- Biotransformation of some monoterpenoid ketones by chlorella vulgaris MCCS 012
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Biotransformation of several monoterpene ketones, including carvone, pulegone, piperitone, menthone, and fenchone, was carried out by the locally isolated unicellular microalgae Chlorella vulgaris. The microalgal strain was isolated during a screening program from soil samples collected from paddy-fields of Fars Province, in the south of Iran. Chlorella vulgaris was cultured in 250 mL conical flasks, each containing 50 mL of BG-11 liquid medium and 20μL levels of terpene substrates, incubated at a temperature of 28±2°C and illuminated continuously with fluorescent lamps with shaking at 80 rpm. The metabolites were identified by thin-layer chromatography and GC-MS. Chlorella vulgaris has the ability to reduce the C=C double bond of carvone to yield trans-dihydrocarvone and cis-dihydrocarvone. The cell line reduced menthone and pulegone to the same product and gave menthol. Study of Chlorella vulgaris with substrates of piperitone and fenchone showed no reaction in these substrates. Chlorella vulgaris MCCS 012 was assigned according to the 18S rRNA gene sequence. The DNA sequence of the 18S rRNA gene of Chlorella vulgaris MCCS 012 was recorded in the NCBI under the accession number EU374170.
- Ghasemi, Younes,Mohagheghzadeh, Abdolali,Ostovan, Zahra,Moshavash, Maryam,Rasoul-Amini, Sara,Morowvat, Mohammad Hossein
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Read Online
- Highly selective synthesis of menthols from citral in a one-step process
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We report for the first time the selective synthesis of menthols from citral in a one-step process. Bifunctional metal/acid catalysts active and selective for menthol synthesis were developed by studying the individual steps involved in the reaction pathway leading to menthols from citral. The metallic component was selected by testing silica-supported metals for citral hydrogenation to citronellal. Acid site requirements to efficiently isomerize citronellal to isopulegols were investigated on different solid acids. Potential bifunctional metal/acid catalysts were then prepared and tested for citral conversion to menthols. The best catalyst was Ni/Al-MCM-41, which yielded about 90% menthols and gave 70-75% of racemic (±)-menthol in the menthol mixture.
- Trasarti,Marchi,Apesteguia
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Read Online
- Catalytic transformations of citral in a continuous flow over bifunctional Ru-MCM-41 extrudates
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The three-step reaction of citral to menthol was investigated in an autoclave and a trickle-bed reactor over Ru-MCM-41 catalysts in powder and shaped forms, respectively, with the same composition and controlled metal location. All catalysts were characterized in detail and the results were correlated with catalytic tests. Activity and selectivity were strongly affected by controlling the location of Ru in the powder catalyst applied in the batch experiments. The catalyst with the largest distance between the metal and acid sites, and at the same time, with the highest total acidity,i.e.with Ru deposited exclusively on a binder Bindzil, displayed the highest yield of menthols. In contrast, in the trickle-bed reactor with extrudates the Ru location was of almost no importance which is related to mass transfer. Comparison between batch and continuous experiments also revealed significant differences in the product distribution. The highest yield of the desired menthol of 6% with stereoselectivity of 66% was obtained at a residence time of 12.5 min after 3 h of time-on-stream over egg-shell extrudates with Ru distribution at the outermost layer, deposition of Ru on both H-MCM-41 and the binder Bindzil, and the smallest Ru particle size.
- Er?nen, Kari,Kumar, Narendra,M?ki-Arvela, P?ivi,Murzin, Dmitry Yu.,Peurla, Markus,Vajglová, Zuzana
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Read Online
- Continuous synthesis of menthol from citronellal and citral over Ni-beta-zeolite-sepiolite composite catalyst
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One-pot continuous synthesis of menthols both from citronellal and citral was investigated over 5 wt% Ni supported on H-Beta-38-sepiolite composite catalyst at 60–70 °C under 10–29 bar hydrogen pressure. A relatively high menthols yield of 53% and 49% and stereoselectivity to menthol of 71–76% and 72–74% were obtained from citronellal and citral respectively at the contact time 4.2 min, 70 °C and 20 bar. Citral conversion noticeably decreased with time-on-stream under 10 and 15 bar of hydrogen pressure accompanied by accumulation of citronellal, the primary hydrogenation product of citral, practically not affecting selectivity to menthol. A substantial amount of defuctionalization products observed during citral conversion, especially at the beginning of the reaction (ca. 1 h), indicated that all intermediates could contribute to formation of menthanes. Ni/H-Beta-38-sepiolite composite material prepared by extrusion was characterized by TEM, SEM, XPS, XRD, ICP-OES, N2 physisorption and FTIR techniques to perceive the interrelation between the physico-chemical and catalytic properties.
