| 1. |
- Argyropoulos, Dimitris D. S., et al.
(författare)
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Kraft Lignin: A Valuable, Sustainable Resource, Opportunities and Challenges
- 2023
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Ingår i: ChemSusChem. - : John Wiley and Sons Inc. - 1864-5631 .- 1864-564X. ; 16:23
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Forskningsöversikt (refereegranskat)abstract
- Kraft lignin, a by-product from the production of pulp, is currently incinerated in the recovery boiler during the chemical recovery cycle, generating valuable bioenergy and recycling inorganic chemicals to the pulping process operation. Removing lignin from the black liquor or its gasification lowers the recovery boiler load enabling increased pulp production. During the past ten years, lignin separation technologies have emerged and the interest of the research community to valorize this underutilized resource has been invigorated. The aim of this Review is to give (1) a dedicated overview of the kraft process with a focus on the lignin, (2) an overview of applications that are being developed, and (3) a techno-economic and life cycle asseeements of value chains from black liquor to different products. Overall, it is anticipated that this effort will inspire further work for developing and using kraft lignin as a commodity raw material for new applications undeniably promoting pivotal global sustainability concerns.
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| 2. |
- Biswas, Srijit, et al.
(författare)
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Atom-Efficient Gold(I)-Chloride-Catalyzed Synthesis of alpha-Sulfenylated Carbonyl Compounds from Propargylic Alcohols and Aryl Thiols : Substrate Scope and Experimental and Theoretical Mechanistic Investigation
- 2013
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 19:52, s. 17939-17950
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Tidskriftsartikel (refereegranskat)abstract
- Gold(I)-chloride-catalyzed synthesis of -sulfenylated carbonyl compounds from propargylic alcohols and aryl thiols showed a wide substrate scope with respect to both propargylic alcohols and aryl thiols. Primary and secondary aromatic propargylic alcohols generated -sulfenylated aldehydes and ketones in 60-97% yield. Secondary aliphatic propargylic alcohols generated -sulfenylated ketones in yields of 47-71%. Different gold sources and ligand effects were studied, and it was shown that gold(I) chloride gave the highest product yields. Experimental and theoretical studies demonstrated that the reaction proceeds in two separate steps. A sulfenylated allylic alcohol, generated by initial regioselective attack of the aryl thiol on the triple bond of the propargylic alcohol, was isolated, evaluated, and found to be an intermediate in the reaction. Deuterium labeling experiments showed that the protons from the propargylic alcohol and aryl thiol were transferred to the 3-position, and that the hydride from the alcohol was transferred to the 2-position of the product. Density functional theory (DFT) calculations showed that the observed regioselectivity of the aryl thiol attack towards the 2-position of propargylic alcohol was determined by a low-energy, five-membered cyclic protodeauration transition state instead of the strained, four-membered cyclic transition state found for attack at the 3-position. Experimental data and DFT calculations supported that the second step of the reaction is initiated by protonation of the double bond of the sulfenylated allylic alcohol with a proton donor coordinated to gold(I) chloride. This in turn allows for a 1,2-hydride shift, generating the final product of the reaction.
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| 3. |
- Bunrit, Anon, et al.
(författare)
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Brønsted Acid-Catalyzed Intramolecular Nucleophilic Substitution of the Hydroxyl Group in Stereogenic Alcohols with Chirality Transfer
- 2015
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 137:14, s. 4646-4649
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Tidskriftsartikel (refereegranskat)abstract
- The hydroxyl group of enantioenriched benzyl, propargyl, allyl, and alkyl alcohols has been intramolecularly displaced by uncharged O-, N-, and S-centered nucleophiles to yield enantioenriched tetrahydrofuran, pyrrolidine, and tetrahydrothiophene derivatives with phosphinic acid catalysis. The five-membered heterocyclic products are generated in good to excellent yields, with high degree of chirality transfer, and water as the only side-product. Racemization experiments show that phosphinic acid does not promote S(N)1 reactivity. Density functional theory calculations corroborate a reaction pathway where the phosphinic acid operates as a bifunctional catalyst in the intramolecular substitution reaction. In this mechanism, the acidic proton of the phosphinic acid protonates the hydroxyl group, enhancing the leaving group ability. Simultaneously, the oxo group of phosphinic acid operates as a base abstracting the nucleophilic proton and thus enhancing the nucleophilicity. This reaction will open up new atom efficient techniques that enable alcohols to be used as nucleofuges in substitution reactions in the future.
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| 4. |
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| 5. |
- Bunrit, Anon, et al.
