Chromophores from hexeneuronic acids: identification of HexA-derived chromophores

Hexeneuronic acids (HexA) have long been known as triggers for discoloration processes in glucuronoxylan-containing cellulosic pulps. They are formed under the conditions of pulping from 4-O-methylglucuronic acid residues, and are removed in an “A stage” along the bleaching sequences, which mainly comprises acidic washing treatments. The chemical structures of HexA-derived chromophoric compounds 4–8, which make up 90% of the HexA-derived chromophores, are reported here for the first time. The compounds are ladder-type, mixed quinoid-aromatic oligomers of the bis(furano)-[1,4]benzoquinone and bis(benzofurano)-[1,4]benzoquinone type. The same chromophoric compounds are generated independently of the starting material, which can be either a) HexA in pulp, b) the HexA model compound methyl 1-¹³C-4-deoxy-β-L-threo-hex-4-enopyranosiduronic acid (1) or c) a mixture of the primary degradation intermediates of 1, namely 5-formyl-furancarboxylic acid (2) and 2-furancarboxylic acid (3). Isotopic labeling (¹³C) in combination with NMR spectroscopy and mass spectrometry served for structure elucidation, and final confirmation was provided by X-ray structure analysis. ¹³C-Isotopic labeling was also used to establish the formation mechanisms, showing all the compounds to be composed of condensed, but otherwise largely intact, 2-carbonylfuran and 2-carbonylfuran-5-carboxylic acid moieties. These results disprove the frequent assumption that HexA-derived or furfural-derived chromophores are linear furanoid polymers, and might have a direct bearing on structure elucidation studies of “humins”, which are formed as dark-colored byproducts in depolymerization of pentosans and hexosans in different biorefinery scenarios.     

Synthesis of trichloro-1,4-benzoquinonyl-substituted 2,2′-bithiazoles

2,2-Bi[5-(2,5-dihydroxy-3,4,6-trichlorophenyl)thiazole] and 6-(2,5-dihydroxy-3,4,6-trichlorophenyl)-2-imino-3,4-dihydro-4H-1,4-thiazin-3-thione are synthesized from 2,5-dihydroxy-3,4,6,7-tetrachloro-2,3-dihydrobenzo[b]furan and dithiooxalyldiamide. The products are oxidized by FeCl₃ to the corresponding trichloro-1,4-benzoquinonyl-substituted sulfur-containing heterocycles. N-Methylation of 2,2-bithiazole by dimethyl sulfate gives 2,2-bi[5-(2,5-dihydroxy-3,4,6-trichlorophenyl)-3-methylthiazolium] bismonomethyl sulfate. The last compound is readily transformed to 2,2-bi[5-(2-hydroxy-5-oxido-3,4,6-trichlorophenyl)-3-methylthiazolium] bisbetaine.Riga Technical University, Riga LV-1048, Latvia, Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 988–992, July, 1999.     

Oxidative opening of the 2,5-dihydroxy-3,4,6,7-tetrachlorocoumaran ring

A method has been developed for the synthesis of (3,5,6-trichloro-1,4-benzoquinone-2-yl)chloroacetaldehyde by the oxidative ring opening of 2,5-dihydroxy-3,4,6,7-tetrachlorocoumaran with nitrogen oxides. The ion-radical salt of (3,5,6-trichloro-1,4-benzoquinone-2-yl)chloroacetaldehyde with N,N,N,N-tetramethyl-p-phenylenediamine (11) has been synthesized. The reaction of 2,5-dihydroxy-3,4,6,7-tetrachlorocoumaran-3-yl) with pyridine gave N-(2,5-dihydroxy-4,6,7-trichlorocoumaran-3-yl)pyridine chloride, which is also formed from the opening of the coumaran ring.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 892–895, July, 1990.     

Complexes of 2,5-dihydroxy-1,4-benzoquinone and chloranilic acid with second and third row transition elements

The synthesis of new 2,5-dihydroxy-1,4-benzoquinone (H2DHBQ) and chloranilic acid (H2CA) complexes cis-[Mo2O5L2]2– (L = DHBQ, CA), [W2O5(DHBQ)2]2–, [WO2(CA)2]2–, trans-[UO2(DHBQ)]·H2O, and trans-[UO2(CA)2]2– is described. Raman, i.r., 1H and 13C n.m.r spectra of the ligands and their complexes are reported and their structures discussed.     

