Benzofuran, Benzothiophene and Indoles, Chemistry tutorial

Introduction to Benzofuran:

Benzofuran is basically the heterocyclic compound comprising of fused benzene and furan rings. This colourless liquid is the component of coal tar. Benzofuran is the 'parent' of numerous related compounds by more complex structures. For illustration, psoralen is a Benzofuran derivative that takes place in various plants.

Benzofuran comprises of an oily chemical compound extracted from the coal tar, which is transformed to a synthetic resin employed in manufacturing. This colorless liquid may be added to paint and varnish to improve resistance to corrosion, and gives water resistance to fabric and paper. Food packaging suppliers make use of the resin as an adhesive, and it symbolizes a common substance in plastic food containers designed for the repeated use. A derivative of Benzofuran takes place naturally in various plants.

Food and drug regulatory agencies let the use of Benzofuran in food containers and packaging at recommended levels, however no human studies have been done to measure the risks of exposure. This chemical might be present in air, water or soil near manufacturing facilities which extract resin from the coal tar. Scientists who studied waterways close to such areas found no contamination in the aquatic life. The chemical has been found in breast milk, though.

The health organizations list possible exposure from eating food sold in packages where the adhesive is present or employing plastic containers prepared by Benzofuran. The substance is as well added to the peelings of citrus fruit that represents the other route of exposure. Direct exposure might take place by contact via the skin.

Benzofuran might be inhaled in the air close to hazardous waste facilities that store it or adjacent to industrial plants transforming coal tar into resin. This is as well found in cigarettes. Scientists recommend against drinking water contaminated by the compound or touching it directly. Nursing mothers with the substance in breast milk are recommended to stop nursing their babies.

The level of Benzofuran in breast milk and blood can be tested, however the analysis is considered complex and not readily available throughout routine physical examinations. Such tests merely recognize recent exposure, and there is no reliable proof to find out how long Benzofuran remains in the human body. This is not categorized as a cancer-causing agent and might give anti-cancer benefits, according to studies by using derivatives of the chemical found in plants.

Use of Benzofuran:

The Benzofuran is derived from crude, heavy solvent naphtha fraction of coal-tar light oil, obtained as a by-product in the coking of bituminous coal, is employed in the preparation of coumarone-indene resin (Budavari, 1989). The fraction of coal-tar oil which distils at 167 to 184 °C includes small quantities (probably 0: 10%) of Benzofuran and around 30% indene, indan, substituted benzenes and associated compounds. Polymerization is initiated through addition of anacid catalyst like boron trifluoride or sulphuric acid.

Coumarone-indene resins harden whenever heated and have been employed to form floor tiles and other products. They are as well utilized as a coating on grapefruit, lemons, oranges, lirnes, tangelos and tangerines and in the production of Corrosion-resistant paints and varnishes, in water-resistant coatings on paper products and fabrics and as adhesives in the food containers.

Production of Benzofuran:

Benzofuran is extracted from the coal tar. It is as well obtained by dehydrogenation of 2-ethylphenol.

Laboratory methods:

Benzofuran can be manufactured via different methods in the laboratory. Notable illustrations comprise:

a) O-alkylation of salicylaldehyde by chloroacetic acid followed through dehydration of the resultant ether.

b) Perkin rearrangement, in which a coumarin is reacted by a hydroxide:

1126_Perkin rearrangement.jpg

Fig: Perkin rearrangement

c) Diels-Alder reaction of nitro vinyl furans by different dienophiles.

1812_Diels–Alder reaction of nitro vinyl furans.jpg

Fig: Diels-Alder reaction of nitro vinyl furans

d) Cycloisomerization of alkyne ortho-substituted phenols.

Introduction to Benzothiophene:

Benzothiophenes, a significant group of heterocycles, are privileged structures, employed as starting materials for the synthesis of the bioactive structures and are present in the pharmaceuticals; like selective estrogen receptor modulators, leukotriene synthesis inhibitors, and antifungal; and most of the natural products. Different substitution patterns in such heterocycles give new opportunities for drug discoveries and other applications in the materials science.

Benzothiophene is the aromatic organic compound having a molecular formula C8H6S and an odor identical to naphthalene (that is, mothballs). It takes place naturally as a constituent of the petroleum-related deposits like lignite tar. Benzothiophene has no household utilization. This is primarily used in industry and research.

Being a heterocyclic compound, benzothiophene finds utilization in research as a starting material for the synthesis of larger, generally bioactive structures. This is found in the chemical structures of pharmaceutical drugs like zileuton, raloxifene and sertaconazole, and as well BTCP. It is as well employed in the preparation of dyes like thioindigo.

Its aromaticity makes it comparatively stable, however as a heterocycle, it consists of reactive sites that allow for functionalization.

