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Continuous synthesis of menthol from citronellal and citral over Ni-beta-zeolite-sepiolite composite catalyst
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
(2022/04/03)

HYDROBORATION-OXIDATION PROCESS
The present invention relates to the field of organic synthesis and, more specifically, it concerns a process for preparing compound of formula (I) by a hydroboration-oxidation reaction of compound of formula (II).
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Page/Page column 9

(2021/09/11)

Biomass- And calcium carbide-based recyclable polymers
Biomass is a renewable source of valuable feedstock for the chemical industry of the future. A promising approach to the utilization of valuable components of biomass is the synthesis of monomers and polymers, if the overall technology is designed for a clean cycle without pollution of the environment with newly created polymers. In this work, we have developed a methodology for the recycling of polymers based on biomass and calcium carbide. First, we modified a series of biomass-derived terpene alcohols with calcium carbide followed by polymerization of the isolated vinyl ethers. Then, to study the recycling potential, the obtained polymers were subjected to pyrolysis at moderate temperatures (200-450 °C). The pyrolysis products were analyzed using TGA-MS, GC-MS, and NMR, and it was found that the polymers can be transformed quite easily. The products of the pyrolysis consisted of the starting terpenols, as well as the corresponding non-toxic ketones or aldehydes: up to 87% of the starting alcohol or up to 100% of the total sum of alcohol + aldehyde or alcohol + ketone (GC-yields). Then, the reaction mixture was hydrogenated and resulted in the formation of starting alcohol only. According to the studied pathway of polymers re-building, a terpene fragment attached to the main polyethylene chain through an oxygen atom promotes the transformation of the obtained polymers. Thus, the products of pyrolysis are environmentally friendly and can be reused in the further synthesis of monomers. The developed system has shown a unique assembling/disassembling ability and advances the concept of reusable bio-derived high value-added materials.
Metlyaeva, Svetlana A.,Rodygin, Konstantin S.,Lotsman, Kristina A.,Samoylenko, Dmitriy E.,Ananikov, Valentine P.
p. 2487 - 2495
(2021/04/07)

Preparation of Neutral trans - Cis [Ru(O2CR)2P2(NN)], Cationic [Ru(O2CR)P2(NN)](O2CR) and Pincer [Ru(O2CR)(CNN)P2] (P = PPh3, P2= diphosphine) Carboxylate Complexes and their Application in the Catalytic Carbonyl Compounds Reduction
The diacetate complexes trans-[Ru(κ1-OAc)2(PPh3)2(NN)] (NN = ethylenediamine (en) (1), 2-(aminomethyl)pyridine (ampy) (2), 2-(aminomethyl)pyrimidine (ampyrim) (3)) have been isolated in 76-88% yield by reaction of [Ru(κ2-OAc)2(PPh3)2] with the corresponding nitrogen ligands. The ampy-type derivatives 2 and 3 undergo isomerization to the thermodynamically most stable cationic complexes [Ru(κ1-OAc)(PPh3)2(NN)]OAc (2a and 3a) and cis-[Ru(κ1-OAc)2(PPh3)2(NN)] (2b and 3b) in methanol at RT. The trans-[Ru(κ1-OAc)2(P2)2] (P2 = dppm (4), dppe (5)) compounds have been synthesized from [Ru(κ2-OAc)2(PPh3)2] by reaction with the suitable diphosphine in toluene at 95 °C. The complex cis-[Ru(κ1-OAc)2(dppm)(ampy)](6) has been obtained from [Ru(κ2-OAc)2(PPh3)2] and dppm in toluene at reflux and reaction with ampy. The derivatives trans-[Ru(κ1-OAc)2P2(NN)] (7-16; NN = en, ampy, ampyrim, 8-aminoquinoline; P2 = dppp, dppb, dppf, (R)-BINAP) can be easily synthesized from [Ru(κ2-OAc)2(PPh3)2] with a diphosphine and treatment with the NN ligands at RT. Alternatively these compounds have been prepared from trans-[Ru(OAc)2(PPh3)2(NN)] by reaction with the diphosphine in MEK at 50 °C. The use of (R)-BINAP affords trans-[Ru(κ1-OAc)2((R)-BINAP)(NN)] (NN = ampy (11), ampyrim (15)) isolated as single stereoisomers. Treatment of the ampy-type complexes 8-15 with methanol at RT leads to isomerization to the cationic derivatives [Ru(κ2-OAc)P2(NN)]OAc (8a-15a; NN = ampy, ampyrim; P2 = dppp, dppb, dppf, (R)-BINAP). Similarly to 2, the dipivalate trans-[Ru(κ1-OPiv)2(PPh3)2(ampy)] (18) is prepared from [Ru(κ2-OPiv)2(PPh3)2] (17) and ampy in CHCl3. The pincer acetate [Ru(κ1-OAc)(CNNOMe)(PPh3)2] (19) has been synthesized from [Ru(κ2-OAc)2(PPh3)2] and HCNNOMe ligand in 2-propanol with NEt3 at reflux. In addition, the dppb pincer complexes [Ru(κ1-OAc)(CNN)(dppb)] (CNN = AMTP (20), AMBQPh (21)) have been obtained from [Ru(κ2-OAc)2(PPh3)2], dppb, and HAMTP or HAMBQPh with NEt3, respectively. The acetate NN and pincer complexes are active in transfer hydrogenation with 2-propanol and hydrogenation with H2 of carbonyl compounds at S/C values of up to 10000 and with TOF values of up to 160000 h-1.
Baldino, Salvatore,Giboulot, Steven,Lovison, Denise,Nedden, Hans Günter,P?thig, Alexander,Zanotti-Gerosa, Antonio,Zuccaccia, Daniele,Ballico, Maurizio,Baratta, Walter
p. 1086 - 1103
(2021/05/06)

