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2,3-BENZOPYRROLE

2,3-Benzopyrrole is a bicyclic aromatic heterocyclic compound with the molecular formula C₈H₇N, consisting of a six-membered benzene ring fused to a five-membered nitrogen-containing pyrrole ring.
From a biological perspective, 2,3-Benzopyrrole serves as a crucial structural scaffold in numerous natural products and biomolecules, most notably the amino acid tryptophan, which makes it indispensable for protein biosynthesis and as a precursor of serotonin, melatonin, and niacin.
2,3-Benzopyrrole’s presence in everyday life—from the fragrances of flowers and perfumes to essential biomolecules in the human body and valuable pharmaceuticals—illustrates its unique ability to bridge natural and synthetic chemistry.

CAS Number: 120-72-9
EC Number: 204-420-7
Molecular Formula: C8H7N
Molar Mass: 117.15 g/mol

Synonyms: Indole, 2,3-Benzopyrrole, 1H‑Indole, 2,3‑Benzopyrrole, Benzopyrrole, Ketole, 1‑Benzazole, 1H‑Indol, Indol, 1‑Benzo[b]pyrrole, 1H-Indole, 2,3-Benzopyrrole, ketole, 1-benzazole, indole, 1H-Indole, 120-72-9, 2,3-Benzopyrrole, Indol, 1-Benzazole, Ketole, 1-Azaindene, 2,3-Benzopyrole, Indole (natural), Caswell No. 498B, 1-Benzo(b)pyrrole, FEMA No. 2593, CCRIS 4421, HSDB 599, EPA Pesticide Chemical Code 025000, AI3-01540, NSC 1964, EINECS 204-420-7, UNII-8724FJW4M5, INDOOLUM, DTXSID0020737, CHEBI:16881, 8724FJW4M5, NSC-1964, DTXCID40737, INDOLE (USP-RS), INDOLE [USP-RS], Indole, 3-Benzopyrrole, 1-benzazole, 204-420-7, Benzopyrrole, Indol [German], 1H-Benzo[b]pyrrole, MFCD00005607, Benzo[b]pyrrole, CHEMBL15844, Indole 100 microg/mL in Acetonitrile, NCGC00167539-01, IND, benzazole, CAS-120-72-9, mono-indole, 1-H-indole, Indole, 7, Indole (8CI), 1H-Indole (9CI), INDOLUM [HPUS], INDOLE [FHFI], INDOLE [HSDB], INDOLE [FCC], INDOLE [MI], Indole, >=99%, SCHEMBL698, bmse000097, Indole, analytical standard, SCHEMBL1188, SCHEMBL1538, Indole, >=99%, FG, SCHEMBL20275, SCHEMBL23200, SCHEMBL23314, SCHEMBL23566, SCHEMBL25894, WLN: T56 BMJ, BIDD:GT0304, SCHEMBL448936, SCHEMBL449240, SCHEMBL449275, SCHEMBL449872, SCHEMBL449943, SCHEMBL450257, SCHEMBL450679, SCHEMBL451288, SCHEMBL451350, SCHEMBL451368, SCHEMBL451603, SCHEMBL451836, SCHEMBL451879, SCHEMBL451985, SCHEMBL452761, SCHEMBL453718, SCHEMBL453859, SCHEMBL454496, SCHEMBL454533, SCHEMBL454580, SCHEMBL454701, INDOLE BENZO-PYRROLE, SCHEMBL8316256, SCHEMBL16861354, NSC1964, 185l, HMS5086O16, BCP27232, STR01201, Tox21_112536, Tox21_201677, Tox21_302937, BBL011739, BDBM50094702, s6358, SBB055980, STL163380, AKOS000119629, Tox21_112536_1, AT36838, CG-0501, CS-W001132, DB04532, HY-W001132, Indole, puriss., >=98.5% (GC), NCGC00167539-02, NCGC00167539-03, NCGC00256348-01, NCGC00259226-01, BP-10563, DS-011308, I0021, NS00010849, ST51046571, EN300-18285, C00463, SBI-0653862.0001, Q319541, SR-01000944736, SR-01000944736-1, Z57833933, F2190-0647, InChI=1/C8H7N/c1-2-4-8-7(3-1)5-6-9-8/h1-6,9, 82451-55-6, 1H-Indole, Ketole, 1-Azaindene, 1-Benzazole, 2,3-Benzopyrrole, Benzopyrrole, Indol, 1-H-indol

2,3-Benzopyrrole is a bicyclic aromatic heterocyclic compound with the molecular formula C₈H₇N, consisting of a six-membered benzene ring fused to a five-membered nitrogen-containing pyrrole ring.
2,3-Benzopyrrole is a colorless to pale yellow crystalline solid with a characteristic strong odor, found naturally in coal tar, fecal matter, and various plants, especially in jasmine and orange blossoms, where it contributes to floral fragrance.

