geraniol kinetic study and mechanism[1]

"geraniol"

"kinetic study and mechanism"

Bibliographic Information

Kinetics and re action mechanism of the controlled oxidation of some industrial alcohols by haloamines. Prabhu, D. V. Department of Chemistry, Wilson College (University of Mumbai), Mumbai, India. Journal of the Indian Chemical Society (2007), 84(11), 1135-1139. Publisher: Indian Chemical Society

Abstract

A kinetic study of the controlled oxidn. of perfumery alcs., geraniol, 1-Ph ethanol and benzyl alc. by Chloramine T in alk. medium and Chloramine B in acidic medium has been carried out in the temp. range 30 C to 50 C. The oxidn. was monitored in the micellar phase using sodium dodecyl sulfate. The oxidn. rate increases with alc. concn. but decreases with the concn. of the oxidising reagent and varies linearly with the concn. of the metal ion catalysts used. The thermodn. activation parameters have been calcd.


Oxidation of primary alcohols by quinolinium dichromate. A kinetic probe. Nongkynrih, I.; Dkhar, J. C.; Kharpuria, E.; Mahanti, M. K. Department of Chemistry, North-Eastern Hill University, Shillong, India. Oxidation Communications (2007), 30(1), 82-87. Publisher: SciBulCom Ltd., Abstract

The oxidn. of primary alcs. by quinolinium dichromate, in acid medium, gave the corresponding aldehydes. The reaction was first order in each - substrate, oxidant and acid. The mechanistic pathway involved the formation of a cyclic chromate ester, which underwent decompn., in the rate-detg. step, to give the product.


An integrated process: Ester synthesis in an enzymatic membrane reactor and water sorption. Trusek-Holownia, Anna; Noworyta, Andrzej. Chemical and Biochemical Processes, Wroclaw University of Technology, Wroclaw, Pol. Journal of Biotechnology (2007), 130(1), 47-56. Publisher: Elsevier B.V.,

Abstract

In the case of such reactions as ester synthesis, water is produced during the reaction. Because these reactions are carried out in hydrophobic solvents an addnl. (water) phase in the system must not be allowed, i.e. the concn. of water satn. in the org. solvent should not be exceeded. In such a case, the reaction kinetics and product equil. concn. undergo undesirable changes because of the partition coeff. of the components and hampered process of product sepn. Hence, removal of the water produced in the reaction dets. whether the process is successful or not. For this purpose, the integrated process with water sorption in the column with mol. sieves was applied. Integration of the process of synthesis and dehydration of a reaction phase, in which a biocatalyst is suspended and not dissolved as in water solns., requires holding up of the catalyst in the reactor before directing the stream of reaction mixt. to dehydration process. This hold-up and a possibility of multiple use of the catalyst may be accomplished by using a sepg. barrier, e.g. an ultrafiltration membrane or by permanent fixing of the catalyst to the matrix, e.g. a polymeric membrane. The efficiency and activity of a biocatalyst (lipase CAL-B) immobilized on a polymer membrane by sorption and chem. binding, were detd. A subject of study was the synthesis of geranyl acetate, one of the most known arom. compd. A hydrophobic (polypropylene)

matrix was shown to be a much better carrier in the reactions performed in an org. solvent than a hydrophilic (polyamide) membrane being tested. The reaction kinetics of geranyl acetate synthesis with the use of geraniol and acetic acid as substrates, was described by the equation defining the "Ping-Pong Bi Bi" mechanism that was related addnl. to the inhibition of a substrate (acetic acid). The following consts.of kinetic equation were obtained k'3 = 0.344 mol g-1 h1, KmA = 0.257 mol l-1, KmG = 1.629 and KiA = 0.288 for the native enzyme and vmax,Gel = 111.579 mol l-1 h1, KmA = 0.255 mol l-1, KmG = 1.91 mol l-1, KiA = 0.238 mol l-1 for the one immobilized by sorption on a polypropylene membrane. Half-life time of the native enzyme activity was 204 h and stability of the immobilized prepn. was 70 h. With respect to the reaction kinetics and stability of the native enzyme and immobilized prepn., from both types of membrane bioreactor more attractive appears to be the one in which the membrane is used not as a catalyst layer but only as a barrier that immobilizes the native enzyme within the bioreactor vol. When an integrated process proceeds, the method to collect water in the sorption column during the process, appeared to work very well. The reaction proceeded with a very high efficiency (after 120 h = 98.2% for native enzyme and 83.2% for immobilized enzyme) and due to low water concn. in the system (0.000% vol./vol.) the second phase was not created.


