硫酸氢钠催化合成羧酸苄酯

讨论了一水硫酸氢钠催化合成乙酸苄酯的条件。羧酸、苄醇和硫酸氢钠的质量比为 3∶2∶0 .1 45 ,以环己烷为溶剂 ,进行回流分水 ,合成了甲酸苄酯、乙酸苄酯、丙酸苄酯和丁酸苄酯 ,其收率为 68.5 %～ 84.1 %     

Carbonylation of Benzyl Halides Over Two-Phase Catalyst of Iron Pentacarbonyl

Carbonylation of benzyl halides to phenylacetic acid was studied in a two-phase system with iron pentacarbonyl as the catalyst precursor. The solutions consisted of a benzyl halide and iron pentacarbonyl in benzene and tetrabutylammonium hydrogen sulfate in aqueous sodium hydroxide. Stirring under carbon monoxide readily produced phenylacetic salts in aqueous phase which were then acidified and extracted with ether. The yields of phenylacetic acid from benzyl iodide and from benzyl bromide were similar at a evel of about 50percnt;, that of the latter being higher by 1%. The yield from benzyl chloride was far less, at a level of only 21%. The rate as studied with gas chromatography was found to decrease in the order benzyl iodide>benzyl bromide>benzyl chloride.     

The role of aromatic radical cations and benzylic cations in the 2,4,6-triphenylpyrylium tetrafluoroborate photosensitized oxidation of ring-methoxylated benzyl alcohols in CH2Cl2 solution

A steady-state and laser flash photolysis (LFP) study of the TPPBF(4)-photosensitized oxidation of ring-methoxylated benzyl alcohols has been carried out. Direct evidence on the involvement of intermediate benzyl alcohol radical cations and benzylic cations in these reactions has been provided through LFP experiments. The reactions lead to the formation of products (benzaldehydes, dibenzyl ethers, and diphenylmethanes) whose amounts and distributions are influenced by the number and relative position of the methoxy substituents. This behavior has been rationalized in terms of the interplay between the stabilities of benzyl alcohol radical cations and benzyl cations involved in these processes. A general mechanism for the TPPBF(4)-photosensitized reactions of ring-methoxylated benzyl alcohols has been proposed, where the alpha-OH group of the parent substrate acts as the deprotonating base promoting alpha-C-H deprotonation of the benzyl alcohol radical cation (formed after electron transfer from the benzyl alcohol to TPP) to give a benzyl radical and a protonated benzyl alcohol, precursor of the benzylic cation. This hypothesis is in contrast with previous studies, where formation of the benzyl cation was suggested to occur from the neutral benzyl alcohol through the Lewis acid action of excited TPP(+) (TPP).     

三丁胺胺化强碱性阴离子交换树脂催化合成羧酸苄酯

用组合化学方法筛选出的对无外加碱条件下的亲核取代催化活性最高的聚合物季铵盐-三丁胺胺化强碱性阴离子交换树脂为相转移催化剂,催化合成了乙酸苄酯、丙酸苄酯、丁酸苄酯、戊酸苄酯等羧酸苄酯。讨论了各种反应条件对合成丙酸苄酯的产率的影响,并对传统合成方法进行了改进。在优化反应条件下,反应产率接近100%。     

Interactions between benzyl benzoate and single- and double-chain quaternary ammonium surfactants

Interactions between benzyl benzoate and two different twin-tailed cationic surfactants have been studied. NMR diffusometry measurements have shown that cationic micelles grow in one dimension when benzyl benzoate is added. The location of benzyl benzoate in the micelles was evaluated by NOESY, showing that benzyl benzoate gave cross-peaks both to the hydrophobic groups in the surfactant and to the surfactant head group. Additions of benzyl benzoate to a lamellar phase of double-tailed quaternary surfactants revealed differences in responses. With an increasing concentration of benzyl benzoate, the structure of the dialkyl quat aggregate goes from lamellar to cubic, while the dialkyl ester quat forms a lamellar structure for all benzyl benzoate concentrations.     

Synthesis of Benzyl Alkyl Ethers by Intermolecular Dehydration of Benzyl Alcohol with Aliphatic Alcohols under the Effect of Copper Containing Catalysts

Synthesis of benzyl alkyl ethers was performed in high yields by intermolecular dehydration of benzyl and primary, secondary, tertiary alcohols under the effect of copper containing catalysts. The formation of benzyl alkyl ethers occurs with participation of benzyl cation.     

Photochemical reaction intermediates of benzyl chloride in condensed phase

Reaction intermediates produced upon the photolysis of benzyl chloride have been studied in glassy matrix and in solution. In the steady-state photolysis both benzyl radicals and structural isomers of benzyl chloride were formed in ethanol, while in 3-methylpentane the structural isomers were predominantly formed. The nanosecond laser photolyses of benzyl chloride in ethanol and in cyclohexane also generated benzyl radicals and structural isomers at room temperature. In acetonitrile, in addition to these species, benzyl cations were observed in the early stage after the photolysis.     

