Solvolytic rate constants for 1-adamantyl iodide (1-AdI) in binary aqueous mixtures of ethanol, methanol, acetone, trifluoroethanol, and hexafluoroisopropyl alcohol and in acetic and formic acids are reported. Additional kinetic data for solvolyses of 1-adamantyl halides in 97% w/w hexafluoroisopropyl alcohol/water were obtained by using a microconductivity cell (volume, ca. 0.4 mL). Kinetic data for iodine-catalyzed solvolyses of 1-AdI in methanol/water mixtures are also reported. A scale of solvent ionizing power for iodides (Yj) is defined by log (A/fc0)i-Adi = Yj, where k is the rate constant for solvolysis of 1-AdI in any solvent at 25 °C relative to 80%
Solvent effects on reactivity for hydrolysis/alcoholysis of benzoyl chloride are consistent with a direct displacement reaction having SN2 character, in competition with a carbonyl addition reaction becoming dominant in less aqueous media.
The pKa of protonation of 15 was determined in the same way and was found to be 2.38.Rearrangement of 18 in Aqueous HC1. A 0.24-g sample of 18 was boiled for 40 min in 1 N HC1 (5 mL). The solution was cooled and rendered alkaline with a 5 N KOH solution (5 mL).
Kinetic data for solvolyses of t-butyl bromide in homogeneous solutions in water and in aqueous binary mixtures with acetone, methanol and ethanol at 25 O C are reported, illustrating the development of simple conductometric techniques for studying relatively fast solvolytic reactions of sparingly soluble solutes. Solvolyses of t-butyl chloride in water and in aqueous ethanol are re-examined. Experimental errors due to (a) equilibration of solute between liquid and vapour phases and (b) formation of hydrophobic aggregates which can be disrupted by ultrasonic irradiation are discussed. Four recent mechanistic proposals are critically reassessed. It is shown that: (1) the induction period observed at low solute concentrations for solvolyses of t-butyl chloride in water is due to the buffering action of absorbed carbon dioxide; (2) recent kinetic data on the effects of ultrasonic irradiation are unreliable; (3) deviations from first-order kinetics for solvolyses of t-butyl chloride in 40% ethanol + water mixtures are due to equilibration of solute between liquid and vapour phases. It is also argued that (4) the most recent interpretations of heat capacities of activation, suggesting partially reversible formation of an intermediate in hydrolysis of t-butyl chloride, do not take adequate account of alternative interpretations.Solvolyses of t-butyl halides, (CH,),CX, provide one of the cornerstones of homogeneous solution kinetics.' The reaction is first order and is believed to occur by rate-determining heterolysis of the carbon-halogen bond to give a contact ion pair. The role of solvent as nucleophile cannot be assessed from the first-order rate law, and it is likely that these reactions proceed with some bimolecular (S,2) character by rearside nucleophilic solvation of the developing positive charge on the a-carbon atom and/or on the P-hydrogen atom.2 Alternatively such reactions could be described as mainly dissociative with weak associative ~h a r a c t e r . ~ More complicated kinetics could arise if there were reaction between the strong acid (HX) produced during solvolysis and another component of the reaction mixture, e.g. isobutene (product) or alcohol (co~olvent)~ may react with HX, or HX may catalyse further reaction of t-butyl halide or of isobutene. Consequently it may be necessary to add a buffer (e.g. 2,6-lutidine, a sterically hindered weak base) to prevent these side reactions.Recently there have been four novel mechanistic proposals, which we now wish to evaluate critically: (1) that an induction period observed at low concentrations of t-butyl chloride in water is due to a requirement for acid catalysis;5 (2) that the effects of ultrasonic irradiation on solvolysis of t-butyl chloride in water and in aqueous ethanol are due to disruption of solvent structure;6 (3) that solvolyses of t-butyl chloride in 40 % ethanol + water mixtures show mechanistically significant deviations 1633
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