- Er?nen, Kari,M?ki-Arvela, P?ivi,Martinez-Klimov, Mark,Muller, Joseph,Murzin, Dmitry Yu.,Peurla, Markus,Simakova, Irina,Vajglova, Zuzana
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- Method for preparing L-menthol by adopting modified homogeneous catalyst
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The invention discloses a method for preparing L-menthol by adopting a modified homogeneous catalyst. The method comprises the following steps: preparing a modified homogeneous catalyst, preparing isopulegol, preparing D, L-menthol, and preparing L-menthol; wherein a ligand is prepared from 2, 6-dimethylpyridine and a ketone compound by using the modified homogeneous catalyst, the ligand is reacted with alkyl aluminum to obtain an organic aluminum compound, and L-menthol is prepared by chemically inducing chiral resolution of D, L-menthol. According to the method, the organic aluminum compoundis used as the catalyst of the ring-closure reaction of citronellal, so that the yield of isopulegol is increased, the selectivity on product isopulegol is high, and the used organic aluminum catalyst is easy to synthesize, high in stereoselectivity to reaction and easy to crystallize and recover; D, L-menthol is split by a chemical induction method, the method is simple to operate, the reactionyield of each step is high, the reaction conditions are stable, the product cannot be partially racemized, and the product loss is small.
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Paragraph 0038; 0041-0042
(2020/03/09)
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- Continuous flow synthesis of menthol: Via tandem cyclisation-hydrogenation of citronellal catalysed by scrap catalytic converters
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A continuous flow synthesis of menthol starting from citronellal catalysed by scrap catalytic converters is reported. The reaction was conducted in a tandem system connecting in series two catalytic systems, with the first having Lewis acid properties (favouring the cyclisation of citronellal to isopulegols) and the second having hydrogenation catalytic activity (catalysing the hydrogenation of isopulegols to menthols). A Lewis acid catalyst was prepared by supporting iron oxide nanoparticles over a waste material, i.e. the ceramic core of scrap catalytic converters (SCATs) via a microwave assisted method. Most importantly, SCATs, containing a low residual noble metal content, could be directly employed in the second step as hydrogenation catalysts. The reaction was performed studying the influence on the yield and selectivity to (-)-menthol of various reaction parameters (T, p and flow rate). Under the best reaction conditions (at a flow rate of 0.1 mL min-1 and at 373 K and 413 K for cyclisation and hydrogenation steps respectively) a conversion of >99% of (+)-citronellal to (-)-menthol with 77% final yield was achieved.
- Zuliani, Alessio,Cova, Camilla Maria,Manno, Roberta,Sebastian, Victor,Romero, Antonio A.,Luque, Rafael
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p. 379 - 387
(2020/02/13)
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- Sodium Arenesulfinates-Involved Sulfinate Synthesis Revisited: Improved Synthesis and Revised Reaction Mechanism
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Reaction of alcohols with sodium arenesulfinates could afford either sulfones or sulfinates, and O-attack of sulfinate anions onto the in situ generated carbocation intermediates from alcohols was the previous proposed reaction mechanism in many syntheses of sulfinates. This concept, which is often used consciously or unconsciously, was revised herein by using isotopic labeling experiments and development of an improved sulfinate synthesis. The improved sulfinate synthetic protocol possesses many advantages such as a high sulfinate/sulfone selectivity, a broad substrate scope, metal-free, and mild reaction conditions. The revised reaction mechanism necessitates revision of many previous proposed reaction mechanisms in literatures.
- Ji, Yuan-Zhao,Li, Hui-Jing,Zhang, Jin-Yu,Wu, Yan-Chao
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p. 1846 - 1855
(2019/02/14)
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- Synthesis, characterization and performance of bifunctional catalysts for the synthesis of menthol from citronellal
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The synthesis of a series of bifunctional catalysts (1 wt% Pt/W-TUD-1 (Technische Universiteit Delft-1) and 1 wt% Pt/WO3/TUD-1) with different tungsten loadings (5-30 wt% WO3) is described. They were characterized using ICP-OES, INAA, N2 physisorption, XRD and TEM. Their catalytic performance (activity and selectivity) was evaluated in the two-step catalytic synthesis of menthol from citronellal using kinetic analysis. Introducing tungsten during the TUD-1 synthesis results in a high WO3 dispersion, essential for the acidity of the catalyst. High tungsten dispersion is also critical for the Pt hydrogenation activity. Therefore, high dispersion combined with optimal tungsten loading resulted in the highest catalytic activity. The best performing catalyst was 1 wt% Pt/W-TUD-1 (silicon to tungsten ratio of 30), with the highest yields of menthol (96%).