Chromophores from hexeneuronic acids (HexA): synthesis of model compounds and primary degradation intermediates

Hexeneuronic acid (HexA) is formed under pulping conditions from 4-O-methyl-glucuronic acid residues in xylans by methanol elimination. It is usually removed by an acidic washing treatment (A-stage) within the pulp bleaching sequence. Hexeneuronic acid has long been recognized as a source of color generation in pulps, but the chemical structure of the actual chromophoric compounds remained elusive. We report the synthesis of isotopically (¹³C) labeled HexA model units carrying a label at any of the six carbon atoms. Confirming pertinent literature accounts, it is shown that HexA forms three primary degradation intermediates, 2-furancarboxylic acid, 5-formyl-2-furancarboxylic acid, and formic acid, under mildly acidic conditions, and their formation mechanism is discussed. 2-Furancarboxylic acid is demonstrated to be deformylation product of 5-formyl-2-furancarboxylic acid. The three primary intermediates are colorless and do not represent chromophores themselves. Their mixture, upon thermal or acidic treatment, gives rise to the same chromophores that are also directly formed from HexA.     

Über 2,5-Endimino-1,4-dithiane

Zusammenfassung Die Untersuchungen über die Reaktion zwischen 2,5-Dihydroxy-1,4-dithianen und Aminen der allgemeinen Formel R–NH₂ und R–NHNH₂ wurden fortgesetzt. Aus 2,5-Dihydroxy-1,4-dithian (I) und Ammoniak bildet sich das trizyklische System des 2,5-Di-(N-2,5-endimino-1,4-dithianyl)-1,4-dithians. Dagegen reagiert 2,5-dimethyl-2,5-dihydroxy-1,4-dithian mit Ammoniak zu 2,5-Dimethyl-2,5-endimino-1,4-dithian. Weiters gibt I mit Thiosemikarbazid N-Thioureido-2,5-endimino-1,4-dithian. Um zu wasserlöslichen Derivaten des Ringsystems zu gelangen, die einer pharmakologischen und bakteriostatischen Untersuchung unterzogen werden können, wurden die zur Salzbildung fähigen Verbindungen N--Diäthylaminoäthyl-2,5-endimino-1,4-dithian und N-Isonicotinsäureamido-2,5-endimino-1,4-dithian hergestellt.Herrn Prof. Dr.F. Wessely zu seinem 60. Geburtstag in aufrichtiger Verehrung gewidmet.     

2,4′:2′,4 Dianhydride of 3-keto-glucoside,a precursor to chromophores of aged,yellow cellulose,and its weak interactions

Studies of cellulose aging and yellowing that involved a 1,4-dimethyl 3-keto β-d-glucoside (compound 1) model of oxidized cellulose led to a hemi-hydrated crystal of title compound 2 (1,6-dihydroxy-3,8-bis-hydoxymethyl-5,10-dimethoxy-4,9-dioxa-tricyclo [5,3,1,1,2,6] dodecane-11,12-dione). The same compound 2 was isolated in low yield from “real-world” oxidized and aged cellulosic pulp. Formation of compound 2 implies cellulose chain cleavage and, unexpectedly, cross-linking during aging. X-ray diffraction revealed an encompassing 10-membered ring whose two carbonyl group bridges define two eight-membered rings and three six-membered rings. The central six-membered ring is antecedent to 2,5-dihydroxy-1,4-benzoquinone (compound 3), a potent and nearly ubiquitous chromophore in aged cellulose; the outer rings derive from the keto-glucosides and have ⁴C₁ and ¹C₄ shapes with gt and rare tg O-6 positions. Weak trans-annular interactions between >C=O carbon and ring oxygen atoms were confirmed with Atoms-in-Molecules theory. That theory was also used to analyze a questionable cyclic hydrogen bond and bonds between adjacent O–H and carbonyl oxygens.     

Synthesis and spectral studies ofN-2-pyridinylcarbonyl-2-pyridinecarxoximidate copper(II) complexes

Summary Dimeric and polymeric copper(II) complexes containing BPCA (N-2-pyridinylcarbonyl-2-pyridinecarboximidate), having general formulae Cu(BPCA)X·nH₂O (X=Cl, Br, NCS, NCO, N₃, or CN) and Cu₂(BPCA)₂-X·nH₂O [X=oxalate anion (OX), chloranilate anion (CA) or the dianion of 2,5-dihydroxy-1,4-benzoquinone (DHBQ)] have been synthesized by the copper(II)-assisted hydrolysis of 2, 4, 6-tris(2-pyridyl)-1, 3, 5-triazine. Spectroscopic results indicate five-coordinate, approximately square-pyramidal, geometry around the copper(II) ion. Half-field absorption in the M _s=±2 region of the X-band e.p.r. powder spectra has been observed for the dimeric species.     

