Highly efficient and chemoselective trimethylsilylation of alcohols and phenols with hexamethyldisilazane (HMDS) catalyzed by reusable electron-deficient [Ti(salophen)(OTf)2]

In the present work, highly efficient trimethylsilylation of alcohols and phenols with hexamethyldisilazane (HMDS) catalyzed by high-valent [Ti^IV(salophen)(OTf)₂] is reported. Under these conditions, primary, secondary and tertiary alcohols as well as phenols were silylated in short reaction times and high yields. It is noteworthy that this method can be used for chemoselective silylation of primary alcohols in the presence of secondary and tertiary alcohols and phenols. The catalyst was reused several times without loss of its catalytic activity.     

[Sn(TPP)(BF4)2]: An efficient and reusable catalyst for chemoselective trimethylsilylation of alcohols and phenols with hexamethyldisilazane

Tin(IV)tetraphenylporphyrinato tetrafluoroborate, [Sn^IV(TPP)(BF₄)₂], was used as an efficient catalyst for trimethylsilylation of alcohols and phenols with hexamethyldisilazane (HMDS). High-valent [Sn^IV(TPP)(BF₄)₂] catalyzes trimethylsilylation of primary, secondary and tertiary alcohols as well as phenols, and the corresponding TMS-ethers were obtained in high yields and short reaction times at room temperature. While, under the same reaction conditions [Sn^IV(TPP)Cl₂] is less efficient to catalyze these reactions. One important feature of this catalyst is its ability in the chemoselective silylation of primary alcohols in the presence of secondary and tertiary alcohols and phenols. The catalyst was reused several times without loss of its catalytic activity.     

Graphene oxide‐bound electron‐deficient tin(IV) porphyrin: a highly efficient and selective catalyst for trimethylsilylation of alcohols and phenols with hexamethyldisilazane

The catalytic activity of graphene oxide‐bound tetrakis(p ‐aminophenyl)porphyrinatotin(IV) trifluoromethanesulfonate, [Sn^IV(TNH₂PP)(OTf)₂], in the trimethylsilylation of alcohols and phenols with hexamethyldisilazane (HMDS) is reported. The prepared catalyst was characterized using inductively coupled plasma analysis, scanning electron microscopy, transmission electron microscopy, and Fourier transform infrared and diffuse reflectance UV–visible spectroscopies. This heterogeneous catalyst was used for selective trimethylsilylation of various alcohols and phenols with HMDS in short reaction times and high yields. Also, the catalyst is of high reusability and stability, in that it was recovered several times without loss of its initial activity. The chemoselectivity of this catalytic system in the silylation of primary alcohols in the presence of secondary and tertiary alcohols and also phenols was investigated.     

Depolymerization of Organosolv Lignin over Silica-alumina Catalysts

E cient conversion of lignin to fine chemicals and biofuel become more and more attractive in biorefinery. In this work, we used a series of silica-alumina catalysts (i.e., SiO₂-Al₂O₃, HY, Hβ, and HZSM-5) to degrade lignin into arenes and phenols. The relationship between the catalyst structure and lignin depolymerization performance was investigated. The results showed that both acidity and pore size of the catalyst could in uence the conversion of lignin. In the volatilizable product, phenols were identified as the main phenolic monomers via gas chromatography-mass spectrometer. SiO₂-Al₂O₃ was the most effcient catalyst, giving 90.96% degree of conversion, 12.91% yield of phenols, and 2.41% yield of arenes in ethanol at 280℃ for 4 h. The Fourier transform infrared spectroscopy and ¹H nuclear magnetic resonance spectroscopy analysis demonstrated that deoxygenation and alkylation occurred in this process. The effect of solvents was also investigated and the results showed that ethanol was the most effcient solvent.     

Chemoselective Borane‐Catalyzed Hydroarylation of 1,3‐Dienes with Phenols

A B(C₆F₅)₃‐catalyzed hydroarylation of a series of 1,3‐dienes with various phenols has been established through a combination of theoretical and experimental investigations, affording structurally diverse ortho‐allyl phenols. DFT calculations show that the reaction proceeds through a borane‐promoted protonation/Friedel–Crafts pathway involving a π‐complex of a carbocation–anion contact ion pair. This protocol features simple and mild reaction conditions, broad functional‐group tolerance, and low catalyst loading. The obtained ortho‐allyl phenols could be further converted into flavan derivatives using B(C₆F₅)₃ with good cis diastereoselectivity. Furthermore, this transformation was applied in the late‐stage modification of pharmaceutical compounds.     