Olefin epoxidation with hydrogen peroxide catalyzed by lacunary polyoxometalate [ -SiW10O34(H2O)2]4-. Kamata, Keigo; Kotani, Miyuki; Yamaguchi, Kazuya; Hikichi, Hiro; Mizuno, Noritaka. Core Res. Evolutional Sci. Technol. (CREST), Japan Sci Technol. Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama, Japan. Chemistry--A European Journal (2007), 13(2), 639-648. Publisher: Wiley-VCH Verlag GmbH & Co. KGaA, CODEN: CEUJED ISSN: 0947-6539. Journal written in English. CAN 146:316397 AN 2007:75043 CAPLUS (Copyright (C) 2007 ACS on SciFinder (R))

Abstract

The tetra-n-butylammonium (TBA) salt of the divacant Keggin-type polyoxometalate [TBA]4[-SiW10O34(H2O)2] (I) catalyzes the oxygen-transfer reactions of olefins, allylic alcs., and sulfides with 30% aq. hydrogen peroxide. The neg. Hammett + (-0.99) for the competitive oxidn. of p-substituted styrenes and the low value of (nucleophilic oxidn.)/(total oxidn.), XSO = 0.04, for I-catalyzed oxidn. of thianthrene 5-oxide (SSO) reveals that a strongly electrophilic oxidant species is formed on I. The preferential formation of trans-epoxide during epoxidn. of 3-methyl-1-cyclohexene demonstrates the steric constraints of the active site of I. The I-catalyzed epoxidn. proceeds with an induction period that disappears upon treatment of I with hydrogen peroxide. 29Si and 183W NMR spectroscopy and CSI mass spectrometry show that reaction of I with excess hydrogen peroxide leads to fast formation of a diperoxo species, [TBA]4[-SiW10O32(O2)2] (II), with retention of a -Keggin type structure. Whereas the isolated compd. II is inactive for stoichiometric epoxidn. of cyclooctene, epoxidn. with II does proceed in the presence of hydrogen peroxide. The reaction of II with hydrogen peroxide would form a reactive species (III), and this step corresponds to the induction period obsd. in the catalytic epoxidn. The steric and electronic characters of III are the same as those for the catalytic epoxidn. by I. Kinetic, spectroscopic, and mechanistic investigations show that the present epoxidn. proceeds via III.


Effect of Internal Diffusion in Supported Ionic Liquid Catalysts: Interaction with Kinetics. Mikkola, Jyri-Pekka; Waern, Johan; Virtanen, Pasi; Salmi, Tapio. Laboratory of Industrial Chemistry, Process Chemistry Centre, Abo Akademi University, Abo-Turku, Finland. Industrial & Engineering Chemistry Research (2007), 46(12), 3932-3940. Publisher: American Chemical Society, CODEN: IECRED ISSN: 0888-5885. Journal written in English. CAN 146:464064 AN 2006:1221417 CAPLUS (Copyright (C) 2007 ACS on SciFinder (R))

Abstract

Kinetics and mass transfer for supported ionic liq. catalysts (SILCAs) were studied for complex catalytic hydrogenations of unsatd. aldehydes. The system can be characterized as a gas-liq.-liq.-solid system, where gaseous hydrogen and an unsatd. aldehyde, citral, diffuse from mol. solvent to a thin layer of ionic liq. contg. the catalytically active species, metallic Pd nanoparticles. The intrinsic kinetics was detd. at 353-423 K (80-150) and pressures of 10 to 50 bar. A kinetic model was proposed that predicts exptl. concn. data successfully. In order to obtain more understanding about the importance of mass-transfer and diffusion limitations for these processes, a no. of models describing the concn. profiles of the reactants in the catalysts were developed. The reaction-diffusion models revealed important insight into the potential limiting phenomena for this type of reaction systems.


Solvent effects in liquid-phase reactions. II. Kinetic modeling for citral hydrogenation. Mukherjee, Samrat; Vannice, M. Albert. Department of Chemical Engineering, Pennsylvania State University, University Park, PA, USA. Journal of Catalysis (2006), 243(1), 131-148. Publisher: Elsevier Ltd., CODEN: JCTLA5 ISSN: 0021-9517. Journal written in English. CAN 145:489409 AN 2006:935263 CAPLUS (Copyright (C) 2007 ACS on SciFinder (R))

Abstract

The initial liq.-phase reaction to hydrogenate any of the three unsatd. bonds in the citral mol. can be described by a Langmuir-Hinshelwood (LH) mechanism that assumes that mol. citral and H atoms are the two most abundant reaction intermediates. It was applicable with each of the eight solvents studied; however, a wide range of values was obtained for the two adsorption equil. consts. contained in the optimized rate equation, Kcit and KH2. Regarding the rate of overall citral disappearance, four possible solvent effects-mass transfer limitations, liq.-phase H2 soly., liq.-phase nonideality, and competitive solvent adsorption - were evaluated in detail to see whether one of them could account for the 3-fold variation in turnover frequency and possibly decrease the variation in adsorption equil. consts. Using the Weisz-Prater criterion established the absence of mass transfer limitations, using H2 concn. provided no benefit, and including thermodn. activity coeffs. for citral gave only minimal benefit. However, introducing solvent adsorption into the site balance equation revealed that a narrow range exists for a single apparent rate const. that is applicable for all of the solvents, makes the KH2 values essentially invariant, and reduces the range of Kcit values to a factor of 7. Kinetic studies at three temps. gave adsorption equil. consts. that provided consistent, meaningful values for the enthalpy and entropy of adsorption for citral, H2, and the solvent. Consequently, this is the best single explanation for the obsd. kinetic behavior. Finally, individual rates of formation were calcd. for the unsatd. alc. (geraniol and nerol) vs. the partially satd. aldehyde (citronellal) and the proposed LH model, either including or excluding competitive solvent adsorption, was able to describe each rate simultaneously using the same optimized adsorption equil. consts. Including the solvent in the rate expression again showed that a single set of apparent rate consts.can exist that simultaneously describe the three reactions. Thermodn. consistency of the adsorption equil. consts. for citral, H2, and the solvent was obtained in all cases.