Chromophores in cellulosics,XI: isolation and identification of residual chromophores from bacterial cellulose

In the present work, bacterial cellulose (BC) was analyzed for its chromophore content with the chromophore release and identification (CRI) method. In aged BC, seven chromophores were unambiguously identified, despite their very low (ppb) presence. The compounds contain 2-hydroxy-[1,4]benzoquinone, 2-hydroxyacetophenone and 5,8-dihydroxy-naphthoquinone moieties. These three classes of key chromophores had also been found in other celluloses such as bleached pulp, fiber and derivatives. The detection of chromophores in lignin-free BC confirms that the chromophores are formed from oxidized and degraded carbohydrate material rather than lignin fragments. Samples that were insufficiently purified before the aging step also yielded three N-heterocyclic compounds. They originated from tryptophan moieties in residual adhering protein and protein degradation products. N-Heteropentacycles 9 and 10 showed strong adsorption onto cellulosic surfaces, and that adsorption aided oxidation of cyclohexadiene derivative 9 into the corresponding aromatic and intensely yellow system 10, consistent with the strain-induced bond localization theory. In purified fresh BC, no chromophores were detectable by the CRI method. The present contribution is the first report on defined chromophoric structures isolated from BC.     

“On-water” organic synthesis: <Emphasis Type="SmallCaps">l</Emphasis>-proline catalyzed synthesis of pyrimidine-2,4-dione-, benzo[<Emphasis Type="Italic">g</Emphasis>]- and dihydropyrano[2,3-<Emphasis Type="Italic">g</Emphasis>]chromene derivatives in aqueous media

In this work, functionalized pyrimidine-2,4-dione-, benzo[g]-, and dihydropyrano[2,3-g]chromene derivatives have been synthesized via a Michael addition of 2-hydroxy-1,4-naphthoquinone or 2,5-dihydroxy-1,4-benzoquinone to the Knoevenagel condensation product of an aldehyde with Meldrum’s acid, dimedone or barbituric acid in the presence of a catalytic amount of l-proline under refluxing conditions in water in good to excellent yields.     

All-Solid-State Rechargeable Air Batteries Using Dihydroxybenzoquinone and Its Polymer as the Negative Electrode

A proof-of-concept study was conducted on an all-solid-state rechargeable air battery (SSAB) using redox-active 2,5-dihydroxy-1,4-benzoquinone (DHBQ) and its polymer (PDBM) and a proton-conductive polymer (Nafion). DHBQ functioned well in the redox reaction with the solid Nafion ionomer at 0.47 and 0.57 V vs. RHE, similar to that in acid aqueous solution. The resulting air battery exhibited an open circuit voltage of 0.80 V and a discharge capacity of 29.7 mAh g_DHBQ⁻¹ at a constant current density (1 mA cm⁻²). With PDBM, the discharge capacity was much higher, 176.1 mAh g_PDBM⁻¹, because of the improved utilization of the redox-active moieties. In the rate characteristics of the SSAB-PDBM, the coulombic efficiency was 84 % at 4 C, which decreased to 66 % at 101 C. In a charge/discharge cycle test, the capacity remaining after 30 cycles was 44 %, which was able to be significantly improved, to 78 %, by tuning the Nafion composition in the negative electrode.     

Synthesis of 2-(β-Hetarylaminoethyl)-3,5,6-trichloro-1,4-benzoquinones

4,6,7-Trichloro-2-hetarylamino-5-hydroxy-2,3-dihydrobenzo[b]furans have been prepared from 4,6,7-trichloro-2,5-dihydroxy-2,3-dihydrobenzo[b]furan and hetarylamines. Reductive opening of the dihydrobenzofuran ring in these compounds gave 3,5,6-trichloro-2-(-hetarylaminoethyl)hydroquinones. The latter could be oxidised to the target 3,5,6-trichloro-2-(-hetarylaminoethyl)-1,4-benzoquinones which are novel 1,4-benzoquinone derivatives with intramolecular charge transfer.     

Experimental and quantum-chemical study of the interaction of cyclohexanediones and their monoethylene ketals with hydrogen peroxide

The reactivity of cyclohexanediones and their monoethylene ketals with hydrogen peroxide was studied. It was established that 1,2- and 1,3-cyclohexanediones virtually do not react with H₂O₂, whereas 1,4-cyclohexanedione forms 1,4-dihydroxy-1,4-dihydroperoxycyclohexane. Monoethylene ketals of cyclohexanediones react with hydrogen peroxide to form the corresponding -hydroxy--hydroperoxides. The stereoelectronic factors determining the difference in reactivity of the carbonyl fragment in cyclohexanone, 1,2-cyclohexanedione, and its monoethylene ketal were analyzed within the framework of the semiempirical quantum chemical method MNDO.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 142–147, January, 1992.     

