High Tg and high organosolubility of novel unsymmetric polyimides

A series of new polyimides (PIs) containing di‐tert‐butyl side groups were synthesized via a polycondensation of 1‐(4‐aminophenoxy)‐4‐(4‐amino‐2‐methylphenyl)‐2,6‐di‐tert‐butylbenzene ( 3 ) with various aromatic tetracarboxylic dianhydrides. The novel unsymmetric PIs exhibited a low dielectric constants (2.78–3.02), low moisture absorption (0.53–1.35%), excellent solubility, and high glass transition temperature (308–450 °C). The PI derived from the new diamine and the very rigid naphthalene‐1,4,5,8‐tetracarboxylic dianhydride (NTDA) was soluble in N‐methyl‐2‐pyrrolidone, chloroform, m‐cresol, and cyclohexanone. The unsymmetric di‐tert‐butyl pendent groups significantly enhance the rotational barrier of the polymer chains; thus these PIs had high T_gs. The ¹H NMR spectrum of the diamine 3 revealed that the protons of 4‐aminophenoxy moiety are not chemical shift equivalent. This is because the steric hindrance of the bulky di‐tert‐butyl groups prevents the benzene ring of 4‐aminophenoxy moiety from rotating freely. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2443–2452, 2009     

Alkyl substituted phenoxyl decay in a hydrogen transfer equilibrium

The kinetics of radical decay in the equilibrium: 2,4,6‐tri‐tert‐butylphenoxyl radical 1 + 2,6‐di‐tert‐butyl‐4‐methylphenol 2 = 2,4,6‐tri‐tert‐butylphenol 3 + 2,6‐di‐tert‐butyl‐4‐methylphenoxyl radical 4 was studied at 298 and 273 K by means of EPR spectroscopy. At 298 K second order prevails, whereas at 273 K the best fit was order 3/2. The extinction of 4 takes place in two steps: dimerization followed by disproportionation of the dimer, but the stable radical 1 enters in crossed dimerization with 4 to yield nonradical products. The mechanism ensures a constant [ 4 ]/[ 1 ] ratio along the decay. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 37: 1–4, 2005     

Sterically hindered phenols in negative ion mobility spectrometry–mass spectrometry

Negative corona discharge atmospheric pressure chemical ionization (APCI) was used to investigate phenols with varying numbers of tert‐butyl groups using ion mobility spectrometry–mass spectrometry (IMS‐MS). The main characteristic ion observed for all the phenolic compounds was the deprotonated molecule [M–H]⁻. 2‐tert‐Butylphenol showed one main mobility peak in the mass‐selected mobility spectrum of the [M–H]⁻ ion measured under nitrogen atmosphere. When air was used as a nebulizer gas an oxygen addition ion was seen in the mass spectrum and, interestingly, this new species [M–H+O]⁻ had a shorter drift time than the lighter [M–H]⁻ ion. Other phenolic compounds primarily produced two IMS peaks in the mass‐selected mobility spectra measured using the [M–H]⁻ ion. It was also observed that two isomeric compounds, 2,4‐di‐tert‐butylphenol and 2,6‐di‐tert‐butylphenol, could be separated with IMS. In addition, mobilities of various characteristic ions of 2,4,6‐trinitrotoluene were measured, since this compound was previously used as a mobility standard. The possibility of using phenolic compounds as mobility standards is also discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

The antioxidant methyl 3‐(3,5‐di‐tert‐butyl‐4‐hydroxyphenyl)propionate

The title compound, C₁₈H₂₈O₃, was prepared by the reaction of 2,6‐di‐tert‐butylphenol with methyl acrylate under basic conditions using dimethyl sulfoxide as the promoter. The structure of this antioxidant indicates significant strain between the ortho tert‐butyl substituents and the phenolic OH group. In spite of the steric crowding of the OH group, it participates in intermolecular hydrogen bonding with the ester carbonyl O atom.     

Attempt to Synthesize Hindered 2,4,6‐Tri‐Aryloxy‐s‐Triazines: Bis(2,4‐di‐tert‐Butylphenyl) Carbonate – Crystal Structure

Some less hindered 2,4,6‐tri‐aryloxy‐s‐triazines were synthesized through the reaction of the corresponding phenols as a starting materials with cyanogen bromide (BrCN) to obtain the corresponding arylcyanates and then trimerized. Unexpectedly, 2,4‐di‐tert‐butyl‐1‐cyanatobenzene derived from 2,4‐di‐tert‐butylphenol did not trimerize but, indeed, yielded bis(2,4‐di‐tert‐butylphenyl) carbonate. The structures of 2,4,6‐tri‐aryloxy‐s‐triazines and bis(2,4‐di‐tert‐butylphenyl) carbonate were characterized by means of IR, ¹H, and ¹³C NMR spectroscopies. Also the structure of the latter compound was studied by X‐ray crystallography.     

