Carbonate ester

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Chemical structure of the carbonate ester group Carbonate ester.png
Chemical structure of the carbonate ester group

In organic chemistry, a carbonate ester (organic carbonate or organocarbonate) is an ester of carbonic acid. This functional group consists of a carbonyl group flanked by two alkoxy groups. The general structure of these carbonates is R−O−C(=O)−O−R' and they are related to esters (R−O−C(=O)−R'), ethers (R−O−R') and also to the inorganic carbonates.

Contents

Monomers of polycarbonate (e.g. Makrolon or Lexan) are linked by carbonate groups. These polycarbonates are used in eyeglass lenses, compact discs, and bulletproof glass. Small carbonate esters like dimethyl carbonate, ethylene carbonate, propylene carbonate are used as solvents, dimethyl carbonate is also a mild methylating agent.

Structures

Structure of dicarbonate (PhOC(O)OC6H4)2CMe2 derived from bis(phenol-A) and two equivalents of phenol. DINWOM10.png
Structure of dicarbonate (PhOC(O)OC6H4)2CMe2 derived from bis(phenol-A) and two equivalents of phenol.

Carbonate esters have planar OC(OC)2 cores, which confers rigidity. The unique O=C bond is short (1.173 Å in the depicted example), while the C-O bonds are more ether-like (the bond distances of 1.326 Å for the example depicted). [1]

Carbonate esters can be divided into three structural classes: acyclic, cyclic, and polymeric. The first and general case is the acyclic carbonate group. Organic substituents can be identical or not. Both aliphatic or aromatic substituents are known, they are called dialkyl or diaryl carbonates, respectively. The simplest members of these classes are dimethyl carbonate and diphenyl carbonate.

Alternatively, the carbonate groups can be linked by a 2- or 3-carbon bridge, forming cyclic compounds such as ethylene carbonate and trimethylene carbonate. The bridging compound can also have substituents, e.g. CH3 for propylene carbonate. Instead of terminal alkyl or aryl groups, two carbonate groups can be linked by an aliphatic or aromatic bifunctional group.

A third family of carbonates are the polymers, such as poly(propylene carbonate) and poly(bisphenol A carbonate) (e.g. Makrolon or Lexan).

Preparation

Organic carbonates are not prepared from inorganic carbonate salts. Two main routes to carbonate esters are practiced: the reaction of an alcohol (or phenol) with phosgene (phosgenation), and the reaction of an alcohol with carbon monoxide and an oxidizer (oxidative carbonylation). Other carbonate esters may subsequently be prepared by transesterification. [2] [3]

In principle carbonate esters can be prepared by direct condensation of methanol and carbon dioxide. The reaction is however thermodynamically unfavorable. [4] A selective membrane can be used to separate the water from the reaction mixture and increase the yield. [5] [6] [7] [8]

Phosgenation

Alcohols react with phosgene to yield carbonate esters according to the following reaction:

2 ROH + COCl2 → ROC(O)OR + 2 HCl

Phenols react similarly. Polycarbonate derived from bisphenol A is produced in this manner. This process is high yielding. However, toxic phosgene is used, and stoichiometric quantities of base (e.g. pyridine) are required to neutralize the hydrogen chloride that is cogenerated. [2] [3] Chloroformate esters are intermediates in this process. Rather than reacting with additional alcohol, they may disproportionate to give the desired carbonate diesters and one equivalent of phosgene: [3]

PhOH + COCl2 → PhOC(O)Cl + HCl
2 PhOC(O)Cl → PhOC(O)OPh + COCl2

Overall reaction is:

2 PhOH + COCl2 → PhOC(O)OPh + 2 HCl

Oxidative carbonylation

Oxidative carbonylation is an alternative to phosgenation. The advantage is the avoidance of phosgene. Using copper catalysts, dimethylcarbonate is prepared in this way: [3] [9]

2 MeOH + CO + 1/2 O2 → MeOC(O)OMe + H2O

Diphenyl carbonate is also prepared similarly, but using palladium catalysts. The Pd-catalyzed process requires a cocatalyst to reconvert the Pd(0) to Pd(II). Manganese(III) acetylacetonate has been used commercially. [10]

Reaction of carbon dioxide with epoxides

The reaction of carbon dioxide with epoxides is a general route to the preparation of cyclic 5-membered carbonates. Annual production of cyclic carbonates was estimated at 100,000 tonnes per year in 2010. [11] Industrially, ethylene and propylene oxides readily react with carbon dioxide to give ethylene and propylene carbonates (with an appropriate catalyst). [2] [3] For example:

