Reactivities of mixed organozinc and mixed organocopper reagents. Part 7. Comparison of the transfer rate of the same group in allylation of mixed and homo diorganozinc reagents

Abstract

Reactivities of mixed organozinc and mixed organocopper reagents. Part 7. Comparison of the transfer rate of the same group in allylation of mixed and homo diorganozinc reagents Melike Kalkan a and Ender Erdik a *A detailed direct kinetic study has been carried out to compare the reaction rate of transferable group, Ph in mixed phenylzinc reagents, RPhZn (R = n-alkyl) and in homo diphenylzinc reagent, Ph 2 Zn in their reactions with allyl bromide in THF at 25-(À15) C. Empirical rata law and activation parameters are consistent with a second-order substitution reaction. The allylation rate of transferable group Ph in RPhZn (R = n-alkyl) has been found higher than the rate of Ph group in Ph 2 Zn. A mechanism which accommodates the kinetic data and higher allylation rate of transferable group Ph in RPhZn than that in Ph 2 Zn is given.

Ultrasound-Induced CO2/H2O Emulsions as a Medium for Clean Product Formation and Separation: The Barbier Reaction as a Synthetic Example

“…D A for most organic compounds in liquids is in the order of 1 × 10 –5 cm 2 s –1 . The intrinsic rate constant, k irr , may be evaluated by taking the pseudo-first-order rate constants for the allylation step (0.2–1.2 × 10 –3 s –1 , depending on allyl bromide, benzaldehyde and catalyst concentrations). , Becasue these zinc-mediated allylations occur much faster in aqueous media, the reaction may be assumed to occur in the H 2 O phase rather than in the CO 2 phase, and thus, the mass transfer coefficient was modeled on benzaldehyde going from the CO 2 to the H 2 O side ( k w = 1.5 × 10 –4 cm s –1 for the silent case and with an effective mass transfer coefficient due to sonication >1.9 × 10 –3 s –1 ) . Inserting these values into generated Ha of 0.3–0.75, indicative of a slow reaction (only reactions with Ha > 2 are considered fast with a high dependence on mass transfer resistance).…”