IUPAC name: Benzo[b]thiophene

Other names: 1-Benzothiophene




Chemical formula:   C8H6S

Molar mass:            134.20 g·mol-1

Appearance:           White solid

Density:                  1.15 g/cm3

Melting point:          32 °C (90 °F; 305 K)

Boiling point:           221 °C (430 °F; 494 K)

Introduction to Indoles:

Indole is basically the aromatic heterocyclic organic compound. It consists of a bicyclic structure, comprising of a six-membered benzene ring fused to a five-membered nitrogen-having pyrrole ring. Indole is broadly distributed in the natural environment and can be prepared by a variety of bacteria. As an intercellular signal molecule, indole regulates different features of bacterial physiology, comprising spore formation, resistance to drugs, plasmid stability, biofilm formation and virulence. The amino acid tryptophan is an indole derivative and the precursor of the neurotransmitter serotonin.

The indole is an organic heterocyclic compound having a bicyclic structure having a nitrogen-comprised pyrrole ring fused to a benzene ring; any product that includes these indolic structures is considered an indole. The compound is aromatic and solid at room temperature, and it consists of most of the applications in the fragrance industry, and increasingly, the pharmaceutical industry. Indoles are mainly produced in the human body as a byproduct of the degradation method of the amino acid, tryptophan. It is processed and generally found to accumulate in human feces and at high concentrations; Indoles have a strong, unpleasant fecal odor. Surprisingly, at extremely low concentrations, they encompass a pleasant, flowery smell and are often employed as a constituent in flower scents, such as orange blossom.

Indoles are significant precursors for other substances made in the human body and are, thus, researched and employed in lifestyle and medical applications. The compound was officially discovered in the year 1866 by a scientist working with the properties of zinc dust who reduced oxindole from the zinc dust to an indole. After the discovery, Indoles became significant constituents of the textile industry, and as more research was conducted, the larger role which Indoles played in the human body system was realized. The indolic nucleus in substances such as tryptophan and auxin has led to a better comprehending of their method in the body.

The complex chemical structure of Indoles make them stabilizing to protein structure. Any structure which comprises the compound or its derivative can assist an enzyme or protein form into its correct structure or even help to correct the structure. One of the proposed techniques of this action is that Indoles readily form hydrogen bonds that are necessary for protein formation. Proteins that have the rings related by indolic structure stand up to heat and chemical manipulation better than proteins devoid of the rings. Most of the Indoles which are harvested nowadays come from coal tar, where it is found in one of its most stable states.

Indole alkaloids are the group of specific chemicals which are found in numerous plants around the world comprising snakeroot and periwinkle. One indole derivative, indole-3-carbinol, is found richly in cruciferous vegetables such as broccoli, cauliflower and cabbage. The properties of this indole derivative are anti-carcinogenic, antioxidant and anti-artherogenic. Such effects have been well-proven in randomized controlled studies. More research will reveal numerous applications that this derivative and others similar to it will encompass in the treatment of lifestyle diseases.

General properties and occurrence of Indoles:

Indole is basically solid at room temperature. Indole can be prepared by bacteria as a degradation product of the amino acid tryptophan. It takes place naturally in human feces and consists of an intense fecal odor. At extremely low concentrations, though, it consists of a flowery smell and is a constituent of numerous flower scents (like orange blossoms) and perfumes. It as well takes place in coal tar.

The corresponding substituent is known as indolyl.

Indole experience electrophilic substitution, mostly at position 3. Substituted Indoles are structural elements of (and for several compounds the synthetic precursors for) the tryptophan-derived tryptamine alkaloids such as the neurotransmitter serotonin and melatonin. The other indolic compounds comprise the plant hormone auxin (that is, indolyl-3-acetic acid, IAA), tryptophol, the anti-inflammatory drug indomethacin, the betablocker pindolol and the naturally occurring hallucinogen dimethyltryptamine.

The term indole is a portmanteau of the words indigo and oleum, as indole was first isolated via treatment of the indigo dye by oleum.

History of Indole:

Indole chemistry began to develop with the study of the dye indigo. Indigo can be transformed to isatin and then to oxindole. Then, in the year 1866, Adolf von Baeyer reduced oxindole to indole by using zinc dust. In the year 1869, he stated a formula for indole.

Some indole derivatives were significant dyestuffs until the end of the 19th century. In the year 1930, interest in indole intensified whenever it became known that the indole nucleus is present in numerous significant alkaloids, and also in tryptophan and auxins, and it remains an active area of research nowadays.

Occurrence of indole in nature:

Indole is biosynthesized by anthranilate. It condenses by serine by Michael addition of indole to PLP-aminoacrylate.

Indole is a main constituent of coal-tar, and the 220 to 260 °C distillation fraction is the most important industrial source of the material.

Applications of Indole:

Natural jasmine oil, utilized in the perfume industry, includes around 2.5% of indole. As 1 kilogram of the natural oil needs processing several million jasmine blossoms and costs around $10,000, indole (among other things) is utilized in the preparation of synthetic jasmine oil (that costs around $10/kg).

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