Acid-catalyzed Dehydration Reaction Research Articles

Rhenium-Catalyzed Dehydration and Deoxydehydration of Alcohols and Polyols: Opportunities for the Formation of Olefins from Biomass

In view of the depletion of petroleum oils, new synthetic routes for the sustainable production of chemicals, fuels, and energy from renewable biomass sources are currently widely investigated. In particular, nonedible sugars and polyols are promising starting materials to produce olefins by dehydration, deoxygenation, or deoxydehydration (DODH) of these poly vicinal alcohols. In this perspective, we highlight the recent evolution of rhenium-catalyzed dehydration and DODH of biomass-derived alcohols and polyols to obtain olefins. Improving over the classical acid-catalyzed dehydration reaction, rhenium-mediated systems are very selective and more active to provide high yields of olefin products, but dehydration alone cannot be used to fully defunctionalize sugars. This issue is addressed by a growing research effort in the field of Re-catalyzed DODH, which allows complete dehydroxylation to form olefins in high yield. Recent developments in this field include the development of new molecular rhenium catal...

Synthesis of steroidal and nonsteroidal vicinal heterocyclic alcohols, N-(1-cycloalkenyl)heterocycles and their antibacterial studies

A solvent free steroidal and nonsteroidal epoxide ring opening reaction by nitrogen containing heterocycles under microwave irradiation is described. Some of the epoxide ring opening compounds were converted to their corresponding N-(1-cycloalkenyl)heterocycles via an acid catalyzed dehydration reaction. The antimicrobial activities of the epoxide ring opening compounds and N-(1-cycloalkenyl)heterocyclic compounds were tested by agar diffusion assay. Compounds 6, 9–12, 24 and 27 showed moderate inhibition against the growth of pathogenic bacteria Escherichia coli, Pseudomonas syringae, Bacillus subtilis, Proteus vulgaris and Staphylococcus aureus.

One-Pot Esterification and Amide Formation via Acid-Catalyzed Dehydration and Ritter Reactions

Esterification of carboxylic acid is achieved using acetonitrile as a water trap. Water liberated during esterification is consumed in cyanide hydrolysis, thereby driving the esterification to completion. Substrates having carboxylic acid and nitrile groups undergo intramolecular dehydration and rehydration to amido esters in the absence of acetonitrile. Cyano acids also undergo esterification and Ritter reaction in one pot when excess alcohol is used. For the first time, we have observed an interesting Ritter reaction of primary alcohols, leading to ester amide product in one pot. [Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]

Conversion of Fructose to 5-HMF(5-hydroxymethylfurfural) in DMSO(dimethylsulfoxide) solvent

Conversion of fructose to 5-hydroxymethylfurfural (5-HMF) was investigated in dimethylsulfoxide (DMSO) solvent with increasing reaction temperatures and impact of residual water from dehydration reaction byproduct. To convert fructose to 5-HMF, increasing reaction temperature led more conversion to 5-HMF than lower temperature at the range of in DMSO solvent. DMSO engaged in the acid-catalyzed dehydration and rearrangement reaction as acid and solvent. Increasing temperature led to more furanose structure than pyranose at the range of . Formed 5-HMF could be degraded to levulinic and formic acid at the presence of acid and water. Removal of water in reaction medium could prevent 5-HMF degradation.

酸化コバルトの酸性度に対する硫酸塩含浸法による硫酸化の影響

To enhance the acidity of cobalt oxide, sulfation was carried out using aqueous solution of cobalt sulfate impregnated on cobalt oxide and the product calcined at high temperatures. Conventional sulfation of oxides by sulfuric acid could not avoid dissolution of cobalt oxide in the sulfuric acid. The activity of cobalt oxide for acid-catalyzed ethanol dehydration reaction was greatly enhanced by sulfation using cobalt sulfate. The activity of the prepared sulfated cobalt oxide was comparable to that of conventional SiO2–Al2O3 acid catalyst. The sulfated cobalt oxide did not show activity for pentane isomerization, which was catalyzed by sulfated zirconia prepared by the same methodology of sulfate salt impregnation, using zirconium sulfate solution was impregnated onto zirconia. The highest activity was obtained by heat treatment at 1073 K. This treatment temperature is the highest among solid acid catalysts reported so far.