2,3-Benzopyrrole is an essential structural motif in many natural products, including the amino acid tryptophan, plant hormones such as auxins, and alkaloids with pharmacological activity.
2,3-Benzopyrrole’s chemical versatility makes it an important building block in organic synthesis, widely used in the production of dyes, fragrances, pharmaceuticals, and agrochemicals.
2,3-Benzopyrrole’s biological significance, combined with its chemical reactivity, ensures its prominence in both natural biochemistry and industrial chemistry.

2,3-Benzopyrrole is a foundational aromatic compound used extensively in perfumery, biochemical synthesis, and industrial chemistry.
While naturally occurring and valuable in complex molecules, 2,3-Benzopyrrole requires cautious handling due to toxicological and environmental considerations.

2,3-Benzopyrrole is an organic compound with the formula C6H4CCNH3.
2,3-Benzopyrrole is classified as an aromatic heterocycle.

2,3-Benzopyrrole has a bicyclic structure, consisting of a six-membered benzene ring fused to a five-membered pyrrole ring.
2,3-Benzopyrroles are derivatives of 2,3-Benzopyrrole where one or more of the hydrogen atoms have been replaced by substituent groups.

2,3-Benzopyrroles are widely distributed in nature, most notably as amino acid tryptophan and neurotransmitter serotonin.
When 2,3-Benzopyrrole is a substituent on a larger molecule, it is called an indolyl group by systematic nomenclature.

2,3-Benzopyrrole undergoes electrophilic substitution, mainly at position 3.
Substituted 2,3-Benzopyrroles are structural elements of (and for some compounds, the synthetic precursors for) the tryptophan-derived tryptamine alkaloids, which includes the neurotransmitter serotonin and the hormone melatonin, as well as the naturally occurring psychedelic drugs dimethyltryptamine and psilocybin.

Other indolic compounds include the plant hormone auxin (indolyl-3-acetic acid, IAA), tryptophol, the anti-inflammatory drug indomethacin, and the betablocker pindolol.
The name 2,3-Benzopyrrole is a portmanteau of the words indigo and oleum, since 2,3-Benzopyrrole was first isolated by treatment of the indigo dye with oleum.

2,3-Benzopyrrole, a heterocyclic organic compound occurring in some flower oils, such as jasmine and orange blossom, in coal tar, and in fecal matter.
2,3-Benzopyrrole is a naturally occurring compound composed of a six-membered benzene ring fused to a five-membered pyrrole ring.

This structure makes 2,3-Benzopyrrole an important building block for many other compounds.
2,3-Benzopyrrole’s molecular formula is C8H7N, which signifies that 2,3-Benzopyrrole is made up of eight carbon atoms, seven hydrogen atoms, and one nitrogen atom.

This unique molecular structure allows 2,3-Benzopyrrole to exhibit both aromatic and basic properties, making it highly reactive and versatile in chemical reactions.
2,3-Benzopyrrole is found in many natural sources, including plant and animal products.

2,3-Benzopyrrole is a critical intermediate in the synthesis of tryptophan, an essential amino acid found in most organisms.
2,3-Benzopyrrole also serves as a precursor for the biosynthesis of 2,3-Benzopyrrole-3-acetic acid (IAA), which is a major plant hormone responsible for regulating growth and development.

2,3-Benzopyrrole is a bicyclic aromatic heteroaromatic organic compound with the molecular formula C₈H₇N, formed by the fusion of a six-membered benzene ring with a five-membered pyrrole ring containing one nitrogen atom.
2,3-Benzopyrrole crystallizes as colorless to pale yellow solids and possesses a strong, distinctive odor that can range from fecal-like in concentrated form to pleasant floral notes when diluted, which explains its presence in both unpleasant and desirable natural aromas.
2,3-Benzopyrrole was first isolated from coal tar in the 19th century and later recognized as a widespread natural compound occurring in animal feces (as a breakdown product of the amino acid tryptophan), in bacterial metabolism, and in a wide variety of plants and flowers, including jasmine, orange blossoms, and gardenia, where it contributes to characteristic floral scents.