- Ten Dam,Ramanathan,Djanashvili,Kapteijn,Hanefeld
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p. 12041 - 12053
(2017/03/08)
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- A synthetic process of L-menthol
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The invention relates to the field of spice synthesis and particularly relates to a synthetic process of L-menthol. The process includes steps of d,l-menthol synthesizing, d,l-menthol rectification, d,l-menthol esterification, d,l-menthyl benzoate rectification, d,l-menthyl benzoate resolution, D-menthol synthesizing, menthol isomerization and L-menthol synthesizing. The process adopts thymol that is a simple, easily available and cheap chemical product as a raw material. Esterification conditions are optimized and the esterification and rectification are performed at the same time so as to allow the esterification to be converted into a way beneficial to d,l-menthyl benzoate production, thus increasing the esterification yield. Crystallization and resolution are optimized by utilization of the d,l-menthyl benzoate. Preparation of the L-menthol by the process is characterized by being high in yield, low in cost, simple and convenient in operation, suitable for continuous and large-scale production, and the like. According to the process, operation of the process is cyclic with a whole system being sealed, and the process is free of waste water, energy-saving and environmental friendly.
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Paragraph 0076; 0077; 0078
(2017/02/24)
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- The effect of catalyst preparation conditions on the synthesis of menthol from citronellal on Ru/H-BEA
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Heterogeneous Ru/H-BEA catalysts are suitable catalysts for the one-pot transformation of citronellal to menthols, which requires a combined cyclization-hydrogenation step. Here, we report the role of different preparation conditions-namely the choice of the Ru-precursor (Ru(NO)(NO3)3), Ru(acac)3, RuCl3 and Ru3(CO)12) as well as the reduction temperature (523-923 K) of the catalyst. Using Ru(NO)(NO3)3 as precursor the highest activity was obtained, while the product distribution was not strongly affected by the choice of the precursor. On the contrary the reduction temperature leads to very different product distributions: Increasing it from 623 K to 923 K for a 1%Ru/H-BEA-25 catalyst the competitive hydrogenation of citronellal was diminished, which leads to an increased selectivity to menthols from 77% to 87% and additional the activity increases with a factor of 3.4. This behaviour might be due to a dealumination of the zeolite during reduction at higher temperatures. Moreover, in combination with appropriate reaction conditions a yield to menthols of 92% can be reached.
- Pl??er, Jutta,Dedeaga, Fatma,Lucas, Martin,Claus, Peter
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p. 100 - 108
(2016/03/05)
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- P450-catalyzed regio- and stereoselective oxidative hydroxylation of disubstituted cyclohexanes: Creation of three centers of chirality in a single CH-activation event This paper is dedicated to the memory of Harry H. Wasserman
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Wild-type P450-BM3 is able to catalyze in a highly regio- and diastereoselective manner the oxidative hydroxylation of non-activated disubstituted cyclohexane derivatives lacking any functional groups, including cis- and trans-1,2-dimethylcyclohexane, cis- and trans-1,4-dimethylcyclohexane, and trans-1,4-methylisopropylcyclohexane. In all cases except chiral trans-1,2-dimethylcyclohexane as substrate, the single hydroxylation event at a methylene group induces desymmetrization with simultaneous creation of three centers of chirality. Certain mutants increase selectivity, setting the stage for future directed evolution work.
- Ilie, Adriana,Agudo, Rubén,Roiban, Gheorghe-Doru,Reetz, Manfred T.
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p. 470 - 475
(2015/02/02)
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- Facile Protocol for Catalytic Frustrated Lewis Pair Hydrogenation and Reductive Deoxygenation of Ketones and Aldehydes
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A series of ketones and aldehydes are reduced in toluene under H2 in the presence of 5 mol % B(C6F5)3 and either cyclodextrin or molecular sieves affording a facile metal-free protocol for reduction to alcohols. Similar treatment of aryl ketones resulted in metal-free deoxygenation yielding aromatic hydrocarbons.
- Mahdi, Tayseer,Stephan, Douglas W.
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supporting information
p. 8511 - 8514
(2015/11/27)
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- PROCESS FOR THE PREPARATION OF MENTHOL
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The invention relates to a process for the preparation of 2-isopropyl-5-methylcyclohexanol (menthol) via the hydrogenation of thymol to neomenthol and the subsequent isomerization to give D/L (+/?)-menthol.
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Paragraph 0052
(2014/03/25)
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- PROCESS FOR THE PREPARATION OF MENTHOL
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The invention relates to a process for the preparation of 2-isopropyl-5-methylcyclohexanol (D,L-menthol) via the hydrogenation of thymol to menthone and subsequent further hydrogenation to give D,L-menthol.
