3.5- di-tert-butylcatechol

The development of catalysts for the efficient oxidation of catechol and its derivatives in water is topic of ongoing work in this laboratory. Towards this end, polyethylene glycol side-chains were incorporated in a pentadentate salen ligand to enhance the water solubility of the complexes derived thereof. A dinuclear copper(II) complex is found to catalyze the oxidation of 3,5-di-tert.-butylcatechol into 3,5-di-tert-butyl-o-benzoquinone more than twice as fast in aqueous organic solution as in purely organic solvents (ly,at/knon= 140,000). Preliminary data are discussed. 

In our ongoing efforts to develop oxidation catalysts that are functional in water as environmentally berrign solvent, we synthesized a water-soluble pentadentate salen ligand with polyethylene glycol side chairts (8). After coordination of copper(II) ions to the salen ligand, a dinuclear copper(II) complex is obtained that is soluble in water, methanol and mixtures of both solvents. The aerobic oxidation of 3,5-di-tert.-butylcatechol (DTBC) into 3,5-di-terr.-butylqitinone (DTBQ) was used as a model reaction to determine the catalytically active species and initial data on its catalytic activity in 80% methanol. 

Catalytic oxidation of 3,5-di-tert.-butylcatechol. The catalytic oxidation of 3,5-di-teri.-butylcatechol, DTBC (8), to 3,5-di-teri.-butylquinone, DTBQ (9), was chosen as a model reaction to test our hypothesis and establish the catalytic abilities of 1 and 7 in organic and aqueous organic solution (eq. 4). 

The preparation and characterization of five co-ordinate [(triphos)Ir(cat)]Z, H2cat = 9,10-phen-anthrenecatechol, 1,2-naphthalenecatecol, 3,5-di-tert-butylcatechol, 4-methylcatechol, 4-carboxy-catechol Et ester, tetrachlorocatechol, Z=BPh4, PF6, have been reported.244 All compounds... 

Various chromogenic reagents have been used for the spectrophotometric determination of boron in seawater. These include curcumin [108,109], nile blue [110], and more recently 3,5 di-tert butylcatechol and ethyl violet [111]. Uppstroem [108] added anhydrous acetic acid (1 ml) and propionic anhydride (3 ml) to the aqueous sample (0.5 ml) containing up to 5 mg of boron per litre as H3BO3 in a polyethylene beaker. After mixing and the dropwise addition of oxalyl chloride (0.25 ml) to catalyse the removal of water, the mixture is set aside for 15-30 minutes and cooled to room temperature. Subsequently, concentrated sulfuric-anhydrous acetic acid (1 1) (3 ml) and curcumin reagent (125 mg curcumin in 100 ml anhydrous acetic acid) (3 ml) are added, and the mixed solution is set aside for at least 30 minutes. Finally 20 ml standard buffer solution (90 ml of 96% ethanol, 180 g ammonium acetate - to destroy excess of protonated curcumin - and 135 ml anhydrous acetic acid diluted to 1 litre... 

The complexes [Ru(bpy)2L]+ (HL = acetylacetone, trifluoroacetylacetone, hexafluoroacetylace-tone, tropolone or dibenzoylmethane) have been prepared and characterized they act as catalysts for the oxidation of alcohols, 3,5-di-tert-butylcatechol and alkanes in the presence of appropriate co-oxidants." Perchlorate salts of [Os(bpy)2L] in which HL = salicylaldehyde, 2-hydroxyaceto-phenone or 2-hydroxynaphthaldehyde, are formed from reactions of [Os(bpy)2Br2] with HL. The structure of the salicylaldehyde derivative has been determined. Chemical and electrochemical oxidations of [Os(bpy)2L]" yield the corresponding low-spin Os species from which [Os(bpy)2L]+ can be regenerated." " [Ru(bpy)2L]" (HL = salicylic acid) has been prepared and structurally characterized as the tetrahydrate. Absorptions at 590 nm, 400 nm, and 290 nm in the electronic spectrum have been assigned to Ru bpy CT transitions electrochemical oxidations of the complex have been investigated." ... 

While only tyrosinase catalyzes the ortho-hydroxylation of phenol moieties, both tyrosinase and catechol oxidase mediate the subsequent oxidation of the resulting catechols to the corresponding quinones. Various mono- and dinu-clear copper coordination compounds have been investigated as biomimetic catalysts for catechol oxidation [21,194], in most cases using 3,5-di-tert-butylcatechol (DTBC) as the substrate (Eq. 16). The low redox potential of DTBC makes it easy to oxidize, and its bulky tert-butyl groups prevent un-... 

Figure 2.3 Molecular structure of [Fe(Me3TACN)(DBC)CI], a model complex for a catechol dioxygenase coordinated to its substrate molecule [28]. Hydrogen atoms have been omitted for clarity. The l,4,7-trimethyl-l,4,7-triazacyclononane (Me3TACN) ligand coordinates facially to the iron center. The remaining three coordination sites are occupied by 3,5-di-tert-butylcatecholate (DBC) and a chlorido ligand.

