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The crosslink density and distribution inside the polymer matrix affect the mechanical properties of rubber nanocomposites (NCs). Since the catalytic activity of zinc has a central role in the formation of crosslinks, this study focuses on the effect that the structure of the catalytic sites and their localization inside the polymer matrix have on the mechanical behavior of rubber materials. To do this, a new highly efficient activator, Zn@SiO2 based on zinc single sites anchored onto the silica surface, is used as double function filler, acting as both activator and reinforcing filler. The mechanical properties of rubber NCs prepared with Zn@SiO2 are compared to NCs conventionally cured with ZnO particles. The results suggest that localizing the catalytic sites at different distance from the filler particles dispersed in the rubber matrix is a promising tool to control the crosslinking density and distribution, which means tuning the mechanical properties of rubber NCs.

Sepiolite (Sep)&ndash, styrene butadiene rubber (SBR) nanocomposites were prepared by using nano-sized sepiolite (NS-SepS9) fibers, obtained by applying a controlled surface acid treatment, also in the presence of a silane coupling agent (NS-SilSepS9). Sep/SBR nanocomposites were used as a model to study the influence of the modified sepiolite filler on the formation of immobilized rubber at the clay-rubber interface and the role of a self-assembled nanostructure in tuning the mechanical properties. A detailed investigation at the macro and nanoscale of such self-assembled structures was performed in terms of the organization and networking of Sep fibers in the rubber matrix, the nature of both the filler&ndash, filler and filler&ndash, rubber interactions, and the impact of these features on the reduced dissipative phenomena. An integrated multi-technique approach, based on dynamic measurements, nuclear magnetic resonance analysis, and morphological investigation, assessed that the macroscopic mechanical properties of clay nanocomposites can be remarkably enhanced by self-assembled filler structures, whose formation can be favored by manipulating the chemistry at the hybrid interfaces between the clay particles and the polymers.

This study addresses the relationship between material morphology (size, growth parameters and interfaces) and optical emissions in ZnO through an experimental approach, including the effect of different material dimensions from bulk to nano-size, and different excitations, from optical sources to ionizing radiation. Silica supported ZnO nanoparticles and ligand capped ZnO nanoparticles are synthesized through a sol&ndash, gel process and hot injection method, respectively. Their optical properties are investigated by radioluminescence, steady-state and time-resolved photoluminescence, and compared to those of commercial micrometric powders and of a bulk single crystal. The Gaussian spectral reconstruction of all emission spectra highlights the occurrence of the same emission bands for all samples, comprising one ultraviolet excitonic peak and four visible defect-related components, whose relative intensities and time dynamics vary with the material parameters and the measurement conditions. The results demonstrate that a wide range of color outputs can be obtained by tuning synthesis conditions and size of pure ZnO nanoparticles, with favorable consequences for the engineering of optical devices based on this material.

Global industry is showing a great interest in the field of sustainability owing to the increased attention for ecological safety and utilization of renewable materials. For the scientific community, the challenge lies in the identification of greener synthetic approaches for reducing the environmental impact. In this context, we propose the preparation of novel biocomposites consisting of natural rubber latex (NRL) and sepiolite (Sep) fibers through the latex compounding technique (LCT), an ecofriendly approach where the filler is directly mixed with a stable elastomer colloid. This strategy favors a homogeneous dispersion of hydrophilic Sep fibers in the rubber matrix, allowing the production of high-loaded sepiolite/natural rubber (Sep/NR) without the use of surfactants. The main physicochemical parameters which control Sep aggregation processes in the aqueous medium were comprehensively investigated and a flocculation mechanism was proposed. The uniform Sep distribution in the rubber matrix, characteristic of the proposed LCT, and the percolative filler network improved the mechanical performances of Sep/NR biocomposites in comparison to those of analogous materials prepared by conventional melt-mixing. These outcomes indicate the suitability of the adopted sustainable procedure for the production of high-loaded clay&ndash, rubber nanocomposites with remarkable mechanical features.