Ruthenium complexes of phosphine-amide based ligands as efficient catalysts for transfer hydrogenation reactions
This work presents three mononuclear Ru(ii) complexes of tridentate phosphine-carboxamide based ligands providing a NNP coordination environment. The octahedral Ru(ii) ion shows additional coordination with co-ligands; CO, Cl and CH3OH. All three Ru(ii) complexes were thoroughly characterized including their crystal structures. These Ru(ii) complexes were utilized as catalysts for the transfer hydrogenation of assorted carbonyl compounds, including some challenging biologically relevant substrates, using isopropanol as the hydrogen source. The binding studies illustrated the coordination of the isopropoxide ion by replacing a Ru-ligated chloride ion followed by the generation of the Ru-H intermediate that was isolated and characterized and was found to be involved in the catalysis.
Yadav, Samanta,Vijayan, Paranthaman,Yadav, Sunil,Gupta, Rajeev
p. 3269 - 3279
(2021/03/16)

Fine-Bubble-Slug-Flow Hydrogenation of Multiple Bonds and Phenols
We describe a promising method for the continuous hydrogenation of alkenes or alkynes by using a newly developed fine-bubble generator. The fine-bubble-containing slug-flow system was up to 1.4 times more efficient than a conventional slug-flow method. When applied in the hydrogenation of phenols to the corresponding cyclohexanones, the fine bubble-slug-flow method suppressed over-reduction. As this method does not require the use of excess gas, it is expected to be widely applicable in improving the efficiency of gas-mediated flow reactions.
Iio, Takuya,Nagai, Kohei,Kozuka, Tomoki,Sammi, Akhtar Mst,Sato, Kohei,Narumi, Tetsuo,Mase, Nobuyuki
supporting information
p. 1919 - 1924
(2020/11/09)

Continuous flow synthesis of menthol: Via tandem cyclisation-hydrogenation of citronellal catalysed by scrap catalytic converters
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
p. 379 - 387
(2020/02/13)

Method of preparing L-menthone from R-citronellal
The invention discloses a method of preparing L-menthone from R-citronellal. Under the action of a Pd-Co-MOF-MMT catalyst, R-citronellal carries out heterogeneous catalytic reactions to generate L-menthone, the conversion rate of R-citronellal can reach 90-99.9%, the yield of L-menthone can reach 85-98%, and the ee value of menthone can reach 95-99.99%.
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Paragraph 0093-0094

(2020/04/06)

Simple H2-free hydrogenation of unsaturated monoterpenoids catalyzed by Raney nickel
A series of monoterpenoids (citral, carvone, menthone, camphor) as well as cyclohexanone and hex-5-en-2-one were subjected to transfer hydrogenation with PriOH/Raney nickel system at 82 or 150 °C. Among monoterpenoids, citral and carvone underwent full conversion at 82 °C within 5 h.
Philippov, Alexey A.,Chibiryaev, Andrey M.,Martyanov, Oleg N.
p. 380 - 381
(2019/08/20)