Solvent‐Free Williamson Synthesis: An Efficient,Simple, and Convenient Method for Chemoselective Etherification of Phenols and Bisphenols

Etherification of phenols with dimethyl‐ and diethylsulfates and benzyl chloride was performed efficiently in the presence of a suitable solid base, NaHCO₃ or K₂CO₃, under solvent‐free conditions. The reaction proceeded rapidly at low temperature, and the corresponding ethers were obtained with high purity and excellent yield. Selective etherification of electron‐poor phenols in the presence of electron‐rich ones and also selective mono‐etherification of bisphenols are the noteworthy advantages of this method. This method is environmentally friendly.     

A Novel QSAR Approach for Estimating Toxicity of Phenols

Abstract

Toxicity values (log IGC^?1 ₅₀) for 60 phenols tested in the 2-d static population growth inhibition assay with the ciliate Tetrahymena pyriformis were tabulated. Each chemical was selected so the series formed uniform coverage of the hydrophobicity/ionization surface. A high quality hydrophobicity-dependent (log K _ow) structure-toxicity relationship (log IGC^?1 ₅₀ = 0.741 (log K_ow) ?1.433; n = 17; r² = 0.970; s = 0.134; F = 486.55; Pr > F = 0.0001) was developed for phenols with pK_a values > 9.8. Similarly, separate hydrophobicity-dependent relationships were developed for phenols with pK_a values of 4.0, 5.1, 6.3, 7.5, and 8.7. Comparisons of intercepts and slopes, respectively, revealed phenols with pK_a values of 6.3 to be the most toxic and the least influenced by hydrophobicity. These relationships were reversed for the more acidic and basic phenols. Plots of toxicity versus pK_a for nitro-substituted phenols and phenols with log K_ow values of either 1.75 or 2.50 further demonstrated bilinearity between toxicity and ionization. In an effort to more accurately model the relationship between toxicity and ionization, the absolute value function |6.3-pK_a| was used to model ionization affects for derivatives with pK_a values between 0 and 9.8. For derivatives with pK_a value > 9.8, a value of 3.50 was used to quantitate ionization effects. The use of log K_ow in conjunction with this modified pK_a (ΔpK_a) resulted in the structure-toxicity relationship (log IGC^?1 ₅₀ = 0.567 (log K_ow)-0.226 (ΔpK_a-0.079; n = 54; r² = 0.926; s = 0.215; F = 321.06; Pr > F = 0.0001). Derivatives with a nitro group in the 4-position typically did not model well with the above equation.     

Microwave-assisted methylation of phenols with tetramethylammonium chloride in the presence of K2CO3 or Cs2CO3

We have evaluated the potential of using tetramethylammonium chloride (Me₄NCl) as an alternative methylating agent for phenols under microwave-assisted conditions. Its chemical behavior was tested in a reaction with 2-naphthol in the presence of various bases and solvents. The method was then applied in 1,2-dimethoxyethane or toluene under heterogeneous conditions for the O-methylation of a series of phenolic compounds. We found that many simple phenols can be methylated in the presence of K₂CO₃, whereas some other less-reactive phenols require the presence of the more reactive Cs₂CO₃.     

Movement of Water Soluble Phenols in Soil Using Thin-Layer Chromatography

Abstract

The movement of water soluble phenols was studied using soil thin-layer chromatographic technique. The mobility was expressed in terms of R_M values.The movement of phenols having meta dihydroxy function was greater than the phenols having ortho dihydroxy function. The lesser movement of orginol in comperison to resoroinol was due to the steric binderance of the additional -CH₃ group in orcinol. The minimum movement of gallic acid was probably due to the additional - COOH group or both the types of inter and intra molecular H-bonding. The movement was also affected by the presence of organic matter, different salt solutions and pH of the leachates.     

