A study was carried out on the solvolysis of the following substituted benzoyl chlorides in sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/isooctane/water microemulsions: 4-CH 3 O, 3,4-(CH 3 O) 2 , 4-CH 3 , 4-H, 4-Cl, 3-Cl, 4-CF 3 , 3-CF 3 , 3-NO 2 , and 4-NO 2 . The benzoyl chlorides are found distributed between the isooctane and the interface, where they react with its hydration water. From the kinetic data we have been able to obtain the true rate constant for the reaction at the interface, k i . Two extreme types of behavior have been observed: for those processes which occur via a predominantly dissociative pathway, k i decreases together with W (W ) [H 2 O]/[AOT]), while for those processes which occur through a predominantly associative pathway, the rate constant at the interface, k i , increases as W decreases. The decrease of k i with W is interpreted as being due to the capacity of interfacial water for solvating the leaving Cl -. For the associative process, the increase in the nucleophilic capacity of the interfacial water as W decreases is the factor responsible for the increase in k i , so that the lesser capacity for solvation of the transition state can be compensated for as the water content of the microemulsion decreases. A comparative analysis of the reactivity of substituted benzoyl chlorides at the interface of the microemulsion shows an increase of the rate of the associative pathway and a decrease of the dissociative counterpart. Hence for W ) 50, the change between the two reaction pathways is observed for the benzoyl chlorides with substituents 4-Cl and 3-Cl, while in bulk water this change takes place with more electron-attracting substituents. When the water content of the microemulsion decreases (W ) 2), only the benzoyl chlorides 4-CH 3 O and 3,4-(CH 3 O) 2 will react predominantly through the dissociative pathway.

To understand the analogies and differences between the cucurbituril and cyclodextrin cavities different solvolytic reactions have been studied in the presence of cucurbit[7]uril, CB7, and beta-CD or its methylated derivative, DM-beta-CD. Solvolysis of 1-bromoadamantane has been used as a test to evaluate the ability of the cavities to solvate the Br(-) leaving group. Obtained results show that in both cases the polarity inside the cavity is similar to that of a 70% ethanol:water mixture. Solvolysis of substituted benzoyl chlorides shows a great difference between the CB7 and DM-beta-CD cavity. Solvolysis of electron withdrawing substituted benzoyl chlorides (associative mechanism) is catalyzed by DM-beta-CD and inhibited by CB7. However, solvolysis of electron donating substituted benzoyl chlorides (dissociative mechanism) is catalyzed by CB7 and inhibited by DM-beta-CD. These experimental behaviors have been explained on the basis of different solvolytic mechanisms. Participation of the hydroxyl groups of the cyclodextrin as a nucleophile can explain the catalytic effect observed for solvolysis of benzoyl chlorides reacting by an associative mechanism. Solvolysis of benzoyl chlorides reacting by a dissociative mechanism is catalyzed by CB7 due to the ability of the CB7 cavity to stabilize the acylium ion developed in the transition state by electrostatic interactions.

The dioxomolybdenum(VI) complex [MoO 2 Cl 2 {p-tolyl(CH 3 DAB)}] has been prepared in good yield by reaction of the solvent adduct MoO 2 Cl 2 (THF) 2 with one equivalent of the bidentate ligand N,N-p-tolyl-2,3-dimethyl-1,4-diazabutadiene. Treatment of the dichloro complex with the Grignard reagent CH 3 MgCl gives the dimethyl derivative [MoO 2 (CH 3) 2 {p-tolyl(CH 3 DAB)}]. The complexes are highly active and selective catalysts for the homogeneous epoxidation of cyclooctene using tert-butyl hydroperoxide (TBHP) as the oxidant. In both cases, the initial activity is ca. 175 mol mol À1 Mo h À1 and cyclooctene oxide is obtained quantitatively within 4 h. It was possible to recover the dimethyl complex at the end of the reaction and reuse it in a second run with only a small decrease in activity. The complexes are also active and selective for the epoxidation of other olefins, such as 1-octene, 2-octene, cyclododecene and (R)-(þ)-limonene, with TBHP. The catalytic production of cyclooctene oxide was investigated in detail, varying either the reaction temperature or the initial concentrations of substrate, oxidant and catalyst precursor. Kinetic studies show that the catalyst precursor-oxygen donor complex formation is first-order in TBHP and in the metal complex [MoO 2 Cl 2 {p-tolyl(CH 3 DAB)}]. A specific rate of 3.2 mol À1 dm 3 s À1 was found for catalyst formation at 25 C. Activation parameters for this reaction have also been measured (DH 6 ¼ ¼ 48 AE 3 kJ mol À1 , DS 6 ¼ ¼ À112 AE 10 J mol À1 K À1).

The host-guest assembly of CB7 with a series of alkyl(trimethyl)ammonium (C(n)TA(+)) surfactants of different chain lengths (n=6-18) has been studied. The complexation behaviour was investigated by NMR spectroscopy, isothermal titration calorimetry and kinetics measurements. The combined results of these techniques provided evidence for the formation of 1:1 inclusion and 2:1 external complexes in the cases of C(n)TA(+) with n=12-18. The binding constants for the 1:1 complexes are independent of the alkyl chain length of the surfactant, whereas a relationship between K(2:1) and the chain length of the surfactant was found for the 2:1 complexes.

We have studied the nitroso group transfer from substituted N-methyl-N-nitrosobenzenesulfonamides to primary and secondary amines, observing that the rate of the reaction increases as a consequence of the presence of electron withdrawing groups on the aromatic ring of the nitrosating agents. The rate constants determined for the nitroso group transfer, ktr, give good Bronsted-type relationships between log ktr (rate constant for nitroso group transfer) and pKaR2NH2+ and pKaleaving group. The study of the nitrosation processes of secondary amines catalyzed by ONSCN and denitrosation catalyzed by SCN-, in combination with the formation equilibrium of ONSCN, has enabled us to calculate the value of the equilibrium constant for the loss of the NO+ group from a protonated N-nitrosamine (pKNOR2N+HNO), which can be defined by analogy with pKaR2NH2+. The value of pKNOX-NO for the loss of the NO+ group from an N-methyl-N-nitrosobenzenesulfonamide was obtained in a similar way. By using values of delta pKNO = pKNOR2N+HNO - pKNOX-NO, we were able to calculate the equilibrium constant for the nitroso group transfer and characterize the transition state. On the basis of Bronsted-type correlations, we have obtained values of beta nuclnorm and alpha lgnorm approximately equal to 0.55, showing a perfectly balanced transition state. In terms of the Marcus theory, the calculation of the intrinsic barriers for the nitroso group transfer reaction shows that the presence of electron withdrawing groups on the aromatic ring of the N-methyl-N-nitrosobenzenesulfonamides does not cause these barriers to vary.