ISOQUINOLINE

Isoquinoline, also known as 2-azanaphthalene, benzo[c]pyridine, or 2-benzanine, is a structural isomer of quinoline. 
Isoquinoline has structural and spectroscopic properties similar to quinoline. 
Isoquinoline was first isolated in 1885 by Hoogewerf and van Dorp from the quinoline fraction of coal tar by fractional crystallization. 

CAS Number: 119-65-3
Molecular Formula: C9H7N
Molecular Weight: 129.16
EINECS Number: 204-341-8

Synonyms: ISOQUINOLINE, 119-65-3, 2-Benzazine, 2-Azanaphthalene, Leucoline, beta-Quinoline, Isochinolin, Benzo[c]pyridine, 3,4-Benzopyridine, Benzo(c)pyridine, FEMA No. 2978, JGX76Y85M6, DTXSID2047644, NSC-3395, DTXCID0027644, CHEBI:16092, RefChem:792283, 204-341-8, 7-methoxy-1,6-dimethylisoquinoline-5,8-dione, 2-Benzanine, .beta.-Quinoline, NSC 3395, MFCD00006898, ISQ, Isochinolin [Czech], CCRIS 5752, EINECS 204-341-8, isochinoline, isoquinolin, UNII-JGX76Y85M6, beta -quinoline, AI3-10035, 2-Azanaphthalene; 2-Benzazine; Benzo[c]pyridine; Benzopyridine; NSC 3395; ss-Quinoline, Isoquinoline, tech, Isoquinoline, 97%, Fasudil Impurity 51, Isoquinoline (Standard), ISOQUINOLINE [MI], EC 204-341-8, ISOQUINOLINE [FHFI], SCHEMBL2080, SCHEMBL9196, SCHEMBL9436, SCHEMBL9654, SCHEMBL18036, SCHEMBL18981, SCHEMBL18987, SCHEMBL18990, WLN: T66 CNJ, CHEMBL12315, SCHEMBL197701, SCHEMBL199205, SCHEMBL448776, SCHEMBL448894, SCHEMBL449142, SCHEMBL449170, SCHEMBL449251, SCHEMBL449453, SCHEMBL449540, SCHEMBL449588, SCHEMBL449810, SCHEMBL449815, SCHEMBL451583, SCHEMBL451616, SCHEMBL451935, SCHEMBL452512, SCHEMBL452611, SCHEMBL452619, SCHEMBL453578, SCHEMBL455076, SCHEMBL455250, orb3025429, orb3029577, SCHEMBL1395705, SCHEMBL7474301, SCHEMBL29355164, SCHEMBL30286035, BDBM60921, FEMA 2978, Isoquinoline, analytical standard, NSC3395, BB_SC-06613, HY-W012732R, Tox21_302503, BBL011362, EBC-48153, MSK159621, SBB060380, STL146455, AKOS000119148, CS-W013448, DB04329, FI01236, HY-W012732, PS-5337, RTE3_000001, Isoquinoline, technical grade, 90-92%, NCGC00188120-01, NCGC00256872-01, CAS-119-65-3, DB-003694, I0182, Isoquinoline(Discontinued,See C4X-136551), NS00010835, ST51046570, EN300-19121, PK04_181276, C06323, F52665, A804333, AC-907/25014235, AC-907/25014236, F227722, Q412316, F0001-0310, Z104472854, InChI=1/C9H7N/c1-2-4-9-7-10-6-5-8(9)3-1/h1-7, 2-Benzanine;Benzopyridine;beta-Quinoline;ISOQUINOLINE 99.9%;ISOQUINOLIN;ISOQUINOLINE, TECH., 90-92%;ISOQUINOLINE 97+%;Isoquinoline (6CI,8CI,9CI)

Isoquinoline is used to prepare dyes, insecticides, and antimalarial compounds, among other things.
Isoquinoline is an individual chemical specimen—a heterocyclic aromatic organic compound—as well as the name of a family of many thousands of natural plant alkaloids, any one of which might be referred to as "an isoquinoline". 
It is a structural isomer of quinoline. 

Isoquinoline and quinoline are benzopyridines, which are composed of a benzene ring fused to a pyridine ring. 
In a broader sense, the term isoquinoline is used to make reference to isoquinoline derivatives. 
Isoquinoline is the structural backbone in many naturally occurring alkaloids such as papaverine. 

The isoquinoline ring in these natural compound derives from the aromatic amino acid tyrosine.
Isoquinoline is a heterocyclic aromatic organic compound with the molecular formula C₉H₇N, structurally composed of a benzene ring fused to a pyridine ring.
It is an isomer of quinoline, differing in the position of the nitrogen atom within the bicyclic system.

Isoquinoline is typically a colorless to pale yellow liquid with a characteristic, slightly unpleasant odor.
Structurally and chemically, isoquinoline is a weak organic base due to the lone pair on the nitrogen atom in the pyridine-like ring.
This nitrogen can be protonated and can participate in coordination and substitution reactions.

