Synthesis of azolylethyl benzhydryl ethers,analogs of diphenhydramine

Alternative approaches to the preparation of azolylethyl benzhydryl ethers have been studied. It was shown that the reaction of diphenylmethyl halide with 2-(azol-1-yl)ethanol in the presence of triethylamine is the optimum way. An efficient method for the synthesis of 2-(imidazol-1-yl)ethanol using phase-transfer catalysis has been developed.     

Polycondensation of benzyl chloride and its derivatives: A study of the reaction at different temperatures

The polycondensation reactions of benzyl chloride, α-chloroethylbenzene, and benzhydryl chloride in the presence of SnCl₄ or AlCl₃ as catalysts have been investigated in the temperature range between +80° and ?135°C. Polycondensations of benzyl chloride and α-chloroethylbenzene are quite similar in the reaction kinetics and are thought to occur by the same displacement mechanism. Polycondensation of benzhydryl chloride, however, seems to involve the formation of benzhydryl carbonium ions. At low temperatures linear polymers tend to be formed, in contrast with branched polymers produced at room temperature. Steric effects are found to play a major role in protecting polymers from branching at lower temperatures. Polybenzyl polymers are found to be less linear than poly(-α-methylbenzyl), even when prepared at ?135°C.     

SYNTHESIS AND PHOTOCROSSLINKING OF BENZYL (METH)ACRYLATE SUBSTITUTED POLYDIMETHYLSILOXANES: INFLUENCE OF PHOTOINITIATOR NATURE

ABSTRACT

The photoinduced crosslinking of silicones containing benzyl acrylate and benzyl methacrylate groups in the presence of different usual radical photoinitiators (TEPO, Darocur® 1173, Darocur 4265) and azo-containing polydimethylsiloxanes or mono- and bis(phenylmaleimide) functionalized disiloxanes has been investigated by photocalorimetric measurements. The influence of photoinitiator type, temperature and of the exposure time on the photocrosslinking kinetics was followed.     

PHOTOREDUCTION OF CRYSTAL VIOLET IN SOLUTION AND IN POLY(VINYL ALCOHOL) FILMS

Abstract— The photolysis of crystal violet oxalate has been studied in aqueous and non-aqueous solutions and in films of poly(viny1 alcohol) at room temperature. Evidence has been obtained from electron-spin-resonance, absorption and fluorescence spectroscopy for the formation of the semireduced dye radical, tri-( p -dimethylaminophenyl)methyl, both in solution and in the solid state. Electron spin resonance and luminescence spectra of the radical produced by electrolytic reduction of the dye are also reported.     

Sodium Bisulfite: An Efficient Catalyst for Ether Formation via Dehydration of Aromatic/Aliphatic Alcohol

Straightforward etherification of benzyl alcohols ( 1 ) via intermolecular dehydration can be efficiently catalyzed by sodium bisulfite under solvent‐free conditions. In the presence of 0.3 mol% or 0.6 mol% amount of sodium bisulfite, symmetric and unsymmetric ethers are prepared from the corresponding alcohols in high yields (up to 95%). Etherification of benzhydryl alcohols is also discussed.     

苯甲醇在二氧化钛超微粒表面的光诱导电子转移和光反应过程研究

本文用自旋捕捆—ESR方法探讨了苯甲醇在超细微粒二氧化钛胶体表面的光诱导电子转移和光化学行为。结果明确地显示出,在不同pH条件下,笨甲醇在二氧化钛胶体表面的光化学行为有显著差别。在很低pH条件下,体系中检出明显的单重态氧加合物的信号,在pH=3.0左右,则以超氧负离子基为主;pH在4—6范围内时,产生较大量的苄氧基,且认pH=6时为最多;在pH为7左右时,除苄氧基外,同时还有一定量的羟甲基(·CH₂OH)和苯基自由基产生。本文对于不同pH条件下的光诱导电子转移和光化学反应机理进行了讨论。     

Studies in organic mass spectrometry. Part 25. Benzyl ion formation in chemical ionisation (methane or isobutane) of some ortho-alkylhetero-substituted diphenylcarbinols

The behaviour of some ortho-alkylhetero-substituted diphenylcarbinols, including deuterium labelled derivatives, under chemical ionisation (methane or isobutane) conditions has been investigated. It has been determined that ortho-alkylhetero diphenylmethyl cations formed by water elimination from the protonated molecule undergo consecutive rearrangements which afford benzyl (or tropylium) ions previously observed for ortho-substituted diphenylcarbenium ions generated by electron ionisation. This reaction also occurs under low-energy collision conditions. Copyright 2000 John Wiley & Sons, Ltd.     

