Synthesis Of Dialkyl Carbonates Research Articles

Comparative Study between 2-Furonitrile and 2-Cyanopyridine as Dehydrants in Direct Synthesis of Dialkyl Carbonates from CO2 and Alcohols over Cerium Oxide Catalyst.

The shift of equilibrium by removing water with nitrile dehydrants is crucial for CeO2 -catalyzed synthesis of dialkyl carbonates from CO2 and alcohols. Two nitriles - 2-cyanopyridine and 2-furonitrile - were previously found as effective dehydrants, yet their detailed comparison as well as exploration of potential of 2-furonitrile remain insufficient. Herein, the performance of 2-cyanopyridine and 2-furonitrile was compared in the synthesis of various dialkyl carbonates. 2-furonitrile was found to be superior to 2-cyanopyridine in the synthesis of dialkyl carbonates from CO2 and bulky or long-chain (≥C3) alcohols. Namely, the yield of diisopropyl carbonate (up to 50 %) achieved using CeO2 and 2-furonitrile is comparable to or even higher than previously reported ones. Meanwhile, 2-cyanopyridine acted as a better dehydrant than 2-furonitrile in the synthesis of dimethyl carbonate and diethyl carbonate. The adsorption experiments and density functional theory calculations have indicated that the better performance of 2-furonitrile compared to 2-cyanopyridine in the synthesis of dialkyl carbonates from bulky or long-chain alcohols is due to the weaker interaction of 2-furonitrile with the CeO2 surface. Such weak interaction of 2-furonitrile offers a larger reaction field on the catalyst surface for both CO2 and alcohols.

Exothermic barrier-free carboxylation of alkali methylates. The highest-yield synthesis of dialkyl carbonates out of alcohols and carbon dioxide rationalized and reformulated through quantum-chemical simulations

While the Earth’s atmosphere represents an abundant source of CO2, its valorization by humanity remains at a nascent stage. Synthesizing added-value products out of CO2 and suitable co-reactants is an urgent and appealing chemical challenge to pursue in our busy times. Herein, we perform a rationalization, extension, and ultimate reformulation of the recently proposed highest-yield synthesis of dimethyl carbonate (DMC) and generally dialkyl carbonates out of alcohols and CO2 employing quantum-chemical reaction modeling. The carboxylation of pure methanol (CH3OH) by CO2 is thermochemically prohibited (+33 kJ/mol) and hindered by a heavy activation energy barrier (160 kJ/mol). The existing catalysts decrease the above barrier twice. The catalyzed carboxylation exhibits yields of 5–15 % of DMC depending on a specific catalyst, dehydration agents, and pressure elevation. In turn, the usage of alkali metal methylates – such as CH3OLi, CH3ONa, CH3OK, and CH3ORb – as reactants, instead of CH3OH, fully eliminates the activation barrier. Furthermore, alcoholates make carboxylation exothermic. We stepwise rationalize the origin of such a desirable behavior in terms of thermochemistry, molecular geometries, atomic nucleophilicities, potential energy landscapes, and computed vibrational spectra. All methylates perform decently and exhibit reasonable similarities as reactants. The most favorable reaction was recorded in the case of sodium alcoholate (according to Gibbs free energy) and lithium alcoholate (according to enthalpy). Since the carboxylation smoothly proceeds with the methylates, the synthesis can be carried out under normal conditions. This is contrary to the elevated temperatures and pressures, which have to be routinely supplied to implement the presently known catalytic schemes. Apart from an organic carbonate, the novel reactions produce LiI, NaI, KI, and RbI as major products. The consumed alkali metals need to be restored, for instance, by utilizing electrolysis, for their repetitive usages. The theoretical results are discussed tightly in the context of the recent experiments. The reactions can take place in liquid CH3OH. Exemplified computationally for the methyl radical, the invented scheme must generally work for larger hydrocarbon moieties. This report will interest synthetic chemists, whose work is devoted to the valorization of CO2.