Inverse temperature dependence due to catalyst deactivation in liquid phase citral hydrogenation over Pt/Al2O3. Maeki-Arvela, Paeivi; Kumar, Narendra; Eraenen, Kari; Salmi, Tapio; Murzin, Dmitry Yu. Process Chemistry Centre, Abo Akademi University, Turku/Abo, Finland. Chemical Engineering Journal (Amsterdam, Netherlands) (2006), 122(3), 127-134. Publisher: Elsevier B.V., CODEN: CMEJAJ ISSN: 1385-8947. Journal written in English. CAN 145:473412 AN 2006:904460 CAPLUS (Copyright (C) 2007 ACS on SciFinder (R))

Abstract

Citral hydrogenation was studied over a Pt/Al2O3 catalysts in cyclohexane and in 2-pentanol. Several kinetic trends, which were correlated to catalyst deactivation, were achieved. Accumulation of trans

isomers in both citral and in unsatd. alcs. was visible under deactivating conditions. The further hydrogenation of citronellal was nearly totally inhibited due to catalyst deactivation, whereas nerol, geraniol and citronellol formation were enhanced at higher temps. and pressures. The main unusual kinetic phenomena in citral hydrogenation in 2-pentanol were, first, a max. obsd. in the initial hydrogenation rates as a function of temp. caused by catalyst deactivation and, second, a min. in citral conversion after prolonged reaction times. The reason for these unusual kinetic phenomena is decarbonylation reaction occurring during hydrogenation, i.e. formation of CO, which was confirmed by temp. programmed desorption of geraniol from a reduced Pt/Al2O3 catalyst.


New Insights into the Mechanism of Palladium-Catalyzed Allylic Amination. Watson, Iain D. G.; Yudin, Andrei K. Davenport Research Laboratories, Department of Chemistry, University of Toronto, Toronto, ON, Can. Journal of the American Chemical Society (2005), 127(49), 17516-17529. Publisher: American Chemical Society, CODEN: JACSAT ISSN: 0002-7863. Journal written in English. CAN 144:128517 AN 2005:1208245 CAPLUS (Copyright (C) 2007 ACS on SciFinder (R))

Abstract

A comparative study into palladium-catalyzed allylic amination of unsubstituted aziridines and secondary amines was carried out. The use of NH aziridines as nucleophiles favors formation of valuable branched products in the case of aliph. allyl acetates. The regioselectivity of this reaction is opposite to that obsd. when other amines are used as nucleophiles. Study provides evidence for the palladium-catalyzed isomerization of the branched (kinetic) product formed with common secondary amines into the thermodn. (linear) product. But the branched allyl products obtained from unsubstituted aziridines do not undergo the isomerization process. Crossover expts. indicate that the isomerization of branched allylamines is bimol. and is catalyzed by Pd0. The reaction has significant solvent effect, giving the highest branched-to-linear ratios in THF. This finding can be explained by invoking the intermediacy of -complexes, which is consistent with NMR data. The apparent stability of branched allyl aziridines towards palladium-catalyzed isomerization is attributed to a combination of factors that stem from a higher degree of s-character of the aziridine nitrogen compared to other amines. The reaction allows for regio- and enantioselective incorporation of aziridine rings into appropriately functionalized building blocks. The resulting methodol. addresses an important issue of forming quaternary carbon centers next to nitrogen. The new insights into the mechanism of palladium-catalyzed allylic amination obtained in this study should facilitate synthesis of complex heterocycles, design of new ligands to control branched-to-linear ratio, as well as abs. stereochem. of allylamines.


Biocatalysis using lipase encapsulated in microemulsion-based organogels in supercritical carbon dioxide. Blattner, Christian; Zoumpanioti, Maria; Kroener, Juergen; Schmeer, Georg; Xenakis, Aristotelis; Kunz, Werner. Institut fuer Physikalische und Theoretische Chemie, Universitaet Regensburg, Regensburg, Germany. Journal of Supercritical Fluids (2006), 36(3), 182-193. Publisher: Elsevier B.V., CODEN: JSFLEH ISSN: 0896-8446. Journal written in English. CAN 144:106692 AN 2005:1165640 CAPLUS (Copyright (C) 2007 ACS on SciFinder (R))

Abstract

Lipases from Candida antarctica and Mucor miehei were encapsulated in lecithin water-in-oil (w/o) microemulsion-based organogels (MBG). These gels were formulated with either hydroxypropylmethyl cellulose (HPMC) or gelatin. The esterification of lauric acid and 1-propanol catalyzed by these MBGs was examd. in supercrit. carbon dioxide (scCO2; 35 C, 110 bar) as solvent for the substrates. The results were compared to those obtained with the ref. substrate solvent isooctane. It turned out that the initial rates of this model reaction in scCO2 were higher than those obsd. in the ref. system. Various parameters affecting the biocatalysis such as pressure, alc. and acid chain length, and gel compn. were investigated. Kinetic studies showed that the ester synthesis catalyzed by the immobilized C. antarctica

lipase occurs via a Ping Pong Bi Bi mechanism in which only inhibition by excess of alc. was identified. Values of all kinetic parameters were detd. In addn., expts. on the reusability of these gels in scCO2 were carried out and the state of water within the organogel was examd. with the help of differential scanning calorimetry. The present study shows that biocatalysis using MBGs in scCO2 is a promising alternative to other bioconversion processes.


