Solvolysis in acetic acid

Ratio of first order rate constant for solvolysis in indicated solvent to that for solvolysis in acetic acid at 25 C... 

Nucleophilic substitution in cyclohexyl systems is quite slow and is often accompanied by extensive elimination. The stereochemistry of substitution has been determined with the use of a deuterium-labeled substrate (entry 6). In the example shown, the substitution process occurs with complete inversion of configuration. By NMR amdysis, it can be determined that there is about 15% of rearrangement by hydride shift accon any-ing solvolysis in acetic acid. This increases to 35% in formic acid and 75% in trifiuoroacetic acid. The extent of rearrangement increases with decreasing solvent... 

Let us now return to the question of solvolysis and how it relates to the stracture under stable-ion conditions. To relate the structural data to solvolysis conditions, the primary issues that must be considered are the extent of solvent participation in the transition state and the nature of solvation of the cationic intermediate. The extent of solvent participation has been probed by comparison of solvolysis characteristics in trifluoroacetic acid with the solvolysis in acetic acid. The exo endo reactivity ratio in trifluoroacetic acid is 1120 1, compared to 280 1 in acetic acid. Whereas the endo isomer shows solvent sensitivity typical of normal secondary tosylates, the exx> isomer reveals a reduced sensitivity. This indicates that the transition state for solvolysis of the exo isomer possesses a greater degree of charge dispersal, which would be consistent with a bridged structure. This fact, along with the rate enhancement of the exo isomer, indicates that the c participation commences prior to the transition state being attained, so that it can be concluded that bridging is a characteristic of the solvolysis intermediate, as well as of the stable-ion structure. ... 

The behavior of compounds A and B on solvolysis in acetic acid containing acetate ion has been studied. The solvolysis of A is about 13 times faster than that of B. Kinetic studies in the case of A show that A is racemized competitively with solvolysis. A single product is formed from A, but B gives a mixture. Explain these results. 

Although it is known that a chlorine atom at the 4-(or 5-)position is more reactive than at the 3- or 6-position for nucleophilic substitution, 3-acetamido-(or amino-)5-chloro-6-methoxypyridazine is resistant to hot aqueous sodium hydroxide and 30% sodium hydrogen sulfide solution, but susceptible to solvolysis in acetic acid containing anhydrous potassium acetate to yield the 5-hydroxy derivative. 

Another interesting a-functionalization of the metallated DMH s is achieved by addition of dimethyl disulfide. Again, the new group is added axially. Hydrolysis produces 2-thiomethylketones. Alternatively, an axial acetoxy or methoxy group is introduced by mercuric chloride catalyzed solvolysis in acetic acid or methanol. 

A non-aqueous analogue of the above examples of base hydrolysis in aqueous solution is solvolysis in acetic acid-acetate solutions. This reaction has been studied for tra/i -CCoCOgC-Rja engl+j where R = o-tolyl or p-tolyl, whose rates of solvolysis are found to decrease with increasing concentration of added acetate. This behaviour is in direct contrast to that of the aqueous system. In acetic acid the V lcb mechanism appears not to operate, and the mechanism must be solvent-assisted dissociation, with ion-pairs less reactive than the free cation. ... 

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