Fast proton transfer at a micelle surface

Abstract

Inhibition of the reaction by dissolved 0 2 is consistent with the proposed mechanism. Formation of 0 2 complexes of carbonyl radicals has been demonstrated in ESR experiments with c O ( c 0 ) 4 and Mn(C0)5.16 In Re(C0)502 the unpaired spin could be localized on 02, as suggested by the ESR hyperfine data for Mn(C0)502, so that the metal possesses a coordinatively saturated (i.e., 18 e-) configuration. The metal is thus probably not substitutionally labile nor capable of hydrogen abstraction from HRe(C0)S.Additional tests of the radical chain hypothesis are in progress. The radical chain process for substitution should be applicable to many other transition metal systems. Extension to other metal hydride systems is especially appealing. Deliberate photochemical initiation with Re2(CO)io or other suitable source of radicals may provide a convenient route to substituted hydrides, both mononuclear and polynuclear. Radical chain processes may be of importance in cobalt carbonyl hydride chemistry. Studies of this and several other systems, including metal carbonyl halides and other substituted metal carbonyl compounds susceptible to radical attack, are also in progress. Am. Chem. SOC., 92, 3653 (1970). M. Wrighton, Chem. Rev., 74, 401 (1974). M. Wrighton and D. Bredesen, J. Organornet. Chern., 50, C35 (1973). The substitution lability of Mn(CO)S produced by irradiation of Mn2(CO)lo has been demonstrated by Wrighton and Ginley. l 2 M. S. Wrighton and D. S. Ginley, J. Am. Chem. SOC., in press.We attribute the induction period to traces of radical chain inhibitors, notably 0 2 , present in low concentrations even in carefully purified systems. Using M Mnn(CO)lo in place of Re2(CO)lo, and irradiating with monochromatic radiation at 350 nm, caused the reaction to proceed to completion after less than 2 min of irradiation. The products in this mstance were HRe(C0)4L and HRe(C0)3L* in 2.51 ratio. Presumably in this instance photochemically generated Mn(C0)5 radicals act as reaction initiators. Irradiation of MHRe(C0)5, MPPh3. and MRe2(CO)la in hexane at 31 I nm results in almost complete reaction to form HRe-(CO).,PPh3 after only 70 sec. The interpretation of these results is complicated by intense absorption of 31 1 nm radiation by PPh3. The ligand may in this case be acting to sensitize the Re2(CO),o dissociation.

An NMR Investigation of Fast Proton Transfer along the Surface of Cationic Micelles

“…two orders of magnitude. This is in good agreement with the observations of Menger 9. Equation (2) allows us to compute unknown proton transfer rates k mic in micelles, and CMC values from experimental k NH values and from rate constants k mono previously measured in dilute solutions, using standard least‐squares curve‐fitting procedures.…”

Ultrafast excited-state proton transfer in reversed micelles

“…Enhanced deprotonation rates of the same magnitude have been observed at the surface of aqueous micelles. 21 The experimental value of kp* in water is (Table I) in agreement with that calculated by the Debye equation22 A proposed model for the ultrafast proton transfer at the hydration shell of the surfactant headgroups in reversed micellar DAP in benzene. Since the concentration of surfactant is in a very large excess over the probe,20 proton transfer must occur from dodecylammonium propionic acid to pyrene 1-carboxylate.…”

Adsorption, displacement, and ionization in water pools

“…A stoppered 10-mm cuvette was filled with 3.00 mL of AOT/H20/«heptane and placed in the therrnostated chamber (25.0 ± 0.1 °C) of a Cary 14 recording spectrophotometer. After waiting about 15 min for thermal equilibration, we traced the baseline, added to the cuvette 25 qL of 1.459 X 10~2 M p-nitrophenol in toluene, stirred the solution with a small glass rod, and ran a spectrum of the solution from 300-500 nm. No time-dependent absorbance changes were observed over a 3-h period.…”