The development of advanced polymer nanocomposites requires a strong filler-polymer interfacial interaction and an optimal filler nanodispersion. The incorporation of the clays into a polymer matrix frequently does not improve the composite mechanical properties, owing to both poor dispersion and macroscopic particle dimensions. In this work, pristine and organically-modified sepiolites (Sep) were structurally modified by an acid treatment, which provides nano-sized sepiolite (NS-Sep) fibers with reduced particle size and increased silanol groups on the surface layer. NS-Sep fibers were used to prepare styrene-butadiene rubber nanocomposites with enhanced mechanical properties. Dynamic-mechanical analysis of clay polymer nanocomposites demonstrated that the NS-Sep fibers provided an excellent balance between reinforcing and hysteretic behavior, compared to the large-sized pristine Sep and isotropic silica. This was related to the enhanced interfacial chemical interaction between NS-Sep and rubber, as well as to the size and self-assembly of anisotropic nanofibers to form filler network structures, as supported by transmission electron microscopy analysis. The preparation of nanocomposites, based on Sep nanofibers obtained by a simple and versatile acid treatment, can thus be considered an alternative approach for the designing of advanced clay polymer nanocomposites.

The present study provides a comprehensive investigation at the micro and nanoscale of the interface between hybrid SiO2@POSS nanofiller, where silica nanoparticles (NPs) and POSS nanocages are intimately interconnected, and Styrene Butadiene Rubber (SBR). SEM and AFM inspection and, more in depth, solid state 1H NMR revealed a remarkable fraction of rigid rubber close to the SiO2@POSS surfaces, which increases with the curing temperature. Instead, a reduced amount of immobilized rubber was detected for SBR/SiO2+POSS nanocomposites, obtained by simply mixing SBR, SiO2 and POSS. The results allowed us to propose a model for the network formation in C-SBR/SiO2@POSS. This is based on the progressive activation by dicumylperoxide (DCP) of the methacryl functionalities of POSS nanounits which, being closely connected to SiO2 NPs in SiO2@POSS, promote crosslinking in proximity of the filler surfaces, and lead to the generation of a tight network strongly bonded to the rubber chains.

Morphology-controlled titania nanocrystals (NCs) are indicated as promising building blocks for the generation of new photocatalytic materials, where precise tailoring of particle size and exposed crystal surfaces enables to fulfill specific reactivity requirements. In fact, beyond the dimensions, the presence of different TiO 2 facets dramatically affects its photoactivity. This has been recently connected to the peculiar electronic band structures of specific surfaces and to their ability in promoting the concentration of different photogenerated defects. The most mature methods for the synthesis of shape-controlled TiO 2 utilize organic surfactants, which commonly remain anchored to the NCs surfaces, often precluding their final use in photocatalytic applications. Although several alternatives have been provided (e.g., ligand exchange), there is still an urgent need to identify approaches for controlling morphology by also granting tunable surface functionalities, easy scalable procedures, and applicability in “friendly” materials (e.g., pellet, membranes, or flexible substrates). Bearing these challenges in mind, this chapter briefly presents the basic synthesis strategies for tuning morphology and surfaces of TiO 2 NCs, focusing on those that may guarantee a transfer of the NCs intrinsic features to technological applicable photocatalytic materials. A brief state of art of the microscopic and spectroscopic techniques utilized for verify and study their morphology-dependent functionalities will be described. In this context and aiming to suggest implementation of TiO 2 reactivity, a special attention will be devoted to spectroscopies (mainly ESR) allowing to monitor quasi “in situ” the photocatalytic mechanism. Finally, some perspectives for the inclusion of shape-controlled TiO 2 NCs in smart materials will be proposed.

A novel hybrid nanofiller, SiO2@POSS, where the silica nanoparticles (NPs) and the POSS belong to the same functional structure, has been synthesized by grafting different loadings of OctaMethacrylPOSS onto silanized commercial SiO2, using a surface reaction mediated by dicumylperoxide (DCP). The peroxide, besides anchoring the nanocages onto the silica surface, ensures the presence of methacryl functionalities in the final structure, which are still available for cross-linking reactions with a polymer host. The hybrid SiO2@POSS NPs were used to prepare, by ex situ blending, SBR nanocomposites. The dynamic-mechanical analysis performed on the cured SBR/SiO2@ POSS composites indicated that the presence of POSS induces a remarkable increase of modulus either at low or at high strain, and a considerable decrease of hysteresis. This has been associated with the peculiar hybrid structure of the SiO2@POSS filler, in which silica NP aggregates are partially interconnected and surrounded by a thin shell of POSS nanounits which, thanks to their high number of reactive functionalities, promote the formation of "sticky regions'' among the silica aggregates and, consequently, a tight filler network wherein rubber is immobilized. This grants a relevant reinforcement and increased hysteretic properties, suggesting SiO2@POSS as a promising filler system for decreasing the energy loss under strain and for leading to a potential reduction of filler utilization in rubber composite formulations.

