Acetylacetone

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Structural formula
Structural formula of acetylacetone
General
Surname Acetylacetone
other names
  • Pentane-2,4-dione ( IUPAC )
  • Diacetyl methane
  • β, δ-dioxopentane
  • 2,4-pentanedione
  • Hacac (as ligand )
Molecular formula C 5 H 8 O 2
Brief description

clear, colorless liquid with a pleasant odor

External identifiers / databases
CAS number 123-54-6
EC number 204-634-0
ECHA InfoCard 100.004.214
PubChem 31261
Wikidata Q413447
properties
Molar mass 100.12 g mol −1
Physical state

liquid

density

0.98 g cm −3

Melting point

−23 ° C

boiling point

approx. 140 ° C

Vapor pressure
  • 9.0 h Pa  (20 ° C)
  • 16.1 hPa (30 ° C)
  • 27.6 hPa (40 ° C)
  • 45.2 hPa (50 ° C)
solubility

easily in water (122 g l −1 at 20 ° C)

Refractive index

1.4494 (20 ° C)

safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary
02 - Highly / extremely flammable 06 - Toxic or very toxic

danger

H and P phrases H: 226-302-311 + 331
P: 210-261-280-302 + 352-312-304 + 340 + 310-403 + 233
MAK

DFG / Switzerland: 20 ml m −3 or 83 mg m −3

Toxicological data
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C

Acetylacetone ( IUPAC name: pentane-2,4-dione) is a colorless, pleasantly smelling, flammable liquid that is easily soluble in water. The liquid is not very volatile, but at higher ambient temperatures vapors that are heavier than air are formed. These vapors can form explosive mixtures with air at temperatures above 34 ° C (flash point).

As a bidentate ligand, acetylacetone is a complexing agent ( acetylacetonate , acac ). It also serves as a synthetic building block for heterocyclic compounds, e.g. B. Medicines such as sulfamethazine or nicarbazine, which inhibit the synthesis of folic acid in bacteria . Acetylacetone is also used in the manufacture of rust converters and anti-corrosion agents . It is also used as a reagent in the acetylacetone method , a standardized method for the quantitative determination of formaldehyde .

properties

Physical Properties

The miscibility with water is limited. As the temperature rises, the solubility of acetylacetone increases or the solubility of water in acetylacetone increases.

Solubilities between acetylacetone and water
temperature ° C 0 9.6 19.8 29.8 39.7 50.1 60.6 70.5 80.3 90.5
Acetylacetone in water in% 14.1 14.9 16.1 17.6 18.9 21.02 24.4 27.0 32.2 40.3
Water in acetylacetone in% 1.7 2.1 2.8 3.5 4.4 5.8 7.8 10.0 13.5 19.9

Safety-related parameters

Acetylacetone forms highly flammable vapor-air mixtures. The compound has a flash point of 34 ° C. The lower explosion limit (LEL) is approx. 1.7 vol.% (71 g / m 3 ). The limit gap width was determined to be 0.92 mm (50 ° C). This results in an assignment to explosion group IIA. The ignition temperature is 340 ° C. The substance therefore falls into temperature class T2.

Keto-enol tautomerism

The relatively high acid strength can be explained by the inductive effect and the mesomeric effect emanating from both carbonyl groups (negative charge of the anion delocalized via a 5-atom π system ). The arrangement of the carbonyl groups also favors enolization , since the double bond of the enol is conjugated with the adjacent carbonyl group and the OH group forms a hydrogen bond to the carbonyl group:

Tautomerism of acetylacetone

Acetylacetone is therefore 80% enol in the liquid state.

safety instructions

The use of the substance, which was previously used as a flavoring substance, has been banned in food within the EU since 2005, as there are indications of genotoxicity .

Acetylacetonate

Acetylacetone has a pKa value of 8.99 ± 0.06 (25 ° C, I = 0), i.e. i.e., it reacts slightly acidic when mixed with water .

Acetylacetonate is widely used as a ligand for transition metals . These metal acetylacetonates are often used as catalysts . In the empirical formula of a complex , acetylacetonate is abbreviated as acac , e.g. B. Rh (CO) 2 acac.

Examples of common metal acetylacetonates are:

use

2,4-Pentanediol can be obtained by asymmetric hydrogenation .

Individual evidence

  1. ↑ Entry on acetylacetone. In: Römpp Online . Georg Thieme Verlag, accessed on June 16, 2014.
  2. ↑ a b c d e f g h i j k l m n o p Entry on pentane-2,4-dione in the GESTIS substance database of the IFA , accessed on November 8, 2017(JavaScript required) .
  3. ↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Physical Constants of Organic Compounds, pp. 3-416.
  4. ↑ Entry on pentane-2,4-dione in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers and / or distributors can expand the harmonized classification and labeling .
  5. ↑ Swiss Accident Insurance Fund (Suva): Limit values ​​- current MAK and BAT values (search for 123-54-6 or acetylacetone ), accessed on November 2, 2015.
  6. ↑ a b WEKA Hazardous Substances Database, WEKA Media GmbH & Co. KG, 2009.
  7. ↑ VDI 3862 sheet 6: 2004-02 measurement of gaseous emissions; Measurement of formaldehyde by the acetylacetone method (Gaseous emission measurement; Measurement of formaldehyde by the acetylacetone method). Beuth Verlag, Berlin, p. 5.
  8. ^ A b R. M. Stephenson: Mutual Solubilities: Water-Ketones, Water-Ethers, and Water-Gasoline-Alcohols in J. Chem. Eng. Data 37 (1992), pp. 80-95, doi : 10.1021 / je00005a024 .
  9. ↑ Decision of the EU Commission of May 18, 2005 amending Decision 1999/217 / EC with regard to the list of flavorings used in or on foods. (pdf) (PDF) .
  10. ↑ J. Michael Chong: (2R, 4R) -2,4-pentanediol . In: Encyclopedia of Reagents for Organic Synthesis . doi : 10.1002 / 047084289X.rp029 .