Alkyl Phenyl Research Articles

THERMAL INDUCED HOMOLYTIC SCISSIONS OF LIGNIN INTERUNITARY BONDS IN THE HARDWOOD LIGNIN SOLUTION. AN ESR STUDY COMBINED WITH A SPIN TRAPPING METHOD

An electron spin resonance (ESR) method combined with a spin trapping reagent was successfully applied to trap and characterize unstable free radicals which were generated by heat-treatment of the dimethylsulfoxide (DMSO) solution of a hardwood, Japanese beech (Fagus crenata) lignin. It was found, consequently, that two unstable secondary carbon radicals, ∼ CH• in the solution were created and the resulting radicals were trapped as the stable nitroxide spin adducts when the DMSO solution was heat-treated in the presence of a spin trapping reagent: 2,4,6-tri-tert-butylnitrosobenzene (BNB) at ca. 91°C. This means that so-called alkyl phenyl ether bonds, ∼ CH-O- phenyl, known as important lignin interunitary bonds were homolytically scissoned by the heat-treatment of the lignin solution. Further the detailed analysis of the observed ESR spectrum revealed that two positions of alkyl phenyl ether bonds, i.e., β-O-4 and/or α-O-4 bonds as the interunitary linkages in the lignin are homolytically scissioned, although the phenoxy radical, Ph-O • as the counter radical of the secondary carbon radicals was not trapped by the BNB spin trap. This suggests that fairly large steric hindrances operate between the syringyl with two methoxy moieties at the ortho positions and/or guaiacyl moieties with a methoxy moiety at the ortho position, and the BNB molecule bearing two bulky ortho tert-butyl groups in the phenyl ring.

ESR studies of radicals generated by ultrasonic irradiation of lignin solution. An application of the spin trapping method

An electron spin resonance (ESR) method combined with a spin trapping reagent was successfully applied to trap and characterize unstable radicals which were generated by ultrasonic irradiation of dimethylsulfoxide (DMSO) solution of hardwood, Fagus crenata lignin. It was found, consequently, that a secondary carbon radical, ∼CH· was trapped as the nitroxide spin adduct when the DMSO solution was subjected to ultrasonic irradiation in the presence of a spin trapping reagent: 2, 4, 6-tri-tert-butylnitrosobenzene (BNB) at 50 °C for 60 minutes under vacuum. This means that the alkyl phenyl ether bonds known as lignin linkage bonds were homolytically scissoned by the ultrasonic irradiation, although the phenoxy radical, Ph-O· as the counter radical of the secondary carbon radical was not trapped by the BNB spin trap. Further, the data showed that the primary carbon radical, ∼OCH2 · is trapped by the BNB to form the corresponding spin adduct, indicating that the hydrogen abstraction from the ortho methoxy group in the syringyl and/or guaiacyl moiety is induced by the secondary carbon radical when irradiated. Based on these findings it was concluded that the Ph-O· radicals produced by the homolytic rupture of the alkyl phenyl ether bonds were not trapped by the BNB spin trap. This suggests that large steric hindrances operate between the syringyl with two methoxy moieties and/or guaiacyl with a methoxy moiety at the ortho position, and the BNB molecule bearing two bulky ortho tert-butyl groups.

Novel inhibitors of the enzyme estrone sulfatase (ES)

We report the initial results of our study into a series of simple 4-sulfamated phenyl alkyl ketones as potential inhibitors of the enzyme estrone sulfatase. The results of the study show that these compounds are potent inhibitors, possessing greater inhibitory activity than COUMATE, but weaker activity than EMATE. Furthermore, the compounds are observed to be irreversible inhibitors.

Kinetic studies of the reactions of some phenols and alkyl aryl ethers with dinitrogen pentoxide in perfluorocarbon solvents

The reaction of dinitrogen pentoxide in perfluorocarbon solvents with phenols and alkyl aryl ethers carrying halogeno ring-substituents results in nitrodehydrogenation. Rate measurements show that the preferred orientation of nitration is ortho > para > meta to the hydroxy group; the kinetic isotope effect, kH/kD, has a value close to unity. Phenols show considerably higher reactivity than similarly substituted alkyl phenyl ethers, and a mechanism is suggested involving initial interaction of N2O5 with the hydroxy function followed by reaction via cyclic transition states.