CHIRAL VARIANTS OF ARYLALKYL SULFUR REAGENTS. (R)-CAMPHOR KETIMINES OF OGIOVANNA AMINOTHIOETHERS AND OXIDES

Abstract

Ketimines la-d derived from ortho-aminosubstituted phenylthioethers were prepared in order to determine the degree of chirality transfer from the chiral auxiliary to the sulfur atom in the formation of the sulfoxide or to the α-carbon atom in the reaction of the anion with alkyl halides or benzaldehyde. Oxidation to the sulfoxide occurred with little or no asymmetric induction. The crystalline benzyl sulfone 4c was deprotonated by alkyllithium or Grignard reagents and reacted with alkyl halides and benzaldehyde, in all cases with little to fair transfer of chirality. The major diastereoisomer from methylation of the anion of 4c with methyl iodide, was isolated, and afforded the enantiomerically pure amine 5 after removal of the chiral auxiliary. An X-ray structure determination of 4d allowed the assignment of the absolute configuration of the asymmetric carbon and revealed that the conformation of the ketimine in the crystal state is not homogeneous.     

The fluorescence lifetimes of the methyl-substituted benzyl,triphenylmethyl and diphenylmethyl radicals

Time resolved fluorescence of some methyl-substituted benzyl, triphenylmethyl, and diphenylmethyl radicals trapped in rigid solvents at low temperature has been observed. These radicals were excited by pulsed N₂ laser at 337 nm. It is found that these radicals exhibit very long fluorescence lifetime. The long lifetimes of these radicals seem to indicate that the first doublet-doublet electronic transitions of the radicals have a forbidden character.     

Fluorescence from Samarium(II) Iodide and Its Electron Transfer Quenching: Dynamics of the Reaction of Benzyl Radicals with Sm(II)

The luminescence from SmI(2) in THF can be readily quenched by a variety of electron acceptors. In the case of organohalides, the reaction is quite fast; for example, for dichloromethane the rate constant is 2.7 x 10(8) M(-)(1) s(-)(1). Electron transfer leads to halide loss and formation of the carbon-centered radical. In the case of benzyl chloride, the benzyl radicals produced can be readily detected using laser flash photolysis techniques. This electron-transfer reaction has been used as a source of benzyl radicals in order to determine the rate constant for their reaction with SmI(2); the value obtained is (5.3 +/- 1.4) x 10(7) M(-)(1) s(-)(1) in THF at room temperature. The effect of HMPA on the spectroscopic properties of SmI(2) has also been examined.     

Two-photon chemistry in the laser jet: generation of radical intermidiates and their photochemical transformations

The novel laser jet technique provides sufficiently high photon densities to permit the observation of the photochemistry of photochemically generated radicals (two-photon chemistry) in the liquid phase. Four recent applications of this novel photochemically useful method are presented: these include the photochemistry of hydroxydiphenylmethyl, 9-hydroxyxanthenyl, diphenylmethyl, and benzoyl radicals under laser jet and normal photolysis conditions.

The regioselectivity of cross-coupling reactions of hydroxydiphenylmethyl or 9-hydroxyxanthenyl radicals with solvent-derived radicals changes when these species are electronically excited,i.e. under the high intensity conditions of the laser jet, cross-coupling at the para position (head-to-tail combination) is significantly enhanced relative to the normal coupling mode at the hydroxy-bearing radical site (head-to-head combination). Semiempirical calculations of the spin density distributions for the ground and first excited states of the radicals confirm the change in spin density from the hydroxy-bearing carbon atom to the conjugating benzene rings in these radical species on photoexcitation.

