Hydration Of Alkynes Research Articles

Base‐Catalyzed Hydration of Silicon‐Containing Activated Alkynes: The Effect of Substituents at the Triple Bond

AbstractMetal‐catalyzed hydration of alkynes is rapidly developing research direction in organic synthesis. However, base‐catalyzed hydration of activated acetylenes remains much less studied. In contrast to the metal‐catalyzed reactions leading to carbonyl compounds, base‐catalyzed hydration gives vinyl ethers of different structure or cyclic products depending on the nature of substituents. So, it is found that 1,4‐diazabicyclo [2.2.2]octane (DABCO)‐catalyzed hydration of trimethylsilylated electron‐deficient alkynes of general formula Me3SiC≡CCOX (X=Ph, NR1R2, OEt) proceeds at room temperature to afford push‐pull divinyl ethers in 56–94 % yields, while 4‐trimethylsilyl‐3‐butyne‐2‐one (X=Me) reacts non‐selectively delivering both symmetrical and unsymmetrical divinyl ethers (dimerization products). Contrary to ketones, amides and esters, 3‐trimethylsilylpropynal gives under the same conditions 4H‐pyran, as we shown earlier.

Synthesis and Catalytic Properties of Metal-N-Heterocyclic-Carbene-Decorated Covalent Organic Framework.

We demonstrate herein that the N-heterocyclic-carbene (NHC)-metal complex (NHC-M)-involved covalent organic framework (COF) can be prepared by the direct polymerization of the NHC-M monomer with its counterpart under solvothermal conditions. The NHC-M-COF with different counterions is readily achieved via solid-state anion exchange. The obtained NHC-AuX-COF (X = Cl- and SbF6-) can be a highly active reusable catalyst to separately promote the carboxylation of the terminal alkyne with CO2 and alkyne hydration under mild conditions.

Silver-catalyzed multicomponent reactions for the construction of γ-carbonyl-α-amino acid derivatives

Silver-catalyzed multicomponent strategy for the construction of highly functionalized γ-carbonyl-α-amino acid derivatives has been developed under mild conditions, in which various γ-carbonyl-α-amino acid derivatives were obtained in moderate to excellent yields. Preliminary mechanistic studies suggested that silver-catalyzed A3-coupling reaction and alkyne hydration process were accomplished in a simple operation.

An Efficient Hydration and Tandem Transfer Hydrogenation of Alkynes for the Synthesis of Alcohol in Water

A practical and efficient method for the synthesis of alcohols in one pot from readily available alkynes via a tandem process by formic acid promoted hydration and metal-ligand bifunctional iridium-catalyzed­ transfer hydrogenation under mild conditions has been described. This transformation is simple, efficient, and can be performed with a variety of alkynes in good yields and with excellent stereoselectivities. Experimental results showed high catalytic activity, and turnover frequency (TOF) up to 25000. Importantly, this transformation can be conducted in water, and is thus green and environmentally friendly.

High-performance of plasma-enhanced Zn/MCM-41 catalyst for acetylene hydration

The influence of plasma pretreatment on the catalytic performance of Zn based catalyst in acetylene hydration was studied. Furthermore, the atmosphere (N2, O2, NH3, air) and process conditions (pretreatment time, pretreatment power, gas flow) of plasma pretreatment were investigated systematically. The activity results showed that both the conversion and selectivity of the P-Zn/MCM-41 catalyst treated by oxygen plasma improved significantly. The characterization results suggested that the plasma treated catalyst enhances the mutual effect between the Zn species and MCM-41 carrier, promotes the dispersion of the active component and inhibits the loss of Zn species.

On the catalytic activation of water-soluble NHC-Au(I) complexes by sonication and microwave irradiation: A comparative assessment

Within the realm of sustainable chemistry and increasing demand for eco-compatible methods, this article describes our attempts to activate some water-soluble N-heterocyclic carbene (NHC)-based gold(I) complexes under two well-known and safe irradiation protocols: microwaves (MW) and ultrasound (US). A textbook reaction, alkyne hydration, was chosen to assess the performance of such activation protocols and their influence on the catalyst's ability to drive the reaction to completion. Reactions can easily be conducted in pure water or aqueous methanol (1:1). We show that sonication significantly enhances this transformation affording the product in higher yields and shorter reaction times than non-assisted reactions in water, while MW energy gives the desire product in quantitative yield in water:methanol after just 1 min.