Enantioselective epoxidation of allylic alcohols by a chiral complex of vanadium: An effective controller system and a rational mechanistic model. Zhang, Wei; Basak, Arindrajit; Kosugi, Yuji; Hoshino, Yujiro; Yamamoto, Hisashi. Department of Chemistry, The University of Chicago, Chicago, IL, USA. Angewandte Chemie, International Edition (2005), 44(28), 4389-4391. Publisher: Wiley-VCH Verlag GmbH & Co. KGaA, CODEN: ACIEF5 ISSN: 1433-7851. Journal written in English. CAN 143:306086 AN 2005:683217 CAPLUS (Copyright (C) 2007 ACS on SciFinder (R))

Abstract

Epoxy alcs. are prepd. enantioselectively in 24-91% yields and in 92-97% ee by oxidn. of either (E)- or (Z)-disubstituted and trisubstituted allylic alcs. with aq. tert-Bu hydroperoxide (TBHP) in the presence of catalysts generated from oxovanadium triisopropoxide and bishydroxamic acids I [R = Ph2CH, Ph3CCH2, (3,5-Me2C6H3)2CH]. Aq. TBHP is an effective oxidant for the epoxidn. reactions; the use of anhyd. TBHP does not increase either the enantioselectivities or yields of epoxidn. reactions. Epoxidn. reactions can be performed at either 0 or room temp. without significant losses in enantioselectivity if the substrates react slowly at -20. Small allylic alcs. such as (E)- and (Z)-crotyl alcs. undergo stereo- and enantioselective epoxidns. using cumene hydroperoxide as the oxidant in the presence of oxovanadium triisopropoxide and I [R = Ph2CH, Ph3CCH2, (3,5-Me2C6H3)2CH]. PhCH(OH)CH:CH2 undergoes kinetic resoln. with aq. TBHP in the presence of oxovanadium triisopropoxide and I (R = Ph2CH) to yield (R)-PhCH(OH)CH:CH2 in 95% ee and epoxy alc. II in 93% ee.

NOH

OHN

O

O

O

HO

Ph

H

R

R I II


Remarkable Substituent Effects on the Oxidizing Ability of Triarylbismuth Dichlorides in Alcohol Oxidation. Matano, Yoshihiro; Hisanaga, Teppei; Yamada, Hisatsugu; Kusakabe, Shingo; Nomura, Hazumi; Imahori, Hiroshi. Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Nishikyo, Kyoto, Japan. Journal of Organic Chemistry (2004), 69(25), 8676-8680. Publisher: American Chemical Society, CODEN: JOCEAH ISSN: 0022-3263. Journal written in English. CAN 142:114195 AN 2004:973496 CAPLUS (Copyright (C) 2007 ACS on SciFinder (R))

Abstract

Substituent effects on the oxidizing ability of triarylbismuth dichlorides were examd. by intermol. and intramol. competition expts. on geraniol oxidn. in the presence of DBU. The oxidizing ability of the dichlorides increases with increasing electron-withdrawing ability of the para substituents, and by introduction of a Me group at the ortho position of the aryl ligands attached to the Bi. The intermol. and intramol. H/D kinetic isotope effects obsd. for the competitive oxidn. of p-bromobenzyl alcs. indicate that the rate-detg. step involves C-H bond cleavage. Several primary and secondary alcs. were oxidized

efficiently under mild conditions by the combined use of newly developed organobismuth(V) oxidants and DBU.


Highly selective, recyclable epoxidation of allylic alcohols with hydrogen peroxide in water catalyzed by dinuclear peroxotungstate. Kamata, Keigo; Yamaguchi, Kazuya; Mizuno, Noritaka. Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency, Kawaguchi, Japan. Chemistry--A European Journal (2004), 10(19), 4728-4734. Publisher: Wiley-VCH Verlag GmbH & Co. KGaA, CODEN: CEUJED ISSN: 0947-6539. Journal written in English. CAN 142:6068 AN 2004:873380 CAPLUS (Copyright (C) 2007 ACS on SciFinder (R))

Abstract

The highly chemo-, regio-, and diastereoselective and stereospecific epoxidn. of various allylic alcs. with only one equiv. of hydrogen peroxide in water can be efficiently catalyzed by the dinuclear peroxotungstate, K2[{W(=O)(O2)2(H2O)}2(-O)] 2H2O (I). The catalyst is easily recycled while maintaining its catalytic performance. The catalytic reaction mechanism including the exchange of the water ligand to form the tungsten-alcoholate species followed by the insertion of oxygen to the carbon-carbon double bond, and the regeneration of the dinuclear peroxotungstate with hydrogen peroxide is proposed. The reaction rate shows first-order dependence on the concns. of allylic alc. and dinuclear peroxotungstate and zero-order dependence on the concn. of hydrogen peroxide. These results, the kinetic data, the comparison of the catalytic rates with those for the stoichiometric reactions, and kinetic isotope effects indicate that the oxygen transfer from a dinuclear peroxotungstate to the double bond is the rate-limiting step for terminal allylic alcs. such as 2-propen-1-ol (1a).