C2H4O + CO2 → C2H4O2CO

Carbonate transesterification

Carbonate esters can be converted to other carbonates by transesterification. A more nucleophilic alcohol will displace a less nucleophilic alcohol. In other words, aliphatic alcohols will displace phenols from aryl carbonates. If the departing alcohol is more volatile, the equilibrium may be driven by distilling that off. [2] [3]

From urea with alcohols

Dimethyl carbonate can be made from the reaction of methanol with urea. Ammonia that is produced can be recycled. Effectively ammonia serves as a catalyst for the synthesis of dimethyl carbonate. The byproducts are methyl- and N-methylcarbamate (the latter from the reaction between dimethyl carbonate and methyl carbamate). This process is not an economical one. [12]

Reactions

Carbonate esters undergo many of the reactions of conventional carboxylic acid esters. With Grignard reagents carbonate esters react to give tertiary alcohols. Some cyclic carbonates are susceptible to polymerization.

Uses

Organic carbonates are used as solvents in lithium batteries. Due to their high polarity, they dissolve lithium salts. The problem of high viscosity is circumvented by using mixtures for example of dimethyl carbonate, diethyl carbonate, and dimethoxyethane.

They are also used as solvents in organic synthesis. [13] Classified as polar solvents, they have a wide liquid temperature range. One example is propylene carbonate with melting point −55 °C and boiling point 240 °C. Other advantages are low ecotoxicity and good biodegradability. Many industrial production pathways for carbonates are not green because they rely on phosgene or propylene oxide. [14]

Dimethyl dicarbonate is commonly used as a beverage preservative, processing aid, or sterilant. [15]

Related Research Articles

<span class="mw-page-title-main">Alkene</span> Hydrocarbon compound containing one or more C=C bonds

In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond. The double bond may be internal or in the terminal position. Terminal alkenes are also known as α-olefins.

<span class="mw-page-title-main">Carboxylic acid</span> Organic compound containing a –C(=O)OH group

In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group attached to an R-group. The general formula of a carboxylic acid is R−COOH or R−CO2H, with R referring to the alkyl, alkenyl, aryl, or other group. Carboxylic acids occur widely. Important examples include the amino acids and fatty acids. Deprotonation of a carboxylic acid gives a carboxylate anion.

<span class="mw-page-title-main">Ether</span> Organic compounds made of alkyl/aryl groups bound to oxygen (R–O–R)

In organic chemistry, ethers are a class of compounds that contain an ether group—an oxygen atom connected to two alkyl or aryl groups. They have the general formula R−O−R′, where R and R′ represent the alkyl or aryl groups. Ethers can again be classified into two varieties: if the alkyl or aryl groups are the same on both sides of the oxygen atom, then it is a simple or symmetrical ether, whereas if they are different, the ethers are called mixed or unsymmetrical ethers. A typical example of the first group is the solvent and anaesthetic diethyl ether, commonly referred to simply as "ether". Ethers are common in organic chemistry and even more prevalent in biochemistry, as they are common linkages in carbohydrates and lignin.

<span class="mw-page-title-main">Ester</span> Compound derived from an acid

In chemistry, an ester is a compound derived from an acid in which the hydrogen atom (H) of at least one acidic hydroxyl group of that acid is replaced by an organyl group. Analogues derived from oxygen replaced by other chalcogens belong to the ester category as well. According to some authors, organyl derivatives of acidic hydrogen of other acids are esters as well, but not according to the IUPAC.

<span class="mw-page-title-main">Phosgene</span> Toxic gaseous compound (COCl2)

Phosgene is an organic chemical compound with the formula COCl2. It is a toxic, colorless gas; in low concentrations, its musty odor resembles that of freshly cut hay or grass. It can be thought of chemically as the double acyl chloride analog of carbonic acid, or structurally as formaldehyde with the hydrogen atoms replaced by chlorine atoms. Phosgene is a valued and important industrial building block, especially for the production of precursors of polyurethanes and polycarbonate plastics.

<span class="mw-page-title-main">Petrochemical</span> Chemical product derived from petroleum

Petrochemicals are the chemical products obtained from petroleum by refining. Some chemical compounds made from petroleum are also obtained from other fossil fuels, such as coal or natural gas, or renewable sources such as maize, palm fruit or sugar cane.

<span class="mw-page-title-main">Ethylene glycol</span> Organic compound ethane-1,2-diol

Ethylene glycol is an organic compound with the formula (CH2OH)2. It is mainly used for two purposes, as a raw material in the manufacture of polyester fibers and for antifreeze formulations. It is an odorless, colorless, flammable, viscous liquid. Ethylene glycol has a sweet taste, but it is toxic in high concentrations. This molecule has been observed in outer space.

