Carboxylic acid anhydrides

Symmetrical (R ¹ = R ² ) and asymmetrical (R ¹ ≠ R ² ) carboxylic acid anhydrides (R ¹ , R ² = H or organyl radical, such as alkyl radical, aryl radical or arylalkyl radical, etc.).

From top to bottom: acetic anhydride, maleic anhydride, phthalic anhydride. The characteristic group of all carboxylic acid anhydrides is marked in blue .

Carboxylic acid anhydrides are a class of substances in organic chemistry that are derived from carboxylic acids and can be referred to as reactive carboxylic acid derivatives . They consist of two acyl groups linked by an oxygen atom. A distinction is made between symmetrical (R ¹ = R ² ) and asymmetrical (R ¹ ≠ R ² ), the symmetrical carboxylic acid anhydrides being more common and more important. There are also both open-chain (e.g. acetic anhydride ) and cyclic carboxylic acid anhydrides (e.g. succinic anhydride or maleic anhydride ).

nomenclature

It should be noted that carboxylic acid anhydrides and acid anhydrides are not one and the same. All carboxylic acid anhydrides are acid anhydrides, but not all acid anhydrides are carboxylic acid anhydrides. So is z. B. nitrous oxide is also an acid anhydride, but is not organic and has no carbon atoms. Thus it is not a carboxylic acid anhydride. A carboxylic acid anhydride is named like the carboxylic acid, from which it was theoretically formed by dehydration, with the additional anhydride. So is z. B. the anhydride of phthalic acid phthalic anhydride. In the case of unsymmetrical carboxylic acid anhydrides, first one acid is mentioned and then the other acid and the ending -anhydride is added. The carboxylic acid anhydride of ethanoic acid and propanoic acid would be the ethanoic acid-propanoic anhydride.

Manufacturing

Synthesis of symmetrical carboxylic acid anhydrides

The dehydration of the corresponding monocarboxylic acid with the aid of phosphorus pentoxide can be used to produce symmetrical carboxylic acid anhydrides .

Large-scale production of acetic anhydride

Acetic anhydride (also called acetic anhydride) is considered the most important carboxylic acid anhydride. It is produced atom-economically using the Wacker process . Here, the ethenone (ketene) is first generated by dehydration of acetic acid or by pyrolysis of acetone , and then acetic acid reacts with ketene (see Wacker process ):

Reactions

Although carboxylic acid anhydrides are less reactive than carboxylic acid chlorides, they are more reactive as reactive carboxylic acid derivatives than other carbonyl compounds .

Alcoholysis

The alcoholysis of carboxylic acid anhydrides produces a carboxylic acid and a carboxylic acid ester . When acetic anhydride reacts with alcohol , acetic acid and an acetic acid ester are formed :

The reaction of a cyclic carboxylic acid anhydride with anhydrous alcohol produces a dicarboxylic acid with an esterified carboxy group . The anhydrous alcoholysis of phthalic anhydride with methanol gives a phthalic acid monomethyl ester as a product:

hydrolysis

Carboxylic acid anhydrides react with water to give two equivalents of the underlying carboxylic acid. The hydrolysis of acetic anhydride produces two equivalents of acetic acid:

Formation of carboxamides

Carboxylic acid anhydrides react with ammonia or amines to form carboxylic acid salts and carboxamides. The desired products are the carboxamides. Carboxylic acid salts can be produced far more easily by the reaction of carboxylic acids with ammonia or amines. The reactions are as follows:

Acetic anhydride reacts with ammonia to form ammonium acetate and acetamide :

Acetic anhydride reacts with a primary amine to form an acetic acid salt and a secondary acetic acid amide :

Acetic anhydride reacts with a secondary amine to form an acetic acid salt and a tertiary acetic acid amide:

Diels-Alder reaction

Due to the electron-poor π system, the cyclic maleic anhydride is an almost ideal dienophile for the Diels-Alder reaction. The [4 + 2] cycloaddition of 1,3-butadiene and maleic anhydride produces tetrahydrophthalic anhydride (see Diels-Alder reaction ):

Friedel-Crafts acylation

The Friedel-Crafts acylation is the most important method for the synthesis of aromatic ketones. You can u. a. perform with carboxylic acid anhydrides. The reaction of an aromatic compound and a carboxylic acid anhydride produces an aryl ketone with the help of a Lewis acid catalyst (see Friedel-Crafts acylation ):

Individual evidence

1. ^ Robert J. Ouellette, J. Davin Rawn: Organic Chemistry: Structure, Mechanism, and Synthesis . Elsevier, Amsterdam 2014, ISBN 978-0-12-800780-8 , pp. 699 .
2. ↑ ^{a b c} Adalbert Wollrab: Organic Chemistry - An introduction for teacher training and minor students . 4th edition. Springer-Verlag, Berlin 2014, ISBN 978-3-642-45143-0 , pp. 672-675 , doi : 10.1007 / 978-3-642-45144-7 .
3. ↑ Hans P. Latscha, Uli Kazmaier, Helmut A. Klein: Organic Chemistry: Chemistry Basics II . 6th edition. Springer-Verlag, Berlin 2008, ISBN 978-3-540-77106-7 , pp. 275-276 , doi : 10.1007 / 978-3-540-77107-4 .
4. ^ Hans Breuer: Chemistry: Organic chemistry and plastics . 9th edition. Deutscher Taschenbuch Verlag, Munich 2006, ISBN 978-3-423-03218-6 , pp. 369-372 .
5. ↑ Maleic anhydride . In: Jürgen Falbe, Manfred Regitz (Ed.): Römpp . 9th edition. Georn Thieme Verlag, Stuttgart 2003, ISBN 3-13-734909-5 , p. 2617 .
6. ↑ ^{a b} Thomas Laue, Andreas Plagens: Named organic reactions . Wiley, 1999, ISBN 0-471-97142-1 , pp. 78-109 .
7. ^ Norman L. Allinger: Organic Chemistry . Ed .: Georg Kossmehl. 1st edition. De Gruyter, Berlin 1980, ISBN 978-3-11-004594-9 , pp. 564-565 .