Dual‐Function of Alcohols in Gold‐Mediated Selective Coupling of Amines and Alcohols

Oxidative coupling of alcohols (methanol and ethanol) and dimethylamine on atomic‐oxygen‐activated Au(111) occurs entirely on the surface to form the corresponding amides when the alkoxy of the alcohol and the amide derived from the amine are co‐adsorbed. For effective oxygen‐assisted coupling the formation of the amide requires excess methanol. Mechanistic studies reveal that molecularly adsorbed methanol removes excess adsorbed atomic oxygen efficiently, precluding either secondary oxidation or oxidative dehydrogenation of dimethylamide to the imine. The adsorbed amide then can react with the aldehyde produced by β‐hydride elimination from the alkoxy to form the hemiaminal, the reactive intermediate leading to coupling. The selectivity for formamide production can be increased to nearly 100 % in excess methanol.     

Fluorometric Assay of Alcohols Using Alcohol Oxidase

Abstract

Fluorometric methods are described for the assay of ethanol, methanol, allyl alcohol and n-propanol using the enzyme alcohol oxidase. The enzyme catalyzes the oxidation of the alcohols to aldehydes with concomitant formation of hydrogen peroxide. The hydrogen peroxide formed is measured fluorometrically using p-hydroxy-phenylacetic acid and peroxidase. From 0.1–100 μg/ml of the alcohols and from 0.0002 to 0.050 unit/ml of alcohol oxidase can be assayed in 2 minutes with a precision of about ± 2%.     

N-甲基甲酰胺与醇的氢键相互作用

The hydrogen bonding interactions between N-methylformamide and primary, secondary, and tertiary alcohols have been studied using the FT1R spectroscopic method. The most likely association complex between alcohol and N-methylformamide is the 1:1 stoichiometric complex formed between the hydroxyl group of alcohol and the carbonyl group of N-methylformamide. The formation constant of the 1:1 complexes has been calculated using the Nash method. It appears that the primary alcohols have larger formation constant compared with the secondary and tertiary alcohols. The results showed that the proton-donating ability of the alcohols decreased in the order: primary＞secondary＞tertiary, and that the association constant increased with the increase in carbon chain of the alkyl group of alcohols.     

N-甲基甲酰胺与醇的氢键相互作用

Amides are used as synthetic reagents and as starting mate- rials for the preparation of insecticides and pharmaceuticals products[1]. Alcohols are industrially and scientifically important organic compounds, and their physical and chemical properties are…     

Facile One-pot Transformation of 2,3-Epoxy Alcohols into Allylic Alcohols

Optically-active allylic alcohols have been frequently used as chiral building blocks for the preparation of optically pure compounds.¹ There are at present various methods for the synthesis of optically active allylic alcohols including the kinetic resolution racemic allylic alcohols,² reductive rearrangement of 2,3-epoxy alcohol by metal, halide and telluium-based chemistry.³ To our knowledge, One-pot Transformation of 2,3-epoxy alcohols into allylic alcohols, especially via epoxy iodides,is limited to Dorta's method³ using a Ph₃P,iodine, imidazole,2,6-lutidine and water system. The original Dorta's method can be successfully applied to the formation of tertiary allylic alcohols, but give unsatisfactory results in formation of secondary allylic alcohols.     

Dual-function of alcohols in gold-mediated selective coupling of amines and alcohols

Oxidative coupling of alcohols (methanol and ethanol) and dimethylamine on atomic-oxygen-activated Au(111) occurs entirely on the surface to form the corresponding amides when the alkoxy of the alcohol and the amide derived from the amine are co-adsorbed. For effective oxygen-assisted coupling the formation of the amide requires excess methanol. Mechanistic studies reveal that molecularly adsorbed methanol removes excess adsorbed atomic oxygen efficiently, precluding either secondary oxidation or oxidative dehydrogenation of dimethylamide to the imine. The adsorbed amide then can react with the aldehyde produced by β-hydride elimination from the alkoxy to form the hemiaminal, the reactive intermediate leading to coupling. The selectivity for formamide production can be increased to nearly 100?% in excess methanol.     

