Formation Of Cyclic Acetals Research Articles

Bifunctional heterogeneous catalyst: A sustainable route for cyclic acetals synthesis through tandem hydroformylation-acetalization reaction

A novel sustainable approach for the synthesis of 2-ethyl 1,3 dioxolane and various short to long-chain or aromatic cyclic acetals through a tandem hydroformylation-acetalization reaction using Rh oxide nanoparticle supported on zirconium phosphate has been established. The Rh oxide nanoparticle supported on zirconium phosphate was synthesized and characterized by various physicochemical methods. The SEM and TEM analysis revealed the average particle size of rhodium oxide was found to be ∼7.56 nm in 2%Rh@ZrP catalyst. Furthermore, the synthesized catalyst was employed to carry out a tandem hydroformylation reaction in a green solvent (ethylene glycol). Experimental results demonstrated that 2 wt.% of Rhodium on zirconium phosphate efficiently activated olefins, leading to the selective formation of cyclic acetals (60–99%) at 80°C for 6 h. In this cascade reaction, significant selectivity towards the desired product, linear cyclic acetals was observed for styrenes. This can be attributed to highly dispersed Rh oxide nanoparticles and plentiful acidic sites on the zirconium phosphate supports, which played a crucial role in tandem hydroformylation and acetalization reactions. The catalyst exhibited the ability to be reused three times without losing significant catalytic activity or selectivity. This is the first report on the synthesis of a fuel additive and other cyclic acetals via a tandem hydroformylation-acetalization reaction using heterogeneous catalysts.

Ruthenium‐Catalyzed Synthesis of Cyclic and Linear Acetals by the Combined Utilization of CO2, H2, and Biomass Derived Diols

Herein a transition-metal catalyst system for the selective synthesis of cyclic and linear acetals from the combined utilization of carbon dioxide, molecular hydrogen, and biomass derived diols is presented. Detailed investigations on the substrate scope enabled the selectivity of the reaction to be largely guided and demonstrated the possibility of integrating a broad variety of substrate molecules. This approach allowed a change between the favored formation of cyclic acetals and linear acetals, originating from the bridging of two diols with a carbon-dioxide based methylene unit. This new synthesis option paves the way to novel fuels, solvents, or polymer building blocks, by the recently established "bio-hybrid" approach of integrating renewable energy, carbon dioxide, and biomass in a direct catalytic transformation.

Studies of the Catalytic Activity of Iron (III) Porphyrins for the Protection of Carbonyl Groups in Homogeneous Media

The protection of carbonyl groups that produce acetal products is a key reaction in fine chemistry due to the high reactivity of aldehydes and ketones in certain media. This process can be catalyzed by protic or Lewis acids. Since metalloporphyrins often possess free axial positions in the central metal, they can be applied as Lewis acid catalysts, allowing the additional coordination of substrates. Therefore, three ferric complexes were selected to be evaluated as catalysts for the acetalization of benzaldehyde with ethanol and triethyl orthoformate (TEOF) in the homogeneous phase: (i) 5,10,15,20-tetrakis(phenylporphyrin) iron (III) chloride (Fe0F); (ii) 5,10,15,20-tetrakis(2,6-difluorphenylporphyrin) iron (III) chloride (Fe2F); and (iii) 5,10,15,20-tetrakis(pentafluorphenylporphyrin) iron (III) chloride (Fe5F). The complex Fe5F showed the highest catalytic activity, and kinetic parameters were evaluated for this reaction, exhibiting an increasing rate of reaction of about 550-fold in comparison with the non-catalyzed reaction. The reaction scope was also investigated, and Fe5F was found to be active for the acetalization of benzaldehyde and acetophenone, with different protective agents such as alcohols, glycols, glycerol, and epoxide being selective for the formation of cyclic acetals. The protection of benzaldehyde with ethylene glycol and propylene glycol were also studied at different temperatures, and turnover frequency (TOF) values of up to 360 h−1 were determined at 40 °C in homogenous media without the need for solvent or drying agents.

Dimethyl sulfoxide/oxalyl chloride: A useful reagent for sulfenyletherification

A facile method for the sulfenyletherification of unsaturated alcohols using dimethyl sulfoxide/oxalyl chloride has been described in this article. Methanesulfenyl chloride is supposed to be the compound responsible for the sulfenyletherification, which is generated by the reaction of oxalyl chloride with 2 equivalents of dimethyl sulfoxide. The formation pathway of methanesulfenyl chloride is discussed based on the formation of cyclic acetals.