Micelle-Hosted Palladium Nanoparticles Catalyze Citral Molecule Hydrogenation in Supercritical Carbon Dioxide. Meric, Pascal; Yu, Kai Man K.; Tsang, Shik Chi. Surface and Catalysis Research Centre, School of Chemistry, University of Reading, Whiteknights, Reading, Berkshire, UK. Langmuir (2004), 20(20), 8537-8545. Publisher: American Chemical Society, CODEN: LANGD5 ISSN: 0743-7463. Journal written in English. CAN 141:367612 AN 2004:694308 CAPLUS (Copyright (C) 2007 ACS on SciFinder (R))

Abstract

Metal particles on micelles were used as catalysts in hydrogenation of org. mols. in the presence of fluorinated surfactant and water in supercrit. carbon dioxide (scCO2). Direct visual evidence of formation of metal microemulsions and the mechanism by which metal located in the soft micellar assemblies affects the reaction selectivity are presented. The Pd nanoparticles were incorporated into perfluorohydrocarboxylate anionic micelles in scCO2 in a stainless steel batch reactor at 40 in a 150 bar CO2/H2 mixt. Homogeneous dispersion of the microemulsion contg. Pd nanoparticles in scCO2 was obsd. through a sapphire window of the reactor at W0 ratio (molar water-to-surfactant ratio) of 2 - 30. The micelle assemblies as metal catalyst nanocarriers were evaluated for product selectivity. The hydrogenation of citral, which contains three reducible groups (aldehyde, double bonds at the 2,3-position and the 6,7-position) was studied. An unusually high selectivity toward citronellal (a high regioselectivity toward the redn. of the 2,3-unsatn.) was obsd. in scCO2. When the reaction was carried out in a conventional liq. or vapor phase over the same reaction time, total hydrogenation of the two double bonds was achieved. The high kinetic reluctance for double bond hydrogenation of the citral mol. at the hydrophobic end (the 6,7-position) is due to the unique micelle environment that is in close proximity to the metal surface in scCO2, which guides a head-on attack of the mol. toward the core metal particle.


Scope, kinetics, and mechanistic aspects of aerobic oxidations catalyzed by ruthenium

supported on alumina. Yamaguchi, Kazuya; Mizuno, Noritaka. Department of Applied Chemistry, School of Engineering, The University of Tokyo, Tokyo, Japan. Chemistry--A European Journal (2003), 9(18), 4353-4361. Publisher: Wiley-VCH Verlag GmbH & Co. KGaA, CODEN: CEUJED ISSN: 0947-6539. Journal written in English. CAN 140:4715 AN 2003:788357 CAPLUS (Copyright (C) 2007 ACS on SciFinder (R))

Abstract

The Ru/Al2O3 catalyst was prepd. by modification of the prepn. of Ru(OH)3nH2O. The present Ru/Al2O3 catalyst has high catalytic activities for the oxidns. of activated, nonactivated, and heterocyclic alcs., diols, and amines at 1 atm of mol. O. Also, the catalyst could be reused seven times without a loss of catalytic activity and selectivity for the oxidn. of benzyl alc. A catalytic reaction mechanism involving a Ru alcoholate species and -hydride elimination from the alcoholate was proposed. The reaction rate has a first-order dependence on the amt. of catalyst, a fractional order on the concn. of benzyl alc., and a zero order on the pressure of mol. O. These results and kinetic isotope effects indicate that -elimination from the Ru alcoholate species is a rate-detg. step.


Cu(ii)-nitroxyl radicals as catalytic galactose oxidase mimics. Dijksman, Arne; Arends, Isabel W. C. E.; Sheldon, Roger A. Laboratory for Biocatalysis and Organic Chemistry, Department of Biotechnology, Delft University of Technology, Delft, Neth. Organic & Biomolecular Chemistry (2003), 1(18), 3232-3237. Publisher: Royal Society of Chemistry, CODEN: OBCRAK ISSN: 1477-0520. Journal written in English. CAN 140:16455 AN 2003:709470 CAPLUS (Copyright (C) 2007 ACS on SciFinder (R))

Abstract

Results from Hammett correlation studies and primary kinetic isotope effects for the CuCl-TEMPO catalyzed aerobic benzyl alc. oxidns. are inconsistent with an oxoammonium based mechanism. We postulate a copper-mediated dehydrogenation mechanism, in which TEMPO regenerates the active Cu(ii)-species. This mechanism is analogous to that obsd. for galactose oxidase and mimics thereof.