The efficiency of sulfur vulcanization reaction in rubber industry is generally improved thanks to the combined use of accelerators (as sulphenamides), activators (inorganic oxides), and co-activators (fatty acids). The interaction among these species is responsible for the formation of intermediate metal complexes, which are able to increase the reactivity of sulfur towards the polymer and to promote the chemical cross-links between the rubber chains. The high number of species and reactions that are involved contemporarily in the process hinders the complete understanding of its mechanism despite the long history of vulcanization. In this process, ZnO is considered to be the most efficient and major employed activator and zinc-based complexes that formed during the first steps of the reaction are recognized to play a main role in determining both the kinetic and the nature of the cross-linked products. However, the low affinity of ZnO towards the rubber entails its high consumption (3–5 parts per hundred, phr) to achieve a good distribution in the matrix, leading to a possible zinc leaching in the environment during the life cycle of rubber products (i.e., tires). Thanks to the recent recognition of ZnO ecotoxicity, especially towards the aquatic environment, these aspects gain a critical importance in view of the urgent need to reduce or possibly substitute the ZnO employed in rubber vulcanization. In this review, the reactivity of ZnO as curing activator and its role in the vulcanization mechanism are highlighted and deeply discussed. A complete overview of the recent strategies that have been proposed in the literature to improve the vulcanization efficiency by reducing the amount of zinc that is used in the process is also reported.

An efficient method for the preparation of stable microcapsules with an industrially relevant core material was investigated for future use in self-repairing coatings. Microcapsules filled with isophorone diisocyanate (IPDI) were synthesized with different polymeric shells: polyurethane PU, poly(urea-formaldehyde) PUF and bi-layer polyurethane/poly(urea-formaldehyde) PU/PUF. Changing the encapsulation process by adding more shell wall monomers and pre-polymers allows the modulation of physical and mechanical properties of microcapsules. The thickness of microcapsules shell walls can be tuned for coating thicknesses and chemical environments. The effect of diverse process parameters and ingredients on the morphology of the microcapsules was observed by scanning electron microscopy (SEM) and optical microscopy (OM). Different techniques for the characterization of the chemical structure and the core content were considered such as Fourier transform infrared spectroscopy (FT-IR) as well as the characterization of thermal properties by differential scanning calorimetry (DSC). High yields of free flowing powder of spherical microcapsules were produced. The application of a liquid phase IPDI in self-healing polymer composite is studied. Diisocyanates, being reactive with water, introduce the possibility of achieving a really autonomous self-healing system in an aqueous or moisture-sensitive environment. © 2013 Elsevier Ltd. All rights reserved.

This article describes the synthesis, characterization, and application of new UV-absorbing microcapsules encapsulating a UV-responsive photochromic dye for application in the damage-sensing field. Microcapsules filled with a photochromic spiropyran, dissolved in sunflower oil as core material, were synthesized by reacting a TDI-based polyisocyanate prepolymer with a benzophenone-based amine to obtain robust UV-absorbing polyurea shells. The newly synthesized UV-screening microcapsules were embedded into a photoresist to realize a new mechanoresponsive polymer. After scratching the coating, the UV-screening microcapsules break and the UV-sensitive core material is released and diffuses into the polymer matrix. Upon exposure to UV-A light, a rapid color change in the region where the damage was made is observed, because of the photoinduced transition of spiropyran to the plane merocyanine form. The novelty of the approach presented in this work lies in the possibility to convert any type of conventional polymeric coating into a UV-light-sensitive mechanoresponsive smart coating by simple addition of our new UV-screening microcapsules. © 2013 American Chemical Society.

The sensing behavior of pyramidal (PY), prismatic hexagonal (EP) and hexagonal rod-like (ER) ZnO micro and sub-microparticles, has been compared with that of commercial ZnO (ZnO®) particles having nanometric size and uneven shape. The performances have been firstly related to the predominance of specific crystal surfaces and then, more in depth, to the paramagnetic defects in ZnO ( and ), detected by Electron Spin Resonance (ESR), in order to associate the particles morphology with the defects amount and reactivity and, in turn, with a particular sensing mechanism. The results showed that the sensing behavior of ZnO® containing irregular nanoparticles is essentially related to the alternate formation and filling of oxygen vacancies during the gas pulse (oxygen vacancy mechanism), while that of ER and EP crystals does not seem to directly involve the defects. In particular, the sensing properties of shape controlled ZnO particles are mainly attributed to the ability of (0001) exposed surfaces in favoring a far better chemisorption of negatively charged oxygen species, then available for the reactions with the reducing gas (i.e. ionosorption mechanism). The outcomes and the approach adopted in this study may positively contribute to the debate still existing between the oxygen vacancy and ionosorption models by giving indications on the predominance of a specific sensing mechanism in shape controlled ZnO.

