Studies of Some Strained-Ring Systems: Tricyclo-Octanes

<p>The present study has been directed towards the synthesis and base promoted rearrangements of some saturated and unsaturated halogenotricyclo-octanes. The preparation of a number of previously unknown 4,4,8- and 4,4,8,8-tetra-halogeno-anti-tricyclo[5,1,0,03,5]- octanes and the corresponding 3,3,8-tri- and 3,3,8,8-tetra-halogeno-anti-tricyclo[5,1,0,02,4] octanes has been accomplished and the stereo-chemistries of their ring systems established. The former tricyclo-octanes are base sensitive and on treatment with potassium t-butoxide give rise to mixtures of (E) - and (Z) -Beta-t-butoxystyrenes. However, the anti-tricyclo[5,1,0,02,4] octanes give no characterisable products on treatment with base. The mechanistic implications of the tricycle-octane - styrene conversion have been studied in some detail and halogenocyclo-octatetraenes and phenylacetylenes have been eliminated as intermediates. The behaviour of several methoxy-substituted 4,4,8,8-tetrahalogeno-anti-tricyclo[5,1,0,03,5] octanes with the same base has been studied, and it has been found that homotropilidenes are formed regiospecifically by 1,4-elimination. These conversions constitute the first known examples of such elimination experienced by ring-fused halogenocyclopropanes. From these studies, evidence is presented which implicates homotropilidenes and bicyclo[4,2,0]octa-2,4-dienes as intermediates in the production of styrenes, and a mechanism for the tricyclo-octane - styrene rearrangement has been proposed. A new and potentially versatile synthesis of 3,3-dihalogeno-anti tricyclo[5,1,0,02,4] oct-5-enes (anti-bishomobenzenes) has been developed. The new route employs readily available starting materials, involves sequential introduction of the cyclopropyl, gem-dihalogenocyclopropyl, and olefinic moieties and proceeds in an overall yield of about 14%. This represents a five-fold increase over the previously reported yields.</p>

Studies of Some Strained-Ring Systems: Tricyclo-Octanes

<p>The present study has been directed towards the synthesis and base promoted rearrangements of some saturated and unsaturated halogenotricyclo-octanes. The preparation of a number of previously unknown 4,4,8- and 4,4,8,8-tetra-halogeno-anti-tricyclo[5,1,0,03,5]- octanes and the corresponding 3,3,8-tri- and 3,3,8,8-tetra-halogeno-anti-tricyclo[5,1,0,02,4] octanes has been accomplished and the stereo-chemistries of their ring systems established. The former tricyclo-octanes are base sensitive and on treatment with potassium t-butoxide give rise to mixtures of (E) - and (Z) -Beta-t-butoxystyrenes. However, the anti-tricyclo[5,1,0,02,4] octanes give no characterisable products on treatment with base. The mechanistic implications of the tricycle-octane - styrene conversion have been studied in some detail and halogenocyclo-octatetraenes and phenylacetylenes have been eliminated as intermediates. The behaviour of several methoxy-substituted 4,4,8,8-tetrahalogeno-anti-tricyclo[5,1,0,03,5] octanes with the same base has been studied, and it has been found that homotropilidenes are formed regiospecifically by 1,4-elimination. These conversions constitute the first known examples of such elimination experienced by ring-fused halogenocyclopropanes. From these studies, evidence is presented which implicates homotropilidenes and bicyclo[4,2,0]octa-2,4-dienes as intermediates in the production of styrenes, and a mechanism for the tricyclo-octane - styrene rearrangement has been proposed. A new and potentially versatile synthesis of 3,3-dihalogeno-anti tricyclo[5,1,0,02,4] oct-5-enes (anti-bishomobenzenes) has been developed. The new route employs readily available starting materials, involves sequential introduction of the cyclopropyl, gem-dihalogenocyclopropyl, and olefinic moieties and proceeds in an overall yield of about 14%. This represents a five-fold increase over the previously reported yields.</p>

Mg-Al-Cr2O7 Hydrotalcite-Like Catalysts Synthesized at Different pH Values for Styrene Oxidation

Dichromate anions were intercalated between two consecutive hydroxide layers of [Mg0.6Al0.4(OH)2]0.40+ via co-precipitation at different pH conditions. The physico-chemical properties of the obtained solids were examined by physical methods such as X-ray diffraction (XRD), Infrared (IR), Scanning Electron Microscopy (SEM), Brunauer-Emmett-Teller (BET) and Energy-Dispersive Spectroscopy (EDS). The experimental results indicated that the amount of dichromate anions in the catalysts varies with the pH media. Also, the morphology, structure and chemical composition of the materials depends strongly on the preparation conditions. The Mg-Al-Cr2O7 hydrotalcite-like compounds are used as heterogeneous catalysts for the styrene oxidation with H2O2 at mild conditions. The styrene conversion is about 20-50% while styrene selectivity remains rather high.