From a biological perspective, 2,3-Benzopyrrole serves as a crucial structural scaffold in numerous natural products and biomolecules.
Most notably, the essential amino acid tryptophan contains an 2,3-Benzopyrrole ring, making it indispensable for protein biosynthesis and as a precursor for important biomolecules such as serotonin, melatonin, and niacin.

2,3-Benzopyrrole derivatives also play roles as plant growth regulators (e.g., 2,3-Benzopyrrole-3-acetic acid, a key auxin) and as alkaloids with diverse pharmacological activities.
Because of its biological ubiquity, 2,3-Benzopyrrole is often described as a "privileged structure" in medicinal chemistry, meaning small modifications on the 2,3-Benzopyrrole skeleton can lead to compounds with wide-ranging biological properties, including antimicrobial, anticancer, anti-inflammatory, and neuroactive effects.

Industrially, 2,3-Benzopyrrole is produced both from natural sources and via synthetic methods such as the Fischer 2,3-Benzopyrrole synthesis, which remains one of the most important reactions for constructing the 2,3-Benzopyrrole framework.
2,3-Benzopyrrole’s applications span multiple sectors: in perfumery and flavor industries, 2,3-Benzopyrrole is used at low concentrations to add depth, warmth, and floral richness to fragrances; in dye chemistry, it serves as a precursor to indigo and related pigments; and in pharmaceuticals and agrochemicals, 2,3-Benzopyrrole derivatives are central in the development of drugs, fungicides, herbicides, and insecticides.

The chemical stability of 2,3-Benzopyrrole arises from its aromaticity, but it also demonstrates rich reactivity due to the electron-donating nature of the nitrogen atom in the pyrrole ring, making it susceptible to electrophilic substitution, especially at the C-3 position.
This dual nature—aromatic stability with selective reactivity—makes 2,3-Benzopyrrole a versatile intermediate in organic chemistry.

In summary, 2,3-Benzopyrrole stands out as a compound of profound chemical and biological importance.
2,3-Benzopyrrole’s presence in everyday life—from the fragrances of flowers and perfumes to essential biomolecules in the human body and valuable pharmaceuticals—illustrates its unique ability to bridge natural and synthetic chemistry.

Market Overview of 2,3-Benzopyrrole:
2,3-Benzopyrrole is a bicyclic aromatic heteroaromatic organic compound with the molecular formula C₈H₇N, formed by the fusion of a six-membered benzene ring with a five-membered pyrrole ring containing one nitrogen atom.
2,3-Benzopyrrole crystallizes as colorless to pale yellow solids and possesses a strong, distinctive odor that can range from fecal-like in concentrated form to pleasant floral notes when diluted, which explains its presence in both unpleasant and desirable natural aromas.
2,3-Benzopyrrole was first isolated from coal tar in the 19th century and later recognized as a widespread natural compound occurring in animal feces (as a breakdown product of the amino acid tryptophan), in bacterial metabolism, and in a wide variety of plants and flowers, including jasmine, orange blossoms, and gardenia, where it contributes to characteristic floral scents.

Uses of 2,3-Benzopyrrole:
2,3-Benzopyrrole has wide-ranging applications across pharmaceuticals, fragrances, agrochemicals, dyes, and chemical synthesis.
In medicine, 2,3-Benzopyrrole is regarded as a “privileged structure,” forming the basis of numerous therapeutic agents, including anti-inflammatory, anticancer, antimicrobial, and neuroactive drugs, while also serving as the core unit of the amino acid tryptophan, the precursor to serotonin, melatonin, and niacin.

In the fragrance industry, despite its unpleasant odor in pure form, 2,3-Benzopyrrole is prized at low concentrations for imparting warm, floral, and musky notes to perfumes, particularly in jasmine, gardenia, and orange blossom compositions, while also contributing subtle flavor tones in food products.
In agriculture, 2,3-Benzopyrrole derivatives such as 2,3-Benzopyrrole-3-acetic acid (IAA) function as essential plant growth regulators, and other derivatives are employed in herbicides, fungicides, and insecticides to improve crop yields.
Additionally, 2,3-Benzopyrrole is a key intermediate in dye production, especially in the synthesis of indigo, one of the most important textile dyes, and it plays a crucial role in organic chemistry as a versatile building block for heterocycles and specialty chemicals.