Encapsulation of N‐heterocyclic carbene–gold (I) catalysts within magnetic core/shell silica gels: A reusable alkyne hydration catalyst

In this study, N‐heterocyclic carbene–Au(I) complex, chloro[1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene]gold (I), was successfully encapsulated within mesopores of a magnetic core/shell (γ‐Fe2O3@SiO2) silica gel through post‐pore‐size reduction by silylation reactions The post‐reduction of the pore size not only minimizes the catalyst leaching during the alkyne hydration reactions but also eliminates any need for covalent modification of the catalyst or support surface. The resulting catalyst exhibits high activity in hydration reactions of various alkynes even under low catalytic loadings. The catalyst can be easily recycled from the reaction mixture using a magnet and can be reused in alkyne hydration reactions up to six times with only 52. wt% Au leaching.

Dimerization of Aromatic Terminal Alkynes Featuring Hydrophilic Functional Groups under Ruthenium and Acid Promoted Catalysis. Competitive Alkyne Hydration upon Substituent Effect

AbstractThe self‐coupling (hydroalkynylation) process of aromatic terminal alkynes RC6H4C≡CH to give dimeric 1,4‐diaryl‐1‐en‐3‐yne products (trans‐RC6H4C≡CCH=CHC6H4R) is catalyzed by the complex [{RuCl(μ‐Cl)(η6‐p‐cymene)}2] with sodium acetate co‐catalyst dissolved in neat acetic acid, the reaction proceeding with high trans‐stereoselectivity under mild conditions (r.t.) even for substrates with protic or polar substituent groups (e. g. R=3‐OH, 4‐CH2OH, 4‐NHAc, ‐CHO, 4‐tetra‐O‐acetyl‐β‐D‐glucopyranoside). In presence of strongly electron donating arene substituents, NMe2 and NH2, the triple bond is activated toward exclusive triple bond hydration by reaction with acetic acid at room temperature also in absence of the ruthenium catalyst.

Polyphenylene-Based Solid Acid as an Efficient Catalyst for Activation and Hydration of Alkynes.

Porous polymer catalysts possess the potential to combine the advantages of heterogeneous and homogeneous catalysis, namely, easy postreaction recycling and high dispersion of active sites. Here, we designed a −SO3H functionalized polyphenylene (PPhen) framework with purely sp2-hybridized carbons, which exhibited high activity in the hydration of alkynes including challenging aliphatic substrates such as 1-octyne. The superiority of the structure lies in its covalent crosslink in the xy-plane with a π–π stacking interaction between the planes, enabling simultaneously high swellability and porosity (653 m2·g–1). High acidic site density (2.12 mmol·g–1) was achieved under a mild sulfonation condition. Similar turnover frequencies (0.015 ± 0.001 min–1) were obtained regardless of acidic density and crosslink content, suggesting high accessibility for all active sites over PPhen. In addition, the substituted benzene groups can activate alkynes through a T-shape CH/π interaction, as indicated by the 8 and 16 cm–1 red shift of the alkyne C–H stretching peak for phenylacetylene and 1-octyne, respectively, in the infrared (IR) spectra. These advantages render PPhen-SO3H a promising candidate as a solid catalyst replacing the highly toxic liquid phase acids such as the mercury salt.

A density functional theory exploration on the Zn catalyst for acetylene hydration.

The acetylene hydration method to produce acetaldehyde has been widely used for over 130years; however, a detailed molecular-level understanding of the reaction mechanism is still lacking. In the present work, we systematically investigated the mechanisms of such reactions on ZnCl2, Zn(OH) Cl, and Zn(OH)2 catalysts through density functional theory (DFT) methods. The Fukui function, condensed Fukui function, and Hirshfeld charges enabled us to predict the active sites of the catalysts and acquire electron transfer information. From these data, we found that catalysts bearing hydroxyl groups exhibited relatively low adsorption performances compared with catalysts without this functionality. The calculations demonstrated that the three studied catalysts had three distinct reaction paths. For the Zn(OH)Cl and Zn(OH)2 catalysts, the reaction took place through a one-shift H2O molecule transfer route, avoiding higher energy barrier pathways. Interestingly, we found that the energy required for breaking the O-H bond in water determined the activation energy of the studied catalytic reactions. The activation barrier increased in the order Zn(OH)Cl ≈ Zn(OH)2 < ZnCl2. This trend suggests that Zn(OH)Cl and Zn(OH)2 are promising catalysts for the hydration of acetylene. Graphical abstract.