ChemInform Abstract: A Sulfoxide Version of the Julia-Lythgoe Olefination: A New Method for the Synthesis of Olefins from Carbonyl Compounds and Sulfoxides with Carbon-Carbon Coupling.

Abstract Reaction of β-mesyloxy (or acetoxy) sulfoxides, derived from alkyl (or arylmethyl) phenyl sulfoxides and carbonyl compounds in two steps, with alkylmetals (n-BuLi, t-BuLi, or EtMgBr) at low temperature gave olefins in good to excellent yields. When the β-hydroxy sulfoxides derived from arylaldehydes were treated with mesyl chloride in the presence of triethylamine, the sulfoxides directly gave E-olefins in good yields. These reactions offer a sulfoxide version of the Julia–Lythgoe olefination. The reductive vicinal elimination was found to take place through the direct sulfoxide–metal exchange. The stereochemistry of the elimination was investigated and found to be stereospecific; however, the stereospecificity was found to be dependent on the substrates.

Potential antifungal activity and structure-activity relationships of some 2-amino acid substituted benzo-1,3,2-dioxaphospholene, oxazaphospholine and diazaphospholine 2-ones.

Application of various organophosphorus compounds as fungicides and theirstructure-activity relationships have been studied extensively e.g. O,O-bisarylalkyl phosphonates (Roy et al. 1996), diaryl dichloromethyl phosphono-dithioates (Roy and Mukerjee 1975), and alkyl phenyl (dichloromethyl)phosphonates (Dureja et al. 1980). Recently, groups of potential fungicideshave been developed derived from diamines (Havis et al. 1996), o-phenylene-diamines (Khan et al. 1995), and o-aminophenols (Bravo and Lazo 1996). Itwas also reported that incorporating

A Sulfoxide Version of the Julia–Lythgoe Olefination: A New Method for the Synthesis of Olefins from Carbonyl Compounds and Sulfoxides with Carbon–Carbon Coupling

Reaction of β-mesyloxy (or acetoxy) sulfoxides, derived from alkyl (or arylmethyl) phenyl sulfoxides and carbonyl compounds in two steps, with alkylmetals ( n-BuLi, t-BuLi, or EtMgBr) at low temperature gave olefins in good to excellent yields. When the β-hydroxy sulfoxides derived from arylaldehydes were treated with mesyl chloride in the presence of triethylamine, the sulfoxides directly gave E-olefins in good yields. These reactions offer a sulfoxide version of the Julia–Lythgoe olefination. The reductive vicinal elimination was found to take place through the direct sulfoxide–metal exchange. The stereochemistry of the elimination was investigated and found to be stereospecific; however, the stereospecificity was found to be dependent on the substrates.

Homolytic Scission of Interunitary Bonds in Lignin Induced by Ultrasonic Irradiation of MWL Dissolved in Dimethylsulfoxide

SummaryAn electron spin resonance (ESR) method combined with a spin trapping technique was applied to trap and characterize unstable radicals which were generated by ultrasonic irradiation of the dimethylsulfoxide (DMSO) solution of a softwood, Yezo Spruce (Picea jezoensiscarr.) lignin. It was found that an unstable secondary carbon radical, ~CH • in the solution was trapped as the stable nitroxide spin adduct when the DMSO solution was subjected to ultrasonic irradiation in the presence of a spin trapping reagent: 2,4,6-tri-tert-butylnitrosobenzene (BNB) at 50°C for 30 min. This means that the alkyl phenyl ether bonds, ~CH-O-phenyl, known as interunitary bonds in lignins were homolytically cleaved by the ultrasonic irradiation, although the phenoxy radical Ph-O •, called guaiacoxy radical, i.e. the counter radical of the secondary carbon radical, was not trapped by the BNB spin trap. This suggests that the trapping of the guaiacoxy radical, having a methoxy group in anortho-position, by the BNB molecule, carrying two bulky butyl groups in theortho-positions, is sterically hindered.