Dehydrogenative Silylation of Alcohols Under Pd-Nanoparticle Catalysis

Pd-nanoparticle-catalyzed dehydrogenative coupling between various hydrosilanes and alcohols was shown to provide silyl ethers in good and reproducible yields. The synthetic methodology is effective for a wide range of simple and bulky silanes and secondary alcohols, while keeping various other functional groups intact. The procedure also exhibits high selectivity for the silylation of primary versus secondary alcohols in 1,2-diols, and allows the successive silylation of alkynols and hydrogenation of the triple bond to afford Z-alkenols in good yields.     

Divergent Synthesis of Alcohols and Ketones via Cross-Coupling of Secondary Alcohols under Manganese Catalysis

A homogeneous manganese-catalyzed cross-coupling of two secondary alcohols for the divergent synthesis of γ-disubstituted alcohols and β-disubstituted ketones is reported. Employing the well-defined Mn-MACHO^Ph as the catalyst, this novel protocol has a broad substrate scope with good functional group tolerance and affords a diverse library of valuable disubstituted alcohols and ketones in moderate to good yields. The strong influence of the reaction temperature on the selective formation of alcohol products was theorized in preliminary DFT studies. Studies have shown that the Gibbs free energy of the formation of alcohols is thermodynamically more favourable than corresponding ketones at a lower temperature.     

Pd‐Colloids‐Catalyzed/Ag2O‐Oxidized General and Selective Esterification of Benzylic Alcohols

Palladium colloids obtained from the degradation of Hermann–Beller palladacycle proved to be an efficient catalytic system in combination with silver oxide as a selective oxidant for the oxidative esterification of differently substituted benzyl alcohols in MeOH as solvent. Excellent reactivity exhibited by the catalytic system also allowed the alcoholic coupling partner to be changed from MeOH to a wide range of alcohols having diverse functionalities. The mildness of the developed protocol also made it possible to employ propargyl alcohol as the coupling partner without any observation of any interference of the terminal alkyne. Selective oxidative coupling of a primary alcoholic functional group over secondary in the case of glycols and glycerols was also made possible using the developed catalyst system. To test the relevancy of Pd/Ag combined catalysis mixed Pd/Ag colloids were synthesized, characterized by TEM, XRD and XPS and applied to oxidative‐esterification successfully.     

The Effects of Various Alcohols on the Stability of Melittin: A Molecular Dynamics Study

In this study, 200 ps molecular dynamics simulations were conducted to investigate the effects of various alcohols on the structural stability of melittin. The averaged helicity of melittin remained 80% in pure butanol, whereas it was below 60% both in pure water and in pure methanol. The α‐helix propensity of melittin increased with the aliphatic chain length of the alcohol. Charge‐charge interaction between Lys21 and Arg24 and polar‐nonpolar interaction between Trp19 and Arg22 are probably responsible for the higher structural integrity of the C‐terminal α‐helix over the N‐terminal one. The weaker dielectric constant of longer aliphatic chain length of alcohol possibly reduces the hydrogen bonding between amide protons and surrounding solvent molecules and simultaneously promotes the intramolecular hydrogen bonding in melittin and therefore stabilizes the secondary structure of melittin. The effect of various alcohols on stabilizing melittin is most likely due to their ability to form clusters on the surface of melittin effectively, favoring the formation of intramolecular hydrogen bonds instead of intermolecular hydrogen bonds and promoting the formation of stable α‐helices.     