Nanoporous Na+-montmorillonite perchloric acid as an efficient and recyclable catalyst for the chemoselective protection of hydroxyl groups
Nanoporous Na+-montmorillonite perchloric acid as a novel heterogeneous reusable solid acid catalyst was easily prepared by treatment of Na+-montmorillonite as a cheap and commercially available support with perchloric acid. The catalyst was characterized using a variety of techniques including X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), energy dispersive X-ray spectroscopy (EDX), pH analysis and determination of the Hammett acidity function. The prepared reagent showed excellent catalytic activity for the chemoselective conversion of alcohols and phenols to their corresponding trimethylsilyl ethers with 1,1,1,3,3,3-hexamethyldisilazane (HMDS) at room temperature. Deprotection of the resulting trimethylsilyl ethers can also be carried out using the same catalyst in ethanol. All reactions were performed under mild and completely heterogeneous reaction conditions in good to excellent yields. The notable advantages of this protocol are: short reaction times, high yields, availability and low cost of the reagent, easy work-up procedure and the reusability of the catalyst during a simple filtration.
Mashhadinezhad, Maryam,Shirini, Farhad,Mamaghani, Manouchehr
p. 2099 - 2107
(2019/01/03)

Cobalt-Nanoparticles Catalyzed Efficient and Selective Hydrogenation of Aromatic Hydrocarbons
The development of inexpensive and practical catalysts for arene hydrogenations is key for future valorizations of this general feedstock. Here, we report the development of cobalt nanoparticles supported on silica as selective and general catalysts for such reactions. The specific nanoparticles were prepared by assembling cobalt-pyromellitic acid-piperazine coordination polymer on commercial silica and subsequent pyrolysis. Applying the optimal nanocatalyst, industrial bulk, substituted, and functionalized arenes as well as polycyclic aromatic hydrocarbons are selectively hydrogenated to obtain cyclohexane-based compounds under industrially viable and scalable conditions. The applicability of this hydrogenation methodology is presented for the storage of H2 in liquid organic hydrogen carriers.
Murugesan, Kathiravan,Senthamarai, Thirusangumurugan,Alshammari, Ahmad S.,Altamimi, Rashid M.,Kreyenschulte, Carsten,Pohl, Marga-Martina,Lund, Henrik,Jagadeesh, Rajenahally V.,Beller, Matthias
p. 8581 - 8591
(2019/09/12)

“Inverse” Frustrated Lewis Pairs: An Inverse FLP Approach to the Catalytic Metal Free Hydrogenation of Ketones
For the first time have boron-containing weak Lewis acids been demonstrated to be active components of Frustrated Lewis Pair (FLP) catalysts in the hydrogenation of ketones to alcohols. Combining the organosuperbase (pyrr)3P=NtBu with the Lewis acid 9-(4-CF3-C6H4)-BBN generated an “inverse” FLP catalyst capable of hydrogenating a range of aliphatic and aromatic ketones including N-, O- and S-functionalized substrates and bio-mass derived ethyl levulinate. Initial computational and experimental studies indicate the mechanism of catalytic hydrogenation with “inverse” FLPs to be different from conventional FLP catalysts that contain strong Lewis acids such as B(C6F5)3.
Mummadi, Suresh,Brar, Amandeep,Wang, Guoqiang,Kenefake, Dustin,Diaz, Rony,Unruh, Daniel K.,Li, Shuhua,Krempner, Clemens
supporting information
p. 16526 - 16531
(2018/10/20)

HYDROSILANE/LEWIS ACID ADDUCT, PARTICULARLY ALUMINUM, IRON, AND ZINC, METHOD FOR PREPARING SAME, AND USE OF SAID SAME IN REACTIONS FOR REDUCING CARBONYL DERIVATIVES
Disclosed is an adduct between a Lewis acid, preferably aluminum trichloride, iron trichloride, or zinc dichloride, and a hydrosilane;—a method for preparing same; and a method for for reducing, particularly, an aldehyde, a ketone, an α,β-unsaturated ketone, an imine, or an α,β-unsaturated imine.
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Paragraph 0210; 0211; 0212; 0213

(2018/02/28)

Dissociative reactions of benzonorbornadienes with tetrazines: Scope of leaving groups and mechanistic insights
Bioorthogonal dissociative reactions boast diverse potential applications in chemical biology and drug delivery. The reaction of benzonorbornadienes with tetrazines to release amines from carbamate leaving groups was recently introduced as a bioorthogonal bond-cleavage reaction. The present study aimed at investigating the scope of leaving groups that are compatible with benzonorbornadienes. Synthesis of several benzonorbornadienes with different releasable groups is reported, and the reaction of these molecules with tetrazine was found to be rapid and afforded high release yields. The tetrazine-induced release of molecules proceeds in a cascade of steps including inverse-electron demand cycloaddition and cycloreversion reactions that form unstable isoindoles/isobenzofuran intermediates and spontaneously eliminate a leaving group of interest. In the case of oxygen-bridged BNBDs at room temperature, we observed the formation of an unproductive byproduct.
Xu,Galindo-Murillo,Cheatham,Franzini
p. 9855 - 9865
(2017/12/12)

