Received: 29 October 2007, Revised: 14 January 2008, Accepted: 15 January 2008, Published online in Wiley InterScience: 22 May 2008 A gemini amphiphilic phase transfer catalyst for dark singlet oxygenation Ce ´ dric Borde a , Ve ´ ronique Nardello a * , Laurent Wattebled b , Andre ´ Laschewsky b,c and Jean-Marie Aubry a A new gemini surfactant phase transfer catalyst, namely diethyl-ether-a,v-bis-(dimethyldodecylammonium molyb- date) codified as 12-EO-12-Mo, was prepared by anion exchange from the analogous gemini dichloride (12-EO-12-Cl 2 ). The physico-chemical properties of these compounds such as Krafft temperature, critical micelle concentration, surface activity and binary water-surfactant behavior were compared and the influence of the molybdate counterion was examined. Though both compounds are highly hydrophilic, the cmc of 12-EO-12-Mo (0.4 mmol L S1 ) is about five times lower than of its dichloride analogue (2.2 mmol L S1 ). Moreover, 12-EO-12-Mo exhibits an additional cubic liquid crystal phase between 53 and 64 wt%. The usefulness of 12-EO-12-Mo as an amphiphilic phase transfer catalyst for the dark singlet oxygenation was demonstrated with the peroxidation of two typical organic substrates: a-terpinene which reacts with 1 O 2 according to a [4 R 2] cycloaddition and the less reactive b-citronellol, which provides two hydroperoxides according to the ene-reaction. 12-EO-12-Mo provides a simple reaction medium with only three components for the preparative peroxidation of hydrophobic substrates by chemically generated singlet oxygen. Copyright ß 2008 John Wiley & Sons, Ltd. Keywords: singlet oxygen; oxidation; catalytic amphiphile; gemini surfactant; phase transfer catalyst; lyotropic liquidcrystal INTRODUCTION In organic synthesis, hydrophobic molecules often have to react with hydrophilic species. Despite the incompatibility between antagonist reactants, interactions and reactions can be favored by several ways using: (i) monophasic media based on dipolar aprotic solvents (DMSO, DMF, NMP...) or homogenous mixtures of water and a miscible organic solvent (alcohols, THF...), (ii) biphasic media of two immiscible solvents, generally associated with a phase transfer catalyst (PTC) typically quaternary ammonium compounds, and (iii) submicronic and thermodyna- mically stable dispersions of two immiscible solvents stabilized by an appropriate amphiphile, that is, microemulsions. [1–4] Among these strategies, phase transfer catalysis is probably the most widely used in industry. This process is applicable to a large number of reactions involving (in)organic anions and organic reactants. [5–8] Therefore, it has known a remarkable development during these last decades, owing to its numerous advantages. Besides its simplicity, reaction rates can considerably be increased compared to a simple biphasic system. [9,10] Still, as most PTC do not exhibit amphiphilic properties, the unstable emulsions formed under stirring are coarse. Moreover, at the end of the reaction, the PTC is partitioned between the two phases, thus complicating the recovery of the products. Furthermore, phase transfer catalysis is unsuitable when short lifetime species have to react with hydrophobic substrates. In particular, it cannot be simply applied to the use of singlet molecular oxygen, 1 O 2 ( 1 D g ). This reagent is efficiently chemically generated in aqueous phase by disproportionation of hydrogen peroxide catalyzed by molybdates anions (Eqn 1): [11–15] 2H 2 O 2 ! MoO 2 4 =water pH 911 2H 2 O þ 1 O 2 ð100%Þ (1) In contrast to ground state molecular oxygen, singlet oxygen is a selective and powerful oxidizing species that has found considerable synthetic utility since it can undergo reactions with a wide variety of electron-rich molecules such as olefins, conjugated dienes, polycyclic aromatic hydrocarbons, phenols, sulfides, and heterocycles. [16–18] However, some drawbacks, inherent to its transitory nature and to its mode of formation, have to be taken into account: (i) owing to its short lifetime (about a few microseconds in water), 1 O 2 must be generated close to the organic substrate, (ii) the disproportionation of the intermediate triperoxomolybdate, MoO(O 2 ) 2 3 , which is the main precursor of 1 O 2 , is efficient solely in an aqueous or highly polar environment, and (iii) poorly reactive substrates require important amounts of hydrogen peroxide that induces an important dilution of the reaction medium resulting in a significant competition between the chemical reaction of 1 O 2 with the substrate S (rate constant k r ) and the physical deactivation by the solvent molecules (rate (www.interscience.wiley.com) DOI 10.1002/poc.1344 Special Issue * LCOM, Equipe Oxydation & Formulation, UMR CNRS 8009, Ecole Nationale Supe ´rieure de Chimie de Lille, BP 90108, F-59652 Villeneuve d’Ascq Cedex, France. E-mail: veronique.rataj@univ-lille1.fr a C. Borde, V. Nardello, J.-M. Aubry LCOM, Equipe Oxydation & Formulation, UMR CNRS 8009, Ecole Nationale Supe ´rieure de Chimie de Lille, BP 90108, F-59652 Villeneuve d’Ascq Cedex, France b L. Wattebled, A. Laschewsky Fraunhofer Institut fu ¨r Angewandte Polymerforschung FhG-IAP, Geisel- bergstr.69, 14476 Potsdam-Golm, Germany c A. Laschewsky Universita ¨t Potsdam, Karl-Liebknechtstr.24–25, 14476 Potsdam, Germany J. Phys. Org. Chem. 2008, 21 652–658 Copyright ß 2008 John Wiley & Sons, Ltd. 652