2,3-Benzopyrrole is used in perfumery and in making tryptophan, an essential amino acid, and 2,3-Benzopyrroleacetic acid (heteroauxin), a hormone that promotes the development of roots in plant cuttings.

2,3-Benzopyrrole is used in Microorganisms:
Many microorganisms, particularly bacteria, produce 2,3-Benzopyrrole as a secondary metabolite.
2,3-Benzopyrrole plays a role in cell-to-cell communication, a process known as quorum sensing.

Through quorum sensing, bacteria can coordinate behaviors such as biofilm formation and antibiotic resistance in response to environmental changes or the presence of other microorganisms.

Pharmaceutical Industry uses:
One of the primary uses of 2,3-Benzopyrrole in industry is in the production of pharmaceuticals.
2,3-Benzopyrrole's structure serves as the backbone for a variety of biologically active compounds, including serotonergic drugs.

Serotonin, as mentioned, is derived from 2,3-Benzopyrrole, and many drugs used to treat depression, anxiety, and other mood disorders work by targeting the serotonin system.
These include selective serotonin reuptake inhibitors (SSRIs), such as fluoxetine (Prozac), which are widely prescribed in psychiatric medicine.

2,3-Benzopyrrole derivatives are also used in the development of antibiotics, anticancer agents, and anti-inflammatory drugs.
Researchers are continuously exploring new ways to modify the 2,3-Benzopyrrole structure to create novel compounds that could treat a wide range of diseases, from infections to chronic conditions.

Fragrance and Flavor Industry uses:
2,3-Benzopyrrole's distinct musky odor has long made it a desirable compound in the fragrance industry.
Despite 2,3-Benzopyrrole’s somewhat unpleasant smell at high concentrations, 2,3-Benzopyrrole has a valuable role in creating complex fragrance profiles.
At lower concentrations, 2,3-Benzopyrrole is used in perfumes and scents to add depth and richness, often contributing to floral and woody notes.

In addition to fragrances, 2,3-Benzopyrrole derivatives are also used in the food industry to produce certain flavor compounds.
These compounds, derived from the basic 2,3-Benzopyrrole structure, help create rich, savory, and unique flavors in processed foods.

Agriculture and Plant Science uses:
2,3-Benzopyrrole-based compounds have wide applications in agriculture.
For instance, 2,3-Benzopyrrole-3-acetic acid, as a plant growth regulator, is used to stimulate root development, especially in agricultural practices such as plant propagation and hydroponics.

The synthetic application of 2,3-Benzopyrrole derivatives enhances plant growth, yields, and resistance to diseases, providing an essential tool for modern farming.

Researchers are also looking into 2,3-Benzopyrrole's potential to promote sustainable agriculture.
By improving the efficiency of water and nutrient uptake in crops, 2,3-Benzopyrrole derivatives may help reduce the need for chemical fertilizers and pesticides, supporting eco-friendly farming practices.

Environmental and Industrial Applications:
2,3-Benzopyrrole and its derivatives are also explored for their potential use in biodegradable plastics and environmental cleanup technologies.
As part of the growing emphasis on green chemistry, 2,3-Benzopyrrole-based compounds offer a way to develop eco-friendly materials that break down more easily in nature.
This has significant implications for reducing plastic waste and improving sustainability across industries.

Medical applications:
2,3-Benzopyrroles and their derivatives are promising against tuberculosis, malaria, diabetes, cancer, migraines, convulsions, hypertension, bacterial infections of methicillin-resistant Staphylococcus aureus (MRSA) and even viruses.

Pharmaceuticals and Medicine:
2,3-Benzopyrrole is a privileged structural scaffold in medicinal chemistry, meaning small modifications to its structure can yield biologically active compounds across many therapeutic areas.
2,3-Benzopyrrole is the core unit in the essential amino acid tryptophan, which is a precursor for serotonin, melatonin, and niacin.

2,3-Benzopyrrole derivatives are widely used in drugs with anticancer, antimicrobial, antiviral, anti-inflammatory, analgesic, antihypertensive, and neuroactive properties.
Examples include indomethacin (an NSAID), vincristine and vinblastine (anticancer alkaloids), and sumatriptan (anti-migraine).

Fragrances and Flavors
In the fragrance industry, 2,3-Benzopyrrole plays a paradoxical role: while pure 2,3-Benzopyrrole has a fecal-like odor, trace amounts provide warm, floral, and animalic notes that enhance complexity in perfumes.
2,3-Benzopyrrole is especially important in jasmine, gardenia, and orange blossom fragrance compositions.
2,3-Benzopyrrole derivatives are also used as flavoring agents to impart subtle cocoa, nutty, or floral notes in food and beverages.