For the diphenylmethyl radical, two reaction pathways have been observed under the high photon densities of the laser jet: the electronically excited diphenylmethyl radical can either abstract a chlorine atom from carbon tetrachloride through an electron transfer process or can be photoionized on further photoexcitation (multiphoton chemistry). The resulting benzhydryl cation was trapped by methanol as the corresponding ether product, which unequivocally demonstrates that carbene formation by photoejection of a hydrogen atom does not take place under laser jet photolysis conditions.

An advantage of the high photon densities produced in laser jet photolysis is the high steady state concentration of short-lived transients that are generated, which enable unprecedented intermolecular reactions to be observed. Thus, about a millimolar concentration of tert-butoxy radicals can be obtained in the laser jet photocleavage of tert-butyl peroxide. When the tert-butoxy radicals are produced in the presence of benzaldehyde, the main product is tert-butyl benzoate. If carbon tetrachloride is also present, chlorobenzene can be detected. This is rationalized as the product derived from chlorine abstraction by phenyl radicals, which are presumably produced by the photodecarbonylation of benzoyl radicals.

An alternative method of obtaining benzoyl radicals is the two-photon cleavage of benzil. The laser jet photolysis of benzil in tert-butyl peroxide yields mainly tert-butyl benzoate, whereas in carbon tetrachloride, benzoyl chloride, chlorobenzene and ,,-trichloroacetophenone are observed. The first two products result from chlorine atom abstraction by the photochemically generated benzoyl and phenyl radicals, and the last product from in-cage cross-coupling between benzoyl and trichloromethyl radicals.

Such product studies provide detailed mechanistic information on the photochemical behaviour of electronically excited, short-lived transients which complements nicely the kinetic and spectral data of time-resolved laser flash studies. Consequently, the laser jet technique constitutes a valuable tool for determining the mechanism of two- photon reactions.     

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).     

Photon-induced unimolecular decay of the benzyl radical: first direct identification of the reaction pathway to C7H6

The thermal unimolecular decay of the benzyl radical has been investigated extensively by several groups. However, the reaction products could not be determined unambiguously. In this work the unimolecular bond fission of the benzyl radical is studied in a molecular beam experiment. The precursor molecules toluene and cycloheptatriene are expanded in a molecular beam and photodissociated with two photons at 248 or 193 nm, yielding in each case hot benzyl radicals. Since the internal energies lie above the dissociation limit, the benzyl radicals decay in a subsequent step. The reaction products are detected in a time-resolved manner with a quadrupole mass spectrometer on the molecular beam axis at low electron energies. The measured time-of-flight spectra provide information on the translational energy distribution of the products. In each case it is found that the hot benzyl radicals C₇H₇ fragment under hydrogen loss to C₇H₆.     

First Total Synthesis of (±)‐Latifolin and Its Antioxidant Mechanism

The first total synthesis of (±)‐latifolin has been accomplished in six steps and 47.8% overall yield. To understand the relative importance of phenolic O? H and benzhydryl C? H hydrogen on the antioxidant activity of latifolin, 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) radical scavenging assay and density functional theory (DFT) studies were carried out. On scavenging DPPH radical in ethanol, the activity of latifolin ( 1 ) bearing phenolic hydrogen is remarkably higher than analogue 10 bearing no phenolic hydrogen. Therefore, Phenolic hydrogen is responsible for latifolin's antioxidant activity rather than benzhydryl C? H hydrogen. Furthermore, the 5‐OH BDE is lower than 2′‐OH and 7‐CH BDEs by a DFT calculation, respectively. Based on theoretical results it is definitely concluded that the phenolic 5‐OH plays a major role in the antioxidant activity of latifolin.     

Experimental verification of the Smoluchowski theory for a bimolecular diffusion-controlled reaction in liquid phase

We report experimental verification of the Smoluchowski theory for diffusion-controlled reactions in solution at the steady-state limit. We have determined both the diffusion coefficients and the self-termination reaction rates of the diphenylmethyl radical simultaneously. Smoluchowski theory is insufficient to discuss the reaction rate for the self-termination reaction of the diphenylmethyl radical, so the reaction rate of an encounter complex based on the Collins-Kimball treatment is estimated.     