Supported N-propylsulfamic acid onto Fe3O4 magnetic nanoparticles as a reusable and efficient nanocatalyst for the protection/deprotection of hydroxyl groups and protection of aldehydes
N-propylsulfamic acid supported onto Fe3O4 magnetic nanoparticles (MNPs-PSA) as an efficient and magnetically reusable nanocatalyst has been reported for the tetrahydropyranylation/depyranylation of a wide variety of alcohols and phenols by changing the solvent medium. Also, the protection of aldehydes as acylals using Ac2O in the presence of catalytic amount MNPs-PSA in good to high yields at room temperature under solvent-free conditions is described. After completing the reaction, the catalyst was easily separated from the reaction mixture with the assistance of an external magnetic field and reused for several consecutive runs without significant loss of their catalytic efficiency.
Rostami, Amin,Tahmasbi, Bahman,Abedi, Fatemeh
p. 3689 - 3701
(2016/04/05)

The effect of catalyst preparation conditions on the synthesis of menthol from citronellal on Ru/H-BEA
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
p. 100 - 108
(2016/03/05)

Improved Second Generation Iron Pincer Complexes for Effective Ester Hydrogenation
Hydrogenation of esters to alcohols with a well-defined iron iPr2PNP pincer complex has been recently reported by us and other groups. We now introduce a novel and sterically less hindered Et2PNP congener that provides superior catalytic activity in the hydrogenation of various carboxylic acid esters and lactones compared to the known complex. Successful hydrogenation proceeds under relatively mild conditions (60°C) with lower catalyst loadings.
Elangovan, Saravanakumar,Wendt, Bianca,Topf, Christoph,Bachmann, Stephan,Scalone, Michelangelo,Spannenberg, Anke,Jiao, Haijun,Baumann, Wolfgang,Junge, Kathrin,Beller, Matthias
supporting information
p. 820 - 825
(2016/03/09)

Introduction of PEG-SANM nanocomposite as a new and highly efficient reagent for the promotion of the silylation of alcohols and phenols and deprotection of the silyl ethers
Poly (ethylene glycol)-sulfonated sodium montmorillonite (PEG-SANM) nanocomposite was prepared by a simple method and characterized using XRD, TGA, SEM, TEM, and FT-IR techniques. After preparation and characterization, this reagent was used as a highly efficient and reusable solid acid catalyst for the chemoselective silylation of alcohols and phenols and deprotection of the obtained silyl ethers. Themethod offers several advantages including high to excellent yields of the products, short reaction times, easy preparation of the catalyst and easy work-up procedure. In addition, the catalyst can be recycled and reused at least for five times without significant decrease in the catalytic activity.
Shirini, Farhad,Shojaei, Abdollah Fallah,Heirati, Seyedeh Zahra Dalil
p. 944 - 951
(2016/07/06)

A synthetic process of L-menthol
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)

Synthesis of supported Ru-nanoparticles for selective hydrogenation of carbonyl compounds
Ru nanoparticles were successfully supported on molecular sieves and it was further characterized by sophisticated analytical methods such as transmission electron microscopy, energydispersive X-ray spectroscopy and nitrogen adsorption techniques. Transmission electron microscopy data confirmed, indicated the formation of metal oxide nanoparticles (4.5±2 nm) on the external surface of molecular sieves. Ru supported molecular sieves were applied as a catalyst for the hydrogenation of carbonyl compounds. Aldehydes as well as ketones were successfully hydrogenated in good yield and selectivity. Easy synthesis of air/moisture stable catalyst, hassle free reaction protocol (no requirement of aqueous work-up), 7 times catalyst recycling and additive free approach were the promising outcomes of the proposed work.
Upadhyay, Praveenkumar,Srivastava, Vivek
p. 528 - 533
(2015/10/05)

The Stereoselective Reductions of Ketones to the Most Thermodynamically Stable Alcohols Using Lithium and Hydrated Salts of Common Transition Metals
A simple method is presented for the highly stereoselective reductions of ketones to the most thermodynamically stable alcohols. In this procedure, the ketone is treated with lithium dispersion and either FeCl2·4H2O or CuCl2·2H2O in THF at room temperature. This protocol is applied to a large number and variety of ketones and is both more convenient and efficient than those commonly reported for the diastereoselective reduction of five- and six-membered cyclic ketones.
Kennedy, Nicole,Cohen, Theodore
p. 8134 - 8141
(2015/09/02)

Facile Protocol for Catalytic Frustrated Lewis Pair Hydrogenation and Reductive Deoxygenation of Ketones and Aldehydes
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.
supporting information
p. 8511 - 8514
(2015/11/27)

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
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.
p. 470 - 475
(2015/02/02)