Agrochemicals:
2,3-Benzopyrrole derivatives such as 2,3-Benzopyrrole-3-acetic acid (IAA) are crucial plant growth regulators (auxins), stimulating root initiation and plant development.
2,3-Benzopyrrole is also used in the synthesis of herbicides, fungicides, and insecticides, helping improve crop yields and protect plants against disease.

Dyes and Pigments:
2,3-Benzopyrrole is an important intermediate in the production of indigo dye, historically significant and still one of the most widely used dyes in the textile industry.
2,3-Benzopyrrole also contributes to the manufacture of other specialty pigments.

Chemical Research and Synthesis:
Due to its electron-rich nitrogen and aromatic character, 2,3-Benzopyrrole is a key building block in organic synthesis.
2,3-Benzopyrrole serves as a starting material or intermediate for a wide range of specialty chemicals, including heterocyclic compounds with industrial and biological relevance.

SYNTHETIC APPLICATION OF GRAMINE OF 2,3-Benzopyrrole:
Gramine and, especially, 2,3-Benzopyrrole's quaternary salts are useful synthetic intermediates as they are easily prepared and the dimethylamino group is easily displaced by nucleophiles for example – reactions with cyanide and acetamidomalonate anions.
The electron donating power of is never better demonstrated than in case of mannich bases.

For the removal of dimethylamino group, normal mannich bases require alkylation to convert them to its quaternary salts before elimination by heating.

However, in case of 2,3-Benzopyrrole derived mannich bases no alkylation is needed and nitrogen of 2,3-Benzopyrrole itself can expel the Me2N group in presence of CN ions.
The reaction is slow but gives high yield.

Biosynthesis and Function of 2,3-Benzopyrrole:
2,3-Benzopyrrole is biosynthesized in the shikimate pathway via anthranilate.
2,3-Benzopyrrole is an intermediate in the biosynthesis of tryptophan, where it stays inside the tryptophan synthase molecule between the removal of 3-phospho-glyceraldehyde and the condensation with serine.

When 2,3-Benzopyrrole is needed in the cell, it is usually produced from tryptophan by tryptophanase.
As an intercellular signal molecule, 2,3-Benzopyrrole regulates various aspects of bacterial physiology, including spore formation, plasmid stability, resistance to drugs, biofilm formation, and virulence.
A number of 2,3-Benzopyrrole derivatives have important cellular functions, including neurotransmitters such as serotonin.

Chemical Reactions of 2,3-Benzopyrrole:

Basicity:
Unlike most amines, 2,3-Benzopyrrole is not basic: just like pyrrole, the aromatic character of the ring means that the lone pair of electrons on the nitrogen atom is not available for protonation.

Strong acids such as hydrochloric acid can, however, protonate 2,3-Benzopyrrole.
2,3-Benzopyrrole is primarily protonated at the C3, rather than N1, owing to the enamine-like reactivity of the portion of the molecule located outside of the benzene ring.

The protonated form has a pKa of −3.6.
The sensitivity of many indolic compounds (e.g., tryptamines) under acidic conditions is caused by this protonation.

Electrophilic substitution:
The most reactive position on 2,3-Benzopyrrole for electrophilic aromatic substitution is C3, which is 10¹³ times more reactive than benzene.
For example, 2,3-Benzopyrrole is alkylated by phosphorylated serine in the biosynthesis of the amino acid tryptophan.
Vilsmeier–Haack formylation of 2,3-Benzopyrrole will take place at room temperature exclusively at C3.

The Vilsmeyer–Haack formylation of 2,3-Benzopyrrole:
Since the pyrrolic ring is the most reactive portion of 2,3-Benzopyrrole, electrophilic substitution of the carbocyclic (benzene) ring generally takes place only after N1, C2, and C3 are substituted.

A noteworthy exception occurs when electrophilic substitution is carried out in conditions sufficiently acidic to exhaustively protonate C3.
In this case, C5 is the most common site of electrophilic attack.

Gramine, a useful synthetic intermediate, is produced via a Mannich reaction of 2,3-Benzopyrrole with dimethylamine and formaldehyde.
2,3-Benzopyrrole is the precursor to 2,3-Benzopyrrole-3-acetic acid and synthetic tryptophan.