Organic compound modification of CeO2 and 2-cyanopyridine hybrid catalyst in carbonate synthesis from CO2 and alcohols

The effect of surface modification of CeO2 and 2-cyanopyridine hybrid catalyst with organic compounds was investigated by using dialkyl carbonate synthesis from CO2 and alcohols. Phenol is the useful modifier for CeO2 and 2-cyanopyridine hybrid catalyst without drastic decrease of the activity. Based on the characterizations of phenol-modified CeO2 and 2-cyanopyridine hybrid catalyst such as TG-DTA, GC, FTIR and UV–vis, phenol and 2-cyanopyridine were adsorbed on CeO2 at the same time and the adsorption ratio to the surface Ce on CeO2 is estimated to be 0.11 and 0.12, respectively (2-cyanopyridine/Ce on CeO2 surface = 0.12, phenol/Ce on CeO2 surface = 0.11). The reactivity of alcohols was changed by the addition of phenol due to the steric hindrance of phenol adsorbed on CeO2. The effect of the steric hindrance was large at the C2 and C3 positions of alcohols, which corresponds to the C2 and C3 positions of phenol. The reactivity was drastically decreased in the cases of C2 position-branched alcohols compared with the case without phenol addition, and the yield ratio (The yield without phenol/the yield with phenol) increased: 61 in the case of 2-ethyl-1-butanol, 9.9 in the case of 2-methyl-1-butanol, and 3.7 in the case of 1-butanol. From the DFT calculations, phenol is adsorbed nearby 2-cyanopyridine adspecies by the π-π interaction between the aromatic rings of these chemicals to decrease the reaction space over CeO2, resulting in the reactivity decrease of the steric alcohols, particularly the alcohols with substituents at the C2 position. Therefore, phenol can restrict the reaction field of CeO2 and 2-cyanopyridine hybrid catalyst by the steric hindrance, enabling the control of the reactivity of alcohols in the synthesis of dialkyl carbonates from CO2 and alcohols.

Sustainable Catalytic Synthesis of Diethyl Carbonate.

New sustainable approaches should be developed to overcome equilibrium limitation of dialkyl carbonate synthesis from CO2 and alcohols. Using tetraethyl orthosilicate (TEOS) and CO2 with Zr catalysts, we report the first example of sustainable catalytic synthesis of diethyl carbonate (DEC). The disiloxane byproduct can be reverted to TEOS. Under the same conditions, DEC can be synthesized using a wide range of alkoxysilane substrates by investigating the effects of the number of ethoxy substituent in alkoxysilane substrates, alkyl chain, and unsaturated moiety on the fundamental property of this reaction. Mechanistic insights obtained by kinetic studies, labeling experiments, and spectroscopic investigations reveal that DEC is generated via nucleophilic ethoxylation of a CO2 -inserted Zr catalyst and catalyst regeneration by TEOS. The unprecedented transformation offers a new approach toward a cleaner route for DEC synthesis using recyclable alkoxysilane.

Two-Step Synthesis of Dialkyl Carbonates through Transcarbonation and Disproportionation Reactions Catalyzed by Calcined Hydrotalcites

A two-step methodology was implemented to prepare dialkyl carbonates from both primary and secondary alcohols, including glycerol acetals, tetrahydrofurfuryl alcohol, and cyclohexanol. Accordingly, alcohols were initially subjected to a batch transcarbonation (carbonate interchange) reaction with the nontoxic dimethyl carbonate, providing the corresponding asymmetrical methyl alkyl carbonates (ROCO2Me). These compounds were then used as reactants for a continuous-flow (CF) disproportionation reaction, producing the corresponding symmetrical dialkyl carbonates (ROCO2R). Although transcarbonation and dismutation took place at different operating temperatures (90 and 180–275 °C, respectively), both reactions were catalyzed by the same heterogeneous Mg/Al mixed oxides catalyst, obtained upon calcination of commercially available hydrotalcites (HTs). Yields and selectivities for methyl alkyl carbonates were excellent, in the range of 93–96% and 95–98%, respectively. CF-disproportionation reactions were strongly affected by the nature/structure of reactants; nevertheless, they provided the corresponding dialkyl carbonates with selectivities and productivities up to 92% and 164 mgprod·(gcat·min)−1, respectively. Overall, the reported methodology displays attractive sustainability features, including a straightforward upgrade of biomass derivatives, development of a continuous-flow intensified process, and improved catalyst recycle and products’ purification, while disclosing stimulating perspectives for further investigations on the reaction mechanism and on the role of HTs as catalyst precursors for the synthesis of organic carbonates.