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Paragraph 0085-0086
(2014/03/25)
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- Highly selective menthol synthesis by one-pot transformation of citronellal using Ru/H-BEA catalysts
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The one-pot transformation of citronellal to menthol requires a combined cyclization-hydrogenation step for which Ru/H-BEA catalysts were identified as highly active and selective catalysts. After identifying zeolite H-BEA as the most promising heterogeneous catalyst for the cyclization of citronellal to the intermediate isopulegol, bifunctional metal/H-BEA catalysts were investigated in the one-pot transformation of citronellal to menthols. Using Pd undesired defunctionalization prevailed, while using Pt and Ru, the formation of menthols predominated. Finally, for Ru/H-BEA catalysts, the effect of catalyst composition (Si:Al ratio, Ru content) and reaction conditions (temperature, hydrogen pressure, and solvent) was investigated to diminish citronellal hydrogenation, dimerization, and defunctionalization. Accordingly, with a 1%Ru/H-BEA-25 catalyst (Ru particle size = 1 nm) in dioxane at 15 bar hydrogen pressure and 373 K, a very high selectivity to menthols of 93% at nearly full conversion was obtained. The catalyst is also highly diastereoselective producing 79% of the desired (±)-menthol.
- Pl?sser, Jutta,Lucas, Martin,Claus, Peter
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p. 189 - 197
(2015/09/28)
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- Highly selective menthol synthesis by one-pot transformation of citronellal using Ru/H-BEA catalysts
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The one-pot transformation of citronellal to menthol requires a combined cyclization-hydrogenation step for which Ru/H-BEA catalysts were identified as highly active and selective catalysts. After identifying zeolite H-BEA as the most promising heterogeneous catalyst for the cyclization of citronellal to the intermediate isopulegol, bifunctional metal/H-BEA catalysts were investigated in the one-pot transformation of citronellal to menthols. Using Pd undesired defunctionalization prevailed, while using Pt and Ru, the formation of menthols predominated. Finally, for Ru/H-BEA catalysts, the effect of catalyst composition (Si:Al ratio, Ru content) and reaction conditions (temperature, hydrogen pressure, and solvent) was investigated to diminish citronellal hydrogenation, dimerization, and defunctionalization. Accordingly, with a 1%Ru/H-BEA-25 catalyst (Ru particle size = 1 nm) in dioxane at 15 bar hydrogen pressure and 373 K, a very high selectivity to menthols of 93% at nearly full conversion was obtained. The catalyst is also highly diastereoselective producing 79% of the desired (±)-menthol.
- Pl?sser, Jutta,Lucas, Martin,Claus, Peter
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p. 189 - 197
(2015/03/31)
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- Highly practical iron-catalyzed C-O cleavage reactions
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Facile iron-catalyzed cleavage of various allyl, cinnamyl and benzyl C-O linkages has been effected in the presence of ethylmagnesium chloride. The protocol is operationally simple (xylene-THF, r.t., 1 h), requires low catalyst loading (1 mol% FeCl2) and tolerates halides, esters, amines, ethers and olefins. The allyl moiety is converted to volatile hydrocarbons which renders laborious product separation unnecessary.
- Gaertner, Dominik,Konnerth, Hannelore,Von Wangelin, Axel Jacobi
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p. 2541 - 2545
(2013/09/24)
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- MOFs as multifunctional catalysts: One-pot synthesis of menthol from citronellal over a bifunctional MIL-101 catalyst
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A bifunctional MOF catalyst containing coordinatively unsaturated Cr 3+ sites and palladium nanoparticles (Pd@MIL-101) has been used for the cyclization of citronellal to isopulegol and for the one-pot tandem isomerization/hydrogenation of citronellal to menthol. The MOF was found to be stable under the reaction conditions used, and the results obtained indicate that the performance of this bifunctional solid catalyst is comparable with other state-of-the-art materials for the tandem reaction: Full citronellal conversion was attained over Pd@MIL-101 in 18 h, with 86% selectivity to menthols and a diastereoselectivity of 81% to the desired (-)-menthol, while up to 30 h were necessary for attaining similar values over Ir/H-beta under analogous reaction conditions. The Royal Society of Chemistry 2012.
- Cirujano,Llabres I Xamena,Corma
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scheme or table
p. 4249 - 4254
(2012/05/07)
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- One-step microwave-assisted asymmetric cyclisation/hydrogenation of citronellal to menthols using supported nanoparticles on mesoporous materials
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The selective conversion of citronellal to menthols, with good diastereoselectivities to (-)-menthol for the case of (+)-citronellal as starting material, can effectively be carried out in a one-step reaction under microwave irradiation catalysed by supported nanoparticles on mesoporous materials. 2% Pt/Ga-MCM-41 was found to be the optimum catalyst for the reaction, with a quantitative conversion of starting material and selectivities above 85% to menthols obtained in short reaction times (typically 15 min). These results constitute the first report of a simple microwave-assisted one-step cyclisation/hydrogenation process for the production of menthols.