Reactions of 2,3-Benzopyrrole:

Reaction with carbene:
Halocarbenes react with 2,3-Benzopyrrole to add onto 2,3 C-C double bond to give a mixture of two products as given below.

Oxidation Reaction:
C2-C3 double bond of 2,3-Benzopyrrole is oxidatively cleaved by the use of reagents such as ozone, sodium periodate, potassium superoxide or CuCl2 in O2 atmosphere.

Reduction Reaction:
The 2,3-Benzopyrrole ring can be reduced selectively in carbocyclic or the heterocyclic ring.
Nucleophilic reducing agents such as LiAlH4 or NaBH4 does not affect 2,3-Benzopyrrole nucleus.

However, lithium/liquid ammonia reduces the benzene ring to 4,7-dihydro2,3-Benzopyrrole as major product.
The heterocyclic ring can be reduced in acidic reagents such as Zn/HCl or NaCNBH3/CH3COOH to give indoline.

Reaction of N-metallated 2,3-Benzopyrroles:
In presence of very strong bases, 2,3-Benzopyrroles behave as weak acid, thus.
2,3-Benzopyrrole can be deprotonated with strong bases to obtain its N-metallated derivatives.

N-metallated 2,3-Benzopyrroles are nucleophiles that can react with suitable electrophiles either at N or at C-3.
These N-sodio derivatives can be prepared by reaction with sodamide in liquid ammonia, or by the use of sodium hydride in organic solvent.

Salts of other metals can be prepared by using various bases such as potassium t-butoxide, Grignard reagent or butyl lithium.
The more ionic sodium and potassium salts tend to react at N, especially with hard electrophiles.
In contrast to 1-indolyl magnesium halides are alkylated and acylated at C-3.

Reaction of C-metallated 2,3-Benzopyrroles:
C-Metallation of 2,3-Benzopyrroles can be brought about only in absence of the much more acidic N-hydrogen.
N-hydrogen can be removed by the N-substitution of 2,3-Benzopyrrole with methyl, ethyl etc. or by the use of a protecting group such as phenylsulfonyl, lithium carboxylate and tbutoxycarbonyl, that can be easily removed after the desired product formation.

Each of these removable substituents assists lithiation at C-2 position of 2,3-Benzopyrrole by intramolecular chelation.
This way obtained lithiated 2,3-Benzopyrroles can be converted into 2-substituted 2,3-Benzopyrroles by reaction with appropriate electrophiles.

CO2 is one of the most convenient N-protecting groups in 2,3-Benzopyrrole α-lithiations because the N-protecting group is installed in situ and, further, falls off during normal work-up.
This technique has been used to prepared 2-halo-2,3-Benzopyrroles and to introduce a variety of substituents by reaction with appropriate electrophiles – aldehydes, ketones, chloroformates, etc.

Production of 2,3-Benzopyrrole:
2,3-Benzopyrrole can be obtained both from natural sources and through synthetic methods, with industrial production relying primarily on chemical synthesis for efficiency and scalability.
Historically, 2,3-Benzopyrrole was first isolated from coal tar, and coal tar distillation remains a minor natural source, although it is not the main commercial route today due to limited yields and environmental concerns.

In modern industry, the most important method is the Fischer 2,3-Benzopyrrole synthesis, which involves the acid-catalyzed rearrangement of aryl hydrazones (derived from aryl hydrazines and aldehydes or ketones) into 2,3-Benzopyrrole derivatives; this reaction is still considered the cornerstone of 2,3-Benzopyrrole production because of its versatility and relatively high yields.
Other laboratory and industrial-scale methods include the Bartoli reaction (reaction of nitroarenes with vinyl Grignard reagents), the Leimgruber–Batcho synthesis (a cost-effective, high-yield route using nitrotoluenes), and transition-metal catalyzed cyclization reactions that allow access to functionalized 2,3-Benzopyrroles.

In the fragrance industry, small amounts of 2,3-Benzopyrrole are also isolated from natural floral oils such as jasmine and orange blossom, though extraction is costly and typically reserved for high-end perfumes.
With the growing pharmaceutical demand, synthetic routes are continuously being optimized to improve atom economy, scalability, and environmental sustainability, ensuring that 2,3-Benzopyrrole remains readily available for diverse industrial applications.

History of 2,3-Benzopyrrole:
2,3-Benzopyrrole was first identified in the mid-19th century during studies on coal tar, one of the richest natural sources of aromatic compounds.
2,3-Benzopyrrole was named in 1869 by the German chemist Adolf von Baeyer, combining the terms indigo and oleum, because it was originally obtained through the destructive distillation of indigo dye in sulfuric acid.