<span class="mw-page-title-main">Epoxide</span> Organic compounds with a carbon-carbon-oxygen ring

In organic chemistry, an epoxide is a cyclic ether, where the ether forms a three-atom ring: two atoms of carbon and one atom of oxygen. This triangular structure has substantial ring strain, making epoxides highly reactive, more so than other ethers. They are produced on a large scale for many applications. In general, low molecular weight epoxides are colourless and nonpolar, and often volatile.

In organic chemistry, hydroformylation, also known as oxo synthesis or oxo process, is an industrial process for the production of aldehydes from alkenes. This chemical reaction entails the net addition of a formyl group and a hydrogen atom to a carbon-carbon double bond. This process has undergone continuous growth since its invention: production capacity reached 6.6×106 tons in 1995. It is important because aldehydes are easily converted into many secondary products. For example, the resulting aldehydes are hydrogenated to alcohols that are converted to detergents. Hydroformylation is also used in speciality chemicals, relevant to the organic synthesis of fragrances and drugs. The development of hydroformylation is one of the premier achievements of 20th-century industrial chemistry.

<span class="mw-page-title-main">Oxalyl chloride</span> Chemical compound

Oxalyl chloride is an organic chemical compound with the formula Cl−C(=O)−C(=O)−Cl. This colorless, sharp-smelling liquid, the diacyl chloride of oxalic acid, is a useful reagent in organic synthesis.

<span class="mw-page-title-main">Propylene carbonate</span> Chemical compound

Propylene carbonate (often abbreviated PC) is an organic compound with the formula C4H6O3. It is a cyclic carbonate ester derived from propylene glycol. This colorless and odorless liquid is useful as a polar, aprotic solvent. Propylene carbonate is chiral, but is used as the racemic mixture in most contexts.

<span class="mw-page-title-main">Dimethyl carbonate</span> Chemical compound

Dimethyl carbonate (DMC) is an organic compound with the formula OC(OCH3)2. It is a colourless, flammable liquid. It is classified as a carbonate ester. This compound has found use as a methylating agent and more recently as a solvent that is exempt from the restrictions placed on most volatile organic compounds (VOCs) in the United States. Dimethyl carbonate is often considered to be a green reagent.

<span class="mw-page-title-main">Ethylene carbonate</span> Chemical compound

Ethylene carbonate (sometimes abbreviated EC) is the organic compound with the formula (CH2O)2CO. It is classified as the cyclic carbonate ester of ethylene glycol and carbonic acid. At room temperature (25 °C) ethylene carbonate is a transparent crystalline solid, practically odorless and colorless, and somewhat soluble in water. In the liquid state (m.p. 34-37 °C) it is a colorless odorless liquid.

<span class="mw-page-title-main">Dimethyl oxalate</span> Chemical compound

Dimethyl oxalate is an organic compound with the formula (CO2CH3)2. It is the dimethyl ester of oxalic acid. Dimethyl oxalate is a colorless or white solid that is soluble in water.

In chemistry, carbonylation refers to reactions that introduce carbon monoxide (CO) into organic and inorganic substrates. Carbon monoxide is abundantly available and conveniently reactive, so it is widely used as a reactant in industrial chemistry. The term carbonylation also refers to oxidation of protein side chains.

<span class="mw-page-title-main">Acetic acid</span> Colorless and faint organic acid found in vinegar

Acetic acid, systematically named ethanoic acid, is an acidic, colourless liquid and organic compound with the chemical formula CH3COOH. Vinegar is at least 4% acetic acid by volume, making acetic acid the main component of vinegar apart from water and other trace elements.

<span class="mw-page-title-main">Diphenyl carbonate</span> Chemical compound

Diphenyl carbonate is the organic compound with the formula (C6H5O)2CO. It is classified as an acyclic carbonate ester. It is a colorless solid. It is both a monomer in combination with bisphenol A in the production of polycarbonate polymers and a product of the decomposition of polycarbonates.

Diethyl carbonate (sometimes abbreviated DEC) is an ester of carbonic acid and ethanol with the formula OC(OCH2CH3)2. At room temperature (25 °C) diethyl carbonate is a colorless liquid with a low flash point.

<span class="mw-page-title-main">C1 chemistry</span> One-carbon molecule chemical processes

C1 chemistry is the chemistry of one-carbon molecules. Although many compounds and ions contain only one carbon, stable and abundant C-1 feedstocks are the focus of research. Four compounds are of major industrial importance: methane, carbon monoxide, carbon dioxide, and methanol. Technologies that interconvert these species are often used massively to match supply to demand.

<span class="mw-page-title-main">Glycerol-1,2-carbonate</span> Organic chemical compound

Glycerol-1,2-carbonate is formally the cyclic ester of carbonic acid with glycerol and has aroused great interest as a possible product from the "waste materials" carbon dioxide CO2 and glycerol (especially from biodiesel production) with a wide range of applications.