PhSeSiR(3)-Catalyzed Group Transfer Radical Reactions.

A novel design for initiating radical-based chemistry in a catalytic fashion is described. The design of the concept is based on the phenylselenyl group transfer reaction from alkyl phenyl selenides by utilizing PhSeSiR(3) (1) as a catalytic reagent. The reaction is initiated by the homolytic cleavage of -C-Se- bond of an alkyl phenyl selenide by the in situ generated alkylsilyl radical (R(3)Si(*)), obtained by the mesolysis of PhSeSiR(3)](*)(-)( )()(1(*)(-)). The oxidative dimerization of counteranion PhSe(-) to PhSeSePh functions as radical terminator. The generation of 1(*)(-) is achieved by the photoinduced electron transfer (PET) promoted reductive activation of 1 through a photosystem comprising of a visible-light (410 nm)-absorbing electron rich DMA as an electron donor and ascorbic acid as a co-oxidant (Figure 1). The optimum mole ratio between the catalyst 1 and alkyl phenyl selenides for successful reaction is established to be 1:10. The generality of the concept is demonstrated by carrying out variety of radical reactions such as cyclization (10, 15-18), intermolecular addition (25), and tandem annulations (32).

Mn-salen catalyzed enantioselective sulfimidation

Enantioselective sulfimidation of alkyl phenyl sulfides was achieved by using ( R, R)-Mn-salen complex 5 as a catalyst. In the sulfimidation of methyl and benzyl phenyl sulfides, high enantioselectivity (up to 89% ee) was attained in the presence of N-methylmorpholine N-oxide (NMO).

Optical resolution of alpha-alkyl phenyl acetonitriles by HPLC on cellulose triacetate chiral stationary phases coated on underivatized silica gel

Microcrystalline celluloses from two sources were used to prepare cellulose triacetate chiral stationary phases (CSPs) coated on underivatized silica gel, which shows discriminating chiral recognition for enantiomers. The chiral separation of four alpha-alkyl phenyl acetonitriles was investigated on the prepared CSPs. It was observed that the concentration of the coating solvent of phenol in dichloromethane plays an important role in the resolution of the solutes. A series of primary alcohols, including secondary and tertiary alcohols, were used as mobile phase modifiers to investigate the effect of the structures of these modifiers on the capacity factors (k') and the separation factors (alpha). Also, the effect of the concentration of alcohol on the capacity factors and separation factors was examined. The chiral recognition mechanism of alpha-alkyl phenyl acetonitriles on the prepared CSPs is discussed. Copyright 2000 Wiley-Liss, Inc.

Mn-salen catalyzed nitrene transfer reaction: Enantioselective imidation of alkyl aryl sulfides

Enantioselective imidation of alkyl aryl sulfides was achieved by using ( R, R)- or ( R, S)-Mn-salen complex [( R, R)-3 or ( R, S)-3] as a catalyst. The optimum reaction conditions are dependent upon the substrates examined. For example, the imidation of alkyl phenyl sulfides with PhI=NTs using Mn-salen complex ( R, R)-3 as a catalyst in the presence of N-methylmorpholine N-oxide showed high enantioselectivity (up to 89% ee). On the other hand, the reaction of methyl 2,4-dinitrophenyl sulfide was effected (97% ee) by using Mn-salen complex ( R, S)-3 as the catalyst in the absence of N-methylmorpholine N-oxide.

17O NMR chemical shifts: a simple and useful rule for substituent additivity on oxygen atoms with a coordination number of two

The 17O chemical shifts of simple aliphatic ethers were studied, and the additivity substituent increments for carbon atoms in the alkyl groups were determined. The additivity parameters were used to establish a linear correlation with experimental data for a series of aliphatic ethers, alcohols, vinyl ethers, trichloroacetyl vinyl ethers, alkyl phenyl ethers, alkyl formates, alkyl acetates and alkyl trichloroacetates. The use of correlation to estimate the 17O chemical shifts allows the calculation of data with an accuracy better than ±2.5 ppm. Copyright © 1999 John Wiley & Sons, Ltd.