Highly efficient homogeneous and heterogenized ruthenium catalysts for transfer hydrogenation of carbonyl compounds
[Ru(acac)2(CH3CN)2] was synthesized from [Ru(acac)3] by refluxing it with zinc powder in ethanol-acetonitrile mixture. The prepared catalyst was characterized by FT-IR, 1H and 13C NMR techniques. The silica supported catalyst ('SiO 2'-NH2-RuII) was prepared by stirring [Ru(acac)2(CH3CN)2] with 'SiO 2'-NH2 in a 1:1 mixture of CH2Cl 2-toluene for 3 days at room temperature. It was characterized by FT-IR, SEM, solid state NMR, ICP and BET surface area methods. The transfer hydrogenation reaction of carbonyl compounds was carried out separately using [Ru(acac)2(CH3CN)2] and 'SiO 2'-NH2-RuII as catalysts. The reaction conditions were optimized with different solvents, bases, catalyst amounts and temperatures using acetophenone as a model system. The scope of the reaction was extended to various substituted aryl ketones including heteroaryl ketones. This journal is the Partner Organisations 2014.
Ganesamoorthy,Jerome,Shanmugasundaram,Karvembu
p. 27955 - 27962
(2014/07/21)

Chloral hydrate as a water carrier for the efficient deprotection of acetals, dithioacetals, and tetrahydropyranyl ethers in organic solvents
The efficient deprotection of several acetals, dithioacetals, and tetrahydropyranyl (THP) ethers under ambient conditions, using chloral hydrate in hexane, is described. Excellent yields were realized for a wide range of both aliphatic and aromatic substrates. The method is characterized by mild conditions (room temperatures or below), simple workup, and the ready availability of chloral hydrate. High chemoselectivity was also observed in the deprotection, acetonides, esters, and amides being unaffected under the reaction conditions. Products were generally purified chromatographically and identified spectrally. These results constitute a novel addition to current methodology involving a widely employed deprotection tactic in organic synthesis. It seems likely that the mechanism of the reaction involves adsorption of the substrate on the surface of the sparingly soluble chloral hydrate.
Chandrasekhar, Sosale,Shrinidhi, Annadka
p. 1904 - 1913
(2014/07/07)

Synthesis and properties of fluorous benzoquinones and their application in deprotection of silyl ethers
1,4-Benzoquinone derivatives bearing trifluoromethyl, perfluorobutyl and perfluorohexyl groups were prepared and employed in the deprotection of silyl ethers. The fluorous character of these compounds was examined by measuring the partition coefficient between the fluorous and organic solvents. The benzoquinone derivatives showed significant fluorous character, indicating that they can be recovered from the reaction mixtures using a fluorous/organic biphasic system. The oxidising ability of the fluorous benzoquinones was estimated by cyclic voltammetry, and these compounds were found to be strong oxidisers. The fluorous benzoquinones were utilised in the oxidative desilylation of silyl ethers to afford the deprotected alcohols in high yield. In addition, the reduced fluorous benzoquinones were recovered from the reaction mixtures in good yields using a fluorous/organic biphasic system. This journal is the Partner Organisations 2014.
Matsubara, Hiroshi,Maegawa, Takahiko,Kita, Yasuaki,Yokoji, Takato,Nomoto, Akihiro
p. 5442 - 5447
(2014/07/21)

Highly selective menthol synthesis by one-pot transformation of citronellal using Ru/H-BEA catalysts
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
p. 189 - 197
(2015/09/28)

METHOD FOR PREPARING MENTHONE FROM ISOPULEGOL
The present invention relates to a method for preparing menthone, starting from isopulegol, using specific homogeneous catalysts.
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Paragraph 0094

(2014/03/25)

PROCESS FOR THE PREPARATION OF MENTHOL
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)

PROCESS FOR THE PREPARATION OF MENTHOL
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 0049-0053

(2014/03/25)

Cerium(IV) sulfate tetrahydrate: A catalytic and highly chemoselective deprotection of THP, MOM, and BOM ethers
Tetrahydropyranyl (THP), methoxymethyl (MOM), and benzyloxymethyl (BOM) phenyl/alkyl ethers were efficiently cleaved to the corresponding parent hydroxyl compounds in good yields using catalytic amounts of Ce(SO 4)2·4H2O by microwave-assisted or conventional heating in methanol solution. Intramolecular and competitive experiments demonstrated the chemoselective deprotection of THP ethers in the presence of triisopropylsilyl (TIPS) and tert-butyldiphenylsilyl (TBDPS) phenyl ethers.
González-Calderón, Davir,González-González, Carlos A.,Fuentes-Benítez, Aydeé,Cuevas-Yá?ez, Erick,Corona-Becerril, David,González-Romero, Carlos
p. 7164 - 7166
(2013/12/04)