- Balu, Alina Mariana,Campelo, Juan Manuel,Luque, Rafael,Romero, Antonio Angel
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experimental part
p. 2845 - 2849
(2010/08/21)
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- One-pot synthesis of menthol catalyzed by a highly diastereoselective Au/MgF2 catalyst
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No toxic compounds such as KCN and no thermal activation is required for the preparation of Au/MgF2 complexes by a simple and facile incipient wetness impregnation method in which hydrogen tetrachloroaurate (HAuCl 4) is the gold precursor. One of the complexes prepared exhibits unique catalytic properties and serves as a heterogeneous catalyst for the highly diastereoselective one-pot synthesis of (±)-menthol from citronellal (see picture).
- Negoi, Alina,Wuttke, Stefan,Kemnitz, Erhard,MacOvei, Dan,Parvulescu, Vasile I.,Teodorescu,Coman, Simona M.
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supporting information; experimental part
p. 8134 - 8138
(2011/02/24)
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- Zr-zeolite beta: A new heterogeneous catalyst system for the highly selective cascade transformation of citral to (±)-menthol
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The transformation of citral to menthols involves hydrogenation steps as well as cyclisation of the intermediate, citronellal. The ability of Zrzeolite beta to catalyse the cyclisation with high diastereoselectivity to (±)-isopulegol is the critical step
- Nie, Yuntong,Jaenicke, Stephan,Chuah, Gaik-Khuan
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experimental part
p. 1991 - 1999
(2009/09/06)
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- Hydrogen-transfer reduction of carbonyl compounds promoted by nickel nanoparticles
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Nickel(0) nanoparticles, generated from nickel(II) chloride, lithium powder and a catalytic amount of 4,4-di-tert-butylbiphenyl (DTBB) in THF at room temperature, have been found to promote the reduction of a variety of ketones and aldehydes by transfer hydrogenation using isopropanol as the hydrogen donor. The nickel nanoparticles were characterised and could be re-utilised with a good performance in the absence of a base. A mechanistic study demonstrates that the reaction proceeds through a dihydride-type mechanism.
- Alonso, Francisco,Riente, Paola,Yus, Miguel
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p. 1847 - 1852
(2008/09/18)
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- Design of catalyst systems for the one-pot synthesis of menthols from citral
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Stable, active, and highly selective bifunctional Ni/Al-MCM-41 catalysts were developed for the one-pot synthesis of menthols from citral. The liquid-phase hydrogenation of citral to citronellal was studied on silica-supported noble (Pt, Pd, Ir) and nonnoble (Ni, Co, Cu) metals. It was found that citronellal is selectively formed at the beginning of the reaction only on Pd and Ni catalysts. The consecutive ene-cyclization of citronellal to isopulegols was investigated on solid acids containing exclusively Lewis (ZnO/SiO2) or strong Broensted (CsHPA) acid sites, and also on catalysts containing both Lewis and Broensted acid sites of either strong (zeolites, SiO2-Al2O3) or moderate (Al-MCM-41) strength. The isopulegol formation rate was higher on samples exhibiting dual Lewis/Broensted acidity, such as SiO2-Al2O3, Al-MCM-41, and zeolite HBEA. Based on these previous results, bifunctional catalysts containing Pd or Ni supported on SiO2-Al2O3, Al-MCM-41, or zeolite HBEA were prepared and tested for citral conversion to menthols. The catalyst stability and the effect of hydrogen pressure and metal loading on menthol productivity were also investigated. The best catalyst was Ni(8%)/Al-MCM-41, which yielded more than 90% menthols at 2026.0 kPa and showed no significant deactivation after two consecutive catalytic tests.
- Trasarti,Marchi,Apesteguia
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p. 155 - 165
(2008/02/03)
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- Carbonyl reduction with CaH2 and R3SiCl catalyzed by ZnCl2
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Ketones and aldehydes were effectively reduced to the corresponding alcohols (or their silyl ethers) by the reaction with CaH2 and R3SiCl in the presence of a catalytic amount of ZnCl2. In the absence of the carbonyl substrate, the reagent reduced R3SiCl to the corresponding hydrosilane under mild reaction conditions.
- Tsuhako, Akiko,He, Jing-Qian,Mihara, Mariko,Saino, Naoko,Okamoto, Sentaro
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p. 9120 - 9123
(2008/09/17)
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- Domino-cyclisation and hydrogenation of citronellal to menthol over bifunctional Ni/Zr-Beta and Zr-beta/Ni-MCM-41 catalysts
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The one-pot conversion of (±)-citronellal to menthol can be selectively catalysed by either a bifunctional Ni/Zr-zeolite beta catalyst or a dual catalyst system of Zr-beta and Ni/MCM-41, giving a high diastereoselectivity to (±)-menthol of 90-94%. The Royal Society of Chemistry 2006.