Linalool to geraniol/nerol isomerization catalyzed by (RO)3VO complexes: studies of kinetics and mechanism. Semikolenov, V. A.; Ilyna, I. I.; Maksimovskaya, R. I. Boreskov Institute of Catalysis, Novosibirsk, Russia. Journal of Molecular Catalysis A: Chemical (2003), 204-205 201-210. Publisher: Elsevier Science B.V., CODEN: JMCCF2 ISSN: 1381-1169. Journal written in English. CAN 140:59784 AN 2003:697990 CAPLUS (Copyright (C) 2007 ACS on SciFinder (R))

Abstract

Highly selective catalytic system {(RO)3VO+[(Bu)4N+]OH} for the process of linalool to geraniol + nerol isomerization within the temp. range of 413-513 K is reported. Using the 51V NMR spectroscopy, compn. and reactivity of vanadium complexes formed in the catalytic system were investigated. Mononuclear vanadium complexes (RO)3-n(R'O)nVO, where RO-linalyl and R'O-geranyl/neryl ligands, n=0, 1 and 2, are active in the isomerization reaction. The reaction of the ligand {linalool/(geraniol+nerol)} exchange is very fast and reversible, the equil. const. of this reaction was estd. The rate detg. step of the isomerization process is the rearrangement of the coordinated to vanadium linalyl- to geranyl/neryl ligands which, probably, proceeds via redn.-oxidn. mechanism. The isomerization of linalool is a reversible reaction and two isomers (geraniol and nerol) are formed by the parallel routs. The equil. const. of the linalool/(geraniol+nerol) as well as geraniol/nerol isomerization slightly depends on temp. The reaction rate is of the first-order on linalool, geraniol and nerol concns. The kinetic scheme and mechanism of linalool to geraniol+nerol isomerization are suggested.


Epoxidation of Allylic Alcohols with TiO2-SiO2: Hydroxy-Assisted Mechanism and Dynamic Structural Changes During Reaction. Beck, C.; Mallat, T.; Baiker, A. Swiss Federal Institute of Technology, Institute for Chemical- and Bioengineering, ETH Hoenggerberg, Zurich, Switz. Catalysis Letters (2003), 88(3-4), 203-209. Publisher: Kluwer Academic/Plenum Publishers, CODEN: CALEER ISSN: 1011-372X. Journal written in English. CAN 139:245575 AN 2003:426562 CAPLUS (Copyright (C) 2007 ACS on SciFinder (R))

Abstract

Epoxidn. of allylic alcs. and cyclohexene with TBHP and titania-silica aerogels contg. 1 and 5 wt% TiO2 has been studied. For the oxidn. of geraniol and cyclohexenol, the regio- and diastereoselectivities and kinetic data indicate an OH-assisted mechanism involving a dative bond between the OH group and the Ti site. This mechanism is disabled in the oxidn. of cyclooctenol due to steric hindrance. The moderate regio- and diastereoselectivities of the aerogels, compared with those of TS-1 and the homogeneous model Ti(OSiMe3)4, are attributed to the presence of non-isolated Ti sites and to a "silanol-assisted" mechanism, according to which model the allylic alc. is anchored to a neighboring SiOH group instead of the Ti-peroxo complex. Kinetic anal. of the initial transient period revealed rapid catalyst restructuring during the first few turnovers. A feasible explanation is the breaking of Si-O-Ti linkages of the carefully predried aerogels by water or TBHP, resulting in active Ti sites with remarkably different catalytic properties.


Oxygen Transfer from Sulfoxides: Selective Oxidation of Alcohols Catalyzed by Polyoxomolybdates. Khenkin, Alexander M.; Neumann, Ronny. Department of Organic Chemistry, Weizmann Institute of Science, Rehovot, Israel. Journal of Organic Chemistry (2002), 67(20), 7075-7079. Publisher: American Chemical Society, CODEN: JOCEAH ISSN: 0022-3263. Journal written in English. CAN 137:352596 AN 2002:667570 CAPLUS (Copyright (C) 2007 ACS on SciFinder (R))

Abstract

Benzylic, allylic, and aliph. alcs. are oxidized to aldehydes and ketones in a reaction catalyzed by Keggin-type polyoxomolybdates, PVxMo(12-x)O40-(3+x) (x = 0, 2), with DMSO as a solvent. The oxidn. of benzylic alcs. is quant. within hours and selective, whereas that of allylic alcs. is less selective. Oxidn. of aliph. alcs. is slower but selective. Further mechanistic studies revealed that, for H3PMo12O40 as a catalyst and benzylic alcs. as substrates, the sulfoxide is in fact an oxygen donor in the reaction. Postulated reaction steps as detd. from isotope-labeling expts., kinetic isotope effects, and Hammett plots include (a) sulfoxide activation by complexation to the polyoxometalate and (b) oxygen transfer from the activated sulfoxide and elimination of water from the alc. The mechanism is supported by the reaction kinetics.


Efficient and Selective Aerobic Oxidation of Alcohols into Aldehydes and Ketones Using Ruthenium/TEMPO as the Catalytic System. Dijksman, Arne; Marino-Gonzalez, Arturo; Mairata i Payeras, Antoni; Arends, Isabel W. C. E.; Sheldon, Roger A. Laboratory for Organic Chemistry and Catalysis Department of Biotechnology, Delft University of Technology, Delft, Neth. Journal of the American Chemical Society (2001), 123(28), 6826-6833. Publisher: American Chemical Society, CODEN: JACSAT ISSN: 0002-7863. Journal written in English. CAN 135:180370 AN 2001:446655 CAPLUS (Copyright (C) 2007 ACS on SciFinder (R))

Abstract

The combination of RuCl2(PPh3)3 and TEMPO affords an efficient catalytic system for the aerobic oxidn.

of a variety of primary and secondary alcs., giving the corresponding aldehydes and ketones in >99% selectivity in all cases. The Ru/TEMPO system displayed a preference for primary vs secondary alcs. Results from Hammett correlation studies ( = -0.58) and the primary kinetic isotope effect (kH/kD = 5.1) for the catalytic aerobic benzyl alc. oxidns. are inconsistent with either an oxoruthenium (O:Ru) or an oxoammonium based mechanism. Therefore, a hydridometal mechanism, involving a RuH2(PPh3)3 species as the active catalyst is postulated. TEMPO acts as a hydrogen transfer mediator and is either regenerated by oxygen, under catalytic aerobic conditions, or converted to TEMPH under stoichiometric anaerobic conditions.


