Paraldehyde

Paraldehyde

Names
IUPAC name 2,4,6-Trimethyl-1,3,5-trioxane
Systematic IUPAC name 2,4,6-Trimethyl-1,3,5-trioxane
Identifiers
CAS Number	123-63-7 Y
3D model (Jmol)	Interactive image
ChEBI	CHEBI:27909 Y
ChEMBL	ChEMBL1410743 N
ChemSpider	21106173 Y
ECHA InfoCard	100.004.219
EC Number	204-639-8
KEGG	D00705 N
MeSH	Paraldehyde
PubChem	31264
UNII	S6M3YBG8QA Y
InChI InChI=1S/C6H12O3/c1-4-7-5(2)9-6(3)8-4/h4-6H,1-3H3 Y Key: SQYNKIJPMDEDEG-UHFFFAOYSA-N Y InChI=1/C6H12O3/c1-4-7-5(2)9-6(3)8-4/h4-6H,1-3H3 Key: SQYNKIJPMDEDEG-UHFFFAOYAO
SMILES CC1OC(C)OC(C)O1
Properties
Chemical formula	C6H12O3
Molar mass	132.16 g·mol−1
Density	0.996 g/cm3
Melting point	12 °C (54 °F; 285 K)
Boiling point	124 °C (255 °F; 397 K)
Solubility in water	soluble 10 % vv at 25 Deg.
Magnetic susceptibility (χ)	-86.2·10−6 cm3/mol
Pharmacology
ATC code	N05CC05 (WHO)
Hazards
Safety data sheet	External MSDS
EU classification (DSD)	Xn C
R-phrases	R10 R20 R21 R22 R34 R45
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YN ?)
Infobox references

Paraldehyde is the cyclic trimer of acetaldehyde molecules. Formally, it is a derivative of 1,3,5-trioxane. The corresponding tetramer is metaldehyde. A colourless liquid, it is sparingly soluble in water and highly soluble in ethanol. Paraldehyde slowly oxidizes in air, turning brown and producing an odour of acetic acid. It quickly reacts with most plastics and rubber.

Paraldehyde was first observed in 1835 by the German chemist Justus Liebig ; its empirical formula was determined in 1838 by Liebig's student Hermann Fehling. Paraldehyde was first synthesized in 1848 by the German chemist Valentin Hermann Weidenbusch (1821–1893), another student of Liebig ; he obtained paraldehyde by treating acetaldehyde with acid (either sulfuric or nitric acid). It has uses in industry and medicine.

Theoretically, four stereoisomeric structures are possible. The structures (1) and (2) are known as cis- and trans-paraldehyde. The structures (3) (a conformer of (2)) and (4) (a conformer of (1)) don't exist for steric reasons.

Heated with catalytic amounts of acid, it depolymerizes back to acetaldehyde:

Since paraldehyde has better handling characteristics, it may be used indirectly or directly as a synthetic equivalent of anhydrous acetaldehyde (b.p. 20 °C). For example, it is used as-is in the synthesis of bromal (tribromoacetaldehyde):

Paraldehyde was introduced into clinical practice in the UK by the Italian physician Vincenzo Cervello (1854–1918) in 1882.

It is a central nervous system depressant and was soon found to be an effective anticonvulsant, hypnotic and sedative. It was included in some cough medicines as an expectorant (though there is no known mechanism for this function beyond the placebo effect).