Dimethyldioxirane Research Articles

Fast, Efficient, Catalyst-Free Epoxidation of Butyl Rubber Using Oxone/Acetone for Improved Filler Dispersion.

Incorporation of a polar filler such as silica into a nonpolar rubber matrix is challenging and energy consuming due to their large difference in polarity. Epoxidation of carbon-carbon double bonds in unsaturated rubber, especially for rubber with low unsaturation such as butyl rubber, is an effective method to introduce polar functional groups to the rubber macromolecules for better filler dispersion. Although different epoxidation reagents including hydrogen peroxide (H2O2), peracid, and meta-chloroperoxybenzoic acid (mCPBA) have been previously reported, these reagents have different drawbacks. In this article, a metal-free epoxidation reagent, dimethyl dioxirane (DMDO), generated from acetone and Oxone is explored for efficient epoxidation of rubber with low unsaturation. The effects of the addition manner of the reactant Oxone and buffer sodium bicarbonate (NaHCO3) and reaction temperature on the epoxide formation are studied. Compared to peracid, a faster and more efficient epoxidation without the generation of a ring-opened product is achieved when DMDO is used as the epoxidation reagent. Furthermore, it is found that the epoxidation using DMDO is not sensitive to the water concentration in the rubber solution up to 20 wt %. The addition of quaternary ammonium salt as a phase transfer catalyst not only improves the conversion but also further increases the water tolerance to 25 wt %. The reaction conditions for preparation of epoxidized butyl rubber with different percentages of epoxide group are optimized by Design of Experiments (DoE). At the end, improved dispersion of silica in the matrix of epoxidized butyl rubber is achieved, as revealed by the rubber process analyzer (RPA) and atomic force microscopy (AFM).

Facile and Efficient Production of Biomass-Derived Isosorbide Dioxides via Epoxidation Using In situ-generated DMDO under Ultrasonication.

Herein, we present a facile synthetic process for producing biomass-derived isosorbide (ISB) dioxides using dimethyl dioxirane (DMDO) as an efficient oxidizing agent, which was generated in situ from acetone and KHSO5 . To achieve high conversion and product yield, the KHSO5 concentration, KHSO5 flow rate, and reaction temperature were optimized. Under the optimal conditions, rapid and efficient epoxidation using the in situ-generated DMDO was observed under ultrasonication, yielding the desired product within 35 min at 0 °C. This study offers a convenient and efficient method for generating biomass-derived ISB building blocks, which have significant potential for the fabrication of bioplastics.

Comparative Advanced Oxidation Decolorization of the Triphenylmethane Dye with Dimethyl Dioxirane and Hydrogen Peroxide

Methyl Violet (MV), a triphenylmethane dye, has been subjected to comparative studies with hydrogen peroxide and dimethyl dioxirane under optimum situations. When employing hydrogen peroxide, the photolysis process becomes slower, but the dye solutions are entirely decolored and mineralized. The decolorization rate exhibits pseudo-first-order kinetics. The effect of pH, oxidant dosage, and methyl violet concentration on the degradation is also examined. Generated o-leucoaniline,1,3-diphenylurea,2-hydroxy benzoic acid, phenol, acetone, water, carbon dioxide, and carbon monoxide are identified and measured by GC-MS analysis. These substances remain in the dye solution along with dimethyl dioxirane, which is released faster during the last stages of degradation. The degradation rates of methyl violet reached 97.9% and 65.8% within 30 mins and 180 min of reaction time using dimethyl dioxirane and hydrogen peroxide.

Investigating the effect of dimethyl dioxirane as oxidizing agent in the degradation of rhodamine B

The degradation of Rhodamime B was carried out at ambient temperature in the presence of dimethyl dioxirane (DMDO). The influence of dye concentration, pH and dimethyl dioxirane dosages was investigated. UV-Visible spectroscopy was used to determine before and after degradation of Rhodamine B dye, the absorption peak decreases gradually after 30min of reaction time. FTIR analysis was carried to determine the functional group. The final degraded product and intermediates were determined by GC-MS analysis. These variables have a significant impact on dye degradation. The proportion of decolouration reduced as the initial dye concentration was increased, as expected. Similarly, increasing the DMDO concentration improved dye decolouration until a certain point, after which it began to decline. 10 mg of rhodamine B dye, 500μl of dimethyl dioxirane at pH 7 were found to be the best operating parameters for the procedure. The dye was decolorized to a maximum of 93% under these conditions.

