What Is Dihydropyran?
Dihydropyran is a cyclic ether with the molecular formula C5H8O, featuring a six-membered ring structure containing one oxygen atom and one double bond.
Several structural isomers of dihydropyran exist, but the most commonly referenced form is 3,4-dihydro-2H-pyran.
Uses of Dihydropyran
Dihydropyran serves as a crucial raw material and reagent in organic synthesis, particularly in protecting the hydroxyl groups of alcohols and phenols. It reacts with alcohols, under acidic catalysts, to form tetrahydropyranyl groups, which act as protective moieties for alcohols. Additionally, it is employed in the production of tetrahydropyran and tetrahydropyranyl ether.
Properties of Dihydropyran
1. Synthesis of 3,4-Dihydro-2H-Pyran
3,4-dihydro-2H-pyran is obtained by heating tetrahydrofurfuryl alcohol with aluminum oxide at temperatures ranging from 300 to 400°C.
2. Basic Information on 3,4-Dihydro-2H-Pyran
3,4-dihydro-2H-pyran, with a molecular weight of 84.12, appears as a colorless to yellow liquid with an ethanol odor at room temperature. It has a melting point of -70°C and a boiling point of 86°C. This compound is highly soluble in ethanol and acetone but insoluble in water. Due to its flammability, it is classified under various safety laws.
3. 3,6-Dihydro-2H-Pyran Basic Information
3,6-dihydro-2H-pyran, with a molecular weight of 84.12, has a boiling point of 92-93°C and a density of 0.943 g/mL. Its CAS registration number is 3174-74-1.
4. Chemical Reaction of 3,4-Dihydro-2H-Pyran
Dihydropyran undergoes hydrogenation using Raney nickel to yield tetrahydropyran. Moreover, under nonaqueous conditions and in the presence of an acid catalyst, 3,4-dihydro-2H-pyran reacts with alcohols to form tetrahydropyranyl ethers, serving as protective groups for alcohols. Deprotection of the tetrahydropyranyl group typically involves acid treatment with water or a large excess of methanol or ethanol instead of water.
5. Tetrahydropyranyl Group
The tetrahydropyranyl group, utilized to protect alcohols, exhibits stability under various conditions except for acidic environments. While cost-effective and easily deprotected under weakly acidic conditions, it introduces complexity in chiral alcohols, affecting NMR spectra and yielding isomeric diastereomers due to its chiral carbon.
Types of Dihydropyrans
Dihydropyran is primarily available as a reagent product for research and development. Although 3,4-dihydro-2H-pyran is the predominant form, derivatives of 3,6-dihydro-2H-pyran, such as the pinacol ester of boronic acid, are also commercially available. 3,4-dihydro-2H-pyran is typically offered in volumes ranging from 25 mL to 500 mL, and it is stored refrigerated or frozen as a reagent product.