Mouse alcohol dehydrogenase 4: kinetic mechanism, substrate specificity and simulation of effects of ethanol on retinoid metabolism. Plapp, B. V.; Mitchell, J. L.; Berst, K. B. Department of Biochemistry, The University of Iowa, Iowa City, IA, USA. Chemico-Biological Interactions (2001), 130-132(1-3), 445-456. Publisher: Elsevier Science Ireland Ltd., CODEN: CBINA8 ISSN: 0009-2797. Journal written in English. CAN 135:30646 AN 2001:259618 CAPLUS (Copyright (C) 2007 ACS on SciFinder (R))

Abstract

Mouse ADH4 (purified, recombinant) has a low catalytic efficiency for ethanol and acetaldehyde, but very high activity with longer chain alcs. and aldehydes, at pH 7.3 and temp. 37C. The obsd. turnover nos. and catalytic efficiencies for the oxidn. of all-trans-retinol and the redn. of all-trans-retinal and 9-cis-retinal are low relative to other substrates; 9-cis-retinal is more reactive than all-trans-retinal. The redn. of all-trans- or 9-cis-retinals coupled to the oxidn. of ethanol by NAD+ is as efficient as the redn. with NADH. However, the Michaelis const. for ethanol is about 100 mM, which indicates that the activity would be lower at physiol. relevant concns. of ethanol. Simulations of the oxidn. of retinol to retinoic acid with mouse ADH4 and human aldehyde dehydrogenase (ALDH1), using rate consts. estd. for all steps in the mechanism, suggest that ethanol (50 mM) would modestly decrease prodn. of retinoic acid. However, if the Km for ethanol were smaller, as for human ADH4, the rate of retinol oxidn. and formation of retinoic acid would be significantly decreased during metab. of 50 mM ethanol. These studies begin to describe quant. the roles of enzymes involved in the metab. of alcs. and carbonyl compds.


A novel chitosan derivative to immobilize -L-rhamnopyranosidase from Aspergillus niger for application in beverage technologies. Spagna, G.; Barbagallo, R. N.; Casarini, D.; Pifferi, P. G. Food Biotechnology Group from the Department of Horticulture, Floriculture, Arboriculture and Agroindustrial Technology (DOFATA), University of Catania, Catania, Italy. Enzyme and Microbial Technology (2001), 28(4-5), 427-438. Publisher: Elsevier Science Ireland Ltd., CODEN: EMTED2 ISSN: 0141-0229. Journal written in English. CAN 134:339824 AN 2001:163317 CAPLUS (Copyright (C) 2007 ACS on SciFinder (R))

Abstract

-L-rhamnopyranosidase (Rha, EC 3.2.1.40) is an enzyme of considerable importance to food technol. in increasing the aroma of wines, musts, fruit juices and other beverages. The aim of this research is the immobilization of the Rha contained in a com. prepn. already used in the winemaking industry. The immobilization supports tested were chitin, chitosan and derivatized chitosan, diethylaminoethyl chitosan (DE-chitosan) never previously used for this type of application. Particularly, on DE-chitosan, the Rha was adsorbed and cross-linked with various bifunctional agents (glutaraldehyde, diepoxyoctane, suberimidate and carbodiimide), whose best results (immobilization yields and activity) were obtained with carbodiimide (EDC) that allowed a redn. in the involvement of the enzyme amine groups that are probably important in catalytic mechanism. In addn., the use of rhamnose and a succinimide (NHS) during crosslinking enhanced the action of the EDC and so increased the immobilization yield and activity. The immobilized Rha retained the kinetic parameters (Km and Vmax) of the free enzyme and increased

stability. Moreover, this biocatalyst allowed an increase in the aroma in a model wine soln. contg. glycosidic precursors with a marked redn. in specificity toward tertiary monoterpenols as compared to the free enzyme.


Oxidation of alcohols by quinolinium dichromate. A kinetic study. Nongkynrih, Irona; Kharpuria, Evarisa; Dkhar, John C.; Mahanti, Mahendra K. Department of Chemistry, North-Eastern Hill University, Shillong, India. Oxidation Communications (2000), 23(3), 399-407. Publisher: Bulgarian-English Academic Publishing House, PublishScieSet, CODEN: OXCODW ISSN: 0209-4541. Journal written in English. CAN 134:17222 AN 2000:763051 CAPLUS (Copyright (C) 2007 ACS on SciFinder (R))

Abstract

The oxidn. of alcs. (primary, secondary and allylic) by quinolinium dichromate, in acid medium, gave the corresponding carbonyl products. The dependence of rate coeffs. on acidity, and kinetic isotope effects support a mechanism in which the rate-detg. step involved the decompn. of a cyclic chromate ester in an electrocyclic manner involving six electrons. Being a Hueckel type system (4n + 2), this was an allowed process.


