Solvolysis equation

In aqueous solution, SO2 is reduced to dithionite by a range of metals or sodium hydride. With metal halides, SO2 forms complexes and may behave as an electron donor (e.g. with AICI3, SnBr4, or TiCU) or undergo solvolysis (equation 16)... 

Platinum.—Continuing studies of the cis-trans isomerization of square-planar m-[Pt(R)Cl(PEt3)2] in alcohols have been quoted as further evidence for a dissociative mechanism in which a three-co-ordinate intermediate [PtR(PEt3)2]+ participates (see also Vol. 5). However, it is argued by Louw that the mass law retardation effect by Cl ions and a similar rate law to that from the dissociative process (5) is obtained for a consecutive displacement mechanism involving initial solvolysis, equations (2)—(4). Kinetic studies by the same author have also shown that the... 

The more extensive problem of correlating substituent effects in electrophilic substitution by a two-parameter equation has been examined by Brown and his co-workers. In order to define a new set of substituent constants. Brown chose as a model reaction the solvolysis of substituted dimethylphenylcarbinyl chlorides in 90% aq. acetone. In the case ofp-substituted compounds, the transition state, represented by the following resonance structures, is stabilized by direct resonance interaction between the substituent and the site of reaction. 

In the solvolysis reaetion, HjO is the solvent as well as a reaetant, and it is present in large exeess. It does not appear in the rate equation, whieh is expressed by... 

In contrast to phosphorus esters, sulfur esters are usually cleaved at the carbon-oxygen bond with carbon-fluorine bond formation Cleavage of esteri nf methanesulfonic acid, p-toluenesidfonic acid, and especially trifluoromethane-sulfonic acid (tnflic acid) by fluoride ion is the most widely used method for the conversion of hydroxy compounds to fluoro derivatives Potassium fluoride, triethylamine trihydrofluoride, and tetrabutylammonium fluoride are common sources of the fluoride ion For the cleavage of a variety of alkyl mesylates and tosylates with potassium fluoride, polyethylene glycol 400 is a solvent of choice, the yields are limited by solvolysis of the leaving group by the solvent, but this phenomenon is controlled by bulky substituents, either in the sulfonic acid part or in the alcohol part of the ester [42] (equation 29)... 

Studies of solvolysis of similar polyfluonnated polycyclic aromatic systems, such as 2,3-(tetrafluorobenzo)bicyclo[2 2 2]octadienes and related compounds, proved the ionic mechanism of this rearrangement [55, 36, 37] (equation 9) Possible nonclassical carbonium ion involvement has been discussed [5S, 39, 40, 41]... 

Because of Us high polarity and low nucleophilicity, a trifluoroacetic acid medium is usually used for the investigation of such carbocationic processes as solvolysis, protonation of alkenes, skeletal rearrangements, and hydride shifts [22-24] It also has been used for several synthetically useful reachons, such as electrophilic aromatic substitution [25], reductions [26, 27], and oxidations [28] Trifluoroacetic acid is a good medium for the nitration of aromatic compounds Nitration of benzene or toluene with sodium nitrate in trifluoroacetic acid is almost quantitative after 4 h at room temperature [25] Under these conditions, toluene gives the usual mixture of mononitrotoluenes in an o m p ratio of 61 6 2 6 35 8 A trifluoroacetic acid medium can be used for the reduction of acids, ketones, and alcohols with sodium borohydnde [26] or triethylsilane [27] Diary Iketones are smoothly reduced by sodium borohydnde in trifluoroacetic acid to diarylmethanes (equation 13)... 

Reactions that occur with the development of an electron deficiency, such as aromatic electrophilic substitutions, are best correlated by substituent constants based on a more appropriate defining reaction than the ionization of benzoic acids. Brown and Okamoto adopted the rates of solvolysis of substituted phenyldimeth-ylcarbinyl chlorides (r-cumyl chlorides) in 90% aqueous acetone at 25°C to define electrophilic substituent constants symbolized o-. Their procedure was to establish a conventional Hammett plot of log (.k/k°) against (t for 16 /wcra-substituted r-cumyl chlorides, because meta substituents cannot undergo significant direct resonance interaction with the reaction site. The resulting p value of —4.54 was then used in a modified Hammett equation. 

We have already encountered the ir, a, and p quantities. The 8h term is inserted to account for the cavity effect. Equation (8-80) is a 12-parameter equation for which considerable generality is claimed, in that it is said to be applicable to chemical rates and equilibria, spectra, solubilities, partition coefficients, and even biological responses. Usually, of course, by judicious selection of solvents, it is possible to reduce the number of parameters by ensuring that some terms are negligible.An example requiring most of the parameters in Eq. (8-80) is the solvolysis/dehydrohalogenation of r-butyl chloride in 21 HBD and non-HBD solvents, for which this correlation was found ... 

The DSP treatment is also instructive for the Na,Np-rearrangement. The rate constants for solvolysis in TFE ( s) yield the dual-parameters equation given in Scheme 8-11, and those for the corresponding Na,Np-rearrangement ( r) yield the equation of Scheme 8-12 (Ravenscroft and Zollinger, 1988). 

Parallel reactions. Consider a mixture of A and B. each of w hich reacts independently to form the same product P. (a) Derive an equation for [P] in a mixture with initial concentrations [A]o and [Bio. (b) Apply this equation to the solvolysis of a mixture of MejCCEtiCl and EtiMeCCMeiCl, in which the HCI produced was titrated as a function of time.18 (c) What is the initial concentration of each Which is which ... 

Based on kinetic investigations the solvolysis of ochloroalkyl sulphoxides 506 in 80% ethanol was found to proceed via a cyclic intermediate formed via anchimeric assistance of the sulphinyl oxygen atom601,602. For a solvolysis of 4-halogenothian-l-oxides see Reference 603 (equation 309). 

Second, while the above experiments indicate the presence of free Br2 during the solvolysis, they do not indicate how it was produced. One possibility tested for is shown in equation 9,... 

In the solvolysis of secondary alkyl sulfonates, competition between nucleophilic solvation and electron donation by the substituents results in a significantly solvent-dependent p, which varies from — 9 to — 1 on going from the non-nucleophilic hexafluoro-2-propanol to 80% aqueous ethanol (Bentley et al, 1981). In contrast, the p -invariance for alkene bromination in H20, M70, MeOH and AcOH [equations (22)-(25)] seems to imply a perfect balance between the two types of charge stabilization. However, this conclusion is probably risky since the nucleophilicities of the solvents implied in (22)-(25) do not vary markedly. Data in non-nucleophilic fluorinated solvents would therefore help to fill the gap in our knowledge. 

The formation of solvent-incorporated products 8 suggested that triarylallenyl cations 7 are formed by photolysis of the corresponding chloroallenes 6 (equation 2). However, the products 8 obtained by photolysis were attributed to attack by nucleophiles at /-positions of the allenyl cation. Although allenyl cations are ambident cations and can produce allenyl or propargyl derivatives by attack at the a- or /-position, respectively, only /-attack was observed in this photolysis of triarylchloroallenes. This result is parallel to that observed by Schiavelli and coworkers9 in the solvolysis of these systems (vide infra) which therefore supports the formation of allenyl cations in the photolysis. 

Solvolysis of the propargyl chlorides E- and Z-24 (stereochemistry based on Cl and Ph25) in 80% aqueous ethanol at 50 °C gave, besides the corresponding solvent captured substituted propargyl products, the allenyl chlorides E- and Z-25 formed with complete retention via the allenyl cation intermediate (equation 6)25. 

If one compares the solvolyses of 2-bromo-l,l-diphenyl-4-(p-methoxyphenyl)-but-l-en-3-yne (57) and 4.4-diphenyl-1 -bromo-1 -(/ -mcthoxyphcny l)-buta-1,2,3-tricncs (58, X = Br) in aqueous ethanol (equation 21), the destabilization of the intermediate cation 59 by the large inductive effect of the triple bond as compared to its conjugative effect is evident42. Only in the case of 58 could the substitution product butatrienyl enol ether 60 be isolated in 40% yield, while it was only detected by UV and IR spectroscopy in the solvolysis product of 57. The faster observed reaction rate of 58 as compared to 57 was ascribed to a difference in their ground-state energies42. 

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