Energy issues in the utilization of CO2 in the synthesis of chemicals: The case of the direct carboxylation of alcohols to dialkyl-carbonates

This paper aims at highlighting the hurdles and traps on the way back from CO2 to chemicals (or even fuels). The case of the synthesis of dialkyl carbonates is discussed, considering several synthetic conditions and comparing the relevant amount of energy necessary for product separation. The calculations show that the post-reaction separation process may share an important part of the energy consumption in the whole synthetic procedure and make, in some conditions, the reaction a strong CO2 emitter more than a CO2 consumer.

A Photocatalyzed Synthesis of Dialkyl Carbonates from Phosgene Generated in situ

The anion exchange resin Amberlite IRA-900, in the chloride form, catalyzes the photolysis of carbon tetrachloride in methanol, ethanol, and n-propanol under visible and near-UV irradiation to produce the corresponding dialkyl carbonate and alkyl chloroformate, the latter readily converted to the carbonate with base. For diethyl carbonate, the rate of reaction increases with the partial pressure of oxygen and is relatively insensitive to either the amount of catalyst present or the fraction of CCl4 in ethanol above approximately 10 mg/mL and 5%, respectively. A yield of 15% could be achieved for diethyl carbonate under appropriate conditions, accompanied by acetaldehyde and chloroform as major side products. The reaction in methanol was slower and that in n-propanol somewhat faster than in ethanol. Keywords: Amberlite, anion exchange resin, carbon tetrachloride, diethyl carbonate, dimethyl carbonate, photocatalysis.

ChemInform Abstract: Non‐Symmetrical Dialkyl Carbonate Synthesis Promoted by 1‐(3‐Trimethoxysilylpropyl)‐3‐methylimidazolium Chloride.

AbstractA simple, efficient and environmentally benign approach for the synthesis of non‐symmetrical dialkyl carbonates (III) (18 examples) via ionic liquid promoted transesterification of dimethyl carbonate is developed.

ChemInform Abstract: New Synthesis of Dialkyl Carbonates from Alkylene Carbonates and Titanium Alkoxides.

Dialkyl carbonates are used in industry as organic solvents, fuel additives, lubricants in refrigerating units, and heat carriers. A conventional procedure for the preparation of dialkyl carbonates is based on the reaction of alcohols with phosgene which is very toxic. Phosgene-free syntheses of organic carbonates are extensively developed; they include oxidative carbonylation of alcohols [1, 2], reactions of alcohols with urea [3, 4], reactions of oxiranes with carbon dioxide [5, 6], and reactions of inorganic carbonates with alkyl halides [5] or alcohols [7, 8]. Also, mutual transformations of alkyl carbonates are possible. We now propose a new phosgene-free synthesis of dialkyl carbonates via reaction of alkylene carbonates with titanium alkoxides. An advantage of the proposed procedure is that it ensures simultaneous preparation of two important products, dialkyl carbonate and alkyl titanate derivative [dialkyl alkanediyl titanate or bis(alkanediyl) titanate]. The latter can be used as curing agent for epoxy resins or as precursor for the synthesis of nanosized titanium dioxide. The titanium-containing residue can be decomposed by treatment with dilute sulfuric acid to regenerate the diol. The reactions were carried out with a number of alkyl titanates and alkylene carbonates. A mixture of 45.62 g (0.2 mol) of tetraethyl titanate and 40.8 g (0.4 mol) of propylene carbonate was slowly heated and distilled through a column, and a fraction boiling in the range from 120 to 130°C was collected. Yield of diethyl carbonate 40.59 g (86%), nD = 1.384 (published data [9]: nD = 1.384). Found, %: C 50.84; H 8.45. Calculated, %: C 50.85; H 8.47.