Inhibition of Escherichia coli porphobilinogen synthase using analogs of postulated intermediates. Jarret, Caroline; Stauffer, Frederic; Henz, Matthias E.; Marty, Maurus; Luond, Rainer M.; Bobalova, Janette; Schurmann, Peter; Neier, Reinhard. Institute of Chemistry, University of Neuchatel, Neuchatel, Switz. Chemistry & Biology (2000), 7(3), 185-196. Publisher: Elsevier Science Ltd., CODEN: CBOLE2 ISSN: 1074-5521. Journal written in English. CAN 133:27942 AN 2000:207755 CAPLUS (Copyright (C) 2007 ACS on SciFinder (R))

Abstract

Background: Porphobilinogen synthase is the second enzyme involved in the biosynthesis of natural tetrapyrrolic compds., and condenses two mols. of 5-aminolevulinic acid (ALA) through a nonsym. pathway to form porphobilinogen. Each substrate is recognized individually at two different active site positions to be regioselectively introduced into the product. According to pulse-labeling expts., the substrate forming the propionic acid sidechain of porphobilinogen is recognized first. Two different mechanisms for the first bond-forming step between the two substrates have been proposed. The first involves carbon-carbon bond formation (an aldol-type reaction) and the second carbon-nitrogen bond formation, leading to an iminium ion. Results: With the help of kinetic studies, we detd. the Michaelis consts. for each substrate recognition site. These results explain the Michaelis-Menten behavior of substrate analog inhibitors: they act as competitive inhibitors. Under std. conditions, however, another set of inhibitors demonstrates uncompetitive, mixed, pure irreversible, slow-binding or even quasi-irreversible inhibition behavior. Conclusions: Anal. of the different classes of inhibition behavior allowed us to make a correlation between the type of inhibition and a specific site of interaction. Analyzing the inhibition behavior of analogs of postulated intermediates strongly suggests that carbon-nitrogen bond formation occurs first.


An integrated process: ester synthesis in an enzymatic membrane reactor and water sorption. Trusek-Holownia Anna; Noworyta Andrzej Wroclaw University of Technology, Team of Chemical and Biochemical Processes, Norwida 4/6, 50-373 Wroclaw, Poland. [email protected] Journal of biotechnology (2007), 130(1), 47-56. Journal code: 8411927. ISSN:0168-1656. Journal; Article; (JOURNAL ARTICLE) written in English. PubMed ID 17434222 AN 2007257421 MEDLINE (Copyright (C) 2008 U.S. National Library of Medicine on SciFinder (R))

Abstract

In the case of such reactions as ester synthesis, water is produced during the reaction. Because these reactions are carried out in hydrophobic solvents an additional (water) phase in the system must not be allowed, i.e. the concentration of water saturation in the organic solvent should not be exceeded. In such a case, the reaction kinetics and product equilibrium concentration undergo undesirable changes because of the partition coefficient of the components and hampered process of product separation. Hence, removal of the water produced in the reaction determines whether the process is successful or not. For this purpose, the integrated process with water sorption in the column with molecular sieves was applied. Integration of the process of synthesis and dehydration of a reaction phase, in which a biocatalyst is suspended and not dissolved as in water solutions, requires holding up of the catalyst in the reactor before directing the stream of reaction mixture to dehydration process. This hold-up and a possibility of multiple use of the catalyst may be accomplished by using a separating barrier, e.g. an ultrafiltration membrane or by permanent fixing of the catalyst to the matrix, e.g. a polymeric membrane. The efficiency and activity of a biocatalyst (lipase CAL-B) immobilized on a polymer membrane by sorption and chemical binding, were determined. A subject of study was the synthesis of geranyl acetate, one of the most known aromatic compound. A hydrophobic (polypropylene) matrix was shown to be a much better carrier in the reactions performed in an organic solvent than a hydrophilic (polyamide) membrane being tested. The reaction kinetics of geranyl acetate synthesis with the use of geraniol and acetic acid as substrates, was described by the equation defining the "Ping-Pong Bi Bi" mechanism that was related additionally to the inhibition of a substrate (acetic acid). The following constants of kinetic equation were obtained k(3)(')=0.344 mol g(-1)h(-1), K(mA)=0.257 mol l(-1), K(mG)=1.629 and K(iA)=0.288 for the native enzyme and v(max,Gel)=111.579 mol l(-1)h(-1), K(mA)=0.255 mol l(-1), K(mG)=1.91 mol l(-1), K(iA)=0.238 mol l(-1) for the one immobilized by sorption on a polypropylene membrane. Half-life time of the native enzyme activity was 204 h and stability of the immobilized preparation was 70 h. With respect to the reaction kinetics and stability of the native enzyme and immobilized preparation, from both types of membrane bioreactor more attractive appears to be the one in which the membrane is used not as a catalyst layer but only as a barrier that immobilizes the native enzyme within the bioreactor volume. When an integrated process proceeds, the method to collect water in the sorption column during the process, appeared to work very well. The reaction proceeded with a very high efficiency (after 120 h alpha=98.2% for native enzyme and 83.2% for immobilized enzyme) and due to low water concentration in the system ( approximately 0.000% v/v) the second phase was not created.

geraniol kinetic study and mechanism[1]

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