Free Ortho Positions Research Articles

Thermosets derived from diallyl-containing main-chain type benzoxazine polymers

To achieve high-performance thermosets, three diallyl-containing main-chain type benzoxazine polymers, (MCBP) were prepared from Mannich condensation of 2,2′-diallyl bisphenol A, paraformaldehyde, and three diamines: 4,4′-diaminodiphenylmethane (DDM), 4,4′-oxydianiline (ODA), and 2,2′-bis(4-(4-aminophenoxy)phenyl)propane (BAPP), respectively. These MCBPs can be cured and general a phenolic hydroxyl type benzoxazine thermosets even though no free ortho and free para positions to the oxygen of oxazine in their structures. After thermally curing, the resulting thermosets display much higher Tg than the thermosets of 2,2′-diallyl bisphenol A/aniline-based, 2-allyl phenol/DDM-based, and 2-allylphenol/ODA-based benzoxazine, demonstrating the advantage of MCBP on thermal properties over monomer type benzoxazines. The refractive index of the thermosets is higher than 1.689 at 589 nm, which is relatively high compared with other polymers. These results demonstrate the advantage of diallyl-containing MCBPs on thermal properties and refractive index over allyl-containing monomer type benzoxazines.

Naturally occurring thiophenes: isolation, purification, structural elucidation, and evaluation of bioactivities

Thiophenes are a class of heterocyclic aromatic compounds based on a five-membered ring made up of one sulfur and four carbon atoms. The thiophene nucleus is well established as an interesting moiety, with numerous applications in a variety of different research areas. Naturally occurring thiophenes are characteristic secondary metabolites derived from plants belonging to the family Asteraceae, such as Tagetes,Echinops,Artemisia, Balsamorhiza,Blumea, Pluchea, Porophyllum and Eclipta. Furthermore, naturally occurring thiophenes are generally composed of one to five thiophene rings that are coupled together through their α-carbons, and carry alkyl chains on their free ortho-positions. Thiophene-containing compounds possess a wide range of biological properties, such as antimicrobial, antiviral, HIV-1 protease inhibitor, antileishmanial, nematicidal, insecticidal, phototoxic and anticancer activities. This review focuses on naturally occurring thiophene derivatives; their sources, physical and spectral data, and biological activities.

Study on the Ring-Opening Polymerization of Benzoxazine through Multisubstituted Polybenzoxazine Precursors

To discuss the mechanism of ring-opening polymerization (ROP) of benzoxazine, a bisphenol A/diaminodiphenylmethane-based polybenzoxazine precursor (PBz-0M), o-dimethylbisphenol A/diaminodiphenylmethane-based polybenzoxazine precursor (PBz-2M), and o-dimethylbisphenol A/o-tetramethyldiaminodiphenylmethane-based polybenzoxazine precursor (PBz-6M) were prepared. Among the polybenzoxazine precursors, free ortho positions to the O of oxazine are available for PBz-0M. No free ortho or para position to the O of oxazine is available for PBz-2M, but free ortho position to the N of oxazine is available. No free ortho positions to the O or N of oxazine are available for PBz-6M. According to DSC, IR, and thermal analysis, we found that the ROP of PBz-2M can be carried out even though no free ortho or para position to the O of oxazine is available. We conclude that the ROP is carried out through the ortho position to the N of oxazine and propose a reaction mechanism to explain the polymerization.

Fully quantitative carbon-13 NMR characterization of resol phenol–formaldehyde prepolymer resins

Different resol phenol–formaldehyde prepolymer resins have been synthesized with different Formaldehyde/Phenol (F/P) ratios or different catalysts and characterized by 13C NMR spectroscopy in solution. A fast quantitative measuring protocol is proposed based on the use of chromium(III)acetylacetonate as a relaxation agent. APT (attached proton test) and DEPT (distortionless enhancement by polarisation transfer) spectra were acquired to enable proper resonance assignments, especially in the regions with severe signal overlap. Equations are presented in which the methylene bridges (MB), the methylol groups (MG) and the dimethylene ether bridges (DMEB) of resol resins are quantitatively taken into account. Important structural factors determined quantitatively for resol prepolymer resins are the F/P ratio after reaction, the degree of polymerization ( n), the number average molecular weight ( M n) and the content of free ortho and para positions.