Optical Resolution and Configurational Stability of Selenoxides Stabilized by Intramolecular Coordination.

2-((Dimethylamino)methyl)phenyl alkyl (or aryl) selenoxides, configurationally stabilized by intramolecular coordination of an amino group to the selenium atom, were optically resolved into their enantiomeric isomers by means of high-performance liquid chromatography using an optically active column packed with amylosecarbamate derivative/silica gel. This is the first example of the isolation of optically pure selenoxides without bulky substituents and also the first isolation of optically pure alkyl aryl selenoxides. The absolute configuration of the (-)-isomers could be assigned to be the S-form by comparison of their specific rotations, circular dichroism spectra, and behavior on the optically active column with those of the sulfur analogue, prepared by Andersen's method. Racemization of the optically active selenoxides was accelerated not only in acidic solution but also in basic media. This result indicates there are two different mechanisms for their racemization in acidic and basic media. The stabilization energy of the selenoxides by the intramolecular coordination of an amino group to the selenium atom was estimated to be ca. 3 kcal mol(-)(1) on the basis of variable-temperature (1)H NMR measurements.

Juvenile hormone analogs active on mosquitoes: synthesis and juvenile hormonal activity of newly synthesized long chain alkoxy alkyl phenyl ethers.

Different 2-(8,12 dimethyl-5-oxa-7(E), 11-tridecadienyl)-alkyl phenyl ethers, their mono oxirane and thirane derivatives were synthesized and tested on Culex pipiens quinquefasciatus Say for their juvenile hormone activity.

Ru3(CO)12-Catalyzed Decarbonylative Cleavage of a C−C Bond of Alkyl Phenyl Ketones

Ru₃(CO)₁₂-Catalyzed Decarbonylative Cleavage of a C−C Bond of Alkyl Phenyl Ketones

Photoinitiation performance of some ketones in the LDPE–acrylic acid surface photografting system

The photoinitiating performance of four kinds of ketones (alkyl-, alkyl phenyl-, phenyl- and di-ketones) and two aldehydes (formaldehyde and acetaldehyde) were examined by measuring their polymerization reactivity, grafting efficiency and surface wetting time with a simple technique, film interlayer photopolymerization (FIP), with LDPE as film substrate, acrylic acid as monomer and an HPM-15 Lamp (2 kW) as UV radiation source. Benzophenone, xanthone, acetophenone and 9-fluorenone are shown to be efficient photografting initiators for obtaining thick grafted layers, while anthraquinone, 4,4-dichlorobenzophenone, 4-benzylbenzophenone, benzoylformic acid and biacetyl are suitable photoinitiators for obtaining thin grafted layers. These results and subsequent analysis show that high triplet state energy, strong UV absorption, stable molecular structure and low initiating reactivity of the resulting ketyl free radical are decisive factors making the ketones efficient initiators for grafting applications.

Ring versus oxygen protonation in metastable ion decompositions of protonated isopropyl phenyl ether

Protonated alkyl phenyl ethers possess more than one stable tautomer. A debate has arisen over whether only one of them gives rise to the principal dissociation pathway observed in their mass-analyzed ion kinetic energy (MIKE) spectra. Alkene loss constitutes the major (often the exclusive) metastable ion decomposition, yielding protonated phenol ions. A hydron deposited by chemical ionization exchanges with some of the alkyl hydrogens (but none of the ring hydrogens) prior to fragmentation. Previously published MIKE spectra have shown that [(CD 3) 2CHOPh]D + gives only m/ z 97 (C 6H 5D 2O +), but that [(CD 3) 2CHOPh]H + gives a mixture of m/ z 96 (C 6H 6DO +) and m/ z 97. Exchange must arise via ion-neutral complexes that result from O-protonated ions, (CD 3) 2CHO(H)Ph +. Current controversy centers around the contribution of ring-protonated ions to the production of unexchanged fragment ions. Here we determine the mole fractions of ring-protonated ( X) and O-protonated (1 − X) parent ions using m/ z 95: m/ z 96: m/ z 97 MIKE ion abundance ratios from H 2O and D 2O CI of (CH 3) 2CHOPh, CH 3(CD 3)CHOPh, and (CD 3) 2CHOPh. Data from the first two compounds give unbiased assessments of X and four other relative rate constants that are obtained using a steady-state kinetic model that gives a set of five equations in five unknowns. The values calculated from the data predict an m/ z 96: m/ z 97 ratio of 4.7 for [(CD 3) 2CHOPh]H + that turns out to be the same ratio as is measured experimentally. This validation of the data analysis corroborates the value of X ≤ 0.01 extracted from the experimental results. The contribution of ring-protonated parent ions to the MIKE spectra of chemically ionized isopropyl phenyl ether is therefore negligible.