- Nie, Yuntong,Chuah, Gaik-Khuan,Jaenicke, Stephan
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p. 790 - 792
(2008/02/03)
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- DIARYLPHENOXY ALUMINUM COMPOUNDS
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The invention relates to diarylphenoxy aluminum compounds that can be obtained by reacting a bis(diarylphenol) ligand of formula (I) with an alkylaluminum compound and/or with a complex aluminum hydride. The invention also relates to the use of diarylphenoxy aluminum compounds as catalysts, and relates to a method for producing isopulegol by cyclizing citronellal in the presence of diarylphenoxy aluminum compounds serving as catalysts. The invention further relates to a method for producing menthol by cyclizing citronellal in the presence of diarylphenoxy aluminum compounds serving as catalysts and the subsequent hydrogenation.
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Page/Page column 35-36
(2008/06/13)
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- A facile, catalytic, and environmentally benign method for selective deprotection of teri-butyldimethylsilyl ether mediated by phosphomolybdic acid supported on silica gel
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An environmentally benign PMA supported on SiO2 is found to be an efficient catalyst for the chemoselective deprotection of TBDMS ethers under very mild conditions. Various labile functional groups such as isopropylidene acetal, OTBDPS, OTHP, Oallyl, OBn, alkene, alkyne, OAc, OBz, N-Boc, N-Cbz, N-Fmoc, mesylate, and azide are found to be stable under the reaction conditions. This "truly catalytic" heterogeneous reaction does not require aqueous workup, and the supported catalyst and the solvent can be readily recovered and recycled.
- Kishore Kumar,Baskaran, Sundarababu
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p. 4520 - 4523
(2007/10/03)
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- METHOD FOR PRODUCING MENTHOL
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To the invention relates to a method for producing menthol by catalytically hydrogenating compounds, which comprise the carbon skeleton of methane having at least one double bond and which are substituted at the 3-position by oxygen, and/or by catalytically rearranging stereoisomers of methanol in the presence of hydrogen and doped nickel catalysts.
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Page/Page column 10
(2008/06/13)
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- Chiral aminoalcohols with a menthane skeleton as catalysts for the enantioselective addition of diethylzinc to benzaldehyde
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Novel chiral aminoalcohols were synthesized by highly diastereoselective addition of Me3SiCN and LiCH2CN to (-)-menthone followed by LiAlH4 reduction. The addition of CH2=CH-MgBr and PhCH=CH-MgBr to menthone and the following epoxidation, provided useful hydroxy epoxides, one of which could be aminolyzed to afford an aminodiol. In one case, the configuration of the newly formed epoxidic stereogenic center was determined by X-ray crystallography. When applied as catalysts in the enantioselective addition of Et2Zn to benzaldehyde, the aminoalcohols induced enantiomeric excesses (e.e.s) of up to 77%.
- Panev, Stefan,Linden, Anthony,Dimitrov, Vladimir
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p. 1313 - 1321
(2007/10/03)
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- Oxidative deprotection of allyl glycosides
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Allyl glycosides can be deprotected under the condition of the Kharasch- Sosnovsky reaction and by photoinduced reaction with di-(t)butylperoxide in the presence of bromotrichloromethane.
- Kraehmer, Ralf,Hennig, Lothar,Findeisen, Matthias,Mueller, Dietrich,Welzel, Peter
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p. 10753 - 10760
(2007/10/03)
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- Organoaluminum-Promoted Cyclization of Olefinic Epoxides. a New and Stereoselective Approach to Cyclohexane Frameworks
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A new, general synthetic method of six-membered carbocycles has been demonstrated, which involves the stereo-controlled cyclization of olefinic epoxides with methylaluminum bis(4-bromo-2,6-di-t-butylphenoxide) (MABR) via the epoxide rearrangement and subsequent intramolecular ene reaction with high stereoselectivity. This strategy is shown to be highly useful in the stereoselective synthesis of the basic skeleton of various terpenes.
- Murase, Noriaki,Maruoka, Keiji,Ooi, Takashi,Yamamoto, Hisashi
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p. 707 - 711
(2007/10/03)
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- Highly regio- and stereoselective reductions of carbonyl compounds in aqueous glycosidic media
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Highly regioselective reductions of α,β-unsaturated ketones to the corresponding allylic alcohols were performed in essentially quantitative yields in aqueous media containing either glycosidic surfactants or amphiphilic carbohydrates. Reductions of cyclohexanones and cyclohexenones lead under the same conditions, stereoselectively to reduced compounds bearing an equatorial alcohol function. Hydrophobic interactions between amphiphilic carbohydrates and lipophilic substrates were modelized and should account for the observed stereodifferentiation.
- Denis, Cecile,Laignel, Benoit,Plusquellec, Daniel,Le Marouille, Jean-Yves,Botrel, Alain
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- Samarium Dibromide, an Efficient Reagent for the Pinacol Coupling Reactions.
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The preparation of SmBr2 from Sm2O3 is described.This samarium (II) compound is a powerful one electron reductant able to very efficiently mediate pinacolic couplings.Cross couplings are effective in some cases, for example a chiral diol can be obtained from benzophenone and camphor.Intramolecular pinacolization of a diketone has been performed.