Palladium-catalyzed cross-coupling of benzyl thioacetates and aryl halides

A method for preparing benzyl aryl thioethers utilizing an in situ deprotection of benzyl thioacetates as an alternative to free thiols as starting materials has been developed and optimized. Good to excellent yields of diverse benzyl aryl thioethers are obtained with air-stable, odor-free, and easy to prepare thioesters. A one-pot protocol for forming benzyl aryl thioethers from a benzyl halide, potassium thioacetate, and an aryl bromide has also been demonstrated.     

Investigation of steric and electronic effects in the copper-catalysed asymmetric oxidation of sulfides

Steric and electronic effects in the copper-catalysed asymmetric oxidation of aryl benzyl, aryl alkyl and alkyl benzyl sulfides have been investigated. The presence of an aryl group directly attached to the sulfur is essential to afford sulfoxides with high enantioselectivities, with up to 97% ee for 2-naphthyl benzyl sulfoxide, the highest enantioselectivity achieved to date for copper-catalysed asymmetric sulfoxidation. In contrast, the benzyl substituent can be replaced by sterically comparable groups with no effect on enantioselectivity. Copper-mediated oxidation of substituted aryl benzyl sulfides display modest steric and electronic effects resulting in comparable or lower enantioselectivities to those obtained with the unsubstituted benzyl phenyl sulfide.     

One-Pot Reductive Mono-N-alkylation of Aromatic Nitro Compounds Using Nitriles as Alkylating Reagents

Palladium catalysed transfer hydrogenation using cyclohexene as the donor is found to deprotect readily alcohol benzyl ethers and aliphatic benzyl esters. The phenol benzyl ethers and benzyl benzoates are stable under these conditions.     

Glycosylation with glycosyl benzyl phthalates as a new type of glycosyl donor

A glucopyranosyl benzyl phthalate, two mannopyranosyl benzyl phthalates, and a 2-deoxyglucopyranosyl benzyl phthalate, which were prepared from the corresponding 1-hydroxy sugars and benzyl hydrogen phthalate, were found to be efficient glycosyl donors in the glycosylations of various glycosyl acceptors using TMSOTf as a promoter.     

Selective catalytic activity of ball-shaped Pd@MCM-48 nanocatalysts

Remarkable selectivity is achieved in the cleavage of benzyl ethers using ball-shaped palladium nanocatalysts, Pd@MCM-48, in an MCM-48 matrix. The unique nanocatalysts not only feature unprecedented complete hydrogenolysis selectivity of a benzyl ether over hydrogenation of a double bond, but also demonstrate selective cleavage of unsubstituted benzyl ether over substituted benzyl ethers.     

High-temperature thermal decomposition of benzyl radicals

The thermal decomposition of the benzyl radical was studied in shock tube experiments using ultraviolet laser absorption at 266 nm for detection of benzyl. Test gas mixtures of 50 and 100 ppm of benzyl iodide dilute in argon were heated in reflected shock waves to temperatures ranging from 1430 to 1730 K at total pressures around 1.5 bar. The temporal behavior of the 266 nm absorption allowed for determination of the benzyl absorption cross-section at 266 nm and the rate coefficient for benzyl decomposition, C6H5CH2 --> C7H6 + H. The rate coefficient for benzyl decomposition at 1.5 bar can be described using a two-parameter Arrhenius expression by k1(T) = 8.20 x 10(14) exp(-40 600 K/T) [s(-1)], and the benzyl absorption cross-section at 266 nm was determined to be sigma(benzyl) = 1.9 x 10(-17) cm2 molecule(-1) with no discernible temperature dependence over the temperature range of the experiments.     

Chemoenzymatic synthesis of naturally occurring benzyl 6-O-glycosyl-beta-D-glucopyranosides

Direct beta-glucosidation between benzyl alcohol and D-glucose (5) using the immobilized beta-glucosidase from almonds with the synthetic prepolymer ENTP-4000 gave a benzyl beta-D-glucoside (1) in 53% yield. The coupling of the benzyl beta-D-glucopyranoside congener (8) derived from 1 with phenyl 2,3,4-tri-O-acetyl-1-thio-beta-D-xylopyranoside (9), ethyl 2,3,4-tri-O-acetyl-1-thio-alpha-L-rhamnopyranoside (13), and 2,3,4-tri-O-acetyl-alpha-L-arabinopyranosyl bromide (15) afforded 10, 14, and 16, respectively, as coupled products. Deprotection of 10, 14, and 16 provided the synthetic benzyl beta-D-xylopyranosyl-(1-->6)-beta-D-glucopyranoside (2), benzyl alpha-L-rhamnopyranosyl-(1-->6)-beta-D-glucopyranoside (3), and benzyl alpha-L-arabinopyranosyl-(1-->6)-beta-D-glucopyranoside (4), respectively.     