(författare)
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H3PO2-Catalyzed Intramolecular Stereospecific Substitution of the Hydroxyl Group in Enantioenriched Secondary Alcohols by N-, O-, and S-Centered Nucleophiles to Generate Heterocycles
- 2020
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Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 10:2, s. 1344-1352
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Tidskriftsartikel (refereegranskat)abstract
- The direct intramolecular stereospecific substitution of the hydroxyl group in enantiomerically enriched secondary benzylic, allylic, propargylic, and alkyl alcohols was successfully accomplished by phosphinic acid catalysis. The hydroxyl group was displaced by O-, S-, and N-centered nucleophiles to provide enantioenriched five-membered tetrahydrofuran, pyrrolidine, and tetrahydrothiophene as well as six-membered tetrahydroquinolines and chromanes in up to a 99% yield and 100% enantiospecificity with water as the only byproduct. Mechanistic studies using both experiments and calculations have been performed for substrates generating 5-membered heterocycles. Rate studies show dependences in a catalyst, an internal nucleophile, and an electrophile, however, independence in an external nucleophile, an electrophile, or water. Kinetic isotope effect studies show an inverse KIE of k(H)/k(D) = 0.79. Furthermore, phosphinic acid does not promote S(N)1 reactivity. Computational studies support a bifunctional role of the phosphinic acid in which activation of both nucleofuge and nucleophile occurs in a bridging S(N)2-type transition state. In this transition state, the acidic hydrogen of phosphinic acid protonates the leaving hydroxyl group simultaneously as the oxo group partially deprotonates the nucleophile. Thereby, phosphinic acid promotes the substitution of the nonderivatized hydroxyl group in enantioenriched secondary alcohols by uncharged nucleophiles with conservation of the chirality from the alcohol to the heterocycle.
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| 6. |
- Bunrit, Anon, 1986-, et al.
(författare)
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H3PO2-Catalyzed Intramolecular Stereospecific Substitution of the Hydroxyl Group in Stereogenic Secondary Alcohols by N-, O-, and S-centered Nucleophiles to Generate Heterocycles
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The direct intramolecular stereospecific substitution of the hydroxyl group in stereogenic secondary alcohols was successfully accomplished by phosphinic acid catalysis. The hydroxyl group was displaced by O-, S-, and N-centered nucleophiles to provide enantioenriched five- and six-membered heterocycles in good to excellent yields and high enantiospecificity with water as the only by product. Mechanistic studies using both experiments and calculations have been performed. Rate order determination shows first-order dependences in catalyst, internal nucleophile, and electrophile concentrations, however, independence on external nucleophile and electrophile. Furthermore, phosphinic acid does not promote SN1 reactivity. Computational studies support a bifunctional role of the phosphinic acid in which activations of both nucleofuge and nucleophile occur in a bridging SN2-type transition state.
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| 7. |
- Bunrit, Anon, et al.
(författare)
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Nucleophilic Substitution of the Hydroxyl Group in Stereogenic Alcohols with Chirality Transfer
- 2016
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Ingår i: Synlett. - : Georg Thieme Verlag KG. - 0936-5214 .- 1437-2096. ; 27:2, s. 173-176
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Tidskriftsartikel (refereegranskat)abstract
- A brief overview of the development of direct substitution of the hydroxyl (OH) group of alcohols in our research group is presented. By applying a BrOnsted acid, an intramolecular substitution of the OH group in stereogenic alcohols with chirality transfer was achieved. Noteworthy, the intramolecular substitution has a wide scope in respect to both the nucleophile and also the nucleofuge. A mechanistic study by both experiments and DFT calculations revealed a unique reaction pathway in which the BrOnsted acid operates in a bifunctional manner to promote an S(N)2-type reaction mechanism.
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| 8. |
- Dahlstrand, Christian, et al.