- Lebrun, Alain,Namy, Jean-Louis,Kagan, Henri B.
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p. 2311 - 2314
(2007/10/02)
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- LOW-VALENT TITANIUM: A NEW APPROACH TO DEPROTECTION OF ALLYL AND BENZYL GROUPS
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A novel method for the deprotection of allyl and benzyl derivatives of alcohols and phenols by low-valent titanium is reported.The possible mechanism is discussed.
- Kadam, S. M.,Nayak, S. K.,Banerji, A.
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p. 5129 - 5132
(2007/10/02)
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- Preparation and Use of Chloromethyl (-)-Menthyl Ether in the Synthesis of Optically Pure α-Branched α-Amino Nitriles
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The synthesis of optically pure chloromethyl (-)-menthyl ether (2b) and its use in the synthesis of di-(-)-menthyl acetal (-)-menthyl (+)-menthyl acetals are described.The diastereomeric mixed acetals 7a,b and 8a,b are easily obtainable from the nitrones 5 and 6, KCN and 2b.The mixture of diastereomers are separated into the pure components 7a, 7b and 8a, 8b by simple silica gel column chromatography.Hydrolysis of these products (H2O2/Na2CO3, ultrasound) followed by N-O cleavage affords the heterocyclic α-methyl-α-amino amides 11a, 11b and 12a, 12b.These are subsequently hydrolyzed to give the corresponding α-methyl-α-amino acids with S and R configuration, respectively.
- Shatzmiller, Shimon,Dolithzky, Ben-Zion,Bahar, Eliezer
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p. 375 - 379
(2007/10/02)
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- ENZYMATIC RECOGNITION OF DIASTEREOMERIC ESTERS
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Aiming to improve the enantioselectivity of enzymatic resolution of esters, lipase catalyzed hydrolysis of (D)- and (L)-2-chloropropanoates of four racemic alcohols and transesterification of ethyl (DL)-2-chloropropanoate with optically pure alcohols was investigated.Thus, (rac)-endo-2-norbornyl (L)-2-chloropropanoate was hydrolized by lipase P about 5 times more selectively than its corresponding (D)-counterpart and optically pure (1R,2S,5R)-menthol was obtained by transesterification of its racemate with ethyl (D)-2-chloropropanoate using Candida cylindracea (CC)lipase.From the results obtained it seems obvious that lipases CC and P mainly can recognize the chirality of an alcohol moiety rather than that of an acid
- Rabiller, C. G.,Koenigsberger, .,Faber, K.,Griengl, H.
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p. 4231 - 4240
(2007/10/02)
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- STEREOSELECTIVE HYDROGENATION OF A MENTHONE-ISOMENTHONE MIXTURE ON HETEROGENEOUS NICKEL, NICKEL-COBALT, AND COBALT CATALYSTS
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A study was carried out on the effect of the nature of the catalysts, additives, and solvents on the stereoselectivity of the liquid-phase hydrogenation of an equilibrium menthone-isomenthone mixture to give menthols.Neoisomenthol, which is the least stable of all the menthol isomers, was predominantly formed on a cobalt catalyst modified by (+)-tartaric acid in ethyl acetate at 130 deg C and 10 MPa.
- Zubareva, N. D.,Klabunovskii, E. I.,Kheifits, L. A.
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p. 1765 - 1768
(2007/10/02)
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- Enantioselective Esterification of Racemic Terpene Alcohols with Fatty Acids by Pseudomonas sp. NOF-5 Strain
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The microbial esterification of (+/-)-menthol with various fatty acids by Pseudomonas sp.NOF-5 strain was investigated.A water insoluble fatty acid higher than caproic acid was esterified with (-)-menthol with high enantioselectivity; especially, when lauric acid was used as the fatty acid, the yield of ester was satisfactory.The microbial esterification of various racemic terpene alcohols with lauric acid by the same microorganism was further studied. (-)-Isopulegol and (-)-trans-carveol were esterified from their racemates with high stereoselectivity.However, the esterification of (+/-)-cis-carveol was with poor enantioselectivity, and (+/-)-citronellol was entirely nonselective
- Inagaki, Takashi,Ueda, Hiroo
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p. 1345 - 1348
(2007/10/02)
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- STEREOCHEMICAL EVIDENCE FOR SINGLE ELECTRON TRANSFER MECHANISM IN THE REDUCTION OF CYCLIC KETONES WITH ALKOXYALUMINIUM DICHLORIDES
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The stereochemical results of the reduction of cyclic ketones with alkoxyaluminium dichlorides do not conform to the conventional polar cyclic mechanism and may be explained by a single electron transfer mechanism.