CATALYTIC SYNTHESIS OF A LINE BY ACETYLENE HYDRATION

Acetone is a valuable chemical product. It can be obtained by oxidative dehydrogenation of isopropyl alcohol, oxidation of propylene, decomposition of acetic acid and ethyl alcohol, oxidation of cymene and others. Among the known processes for the production of acetone, the most promising is the synthesis by hydration of acetylene in the presence of catalysts. The advantage of this method is the possibility of carrying out the process in existing plants for the production of acetic aldehyde. On the other hand, the process of simultaneously producing acetaldehyde and acetone under the influence of multifunctional catalysts and carrying out the process using flexible technology is promising. The vapor-phase hydration of acetylene with the formation of acetone on polyfunctional catalysts was studied. Process parameters are found that provide acetone with high selectivity and acetylene conversion. At present, acetic aldehyde is mainly obtained by two methods - hydration of acetylene and oxidation of ethylene. The process of hydration of acetylene to acetic aldehyde in the presence of catalysts has been studied quite well. Numerous catalysts have been proposed for this process. Among the known catalysts for hydration of acetylene to acetic aldehyde, the most active was the cadmium calcium phosphate catalyst (CCF), which is recommended for industrial use. However, cadmium calcium phosphate catalyst is not without drawbacks. The average yield of acetaldehyde in one pass of acetylene does not exceed 7.0%. The CCF catalyst is very sensitive to temperature changes, its service life before regeneration does not exceed 72-76 hours. Keywords: acetone, propylene, hydration process, catalyst, crosslinking, multifunctional properties.

Regioselective Crossed Aldol Reactions under Mild Conditions via Synergistic Gold-Iron Catalysis

A synergistic gold/iron catalytic system was developed for sequential alkyne hydration and vinyl gold addition to aldehydes or ketones. Fe(acac)3 was identified as an essential co-catalyst in preventing vinyl gold protodeauration and facilitating nucleophilic additions. Effective C-C bond formation was achieved under mild conditions (r.t.) with excellent regioselectivity and high efficiency (1% [Au], up to 95% yields). Extending reaction scope to intramolecular fashion achieved successful macrocyclization (16-31 ring sizes) with excellent yields (up to 90%, gram-scale) without extended dilution (0.2 M), which highlighted the great potential of this new crossed-aldol strategy in challenging target molecule synthesis.

Synthesis of 1,4,6-Tricarbonyl Compounds via Regioselective Gold(I)-Catalyzed Alkyne Hydration and Their Application in the Synthesis of α-Arylidene-butyrolactones.

We report a direct, straightforward, and regioselective hydration of 1,4-enynes designed from Morita–Baylis–Hillman adducts. Under smooth conditions and short reaction times, gold-catalyzed hydration of internal alkynes provides synthetically useful ketones as single regioisomers in yields higher than 90%. The synthetic usefulness of this protocol was demonstrated by the conversion of selected ketones into biologically valuable α-alkylidene-γ-lactones upon reduction with sodium borohydride. In the course of the scope evaluation, we discovered that this methodology could also furnish α-arylidene-β,γ-butenolides.

SO3H-functionalized porous organic polymer with amphiphilic and swelling properties: A highly efficient solid acid catalyst for organic transformations in water

Abstract SO3H-Functionalized porous organic polymers were successfully synthesized by a solvothermal, free radical copolymerization, and successive ion exchange method. Physicochemical characterizations suggested that the prepared polymers featured relatively large surface areas, large pore volumes, excellent surface amphiphilicity, and nice swelling properties. These characteristics enabled the polymers as efficient acid catalysts for organic transformations in water. We demonstrated the use of these solid catalysts for hydrolysis of cyclohexyl acetate and hydration of phenyl acetylene as two case reactions. The results of catalytic tests suggested that the prepared solid acid exhibited excellent catalytic activities in both cases, which outperformed the homogeneous sulfuric acid and phenylsulfonic acid, as well as commercial amberlyst-15 resin. Furthermore, the solid acid was stable in water, and could be used repetitively for at least four times. This study provides an active and water-compatible solid acid catalyst for organic transformations in water, as well as a facile copolymerization approach for the preparation of amphiphilic heterogeneous catalyst.

Acylruthenium Complexes from Reactions of RuCl2(PPh3)3 with Terminal Alkynes

AbstractReactions of 1‐phenylethyne HC≡C−Ph and 1‐octyne HC≡C‐(CH2)5CH3 with RuCl2(PPh3)3 (1) were carried out in the presence of concentrated HCl aqueous solution, and new acyl complexes Ru(=C=CHPh)(‐C(=O)CH2Ph)Cl(PPh3)2 (2) and Ru(‐C(=O)(CH2)6CH3)Cl(CO)(PPh3)2 (3) are isolated. Further decarbonylation produces Ru(‐C(CH2Ph)=CHPh)Cl(CO)(PPh3)2 (4) and RuHCl(CO)2(PPh3)2 (5), respectively. These are the first examples of stoichiometric anti‐Markovnikov hydration of terminal alkynes involving complexes without polydentate ligands.

