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.     

Chlorination of substituted phenols with chloramine T. A kinetic study

Kinetics of chlorination of substituted phenols with a particular emphasis on p-nitrophenol (PNP) have been extensively studied using chloramine T (CAT). The effect of added mineral acids, neutral salts, and chloride have been investigated in detail. In aqueous acetic acid at high acidities the reactive phenols follow a zero-order process, while PNP or the disubstituted derivatives give a fractional-order dependence on substrate concentration. The concentration dependence of rate with respect to PNP, the chlorinating agent, and acid reveals the rate law 1/k_obs versus 1/[PNP] gave a straight line with a finite intercept. In aqueous dimethylformamide (DMF) and dimethylsulfoxide (DMSO) the reaction shows a second-order dependence on CAT and a first-order dependence on PNP in the case of DMF and a slight increment in order in DMSO. Addition of water increases the rate both in aqueous acetic acid and in dipolar aprotic solvents such as DMF and DMSO. The order of the reaction with respect to CAT is found to be dependent on pH as well as the reactivity of the phenols. In buffered acetic acid medium a second-order dependence on CAT was followed up to pH 7. The rate variations with temperature in the range of 30°¨Dot;50°C have been studied for all the substituted phenols, and the respective activation parameters have been calculated. The empirical rate law is accounted for by a mechanism involving species generated from CAT complexing PNP. Protonated CAT, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm H}_{\rm 2} \mathop {\rm O}\limits^{\rm + } {\rm Cl} $\end{document}, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm Cl}\mathop {\rm O}\limits^{\rm + } {\rm AcH} $\end{document}, and dichloramine T (DCT) are considered important depending on reaction media. The effect of salts, pH, structural variations, and solvent dependence have been accounted for by the proposed mechanism. An attack by positive chlorine on oxygen of the phenol is the preferred mode of attack.     

Beiträge zur Chemie der Silicium-Schwefel-Verbindungen. 47 [1]. Über die protolytische Spaltung der Si?S-Bindung in Trialkoxysilanthiolen und Darstellung von Trialkoxyorganoxysilanen

Contributions to the Chemistry of Silicon-Sulphur Compounds. 47. On Protolytic Splitting of the Si? S Bond of Trialkoxysilanethiols and Preparation of Trialkoxyorganoxysilanes The conditions of the reaction of protolytic splitting of the Si? S bond of (RO)₃SiSH by alcohols or phenols were optimized by use of pyridine. Some new trialkoxyorganoxysilanes have been prepared. By kinetic measurements the relationship between the structure of phenol and reaction rate were elucidated. The role of pyridine in the reaction mechanism has been proposed as nucleophile catalysis.     

Kinetics and mechanism of the reactions of diethylzinc with phenols in cyclic ethers

Reactions of diethylzinc and phenols (phenol, 2-ethylphenol, 2-chlorophenol, 3-ethylphenol, 3-chlorophenol, 4-ethylphenol and 4-chlorophenol) have been carried out in tetrahydrofuran and 1,4-dioxane as solvents. Monomeric ethylzinc phenoxide has been found to be a product of the diethylzinc and phenol (1:1) reaction in 1,4-dioxane solution. Kinetic studies on the ethylzinc phenoxides and phenols reaction in tetrahydrofuran solution established the rate constants and the S_Ei mechanism of the reaction.     

Insights into the Mechanism of the Reaction between Tetrachloro‐p‐Benzoquinone and Hydrogen Peroxide and their Implications in the Catalytic Role of Water Molecules in Producing the Hydroxyl Radial

Detailed mechanisms for the formation of hydroxyl or alkoxyl radicals in the reactions between tetrachloro‐p‐benzoquinone (TCBQ) and organic hydroperoxides are crucial for better understanding the potential carcinogenicity of polyhalogenated quinones. Herein, the mechanism of the reaction between TCBQ and H₂O₂ has been systematically investigated at the B3LYP/6‐311++G** level of theory in the presence of different numbers of water molecules. We report that the whole reaction can easily take place with the assistance of explicit water molecules. Namely, an initial intermediate is formed first. After that, a nucleophilic attack of H₂O₂ onto TCBQ occurs, which results in the formation of a second intermediate that contains an OOH group. Subsequently, this second intermediate decomposes homolytically through cleavage of the O? O bond to produce a hydroxyl radical. Energy analyses suggest that the nucleophilic attack is the rate‐determining step in the whole reaction. The participation of explicit water molecules promotes the reaction significantly, which can be used to explain the experimental phenomena. In addition, the effects of F, Br, and CH₃ substituents on this reaction have also been studied.     