Hydroxylation of 4-arylimino-5-hydroxy-1,4-dihydronaphthalen-1-ones

Heating of 4-arylimino-5-hydroxy-1,4-dihydronaphthalen-1-ones with sodium hydroxide in the presence of K₃Fe(CN)₆ gives the corresponding 2,5-dihydroxy derivatives, while in the reaction with FeCl₃ 6H₂O 4-arylimino-3,5-dihydroxy-1,4-dihydronaphthalen-1-ones are formed.Translated from Zhurnal Organicheskoi Khimii, Vol. 40, No. 9, 2004, pp. 1334–1336.Original Russian Text Copyright © 2004 by Bukhtoyarova, Ektova.     

Reactions of <Emphasis Type="Italic">N</Emphasis>-Allyl- and <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-Diallyltrifluoromethanesulfonamides with Carboxylic Acid Amides under Oxidizing Conditions

Reactions of acetamide and benzamide with N-allyltrifluoromethanesulfonamide in the presence of t-BuOCl–NaI afforded exclusively 2,5-bis(chloromethyl)-1,4-bis(trifluoromethanesulfonyl)piperazine. Analogous reaction with N,N-diallyltrifluoromethanesulfonamide gave mixed halogenation product at only one C=C double bond of the substrate.     

Chiral building blocks from biomass: 2,5-diamino-2,5-dideoxy-1,4-3,6-dianhydroiditol

An efficient route towards the synthesis of 2,5-diamino-2,5-dideoxy-1,4-3,6-dianhydroiditol 4 has been developed resulting in significant improvements in both isolated yields and purity when compared to literature procedures. As a consequence, resin-grade 2,5-diamino-2,5-dideoxy-1,4-3,6-dianhydroiditol 4 has become available for laboratory scale step-growth polymer synthesis. Additionally, an interesting renewable chiral 2-amino-2-deoxy-1,4-3,6-dianhydroiditol 10, has been isolated.     

Alkaline hydrogen peroxide bleaching of cellulose

A closed system bleaching apparatus was designed to determine the kinetics and effects of various factors on alkaline hydrogen peroxide bleaching of textile cellulose fabrics. It was confirmed that perhydroxyl anion is the primary bleaching moiety in alkaline hydrogen peroxide systems. The use of the apparatus in the measurement of fabric color, waste oxygen, and the subsequent calculation of hydroxyl ion, and molecular hydrogen peroxide confirmed that pH and titration of 'free' hydrogen peroxide in alkaline bleaching systems are not good indicators of bleaching mechanism. The role of the cellulose itself in the chemical bleaching system was determined. The rate of bleaching on cotton fabric was shown to be a first order reaction in concentration of perhydroxyl anion at 60 and 90°C. An activation energy of 17kcal/mole was estimated. Decomposition of H₂O₂ into waste oxygen was found to be second order kinetics.     

Enantiomeric separation of close analogs to naturally occurring 1,4-benzoxazin-3-ones by liquid chromatography using β-cyclodextrin-modified stationary phase

Summary A liquid chromatographic procedure on a 5 m LiChroCART column using chemically bonded -cyclodextrin (ChiraDex) as chiral selector was developed for the enantiomeric separation of four 2H-1,4-benzoxazin-3(4H)-ones which are close analogs of the cyclic hydroxamic acids 2,4-dihydroxy-2H-1,4-benzoxazin-3(4H)-one (DIBOA) and 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3 (4H)-one (DIMBOA) naturally occurring inGramineae species.     

Iron pentacarbonyl assisted photochemical route to 2,5- and 2,6-divinyl-substituted 1,4-benzoquinones from 1-ene-3-ynes

Photochemical reaction between the enynes, (Z)-1-methoxybut-1-ene-3-yne, 1 or isopropenyl acetylene, 2 with CO in presence of Fe(CO)₅ yields the 2,6- and 2,5-divinyl-substituted 1,4-benzoquinones: 2,6-bis{(Z)-2-methoxyvinyl}-1,4-benzoquinone (3, 42%), 2,5-bis{(Z)-2-methoxyvinyl}-1,4-benzoquinone (4, 31.5%), [{η²,η²:2,6-di(prop-1-en-2-yl)-1,4-benzoquinone}tricarbonyliron] (5, 45%), and {η²,η²:2,5-di(prop-1-en-2-yl)-1,4-benzoquinone}tricarbonyliron] (6, 65%).     

Construction of polyheterocyclic spirotetrahydrothiophene derivatives via sulfa-Michael/aldol cascade reaction

A series of polyheterocyclic spirotetrahydrothiophene derivatives were obtained in moderate to excellent yields via a catalyst-free sulfa-Michael/aldol cascade reaction of chalcones 1 and commercially available 1,4-dithiane-2,5-diol 2 under mild conditions. We also present the first asymmetric sulfa-Michael/aldol cascade reaction of chalcones 1 and commercially available 1,4-dithiane-2,5-diol 2 with moderate to good enantioselectivities catalyzed by readily available chiral phase-transfer catalysts (PTCs).