A kinetic distribution model of evaporation, biosorption and biodegradation of polychlorinated biphenyls (PCBs) in the suspension of Pseudomonas stutzeri

Kinetics of distribution of PCBs in an active bacterial suspension of Pseudomonas stutzeri was studied by monitoring the evaporated amounts and the concentration remaining in the liquid medium with the biomass. To determine the biodegradation rate constants of the individual congeners of the PCB formulation Delor 103, a model considering biosorption, evaporation, and primary biodegradation constructed previously was used. Rate constants of biodegradation imply that biodegradation of individual congeners is structure-dependent process. Biodegradability decreases with increasing number of chlorine substituents in the molecule, especially if they are in the ortho and para positions. On the other hand, the increasing number of free ortho and meta positions in the biphenyl molecule leads to better biodegradability. For a simple empirical determination of the influence of the chlorine substitution pattern on biodegradability, the di- and trichlorobiphenyl rate constants of biodegradation were analysed.

Annelated Calixarenes Composed of Calix[4]arenes with Hydroxy Groups in the Endo and Exo Position.

Various phenol-derived calix[4]arenes (3) bearing four hydroxy groups in the exo position have been prepared by uncatalyzed condensation of suitable dimers or tetramers with formaldehyde in xylene in yields up to 44%. The tetra-tert-butyl compound (3a) has been shown by X-ray analysis to adopt a regular cone conformation (nearly identical in shape with the endo isomer) with two intramolecular O-H.O hydrogen bonds, while the corresponding dimer (6c) prefers a conformation (not possible in the calixarene) with two intramolecular O-H.pi(arene) interactions. Condensation of exo-calix[4]arenes 3f,g with free ortho positions (easily available by debutylation) with bisbromomethylated dimers gave annelated double (9) and triple (10) calixarenes consisting of endo- and exo-calix[4]arene substructures in yields up to 24% and 10%, respectively. Molecular dynamics calculations suggest that the exo-calixarene part in 9 is less mobile than the entirely flexible 3, while the endo-calixarene part shows a higher mobility than usual. A complete interconversion cone --> cone is impossible, however, which enables the construction of inherently chiral molecules.

Strategic synthesis of model novolac resins

Model novolac resins which contain the maximum number of free ortho positions for reaction with the curing agent hexamethylenetetramine (HMTA) have been prepared. The key transformation was the ion assisted ortho-specific phenol-formaldehyde oligomerization of suitably protected precursors.

Closure of the pyridine ring in the combes quinoline synthesis (Review)

Closure of the pyridine ring in the Combes quinoline synthesis occurs by a type of intramolecular electrophilic substitution. With two free ortho positions the direction of ring formation depends both on the initial electrophilic attack, i.e., the nucleophilicity of the ortho carbon atom, and on the possibility of stabilizing the intermediate complex. The steric requirements of substituents both in the enaminoketone chain and in the position ortho to the point of attack exert a significant effect on the direction of ring closure. The steric factor is decisive when forming condensed angular quinoline structures.

Investigation of the reaction of phenols with hexamethylene tetramine using a gas evolution technique

A study has been made of gas evolution during the cure of o-, p-cresols, o- and p-tert-butylphenols, 4-methyl-2-tert-butylphenol and 2,6-di-tert-butylphenol by hexamethylene tetramine. It is shown that at 403–448 K ∼0·5 mole of ammonia is evolved per ortho-position of phenols; under these conditions p-phenols react at a low rate with hexamethylene tetramine. It was found that from 4-methyl-2-tert-butylphenol, with a tritium labelled hydroxyl ∼ 92 wt.% of tritium is evolved in the ammonia. It is shown that N-hydroxybenzyl dihydrobenzoxazines are formed from phenols having one free ortho-position, while polydihydrobenzoxazines are formed from those with two free ortho-positions.

A general method for coulometric titration of alkylphenols with bromine

A general method for coulometric titration of alkylphenols with anodically generated bromine is described. The reaction is carried out in a water-acetic acid medium and the reactivity is governed by varying the water content and the concentration of bromide ion and by the addition of pyridine. In that way all types of alkylphenols can be titrated quantitatively. For phenols containing more than one free ortho and para position, the titration can also be carried out either to the monobromination stage or to the full bromination stage. The mean relative error is +/- 1.2% for monobromination and +/-1.5% for full bromination. A method for rapid determination of the number of free ortho and para positions in alkylphenols by using two coulometric titrations is also described.