The rearrangement of benzylic trichloromethane-sulfenates to sulfoxides and chlorides

While benzyl trichloromethanesulfenate undergoes no rearrangement to sulfoxide even at high temperatures, the corresponding anisyl ester rearranges to p-anisyl trichloromethyl sulfoxide in hexane under mild conditions. Substitution of hexane by chloroform under similar conditions, lead to the formation of p-anisyl chloride and dichlorosulfine as main reaction products. This process is enhanced by the use of more polar solvents and higher temperatures. The conversion of trichloromethanesulfenate to chloride has also been observed with the benzyl and benzhydryl esters on heating in various solvents, though at very differing rates. Both rearrangements are suggested to take place by an ionization mechanism. Depending on the reaction conditions and nature of the substrate, the sulfenate anion can either recombine with the cation to give sulfoxide, or further dissociate to dichlorosulfine and chloride ion, which gives the benzyl chloride. The observation of an S_N1 type mechanism for rearrangement of sulfenates appears to be unique.     

PHOTOCHROMISM AND LUMINESCENCE OF DOPANT CHROMOPHORES THROUGH TWO-PHOTON IONIZATION IN POLYMER FILMS

Two-photon ionization and recombination processes of an aromatic chromophore doped in polymer films werestudied and the features of these processes were discussed in relation to photofunctional polymers, An aromatic moleculehaving low ionization potential, e.g., N,N,N',N'-tetramethyl-p-phenylene diamine doped in poly(methyl methacrylate)(PMMA) film was easily photoionized by intense laser ligh excitation, giving a colored radical cation (photochromism) anda trapped electron in PMMA matrix. As a reversed process, the radical cation recombined with the trapped electron, showingdiscoloration and emitting luminescence, either isothermal luminescence (ITL), or thermoluminescence (TL). In this report,ITL and TL through the charge recombination process were studied and the luminescence was suggested as a mean of the read-out of photorecording.     

Kinetic Comparison of Trifluoroacetic Acid Cleavage Reactions of Resin-Bound Carbamates, Ureas, Secondary Amides, and Sulfonamides from Benzyl-, Benzhydryl-, and Indole-Based Linkers

The kinetics of cleavage reactions of 16 resin-bound carbamates, ureas, secondary amides, and sulfonamides from four different acid labile linkers including benzyl, benzhydryl, and indole linkers has been investigated. The optimized cleavage conditions are generally milder than those commonly used and reported (e.g., 0.5% TFA as opposed to 5%). Among various linkers studied in this work, the indole linker has been found to be the most acid labile followed by the Rink linker. The rate of cleavage of compounds linked to the resin via various functional groups can be summarized as follows: sulfonamide >carbamate approximately urea > amide. This study shows that cleavages of 16 compounds from four different acid labile linkers have been optimized to much milder conditions in terms of TFA concentration and the reaction time. It also demonstrates that single bead FTIR is an effective tool for optimizing cleavage conditions.     

ENDOR AND ESR STUDIES OF RADICALS FORMED IN FRIEDEL-CRAFTS REACTIONS

The present study deals with the study of some Friedel-Crafts alkylating system and the accurate measurement of hyperfine coupling constants by ESR and ENDOR techniques. The results indicate that the observed ESR spectra are due to polycyclic aromatic radical cations formed from their parent hydrocarbons.It is suggested that benzyl halides produced in the Friedel-Crafts alkylating reaction undergo Scholl condensation reaction to give polycyclic aromatic hydrocarbons, which were converted into the corresponding polycyclic aromatic radical cations in the presence of aluminum chloride.     

VOLATILITY AND SOLUBILIZATION OF SYNTHETIC FRAGRANCES BY PLURONIC P-85

The volatility of synthetic fragrances (benzyl formate, benzyl acetate, benzyl propionate) from pluronic P-85 aqueous solution has been investigated by the dynamic headspace method The experimental results showed that the volatility of a more hydrophobic fragrance was strongly controlled by pluronic P-85. This volatile behavior was explained by the solubilization constants of fragrances between the micelle and bulk phase by semiequilibrium dialysis method.