The present study reports on the preparation and characterization of innovative “self-cleaning” nano-TiO2 treatments to be used in cultural heritage, based on dispersion of solar-light activated TiO2 nanocrystals. The semiconductor has been prepared by an easy and low-cost non-aqueous procedure, providing anatase (NA_TiO2) nanoparticles photo-active not only under UV-light but also under solar irradiation. NA_TiO2 allows obtaining very stable dispersions either in water or in ethylene glycol used to produce homogeneous nano-TiO2 treatments on Noto stone and Carrara marble, which display excellent aesthetic compatibility, do not remarkably affect the capillary water absorption of the stones and slightly increase their wettability. The new treatment exhibits higher photocatalytic activity compared to that based on commercial TiO2 (P25_TiO2). This behavior has been attributed not only to the morphological properties of the treatments and of the stones, but also to the presence of residual benzyl alcohol molecules anchored on the anatase NP surfaces. This provides solar light absorption and partially improves the charge trapping, thus increasing the photoefficiency. The overall results suggest that the positive combination of high dispersion, solar-light absorption and reduced recombination effects in NPs plays a key role in the development of efficient photocatalytic treatments for stone restoration.

The synthesis of new 4-carboxy oxazoles, thiazoles and thiazolidines by condensation of serine or cysteine with aldehydes or acids is described. Due to the optimization of a mild and selective procedure, which takes advantage of the positive effect of microwave irradiation on the MnO2 mediated oxidation step, the 2-substituted-4-carboxy derivatives can be obtained in multi-gram scale. Examples of coordination chemistry to Ni(II) and Co(II) are described.

The hydrothermal (solvothermal) reactions of ZnII, Co II, and CuII salts with the thiazole-based ligands 2-Htzc (thiazole-2-carboxylic acid), 4-Htzc (thiazole-4-carboxylic acid), and Htzc-py [2-(2-pyridyl)thiazole-4-carboxylic acid] led to the formation of coordination complexes with assorted geometry at the metal centers. The new complexes were characterized by conventional spectroscopic methods as well as by single-crystal X-ray analysis, TG-MS, and PXRD. Crystallographic studies have shown that an extended supramolecular network is generated in the solid state through the formaton of hydrogen bonds between the several polar groups present in the complex frameworks. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

We comprehensively explored the photocatalytic properties, in H2 production by methanol photosteam reforming, of anatase nanocrystals with nearly rectangular (RC), rhombic (R), and nanobar (NB) shapes having exposed {001}, {101}, and {010} surfaces. The aim was to relate the reactivity both to the type of crystal facets and to the photogenerated defects. The electron spin resonance (ESR) spectra reveal that the amount of Ti3+ (electron traps) is parallel to the H2 evolution rate and becomes a maximum for the RC nanocrystals, which display the highest area of {001} surfaces and the lowest {101} area but also involve a significant area of {010} facets. This points out that the H2 production cannot be related only to the envisaged reducing {101} facets, but that the {010} facets also play a key role. We suggest that the contiguous {001}, {101}, and {010} facets form a highly effective "surface heterojunction" within a RC nanoparticle which drives the electrons photogenerated on {001} facets not just toward the {101} but also to the {010} facets, while the holes are driven toward the {001} facets. This transfer improves the charge separation, thus boosting the photoefficiency of RC nanocrystals compared to that of NB and R nanocrystals. The ESR spectra performed after ultraviolet excitation in the presence of MeOH show the partial annihilation of the Ti3+ features, mainly for highly reactive RC nanocrystals. Because H2 production involves an electron transfer to the proton, a relevant role in H+ photoreduction of the Ti3+ centers present on the exposed {010} and {101} surfaces is suggested. These findings underline the importance of determining the relationship between the photogenerated defects and the exposed crystal surfaces to optimize the photocatalytic properties of anatase nanocrystals. (Figure Presented).