Die durch Silberionen katalysierte Umlagerung von Propargyl‐phenyläther

AbstractIt is known that propargyl‐phenylethers rearrange at about 200° to 2 H‐chromenes [1–4]. It is shown that this rearrangement occurs in benzene or chloroform at lower temperatures (20–80°) in the presence of silver‐tetrafluoroborate (or‐trifluoracetate). The ethers examined are presented in Scheme 1. Thus in chloroform at 61° in the presence of AgBF4, phenyl‐propargylether (3) yields 2 H‐chromene (13). With 0.78 molar equivalents AgBF4 in benzene at 80° the same ether 3 yields a 3:1 mixture of 2‐methyl‐cumaron (14) and 2 H‐chromene (13). From 1′‐methylpropargyl‐phenylether (4) and 2′‐butinyl‐3,5‐dimethylphenylether (5) under similar conditions the corresponding chromenes 16 and 17 resp. are obtained. Rearrangement of propargyl‐ and 2′‐butinyl‐1‐methyl‐2‐naphthylether (6 and 7 resp.) in benzene at 80° in the presence of AgBF4 gives the corresponding allenyl‐naphthalenones 18 and 19 resp. Treatment of propargyl‐ and 2′‐butinyl‐mesityl‐ether (8 and 9 resp.), and propargyl‐ and l′‐methylpropargyl‐2,6‐dimethyl‐phenylether (10 and 11 resp.) in benzene at 80° with AgRF, yields as the only product the corresponding 3‐allenyl‐phenols 21, 22,24 and 25 (Scheme 3). It is shown that in the presence of μ‐dichlor‐dirhodiuni (1)‐tetracarbonyl in benzene a t 80° the ether 4 rearranges to 2‐methyl‐2H‐chromene (16). However with this catalyst the predominant reaction is a cleavage to phenol. No reaction was observed when ethers 3 and 12, (Scheme 7 ) were treated with the tris‐(trimethylsily1)‐ester of vanadic acid in benzene a t 80° (see also [8]).By analogy with the known mechanism for thc silver catalysis of the reversible propargylesterl/allenylester rearrangement [S], the silver (1)ion is assumed to form a pre‐equilibrium π‐complex with the C, C‐triplebond of the substrate. This complex then undergoes a [3s, 3s]‐sigmatropic rearrangement (Scheme 2). In the case of the others 6, 7 and 12 the resulting allenyldienones were isolated. The 2,G‐dimethyl substituted ethers 8, 9, 10 and 11 resp. first give the usual allenyl‐ dienones (Scheme 3). These then undergo a novel silver catalysed dienon‐phenol‐rearrangement (Sclzenzu4) to give the 3‐allenylphenols 21, 22, 24 and 25. Thc others 3, 4 and 5 with free ortho positions presumably rearrange first to the non‐isolated 2‐allenyl‐phenols 15, 42 and 43 resp.(Scheme 7). These then rearrange, either thermally or by silver (1)ion catalysis to the 2H‐chromenes 13,16 and 17 resp. The rate of the rearrangement of 2‐allenylphenol (15) to 13 at room temperature in benzene or chloroform is approximately doubled when silver ions are present as catalyst.

Pigments of Elsinoe species. Part IV. Confirmatory evidence for the structure of elsinochrome A and its ethers from studies of nuclear magnetic resonance (solvent and overhauser effects) and electron spin resonance

The structures assigned to elsinochrome A and its two isomeric dimethyl ethers have been confirmed by the use of special techniques of magnetic resonance spectroscopy. Nuclear Overhauser effects involving methoxy-groups and adjacent aromatic protons have been observed; signals from such methoxy-groups show larger half-line-widths in the unperturbed n.m.r. spectra than do those of groups without free ortho-positions. These observations should be helpful in structure elucidations.

Alkali catalyzed phenol formaldehyde reaction – part II. Formation of dimethylol phenols

AbstractThe kinetic study has been made of the sodium hydroxide‐catalyzed interaction of o‐ and p‐methylol phenols with formaldehyde to give dimethylol phenols. At 0.006 M NaOH and within less than 10% of the reaction, first order kinetic behaviour was obtained. The rate constant, at 80°C., for the formation of 2,4‐dimethylol phenol from p‐methylol phenol and formaldehyde, was found to be 1.17·10−5 sec−1 and the activation energy, 23.92 kcal/mole, whereas for formation of 2,6‐ and 2,4‐dimethylol phenols from o‐methylol phenol, the rate constants were respectively 0.55 and 1.11·10−5 sec −1, the corresponding activation energies being, 25.10 and 23.37 kcal/mole. In terms of these data and those present in Part I, the relative reactivites of the free ortho and para positions in phenol and substituted phenols are evaluated and shown to be, unlike those reported by FREEMAN et al.5, consistent among themselves and with theoretical requirements.

Determination of the Number of Free ortho and para Positions in Phenols.

Determination of the Number of Free ortho and para Positions in Phenols.