A new synthesis of 5-hydroxy-6-methyluracil

Dehydration of 5,6-dihydro-5,6-dihydroxy-6-methyl- and 5,6-dihydro-5,6-dihydroxy-1,3,6-trimethyl-uracil in 0.4M aqueous sulfuric acid gives 5-hydroxy-6-methyl- and 5-hydroxy-1,3,6-trimethyluracil in quantitative yields. Two possible mechanisms have been examined using the mPW1k/6-311+G(2df,2pd)//mPW1k/6-31+G(d,p) method for the transformation of methylated and non-methylated 5,6-dihydro-5,6-dihydroxy-6-methyluracils into the corresponding 5-hydroxy-6-methyluracils. The first is a hydride C5–C6 shift occurring in concert with the loss of a water molecule and formation of the corresponding protonated 5,6-dihydro-5-oxo-6-methyluracils. The second is an acid-catalyzed dehydration reaction to yield 5-hydroxy-6-methyluracils. The calculations demonstrated that the second pathway was energetically most favorable.

ChemInform Abstract: Mechanisms and Energetics for Bronsted Acid‐Catalyzed Glucose Condensation, Dehydration and Isomerization Reactions

AbstractReview: 36 refs.

Mechanisms and Energetics for Brønsted Acid-Catalyzed Glucose Condensation, Dehydration and Isomerization Reactions

The mechanisms and energetics for Bronsted acid-catalyzed glucose condensation, dehydration and isomerization reactions were discussed based on our earlier CPMD–MTD simulation results. Glucose condensation reaction is initiated by the protonation of C1–OH, whereas both dehydration and isomerization reactions are initiated by the protonation of C2–OH to form a common 5-member ring intermediate. Glucose dehydration to form HMF occurs via the direct cyclic mechanism, rather than via the open chain mechanism converting glucose to fructose then to HMF. Fructose is formed via a 1,2 hydride shift process following the formation of 5-member ring intermediate. The barriers for Bronsted acid-catalyzed glucose reactions are largely solvent induced due to the competition for proton from the solvent molecules.

The Synergy of the Support Acid Function and the Metal Function in the Catalytic Hydrodeoxygenation of m-Cresol

The hydrodeoxygenation (HDO) of m-cresol is investigated as a model for the HDO of phenolic compounds from lignin pyrolysis. Pt catalysts supported on γ-Al2O3 and SiO2 are effective for the conversion of m-cresol to toluene and methylcyclohexane at 533 K and 0.5 atm H2. Experiments using Pt/γ-Al2O3 show that the reaction proceeds by a combination of Pt-catalyzed hydrogenation and acid-catalyzed dehydration reactions. Dehydration of a partially hydrogenated oxygenate intermediate is most likely the dominant reaction pathway to toluene. The acidity of the γ-Al2O3 support was modified by base (K2CO3) and acid (NH4F) treatments, and increasing the number and strength of acid sites was found to increase the rate of HDO. Pt/SiO2 was more active for m-cresol HDO than Pt/Al2O3. The reaction rate on Pt/Al2O3 and Pt/SiO2 decreased after 5 h on stream, but Pt/Al2O3 regained initial reactivity after reductive treatment in H2.

Selective Hydrogenolysis of Polyols and Cyclic Ethers over Bifunctional Surface Sites on Rhodium–Rhenium Catalysts

A ReO(x)-promoted Rh/C catalyst is shown to be selective in the hydrogenolysis of secondary C-O bonds for a broad range of cyclic ethers and polyols, these being important classes of compounds in biomass-derived feedstocks. Experimentally observed reactivity trends, NH(3) temperature-programmed desorption (TPD) profiles, and results from theoretical calculations based on density functional theory (DFT) are consistent with the hypothesis of a bifunctional catalyst that facilitates selective hydrogenolysis of C-O bonds by acid-catalyzed ring-opening and dehydration reactions coupled with metal-catalyzed hydrogenation. The presence of surface acid sites on 4 wt % Rh-ReO(x)/C (1:0.5) was confirmed by NH(3) TPD, and the estimated acid site density and standard enthalpy of NH(3) adsorption were 40 μmol g(-1) and -100 kJ mol(-1), respectively. Results from DFT calculations suggest that hydroxyl groups on rhenium atoms associated with rhodium are acidic, due to the strong binding of oxygen atoms by rhenium, and these groups are likely responsible for proton donation leading to the formation of carbenium ion transition states. Accordingly, the observed reactivity trends are consistent with the stabilization of resulting carbenium ion structures that form upon ring-opening or dehydration. The presence of hydroxyl groups that reside α to carbon in the C-O bond undergoing scission can form oxocarbenium ion intermediates that significantly stabilize the resulting transition states. The mechanistic insights from this work may be extended to provide a general description of a new class of bifunctional heterogeneous catalysts, based on the combination of a highly reducible metal with an oxophilic metal, for the selective C-O hydrogenolysis of biomass-derived feedstocks.

