Obtaining β-naphthyl methyl ether

Objective

The purpose of this experiment is to obtain an asymmetric ether of industrial interest from naphthalen-2-ol (β-naphthol) using two synthetic methods.

Background

2-methoxynaphthalene (β-naphthyl methyl ether) is a white solid with a melting point of 73 ºC that goes by the trade name of neroline. It is used in perfumery for its floral odor, as a stabilizer for specialty powders and as an intermediate for the synthesis of non-steroidal anti-inflammatory drugs. It can be obtained by two synthetic methods: using the Williamson reaction or by treatment of MeOH and β-naphthol with hot H2SO4.

As is known, Williamson synthesis is a process that allows the preparation of a wide range of ethers, both symmetric and asymmetric by an SN2-type mechanism.

The second procedure, which we will use in this experiment, is based on the use of the alkoxonium ion, formed by the reaction of MeOH with H2SO4. This alkoxonium ion in a subsequent stage is attacked by a molecule of β-naphthol producing the corresponding β-naphthyl methyl ether.

Experimental procedure

Obtaining β-naphthyl methyl ether by Williamson synthesis

In a 100 ml round bottom flask fitted with a stir bar, 2.88 g (20 mmol) of β-naphthol (2-hydroxynaphthalene), 1.46 g (26 mmol) KOH and 20 ml of MeOH are mixed. A stopper is attached and the mixture is stirred at room temperature until dissolution of the solid. With the aid of a syringe, 1.4 ml (23 mmol) methyl iodide (CH3I) is added.

¡DANGER! «Conduct the experiment in a fume cupboard due to the hazardous nature of methyl iodide (CH3I).«

Next, a reflux condenser and a drying tube are coupled and heated for 1 h. The mixture is allowed to cool to room temperature and water is added until a precipitate appears. The mixture is cooled to room temperature and water is added until a precipitate appears. The solid is filtered under vacuum and recrystallized in EtOH (estimated yield 75 %, melting point 73 °C).

Obtaining β-naphthyl methyl ether in an acid medium

In a 100 ml round bottom flask, 5 g of β-naphthol, 25 ml of MeOH and 5 ml of H2SO4 are placed. The mixture is kept at reflux for 1 h.

The reaction crude is allowed to cool and poured over 100 ml ice/water. The precipitated ether is filtered off under vacuum. The precipitate is washed in the Büchner twice with ice water, once with 20 ml 10 % NaOH and once with ice water.

The product obtained is recrystallized in EtOH, decolorized with activated carbon if necessary (estimated yield 70 %).

International Chemical Identifier

The IUPAC InChI key identifiers for the main compounds used in this experiment are provided to facilitate the nomenclature and formulation of chemical compounds and the search for information on the Internet for these compounds.

β-naphthyl methyl etherLUZDYPLAQQGJEA-UHFFFAOYSA-N
β-naphtholJWAZRIHNYRIHIV-UHFFFAOYSA-N
CH3IINQOMBQAUSQDDS-UHFFFAOYSA-N
H2SO4QAOWNCQODCNURD-UHFFFAOYSA-N
EtOHLFQSCWFLJHTTHZ-UHFFFAOYSA-N
NaOHHEMHJVSKTPXQMS-UHFFFAOYSA-M
MeOHOKKJLVBELUTLKV-UHFFFAOYSA-N

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