Stereoinversion of Unactivated Alcohols by Tethered Sulfonamides

The direct, catalytic substitution of unactivated alcohols remains an undeveloped area of organic synthesis. Moreover, catalytic activation of this difficult electrophile with predictable stereo‐outcomes presents an even more formidable challenge. Described herein is a simple iron‐based catalyst system which provides the mild, direct conversion of secondary and tertiary alcohols to sulfonamides. Starting from enantioenriched alcohols, the intramolecular variant proceeds with stereoinversion to produce enantioenriched 2‐ and 2,2‐subsituted pyrrolidines and indolines, without prior derivatization of the alcohol or solvolytic conditions.     

Production of Mixed Alcohols from Bio-syngas over Mo-based Catalyst

A series of Mo-based catalysts prepared by sol-gel method using citric acid as complexant were successfully applied in the high effcient production of mixed alcohols from bio-syngas, derived from the biomass gasification. The Cu₁Co₁Fe₁Mo₁Zn_0.5-6%K catalyst exhibited a higher activity on the space-time yield of mixed alcohols, compared with the other Mo-based catalysts. The carbon conversion significantly increases with rising temperature below 340 oC, but the alcohol selectivity has an opposite trend. The maximum mixed alcohols yield derived from biomass gasification is 494.8 g/(kg_catal·h) with the C2⁺ (C2-C6 higher alcohols) alcohols of 80.4% under the tested conditions. The alcohol distributions are con-sistent with the Schulz-Flory plots, except methanol. In the alcohols products, the C2⁺ alcohols (higher alcohols) dominate with a weight ratio of 70%-85%. The Mo-based cata-lysts have been characterized by X-ray diffraction and N2 adsorption/desorption. The clean bio-fules of mixed alcohols derived from bio-syngas with higher octane values could be used as transportation fuels or petrol additives.     

Effect of Alcohols on the Photooxidative Behavior of Diethyl Sulfide

The reactions of singlet oxygen with diethyl sulfide (Et(2)S) in benzene alcohol mixtures have been examined. The salient discoveries include: (1) the rate constants of product formation, k(r), in benzene/methanol mixtures are a function of the concentration of methanol, (2) the ability of alcohols to supress physical quenching are a function of their pK(a)'s, and (3) trapping experiments with diphenyl sulfoxide are consistent with two distinct intermediates. A mechanism which involves formation of a persulfoxide followed by reaction with methanol to give a hydroperoxy-methoxy sulfurane is consistent with all of the results.     

Manganese-Catalyzed β-Methylation of Alcohols by Methanol

We report an earth-abundant-metal-catalyzed double and single methylation of alcohols. A manganese catalyst, which operates at low catalyst loadings and short reaction times, mediates these reactions efficiently. A broad scope of primary and secondary alcohols, including purely aliphatic examples, and 1,2-aminoalcohols can be methylated. Furthermore, alcohol methylation for the synthesis of pharmaceuticals has been demonstrated. The catalyst system tolerates many functional groups among them hydrogenation-sensitive examples and upscaling is easily achieved. Mechanistic investigations are indicative of a borrowing hydrogen or hydrogen autotransfer mechanism involving a bimetallic K-Mn catalyst. The catalyst accepts hydrogen as a proton and a hydride from alcohols efficiently and reacts with a chalcone via hydride transfer.     

Direct Trifluoromethylation of Alcohols Using a Hypervalent Iodosulfoximine Reagent

The direct trifluoromethylation of a variety of aliphatic alcohols using a hypervalent iodosulfoximine reagent afforded the corresponding ethers in moderate to good yields (14–72 %). Primary, secondary, and even tertiary alcohols, including examples derived from natural products, underwent this transformation in the presence of catalytic amounts of zinc bis(triflimide). Typical reaction conditions involved a neat mixture of 6.0 equivalents of the alcohol with 1.0 equivalent of the reagent, with the majority of reactions complete within 2 h with 2.5 mol % of the Lewis acid catalyst. Furthermore, experimental evidence was provided that the C−O bond-forming process occurred via the coordination of the alcohol to the iodine atom and subsequent reductive elimination.     

