2-Hydroxy-1,4-naphoquinone

Chemical properties

Yellow crystal powder

History

Lawsone (CI Natural Orange 6; CI 75420), also known as henna and isojuglone, occurs in the shrub henna (Lawsone alba). In England, the plant is known as Egyptian privet. The dye was extracted from the leaves of the plant, using sodium bicarbonate, and the extracts used to dye protein fibers an orange shade. Henna is probably the oldest cosmetic known. The ancient Egyptians used it as a hair dye and for staining fingernails. It is said that Mohammed dyed his beard with henna. Lawsone has been identified as 2-hydroxy-1,4-naphthoquinone. It has been synthesized by the Thiele acetylation of 1,4-naphthoquinone followed by hydrolysis and oxidation.

The Uses of 2-Hydroxy-1,4-naphoquinone

antifungal, sunscreen, antibacterial, antineoplastic

The Uses of 2-Hydroxy-1,4-naphoquinone

2-Hydroxy-1,4-naphthoquinone is used for preparing decorative hair and skin dyes. 2-Hydroxy-1,4-naphthoquinone also demonstrates antimicrobial and antioxidant effects. It also suppress the formation of hydrogen peroxide and superoxide radical anion by aldehyde oxidase-catalyzed reactions.

Definition

A coloring principle obtained from dried leaves of certain tropical plants (North Africa, India).

Synthesis Reference(s)

The Journal of Organic Chemistry, 53, p. 808, 1988 DOI: 10.1021/jo00239a023
Tetrahedron Letters, 25, p. 533, 1984 DOI: 10.1016/S0040-4039(00)99930-1

General Description

Yellow prisms or yellow powder.

Air & Water Reactions

Insoluble in water.

Reactivity Profile

Phenols, such as 2-Hydroxy-1,4-naphoquinone, do not behave as organic alcohols, as one might guess from the presence of a hydroxyl (-OH) group in their structure. Instead, they react as weak organic acids. Phenols and cresols are much weaker as acids than common carboxylic acids (phenol has Ka = 1.3 x 10^[-10]). These materials are incompatible with strong reducing substances such as hydrides, nitrides, alkali metals, and sulfides. Flammable gas (H2) is often generated, and the heat of the reaction may ignite the gas. Heat is also generated by the acid-base reaction between phenols and bases. Such heating may initiate polymerization of the organic compound. Phenols are sulfonated very readily (for example, by concentrated sulfuric acid at room temperature). The reactions generate heat. Phenols are also nitrated very rapidly, even by dilute nitric acid. Nitrated phenols often explode when heated. Many of them form metal salts that tend toward detonation by rather mild shock.

Health Hazard

ACUTE/CHRONIC HAZARDS: 2-Hydroxy-1,4-naphoquinone may be absorbed through the skin and can cause skin irritation.

Fire Hazard

Flash point data for 2-Hydroxy-1,4-naphoquinone are not available but 2-Hydroxy-1,4-naphoquinone is probably combustible.

Contact allergens

Henna, prepared by powdering the dried leaves of henna plant (Lawsonia inermis L.), is used for coloring and conditioning hair and nails, particularly by Muslims or Hindus. It contains Lawsone, which very rarely induces contact allergy. Most dermatitis caused by “black henna” is due to PPD and derivatives

Purification Methods

Crystallise Lawsone B from *C6H6 or AcOH (m 192.5o, 195-196o). It sublimes in a vacuum (m 194o). It has UV with max at 455nm (aqueous NaOH). [Beilstein 8 H 300, 8 I 635, 8 II 344, 8 III 2543, 8 IV 2360.]