Radu Bacaloglu

Effects of submicellar aggregates on nucleophilic aromatic substitution and addition

Abstract In dilute cationic surfactants (C16H33NR3X; R = Me, Et, n-Pr, n-Bu; X = Cl, Br) rate constants of reaction of 2,4-dinitrochloronaphthalene with OH−, N3−, aniline, or morpholine, and of equilibrium formation of a Meisenheimer complex from 1,3-dinitronaphthalene and OH−, go through double rate maxima with increasing [surfactant]. The first maximum is ascribed to reaction in submicellar aggregates and the second to reaction in normal micelles.

Surfactant effects upon nucleophilic aromatic substitution: Observation of double rate maxima

Abstract First order rate constants of the reaction of 2,4-dinitrochloronaphthalene (DNCN) with excess OH − go through double maxima with increasing concentrations of cetyltrialkylammonium chloride or bromide (C 16 H 33 NR 3 X; CTAX, R = Me; CTEAX, R = Et; CTPAX, R = n -Pr; CTBAX, R = n -Bu; X = Cl, Br). The relative heights of the two maxima depend upon [DNCN] and there is only a single maximum with very dilute DNCN (4 × 10 −6 M ) and with added NaBr. There are also double rate maxima in reactions of DNCN with N 3 − and with morpholine. The first rate maxima are ascribed to reactions mediated by submicellar assemblies and the second to reaction in micelles. Tri- n -octylalkylammonium mesylates (alkyl = Me, Et) do not micellize but they speed reactions of DNCN with OH − and N 3 − . Rates of reaction of OH − with p -nitrophenyl diphenyl phosphate go through a single maximum in micellized CTBABr. These observations suggest that interaction of submicellar assemblies activates the substrate toward nucleophiles but that micelles assist reaction by concentrating both reactants in the small interfacial volume.

Structural and conformational analysis of 2-triphenylphosphoranylidene succinic acid derivatives by 1H, 13C and 31P one and two dimensional NMR spectroscopy and molecular modelling

The structure and conformation of 2-triphenylphosphoranylidenesuccinic acid derivatives have been studied by 1H, 13C and 31P NMR spectroscopy, in various solvents and at variable temperatures. In 2-triphenylphosphoranylidenesuccinic anhydride (1) the conformation is constrained but in the corresponding monoethyl (2) and the diethyl (3) esters there is an anticlinal relationship between the phosphorus and hydrogens on C-3 and signals of Z and E isomers were observed with the diethyl ester 3 in solvent-dependent ratios based on 1H, 13C and 31P resonances. Similar results were obtained with the diethyl ester of the 3-methyl derivative 4. Protonation (deuteronation) of 2 and 3 changes their conformation and P–H couplings. The NMR evidence on conformations of the phosphoranylidenesuccinic acid esters is consistent with T1 relaxation times and results of molecular modelling.

The reaction of 1,2-Dichloro-4,5-dinitrobenzene with hydroxide ion: roles of meisenheimer complexes and radical pairs

The reaction of 1,2-dichloro-4,5-dinitrobenzene (DCDNB) with aqueous OH- produces (after acidification) 2-nitro-4,5-dichlorophenol with loss of NO2. Nevertheless, with > 2 mol L-1 OH-, only DCDNB was recovered due to the formation of the long-lived 3,6-dihydroxy Meisenheimer complex (M2-), and that in acid, reverted to the starting material. Fast formation of monohydroxy Meisenheimer complex (M1-) can be followed in DMSO:H2O 7:3 v/v and rate constants for its interconversion with DCDNB and for formation and return with M2- complex were estimated, with evidence for these reactions in DMSO:H2O 1:1 v/v and H2O. The rapid hydrogen exchange in OD- /D2O limits the use of1 H nuclear magnetic resonance (NMR) spectroscopy in identifying intermediates. 1 H and13 C NMR signals of M2- complex were observed in DMSO-H2O-KOH. There is evidence for the formation of free radicals in DMSO:H2O 4:1 v/v, and overall kinetics in more aqueous medium were treated in terms of the transient existence of anionic radical pairs.