Kinetic Resolution of Allylic Alcohols Promoted by Electrophilic Selenium Reagents

Abstract

The first example of a kinetic resolution process promoted by an electrophilic selenium reagent is reported. Racemic allylic alcohols react with half equivalents of a selenenylating agent in methanol leading to the regiospecific formation of the corresponding addition products with a very high level of facial selectivity (98% de). The unreacted alcohol can be recovered in a optically enriched form (92% ee).     

A TEMPO‐Free Copper‐Catalyzed Aerobic Oxidation of Alcohols

The copper‐catalyzed aerobic oxidation of primary and secondary alcohols without an external N‐oxide co‐oxidant is described. The catalyst system is composed of a Cu/diamine complex inspired by the enzyme tyrosinase, along with dimethylaminopyridine (DMAP) or N‐methylimidazole (NMI). The Cu catalyst system works without 2,2,6,6‐tetramethyl‐l‐piperidinoxyl (TEMPO) at ambient pressure and temperature, and displays activity for un‐activated secondary alcohols, which remain a challenging substrate for catalytic aerobic systems. Our work underscores the importance of finding alternative mechanistic pathways for alcohol oxidation, which complement Cu/TEMPO systems, and demonstrate, in this case, a preference for the oxidation of activated secondary over primary alcohols.     

几种低碳醇在Pt／TiO2上的光催化产氢速率的研究

主要考察了无氧条件下低碳醇（甲、乙、丙醇）在Pt/TiO2表面光催化重整反应制氢。深入探讨了几种低碳醇与其放氢速率的构-效关系,提出了低碳醇在Pt/TiO2光催化剂表面吸附态的模型。     

Preparation of Colloidal Transition Metals in Polymers by Reduction with Alcohols or Ethers

Colloidal dispersions of rhodium, palladium, osmium, iridium, and platinum are prepared by refluxing the methanol-water solutions of rhodium(III) chloride, palladium(II) chloride, osmium(VIII) oxide, sodium chloroiridate, and chloroplatinic acid, respectively, in the presence of poly(vinyl alcohol) as a protective colloid. The preparations of colloidal dispersions of rhodium are successful in the presence of vinyl polymer with polar group such as poly(vinyl alcohol), polyvinylpyrrolidone, or poly(methyl vinyl ether). Polyethyleneimine, gelatin, polyethylene glycol), and dextran are ineffective as the protective colloid. Water-soluble primary alcohols such as methanol and ethanol, water-soluble secondary alcohols such as 2-propanol, and water-soluble diethers such as 1,4-dioxane are available as reductants for preparation of the colloidal dispersion of rhodium. The average diameters of metal particles in the colloidal dispersions of palladium, rhodium, platinum, iridium, and osmium in poly(vinyl alcohol) are determined by electron microscopy to be 53, 40, 27, 14, and < 10 Å, respectively. The particle size distribution in each colloidal dispersion is sharp within 50 Å wide. The particles in the colloidal dispersions of both iridium and osmium are highly dispersed with no aggregation, while in the colloidal dispersions of rhodium, palladium, and platinum, there exist aggregates of 5-15, 5-30, and 100-200 particles, respectively. Colloidal dispersions of rhodium, palladium, osmium, and platinum are effective as catalysts for hydrogenation of cyclohexene at 30.0°C under atmospheric hydrogen pressure.     

Visible-Light-Induced Cross-Dehydrogenative Coupling of Heteroarenes with Aliphatic Alcohols Mediated by Iodobenzene Dichloride

With the irradiation of visible light, α-heteroarylation of aliphatic alcohol was selectively achieved under gentle conditions in the present of iodobenzene dichloride. The Minisci-type cross-dehydrogenative coupling reaction was performed in the absence of metal and acid. Readily available primary alcohols and electron-withdrawing heteroarenes can be applied smoothly. Mechanism studies indicated that the PhICl radical and chlorine radical formed from iodobenzene dichloride were responsible for the selective hydrogen atom abstraction of alcohols.