Selective deprotection of TBDMS alkyl ethers in the presence of TIPS or TBDPS phenyl ethers by catalytic CuSO4·5H2O in methanol
TBDMS alkyl ethers are efficiently cleaved to the corresponding hydroxyl compounds upon heating (conventional or microwave) in methanol solution containing 20 mol % CuSO4·5H2O. Intramolecular chemoselective experiments showed that TBDMS alkyl ethers are selectively cleaved in the presence of TIPS or TBDPS aryl ethers. Competition experiments also showed that TBDMS alkyl ethers were selectively cleaved in the presence of TBDPS alkyl ethers.
González-Calderón, Davir,Benítez-Puebla, Luis J.,González-González, Carlos A.,Assad-Hernández, Salomón,Fuentes-Benítez, Aydeé,Cuevas-Yá?ez, Erick,Corona-Becerril, David,González-Romero, Carlos
p. 5130 - 5132
(2013/08/28)

Controlled fragrance delivery in functionalised ionic liquid-enzyme systems
It is often believed that both ionic liquids and surfactants generally behave as non-specific denaturants of proteins. In this paper, it is shown that amphiphilic ionic liquids bearing a long alkyl chain and a target molecule, where the target molecule is appended via a carboxylic ester functionality, can represent super-substrates that enable the catalytic activity of an enzyme, even at high concentrations in solution. Menthol has been chosen as the target molecule for slow and controlled fragrance delivery, and it was found that the rate of the menthol release can be controlled by the chemical structure of the ionic liquid. At a more fundamental level, this study offers an insight into the complex hydrophobic, electrostatic, and hydrogen bond interactions between the enzyme and substrate.
Blesic, Marijana,Nimal Gunaratne,Nockemann, Peter,McCarron, Philip,Seddon, Kenneth R.
p. 329 - 333
(2013/04/10)

Highly practical iron-catalyzed C-O cleavage reactions
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
p. 2541 - 2545
(2013/09/24)

1-(Hydroxyacetyl)pyrene a new fluorescent phototrigger for cell imaging and caging of alcohols, phenol and adenosine
1-(Hydroxyacetyl)pyrene has been introduced as a new fluorescent phototrigger for alcohols and phenols. Alcohols and phenols were protected as their corresponding carbonate esters by coupling with fluorescent phototrigger, 1-(hydroxyacetyl)pyrene. Photophysical studies of caged carbonates showed that they all exhibited strong fluorescence properties. Irradiation of the caged carbonates by visible light (≥410 nm) in aqueous acetonitrile released the corresponding alcohols or phenols in high chemical (95-97%) and quantum (0.17-0.21) yields. The mechanism for the photorelease was proposed based on Stern-Volmer quenching experiments and solvent effect studies. Importantly, 1-(hydroxyacetyl)pyrene showed as a phototrigger for rapid photorelease of the biologically active molecule adenosine. In vitro biological studies revealed that 1-(hydroxyacetyl)pyrene has good biocompatibility, cellular uptake property and cell imaging ability. The Royal Society of Chemistry and Owner Societies 2012.
Jana, Avijit,Saha, Biswajit,Ikbal, Mohammed,Ghosh, Sudip Kumar,Singh, N. D. Pradeep
p. 1558 - 1566
(2013/02/26)

Alkaline modifiers as performance boosters in citral hydrogenation over supported ionic liquid catalysts (SILCAs)
Supported ionic liquid catalysts (SILCAs) consist of nano-scale catalytic species immobilized in an ionic liquid layer which, in turn, is immobilized on a solid support. In this work, novel SILCAs containing various inorganic alkaline modifiers (e.g. potassium hydroxide) were prepared and applied in citral hydrogenation reactions. The supported ionic liquid catalyst systems demonstrated enhanced reaction rates and improved selectivities toward citronellal in citral hydrogenation. With the addition of an alkaline modifier into ionic liquid layer, the catalyst selectivity increased from 16% to 74%. In fact, a highly selective reaction route toward citronellal was accomplished.
Salminen, Eero,Virtanen, Pasi,Kordás, Krisztián,Mikkola, Jyri-Pekka
p. 126 - 131
(2013/01/15)