(författare)
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Exploration of the π-Electronic Structure of Singlet, Triplet, and Quintet States of Fulvenes and Fulvalenes Using the Electron Localization Function
- 2012
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 116:20, s. 5008-5017
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Tidskriftsartikel (refereegranskat)abstract
- The singlet ground states and lowest triplet states of penta- and heptafulvene, their benzannulated derivatives, as well as the lowest quintet states of pentaheptafulvalenes, either the parent compound or compounds in which the two rings are intercepted by either an alkynyl or a phenyl segment, were investigated at the (U)OLYP/6-311G(d,p) density functional theory level. The influence of (anti)-aromaticity was analyzed by the structure-based aromaticity index HOMA, the harmonic oscillator model of aromaticity. The extent of (anti)aromatic character was also evaluated in terms of the pi-electron (de)localization as measured by the pi component of the electron localization function (ELF pi). The natural atomic orbital (NAO) occupancies were calculated in order to evaluate the degree of pi-electron shift caused by the opposing electron-counting rules for aromaticity in the electronic ground state (S-0; Hiickel's rule) and the first pi pi* excited triplet state (T-1; Baird's rule). Pentaheptafulvalene (5) shows a shift of 0.5 pi electrons from the 5-ring to the 7-ring when going from the S-0 state to the lowest quintet state (Qu(1)). The pentaheptafulvalene 5 and [5.6.7]quinarene 7 were also investigated in their 90 degrees twisted conformations. From our study it is apparent that excitation localization in fulvalenes, but not in fulvenes, to a substantial degree is determined by aromaticity localization to triplet biradical 4n pi-electron cycles. Isolated benzene rings in these compounds tend to remain as closed-shell 6 pi-electron cycles.
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| 9. |
- Dahlstrand, Christian
(författare)
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Ground and Excited State Aromaticity : Design Tools for π-Conjugated Functional Molecules and Materials
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main focus of this thesis is on the aromaticity of the ground state and electronically excited states of π-conjugated molecules and polymers, as well as how aromaticity is connected to their properties.The electronic structures of polybenzenoid hydrocarbons (PBHs) were explored through density functional theory (DFT) calculations and the π-component of the electron localization function (ELFπ). The study revealed how the π-electronic structure is influenced by the fusion of double bonds or benzene rings to the PBHs. We also demonstrated that the π-electrons of benzene extend to accommodate as much aromaticity as possible when bond length distorted. The aromatic chameleon property displayed by fulvenes, isobenzofulvenes, fulvalenes, bis(fulvene)s, and polyfulvenes were investigated using DFT calculations. The tria-, penta-, and heptafulvenes were shown to possess ionization energies and electron affinities which can be tuned extensively by substitution, some of which even outperform TTF and TCNQ, the prototypical electron donor and acceptor, respectively. The singlet-triplet energy gap of pentafulvenes can be tuned extensively by substitution to the point that the triplet state is lower than the singlet state and thus becomes the ground state. The ELFπ of isobenzofulvene shows that the benzene ring in an electronically excited state can be more aromatic than the corresponding ring in the ground state. We have shown that the 6-ring of [5.6.7]quinarene is influenced by a Hückel aromatic resonance structure with 4n+2 π-electrons in the excited quintet state. The bis(fulvene)s which are composed of a donor type heptafulvene and an acceptor type pentafulvene, retain the basic donor-acceptor properties of the two fragments and could function as compact donor-acceptor dyads. A few of the designed polyfulvenes were found to have band gaps below 1 eV at the PBC-B3LYP/6-31G(d) level.Various 2,7-disubstituted fluorenones and dibenzofulvenes were synthesized and their excited state properties were investigated by absorption spectroscopy and time-dependent DFT calculations. It was found that the 1A → 1B transition of ππ* character can be tuned by substitution in the 2,7-positions. The 2,7-bis(N,N-dimethyl) derivatives of fluorenone and dibenzofulvene displayed low energy transitions at 2.18 and 1.61 eV, respectively, in toluene.
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| 10. |
- Dahlstrand, Christian, et al.
(författare)
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Polyfulvenes : Polymers with "Handles" That Enable Extensive Electronic Structure Tuning
- 2015
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:46, s. 25726-25737
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Tidskriftsartikel (refereegranskat)abstract
- The fundamental electronic structure properties of substituted poly(penta)fulvenes and pentafulvene-based polymers are analyzed through qualitative molecular orbital (MO) theory combined with calculations at the B3LYP and HSE06 hybrid density functional theory (DFT) levels. We argue that the pentafulvene monomer unit has a unique character because electron density in the exocyclic C=C double bond can be polarized into and out of the five-membered ring, a feature that is not available to other more commonly used monomers. It is investigated how the energy gaps between the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO, respectively), as approximate band gaps, are influenced by exocyclic substitution, introduction of linker groups, benzannulation, and ring substitution. In particular, the exocyclic positions of the fulvene act as handles by which the electronic structure of the polymer can be tuned between the quinoid and fulvenoid valence bond isomers; electron-withdrawing exocyclic substituents lead to polyfulvenes in the quinoid form while those with electron-donating substituents prefer the fulvenoid. Taken together, the HOMO-LUMO gaps of polyfulvenes can be tuned extensively, varying in ranges 0.77-2.44 eV (B3LYP) and 0.35-2.00 eV (HSE06) suggesting that they are a class of polymers with highly interesting, yet nearly unexplored, properties.
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