Multifunctional self-assembling hydrogel from guar gum

Facile and “green” techniques for hydrogel fabrication are in high demand to satisfy a wide range of practical applications. To the best of our knowledge, this report presents the first description of an efficient, one-flask method for preparing a guar gum (GG)-based self-assembling hydrogel, which takes advantage of the formation of cyclic acetals between the vicinal hydroxyl groups and carbonyl groups, as introduced via the regioselective oxidation of GG using sodium periodate (NaIO4). The final product was achieved without the addition of any crosslinking agents. The self-assembling hydrogel was rapidly formed under ambient conditions, and demonstrated remarkable self-healing performance, as well as thermally responsive properties associated with sol-gel transitions. Furthermore, the GG hydrogel had the ability to remove copper ions (Cu2+) from the surrounding aqueous solution. This removal can be accounted for due to the large number of active sites (i.e., hydroxyl groups) within its porous three-dimensional structure. The adsorption equilibrium was achieved after 5h, and the amount of adsorbed Cu2+ was 944mg/g GG when an initial concentration of 25mg/mL CuSO4 in solution was used. The adsorption isotherm data correlated well with the Freundlich model (R2>0.99), suggesting that the Cu2+ was removed through multilayered and complex adsorption mechanisms.

Sulfated and phosphated H-type niobate nanotubes as solid acid catalysts

Highly pure sodium niobate nanotubes (NaNbNTs) were prepared by treating nonporous Nb2O5 powder with 1.0 M NaOH solution at 423 K. SEM revealed that these NaNbNTs formed nanotube-bundles with diameters of 50–250 nm and lengths of several microns. A TEM image of nanotubes indicated that they had outer diameters of 15–20 nm and inner pore diameters of 3–4 nm. BET surface area and pore volume of NaNbNTs were 65 m2 g−1 and 0.17 mL g−1, respectively. Treatment with diluted phosphoric or sulfuric solutions transformed NaNbNTs into phosphate- or sulfate-promoted protonated niobate nanotubes (PO4−3/HNbNTs and SO4−2/HNbNTs), which had a surface area of ∼80 m2 g−1, a pore volume ∼ 0.26 mL g−1 and a surface that was densely covered with acid sites (1.0–1.5 mmol g−1). Owing to the high density of its acid sites, SO4−2/HNbNTs outperformed a superacidic sulfated metal oxide like SO4−2/HfO2 in catalyzing the formation of cyclic acetals from carbonyl compounds and ethylene glycol. TPD/NH3 investigations indicated that the acid site density in PO4−3/HNbNTs was even higher than in SO4−2/HNbNTs, but its activity in catalyzing the formation of cyclic acetals was lower. These results reveal that acid sites in PO4−3/HNbNTs had a severe steric effect owing to the thick surface phosphate layer, permitting only the adsorption of small molecules. Large molecules, like heptanal, may not be easily adsorbed on a surface that is densely populated with PO4−3 groups, causing PO4−3/HNbNTs to have a lower activity than SO4−2/HNbNTs, which had a lower surface population of equally bulky SO4−2 groups.

Configurational and Conformational Control on Formation and Oligomerization of 2-C Mono-Arylated Pseudo-Proline Dipeptide Building Units by Aromatic Stacking Interactions

Electrophilically induced cyclic acetal formation of the O-benzyl dipeptide esters Fmoc-NMeIle-Thr-OBn (1) and of Fmoc-Pro-Thr-OBn (6) has been observed to lead predominantly to the (R) diastereomers 2b and 8b at the 2-C position of the resulting substituted Id-oxazolidine (Psi Pro) unit, while upon acetalization of the corresponding O-methyl ester 4 the 2-C(S) epimer 5a is predominantly formed under the same proton catalyzed cyclization conditions. With boron trifluoride etherate as Lewis acid the reaction is particularly fast and leads selectively to the prolyl threonine derived 2-C(R) dipeptide building block 8b, which could conveniently be assembled into a nonamer with a virtually solvent independent CD-spectrum of the polyproline type I (cis amide bonds).