This connection to indigo was historically significant, as 2,3-Benzopyrrole chemistry soon became closely tied to the large-scale production of dyes in the textile industry.
In the late 19th and early 20th centuries, chemists began to recognize 2,3-Benzopyrrole not only as a component of coal tar but also as a naturally occurring substance in plants and animals.

2,3-Benzopyrrole’s presence in the amino acid tryptophan, discovered around the same time, revealed its biological importance, linking 2,3-Benzopyrrole to essential metabolic pathways and neurotransmitters such as serotonin.
Throughout the 20th century, synthetic methods such as the Fischer 2,3-Benzopyrrole synthesis (discovered by Emil Fischer in 1883) revolutionized the accessibility of 2,3-Benzopyrrole and its derivatives, enabling large-scale pharmaceutical and industrial applications.

Over time, 2,3-Benzopyrrole shifted from being a curiosity of coal tar chemistry to a central structure in organic, medicinal, and agricultural chemistry, underpinning discoveries in drug development, plant growth regulation, and fragrance chemistry.
Today, 2,3-Benzopyrrole’s history reflects its transformation from a dye-related byproduct into one of the most versatile and valuable heterocyclic compounds in science and industry.

Handling and Storage of 2,3-Benzopyrrole:
2,3-Benzopyrrole should be handled in well-ventilated areas, away from sources of ignition, heat, and strong oxidizing agents.
Direct skin or eye contact and inhalation of vapors should be avoided.

Use only in closed systems or under fume hoods.
For storage, 2,3-Benzopyrrole must be kept in tightly sealed containers, in a cool, dry, and well-ventilated place, protected from light and moisture.

Recommended storage temperature is below room temperature to prevent decomposition and odor intensification.
Containers should be clearly labeled and kept away from incompatible chemicals.

Stability and Reactivity of 2,3-Benzopyrrole:
2,3-Benzopyrrole is relatively stable under normal storage and handling conditions, but it is sensitive to light, air, and prolonged exposure to elevated temperatures.
2,3-Benzopyrrole may undergo oxidation, leading to discoloration or degradation.

2,3-Benzopyrrole reacts with strong oxidizing agents, strong acids, and strong bases.
When heated to decomposition, 2,3-Benzopyrrole may release hazardous fumes including nitrogen oxides (NOₓ) and carbon oxides (CO, CO₂).

First Aid Measures of 2,3-Benzopyrrole:

Inhalation:
Remove the affected person to fresh air.
If breathing is difficult, administer oxygen.
Seek medical attention if symptoms persist.

Skin contact:
Wash the affected area immediately with plenty of water and soap.
Remove contaminated clothing.
Seek medical advice if irritation develops.

Eye contact:
Rinse cautiously with water for several minutes.
Remove contact lenses if present and easy to do.
Continue rinsing and seek medical attention.

Ingestion:
Rinse mouth thoroughly with water.
Do not induce vomiting unless directed by medical personnel.
Seek immediate medical assistance.

Firefighting Measures of 2,3-Benzopyrrole:
2,3-Benzopyrrole is combustible though not highly flammable.
In case of fire, use dry chemical, carbon dioxide (CO₂), alcohol-resistant foam, or water spray.

Avoid direct water jets, which may spread the material.
Firefighters should wear self-contained breathing apparatus (SCBA) and full protective gear to prevent exposure to hazardous decomposition products such as nitrogen oxides and carbon oxides.
Containers exposed to fire should be cooled with water spray.

Accidental Release Measures of 2,3-Benzopyrrole:
In case of a spill or leak, evacuate unnecessary personnel and ensure adequate ventilation.
Wear appropriate personal protective equipment (PPE).

Avoid release into drains or waterways.
Small spills should be absorbed with inert materials (sand, vermiculite, or diatomaceous earth) and placed in suitable waste containers for disposal.

Large spills should be contained and collected mechanically if possible.
Contaminated surfaces should be washed with water and detergent.

Exposure Controls / Personal Protective Equipment of 2,3-Benzopyrrole:

Engineering controls:
Use in fume hoods or well-ventilated environments to minimize exposure.

Respiratory protection:
If exposure limits are exceeded or ventilation is inadequate, wear an approved respirator suitable for organic vapors.

Skin protection:
Wear protective gloves (nitrile, neoprene) and long-sleeved protective clothing.

