Metaldehyde

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Structural formula
Structure of Metaldeyhds
Structural formula of the tetramer of acetaldehyde without stereochemistry
General
Surname Metaldehyde
other names
  • 2,4,6,8-tetramethyl-1,3,5,7-tetroxocan
  • Metacetaldehyde
Molecular formula C 8 H 16 O 4
Brief description

colorless, tasteless, highly flammable solid with a weak characteristic odor

External identifiers / databases
CAS number
  • 108-62-3
  • 9002-91-9 (homopolymer)
PubChem 61021
Wikidata Q412303
properties
Molar mass 176.21 g mol −1
Physical state

firmly

density

1.27 g cm −3  (20 ° C)

Melting point

45.5 ° C

Vapor pressure

0.3 h Pa (20 ° C)

solubility
  • very bad in water (222 mg l −1 at 20 ° C)
  • slightly soluble in ether and ethanol
  • soluble in benzene and chloroform
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: 228-301-330
P: 210-301 + 310 + 330-304 + 340 + 310
Toxicological data

227–690 mg kg −1 ( LD 50 ,  rat ,  oral )

As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Metaldehyde is a cyclic ether . It is the cyclic tetramer of acetaldehyde . The trimer is called paraldehyde . Polymeric acetaldehyde (CH 3 CHO) n is also marketed under the name metaldehyde . It is used as a dry fuel and molluscicide , but may, according to German Cosmetics Regulation not be used in the manufacture or treatment of cosmetic products. Metaldehyde is found in slug pellets, for example .

Extraction and presentation

Metaldehyde is formed by the cyclization of four molecules of acetaldehyde in the presence of sulfuric acid at low temperatures. The product formation of the cyclization reaction is temperature dependent. The formation of the trimer paraldehyde is preferred at room temperature . At lower temperatures around −10 ° C, the tetrameric metaldehyde is more likely to form.

Synthesis of paraldehyde and metaldehyde

properties

Metaldehyde is a colorless, tasteless, highly flammable solid with a faint characteristic odor and a melting point of 45.5 ° C. The melting and sublimation temperatures between 100 ° C and 250 ° C given in the literature relate to polymeric acetaldehyde and rather result from depolymerization processes.

As with paraldehyde , several stereoisomers can be formulated for the molecular structure of metaldehyde . The methyl groups can each be axial or equatorial on the ring.

The calorific value is 3370 kJ / mol, corresponding to 19.1 MJ / kg.

See also

Web links

Individual evidence

  1. ↑ Data metaldehyde in AlfaAesar, accessed on 14 April 2010 ( PDF )(JavaScript required) .
  2. ↑ a b c d enius: metaldehyde , accessed on 4 February 2018th
  3. ↑ a b c d e f Entry on 2,4,6,8-tetramethyl-1,3,5,7-tetraoxacycloctane in the GESTIS substance database of the IFA , accessed on January 8, 2020(JavaScript required) .
  4. ^ A b E.C. Craven, H. Jowitt, WR Ward: Polymeric forms of acetaldehyde. In: Journal of Applied Chemistry. 12, 1962, pp. 526-535, doi : 10.1002 / jctb.5010121202 .
  5. ↑ David R. Lide: CRC Handbook of Chemistry and Physics . 85th edition, 2005, CRC Press, chap. 3, p. 356.
  6. ↑ Entry on 2,4,6,8-tetramethyl-1,3,5,7-tetraoxacyclooctane in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can use the harmonized classification and labeling expand .
  7. ↑ WHO / FAO Data Sheet on Pesticides (PDS) for Metaldehydes , accessed December 9, 2014.
  8. ↑ a b Aldrich Catalog Manual Fine Chemicals and Laboratory Equipment 2009/2010.
  9. ↑ HP Lacha; U. Kazmaier; HA Klein: Chemistry for Biologists , Springer Verlag 2005, p. 515, ISBN 3-540-21161-6 .
  10. ^ Entry on Metaldehyde in the Hazardous Substances Data Bank , accessed on February 10, 2019.