cannot be differentiated by ion-budget calculations, but they may be distinguished on the basis of kinetics. In early experiments to investigate the role of sediments as buffers, sequential additions of sulfuric acid to well-mixed sediment slurries produced rapid increases in soluble Ca2+ that reached stable concentrations within 24 h (53, 54). The rapid production of cations suggested that the dominant process was ion exchange... 

On the basis of mass balance calculations through the first 3 years of acid additions (17), only 33% of the added acid resulted in a decrease in lake alkalinity. A second 33% was neutralized by in-lake (IAG) processes, of which sulfate reduction accounted for slightly more than half and cation production for slightly less than half. Approximately 33% of the total sulfate load (wet and dry deposition, and acid additions) was lost via outflow. Therefore, about half of the added acid remained in the water column two thirds of it was unreacted and one third was neutralized by base cations. 

Four forms of the basic IAG model (27, 46) are described here to predict rates of recovery of LRL alkalinity. The models are described in order of increasing complexity and realism, reflecting the inclusion of IAG contributions from more biogeochemical processes (4,17). As previously discussed, chemical budgets from the first 3 years of acidification indicated that the main processes controlling IAG are sulfate reduction and cation production by ion exchange (in order of importance). Effects of nitrate and ammonium retention roughly cancel each other (in terms of net alkalinity production) (17). 

Model 3 includes S042 reduction, cation production, and ion losses by outflow. The apparent cation-production term (CP ), was calculated on the basis of the observed increase in water-column base cations. It includes production via both weathering and ion exchange, and was treated as a zero-order (constant) term because a more accurate functional relationship is not available. Model 3 is described by the following coupled equations ... 

Apparent cation production, CP, remains constant and represents contributions by mineral weathering or hydrologic input. The model resulting from these assumptions, Model 4, is described by the following equations ... 

Results of the four models (Figure 9a) illustrate the effect on predicted recovery rates of including various alkalinity-generating processes. Models 1 and 2 probably yield upper and lower limits of the time required to recover to the preacidification alkalinity level. Model 3 probably yields an underestimate of recovery time, in that it does not consider the need to neutralize acidified surficial sediments (and restore base cations on sediment-exchange sites that have been lost during the last years of acid loading). Model 4 probably yields the most accurate estimate of recovery time, but it does not provide a functional relationship for the cation-production term. Based on Model 4, the north basin will reach 50% of the preexperimental alkalinity concentrations in 3-5 years and 90% in 8 years. Complete recovery is predicted to occur in 12.5-15 years. 

Figure 9. Recovery predictions. Part a Model 1, reference-basin IAG only Model 2, sulfate reduction only Model 3, sulfate reduction, cation production, and outflow and Model 4, sulfate reduction, cation production, outflow, and sediment neutralization. Part b, Autumn pH-alkalinity correlation ...

Mass-balance calculations for the first 3 years of acid additions indicate that the principal IAG processes are sulfate reduction and cation production. Specifically, one-third of the total sulfate input (added acid and deposition) was neutralized by in-lake processes. Increased sulfate reduction consumed slightly more than one-sixth and production of cations neutralized somewhat less than one-sixth of the acid added. Of the remaining sulfate, one-third was lost by outflow, and one-third decreased lake alkalinity. Laboratory determinations suggest that sediment-exchange processes occurring in only the top 2 cm of surficial sediments can account for the observed increase in water-column cations. Acidification of the near-surface sediments (with partial loss of exchangeable cations) will slow recovery because of the need to exchange the sediment-bound H+ and neutralize it by other processes. Reactor-based models that include the primary IAG processes predict that... 

Observations pertinent to Scheme 2 are as follows (61, 64-66) as followed by H NMR, CH3S03F reacts slowly with 39 at - 70°C but rapidly at -40°C. However, under no conditions (including inverse addition, use of other methylating agents, etc.) can the formation of 54 from 39 be directly observed. Rather, H NMR indicates that substantial quantities of methoxymethyl complex 57 build up. The carbonyl cation product 56 is also present. These data are readily explained if, subsequent to initial O-methylation (Scheme 2, step a), rapid hydride transfer from unreacted 39 to 54 occurs (step b). As shown in Eq. (25), this reaction (conducted with independently synthesized samples) is indeed rapid at -70°C. 

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