Oxidant‐Controlled Catalytic Transformations of Phenols with Unexpected Cleavage of Aromatic Rings

Oxidative transformations of phenols have attracted significant attention of chemists due to their importance in biological process and organic synthesis. In contrast to the relatively well‐developed oxygenation and coupling reactions of phenols, the highly efficient and selective oxidative ring cleavage of phenols is under‐represented. This work describes a novel CuCl‐catalyzed tandem homocoupling/skeletal rearrangement of phenols that realizes the cleavage of the phenol ring by using air or Ag₂CO₃ as the oxidant. Interestingly, simply changing the oxidant to K₂S₂O₈ results in the oxidative coupling/cyclization of phenols to give dibenzofurans. These results set an important precedent of oxidant‐controlled catalytic transformations of phenols.     

Rapid,highly efficient and chemoselective trimethylsilylation of alcohols and phenols with hexamethyldisilazane (HMDS) catalyzed by reusable electron‐deficient tin(IV)porphyrin

In this paper, rapid and highly efficient trimethylsilylation of alcohols and phenols with hexamethyldisilazane (HMDS) in the presence of catalytic amounts of high‐valent [Sn^IV(TPP)(OTf)₂] is reported. This catalytic system catalyzes trimethylsilylation of primary, secondary and tertiary alcohols as well as phenols, and the corresponding TMS‐ethers were obtained in high yields and short reaction times at room temperature. It is noteworthy that this method can be used for chemoselective silylation of primary alcohols in the presence of secondary and tertiary alcohols and phenols. The catalyst was reused several times without loss of its catalytic activity. Copyright © 2009 John Wiley & Sons, Ltd.     

Kinetic Evaluation of Reactivity of Phenolic Derivatives as Antioxidants for Polypropylene

Reactivity of commercial phenols as antioxidants for plastics, especially polypropylene, was examined under kinetic considerations. Inhibitive rate constants, k_inh, were found to decrease in the order: SWP ? Topanol CA ? BMP > Ionox 330 > Irganox 1076 > Irganox 1010, while numbers n′ of free radicals trapped by the phenolic moiety decreased in the order: Irganox 1076 > Irganox 1010 ? Ionox 330 > BMP ? Topanol CA > SWP (the structures of these antioxidants are given in the text). In practical use of phenols for polypropylene, it was found that effective phenols are not those having higher values of of k_inh., but n′ values nearly two. The effect of substituents, especially para substituents, of phenols on their activities was elucidated.     

Highly efficient tetrahydropyranylation of alcohols and phenols catalyzed by a new and reusable high-valent vanadium(IV) porphyrin

In the present work, the catalytic activity of high-valent tetraphenylporphyrinatovanadium(IV) trifluoromethanesulfonate, [V^IV(TPP)(OTf)₂], in the tetrahydropyranylation of alcohols and phenols with 3,4-dihydro-2H-pyran (DHP) is reported. This new electron-deficient V(IV) compound was used as a highly efficient catalyst for pyranylation of primary (aliphatic and benzylic), sterically-hindered secondary and tertiary alcohols with DHP. Tetrahydropyranylation of phenols with DHP was also performed to afford the desired THP-ethers. The chemoselectivity of this method was also investigated. The results indicated that primary alcohols are more reactive in the presence of secondary and tertiary alcohols and phenols. This catalyst was reused several times without loss of its activity.     

One-pot conversion of phenols to anilines via Smiles rearrangement

A convenient one-pot synthesis of phenols to anilines using 2-chloroacetamide/K₂CO₃/DMF system catalyzed by KI via Smiles rearrangement has been described. The synthesis of extensive amino aromatic products from phenols containing electron withdrawing group, has been performed in moderate to excellent yields to demonstrate the potentiality of this method in bio-medicinal and pharmaceutical applications.     

A practical synthesis of aryl tetrafluoroethyl ethers via the improved reaction of phenols with 1,2-dibromotetrafluoroethane

An efficient and practical synthesis of various aryl tetrafluoroethyl ethers by the reaction of phenols with 1,2-dibromotetrafluoroethane and the subsequent reduction with zinc dust was described. The nucleophilic substitution of 1,2-dibromotetrafluoroethane with phenols initiated by bromophilic attack was improved by using Cs₂CO₃ as a base and DMSO as a solvent.     