Degradation of 5‐Hydroxymethylfurfural in Honey

5-Hydroxymethylfurfural (HMF) is the most important intermediate product of the acid-catalyzed dehydration reaction of hexoses and/or Maillard reaction; furthermore, it is the most used index to evaluate thermal damages or ageing in food products. Usually its degradation reactions, being very slow, are neglected. This study reports the findings concerning the degradation kinetics of HMF, in honeys of different floral origin at a temperature between 25 and 50 degrees C. The results highlighted higher degradation rates (k(HMF) (degradation)) compared to the corresponding formation rates (k(HMF) (formation)) in chestnut and citrus samples. Similar k-values were found in multifloral honey. Moreover, the reaction of HMF degradation was characterized by lower activation energy (E(a)) values compared to E(a) formation values. The final concentration of HMF in honey, during storage at room temperature, should be ascribed to high sugar concentration. The fluctuation of HMF in honeys could depend on the equilibrium between the accumulation and the degradation processes. This can affect the validity of HMF as storage index in some honeys, above all during the analysis of those honeys whose legislation is too restrictive (citrus) or in chestnut honey analysis where it does not accumulate.

Unusual Rate Acceleration in Brønsted Acid Catalyzed Dehydration Reactions: Local Hydrophobic Environment in Aggregated N‐(2,6‐diphenylphenyl)‐N‐mesitylammonium Pentafluorobenzenesulfonates

Bulky diarylammonium pentafluorobenzenesulfonates effectively promote dehydration reactions, such as condensation reactions to give esters and the dehydrative cyclization of 1,3,5-triketones. In particular, N-(2,6-diphenylphenyl)-N-mesitylammonium pentafluorobenzenesulfonate shows much higher catalytic activity than C6F5SO3H under reaction conditions without the removal of generated water, even though the former is a weaker acid. Its crystallization gives an aggregated cyclic ion pair, which is composed of two diarylammonium cations, four pentafluorobenzenesulfonate anions, and two oxonium cations. This ion pair is strongly stabilized by four intermolecular and two intramolecular pi-pi attractive interactions and 10 hydrogen bonds. The extremely high catalytic activity of N-(2,6-diphenylphenyl)-N-mesitylammonium pentafluorobenzenesulfonate in the dehydration reactions may be ascribed to the local hydrophobic environment of the tightly aggregated ammonium salts.

The carbon skeleton of the belt region of fullerene C84 (D2).

The synthesis and structural characterization of the double-stranded carbon skeleton in the belt region of a C84 fullerene has been achieved. The synthetic methodology used is based on cyclic dimerization of diastereomeric AB-type monomers 18 by a non-diastereospecific Diels-Alder reaction with isobenzofuran and acenaphthylene groups as reactive termini. Four diasteromeric monomer precursors 17 were prepared for the first time by the use of dihydropyracylene (12) in a multistep synthesis. The synthesis of dihydropyracylene itself has been optimized to the degree that it is now available on the 10 g scale. The belt-shaped macrocycle 19, obtained from dimerization of the monomers 17, could be partly aromatized by an acid-catalyzed dehydration reaction to give 23, which differs from the fully unsaturated belt by two water molecules. Semiempirical AM1 calculations of the electronic and thermodynamic properties of cyclic fluoranthenes revealed strain energy as the essential reason for the incomplete aromatization of 19. The structures of the macrocycles 19 and 23, one of the monomer precursors, and two diastereomeric epoxybenzo[k]fluoranthenes were elucidated by single-crystal X-ray crystallography.

