Lactic acid is a renewable and versatile chemical for food, pharmaceuticals, cosmetics, and other chemicals. Lactic acid can be produced from biomass‐derived dihydroxyacetone. However, selective and recyclable water‐tolerant acid catalysts need to be developed for the specific production of lactic acid. Here we show that the MIL‐101(Al)−NH2metal‐organic framework (MOF) is a water‐tolerant and selective solid Lewis acid catalyst for dihydroxyacetone isomerization to lactic acid. The Lewis acidic MIL‐101(Al)−NH2catalyst promoted a high lactic acid selectivity of 91 % at 96 % dihydroxyacetone conversion at 120 °C in water. The reaction proceeded by temperature and/or MIL‐101(Al)−NH2MOFs mediated dihydroxyacetone dehydration to pyruvaldehyde. Subsequently, the MIL‐101(Al)−NH2facilitated rehydration of the pyruvaldehyde to lactic acid. The Lewis acidic MIL‐101(Al)−NH2catalyst was stable and reusable four times without any decrease in catalytic performance.
Enhanced Reactivity for Aromatic Bromination via Halogen Bonding with Lactic Acid Derivatives
We report a new method for regioselective aromatic bromination using lactic acid derivatives as halogen bond
acceptors with N-bromosuccinimide (NBS). Several structural analogues of lactic acid affect the efficiency of aromatic brominations,
presumably via Lewis acid/base halogen-bonding interactions. Rate comparisons of aromatic brominations demonstrate the
reactivity enhancement available via catalytic additives capable of halogen bonding. Computational results demonstrate that Lewis
basic additives interact with NBS to increase the electropositive character of bromine prior to electrophilic transfer. An optimized
procedure using catalytic mandelic acid under aqueous conditions at room temperature was developed to promote aromatic
bromination on a variety of arene substrates with complete regioselectivity.
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- NSF-PAR ID:
- 10335933
- Date Published:
- Journal Name:
- The Journal of Organic Chemistry
- ISSN:
- 0022-3263
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract -
Sodium sulfite, sodium thiosulfate, and ascorbic acid are commonly used to quench free chlorine and free bromine in studies of disinfection byproducts (DBPs) in drinking water, wastewater, and recreational water. The reducing capabilities of these quenchers, however, can lead to the degradation of some redox-labile analytes. Ammonium chloride, another common quencher, converts free chlorine into monochloramine and is therefore inappropriate for analytes susceptible to chloramination. Herein, we demonstrate the utility of 1,3,5-trimethoxybenzene (TMB) as a quencher of free chlorine and free bromine. The reactivity of TMB toward free chlorine was characterized previously. The reactivity of TMB toward free bromine was quantified herein ( k HOBr,TMB = 3.35 × 10 6 M −1 s −1 ) using competition kinetics. To explore the feasibility of TMB serving as a free halogen quencher for kinetic experiments, chlorination of 2,4-dichlorophenol, bromination of anisole, and chlorination and bromination of dimethenamid-P were examined. Although TMB does not react with free chlorine or free bromine as quickly as do some (but not all) traditional quenchers, there was generally no significant difference in the experimental rate constants with TMB (relative to thiosulfate) as the quencher. By monitoring the chlorination and bromination products of TMB, free halogen residuals in quenched samples were quantified. Furthermore, TMB did not affect the stabilities of DBPs ( e.g. , chloropicrin and bromoacetonitriles) that otherwise degraded in the presence of traditional quenchers. TMB could, therefore, be an appropriate quencher of free chlorine and free bromine in aqueous halogenation experiments involving redox-labile analytes and/or when selective quantification of residual free halogens is desired.more » « less
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The literature contains numerous instances where pairs of anions engage in a stable complex with one another, held together by hydrogen, halogen, and related noncovalent bonds, within the confines of a polarizable medium such as a crystal or solvent. But within the context of the gas phase, such pairs are only metastable, higher in energy than separated monomers, whose favorable dissociation is hindered by an energy barrier. Quantum calculations search for pairs of anions that might engage in a fully stable halogen-bonded dimer in the gas phase, lower in energy than the separate monomers. Each Lewis acid candidate contains an I atom attached to an alkyne, alkene, or alkane chain of variable length, terminated by a O − or COO − group, and decorated with electron-withdrawing CN substituents. Also considered are aromatic systems containing I and COO − , along with four CN substituents on the phenyl ring. Lewis bases considered were of two varieties. In addition to the simple Cl − anion, an NH 2 group was separated from a terminal carboxylate by an alkyne chain of variable length. Exothermic association reactions are achieved with Cl − paired with CN-substituted alkenes and alkanes where the I and COO − of the Lewis acid are separated by at least four C atoms. The energetics are especially favorable for the longer alkanes where Δ E is roughly −30 kcal mol −1 .more » « less
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Similarities and differences of halogen and hydrogen bonding were explored via UV–Vis and 1H NMR measurements, X-ray crystallography and computational analysis of the associations of CHX3 (X=I, Br, Cl) with aromatic (tetramethyl-p-phenylenediamine) and aliphatic (4-diazabicyclo[2,2,2]octane) amines. When the polarization of haloforms was taken into account, the strengths of these complexes followed the same correlation with the electrostatic potentials on the surfaces of the interacting atoms. However, their spectral properties were quite distinct. While the halogen-bonded complexes showed new intense absorption bands in the UV–Vis spectra, the absorptions of their hydrogen-bonded analogues were close to the superposition of the absorption of reactants. Additionally, halogen bonding led to a shift in the NMR signal of haloform protons to lower ppm values compared with the individual haloforms, whereas hydrogen bonding of CHX3 with aliphatic amines resulted in a shift in the opposite direction. The effects of hydrogen bonding with aromatic amines on the NMR spectra of haloforms were ambivalent. Titration of all CHX3 with these nucleophiles produced consistent shifts in their protons’ signals to lower ppm values, whereas calculations of these pairs produced multiple hydrogen-bonded minima with similar structures and energies, but opposite directions of the NMR signals’ shifts. Experimental and computational data were used for the evaluation of formation constants of some halogen- and hydrogen-bonded complexes between haloforms and amines co-existing in solutions.more » « less
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Developing a comprehensive method to compute bond orders is a problem that has eluded chemists since Lewis's pioneering work on chemical bonding a century ago. Here, a computationally efficient method solving this problem is introduced and demonstrated for diverse materials including elements from each chemical group and period. The method is applied to non-magnetic, collinear magnetic, and non-collinear magnetic materials with localized or delocalized bonding electrons. Examples studied include the stretched O 2 molecule, 26 diatomic molecules, 3d and 5d transition metal solids, periodic materials with 1 to 8748 atoms per unit cell, a biomolecule, a hypercoordinate molecule, an electron deficient molecule, hydrogen bound systems, transition states, Lewis acid–base complexes, aromatic compounds, magnetic systems, ionic materials, dispersion bound systems, nanostructures, and other materials. From near-zero to high-order bonds were studied. Both the bond orders and the sum of bond orders for each atom are accurate across various bonding types: metallic, covalent, polar-covalent, ionic, aromatic, dative, hypercoordinate, electron deficient multi-centered, agostic, and hydrogen bonding. The method yields similar results for correlated wavefunction and density functional theory inputs and for different S Z values of a spin multiplet. The method requires only the electron and spin magnetization density distributions as input and has a computational cost scaling linearly with increasing number of atoms in the unit cell. No prior approach is as general. The method does not apply to electrides, highly time-dependent states, some extremely high-energy excited states, and nuclear reactions.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acs.joc.2c00611