Computational Study of the Mechanism of Cyclic Acetal Formation via the Iridium(I)-Catalyzed Double Hydroalkoxylation of 4-Pentyn-1-ol with Methanol

The mechanism of Ir(I)-catalyzed double hydroalkoxylation of 4-pentyn-1-ol with methanol to form cyclic acetals has been investigated with density functional theory calculations. Using a model [Ir(PyP′)(CO)2]+ catalyst (PyP′ = 1-[2-phosphinoethyl]pyrazole) the key steps in the first hydroalkoxylation are shown to be (i) electrophilic activation of the alkyne at the cationic Ir(I) metal center; (ii) rate-limiting C−O bond formation via intramolecular nucleophilic attack by the pendant OH group at the C4 position of the bound alkyne; and (iii) facile H+ transfer to form an Ir-bound cyclic vinyl ether intermediate. The key C−O bond forming cyclization step is greatly facilitated by the presence of an external H-bonded MeOH molecule that stabilizes the positive charge that develops at the hydroxyl proton of the bound alkyne. External MeOH also plays a key role in the H+ transfer step, for which a number of kinetically competitive pathways corresponding to either retention of the hydroxyl proton in the product...

ChemInform Abstract: Stereochemical Study on Cyclic Acetal Formation During Anodic Oxidation of Naphthalene Derivatives by Transformation of Chiral Alcohol to Achiral Acetal.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Gold catalysts and solid catalysts for biomass transformations: Valorization of glycerol and glycerol–water mixtures through formation of cyclic acetals

The valorization of pure glycerol and glycerol in water has been achieved by reaction with aldehydes to form valuable acetals. While soluble PTSA is more active than solid Brønsted acids such as zeolites and resins when reacting with pure glycerol, the synthesis of a hydrophobic zeolite with the adequate ratio of polarity/acidity leads to a better catalyst when reacting with glycerol–water mixtures. Best results (up to 94% yield) were obtained with gold as Lewis acid catalysts under very mild reaction conditions. The preparation of a recoverable and reusable gold catalyst allows to achieve high turnover numbers.

A Facile Synthesis of Both Enantiomers of 6‐Acetoxy‐5‐hexadecanolide, a Major Component of Mosquito Oviposition Attractant Pheromones

AbstractThe stereoselective synthesis of (–)‐(5R,6S)‐erythro‐6‐acetoxy‐5‐hexadecanolide, the major component of a mosquito oviposition attractant pheromone, and its enantiomer are reported. The synthesis was completed over seven steps in 28 % overall yield by using Sharpless asymmetric epoxidation and ZrCl4‐catalyzed cyclic acetal formation as the key steps. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

ChemInform Abstract: Cyclic Acetal Formation Between 2‐Pyridinecarboxyaldehyde and γ‐Hydroxy‐α,β‐acetylenic Esters.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Cyclic acetal formation between 2-pyridinecarboxyaldehyde and γ-hydroxy-α,β-acetylenic esters

A new transformation between 2-pyridinecarboxyaldehyde and γ-hydroxy-α,β-acetylenic esters to form highly functionalized cyclic acetals was discovered. This transformation proceeds under very mild conditions without any additives and is promoted by the basic nature of the pyridine ring.

A selective and convenient ruthenium mediated method for the synthesis of mixed acetals and orthoesters

Addition of alcohols and phenols to O-allyl compounds (allyl ethers and acrolein acetals), catalyzed by [RuCl 2(PPh 3) 3], was examined. Intramolecular addition of an OH group, leading to the formation of cyclic acetals and orthoesters, was also investigated. As a result, a new, selective and convenient method for the synthesis of symmetrical and unsymmetrical (mixed) acetals and orthoesters was developed.

Acetalization and thioacetalization of cabonyl compounds: A case study based on global and local electrophilicity descriptors

Acetalization of benzaldehyde and substituted benzaldehydes (containing both electron-donating and electron-withdrawing groups) is explained qualitatively on the basis of global electrophilicity descriptor, w, as proposed by Parr and coworkers. The generated values of w can explain qualitatively the preferential electrophilic addition, and hence, the yield of acetalization obtained in an earlier experimental study carried by Patel and coworkers. The present study also reveals that although both steric and electronic factors affect the yield, only later can be taken care of by w. In the case of a competitive formation of cyclic acetals and cyclic thioacetals from a reaction mixture containing p-hydroxybenzaldehyde, p-nitrobenzaldehyde, 1,2-ethanediol (i.e., glycol), and 1,2-ethanedithiol, the relative experimental yields could be explained from the difference of the global electrophilicity values between aldehydes and acetalizing agents in the same line of arguments of Maynard et al.