New synthesis of Dialkyl carbonates from alkylene carbonates and titanium alkoxides

Dialkyl carbonates are used in industry as organic solvents, fuel additives, lubricants in refrigerating units, and heat carriers. A conventional procedure for the preparation of dialkyl carbonates is based on the reaction of alcohols with phosgene which is very toxic. Phosgene-free syntheses of organic carbonates are extensively developed; they include oxidative carbonylation of alcohols [1, 2], reactions of alcohols with urea [3, 4], reactions of oxiranes with carbon dioxide [5, 6], and reactions of inorganic carbonates with alkyl halides [5] or alcohols [7, 8]. Also, mutual transformations of alkyl carbonates are possible. We now propose a new phosgene-free synthesis of dialkyl carbonates via reaction of alkylene carbonates with titanium alkoxides. An advantage of the proposed procedure is that it ensures simultaneous preparation of two important products, dialkyl carbonate and alkyl titanate derivative [dialkyl alkanediyl titanate or bis(alkanediyl) titanate]. The latter can be used as curing agent for epoxy resins or as precursor for the synthesis of nanosized titanium dioxide. The titanium-containing residue can be decomposed by treatment with dilute sulfuric acid to regenerate the diol. The reactions were carried out with a number of alkyl titanates and alkylene carbonates. A mixture of 45.62 g (0.2 mol) of tetraethyl titanate and 40.8 g (0.4 mol) of propylene carbonate was slowly heated and distilled through a column, and a fraction boiling in the range from 120 to 130°C was collected. Yield of diethyl carbonate 40.59 g (86%), nD = 1.384 (published data [9]: nD = 1.384). Found, %: C 50.84; H 8.45. Calculated, %: C 50.85; H 8.47.

Synthesis of Dimethyl Carbonate through Vapor‐Phase Carbonylation Catalyzed by Pd‐Doped Zeolites: Interaction of Lewis Acidic Sites and Pd Species

All doped up: The interaction between Lewis (L) acidic sites and Pd species in the vapor-phase carbonylation reaction of methyl nitrite over Pd/Faujasite (FAU) catalysts is determined quantitatively. By keeping the Pd species in an electron-deficient state, the Lewis acids of the Pd/FAU catalysts promote the synthesis of dialkyl carbonates.

Non-symmetrical dialkyl carbonate synthesis promoted by 1-(3-trimethoxysilylpropyl)-3-methylimidazolium chloride

An efficient synthesis of non-symmetrical dialkyl carbonates promoted by 1-(3-trimethoxysilylpropyl)-3-methylimidazolium chloride ionic liquid as a reaction medium is described. The ionic liquid can easily be recovered and reused several times without significant change in the activity and selectivity.

Synthesis of dialkyl carbonates from CO2 and alcohols via electrogenerated N-heterocyclic carbenes

Here we describe the utilization of NHC–CO2 which transfers CO2 to alcohols for the synthesis of dialkyl carbonates under mild conditions with high conversion and excellent selectivity. In addition NHC–CO2 formation was supported by electrochemical analysis. This study provides a new procedure for the synthesis of dialkyl carbonates of chemical and pharmaceutical interest, as well as expands the applications of NHCs in CO2 fixation.

Experimental and Theoretical Study of Chemical Equilibria in the Reacting System of the di-Alkyl Carbonate Synthesis.

The chemical equilibrium of the reactive system (propylene carbonate + butanol = dibutyl carbonate +1,2-propanediol) was studied in the temperature range (303 to 373) K in the liquid phase using th...

Investigating the formation of dialkyl carbonates using high speed ball milling

We investigated the synthesis of dialkyl carbonates under solvent-free high speed ball milling conditions. We converted various metal carbonates with the assistance of metal complexing reagents into a variety of dialkyl carbonates. We also observed the increased reactivity of urea under similar reaction conditions.