Twist conformational effects on the excited triplet states of aromatic ketones studied by multifrequency TREPR and pulsed EPR spectroscopy

Employing X- and Q-band time-resolved EPR and pulsed EPR techniques, we have investigated effects of twist conformation on the electronic structures and magnetic properties of the lowest excited triplet states of alkyl phenyl ketones. The conformational variation due to steric hindrance of a bulky substituent on the α-position drastically leads to a decrease of the zerofield splitting constant of |D| and an increase of the energy gap between 3nπ* and 3ππ* states. Hydrogen bonding with H2O destabilized significantly the 3nπ* state and switched the T1 state to the 3ππ* state. t-Butyl phenyl ketone gave unusually broad EPR spectra in rigid glassy matrices. The multifrequency and pulsed EPR measurements clarified that the inhomogeneously broadening spectra were ascribable to the distribution of the dihedral angle about a twist conformation. Asymmetric distribution of the ZFS parameters was interpreted in terms of the perturbation of spin—orbit interactions to the spin sublevels.

Regio- and Stereochemistry of Alkene Expulsion from Ionized sec-Alkyl Phenyl Ethers

Photoionization mass spectrometry of isotopically substituted 2-phenoxypropane (iPrOPh), 2-phenoxybutane (sBuOPh), and 3-phenoxypentane (3AmOPh) permits the analysis of branching ratios for competing pathways by which the radical cations expel neutral alkene to yield ionized phenol. Ionization energies (IEs) of 2-phenoxyalkanes do not differ significantly between 2-phenoxypropane and 2-phenoxyoctane and are unaffected by deuterium substitution. IEs for 3-phenoxyalkanes are 0.04 eV lower than for the 2-phenoxyalkanes. Measurements of PhOD•+:PhOH•+ ratios from deuterated analogues as a function of photon energy lead to a dissection of two mechanisms: direct syn elimination via four-member transition states (which differentiates between stereochemically distinct positions on an adjacent methylene group) and formation of ion−neutral complexes (which affords hydrogen transfer from all positions of the side chain). Syn elimination from ionized sBuOPh partitions among trans-2-butene, cis-2-butene, and 1-butene in a ratio of approximately 6:5:4, exhibiting no systematic variation with internal energy. The proportion of ion−neutral complex formation for sBuOPh increases with energy, from virtually nil at 9.6 eV to about 20% at 9.81 eV to slightly more than one-half at 11.92 eV. Ion−neutral complexes from sBuOPh yield nearly equal proportions of 1-butene and 2-butenes, with little variation as a function of internal energy, while those from 3AmOPh yield about 80−90% 2-pentenes. DFT calculations confirm the preference for syn elimination from ionized iPrOPh at low internal energies. The computed energy of that transition state agrees with published experimental determinations. Analysis of the electron density using the atoms-in-molecules approach shows that the transition state does not possess cyclic topology, unlike vicinal eliminations from neutral molecules (which pass through bona fide cyclic transition states). Cyclic topology is seen for a structure that precedes the potential energy maximum, but that ring disappears at the top of the barrier. Both syn elimination and ion−neutral complex formation from the radical cation proceed far along the pathway for bond heterolysis before arriving at a point at which the two types of mechanism diverge from one another.