- Nasipuri, Dhanonjoy,Gupta, Mita Datta,Banerjee, Satinath
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p. 5551 - 5554
(2007/10/02)
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- Enzymic Resolution of (+/-)-axial-Alcohols via Asymmetric Hydrolysis of Corresponding Chloroacetates by Microorganisms
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Asymmetric hydrolysis of chloroacetates of (+/-)-axial-alcohols (+/-)-neomenthol (2), (1RS,4aRS,8aSR)-decahydro-1-naphthol (6) by Trichoderma koningi gave (-)-(1S,3R,4R)-neomenthol (2) (54percent optical purity, o.p.) and (-)-(1R,4aR,8aS)-decahydro-1-naphthol (6) (66percent o.p.) with their enantiomeric chloroacetates.However, the chloroacetate of (2RS,4aRS,8aSR)-decahydro-2-naphthol (10) was hydrolyzed by T. koningi to give the (-)-alcohol (10) (12percent o.p.) with low enantioselectivity.
- Oritani, Takayuki,Ichimura, Michio,Hanyu, Yoshifumi,Yamashita, Kyohei
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p. 2613 - 2618
(2007/10/02)
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- PHOSPHINERHODIUM COMPLEXES AS HOMOGENEOUS CATALYSTS. XVI. STEREOSELECTIVE HYDROGENATION OF CYCLIC KETONES
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Cyclic ketones have been hydrogenated stereoselectively with various phosphinerhodium complexes as catalysts.Systems containing phosphines of high basicity and consequently forming RhIII dihydrides as active species yielded mainly the thermodynamically more stable alcohol isomers.Catalysts prepared from aryl-type phosphines of low basicity and modified with Et3N, which contain RhI monohydrides as active complexes, afforded the less stable alcohol isomers as the major products.The ratio of RhIII and RhI hydrides, which determines the stereoselectivity of the catalysts prepared in situ could be changed by suitable choice of base.
- Toros, Szilard,Kollar, Laszlo,Heil, Balint,Marko, Laszlo
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p. 377 - 384
(2007/10/02)
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- AN EFFICIENT DEPROTECTIVE METHOD FOR ALLYLIC ALCOHOLS PROTECTED AS METHOXYETHOXYMETHYL (MEM) AND METHOXYMETHYL (MOM) ETHERS
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Methoxyethoxymethyl ethers (MEM) and methoxymethyl ethers (MOM) of allylic alcohols are readily cleaved by pyridinium paratoluenesulfonate (PPTS) in 2-butanone or t-butyl alcohol.This procedure is also efficient for deprotection of benzylic and aliphatic alcohols.
- Monti, H.,Leandri, G.,Klos-Ringuet, M.,Corriol, C.
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p. 1021 - 1026
(2007/10/02)
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- Novel chiral ethers and their use in resolution of alcohols and phenols
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Novel ethers of organic compounds containing chiral atoms of the formula STR1 wherein A is a hydrocarbonated chain of 1 to 10 groups, the said chain containing one or more heteroatoms, one or more unsaturations, the assembly of the groups constituting the chain may represent a mono- or polycyclic system, including a system of the spiro or endo type, the chain A can contain one or more chiral atoms or the lactone moiety can present a chirality due to the dissymetric spatial configuration of the whole of the molecule and Z is selected from the group consisting of primary, secondary or tertiary alcohol moiety containing at least an asymetric carbon atom, a phenol moiety substituted comprising at least one asymetric carbon atom and an substituted alcohol or phenol moiety with a chirality due to the dissymetric spatial configuration of the whole of the molecule, with the proviso Z is not (R) or (S) α-cyano-3-phenoxy-benzyl when A is STR2 which are useful for the resolution of compounds of the formulae STR3 wherein A and Z have the above definitions and X is selected from the group consisting of hydrogen and alkyl of 1 to 4 carbon atoms.
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- Hydrogen Participation vs. Elimination. The Role and Fate of Neighboring Hydrogen in Solvolysis of Neomenthyl Tosylate
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Product composition and α-d1 and β-d3 isotope effects in the solvolysis of neomenthyl tosylate (8-OTs) were determined in 70 percent aqueous trifluoroethanol and 70 percent aqueous ethanol.Both trifluoroethanolysis and ethanolysis gave 1-2 percent neomenthol (97percent d3), 12-13percent cis-4-menthanol (100percent d3), 2-3percent trans-4-menthanol (100percent d3), 66-70percent 3-p-menthene (83percent d3 and 17percent d2), and 5-9percent 4,8-p-menthene (97percent d3), respectively.These results and the high value of the β-d3 isotope effect (kH/kD=2.45) were interpreted in terms of rate-determining hydride shift followed by elimination which accounts for 75percent of all products.In 85percent of the elimination productsthe migrating hydrogen (deuterium) is not the one being eliminated.
- Hirsl-Starcevic, Sanja,Majerski, Zdenko,Sunko, Dionis E.
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p. 3388 - 3393
(2007/10/02)
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