Silver(I) Dicyanonitrosomethanide, Ag[ONC(CN)2] Complex as Catalyst for the Selective Oxidation of Styrene to Benzaldehyde

Silver(I) dicyanonitrosomethanide, Ag[ONC(CN)2] represent a 3D interwoven coordination polymer organization in which all the donor atoms of the functional groups of ONC(CN)2- are coordinated to the Ag(I). Oxidation of styrene utilizing H2O2 as an oxidant in acetonitrile (CH3CN) was used as a model reaction to investigate the catalytic potential of the Ag(I) complex. The CH3CN was chosen as the solvent based on the data collected from Conductor like Screening Model for Real Solvents (COSMO-RS) study. The data indicate that the Ag[ONC(CN)2] complex was compatible and soluble in CH3CN. Different parameters such as styrene:H2O2 molar ratio, reaction time, catalyst mass, and reaction temperature were studied. Highest styrene conversion (36%) with 100% selectivity towards benzaldehyde (BZ) was achieved when 25 mg catalyst, 1:1 styrene to H2O2 molar ratio were used. The reaction was carried out at 303 K for 3 h. The catalytic conversion of styrene to BZ is proposed to take place via [Ag-H2O2] adduct with styrene oxide (StO) as an intermediate. Molecular Electrostatic Potential (MEP) shows that the Ag atom has the highest probability to coordinate with the oxygen atom of H2O2. The MEP data confirms the proposed mechanism.

CONVERSION OF STYRENE INTO BENZALDEHYDE AND STYRENE EPOXIDE OVER MgCoAl-LDH CATALYSTS

Co-containing hydroxides have been successfully synthesized by the co-precipitation of starting-metal salts. The obtained materials were characterized by some physical means including XRD, EDS, BET… It is found that Co2+ ions are present in the layered double hydroxide (LDH) sheets. The presence of cobalt ions in LDH plays as active sites for the oxidation of styrene with air. The catalysts exhibited a very high activity in the conversion of styrene into two main products (benzaldehyde and styrene oxide). The highest styrene conversion is about 90-95% and the total selectivity to benzaldehyde and styrene oxide is in the range of 80-85% under reported experimental conditions.

Utilization Low Rank Coal Bottom Ash as TiO2 Support for Oxidation Catalyst of Styrene with Hydrogen Peroxide Aqueous

One of the coal combustion ashes is coal bottom ash. Low rank coal bottom ash can act as TiO2 catalyst’s support which was calcined at varying temperature, has been created. The low rank coal bottom ash model was collected from low rank coal which burned in muffle furnace at 800 °C for 2 h. Subsequently, the low rank coal bottom ash was impregnated with titanium (IV) isopropoxide (Ti (PrO)4) 500 μmol, and then calcined at variation temperature of 300, 400, 500, 600 and 700 °C. The modified physiochemical property of catalysts were determined UV-vis spectroscopy, N2 adsorption-desorption and hydrophobicity test. The performances of the catalysts were tested for styrene oxidation with H2O2 aqueous as oxidant. It is found that the low rank coal bottom ash was as good catalyst support, whereby TiO2 supported low rank coal bottom ash which calcined at 400 °C possessed the best catalytic activity with styrene conversion 45% and selectivity 87%.

Optimization of Styrene Reactor Using Tabu Search and Genetic Algorithm Methods

This paper deals with multi-objective optimization of styrene reactor using Tabu search (TS) and genetic algorithm (GA) methods. Styrene is produced commercially by catalytic dehydrogenation of ethyl benzene. As styrene is an important monomer, the capacity of the plant is usually very high, as a result the investment cost is also very high, and even a small enhancement in the plant operation can generate major income. The adiabatic reactor using the pseudo homogeneous model was considered in this study for maximizing the styrene conversion and selectivity. A computer program was written to simulate an adiabatic reactor in order to evaluate the possibility of optimizing the process in simulation environment. The simulation results were compared with the experimental data. This comparison indicated that the value of overall mean squarer of errors for conversion of the compounds was 7.09E-05 and overall means relative error of them was 2.18 percent. In order to optimize the performance of the reactors, conversion of styrene was adopted as the objective function. Six decision variables, namely, ethyl benzene feed temperature at the entrance of each bed, pressure, the ratio of steam to ethyl benzene and initial ethyl benzene flow rate were used for the optimization. The results of GA optimization showed final conversion of styrene increased from an initial value of 0.710 to 0.75 after 100 generation of population. Applying Tabu algorithm optimization, the value rose from 0.725 to 0.813 after generation of 100 neighborhoods. The results revealed that the CPU time needed to optimize the reactor for TS was shorter than that of GA method. In addition, using the same iteration numbers for both methods, the optimum value of styrene conversion was greater when TS method was applied.