Investigation of electro-oxidation of methanol and benzyl alcohol at boron-doped diamond electrode: evidence for the mechanism for fouling film formation

Boron-doped diamond (BDD) and glassy carbon (GC) electrodes are compared for electrochemical oxidation of methanol and benzyl alcohol. Cyclic voltammograms reveal that BDD electrode produces good oxidation signals for both methanol and benzyl alcohol, while GC produces no significant oxidation signal for either methanol or benzyl alcohol. Amperometric measurement of oxidation of methanol and benzyl alcohol on BDD shows development of a fouling film for benzyl alcohol but not for methanol. Prolonged (24 h) polarization of the BDD electrode at +2.0 V in benzyl alcohol generated enough fouling film for investigation by AFM, SEM, Raman, and FTIR techniques. AFM and SEM microscopy images confirm a fouling film confined to the low-lying regions of the polycrystallite BDD surface, indicating that the active sites of benzyl alcohol oxidation are located within these low-lying regions. The fouling material generated in the process of benzyl alcohol oxidation was identified from Raman and FTIR spectroscopy as polyester. Experiments confirm the fouling film can be removed and the electrode surface reactivated by brief polarization at +3.0 V. Amperometric results of concentration dependence confirm the BDD electrode is well suited for quantitative analysis applications of methanol and benzyl alcohol, with recognizable oxidation currents at micromolar concentration levels.     

Design of latent catalysts and their application to polymer synthesis

Design of latent catalysts such as benzyl sulfonium, benzyl ammonium, benzyl pyridinium, benzyl phosphonium, and hydrazinium salts, and their application to polymer synthesis have been described. They have been demonstrated as excellent thermal or photolatent catalysts for polymerizations of cyclic monomers such as epoxides, bicyclo orthoesters, spiro orthocarbonates, and vinyl monomers such as styrene and vinyl ethers.     

Direct Arylation/Alkylation/Magnesiation of Benzyl Alcohols in the Presence of Grignard Reagents via Ni-, Fe-, or Co-Catalyzed sp(3) C-O Bond Activation

Direct application of benzyl alcohols (or their magnesium salts) as electrophiles in various reactions with Grignard reagents has been developed via transition metal-catalyzed sp(3) C-O bond activation. Ni complex was found to be an efficient catalyst for the first direct cross coupling of benzyl alcohols with aryl/alkyl Grignard reagents, while Fe, Co, or Ni catalysts could promote the unprecedented conversion of benzyl alcohols to benzyl Grignard reagents in the presence of (n)hexylMgCl. These methods offer straightforward pathways to transform benzyl alcohols into a variety of functionalities.     

Synthesis of stereoregular poly(alkyl malolactonates)

Optically pure methyl, ethyl, isopropyl, and benzyl (R)-malolactonate were prepared from (S)-(-)-malic acid and were polymerized in the bulk with tetraethylammonium benzoate as the initiator to yield high-molecular-weight, crystalline polymers. The optical purity of methyl and benzyl malolactonate was determined by ¹H NMR spectroscopy of the β-lactone complexed with a chiral europium shift reagent. Enantiomeric excesses of 100% were found (the experimental error was 3%). Optically active poly(β-malic acid) was obtained from optically active poly[benzyl (S)-malate] by catalytic hydrogenolysis of the pendent benzyl esters. Ethyl and benzyl (R)-malolactonate were also copolymerized, and the benzyl esters of the resulting copolymer were converted into carboxylic acid units by hydrogenolysis.     

PHOTOLYSIS OF SOME ARYLALKYL THIOCYANATES, ISOTHIOCYANATES AND DISULFIDES IN RIGID GLASSES AT 77K: FORMATION AND TRAPPING OF ARYLALKYL FREE RADICALS

Abstract Photolysis of benzyl and benzhydryl thiocyanates and of benzyl, benzhydryl and trityl isothiocyanates and disulfides has been studied in rigid glasses at liquid nitrogen temperature. Most intermediate and final products of photolysis have been identified by absorption and fluorescence spectroscopy. Evidence has been obtained for benzyl, diphenylmethyl and triphenylmethyl trapped radicals. A number of new luminescence bands of benzyl radical, in the 550–610 nm region, and the hitherto unknown lowest energy luminescence spectrum (doublet-doublet) of diphenylmethyl radical, are reported.     

Chemoselective and Direct Functionalization of Methyl Benzyl Ethers and Unsymmetrical Dibenzyl Ethers by Using Iron Trichloride

Methyl and benzyl ethers are widely utilized as protected alcohols due to their chemical stability, such as the low reactivity of the methoxy and benzyloxy groups as leaving groups under nucleophilic conditions. We have established the direct azidation of chemically stable methyl and benzyl ethers derived from secondary and tertiary benzyl alcohols. The present azidation chemoselectively proceeds at the secondary or tertiary benzylic positions of methyl benzyl ethers or unsymmetrical dibenzyl ethers and is also applicable to direct allylation, alkynylation, and cyanation reactions, as well as the azidation. The present methodologies provide not only a novel chemoselectivity but also the advantage of shortened synthetic steps, due to the direct process without the deprotection of the methyl and benzyl ethers.