Hydration of alkynes catalyzed by [Au(X)(L)(ppy)]X in the green solvent γ-valerolactone under acid-free conditions: the importance of the pre-equilibrium step

Stable and robust [Au(H2O)(NHC)(ppy)](X)2 successfully catalyses the hydration of alkynes in GVL, under acid-free conditions. DFT calculation and NMR measurements suggest that pre-equilibrium is the key step of the whole process.

Synthesis of an N-Heterocyclic Carbene-based Au(I) Coordinate Surfactant: Application for Alkyne Hydration Based on Au Nanoparticle Formation.

In this study, an N-heterocyclic carbene (NHC)-based metal coordinate surfactant (MCS), NHC-Au-MCS, in which the NHC framework afforded the bonding of the Au(I) at the linkage of the hydrophilic and hydrophobic moieties, was synthesized. The structure of NHC-Au-MCS was confirmed by 1H and 13C NMR spectroscopic measurements together with elemental analysis. Matrix-assisted laser desorption/ionization (MALDI), laser desorption/ionization (LDI), and electrospray ionization mass spectrometry (ESI-MS) indicated the distinct reactivity of NHC-Au-MCS, such as the exchange of Br to Cl and the formation of a cationic Au complex, where the two NHC ligands were coordinated to an Au(I) center upon laser activation. The surface tension and dynamic light scattering (DLS) measurements revealed that the coordination of Au(I) to NHC reduced the critical micelle concentration (CMC) of NHC-Au-MCS (1.3×10-5 M), which resulted in the formation of micelles at concentrations higher than the CMC in water. We also confirmed that the surface-active Au(I) complex of NHC-Au-MCS catalyzed the hydration of 1-dodecyne to 2-dodecanone in water in the absence of an organic solvent. On the basis of the detailed mechanistic investigations regarding the reactivity of NHC-Au-MCS, we revealed that NHC-Au-MCS partially translated into Au nanoparticles (AuNPs), which facilitated alkyne hydration. These mechanistic studies were supported by UV-vis measurements, transmission electron microscopy (TEM), and LDI-MS.

Improving process efficiency of gold-catalyzed hydration of alkynes: merging catalysis with membrane separation

In this report, we investigate the integration of a membrane separation protocol in line with the gold-catalyzed hydration of alkynes.

A Porous Polymer-Based Solid Acid Catalyst with Excellent Amphiphilicity: An Active and Environmentally Friendly Catalyst for the Hydration of Alkynes

Developing efficient solid acid catalysts for aqueous organic reactions is of great importance for the development of sustainable chemistry. In this work, a porous polymeric acid catalyst was synthesized via a solvothermal copolymerization and a successive ion-exchange method. Physicochemical characterizations suggested that the prepared polymers possessed large Brunauer-Emmett-Teller (BET) surface areas, a hierarchically porous structure, excellent surface amphiphilicity, and nice swelling properties. Notably, an activity test in phenylacetylene hydration indicated that the prepared solid acid exhibited high catalytic activity in water, which outperformed commercial amberlyst-15, sulfuric acid, and benzenesulfonic acid. Moreover, the prepared solid acid can be easily recovered and reused at least four times. Additionally, a variety of aromatic and aliphatic alkynes could be effectively transformed into corresponding ketones under optimal reaction conditions.

Discovery and Comparison of Homogeneous Catalysts in a Standardized HOT‐CAT Screen with Microwave‐Heating and qNMR Analysis: Exploring Catalytic Hydration of Alkynes

AbstractA HOT‐CAT (homogeneous thermal catalysis) screen using microwave‐heating and quantitative NMR (qNMR) analysis has been developed for identification and comparison of catalyst activity in homogeneous metal‐based catalysis. The hydration of terminal alkynes to ketones or aldehydes served as a model reaction in this proof‐of‐concept study. Key aspects of the screen are the use of a high‐temperature setting (e. g., 160 °C) at a fixed, short reaction time (e. g., 15 min) for all samples. Analysis of crude reaction mixtures by a standardized, quantitative 1H NMR protocol gives a comprehensive picture of catalyst chemo‐ and regioselectivity, which permits broad comparisons and the discovery of non‐target reactivity. For catalytic alkyne hydration, data for 105 runs involving 81 catalyst systems with 15 different metals is presented. The activity of all established catalyst systems was reproduced, and new catalyst systems with Markovnikov hydration selectivity were discovered and applied to preparative runs, namely Cu2O−CSA (CSA=camphorsulfonic acid), Co(OAc)2−tetraphenylporphyrin−CSA and [IrCl(COD)]−CSA.