Theoretical Studies of the Cross-Linking Mechanisms between Cytosine and Tyrosine

DNA-protein cross-linking is one of the many DNA lesions mediated by hydroxyl radicals, the most damaging among the reactive oxygen species in biological systems. Density functional theory methods are employed to investigate the complex reaction mechanisms of the formation of cytosine-tyrosine cross-links as observed in gamma-irradiated aqueous solutions of cytosine and tyrosine, as well as in gamma-irradiated nucleohistone. The majority of the radical addition mechanisms considered are found to have significant barriers and therefore to be thermodynamically unfavorable for the formation of the initial cross-linked product. Our calculated reaction potential energy surfaces suggest that a feasible complete mechanism consists of radical combination forming the initial cross-linked product, a hydrogen shuffle within the initial cross-linked product, and an acid-catalyzed dehydration reaction. Water and hydrogen-bonding interactions are suggested to play a key role in catalyzing the hydrogen-transfer step of the reaction.

Ethylene glycol to acetaldehyde-dehydration or a concerted mechanism

Two possible mechanisms have been proposed to account for the rearrangement of ethylene glycol to acetaldehyde. The first is a rearrangement with a hydride shift occurring in concert with the loss of a water molecule. The second is an acid catalyzed dehydration reaction proceeding through the enol to yield acetaldehyde. DFT calculations are presented which show the first postulation to be the lower energy pathway by a considerable margin.

The kinetics of a negative-tone acrylic photoresist for 193-nm lithography

Polymethacrylates with tert-alcohol ester were synthesized as negative-tone chemical amplification photoresists (CAMPs) for 193-nm microlithography. The acid-catalyzed dehydration reaction of the CAMPs was analyzed via Fourier transform infrared. The crosslinking behavior following the dehydration reaction of the exposed CAMPs made it possible for them to be used as negative-tone photoresists. During the postexposure-baking process of the resists, the decay of the active proton concentration due to the evaporation and trapping of the active acid was lumped to a time constant (τ). Kinetic studies revealed this dehydration reaction was the first order to the hydroxy group and proton concentration. The introduction of the isobornyl methacrylate monomer into the resists produced a higher glass-transition temperature as well as a higher reactive ion etching resistance. The lithographic performance was investigated by use of isopropyl alcohol as a developer under various processing conditions. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 954–961, 2000

Practical Total Syntheses of (R)-(+)- and (S)-(-)-14-Hydroxy-4,14-retro-retinol.

Practical and facile total syntheses of the remarkably unstable (R)-(+)-14-hydroxy-4, 14-retro-retinol [(R)-14HRR] 1 and of its enantiomer 2 have been achieved via an acid-catalyzed dehydration reaction of the respective tetraeneol intermediates 10 and its enantiomer obtained from (R)-(+)-1, 2-O-isopropylidene-butane-1, 2, 3-triol 3.

Carbonylation of diols and their ethers and esters with ruthenium catalysts: synthesis of lactones and hydroxyacids ethers and esters

Diols and their formic or acetic esters can be carbonylated to give lactones or the corresponding hydroxyacid esters of ethers in the presence of carbonylruthenium iodide systems, [Ru(CO) 3I 3] −/alkyl or metal iodide, at a temperature of 200°C and CO pressure of 10-20 MPa. The reaction in the case of 1,3-propanediol gives γ-butyrolactone, with a selectivity of 60-% . Side reactions of homologation to 1,4-butanediol derivatives and hydrogenolysis to n-propyl derivatives by H 2 produced by the water gas shift reaction (WGSR) also occur, together with acid-catalyzed dehydration to give linear polypropylene glycols, α,ω-diols with more than 3 carbon atoms in the chain preferentially give hydroxyacid esters and ethers. The cyclic ether by-products and linear polyether by-products can be further activated and carbonylated under the reaction conditions to give lactones or hydroxy-acid derivatives thus increasing the total yield of carbonylation products. The formation of H 2 by WGSR involving water produced by the acid-catalyzed dehydration reactions, and the subsequent hydrogenolysis and homologation reactions cannot be avoided.

Gas—liquid and high-performance liquid chromoatographic analyses of the acid-catalyzed dehydration reaction of xylitol

Reactions of xylitol with concentrated hydrochloric acid or diluted sulfuric acid were studied under various conditions. Complete separation of reaction products was achieved by means of gas—liquid chromatography on a capillary column coated with SE-30. The chemical structures of the compounds obtained were assigned using mass spectrometry. The major components of reaction mixtures were seperated by high-performance liquid chromatography. The analytical methods so developed were applied to estimate the usefulness of preparative methods.