Dihydropyran

Structural formula
General
Surname	Dihydropyran
other names	3,4-dihydro-2 H -pyran ( IUPAC ) 2,3-dihydro-4 H -pyran 2,3-dihydro-γ-pyran DHP
Molecular formula	C 5 H 8 O
Brief description	yellow, foul-smelling liquid
External identifiers / databases
CAS number 110-87-2 EC number 203-810-4 ECHA InfoCard 100.003.465 PubChem 8080 ChemSpider 7789 Wikidata Q419349
properties
Molar mass	84.12 g mol −1
Physical state	liquid
density	0.927 g cm −3 (20 ° C)
Melting point	−70 ° C
boiling point	89 ° C
Vapor pressure	120 hPa (20 ° C) 400 hPa (50 ° C)
solubility	slightly soluble in water (20 g l −1 at 20 ° C) soluble in ethanol
Refractive index	1,440
safety instructions
GHS labeling of hazardous substances danger H and P phrases H: 225-315-317-319-412 EUH: 019 P: 210-223-302 + 352-305 + 351 + 338-403 + 235
Toxicological data	> 4000 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 . Refractive index: Na-D line , 20 ° C

Dihydropyran (according to IUPAC nomenclature: 3,4-dihydro-2 H -pyran , abbreviated as DHP ) is an organic-chemical compound from the group of oxygen heterocycles or enol ethers .

Extraction and presentation

The technical production of dihydropyran takes place by the dehydration of tetrahydrofurfuryl alcohol at temperatures of 300-350 ° C under normal pressure over a heterogeneous aluminum oxide catalyst in tubular reactors.

This reaction is more precisely a dehydration with subsequent ring expansion .

properties

Physical Properties

From a chemical point of view, it is an enol ether, which means that the ether oxygen is directly bound to a carbon-carbon double bond . Due to the + M effect of oxygen, enol ethers are electron-rich, unsaturated compounds that can easily react with electrophiles such as protons (H ⁺ ).

Chemical properties

In organic syntheses , the 2- tetrahydropyranyl group is used as a protective group for alcohols and thiols. The reaction of an alcohol with dihydropyran leads to the formation of a base-stable tetrahydropyranyl ether or a cyclic acetal , whereby the alcohol is protected from a large number of undesirable side reactions. The alcohol can then easily be released again by acid hydrolysis . 5-Hydroxypentanal is produced as a by-product .

Safety-related parameters

The compound forms highly flammable vapor-air mixtures. The flash point is −9 ° C. The explosion range is between 1.1 vol.% As the lower explosion limit (LEL) and 13.8 vol.% As the upper explosion limit (UEL). The ignition temperature is 240 ° C. The substance therefore falls into temperature class T3.

use

Dihydropyran is an intermediate for the manufacture of crop protection products and pharmaceuticals. It also serves to form a protective group for various functional groups (e.g. alcohols, thiols , amines and amides ) in organic syntheses.

safety instructions

Dihydropyran is highly flammable, highly volatile and forms explosive peroxides with air when exposed to light .

See also

• Pyrans

Web links

• NMR spectrum of dihydropyran

Individual evidence

1. ↑ ^{a b c d e f g h i j k} Entry on 3,4-dihydro-2H-pyran in the GESTIS substance database of the IFA , accessed on April 23, 2019(JavaScript required) .
2. ↑ Information from UBE Chemical ( Memento of February 5, 2007 in the Internet Archive ) (English).
3. ↑ CRC Handbook of Tables for Organic Compound Identification , Third Edition, 1984, ISBN 0-8493-0303-6 .
4. ↑ ^{a b} Data sheet 3,4-Dihydro-2H-pyran (PDF) from Merck , accessed on April 23, 2019.
5. ↑ Niklaus Künzle: A process for preparing dihydropyran and its use as protective agent. In: Google Patents. Lonza Ltd., April 7, 2011, accessed April 23, 2019 . 
6. ↑ ^{a b} entry on 3,4-dihydro-2H-pyran. In: Römpp Online . Georg Thieme Verlag, accessed on April 23, 2019.
7. ^ E. Brandes, W. Möller: Safety-related parameters - Volume 1: Flammable liquids and gases Wirtschaftsverlag NW - Verlag für neue Wissenschaft GmbH, Bremerhaven 2003.