References

  1. 1 2 Perez, Serge; Scaringe, Raymond P. (1987). "Crystalline features of 4,4'-isopropylidenediphenylbis(phenyl carbonate) and conformational analysis of the polycarbonate of 2,2-bis(4-hydroxyphenyl)propane". Macromolecules. 20 (1): 68–77. Bibcode:1987MaMol..20...68P. doi:10.1021/ma00167a014.
  2. 1 2 3 4 Shaikh, Abbas-Alli G.; Swaminathan Sivaram (1996). "Organic Carbonates". Chemical Reviews. 96 (3): 951–976. doi:10.1021/cr950067i. PMID   11848777.
  3. 1 2 3 4 5 6 Buysch, Hans-Josef (2012). "Carbonic Esters". Ullmann's Encyclopedia of Industrial Chemistry . Weinheim: Wiley-VCH. doi:10.1002/14356007.a05_197.
  4. ↑ Zhang, Zhi-Fang (2011). "Synthesis of Dimethyl Carbonate from Carbon Dioxide and Methanol over CexZr1-xO2and [EMIM]Br/Ce0.5Zr0.5O2". Industrial & Engineering Chemistry Research. 50 (4): 1981–1988. doi:10.1021/ie102017j.
  5. ↑ Li, Chuan-Feng (2003). "Study on application of membrane reactor in direct synthesis DMC from CO2 and CH3OH over Cu–KF/MgSiO catalyst". Catalysis Today. 82 (1–4): 83–90. doi:10.1016/S0920-5861(03)00205-0.
  6. ↑ Vermerris, René. Membrane enhanced conversion of methanol and carbon dioxide into dimethyl carbonate (PDF) (Report). Archived (PDF) from the original on 2013-10-05.
  7. ↑ Aouissi, Ahmed; Al-Othman, Zeid Abdullah; Al-Amro, Amro (2010). "Gas-Phase Synthesis of Dimethyl Carbonate from Methanol and Carbon Dioxide over Co1.5PW12O40 Keggin-Type Heteropolyanion". International Journal of Molecular Sciences. 11 (4): 1343–1351. doi: 10.3390/ijms11041343 . PMC   2871119 . PMID   20480023.
  8. ↑ Bian, Jun (2009). "Highly effective synthesis of dimethyl carbonate from methanol and carbon dioxide using a novel copper–nickel/graphite bimetallic nanocomposite catalyst". Chemical Engineering Journal. 147 (2–3): 287–296. doi:10.1016/j.cej.2008.11.006.
  9. ↑ Shaikh, Abbas-Alli G.; Sivaram, Swaminathan (1996-01-01). "Organic Carbonates". Chemical Reviews. 96 (3): 951–976. doi:10.1021/cr950067i. ISSN   0009-2665. PMID   11848777.
  10. ↑ Grigorii L. Soloveichik1 (2016). "Oxidative Carbonylation: Diphenyl Carbonate". In Shannon S. Stahl; Paul L. Alsters (eds.). Liquid Phase Aerobic Oxidation Catalysis: Industrial Applications and Academic Perspectives. Title Liquid Phase Aerobic Oxidation Catalysis: Industrial Applications and Academic Perspectives: Industrial Applications and Academic Perspectives. Wiley-VCH. pp. 189–208. doi:10.1002/9783527690121.ch12. ISBN   9783527337811.
  11. ↑ North, Michael; Pasquale, Riccardo; Young, Carl (2010). "Synthesis of cyclic carbonates from epoxides and CO2". Green Chem. 12 (9): 1514. doi:10.1039/c0gc00065e.
  12. ↑ "Archived copy" (PDF). Archived from the original (PDF) on 2013-10-05. Retrieved 2013-10-04.{{cite web}}: CS1 maint: archived copy as title (link)
  13. ↑ Schäffner, B.; Schäffner, F.; Verevkin, S. P.; Börner, A. (2010). "Organic Carbonates as Solvents in Synthesis and Catalysis". Chemical Reviews. 110 (8): 4554–4581. doi:10.1021/cr900393d. PMID   20345182.
  14. ↑ Sibiya, Mike Sbonelo (19 May 2008). Catalytic transformation of propylene carbonate into dimethyl carbonate and propylene glycol (Master of Science in Chemistry thesis). University of Johannesburg. Archived from the original on 2020-08-18. Retrieved 2022-04-12.
  15. ↑ Uhr, Hermann; Mielke, Burkhard; Exner, Otto; Payne, Ken R.; Hill, Edward (2013). "Biocides". Ullmann's Encyclopedia of Industrial Chemistry . Weinheim: Wiley-VCH. pp. 1–26. doi:10.1002/14356007.a16_563.pub2.
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