A High‐Yielding, One‐Pot Synthesis of Dialkyl Carbonates from Alcohols Using Mitsunobu′s Reagent.

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, please click on HTML or PDF.

A high yielding, one-pot synthesis of dialkyl carbonates from alcohols using Mitsunobu’s reagent

A Mitsunobu-based protocol has been developed for the synthesis of symmetrical and unsymmetrical dialkylcarbonates from a variety of primary, secondary and tertiary alcohols using gaseous carbon dioxide, in good to excellent yields. This protocol is mild and efficient compared to other reported methods.

Direct carboxylation of alcohols to organic carbonates: Comparison of the Group 5 element alkoxides catalytic activity: An insight into the reaction mechanism and its key steps

The reaction of carboxylation of alcohols is a sustainable technology for the synthesis of dialkylcarbonates that avoids the use of phosgene. In this paper we describe the behaviour of metal alkoxides of Group 5 elements as homogeneous catalysts in the above reaction, and the isolation and characterization of the active species, i.e. the hemicarbonates formed upon insertion of carbon dioxide into the M–OR bond. Ta and V alkoxo complexes are comparatively discussed with respect to the Nb-analogues, whose synthesis and catalytic properties have been published [M. Aresta, A. Dibenedetto, C. Pastore, Inorg. Chem. 42 (10) (2003) 3256, and references therein]. In this paper, we report for the first time the evidence of insertion of carbon dioxide in tantalum alkoxides [Ta(OR) 5] 2 [R = methyl (Me), ethyl (Et)]. The relevant hemicarbonates Ta(OR) 4[OC(O)OR] have been characterized using spectroscopic techniques (IR and NMR). Tantalum alkoxides and the vanadium compound VO(OR) 3 are shown to be able to catalyze the carboxylation of alcohols at 413 K and 5.5 MPa of CO 2. The trend of reactivity for the Group 5 alkoxides as catalysts for the carboxylation of alcohols is Nb ≫ Ta > V.

Controlled Synthesis of Asymmetric Dialkyl and Cyclic Carbonates Using the Highly Selective Reactions of Imidazole Carboxylic Esters

A new highly selective synthesis of dialkyl carbonates is described. The procedures rely on the previously unknown selectivity of imidazole carboxylic esters synthesized by the reaction of 1,1‘-carbonyldiimidazole with alcohols. The imidazole carboxylic esters of secondary or tertiary alcohols form carbonates through the exclusive reaction with primary alcohols in polyols containing mixtures of primary, secondary, and tertiary hydroxyl groups without the need for protection. Controlled cyclic carbonate formation is also described.

Investigation of dialkyltin compounds as catalysts for the synthesis of dialkyl carbonates from alkyl carbamates

New syntheses for dibutyldimethoxytin, dibutyldiisocyanatotin and 1,1,3,3-tetrabutyl-1,3-diisocyanatodistannoxane as well as the novel compounds dibutylisocyanatomethoxytin and 1,1,3,3-tetrabutyl-1-methoxy-3-isocyanatodistannoxane are described. These compounds were characterized by elemental analyses as well as 119Sn, 13C, and proton NMR, FTIR, MS and HPLC. They were found to have good catalytic activity for the synthesis of symmetrical dialkyl carbonates from alkyl carbamates and the corresponding alcohols. Extensive NMR and IR data indicate that tin compounds containing both an alkoxy and an isocyanato moiety bounded to tin are reaction intermediates in the synthesis of dialkyl carbonate and their formation is a key step in this catalytic process. The mechanism of carbonate synthesis involves the interconversion of the various tin species present in the reaction mixture to these reaction intermediates. Dibutyldimethoxytin, dibutylisocyanatomethoxytin and 1,1,3,3-tetrabutyl-1-methoxy-3-isocyanatodistannoxane have similar activity and are more active (10–14%) than dibutyloxotin for the synthesis of symmetrical dialkyl carbonates.