Carbonic acid ester

Structure of the carbonic acid ester; in the case of a half ester, R ² = H

Carbonic acid esters (often also called imprecisely carbonates ) are the esters of the essentially unstable carbonic acid . Their general semi-structural formula is R ¹ -O-C (= O) -O-R ² , where R ¹ and R ^{2 are} carbon-containing alkyl or aryl radicals . In the case of R ¹ = R ² the carbonic acid ester is symmetrical, in the case of R ¹ ≠ R ² the carbonic acid ester is asymmetrical. If R ¹ and R ² belong to the same molecule, a ring-shaped compound such as propylene carbonate is formed . If the carbonic acid function is unfunctionalized on one side (R = H), one speaks of a half ester. The urethanes can also be classified as half-esters of carbonic acid, at the same time they are half-amides of carbonic acid.

Manufacturing

Carbonic acid esters can be produced from phosgene and alcohols with the elimination of hydrogen chloride :

${\displaystyle \mathrm {COCl_{2}+2\ R{-}OH\ \longrightarrow \ 2\ HCl+CO(OR)_{2}} }$

With 1,2-glycols, the cyclic carbonates ethylene carbonate and propylene carbonate are only formed as by-products in addition to polycarbonates.

use

As a very polar solvent, carbonic acid esters show a certain solubility of inorganic salts and are therefore used as electrolyte liquids ( Li-ion batteries ). Particularly well-known carbonic acid esters are the polycarbonates , which are used in many different ways as plastics. The so-called triphosgene (carbonic acid bis-trichloromethyl ester) can be used as a less dangerous substitute for phosgene in syntheses.

additional

In addition to the carbonic acid esters of the general formula CO (OR) _2, there are also so-called orthocarbonic acid esters C (OR) ₄ (see also orthoesters ). These can be obtained by reacting chloropicrin with alcoholates :

${\displaystyle \mathrm {CCl_{3}NO_{2}+4\ R{-}O^{-}\ \longrightarrow \ C(OR)_{4}+3\ Cl^{-}+NO_{2}^{-}} }$

Examples

• Carbonic acid dimethyl ester
• Carbonic acid diethyl ester
• Diphenyl carbonate

literature

• Benjamin Schäffner, Sergey P. Verevkin and Armin Börner: Organische Carbonate , Chem. Unserer Zeit 43 (2009) 12–21.

Individual evidence

1. ↑ Entry on carbonic acid esters. In: Römpp Online . Georg Thieme Verlag, accessed on June 16, 2014.
2. ^ ^{A b} Beyer, Walter: Textbook of Organic Chemistry , 23rd edition, S. Hirzel Verlag 1998.