摘要:

AbstractApproaches used to effect selective reaction at one of two or more similar sites in a molecule are reviewed. The nature of the problem is defined and the strategic advantage to be gained through the use of symmetrical intermediates is outlined early and re‐emphasised throughout the discussion with specific examples of multistage syntheses of important products. The various tactics used to effect site selectivity in a late synthetic step are described in a logical sequence and presented in a form aimed to help in the design of syntheses of unsymmetric products from symmetric intermediate

ISSN:0268-2575    

DOI:10.1002/jctb.280630402

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThis study investigates the applicability of the bubble column as a reactor to perform the dehydration of ortho‐boric acid efficiently and economically. The effects of operating conditions such as reaction time, temperature, gas flow rate, particle size and solid content in the slurry phase on the fractional conversion of the reaction have been determined, and the performance of the three‐phase bubble column reactor operating at low pressure (92 kPa) has been discussed. It can be noted from this study that the reaction time has been reduced and the particle size and solid content which are required in the slurry phase for favourable fractional conversion have been increased in the bubble column reactor in comparison with those in the continuous stirred tank reactor. The reaction could be described by means of a fluid–solid heterogeneous reaction

ISSN:0268-2575    

DOI:10.1002/jctb.280630403

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractA series of experiments was conducted on the integrated chemical–biological treatment of14C‐labelled polychlorinated biphenyl congeners in soil/sediment‐containing systems. The hydroxyl radicals, generated by Fenton's reagent (1% (v/v) H2O2, 1 mmol dm−3FeSO4), followed by inoculation withPseudomonassp., strain LB400, andAlcaligenes eutrophus, strain H850, increased the overall extent of 2‐chlorobiphenyl mineralisation in slurries of contaminated manufactured gas plant soil and sediment by 2·9 and 7·4 times, respectively, compared with biodegradation alone. In uncontaminated topsoil slurries the effect of chemical pretreatment was not observed. In the systems amended with 2,2′,4,4′‐tetrachlorobiophenyl, the application of Fenton's reagent increased the overall extent of mineralisation by 2·4 times, compared with the biological treatment alone, but had no effect in the slurries of contaminated soil and sediment. The increased level of radioactivity in the liquid phase of experimental systems suggests that intermediates produced in the process of chemical oxidation are less hydrophobic than parent polychlorinated biphenyls and therefore more available for furt

ISSN:0268-2575    

DOI:10.1002/jctb.280630404

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractComposite membranes (CM) were prepared by coating the dense surface of different asymmetric polysulfone flat membranes (AM) with a solution of silicone rubber polymer. The surface porosity (ε) of the dense skin AM samples varied between 4 × 10−5and 1·5 × 10−8, with an average mean pore size between 0·10 and 0·07 μm. Scanning electron microscopy (SEM), gas permeation experiments (H2, N2, CH4, CO2) and a simple resistance model were used for the determination of structure‐permeability relationships. This study indicates that the CM prepared with polysulfone AM having ε<3 × 10−7, coated with a concentration of 6% silicone solution and a contact time of 1 min, has the best gas separation performance, with selectivities very close to the intrinsic polysulfo

ISSN:0268-2575    

DOI:10.1002/jctb.280630405

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractA novel amperometric biosensor for the determination of citric acid in food samples and fermentation broths has been developed. The sensor is composed of citrate lyase (CL, EC 4.1.3.6), oxaloacetate decarboxylase (OAC, EC 4.1.1.3) and pyruvate oxidase (POP, EC 1.2.3.3), co‐immobilized in gelatin, and an amperometric transducer. A Clark‐type O2‐electrode and a modified Clark‐type H2O2‐electrode were alternatively used as a transducer. The biosensor covers a linear detection range from 1 μmol dm−3to 1 mmol dm−3citrate, with a response time of 2·5 min for the steady state response. The lower detection limit for citrate is 0·5 μmol dm−3. The response of the sensor remained constant for 8 days and decreased to 25% after 18 days at 20–23°C. The results obtained from citrate determinations in food samples and fermentation broths agree well with those determined by enzymatic sample anlaysis. The relative standard deviation for citrate determinations with the new bio

ISSN:0268-2575    

DOI:10.1002/jctb.280630406

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe effectiveness of a macroreticular matrix in reducing side‐reactions in the reaction of acetyl polystyrenesulphonate with aqueous aniline has been investigated. Results were comparable with those for the 2% cross‐linked resins and the use of four non‐aqueous solvents gave neither any improvement in the acetanilide yield nor in its purity. The synthesis of isopropenyl acetates by reacting the reagent with acetone was exp

ISSN:0268-2575    

DOI:10.1002/jctb.280630407

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe substrate removal efficiencies of the conventional (taper angle of 0°) and three tapered anaerobic fluidized‐bed bioreactors (tape angles of 2·5°, 5° and 10°) predicted from a kinetic model correlated with the average biofilm thickness measured. The predicted substrate removal efficiencies of the three tapered bioreactors were higher than that of the conventional bioreactor. This result was also confirmed by the experimental study, implying the performance of the conventional bioreactor can be significantly enhanced by changing the geometrical configuration to a tapered form. Moreover, the rate‐limiting step of acetate methanogenesis in the bioreactors was reaction‐controlled and the biofilm was fully

ISSN:0268-2575    

DOI:10.1002/jctb.280630408

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThis research deals with the oxidation of thioxanthen‐9‐one with the superoxide anion to the sulfoxide and to the sulfone. We were also interested in determining whether the thioxanthen‐9‐one could be oxidized further to carbon dioxide. The experiments revealed that no carbon dioxide was formed from the oxidation of thioxanthen‐9‐one. However, it was found that carbon dioxide was formed from the anode reacting with the super

ISSN:0268-2575    

DOI:10.1002/jctb.280630409

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe kinetics of alcoholic fermentation of a strain ofZymomonas mobilis, isolated from sugarcane juice, has been studied with the objective of determining the constansts of a non‐structured mathematical model that represents the fermentation process. Assays in batch and in continuous culture have been carried out with different initial concentrations of glucose. The final concentrations of glucose, ethanol and biomass were determined. The following kinetic parameters were obtained: μmax, 0·5 h−1;Ks, 4·64 g dm−3;Pmax, 106 g dm−3;Yx/s, 0·0265 g g−1;m, 1·4 g g−1h−1; α, 17·38 g g

ISSN:0268-2575    

DOI:10.1002/jctb.280630410

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe kinetics of the reaction between acetic acid and epichlorohydrin in the presence of lithium, sodium and potassium acetates have been studied. The composition of the reaction mixture was followed chromatographically. Beside the two isomeric products of addition of epichlorohydrin to acetic acid, the presence was found of glycidyl acetate, glycerine dichlorohydrin and other products of parallel and subsequent reactions between the substrates and chlorohydroxyesters. A mechanism of the reaction, which takes into account the formation of the identified compounds has been proposed and a set of appropriate differential and balance equations developed. The rate constants for individual reactions as well as the catalysts used have been determined.

ISSN:0268-2575    

DOI:10.1002/jctb.280630411

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY