Isopropenyl Acetate Research Articles

Selective Modification of Aliphatic Hydroxy Groups in Lignin Using Ionic Liquid

A facile, sustainable method for the selective modification of aliphatic hydroxy (R–OH) groups in Kraft lignin was developed using an ionic liquid, 1-ethyl-3-methylimidazolium acetate (EmimOAc), as a solvent and catalyst. Selective R–OH modification was achieved by a one-pot, two-step homogeneous reaction: (i) acetylation of R–OH and aromatic OH (Ar–OH) groups with isopropenyl acetate (IPAc) as an acyl donor and (ii) subsequent selective deacetylation of the generated aromatic acetyl (Ar–OAc) groups. In step (i), IPAc reacts rapidly with Ar–OH but slowly with R–OH. The generated Ar–OAc is gradually deacetylated by heating in EmimOAc, whereas the aliphatic acetyl (R–OAc) groups are chemically stable. In step (ii), all R–OH is acetylated by IPAc and Ar–OAc which is a better acyl donor than IPAc, contributing to the rapid acetylation of the remaining R–OH, and selective deacetylation of the residual Ar–OAc is completed by adding a tiny amount of water as a proton source. This two-step reaction resulted in selective R–OH modification (>99%) in Kraft lignin with the remaining being almost all Ar–OH groups (93%). Selectively modified Kraft lignin was obtained with an acceptably high isolated yield (85%) and repeatability (N = 3). Furthermore, despite the lower substitution degree, it exhibited solubility in common solvents, heat-meltability, and thermal stability comparable to completely acetylated Kraft lignin.

Concatenated Batch and Continuous Flow Procedures for the Upgrading of Glycerol-Derived Aminodiols via N-Acetylation and Acetalization Reactions

An unprecedented two-step sequence was designed by combining batch and continuous flow (CF) protocols for the upgrading of two aminodiol regioisomers derived from glycerol, i.e., 3-amino-1,2-propanediol and 2-amino-1,3-propanediol (serinol). Under batch conditions, at 80–90 °C, both substrates were quantitatively converted into the corresponding amides through a catalyst-free N-acetylation reaction mediated by an innocuous enol ester as isopropenyl acetate (iPAc). Thereafter, at 30–100 °C and 1–10 atm, the amide derivatives underwent a selective CF-acetalisation in the presence of acetone and a solid acid catalyst, to afford the double-functionalized (amide-acetal) products.

Fermented solids that contain lipases produced by Rhizopus microsporus have an S-enantiopreference in the resolution of secondary alcohols

Lipases are widely used as biocatalysts in the resolution of racemates, where high chemo-, regio- and enantioselectivity are required. In this work, we produced lipases by culturing Rhizopus microsporus in solid-state fermentation. After the fermentation, the solids were dried, producing “Rhizopus microsporus fermented solids” (RMFS). The lipases in RMFS had high activity in the synthesis of ethyl oleate in n-heptane, retaining 100 % activity after 23 successive esterification cycles, each for 4 h at 40 °C. In the kinetic resolution of three aromatic secondary alcohols by transesterification with isopropenyl acetate, in n-heptane, RMFS showed preference for the (S)-enantiomers, in other words, an anti-Kazlauskas enantiopreference. The best results were a conversion of 23 % and an enantiomeric ratio (ESR, i.e. S relative to R) of 26 for resolution of (RS)-1-phenyl-1-ethanol, after 96 h at 40 °C. Since it is rare for lipases to have an (S)-enantiopreference, RMFS have the potential as low-cost biocatalysts for the resolution of racemates of secondary alcohols.

Insights into Design of Biomimetic Glycerol-Grafted Polyol-Based Polymers for Ice Nucleation/Recrystallization Inhibition and Thermal Hysteresis Activity.

Many species living in colder regions of the world have adapted to the extreme climate by producing antifreeze (glycol) proteins (AF(G)P) which exhibit ice recrystallization inhibition (IRI), thermal hysteresis activity (THA), as well as other interactions with the freezing process of water. Although several synthetic approaches for the exploitation of these proteins have been investigated, challenges remain in the synthetic design of biomimetic polymers. Similar to biological antifreezes, poly(vinyl alcohol) (PVA) has potent IRI activity; however, by comparison, PVA has very little THA. In this study, we explored structural variations to polyol-based polymers to contrast with PVA as a control and identified several key structural elements for performance in IRI, THA, as well as in ice nucleation inhibition (INI). These structural features are bioinspired by the typical ice-binding plane of AFPs yet are surprisingly simple to produce with potency approaching that of typical AFPs. Key to the performance is positioning small organic functionalities with known antifreeze properties (such as ethylene glycol) pendent to a host polymer chain with consideration of their conformational freedom. To build systematic variations into both the backbone and side-chain structures, we used poly(vinyl alcohol), poly(isopropenyl acetate), poly(acrylic acid), and poly(methacrylic acid) parent polymers for such pendent modifications. One structure in particular, glycerol-grafted-PVA (G-g-PVA), shows potency rivaling that of AFPs at similar micromolar concentration. The findings in this study help guide the rational design of synthetic antifreeze polymers useful for applications such as anti-icing coatings through to cryopreservation methods for organ transport and cell preservation.

Controlled acetylation of kraft lignin for tailoring polyacrylonitrile-kraft lignin interactions towards the production of quality carbon nanofibers

Lignin/polyacrylonitrile (PAN) precursors can provide a green solution for lowering the cost while adequately maintaining the mechanical performance of carbon fibers, opening the gates for energy efficient lightweight materials to reach price-sensitive markets. We anticipated that improving the interactions between hydrophobic PAN chains and lignin, abundant in hydrophilic –OH groups, is important issue for obtaining a more aligned polymeric network, advantageous for the mechanical performance of carbon fibers. A controlled acetylation using acetic anhydride or isopropenyl acetate (IPA; in DMSO/EmimOAc) allowed us to step-by-step increase the degree of substitution of lignin and fine-tune the thermal characteristics as well as the miscibility of the blends, thus tailoring the mechanical properties of the resulting electrospun carbon fiber mats, along with the morphological evolution of the fibrous network. Differential scanning calorimetry and rheometry results indicated that by increasing the amount of substituents, the complex hydrogen bonding network connecting lignin molecules gradually breaks down leading to an increase in lignin/PAN polymer blend miscibility. However, it also became apparent that by masking hydroxyl groups important free radical mediated processes during the stabilization step might be inhibited, this phenomenon appeared to be more pronounced when aliphatic hydroxyl groups are selectively acetylated (IPA in DMSO/EmimOAc). Carbon fiber mats with the best mechanical performance were obtained only via controlled partial acetylation of kraft lignin with an almost 3-fold improvement in tensile strength (about 2-fold increase in elastic modulus) compared to the unmodified lignin-based fibrous materials. Our study holds promise for the realization of potentially low-cost quality carbon fibers.

Amano Lipase PS from Burkholderia cepacia- Evaluation of the Effect of Substrates and Reaction Media on the Catalytic Activity

: Lipases in the native or immobilized form have commonly been used as catalysts in the chemical and pharmaceutical industry. One of the widely available enzyme catalysts on the market is lipase from Burkholderia cepacia (BCLs), previously called Pseudomonas cepacia (PCLs). This enzyme is applied, among others, in the stereoselective acylation of molecules to achieve chiral pure enantiomers of drugs or their building blocks. In this study, Amano lipase PS (APS-BCL), which is a commercial lipase from Burkholderia cepacia (BC) was tested. The lipolytic activity of APS-BCL by hydrolysis of vegetable oils and enantioselective activity of APS-BCL by the kinetic resolution of (R,S)-1-phenylethanol with using isopropenyl acetate as an acyl donor were evaluated. An effect of reaction media with different logP values (t-butyl methyl ether, dichloromethane, diisopropyl ether, toluene, cyclohexane, n-hexane, isooctane and n-heptane) on the enantioselective activity of lipase was also studied. The high value of the enantiomeric ratio (E =308.5) with the utilization of isopropenyl acetate was achieved. Whereas, the best reaction medium turned out to be diisopropyl ether, C =47.9%, eep =98%, ees =90%, after 24 h of incubation. Moreover, the influence of ω6/ω9 polyunsaturated fatty acids (PUFAs) ratio in commercial (peanut, camelina, rape, pumpkin seed, walnut, sesame, avocado, rice, corn, black cumin, hemp, safflower, grape seed) oils was investigated for the lipase activity. For the first time, the cut-off limit of ω6/ω9 ratio was proposed. The ratio equal to or higher than 2.3 allows achieving higher lipolytic activity.

Green Synthesis and Fractionation of Cellulose Acetate by Controlling the Reactivity of Polysaccharides in Sugarcane Bagasse

A green synthetic protocol was developed to prepare cellulose acetate (CA) directly from sugarcane bagasse without using any pretreatments or corrosive reagents, such as strong acids, bases, or halogenated chemicals. The key in this method is to control the reactivities of cellulose and xylan-based hemicellulose in bagasse under mild conditions, making their solubilities in acetone different. Homogeneous transesterification was performed for bagasse at 50 °C using isopropenyl acetate as an acetyl donor and 1-ethyl-3-methylimidazolium acetate as a solvent and catalyst. By controlling the reaction temperature, the degree of substitution for cellulose was adjusted to 2.5–2.8 to maintain solubility in acetone, while the acetylation of hemicellulose was suppressed to prevent its dissolution in acetone. In the subsequent fractionation process, the hemicellulose-rich component was first precipitated in acetone and removed by filtration. The filtrate was subsequently separated into lignin- and cellulose-rich fractions by solid–liquid separation using methanol. Then, CA as the target compound was collected as the acetone-soluble and methanol-insoluble fraction, with a sufficiently high purity (∼90%), according to FT-IR and 1H NMR analyses.

A transesterification–acetalization catalytic tandem process for the functionalization of glycerol: the pivotal role of isopropenyl acetate

A catalytic tandem sequence was implemented by which a pool of innocuous reactants (isopropenyl acetate, acetic acid and acetone) allowed upgrading of glycerol through selective acetylation and acetalization processes.

Iron powder and tin/tin chloride as new reducing agents of Meerwein arylation reaction with unexpected recycling to anilines

Simple and rapid route for Meerwein arylation reaction using iron powder or a mixture of tin/tin chloride has been developed. In the presence of iron powder, different aryl diazonium salts reacted with methyl vinyl ketone, acrylates, and isopropenyl acetate. Production of oximes was detected as the main product with acrylates or in a mixture with β-aryl methyl ketones in the case of methyl vinyl ketone. The in situ produced HNO2 from an excess of NaNO2/HCl was trapped by alkyl aryl radical to form oximes in the E configuration form. The presence of tin/tin chloride mixture in the reaction of the aryl diazonium salts with methyl vinyl ketone produced Michael products along with β-aryl methyl ketones. The predicted α-aryl methyl ketones from the reaction of isopropenyl acetate with the diazotized anilines were obtained using iron or tin/tin chloride mixture.

Metal-Free Hyperbaric Multicomponent Approach to 4-Aryl[2.2]Paracyclophanes

Herein, we report the first metal-free synthesis of 4-aryl[2.2]paracyclophanes, an important scaffold in organic ligands and material science panorama. In order to avoid the use of toxic and expensive metal catalyst, a multicomponent hyperbaric protocol has been envisaged. First, easy-to-synthesize paracyclophane-substituted butenones underwent acid-catalyzed enol acetylation in the presence of isopropenyl acetate to generate in situ acetoxy-diene intermediates, which were then reacted with methyl propiolate in a hyperbaric regioselective Diels-Alder reaction. Oxidation of the resulting cycloadducts delivered the expected products showing the potential for further functionalization.

Dual Catalytic Activity of an Ionic Liquid in Lignin Acetylation and Deacetylation

An ionic liquid, 1-ethyl-3-methylimidazolium acetate (EmimOAc) better catalyzed the acetylation of the aliphatic hydroxyl groups of lignin than the phenolic hydroxyl groups using isopropenyl acetate as an acetyl donor. However, in situ 1H NMR analyses performed on model compounds revealed that EmimOAc more effectively promoted the acetylation of phenol than 2-phenethyl alcohol. EmimOAc was also found to selectively catalyze the deacetylation of aromatic acetate, and thus the aliphatic hydroxyl groups of lignin were preferentially acetylated.

S-Acetylation of Thiols Mediated by Triflic Acid: A Novel Route to Thioesters

This paper demonstrates an efficient, mild, and chemoselective synthesis of various thioesters via a HOTf-catalyzed S-acetylation of aromatic and aliphatic thiols using isopropenyl acetate as a cheap and convenient acetylating agent. During our tests, we also investigated the differences between the activities of metal triflates and triflic acid as catalysts in the acetylation of thiols. Finally, the potential of our concept has been increased by the implementation of Nafion as a heterogeneous catalyst for S-acetylation of thiols.

High-Temperature Batch and Continuous-Flow Transesterification of Alkyl and Enol Esters with Glycerol and Its Acetal Derivatives

A new procedure for the transesterification of alkyl acetates and formates with model glycerol acetals (GAs: Solketal and glycerol formal) was explored in the absence of any catalysts at 180–275 °C. Highly selective transformations occurred in both batch and continuous-flow (CF) modes; particularly, the enol derivative isopropenyl acetate (iPAc) was the best performing reactant by which quantitative acetylation reactions were achieved with yields on GAs acetates >95%. An excess acylating agent was necessary (2–20 molar equivs), but the unconverted ester was fully recovered and could be reused. The reaction plausibly involved multiple mechanisms where either the electrophilic and the nucleophilic activation of reagents took place through both traces of acetic acid (formed in situ by the hydrolysis of esters) and the autoprotolysis of GAs. iPAc confirmed a superior performance than other esters also for the high-temperature conversion of glycerol; in this case, although acylation and acetalization processes...

Gas-phase kinetic and mechanism study of the reactions of O3, OH, Cl and NO3 with unsaturated acetates

Environmental contextAcetate esters, emitted into the atmosphere from both natural and anthropogenic sources, can participate in photochemical processes leading to the formation of secondary organic aerosols. We report a study on the kinetics and mechanisms of the reaction of two acetate esters with O3, OH, NO3, and Cl radicals. The results help our understanding of the chemical behaviour of this important class of compounds in the atmosphere. AbstractThe photodegradation reactions of isopropenyl acetate (IPA) and 2-methyl-2-propenyl acetate (MPA) initiated by O3, OH, Cl and NO3 radicals have been investigated in a 100 L Teflon reactor at 293 ± 3 K, by using gas chromatography with flame-ionisation detection as well as thermal desorption–gas chromatography–mass spectrometry to monitor the reactants and the products. The rate constants for the reactions of IPA and MPA with the four atmospheric oxidants were determined by using either absolute or relative rate methods. The following rate constants (in units of cm3 molecule−1 s−1) were obtained: k(O3 + IPA) = (0.37 ± 0.06) × 10−18, k(OH + IPA) = (6.44 ± 0.74) × 10−11, k(Cl+ IPA) = (4.33 ± 0.52) × 10−10, k(NO3 + IPA) = (1.62 ± 0.22) × 10−14, k(O3 + MPA) = (2.76 ± 0.40) × 10−18, k(OH + MPA) = (7.41 ± 0.92) × 10−11, k(Cl + MPA) = (3.33 ± 0.39) × 10−10, k(NO3 + MPA) = (1.34 ± 0.23) × 10−14. With the exception of the kinetic study of the reactions of O3 and OH with IPA and the mechanistic study of the reaction of IPA with O3, the current research reports the first kinetic and mechanistic investigation for these reactions at atmospheric pressure. Acetic anhydride and 1-acetoxyacetone are the main products of the reactions of IPA and MPA, respectively. On the basis of the products and estimated tropospheric lifetimes of the two esters, reaction mechanisms are proposed and the atmospheric implications are discussed.

Homogenous esterification of cellulose pulp in [DBNH][OAc

Cellulose acetate is widely used in films, filters, textiles, lacquer and cosmetic products. Herein we demonstrate the production of cellulose esters under homogeneous conditions using 1,5-diazabicyclo[4.3.0]non-5-ene acetate ([DBNH][OAc]) as solvent. The reagents have been chosen such that the system is recyclable, i.e. by-products are low boiling and easy to remove. It is demonstrated that cellulose acetate can be synthesized with different degree of substitution (DS) values, and that some commonly used acylation regents, like vinyl carboxylates react well without additional base catalyst. Low to high DS values are possible with good recovery of high purity ionic liquid (IL). A linear correlation method of two separate methods, IR and 31P NMR, is proposed to reliably assess the DS of the products. The recyclability of the solvent is demonstrated by acetylating cellulose with isopropenyl acetate to high degree and regeneration into water. After regeneration of cellulose acetate from the IL with addition of water, the residual water was entrained using n-butanol to minimize hydrolysis of [DBNH][OAc], to allow for high recovery and high purity of the ionic liquid. Thus, an overall scheme for batch cellulose acetylation and recovery of [DBNH][OAc] from aqueous solutions is proposed.

Lipase‐Catalyzed Kinetic Resolution of N‐Substituted 1‐(β‐Hydroxypropyl)indoles by Enantioselective Acetylation

A new, concise, and efficient route towards both antipodes of N‐(β‐hydroxypropyl)indoles is described. The key step is an enantioselective lipase‐mediated acetylation of racemic indolic alcohols [1‐(1H‐indol‐1‐yl)propan‐2‐ol, 1‐(2‐methyl‐1H‐indol‐1‐yl)propan‐2‐ol, and 1‐(5‐bromo‐1H‐indol‐1‐yl)propan‐2‐ol] with enol esters (vinyl acetate and isopropenyl acetate) as acyl group donors, performed under kinetically controlled conditions. A substantial influence of enzyme type, acyl group donor, and organic solvent on conversion rates and enantioselectivity of the enzymatic kinetic resolutions (EKRs) of the respective racemates was examined in detail. The best results in terms of enantioselectivity were obtained for the resolutions performed with native lipase from Pseudomonas fluorescens (PFL, Amano AK) in diisopropyl ether (DIPE) or tert‐butyl methyl ether (TBME) solution. To support the assignment of the absolute configurations of EKR products, chemical correlations with enantiomerically enriched analytical standards and single‐crystal X‐ray diffraction analysis were applied.

High‐Pressure‐Promoted Multicomponent and Metal‐Free Synthesis of Polyfunctionalized Biaryls

An efficient and metal‐free synthesis of biaryls and heterobiaryls has been developed through a key three‐component reaction involving benzylideneacetones, isopropenyl acetate and methyl propiolate under high pressure (9 kbar) and mild reaction temperatures (40 °C). The described synthetic protocol provides rapid access to novel, highly functionalized and metal‐uncontamined 1,1′‐biaryls and heterobiaryls in an energy‐ and step‐economic fashion.

Isopropenyl acetate: A cheap and general acylating agent of alcohols under metal-free conditions

Functionalized primary, secondary and tertiary alcohols are efficiently acetylated by isopropenyl acetate and catalytic p-TsOH.

Acetylation of Microcrystalline Cellulose by Transesterification in AmimCl/DMSO Cosolvent System.

Recently, IL/cosolvent systems have generated a lot of interest as cellulose-dissolving solvents and reaction media for various kinds of cellulose modification. In the present study, both 1-allyl-3-methylimidazolium chloride (AmimCl)/dimethyl sulfoxide (DMSO) and AmimCl/N,N-dimethylformamide (DMF) systems were employed to synthesize cellulose acetate by transesterification. Microcrystalline cellulose, 1,8-diazabicyclo[5.4.0]undec-7-ene and isopropenyl acetate were chosen as the raw material, catalyst and acetylation reagent, respectively. The results revealed that DMSO was a suitable cosolvent for the transesterification in the homogeneous solution. Moreover, DMSO had a positive effect on the reaction as the cosolvent under the given conditions and the degree of the substitution of cellulose acetate could be significantly enhanced through increasing the molar ratio of DMSO. The synthesized products were characterized by Fourier transform infrared (FT-IR) spectroscopy, 1H and 13C nuclear magnetic resonance spectroscopy (1H-NMR and 13C-NMR), correlation spectroscopy (COSY), heteronuclear single quantum correlation (HSQC) spectroscopy, and X-ray diffraction (XRD) to confirm the chemical and physical structure of the cellulose acetate generated. The thermal properties were also evaluated using thermogravimetric analysis (TGA)/derivative thermogravimetry (DTG).

Formation of Bicyclic Cyclopentenone Derivatives by Robinson-Type Annulation of Cyclic β-Oxoesters Containing a 1,4-Diketone Moiety

Robinson-type cyclopentannulations of cyclic β-oxoesters possessing a 1,4-diketone moiety are accomplished under four different Brønsted basic reaction conditions. Using pyrrolidine/acetic acid in DMSO, an oxohexahydrocyclopenta[a]indene (42%) and an N-Boc-protected oxohexahydrocyclopenta[c]pyridine derivative (62%) are obtained with retention of the ester moieties. The latter compound defines an interesting new scaffold for medicinal chemistry with three positions allowing further derivatizations. The use of KOtBu in DMSO or NaH in toluene leads to cyclopentene derivatives with either partial ester saponification and decarboxylation or displacement of the ester moiety within the carbon skeleton. With aqueous KOH, the cyclopentannulations are successful in almost all cases, but with the ester moieties cleaved off. The respective bicyclic and tricyclic products are obtained in good to excellent yields. The 1,4-diketone starting materials are prepared by cerium-catalyzed oxidative coupling of β-oxoesters with isopropenyl acetate. Alternatively, a two-step sequence consisting of α-propargylation followed by palladium-catalyzed alkyne hydration is used.