What Is Indole?
Indole is a nitrogen-containing heterocyclic organic compound with the molecular formula C8H7N.
The CAS No. of indole is 120-72-9. It has a molecular weight of 117.15, a melting point of 52-54°C, and a boiling point of 253-254°C. It has a strong pungent odor. It has a density of 1.22 g/cm3, an acid dissociation constant pKa of 16.2, and a base dissociation constant pKb of 17.6.
It is a substance produced as a breakdown product when bacteria break down tryptophan, a type of amino acid. It is also found in jasmine oil, coal tar, putrefactive proteins, and mammalian excrement.
Uses of Indole
The odor of indole are described as similar to that of feces, but in very low concentrations, the substance has a floral aroma. Natural jasmine oil is estimated to contain approximately 2.5% indole, but due to the high cost of natural oils, indole are also used in the production of synthetic jasmine oil.
The indole structure (indole ring) is also found in a variety of organic compounds, especially biological substances.
Some indole derivatives were used as components of important dyes until the end of the 19th century. The name indole are derived from “indigo,” a plant-derived dye substance. Chemically, indole are used to detect nitrite ions and as a raw material for organic synthesis (dyes, alkaloids, etc.), among other uses.
Properties of Indole
1. Properties of Indole
Indole is an organic compound consisting of a benzene ring fused with a pyrrole ring. Like pyrrole, indole are not base, since the lone electron pair of the nitrogen atom is responsible for the formation of the aromatic ring.
However, indole can be protonated by using a strong acid such as hydrochloric acid. In this case, the protonation occurs at the C3 position instead of the N1 position because it shows the same reactivity as enamine. group. Examples of indole chemistry include electrophilic substitution at the C-3 position, lithiation at the C-2 position, oxidation, and cycloaddition.
2. Group of Indole Derivatives
Indole rings are found in a variety of organic compounds. Typical examples include tryptophan and indole alkaloids.
Indole are susceptible to electrophilic substitution reactions at the 3-position, so 3-substituted derivatives are common. Typical examples are the neurotransmitters serotonin and melatonin, and alkaloids with hallucinogenic effects (eg, wheat alkaloids). Indole structures can also be seen in auxins (a type of plant hormone) such as indolyl-3-acetic acid and IAA, and in pharmaceuticals such as indomethacin (a non-steroidal anti-inflammatory drug) and pindolol (a beta blocker).
3.Synthesis of Indole
Indole are major component of coal tar and can be obtained from distillation fractions at temperatures ranging from 220°C to 260°C. Although indoles and their derivatives can be synthesized in a variety of ways, but the main industrial synthetic route uses aniline and ethylene glycol as starting materials. The synthesis is carried out in the presence of a catalyst at temperatures between 200°C and 500°C. The reaction proceeds by gas phase reaction. Typical yields are around 60%.
Various other synthetic methods for the synthesis of indole and its derivatives has been reported, but the most famous synthetic methods include Fischer’s indole synthesis and Fukuyama’s indole synthesis.
Types of Indoles
Indole currently available in the market are mainly a reagent product for developmental research. The product is sold in capacities that are easy to handle in the laboratory, such as 1 g, 10 g, 25 g, 100 g, and 500 g. Depending on the manufacturer, indole may be stored at room temperature or handled as refrigerated storage.