The Diels-Alder Approach towards Cannabinoid Derivatives and Formal Synthesis of Tetrahydrocannabinol (THC).

Based on the Diels‐Alder reaction of vinylchromenes with electron‐poor dienophiles, we developed a strategy for the synthesis of tetrahydrocannabinol derivatives. Substituted vinyl chromenes could be converted with several dienophiles to successfully isolate several complex molecules. These molecules already contain the cannabinoid‐like base structure and further processing of one such derivative led to a precursor of Δ9‐tetrahydrocannabinol. The most challenging step towards this precursor was an epoxidation step that was ultimately achieved via dimethyl dioxirane.

Highly reactive novel biobased cycloaliphatic epoxy resins derived from nopol and a study of their cationic photopolymerization

In this work three biobased epoxy monomers derived from nopol were successfully prepared. Different strategies were employed to synthesize the monomers, such as alkylation of nopol with epichlorohydrin, nucleophilic aromatic substitution using the alkoxide of nopol and cyanuric chloride, and acetalization of nopol with 3-cyclohexene 1-carboxyaldehyde. All unsaturated intermediates were subsequently epoxidized using dimethyl dioxirane as the oxidizing agent. The kinetics of photopolymerization demonstrated that the three synthesized epoxy monomers exhibited high reactivity due to the highly strained epoxy group situated in the already highly strained bicyclic structure of nopol. The glass transition temperatures determined by Differential Scanning Calorimetry (DSC) were 66 °C and 60 °C for the trifunctional monomers 2, 4, 6-tris (2-(7, 7-dimethyl-3-oxatricyclo [4.1.1.0 2,4] octan-2-yl) ethoxy)- 1, 3, 5-triazine (N2) and 2,2′-(((7-oxabicyclo [4.1.0] heptan-3-yl methylene) bis (oxy)) bis (ethane-2,1-diyl)) bis (7, 7-dimethyl-3-oxatricyclo [4.1.1.02,4] octane) (N3) respectively, and of 12 °C for bifunctional monomer 7, 7-dimethyl-2- (2-(oxiran-2-yl-methoxy) ethyl)-3-oxatricyclo [4.1.1.0 2,4] octane (N1). The aromatic triazine epoxy monomer N2 displayed the highest thermal stability in comparison with the other two monomers, with an onset of degradation of 302 °C as determined by the Thermogravimetric Analysis (TGA).

Immobilization of gold on short-channel mesoporous SBA-15 functionalized with thiol and hydrophobic groups for oxidation reactions

Abstract Nanosized gold entities immobilized on short-channel SBA-15 mesoporous materials functionalized solely with mercaptopropyl groups and together with propyl and octyl moieties have been prepared following a two-steps procedure. These materials have been used as catalysts for the oxidation of cyclohexene with molecular oxygen in liquid phase at atmospheric pressure. First, SBA-15 materials functionalized only with mercaptopropyl groups and with a combination of these groups with two hydrophobic moieties, namely propyl and octyl, have been synthesized in the presence of the non-ionic surfactant P104. Small particles having short channel length have been identified by TEM and SEM. In order to study the influence of the nature of the sulphur functional group, these S-bearing materials were also oxidized with hydrogen peroxide or dimethyldioxirane (DMD) to sulfonic groups prior to gold immobilization. The effectiveness of these oxidation methods was assessed by 29Si MAS NMR, 13C CP MAS NMR, XPS, chemical and thermal analysis, and it has been found that DMD oxidized efficiently thiol groups to sulfonic groups, but H2O2 leaves a fraction of unreacted thiol. In a second step, nanosized gold entities have been prepared by a two-liquid phases route involving rosemary oil as organic phase and an aqueous phase formed by dissolving gold in a solution of ammonium chloride in concentrated nitric acid (aqua regia). Following this method, a fraction of the Au dissolved in the aqua regia solution is spontaneously reduced and transferred to the essential oil phase. Upon contacting the gold-bearing organic layer with the mesoporous materials, gold is actually immobilized on them, rendering metal contents in the range 1.1-0.2 wt.%, being those functionalized with alkyl chains the least efficient in capturing gold from the organic phase. No surface plasmon resonance band at 520 nm characteristic of gold nanoparticles has been detected by UV–vis spectroscopy in these Au-containing materials. All of them are active and selective for the allylic oxidation of cyclohexene, but their specific activity varies as a function of the nature of the functional groups. It has been found that the most active catalysts are those pre-oxidized with DMD. The presence of hydrophobic octyl groups increases substantially the turnover number of the reaction (TON), while the short-chain propyl moieties hardly affect the activity. It has been found that the nanosized gold entities initially present in the catalysts evolve in the reaction medium towards the formation of nanoparticles.