Silica/styrene butadiene rubber (SBR) nanocomposites were prepared by blending method using shape-controlled spherical and rod-like nanoparticles with different aspect ratios as filler for the rubber reinforcement. The differently shaped silica particles were synthesized by sol-gel method using tetraethoxysilane (TEOS) and (3-mercaptopropyl) trimethoxysilane (MPTSM) as silica precursors, and cetyltrimethylammonium bromide (CTAB) as structure directing agent. This strategy allowed to study the influence of the particle morphology on the reinforcing effect independently of the silica surface chemistry and considering the aspect ratio as the only geometrical variance. Spherical and anisotropic rod-like particles, dispersed in the nanocomposites, formed a network of particles bridged by thin rubber layers throughout the SBR matrix. Moreover, differently oriented domains of aligned rods are observed when the aspect ratio of particles increases and is >=2. Dynamic-mechanical properties demonstrated that the rod-like particles with the higher aspect ratio provided stronger reinforcement of the rubber. This was related to the self-alignment of the anisotropic particles and to the consequent larger filler/polymer interface, compared to that of spherical ones. © 2014 Elsevier Ltd. All rights reserved.

The polytopic ligand thiazolidine-2,4-dicarboxylic acid (H2L) has been synthesised on a large scale starting from the naturally occurring amino acid l-cysteine. The (R,R)/(S,R)diastereomeric mixture has been separated into its constituents through selective precipitation of the pure (R,R) isomer from concentrated H2O/MeOH solutions. The enantiomerically pure ligand (H2L-RR) has been reacted with CoCl2·6H 2O under hydrothermal conditions, with the final product being [Co(L-RR)(H2O)·H2O]∞ (1). The obtained coordination polymer is optically pure, and it maintains the chiral information that is present in its building block. Two different kinds of channels are present in the 3D structure of 1: one hydrophobic (with the sulfur atoms of the thiazolidine rings exposed) and the other hydrophilic [with the aquo ligand on Co(ii) exposed, and hosting the crystallization water solvent]. 1 has been characterized through a combination of X-ray diffraction (single-crystal and powder) and spectroscopic (CD, IR, UV-Vis, XANES, EXAFS) techniques. Finally, CO2 adsorption tests conducted at 273 K and (pCO2)max = 920 torr have shown a good carbon dioxide uptake, equal to 4.7 wt%. © 2012 The Royal Society of Chemistry.

A mild and selective procedure for the synthesis of 4-carboxy thiazoles and thiazolidines starting from naturally occurring cysteine by condensation with aldehydes is described. The optimized procedure, taking advantage of the positive effect of microwave irradiation on the MnO2-mediated oxidation step, is suitable for multigram scale. Coordination of these ligands towards a variety of transition metal ions gave new interesting metallorganic supramolecular architectures in which an extensive 3D network is created through hydrogen bonding. Copyright © Taylor and Francis Group, LLC.

The hydrothermal (solvothermal) reactions of ZnII, CoII, and CuII salts with the thiazole-based ligands 2-Htzc (thiazole-2-carboxylic acid), 4-Htzc (thiazole-4-carboxylic acid), and Htzc-py [2-(2-pyridyl)thiazole-4-carboxylic acid] led to the formation of coordination complexes with assorted geometry at the metal centers. The new complexes were characterized by conventional spectroscopic methods as well as by single crystal X-ray analysis, TG-MS, and PXRD. Crystallographic studies have shown that an extended supramolecular network is generated in the solid state through the formaton of hydrogen bonds between the several polar groups present in the complex frameworks

New enantiomerically enriched 1,4,5-piperazines and 1,4,5-dihydro-2H-pyrazines have been prepared by reduction of the corresponding 2-oxo-piperazines. Selective reduction can be achieved by careful control of the reaction conditions using LiAlH4. Notably the two nitrogen atoms of the final compounds are orthogonally protected. © 2010 Elsevier Ltd. All rights reserved