Silver(I)‐Catalyzed Addition of Phenols to Alkyne Cobalt Cluster Stabilized Carbocations

A smooth catalytic method to use phenols as the nucleophilic partner in the Nicholas reaction has been developed. The method uses either Ag^I or Au^I catalysts with AgClO₄ or AgBF₄ as the most efficient catalysts tested. Neither additional additives nor cocatalysts were required and the formation of the corresponding phenol adducts occurred in excellent yields. The process has the single limitation of the inability of less nucleophilic phenols (4‐nitrophenol) to generate the corresponding adducts. Additionally, the reaction is highly diastereoselective. DFT calculations allow a catalytic cycle to be proposed that involves trimetallic intermediates; the rate‐determining step of the reaction is hydroxy‐group elimination in a cobalt–silver trimetallic intermediate.     

Reactions of p‐Substituted Phenols with Nitrous Acid in Aqueous Solution

The reaction of phenols with nitrite (nitrous acid HONO, or its conjugated base, NO₂^?) is of importance in stomach fluids (low pH) and in atmospheric hydrometeors (mild acid and basic pH). The initial reaction associated with the oxidation/nitration of 4‐substitued phenols promoted by HONO/NO₂ depends on the pH of the solution. At low pH, the initial step involves the reaction between HONO and phenol, whereas at basic conditions this involves an electron transfer from the phenoxy anion to nitrogen dioxide (NO₂) producing the nitrite anion. The rate of both processes is determined by the donor capacity of the substituent at the 4‐position of the phenol, and the data obtained at pH 2.3 follow a linear Hammett‐type correlation with a slope equal to –1.23. The partition of the gaseous intermediates (NO and NO₂) makes the rate of HONO‐mediated oxidation dependent on their gas–liquid distribution. At low pH, the main process is phenol oxidation, even in oxygen‐free conditions, and the presence of any 4‐substituted phenol decreases the rate of HONO auto‐oxidation.     

Kinetics of the Anaerobic Reaction of para‐Substituted Phenols with Nitrogen Dioxide

para‐Substituted phenols in aqueous solution under anaerobic conditions readily react with nitrogen dioxide (NO₂^●) over a wide range of experimental conditions. The rate and rate law of the process were dependent on phenol concentration and solution pH. The kinetic order in phenol changed from one (low concentration) to zero (high concentration), a result attributable to total NO₂^● capture. Initial consumption rate (r ₀) of phenols versus pH plots showed parabolic behavior with a minimum rate at pH ca. 5. On the other hand, the maximum rate took place at high pH (pH>10) and involved the protonated phenols. The reaction rate of para‐substituted phenols with NO₂^● correlated with the bond dissociation energy and with Hammett's parameter. Based on such results and also supported by analysis of products carried out by HPLC‐MS/MS, our data conclusively show that, in spite of the fast acid–base interchanges of phenols and the interconversion of the different nitrogen oxides, the mechanisms of phenols nitration mediated by NO₂^● or HONO are clearly different.     

Regioselective Nitration of Phenols by NaNO3 in Microemulsion

Highly regiospecific mononitration of phenols and substituted phenols was carried out in TX100-based microemulsion. The use of inexpensive and relatively nontoxic acidic reagent is an advantage of this method. The effect of various parameters such as concentration of NaNO₃, temperature, and agitation speed on reaction system have been investigated. Exclusive ortho-selectivity was observed for all the phenols subjected to this protocol.     

5-membered cyclic acyl phosphates : A new class of extremely reactive phosphorylating agents

The reaction of phosgene with the oxyphosphorane made from biacetyl and trimethyl phosphite gives an α-(dimethylphosphato)-β-ketoacid chloride, which undergoes an intramolecular loss of methyl chloride under catalysis; by CuSO₄, and yields the first reported 5-membered cyclic acyl phosphate. The acyl phosphate is attacked exclusively at phosphorus by water, alcohols and phenols, at an extraordinarily rapid rate. In contrast, tertiary amines attack only the Me carbon of the exocyclic OMe group of the acyl phosphate to give quaternary ammonium salts of 5-membered cyclic acyl phosphates. These cyclic mixed anhydrides of phosphoric acid are the most powerful phosphorylating agents for oxygen-containing nucleophiles known at present. The end-products of the phosphorylations are phosphotriesters, phosphodiesters, and phosphomonoesters, containing the easily removable acetoinyl group, [(CH₃CO)(CH₃)CHO]P(O)(OR)(OR′).