Preparation, characterization and use of 1,3-disulfonic acid imidazolium hydrogen sulfate as an efficient, halogen-free and reusable ionic liquid catalyst for the trimethylsilyl protection of hydroxyl groups and deprotection of the obtained trimethylsilanes
Novel 1,3-disulfonic acid imidazolium hydrogen sulfate, a halogen-free ionic liquid, is a recyclable and eco-benign catalyst for the trimethylsilyl protection of hydroxyl groups at room temperature under solvent free conditions to afford trimethylsilanes in excellent yields (92-100%) and in very short reaction times (1-5 min). Deprotection of the resulting trimethylsilanes can also be achieved using the same catalyst in methanol. The catalyst was characterized by IR, 1H NMR, 13C NMR and MS studies. All the products were extensively characterized by IR, 1H NMR, MS, and elemental and melting point analyses. This new method consistently has the advantages of excellent yields and short reaction times. Further, the catalyst can be recovered and reused for several times without loss of activity. The work-up of the reaction consists of a simple separation, followed by concentration of the crude product and purification.
Shirini, Farhad,Khaligh, Nader Ghaffari,Akbari-Dadamahaleh, Somayeh
p. 15 - 23
(2013/01/14)

MOFs as multifunctional catalysts: One-pot synthesis of menthol from citronellal over a bifunctional MIL-101 catalyst
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
scheme or table
p. 4249 - 4254
(2012/05/07)

Anhydrous FePO4 as a cost-effective and recyclable catalyst for tetrahydropyranylation and tetrahydrofuranylation of alcohols and phenols
In this article, a mild and efficient protocol for the tetrahydropyranylation and tetrahydrofuranylation of various aliphatic and benzylic alcohols and phenols into their corresponding THP and THF ethers (with 3,4-dihydro- 2H-pyran, DHP and 2,3-dihydrofuran, DHF) has been developed using a catalytic amount of anhydrous FePO4 at room temperature and relatively short reaction times in good to excellent yields.
Behbahani, Farahnaz K.,Farahani, Mona
experimental part
p. 431 - 435
(2012/04/17)

Citral hydrogenation over Rh and Pt catalysts supported on TiO2: Influence of the preparation and activation protocols of the catalysts
During citral hydrogenation, the products distribution obtained on Rh/TiO2 and Pt/TiO2 catalysts depends on their preparation and activation protocols: (i) the unsaturated alcohols (the intended products) are formed in higher quantity on samples reduced at 500 °C and more notably with Pt/TiO2 catalyst; (ii) samples prepared by impregnation of the metallic precursor salt in HCl medium and activated at 300 °C are the only ones to lead to the formation of isopulegol as by-product. On the catalysts activated at 500 °C, these results can be explained by the presence of the SMSI effect beneficial to hydrogenate selectively the CO bond of citral towards unsaturated alcohols.
Ekou, Tchirioua,Ekou, Lynda,Vicente, Aurélie,Lafaye, Gwendoline,Pronier, Stéphane,Especel, Catherine,Marécot, Patrice
experimental part
p. 82 - 88
(2011/04/18)

A new crystal engineering approach for the synthesis of {[K.18-Crown-6]I3}n as a nanotube-like and recyclable catalyst for the chemoselective silylation of alcohols
Reaction of 18-crown-6 with KI in ethanol solution followed by addition of iodine (I2) afforded a unique triiodide salt with a nanotube-like structure ({[K.18-Crown-6]I3}n). It is shown that this reagent may be used for the chemoselective trimethylsilylation of alcohols. The synthesis of the crystalline reagent is a good example of crystal engineering. Reagent was recycled and reused.
Zolfigol,Kolvari,Koukabi,Salehzadeh,Chehardoli,Tidmarsh,Niknam
experimental part
p. 484 - 494
(2012/06/18)

One-pot synthesis of menthol catalyzed by a highly diastereoselective Au/MgF2 catalyst
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.
supporting information; experimental part
p. 8134 - 8138
(2011/02/24)

(PhCH2PPh3)+Br3-: A versatile reagent for the preparation, deprotection, and oxidation of trimethylsilyl ethers
Benzyltriphenylphosphonium tribromide (BTPTB), as a stable solid reagent, is easily prepared by the reaction of benzyltriphenylphosphonium bromide with Br2. This reagent can be used as an efficient catalyst for the conversion of alcohols to their corresponding trimethylsilyl ethers (TMS ethers) with hexamethyldisilazane (HMDS). Desilylation of TMS ethers is also catalyzed by BTPTB in MeOH at room temperature in high yields. BTPTB is also able to oxidize the TMS ethers to their corresponding carbonyl compounds in a mixture of MeOH/H2O in good to high yields. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.
Shirini,Imanzadeh,Mousazadeh,Mohammadpoor-Baltork,Aliakbar,Abedini
experimental part
p. 641 - 646
(2010/06/17)

One-step microwave-assisted asymmetric cyclisation/hydrogenation of citronellal to menthols using supported nanoparticles on mesoporous materials
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
experimental part
p. 2845 - 2849
(2010/08/21)

