Chemical Properties
Indole has an unpleasant odor at high concentration, odor becomes floral at higher dilutions
Chemical Properties
white crystals with an unpleasant odour
Physical properties
Colorless to yellow scales with an unpleasant odor. Turns red on exposure to light and air. Odor
threshold of 0.14 ppm was reported by Buttery et al. (1988).
Occurrence
Reported occurring in several natural products as a complex compound that decomposes during enfleurage or
steam distillation yielding free indole; reported found in the essential oil from flower of Jasminum grandiflorum, in neroli oil and in
the oil extracted from flowers of bitter orange; also reported in the flowers of several plants: lemon, coffee, Hevea brasiliensis and
Randia formosa in the oil extracted from flowers of Jasminum odoratissinium L. and in the oil of Narcissus jonquilla. Also reported
found in apricot, mandarin orange peel oil, grapes, kohlrabi, French fried potato, crispbread, cheeses, butter, milk, milk powder,
boiled egg, fish oil, chicken, beef, pork, beer, rum, Finnish whiskey, red and white wine, coffee, tea, soybean, mushrooms, cauliflower, figs, rice, licorice, buckwheat, malt, wort, elder flower, clary sage, shrimp, okra, crab, clam, squid and green maté
Definition
indole: A yellow solid, C8H7N, m.p.52°C. Its molecules consist of a benzenering fused to a nitrogen-containingfive-membered ring. It occurs insome plants and in coal tar, and isproduced in faeces by bacterial action.It is used in making perfumes.Indole has the nitrogen atom positionednext to the fused benzenering. An isomer with the nitrogentwo atoms away from the fused ringis called isoindole.
Preparation
Obtained from the 220 to 260°C boiling fraction of coal tar or by heating sodium phenyl-glycine-o-carboxylate with
NaOH, saturating the aqueous solution of the melt with CO2 and finally reducing with sodium amalgam; can be prepared also by the
reduction of indoxyl, indoxyl carboxylic acid or indigo.
Aroma threshold values
Detection: 140 ppb
General Description
Indole is classified under the volatile flavor compounds (VFCs). It is known to play significant role in various biological functions such as anti-inflammatory, anticonvulsant, cardiovascular and antibacterial activities.
Health Hazard
Low to moderate toxicity was observed inexperimental animals resulting from oral orsubcutaneous administration of indole. Theoral LD50 value in rats is 1000 mg/kg. It is ananimal carcinogen. It caused tumors in bloodand lungs in mice subjected to subcutaneousadministration.
Fire Hazard
Noncombustible solid.
Flammability and Explosibility
Notclassified
Biochem/physiol Actions
Taste at 0.3-2 ppm
Source
Indole was detected in jasmine flowers (Jasminum officinale), licorice (Glycyrrhiza
glabra), kohlrabi stems (Brassica oleracea var. gongylodes), and hyacinth flowers (Hyacinthus
orientalis) at concentrations of 42 to 95, 2, 1.33, and 0.24 to 3.45 ppm, respectively. Indole also
occurs in tea leaves, black locust flowers, corn leaves, petitgrain, and yellow elder (Duke, 1992).
A liquid swine manure sample collected from a waste storage basin contained indole at a
concentration of 4.8 mg/L (Zahn et al., 1997).
Environmental Fate
Biological. In 9% anaerobic municipal sludge, indole degraded to 1,3-dihydro-2H-indol-2-one
(oxindole), which degraded to methane and carbon dioxide (Berry et al., 1987). Heukelekian and
Rand (1955) reported a 5-d BOD value of 1.70 g/g which is 65.4% of the ThOD value of 2.48 g/g.
Chemical/Physical. The aqueous chlorination of indole by hypochlorite/hypochlorous acid,
chlorine dioxide, and chloramines produced oxindole, isatin, and possibly 3-chloroindole (Lin and
Carlson, 1984).
Metabolic pathway
The indole is metabolized in a mineral salt medium
inoculated with 9% anaerobically digested nitrate-
reducing sewage sludge, resulting in the sequential
occurrence of four structurally related compounds:
oxindole, isatine, dioxindole, and anthranilic acid.
Indole is metabolized by fungus via indoxyl (3-hydroxyindole), N-formylanthranilic acid, anthranilic
acid, 2,3-dihydroxybenzoic acid, and catecol, which is
further degraded by an ortho cleavage.
Metabolism
Indole is oxidized to 3-hydroxyindole (indoxyl) which is conjugated with glucuronic and sulphuric acids before excretion. The sulphate conjugate seems to be the main product in rabbits and, even with relatively large doses of indole, the sulphate conjugation always exceeds that of glucuronic acid(Williams, 1959).
Purification Methods
It can be further purified by sublimation in a vacuum or by zone melting. The picrate forms orange crystals from EtOH and has m 175o. [Beilstein 20 II 196, 20 III/IV 3176, 20/7 V 5.]
Toxicity evaluation
Indole causes oxidative damage to membranes.