Electroanalytical Studies on Cobalt(II) Ion‐Selective Sensor of Polymeric Membrane Electrode and Coated Graphite Electrode Based on N2O2 Salen Ligands

Poly(vinyl chloride)‐based membranes of salen ligands, 2‐((E)‐((1R,2S)‐2‐((E)‐5‐tert‐butyl‐2‐hydroxybenzylideneamino)cyclohexylimino)methyl)‐4‐tert‐butyl phenol (S₁) and 2‐((E)‐((1R,2S)‐2‐((E)‐3,5‐di‐tert‐butyl‐2‐hydroxybenzylideneamino)cyclohexylimino)methyl)‐4,6‐di‐tert‐butylphenol (S₂) were fabricated and explored as cobalt(II) selective electrodes. The performance of the polymeric membrane electrode (PME) and coated graphite electrode (CGE) were compared and it was observed that CGE showed a wide working concentration range of 1.1×10^?8 to 1.0×10^?1 mol L^?1 with a limit of detection of 7.0×10^?9 mol L^?1 exhibiting the Nernstian slope 29.6 mV/decade of activity in the pH range 3.0–9.0. It was used for the determination of cobalt(II) ions in water, soil, beer, pharmaceutical samples and medicinal plants and would be used as an indicator electrode in potentiometric titration with EDTA.     

Development of a fabric phase sorptive extraction with high‐performance liquid chromatography and ultraviolet detection method for the analysis of alkyl phenols in environmental samples

A novel analytical method has been developed and validated for the quantification of alkyl phenols in aqueous and soil samples. Fabric phase sorptive extraction, a new sorptive microextraction technique, has been employed for the preconcentration of some endocrine‐disruptor alkylphenol molecules, namely, 4‐tert‐butylphenol, 4‐sec‐butylphenol, 4‐tert‐amylphenol, and 4‐cumylphenol, followed by high‐performance liquid chromatography with ultraviolet detection. Various parameters influencing the fabric phase sorptive extraction performance, namely, extraction time, eluting solvent, elution time and pH of the sample matrix, were optimized. The chromatographic separation was carried out with a mobile phase of acetonitrile/water (60:40 v/v) at an isocratic flow rate of 1.0 mL/min using a reversed‐phase C₁₈ column at λ_max 225 nm. The calibration curves of target analytes were prepared in the concentration range 5–500 ng/mL with good coefficient of determination values (R² > 0.992). Extraction efficiency values were 74.0, 75.6, 78.0, and 78.3 for 4‐tert‐butylphenol, 4‐sec‐butylphenol, 4‐tert‐amylphenol, and 4‐cumylphenol, respectively. The limits of detection range from 0.161 to 0.192 ng/mL. Subsequently, the new fabric phase sorptive extraction with high‐performance liquid chromatography and ultraviolet detection was successfully applied for the recovery of alkyl phenols from spiked ground water, river water, and treated water from a sewage treatment plant, and soil and sludge samples.     

A highly efficient antioxidant based on boron and a Schiff base bridged phenolic diphenylamine: synthesis,crystal structure and thermal and antioxidant properties

Antioxidants can effectively protect vegetable‐oil‐based lubricants against oxidative degradation and prolong their service life. A novel compound, (E)‐4‐({3,5‐di‐tert‐butyl‐2‐[(diphenylboranyl)oxy]benzylidene}amino)‐N‐phenylaniline (BSPD) or {2‐[(4‐anilinophenyl)iminomethyl‐κN]‐4,6‐di‐tert‐butylphenolato‐κO}diphenylboron, C₃₉H₄₁BN₂O, was synthesized by a one‐pot reaction of the Schiff base bridged phenolic diphenylamine 2,4‐di‐tert‐butyl‐6‐{N‐[4‐(phenylamino)phenyl]carboximidoyl}phenol (SPD) with phenylboronic acid. The corresponding single‐crystal X‐ray study revealed that the B atom in BSPD has a typical tetrahedral geometry, and the N,O‐chelated six‐membered ring adopts a chair conformation. According to thermogravimetric analysis, the 5% weight‐loss temperature of BSPD increases to 328 °C and the 95% weight‐loss temperature is up to 414 °C. More importantly, the antioxidant capability of BSPD in vegetable oil is much better than that of commercial antioxidants [diphenylamine (DPA) and 2,6‐di‐tert‐butyl‐4‐methylphenol (BHT)] and unmodified SPD.     