The reaction of [CpRuCl(PPh(3))(2)] (Cp = cyclopentadienyl) and [CpRuCl(dppe)] (dppe = Ph(2)PCH(2)CH(2)PPh(2)) with bis- and tris-phosphine ligands 1,4-(Ph(2)PC[triple bond]C)(2)C(6)H(4) (1) and 1,3,5-(Ph(2)PC[triple bond]C)(3)C(6)H(3) (2), prepared by Ni-catalysed cross-coupling reactions between terminal alkynes and diphenylchlorophosphine, has been investigated. Using metal-directed self-assembly methodologies, two linear bimetallic complexes, [{CpRuCl(PPh(3))}(2)(mu-dppab)] (3) and [{CpRu(dppe)}(2)(mu-dppab)](PF(6))(2) (4), and the mononuclear complex [CpRuCl(PPh(3))(eta(1)-dppab)] (6), which contains a "dangling arm" ligand, were prepared (dppab =1,4-bis[(diphenylphosphino)ethynyl]benzene). Moreover, by using the triphosphine 1,3,5-tris[(diphenylphosphino)ethynyl]benzene (tppab), the trimetallic [{CpRuCl(PPh(3))}(3)(mu(3)-tppab)] (5) species was synthesised, which is the first example of a chiral-at-ruthenium complex containing three different stereogenic centres. Besides these open-chain complexes, the neutral cyclic species [{CpRuCl(mu-dppab)}(2)] (7) was also obtained under different experimental conditions. The coordination chemistry of such systems towards supramolecular assemblies was tested by reaction of the bimetallic precursor 3 with additional equivalents of ligand 2. Two rigid macrocycles based on cis coordination of dppab to [CpRu(PPh(3))] were obtained, that is, the dinuclear complex [{CpRu(PPh(3))(mu-dppab)}(2)](PF(6))(2) (8) and the tetranuclear square [{CpRu(PPh(3))(mu-dppab)}(4)](PF(6))(4) (9). The solid-state structures of 7 and 8 have been determined by X-ray diffraction analysis and show a different arrangement of the two parallel dppab ligands. All compounds were characterised by various methods including ESIMS, electrochemistry and by X-band ESR spectroscopy in the case of the electrogenerated paramagnetic species.

A highly stereoselective approach to 1,3,4,5- and 1,3,3′,4,5-polysubstituted 2-oxopiperazines is reported. The method is based on the synthetic elaboration of naturally occurring amino acids to obtain enantiomerically enriched C-5 substituted oxopiperazines, which are further functionalized at C-3 via enolate formation and reaction with electrophiles. Notably, the two nitrogens of the ring can be orthogonally protected.

The solvothermal reaction of magnesium(II) salts with formic acid in N,N-dimethylformamide/H2O at 140 degrees C for 24 h afforded two different polymeric magnesium(H) formates, depending on the relative DMF/H2O content. A trigonal (space group R3c) anhydrous phase Mg(HCOO)(2)(HCOOH) superset of (CH3)(2)NH (1) is formed under "dilute" conditions, while the orthorhombic (space group Pbca) dihydrate Mg(HCOO)(2)center dot 2H(2)O (2) is the main product when the water content is higher. When 2 is dehydrated at 300 degrees C and subsequently exposed to water vapors, a quasi -reversible phase transition was observed, leading to a different polymorph of the same species (2a, monoclinic, space group P2(1)/c). The process was entirely followed by X-ray powder diffraction (XRPD) at variable temperatures, and the same XRPD technique was used for structure solution and refinement of compound 2a. Finally, CO2 adsorption isotherms at ambient temperature were recorded for (preactivated) 2, in order to test it as greenhouse gas storage material. A (promising) maximum value of 1.32 wt% CO2 is stored under these conditions, but the plateau in the adsorption curve was not reached because of the higher carbon dioxide pressures required.

A highly stereoselective approach to 1,3,4,5- and 1,3,3′,4,5-polysubstituted 2-oxopiperazines is reported. The method is based on the synthetic elaboration of naturally occurring amino acids to obtain enantiomerically enriched C-5 substituted oxopiperazines, which are further functionalized at C-3 via enolate formation and reaction with electrophiles. Notably, the two nitrogens of the ring can be orthogonally protected. © 2007 Elsevier Ltd. All rights reserved

This work describes the stereochemistry and the relative rates of epoxidation reactions of the title compounds with sulfur ylides (methylenedimethylsulfurane and methylenedimethyloxysulfurane) in DMSO and C6H6. The electronic perturbative effect of substituent X depends on the solvent and on the reactant. It is transmitted in opposite way in solvents of different polarity depending on the reactant. The electronegativity of the substituent scarcely affects the percentages of axial/equatorial attack. The percentage of equatorial attack with methylenedimethyloxysulfurane is markedly lower for 5-X-adamantan-2-ones than for 4-X-cyclohexanones. © 2005 The Japan Institute of Heterocyclic Chemistry All rights reserved