Amplification of Dynamic Chiral Crown Ether Complexes During Cyclic Acetal Formation

Amplification of Dynamic Chiral Crown Ether Complexes During Cyclic Acetal Formation

Amplification of dynamic chiral crown ether complexes during cyclic acetal formation.

The dynamic duo: A more than tenfold increase in the yield of the chiral macropolycyclic polyether containing two 2,6-disubstituted 1,3,5,7-cis-tetraoxadecalin systems was obtained under thermodynamic conditions from a dynamic combinatorial virtual library with templating cesium ions (>95 % yield, see schematic representation) relative to kinetic syntheses (<8 % yields in their macropolycyclization steps), even when the same template was used. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2003/z51558_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Formation of Cyclic Acetals from Allylic Hydroxy Phosphonates via Intramolecular Oxymercuration

Treatment of allylic hydroxy phosphonates in aldehyde solution with mercuric trifluoroacetate, followed by the reduction of the organomercurial intermediate, afforded the cyclic acetal derivatives. The reaction displays high diastereo- and regio-selectivity. 31 P NMR studies showed the formation of an intermediate hemiacetal and rapid formation of the organomercurial upon addition of mercuric trifluoroacetate. However, the oxymercuration was reversible, and attempts to remove the excess aldehyde often led to recovery of the starting material. Fortunately, reduction of the organomercurial intermediate with sodium cyanoborohydride in the presence of the aldehyde led to more reproducible yields.

Coagulation protein function VI: augmentation of anticoagulant function by acetaldehyde-treated heparin.

Acetaldehyde (AcH) at preincubation concentrations of 447, 89.4, and 17.9 mM potentiates the effects of heparin on the clotting time of plasma. While control plasma clotted in the range of 12.6+/-0.1 to 13.8+/-0.1 sec, and heparin-treated plasma clotted in a range from 131.5+/-2.5 to 168.2+/-1.2 sec, heparin that was preincubated at room temperature for 30 min with 89.4 or 447 mM AcH did not clot plasma in 300 sec. Heparin exposed to 17.9 mM AcH clotted plasma in 193+/-1.1 sec. Ethanol at a 404 mM concentration also prolonged the clotting time of heparin-treated plasma >300 sec, while 202 mM ethanol prolonged the clotting time of heparin-treated plasma from 149.0+/-2.0 sec to 219.5+/-1.7 sec. It is suggested that AcH alters the tertiary structure of heparin by adduct formation, possibly by formation of cyclic acetals with iduronic and glucuronic acids, thereby more readily affecting binding of the glycosaminoglycan to antithrombin III and/or thrombin, prolonging clotting time. Ethanol, which does not react covalently with heparin, might affect its conformation as a consequence of an organic solvent effect. Protamine sulfate prolonged the clotting time of plasma from 13.6+/-0.1 sec to 17.9+/-0.2 sec. Protamine sulfate-treated heparin clotted plasma in 21.0+/-0.4 sec relative to heparin-treated plasma (160.4+/-1.7 sec). In subsequent experiments, AcH-treated protamine sulfate extended the clotting time of protamine sulfate from 17.9+/-0 sec to 33.7+/-0.6 sec. Prior addition of protamine sulfate to AcH-heparin mixtures or heparin to protamine sulfate-AcH mixtures before addition to plasma resulted in clotting times of 22.0+/-0.4 sec and 24.1+/-0.5 sec, respectively, relative to control clotting times of 162.3+/-2.6 sec for plasma-heparin mixtures. These results confirm both the reduction in coagulation time of heparin-treated plasma by protamine sulfate and the prolongation of clotting time of plasma by protamine sulfate. Furthermore, and importantly, they indicate that acetaldehyde-treated protamine sulfate is a more effective anticoagulant than protamine sulfate. It is suggested that reversible adduct formation between acetaldehyde, heparin, and protamine sulfate may occur as a means explaining the essentially identical coagulation time of these mixtures when added to plasma regardless of the order of premixing. Ethanol (404 mM) did not influence protamine sulfate effects. Lastly, the potentiation of the anticoagulant function of heparin by acetaldehyde suggests that a structural modification of the glycosaminoglycan may occur in alcoholics.

A highly efficient iterative approach to fused ether ring systems

An iterative synthesis of fused ether ring systems has been developed. This strategy couples a cyclic enol ether oxidation and carbon-carbon bond forming reaction in one flask with an acid catalyzed cyclic acetal formation and alkoxide elimination in another flask. The result is a general and highly efficient two flask synthesis of fused ethers as are present in a wide variety of bioactive natural products.