Spin Trapping of Radical Intermediates Generated by the Oxidation of Substituted 4‐Methylphenols

A series of substituted 4‐methylphenols 1 and 2 was oxidized with PbO₂ in the presence of nitroso compounds 3 – 10 . The formation of adducts of benzyl radicals with the nitroso spin traps in the reaction mixture was established, suggesting the abstraction of an H‐atom from the methyl substituent of 1 or 2 . In the consecutive steps, the adducts underwent a further rearrangement to the corresponding nitrones. When the starting phenol contained bulky ^tBu groups in ortho‐position (see 2,6‐di(tert‐butyl)‐4‐methylphenol ( 1a )), the stable 2,6‐di(tert‐butyl)‐4R‐phenoxy radicals (R=? CH?N⁺(O^?)? X) were detected as the final radical products. The indirect evidence of nitrones in the reaction mixture was performed in one case by the reaction with a RO radicals.     

Convenient Synthesis of tert‐Butyl Esters of Indole‐5‐carboxylic Acid and Related Heterocyclic Carboxylic Acids

The tert‐butyl esters of indole‐5‐carboxylic acid and related compounds such as benzofuran‐ and benzothiophene‐5‐carboxylic acid were readily accessed by reacting the appropriate carboxylic acids with tert‐butyl trichloroacetimidate. To obtain the tert‐butyl esters of the 5‐carboxylic acids of 1H‐benzotriazole and 1H‐benzimidazole, position 1 of these heterocycles had to be protected by acetylation prior to reaction with tert‐butyl trichloroacetimidate. Cleavage of the acetyl residue of the obtained intermediates by dilute aqueous NaOH in ethanol led to the desired tert‐butyl 1H‐benzotriazole‐and 1H‐benzimidazole‐5‐carboxylates.     

Das erste Oxatetraphospholan, (PBut)4O

Contributions to the Chemistry of Phosphorus. 244. The First Oxatetraphospholane, (PBu^t)₄O Under suitable conditions, the reaction ot tri‐tertbutylcyclotriphosphane, (PBu^t)₃, with di‐tert‐butylperoxide gives rise to a mixture of 2,3,4,5‐tetra‐tert‐butyl‐1,2,3,4,5‐oxatetraphospholane, (PBu^t)₄O ( 1 ), and 1,2‐di‐tert‐butyl‐1,2‐di‐tert‐butoxidiphosphane, [Bu^t(Bu^tO)P]₂ ( 2 ). Both compounds have been isolated in the pure state. The oxatetraphospholane 1 is a constitutional isomer of 1,2,3,4‐Tetra‐tert‐butyl‐1‐oxocyclotetraphosphane, which has been reported recently [1]. The corresponding reaction of tetra‐tert‐butylcyclotetraphosphane furnishes only small amounts of 1 because of the kinetic stability of (PBu^t)₄. The diphosphane 2 is presumably a secondary product of primarily formed oxocyclotetraphosphanes (PBu^t)₄O_1–4. The NMR parameters of 1 and 2 are reported and discussed.     

SO2‐Extrusion of an 8‐thiabicylo[3.2.1]octa‐2,6‐diene 8,8‐dioxide and rearrangement of the resulting cycloheptatriene

The reaction of 3,4‐di‐tert‐butyl‐thio‐phene 1‐oxide ( 8 ) with tetrachlorocyclopropene provided 6,7‐di‐tert‐butyl‐2,3,4,4‐tetrachloro‐8‐thia‐bicylo[3.2.1]octa‐2,6‐diene 8‐oxide ( 10 ), which was oxidized to the corresponding 8,8‐dioxide 16 by m‐chloroperbenzoic acid. The thermolysis of 16 in refluxing chlorobenzene, xylene, or octane gave 5‐tert‐ butyl‐1,2‐dichloro‐3‐[(1,1‐dich‐loro‐2,2‐dimethyl)‐pro‐ pyl]‐benzene ( 18 ) with extrusion of SO₂ and 2‐tert‐butyl‐4,5,6‐trichloro‐9,9‐dimethylbicyclo[5.2.0]nona‐1,3,5‐triene ( 19 ) with extrusion of SO₂ and HCl in 73–78% combined yields. On the other hand, the thermolysis of 16 in the presence of triethylamine gave 19 as the sole product in 98% yield. A mechanism that involves the initial formation of 4,5‐di‐tert‐butyl‐1,2,7,7‐tetrachlorocycloheptatriene ( 17 ) is proposed to ex‐ plain the observed products. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:132–222, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20079     

Synthesis of 2‐Styrylbenzoxazole Derivatives by the Reaction of Styrylphenolic Schiff Bases with Thianthrene Cation Radical

A simple and fast preparative method of 2‐styrylbenzoxazoles by oxidative intramolecular cyclization of styrylphenolic Schiff bases with thianthrene cation (Th^+.ClO₄^?) is described. The oxidative cyclization of Schiff bases in the presence of 2,6‐di‐tert‐butyl‐4‐methylpyridine (DTBMP) gives 2‐styrylbenzoxazole derivatives in better yields than those in the absence of DTBMP.     