Acidification of solutions containing [0s02(Rcat)]2+ or direct treatment of the catechol with 0s04 in acetone gives dark blue, polymeric species [OsO(Rcat)2] hH2 O, thought to contain Os—O—Os —O---chains (R-cat = 4-methylcatechol, 4-terf-butylcatechol, 3,5-di-tert-butylcatechol). These are remarkably stable species, unreactive even towards boiling pyridine.4 6... 

In 2005, a selection of pre-catalysts were employed in the vanadium-catalyzed oxygenation of 3,5-ditert-butylcatechol. ESI-MS experiments that were conducted on the post-reaction solutions led to the detection of two common negative ions [V0(DTBC)2]- (Eig. 2C) and [V(DTBC)3]- (DTBC = 3,5-di-tert-butylcatecholate dianion) [41]. Through kinetic experiments the species corresponding to [V(DTBC)3] was ruled out as the catalytically active species and the neutral species that was shown to correspond to [VO(DTBC)2] , namely (VO(DBSQ)(DTBC))2 (DBSQ=3,5-di-tert-butylsemiquinone anion), was reported as a common catalyst for this reaction. While this study describes an adventitiously-charged system (the proposed active catalyst is in fact neutral), it is described here along with the other vanadium-catalyzed systems for cohesion. 

Reaction of OSO4 with catechol or substituted catechols Rcat in chloroform yields the deep blue diamagnetic Os(Rcat)j species (Rcat = catechol, 4-tert-octyl-, 4-rerr-butyl-, 3,5-di-terf-butyl-catech-ol). X-Ray crystal structures of Os(cat)3 and of the tris complex with 3,5-di-tert-butylcatechol show these to have Dj symmetry the Os—O distances fall within the range 1.947 to 1.985 A (mean 1.960 A) and the C— distances are between 1.30 and 1.35 A the catecholato (O2C6H4 or O2QH2) rings are essentially planar. For Os(cat)3, IR, Raman, HNMR and electrochemical data were obtained the latter showed two one-electron reversible reductions, presumably to [Os(cat)j] and [Os(cat)3] . The diamagnetism of these formally osmium(VI) species probably arises from the distortion from octahedral to Z), symmetry." ... 

Scheme 10. The proposed catalytic cycle for the selective oxidation of 3,5-di-tert-butylcatechol to 3,5-di-tert-butyl-o-benzoquinone.

Bis(3,4-dicarboxybenzoyl)phthalocyanines with M = Co(II) or Cu(II) have been covalently bound to linear polystyrene by a Friedel-Crafts reaction [130], The polymers contained 0.13 mmol g (12.4 wt.%) phthalocyanine moieties. The sensitivity of the polymers toward toxic gases were investigated by quartz balance transducers. The sensitivities are 6T0" m mL for NO2 and 2T0 m mL for chloroform and perchloroethylene, respectively. 52 (R = SO2CI, M = Fe) has been covalently bound to the amino groups of a cross-linked, hydrophilic polymer consisting of A/ -acryloyl-P-alanine-(aminoethyl-ene)-amide, A -acryloylpyrrolidine and 7V,A -bis(methacryloyl)-l,2-diamino-ethane as comonomers [131]. The polymer obtained, 52, contains 20 pmol phthalocyanine units per g. The catalytic oxidation of 2,4,6-trichlorophenol or 3,5-di-tert-butylcatechol in the presence of H2O2 or KHSO5 as oxidant has been studied. Around 80% of the trichlorophenol was catalytically oxidized within 2 h at pH 7. 

The additives of water can serve as mechanistic probes and aid in obtaining true mechanistic understanding in some organocatalytic reactions [123]. The water is nucleophile in palladium-catalyzed oxidative carbo-hydroxylation of allene-substituted conjugated dienes [124]. This is an example of Pd- catalyzed oxidation leading to C -C bond formation in water with subsequent water attack on a (rr-allyl) palladium intermediate. The different effect of the water concentration on the intra- and extra-diol oxygenations of 3,5-di-tert-butylcatechol with O2, catalyzed by FeC in tetrahydrofuran-water indicates that the intermediates for two reactions are different (model for Catechol-2,3-dioxygenases) [125]. 

Abbreviations TPP = tetraphenylporphyrin py = pyridine Im = imidazole Cat = catecholate CUcat = tetrachlorocatecholate N02cat = 4-nitrocatecholate DTB cat = 3,5-di-tert-butylcatecholate Sap = N-salicylidene-2-aminophenolate Et2dtc = N,N-diethyldithiocarbamate PC = propylene carbonate... 

Binuclear Co(II) complexes derived from 2,6-diformyl-4-methylphenol and various aromatic monoamines have been prepared and investigated. The Co(II) complexes have the composition C02L2CI2, where L represents the organic ligand. The complexes are active catalysts in the oxidation of 3,5 -di-tert-butylcatechol. 

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