Eye protection:
Use safety goggles or face shields to prevent eye contact.

Hygiene measures:
Wash hands, face, and any exposed skin thoroughly after handling.
Do not eat, drink, or smoke while handling the material.

Identifiers of 2,3-Benzopyrrole:
IUPAC Name: 1H-2,3-Benzopyrrole
Common Name: 2,3-Benzopyrrole
CAS Number: 120-72-9
EC Number (EINECS): 204-420-7
PubChem CID: 798
ChemSpider ID: 776
Molecular Formula: C₈H₇N
Molecular Weight: 117.15 g/mol
InChI: InChI=1S/C8H7N/c1-2-6-8-7(5-9-8)3-4-6/h2-5,9H,1H2
InChI Key: SORQZNGVMJJTQQ-UHFFFAOYSA-N
SMILES: c1ccc2c(c1)c[nH]c2

CAS Number: 120-72-9
EC Number: 204-420-7
Hill Formula: C₈H₇N
Molar Mass: 117.15 g/mol
MDL Number: MFCD00005607
UNSPSC Code: 12352005
HS Code: 2933 99 20

IUPAC Name: 1H-2,3-Benzopyrrole
CAS Number: 120-72-9
EC Number (EINECS): 204-420-7
RTECS Number: NL3675000
PubChem CID: 798
ChemSpider ID: 776
ChEBI ID: 16881
UNII (FDA Unique Ingredient Identifier): 8YH59F81YN
Beilstein Registry Number: 103670
Merck Index: 12, 4914
HS Code (Customs Tariff): 2933.99
Chemical Formula: C₈H₇N
Molecular Weight: 117.15 g/mol
InChI: InChI=1S/C8H7N/c1-2-6-8-7(5-9-8)3-4-6/h2-5,9H,1H2
InChI Key: SORQZNGVMJJTQQ-UHFFFAOYSA-N
SMILES (Canonical): C1=CC=C2C(=C1)C=CN2
SMILES (Isomeric): c1ccc2c(c1)c[nH]c2

Properties of 2,3-Benzopyrrole:
Molecular Formula: C₈H₇N
Molecular Weight: 117.15 g/mol
Appearance: Colorless to pale yellow crystalline solid; may appear as flaky crystals or powder.
Odor: Strong, penetrating odor; fecal-like at high concentration, floral and jasmine-like at very low concentrations.
Taste: Bitter, unpleasant (not intended for ingestion).

State at Room Temperature: Solid
Crystal Structure: Monoclinic
Density: ~1.22 g/cm³ at 20 °C
Melting Point: 52 – 54 °C
Boiling Point: 253 – 254 °C at 760 mmHg
Flash Point: ~121 °C (closed cup)
Autoignition Temperature: ~540 °C

Appearance: White to pale-yellow crystalline solid or flakes
Physical State: Crystalline, solid
Color: White to beige
Odor: Characteristic fecal at high concentrations; floral (jasmine-like) at trace levels
Melting Point: 52–54°C
Boiling Point: 253–254°C (1.013 hPa)
Flash Point: 121 °C (closed cup)
Density: 1.22 g/cm³ at 20°C
Bulk Density: ~230 kg/m³

Water Solubility: 0.19 g/100 mL at 20 °C; soluble in hot water
pKa: 16.2 (in water), ~21 in DMSO
Magnetic Susceptibility: –85.0×10⁻⁶ cm³/mol
Dipole Moment: 2.11 D (in benzene)
Crystal Structure: Orthorhombic Pna2₁, planar aromatic heterocycle
Vapor Pressure: 0.016 hPa at 25°C
Log P (n-octanol/water): 2.14 (literature)

Partition Coefficient: Bioaccumulation is not expected
Decomposition Temperature: > 253 °C
pH (1000 g/L in H₂O, 20 °C): 5.9

XLogP3: 2.1
Hydrogen Bond Donor Count: 1
Hydrogen Bond Acceptor Count: 0
Rotatable Bond Count: 0
Exact Mass: 117.057849228 Da
Monoisotopic Mass: 117.057849228 Da
Topological Polar Surface Area: 15.8 Å²
Heavy Atom Count: 9
Complexity: 101
Isotope Atom Count: 0
Defined Atom Stereocenter Count: 0
Undefined Atom Stereocenter Count: 0
Defined Bond Stereocenter Count: 0
Undefined Bond Stereocenter Count: 0
Covalently-Bonded Unit Count: 1
Compound Is Canonicalized: Yes