How to Synthesize 2,7-Dihydroxynaphthalene?

Background and Overview

2,7-Dihydroxynaphthalene (CAS No: 582-17-2) is soluble in ethanol, ether, and hot water, slightly soluble in benzene and chloroform, and almost insoluble in petroleum ether. Its solution quickly darkens in the air. The LD50 (mouse, intraperitoneal) is 102mg/kg. It has irritant effects on the eyes, respiratory system, and skin. It is widely used as a dye, pharmaceutical intermediate, and analytical reagent.

Figure 1: Synthesis reaction of 2,7-Dihydroxynaphthalene

Preparation

The current industrial method for synthesizing 2,7-Dihydroxynaphthalene is as follows: using 2,7-naphthalenedisulfonic acid sodium as the raw material, sodium hydroxide as the alkaline melting solvent, alkaline melting is carried out at high temperature, and then the resulting mixture is acidified with concentrated sulfuric acid to obtain 2,7-Dihydroxynaphthalene. The main problems with the existing process are: (1) the need for a significantly excessive amount of sodium hydroxide (usually more than 20 times the molar amount of the substrate); (2) water is generated during the alkaline melting process, and under high-temperature alkaline melting conditions, the sulfonic acid group on one side of the 2,7-naphthalenedisulfonic acid sodium is hydrolyzed and detached, resulting in a large amount of 1-hydroxynaphthalene as a byproduct; (3) the alkaline melting temperature is often above 350°C, and due to the severe reaction conditions, a large amount of tar is produced, resulting in a very low yield of 2,7-Dihydroxynaphthalene.

Experimental Procedure:

Method 1:

In a 250ml autoclave, add 33.2g of 2,7-naphthalenedisulfonic acid sodium, 8.0g of sodium hydroxide, 12.4g of sodium oxide, and 50.0g of dodecane. Stir and heat up to 290°C and react for 8 hours at this temperature. Then, cool the resulting solution to room temperature with stirring, filter, and neutralize the obtained filter cake with a 30% sulfuric acid solution to pH 1. Dry the suspension after filtration to obtain 16.1g of 2,7-dihydroxynaphthalene with a yield of 69.1%.

Method 2:

In a 250ml autoclave, add 33.2g of 2,7-naphthalenedisulfonic acid sodium, 12.0g of sodium hydroxide, 12.4g of sodium oxide, and 50.0g of dodecane. Stir and heat up to 290°C and react for 8 hours at this temperature. Then, cool the resulting solution to room temperature with stirring, filter, and neutralize the obtained filter cake with a 30% sulfuric acid solution to pH 1. Dry the suspension after filtration to obtain 18.2g of 2,7-dihydroxynaphthalene with a yield of 75.9%.

References

[1] CN 108329195 B