Ultrasonic and Catalyst-Free Epoxidation of Limonene and Other Terpenes Using Dimethyl Dioxirane in Semibatch Conditions

Limonene dioxide is a key intermediate molecule for the development of biobased polycarbonates or nonisocyanate polyurethanes. In this work the epoxidation of limonene to limonene dioxide using in-situ-generated dimethyl dioxirane as the oxidizing agent under both conventional agitation and ultrasound has been compared. The time required to completely convert limonene to limonene dioxide with 100% yield using ultrasound was only 4.5 min at room temperature. In comparison, when conventional agitation using a magnetic stirrer is used, the required time to reach a 97% yield of limonene dioxide was 1.5 h. The epoxidation of α-pinene has also been studied using both agitation techniques. Epoxidation of α-pinene to α-pinene oxide under ultrasound required only 4 min with an obtained yield of 100%, while in comparison with the conventional method the reaction time was 60 min. As for other terpenes, β-pinene was converted to β-pinene oxide in only 4 min whereas farnesol yielded 100% of the triepoxide in 8 min. Ca...

Catalyst-Free Epoxidation of Limonene to Limonene Dioxide

Limonene dioxide is a platform molecule for the production of new biopolymers. First attempts at limonene epoxidation were made by using low-coordination titanium supported on SBA-16 as the catalyst using tert-butyl hydroperoxide as the oxidizing agent, but no limonene dioxide was obtained. When limonene was substituted by 1,2-limonene oxide, the yield of limonene dioxide was only 13% in the same conditions. Two other techniques, both using in situ generated dimethyl dioxirane by the reaction of acetone with Oxone, have been studied and compared. These reactions are carried out in semibatch conditions and at room temperature. The first double epoxidation of limonene was performed in a conventional biphasic organic–water system and the other in excess acetone. The former epoxidation of limonene using ethyl acetate as the organic phase allowed reaching 95% conversion and yielding 33% of limonene dioxide. In comparison, when the reaction was performed in acetone, a limonene dioxide yield of 97% was observed ...

Enantioselective epoxidation of styrene using in-situ generated dimethyldioxirane and dimeric homochiral Mn(III)-Schiff base complex catalyst

The enantioselective epoxidation of styrene using in-situ generated dimethyldioxirane (DMD) and dimeric homochiral Mn(III)-Schiff base catalyst 1 has been explored. The parameters evaluated were olefin/oxidant molar ration, catalyst loading, reaction temperature and presence of nitrogen coordinating co-catalysts. Conversions of more than 99% and enantiomeric excess 66% were obtained. The selectivity is complete towards styrene oxide using 2 mol% catalyst loading, 1.36 mmol KHSO 5 in 8 ml of water, absence of co-catalyst and 17 °C as reaction temperature. Furthermore, the catalyst could be recycled up to three times with slightly decrease of catalytic activity due mainly to the physical loss of the catalyst during the recovery step and at a lesser extent as a consequence of its oxidative degradation.

Heterolytic (2 e) vs Homolytic (1 e) Oxidation Reactivity: N-H versus C-H Switch in the Oxidation of Lactams by Dioxirans.

Dioxiranes are powerful oxidants that can act via two different mechanisms: 1) homolytic (H abstraction and oxygen rebound) and 2) heterolytic (electrophilic oxidation). So far, it has been reported that the nature of the substrate dictates the reaction mode independently from the dioxirane employed. Herein, we report an unprecedented case in which the nature of the dioxirane rules the oxidation chemoselectivity. In particular, a switch from C-H to N-H oxidation is observed in the oxidation of lactams moving from dimethyl dioxirane (DDO) to methyl(trifluoromethyl)dioxirane (TFDO). A physical organic chemistry study, which combines the oxidation with two other dioxiranes methyl(fluoromethyl)dioxirane, MFDO, and methyl(difluoromethyl)dioxirane, DFDO, with computational studies, points to a diverse ability of the dioxiranes to either stabilize the homo or the heterolytic pathway.