Voltammetric Determination of BHT Antioxidant at Gold Electrode in Biodiesel

The voltammetric determination of synthetic antioxidant 2,6‐di‐tert‐butyl‐4‐methylphenole (BHT) was studied using linear‐sweep voltammetry (LSV) and cyclic voltammetry (CV) with a gold electrode and performed in isopropanol media containing either 0.1 mol L^?1 H₂SO₄ or 0.1 mol L^?1 LiClO₄ as supporting electrolyte. The results obtained have revealed that the most reliable detection was acquired in acidic media (isopropanol–H₂SO₄) whereas the use of isopropanol? LiClO₄ solution exhibited poorer reproducibility due to possible passivation of the electrode. Real samples of biodiesel mixture were analyzed without any special sample treatment or separation and results were compared with those obtained by FTIR‐spectroscopy.     

Novel Dinuclear Redox‐isomeric Complexes with a Tetrapodal Pyridine‐based Ligand

Tris‐o‐semiquinonato cobalt complexes react with a tetrapodal pyridine‐derived ligand to form dinuclear cobalt compounds of general formula (OMP)[CoQ₂]₂, where OMP = 2,2′‐(pyridine‐2,6‐diyl)bis(N¹,N¹,N³,N³‐tetramethylpropane‐1,3‐diamine), Q = mono‐ or dianion of 3,6‐di‐tert‐butyl‐o‐benzoquinone (complex 1 ) and it derivatives: 3,6‐di‐tert‐butyl‐4,5‐N,N′‐piperazino‐o‐benzoquinone (complex 2 ), and 3,6‐di‐tert‐butyl‐4‐Cl‐o‐benzoquinone (complex 3 ). Single crystal X‐ray crystallography of 1 and 3 indicates two bis‐quinonato cobalt units bound by an OMP ligand, which acts as a bridge. Each central cobalt atom is chelated by one N¹,N¹,N³,N³‐tetramethylpropane‐1,3‐diamine and two o‐quinonato fragments. The nitrogen atom of the pyridine ring is uncoordinated. All complexes were characterized by NIR‐IR and EPR spectroscopy, precise adiabatic vacuum calorimetry, and by variable‐temperature magnetic susceptibility measurements. All data indicate a reversible thermally driven redox‐isomeric (valence tautomeric) transformation in the solid state for all complexes.     

Selective Monoarylation of Primary Amines Using the Pd‐PEPPSI‐IPentCl Precatalyst

A single set of reaction conditions for the palladium‐catalyzed amination of a wide variety of (hetero)aryl halides using primary alkyl amines has been developed. By combining the exceptionally high reactivity of the Pd‐PEPPSI‐IPent^Cl catalyst (PEPPSI=pyridine enhanced precatalyst preparation, stabilization, and initiation) with the soluble and nonaggressive sodium salt of BHT (BHT=2,6‐di‐tert‐butyl‐hydroxytoluene), both six‐ and five‐membered (hetero)aryl halides undergo efficient and selective amination.     

Amino‐ und halogenfunktionelle Siloxititane

Amino‐ and halofunctional Siloxititanes Amino‐di‐tert‐butylsilanol reacts with tetrabutoxititane in a molar ratio of 2:1 to give di‐n‐butoxi(bis(di‐tert‐butyl‐n‐butoxi)siloxi)titane, (C₄H₉OSi(CMe₃)₂‐O)₂Ti(OC₄H₉)₂ ( 1 ), and lithium‐di‐tert‐butylchlorosilanolate in a molar ratio of 3:1 to give n‐butoxi(tris(di‐tert‐butyl‐n‐butoxi)siloxi)titane, (H₉C₄OSi(CMe₃)₂‐O)₃TiOC₄H₉ ( 2 ). The amino‐di‐tert‐butylsilanol substitutes the four chloroatoms of TiCl₄ in the presence of triethylamine as HCl‐acceptor. The tetrakis(amino‐di‐tert‐butyl)siloxititane ( 3 ) is formed. The lithium salt of di‐tert‐butylfluorosilanol reacts with TiCl₄ in a molar ratio of 2:1 to give 1, 1, 3, 3‐tetra‐tert‐butyl‐1‐fluoro‐3‐trichlorotitoxi‐1, 3‐disiloxane, FSi(CMe₃)₂‐O‐Si(CMe₃)₂‐O‐TiCl₃ ( 4 ). In the reaction of di‐tert‐butyl‐chlorosilanol and TiCl₄, the anion [chlorosiloxi‐octa(tri‐μ²‐chlorotitanate)]^— ( 5 ) with protonated diethylether as counterion is obtained by using diethylether as HCl‐acceptor. The crystal structure determinations of 3 and 5 are reported.     