Kinetics and structure-activity relationship of dendritic bridged hindered phenol antioxidants to protect styrene against free radical induced peroxidation

A series of dendritic poly(amido-amine) (PAMAM) bridged hindered phenols antioxidants were synthesized. The active antioxidant group (3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid) was attached to two generations of PAMAM dendrimers, and their structure was verified by nuclear magnetic resonance (NMR) and fourier transform infrared spectra (FT-IR). The antioxidant abilities of the dendritic phenols to inhibit the oxidation of styrene were evaluated and the relationships between the length of core, the generation of dendrimers and the antioxidant activities were established. The reaction kinetics of scavenging peroxyl radicals was followed by oxygen consumption. The inhibition time (t_inh) values showed the dendritic phenols had the ability of scavenging peroxyl radicals, and that the antioxidant ability increased with the increasing length of the core and the generation. The kinetic analysis demonstrated that dendritic phenols could slow the rate of styrene peroxidation induced by AIBN, as shown by the number of trapping ROO· (n), and this role was in accordance with that of the t_inh values.     

One‐Pot Alkoxylation of Phenols with Urea and 1,2‐Glycols

A one‐pot epoxide‐free alkoxylation process has been developed for phenolic compounds. The process involves heating phenols and urea in 1,2‐glycols at 170‐190 °C using Na₂CO₃/ZnO as co‐catalysts under atmospheric conditions. During the course of this new alkoxylation reaction, a five‐membered ring cyclic carbonate intermediate, ethylene carbonate (EC) or propylene carbonate (PPC), was produced in‐transit as the key intermediate and was subsequently consumed by phenols to form alkoxylated ether alcohols as final products in excellent yields. For instance, phenol, bisphenol A (BPA), hydroquinone and resorcinol were converted into their respective mono‐alkoxylated ether alcohols on each of their phenolic groups in 80‐95% isolated yields. In propoxylation of phenols, this approach shows great product selectivity favoring production of high secondary alcohols over primary alcohols in isomeric ratios of nearing 95/5. Since ammonia (NH₃) and carbon dioxide (CO₂) evolving from the reaction can be re‐combined in theory into urea for re‐use, the overall net‐alkoxylation by this approach can be regarded as a simple condensation reaction of phenols with 1,2‐glycols giving off water as its by‐product. This one‐pot process is simple, safe and environmentally friendlier than the conventional alkoxylated processes based on ethylene oxide (EO) or propylene oxide (PO). Moreover, this process is particularly well‐suited for making short chain‐length alkoxyether alcohols of phenols.     

Polystyrene‐Gallium Trichloride Complex: A Mild,Highly Efficient,and Recyclable Polymeric Lewis Acid Catalyst for Chemoselective Silylation of Alcohols and Phenols with Hexamethyldisilazane

Polystyrene‐supported gallium trichloride (PS/GaCl₃) as a highly active and reusable heterogeneous Lewis acid effectively activates hexamethyldisilazane (HMDS) for the efficient silylation of alcohols and phenols at room temperature. In this heterogeneous catalytic system, primary, secondary, and tertiary alcohols as well as phenols were converted to their corresponding trimethylsilyl ethers with short reaction times and high yields under mild reaction conditions. The heterogenized catalyst is of high reusability and stability in the silylation reactions and was recovered several times with negligible loss in its activity or a negligible catalyst leaching, and also there is no need for regeneration. It is noteworthy that this method can be used for chemoselective silylation of different alcohols and phenols with high yields.     

Selective tetrahydropyranylation of alcohols and phenols using titanium(IV) salophen trifluoromethanesulfonate as an efficient catalyst

Titanium(IV) salophen trifluoromethanesulfonate, [Ti^IV(salophen)(OSO₂CF₃)₂], as a catalyst enables selective tetrahydropyranylation of alcohols and phenols with 3,4‐dihydro‐2H‐pyran. Using this catalytic system, primary, secondary and tertiary alcohols, as well as phenols, were converted to their corresponding tetrahydropyranyl ethers in high yields and short reaction times at room temperature. Investigation of the chemoselectivity of this method showed discrimination between the activity of primary alcohols in the presence of secondary and tertiary alcohols and phenols. This heterogenized catalyst could be reused several times without loss of its catalytic activity. Copyright © 2016 John Wiley & Sons, Ltd.