Anodic oxidation: An attractive alternative to CAN-mediated cleavage of para-methoxyphenyl ethers
para-Methoxyphenyl (PMP) ether is a very convenient protecting group for the alcohol function; however, its cleavage requires strong oxidative conditions. In this field, the use of powerful eerie ammonium nitrate has been widely described, despite the fac
Vaxelaire, Carine,Souquet, Florence,Lannou, Marie-Isabelle,Ardisson, Janick,Royer, Jacques
supporting information; experimental part
p. 3138 - 3140
(2009/12/05)

Osmium pyme complexes for fast hydrogenation and asymmetric transfer hydrogenation of ketones
The osmium compound trans,cis-[OsCl2(PPh3) 2(Pyme)] (1) (Pyme = 1 -(pyridin-2-yl)methanamine), obtained from [OsCl2(PPh3)3] and Pyme, thermally isomerizes to cis,cis-[OsCl2(PPh3)2(Pyme)] (2) in mesitylene at 150°C. Reaction of [OsCl2(PPh3) 3] with Ph2P(CH2)4PPh2 (dppb) and Pyme in mesitylene (150°C, 4h) leads to a mixture of trans-[OsCl2(dppb)(Pyme)] (3) and cis-[OsCl2(dppb)(Pyme)] (4) in about an 1:3 molar ratio. The complex trans-[OsCl2(dppb)(Pyet) ] (5) (Pyet = 2-(pyridin-2-yl)ethanamine) is formed by reaction of [OsCl 2(PPh3)3] with dppb and Pyet in toluene at reflux. Compounds 1, 2, 5 and the mixture of isomers 3/4 efficiently catalyze the transfer hydrogenation (TH) of different ketones in refluxing 2-propanol and in the presence of NaOiPr (2.0 mol%). Interestingly, 3/4 has been proven to reduce different ketones (even bulky) by means of TH with a remarkably high turnover frequency (TOF up to 5.7 × 105h-1) and at very low loading (0.05-0.001 mol%). The system 3/4 also efficiently catalyzes the hydrogenation of many ketones (H2, 5.0 atm) in ethanol with KOtBu (2.0 mol %) at 70°C (TOF up to 1.5 × 104h-1). The in-situ-generated catalysts prepared by the reaction of [OsCl2- (PPh3)3] with Josiphos diphosphanes and (±)-1-alkyl-substituted Pyme ligands, promote the enantioselective TH of different ketones with 91-96% ee (ee = enantiomeric excess) and with a TOF of up to 1.9×104h-1 at 60°C.
Baratta, Walter,Ballico, Maurizio,Del Zotto, Alessandro,Siega, Katia,Magnolia, Santo,Rigo, Pierluigi
experimental part
p. 2557 - 2563
(2009/04/11)

Silica triflate as a new, efficient, and reusable reagent for the chemoselective silylation of alcohols and phenols and deprotection of silyl ethers
Silica triflate was easily prepared via reaction of silica gel and trifluoromethane sulfonyl chloride at room temperature. This compound can be employed as an efficient and reusable reagent for the chemoselective silylation of alcohols and phenols in solution and under solvent-free conditions. This reagent also effectively catalyzed the deprotection of silyl ethers in refluxing methanol.
Shirini,Marjani,Nahzomi, H. Taherpour,Zolfigol
p. 168 - 177
(2008/12/22)

Vanadium hydrogen sulfate (I): Chemoselective trimethylsilylation of alcohols and deprotection of trimethylsilyl ethers
Trimethylsilylation of alcohols with hexamethyldisilazane (HMDS) catalyzed by V(HSO4)3 under mild and completely heterogeneous reaction condition is reported. The method is highly chemoselective for the protection of alcohols in the presence of phenols, amines and thiols. Also, the deprotection of trimethylsilyl ethers is performed in the presence of V(HSO 4)3 at room temperature in good to high yields.
Shirini, Farhad,Zolfigol, Mohammad Ali,Abedini, Masoumeh,Sakhaei, Ali Reza
experimental part
p. 943 - 946
(2009/12/24)

Hydrogen-transfer reduction of carbonyl compounds promoted by nickel nanoparticles
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
p. 1847 - 1852
(2008/09/18)

Silica triflate as a new, mild and efficient catalyst for tetrahydropyranylation of alcohols and deprotection of tetrahydropyranyl ethers
Silica triflate, a new stable derivative of silica gel, is easily prepared by the reaction of silica gel with trifluoromethanesulfonyl chloride. Silica triflate acts as a highly effective and reusable catalyst for tetrahydropyranylation of alcohols and deprotection of tetrahydropyranyl ethers under mild and completely heterogeneous reaction conditions.
Shirini,Marjani,Nahzomi, H. Taherpour
p. 2235 - 2240
(2008/02/08)