Copper(II)‐Mediated Transformation of a Tridentate Non‐Innocent Ligand into a Tetradentate Salen‐Type Innocent Ligand

A non‐innocent ligand, H₄L, was synthesized by introducing a ? CH₂NH₂ group at the ortho carbon atom to the aniline moiety of 2‐anilino‐4,6‐di‐tert‐butylphenol. The new ligand was characterized by IR and NMR spectroscopy and mass spectrometry techniques. Upon treatment with CuCl₂ ? 2 H₂O, this non‐innocent ligand provided a mononuclear four‐coordinate salen‐type Cu^II complex by complete modification of the ligand backbone. The complex was characterized by IR spectroscopy, mass spectrometry, X‐ray single‐crystal diffraction, electron paramagnetic resonance (EPR) spectroscopy, and UV/Vis/near‐IR spectroscopy techniques. X‐ray crystallographic analysis showed an asymmetric environment around the Cu^II center with a small (≈12°) twist between the two biting planes. Analysis of the X‐band EPR spectrum also supported the asymmetric environment and also indicated the presence of an unpaired electron on the d orbital. The UV/Vis/near‐IR spectrum showed strong absorption bands for metal‐to‐ligand charge transfer and ligand‐to‐metal charge transfer along with a Cu^II‐centered d–d transition. Mechanistic investigation of the formation of complex 1 indicated that modification of the ligand backbone proceeded through ligand‐centered amine to imine oxidation as well as through C? N bond‐breaking processes. During these processes, 3,5‐di‐tert‐butyl‐1,2‐benzoquinone and 2‐aminobenzylidene were produced. Ammonia, generated in situ through hydrolysis of the imine to the aldehyde, reacted with 3,5‐di‐tert‐butyl‐1,2‐benzoquinone to form the corresponding 3,5‐di‐tert‐butyl‐1,2‐iminobenzoquinone moiety, which upon two‐electron reduction in the reaction medium formed 3,5‐di‐tert‐butyl‐1,2‐aminophenol. This aminophenol underwent condensation with the H₂L5 ligand that was formed by self‐condensation of two molecules of 2‐aminobenzaldehyde and provided the modified ligand backbone.     

New Aspects of 1,3‐Diphosphacyclobutane‐2,4‐diyls

1,3‐Di(tert‐butyl)‐2,4‐bis[2,4,6‐tri(tert‐butyl)phenyl]‐1,3‐diphosphacyclobutane‐2,4‐diyl was formed from [2,4,6‐tri(tert‐butyl)phenyl]phosphaacetylene and t‐BuLi. In addition, the X‐ray diffraction analysis was carried out, together with theoretical calculations of the structure and NMR data.     

一种大环化合物的晶体结构及其双核铜配合物的酪氨酸酶活性研究

A ring-contracted form macrocycle, 29,30-dioxo-3,6,9,17,20,23,29,30-octaazapentacyclo[23,3,1,1^11,15,0^2,6,0^16,20]-triacontaneocta- 1 (28),9,11 (12), 13,15(30),23,25(29),26-ene (L) was synthesized by condensation of diethyltriamine with pyridine-1-oxide-2,6-dicarboxaldehyde. A porous three-dimensional layer structure in its crystal was formed by self-assembly through hydrogen bonds and π-π interaction. Its dinuclear copper(I) complex [Cu2L(MeOH)2]-(BF4)2*2H2O and dinuclear-copper(II) complex [Cu2L(MeOH)2](ClO4)4*2H2O were obtained and could oxidize catalytically four phenolic substrates hydroquinone, 2-methyl-hydroquinone, 2,6-di-tert-butylphenol and 2,6-dimethylphenol, in a mixture of methanol and acetonitrile (V : V, 4 : 1). The copper(I) complex reacted with dioxygen to form an oxygenated species as an initial active intermediate for oxidation of the phenols. Oxidation of the substrates by the copper(II) complex produced a copper(I) complex and the oxidation products of the substrates.