Synthesis, characterization and reactivity of trans-dihydroxy platinum(IV) porphyrins

Synthesis of two trans-dihydroxy platinum(IV) porphyrins (TPP, tetraphenylporphyrin and F[Formula: see text]TPP, tetrakispentafluorophenylporphyrin) by dimethyl dioxirane (DMD) oxidation of their Pt[Formula: see text] porphyrin precursors have been described. The oxidation state of Pt cation in such complexes was assessed by X-ray photoelectron spectroscopy and shown to be [Formula: see text]4. More importantly, proton was found to promote the formation and stabilization of the trans-dihydroxy platinum(IV) porphyrins, as revealed by UV-vis spectroscopic results and single crystal structures. In addition, these trans-dihydroxy Pt[Formula: see text] porphyrins were much easier to be reduced than their Pt(II) counterparts and capable to transfer oxygen atom to triphenylphosphine and thioanisol, which is important for further application of Pt(IV) complexes in catalytic reactions.

Oxidación catalítica heterogénea de R-(+)-limoneno sobre catalizadores tipo Jacobsen

<p>El desarrollo de procesos catalíticos heterogéneos es muy deseable dado que se pueden superar las dificultades que presentan los catalizadores homogéneos, tales como la separación y el reciclado de estos<br />catalizadores. En este trabajo, reportamos que los catalizadores tipo Jacobsen son eficientes y selectivos<br />para la oxidación de R-(+)-limoneno a sus correspondientes diepóxidos cuando dimetildioxirano generado<br />in situ es utilizado como agente oxidante. Se demostró que la adición de NaHCO3 sólido, al inicio de la<br />reacción, mejora la actividad catalítica. Además, el catalizador puede ser recuperado y reutilizado al menos<br />dos veces sin pérdida significativa de su actividad catalítica inicial.</p>

Procedure—economical enantioselective total syntheses of asperlicins C and E

We report a procedure—economical method for the highly enantioselective and protecting-group free total syntheses of nonpeptidal CCK antagonists asperlicins C and E. Starting from l-tryptophan, the synthesis of asperlicin C has been achieved in three steps, which features the low-valent titanium (LVT: TiCl4–Zn combination)-mediated reductive cyclization of o-nitrobenzamide to construct the (3H)-quinazolin-4-one moiety. This is the first employment of LVT for the synthesis of asperlicin C, which allowed accessing asperlicin C in >99% enantioselectivity. Asperlicin C was converted, in one-pot, into asperlicin E and 2,3-di-epi-asperlicin E by dimethyl dioxirane (DMDO)-mediated tandem reactions. The use of DMDO as a green, cheap, and easily available oxidant to replace the photochemical method renders the synthesis of asperlicin E experimentally convenient.

Green synthesis of 6-cyano-2,2-dimethyl-2-H-1-benzopyran and its subsequent enantioselective epoxidation

The clean synthesis of 6-cyano-2,2-dimethyl-2-H-1-benzopyran epoxide starting from 3-methyl-2-butenal is reported using recyclable catalysts. H4PMo11VO40 (PMo11V) and (PyH)3HPMo11VO40 (Py3–PMo11V) Keggin-type heteropolyacids were used to synthesize 6-cyano-2,2-dimethyl-2-H-1-benzopyran in two steps with 35% yield. This is an alternative procedure to the traditional methodology with pyridine or picoline as catalyst, where 6-cyano-2,2-dimethyl-2-H-1-benzopyran is obtained by condensation of 4-cyanophenol with 1,1-diethoxy-3-methyl-2-butene. The 6-cyano-2,2-dimethyl-2-H-1-benzopyran epoxide was obtained using Jacobsen-type catalysts, and in situ generated dimethyldioxirane (DMD) as oxidizing agent, that in comparison to m-CPBA/4-NMO and NaOCl/4-PPNO did not degrade the catalyst. In presence of 4-phenylpyridine N-oxide (4-PPNO) at 4°C, enantioselectivities of 87% for 3S,4S-epoxide and 68% for 3R,4R-epoxide were obtained with the S,S- and R,R-Jacobsen catalysts, respectively. Overall yield was approximately 17% for 3S,4S-epoxide.

Cloisite 15Aº nanoclay as an effective PTC for the epoxidation of hydroxyl terminated polybutadiene (HTPB)

A simple method is reported for the epoxidation of hydroxyl-terminated polybutadiene (HTPB) by using in-situ generated dimethyl dioxirane (DMD) as an oxidant and Cloisite 15Aº nanoclay as a phase-transfer catalyst (PTC). In order to find the optimum reaction conditions, real time analyses of the products as well as epoxidation progress, followed by ¹HNMR and FTIR techniques at various reaction times and different PTC concentrations, were done. Obtained data revealed the selectivity of DMD/ Cloisite 15Aº in predominant cis double bonds epoxidation in comparison with trans and pendant vinyl functional groups.

Semisynthesis of Polymethoxyflavonoids from Naringin and Hesperidin

Polymethoxyflavonoids (PMFs) possess important biological activities, notably as anticancer agents. Semisynthesis of a series of PMFs were performed by glycoside hydrolysis, dehydrogenation, bromination, aromatic nucleophilic substitution, O-methylation, dimethyldioxirane oxidation and regioselective demethylation, starting from abundant and inexpensive natural sources naringin and hesperidin. A new synthetic method for selective methylation using CuBr catalysed and microwave-assisted reaction was developed, and the dimethyl dioxirane oxidation of flavones to flavonols was much improved. The new semisynthetic route has the advantages of easy availability of starting materials, simple operation and good yields.

Catalytic performances of copper and lead (2-guanidino-benzimidazoliume) complexes in polybutadiene (PB) and hydroxyl-terminated PB epoxidation

Polybutadiene (PB) and hydroxyl-terminated PB were epoxidized using in situ-generated dimethyl dioxirane as an oxidant in the attendance of different concentrations of copper and lead (2-guanidinobenzimidazoliume) (GBH) complexes as the catalyst at 25°C. The potential of cis, trans, and vinyl double bonds toward epoxidation was considered in detail at various reaction times. The products were characterized using proton nuclear magnetic resonance and Fourier transform infrared spectroscopy techniques and data revealed that the formation of desired products were obtained without any side reaction. The results indicated the performance of calculated 0.252 mmol of GBH complexes in obtaining maximum epoxidation yield as well as selectivity in the epoxidation of cis double bonds in comparison with trans and vinyl ones.

Immobilization of Jacobsen type catalysts on modified silica

Several immobilized Jacobsen type catalysts were covalently anchored on modified SiO2 using 3-aminopropyltriethoxysilane (3-APTES) as a reactive surface modifier. Characterization of the heterogeneous catalysts, as well as their precursors, by FTIR, DR UV-VIS, TGA and AAS confirms the successful immobilization of chiral Mn(III) salen complexes. These catalysts were examined for the diastereoselective epoxidation of R-(+)-limonene with in situ generated dimethyldioxirane (DMD) as oxidizing agent, yielding 1,2-epoxide as the main product. When compared to homogeneous catalysts, under similar experimental conditions, only a slight selectivity decrease over heterogeneous catalysts was observed. The immobilized catalysts were used three times maintaining the initial selectivity. However, after reusing them more than three times, selectivity to 1,2-epoxide decreased. FTIR results suggest partial degradation of the catalytic species. Despite the immobilization method was chosen to minimize changes in the structure of the homogeneous catalysts the diastereoselectivity (d.e.) of heterogeneous catalysts underwent a remarkable decay.

氟烷磺酰氟／双氧水／碱／丙酮体系与苄醇衍生物的氧化反应

研究了氟烷磺酰氟／双氧水／氢氧化钠／丙酮体系与6个苄醇衍生物的氧化反应，其中氟烷磺酰氟包括HCF2CF2OCF2CF2SO2F，n-C4F9S02F和n-C8F12SO2F．最优反应条件为n（苄醇衍生物）：n（氟烷磺酰氟）：n（双氧水）：n（氢氧化钠）=1：4：8：8，溶剂为丙酮，反应温度为20℃，反应时间为24h．产物酮的收率为23％-92％．探讨了该氧化反应的机理，原位生成的氟烷基过氧磺酸中间体可将丙酮氧化为二甲基二氧杂环丙烷，进而将反应体系中共存的苄醇衍生物氧化成相应的产物酮．氟烷磺酰氟／双氧水／氢氧化钠／丙酮体系原位生成的二甲基二氧杂环丙烷氧化苄位羟基的能力和传统的Oxone／CH3COCH3体系相当．本研究提供了一种新颖的原位制备二甲基二氧杂环丙烷的方法．