The aromatic fused-ring system gives isoquinoline high thermal stability and characteristic reactivity in electrophilic and nucleophilic reactions.
Physical properties of isoquinoline include low water solubility and good miscibility with many organic solvents such as alcohols, ethers, and hydrocarbons.

Isoquinoline has a relatively high boiling point compared to simple monocyclic aromatics.
These properties make it suitable for use in organic synthesis and laboratory-scale reactions.

In organic and industrial chemistry, isoquinoline is mainly used as a chemical intermediate.
It serves as a starting material for the synthesis of pharmaceuticals, agrochemicals, dyes, and specialty heterocyclic compounds.
Many substituted isoquinoline derivatives exhibit important biological and functional properties.

In pharmaceutical research, isoquinoline is a key structural motif found in numerous natural alkaloids and synthetic drugs.
Isoquinoline-based compounds appear in antispasmodic, vasodilator, antitumor, and antimicrobial agents.
It is also used as a reference compound and impurity standard in drug development and quality control.

In coordination and catalytic chemistry, isoquinoline acts as a nitrogen-containing ligand.
It can coordinate to transition metals through the nitrogen atom, influencing catalytic activity and selectivity.
Such complexes are studied in homogeneous catalysis and organometallic chemistry.

Toxicological considerations indicate that isoquinoline can cause irritation to the skin, eyes, and respiratory tract.
Inhalation or prolonged exposure may lead to headache, dizziness, or discomfort.
Isoquinoline should therefore be handled with appropriate ventilation and personal protective equipment.

Environmental behavior suggests limited water solubility and potential toxicity to aquatic organisms at elevated concentrations.
Isoquinoline is expected to undergo biodegradation, but uncontrolled release should be avoided.
Waste handling must comply with chemical safety and environmental regulations.

Regulatory classification identifies isoquinoline as an industrial and laboratory chemical rather than a consumer substance.
Isoquinoline is listed under CAS No. 119-65-3 and appears in chemical inventories such as EINECS and toxicological databases.
Its use is generally restricted to controlled research, pharmaceutical, and industrial environments.

Isoquinoline is a bicyclic nitrogen-containing aromatic compound of high importance in chemistry.
Its structural versatility and reactivity make it valuable as a building block in synthesis and research.
However, due to its irritant properties, careful handling and regulatory compliance are essential.

Isoquinoline is a colorless hygroscopic liquid at temperatures above its melting point with a heavy sweet balsamic, herbaceous odor. 
Impure samples can appear brownish, as is typical for nitrogen heterocycles. 
Isoquinoline is a slightly stronger base than quinoline (pKa=5.14) and has a larger dipole of 2.60D.

Isoquinoline is important because this nucleus is present in a large number of alkaloids like berberine and papavarine, and is also a useful template for medicinal chemistry. 
Papaverine, an opium alkaloid, finds use as a muscle relaxant and a vasodilator. 
Antihypertensive drugs like debrisoquine, quinalapril, and quinalaprilat all contain an isoquinoline nucleus. 

Quinisocaine or dimethisoquin is a topical anesthetic, which finds use as an antipruritic. 
Isoquinoline, which is used as a topical antiseptic, is prepared by Nalkylation of isoquinoline with an appropriate allkyl halide.

Melting point: 26–28 °C (lit.)
Boiling point: 242–243 °C (lit.)
Density: 1.099 g/mL at 25 °C (lit.)
Vapor pressure: 5 Pa at 20 °C
FEMA: 2978 (ISOQUINOLINE)
Refractive index: n²⁰/D 1.623 (lit.)
Flash point: 225 °F
Storage temperature: 2–8 °C
Solubility: 5 g/L
pKa: 5.42 at 20 °C
Form: Low-melting solid
Color: Light brown
pH: 7.5 (5 g/L, H₂O, 20 °C)
Odor: At 0.10 % in triacetin; sweet, balsamic, herbal, benzaldehyde, anise
Odor type: Balsamic
Water solubility: Practically insoluble
Merck Index: 14,5222
JECFA number: 1303
BRN: 107549
Dielectric constant: 10.7 at 20 °C
InChI: 1S/C₉H₇N/c1-2-4-9-7-10-6-5-8(9)3-1/h1-7H
InChIKey: AWJUIBRHMBBTKR-UHFFFAOYSA-N
SMILES: c1ccc2cnccc2c1
LogP: 2.08
Dissociation constant: 5.19 at 25 °C

Isoquinoline is an ortho-fused heteroarene that is a benzopyridine in which the N atom not directly attached to the benzene ring. 
Isoquinoline is a mancude organic heterobicyclic parent, an azaarene, an ortho-fused heteroarene and a member of isoquinolines.
Isoquinoline is aromatic with a resonance energy of 143 kJ/ mol and is considered to be a resonance hybrid of the following contributing structures. 

Structures I, II, and II, which are of lower energy, are the major contributors to the resonance hybrid. 
Additional charged structures IV-VIII are also possible, but there is disruption of the π system of both rings in these structures.
Reaction with bases: Strong bases like Grignard reagent and organolithium tend to react like nucleophiles with isoquinoline. 

There are examples where isoquinoline has been converted into Grignard reagent by treatment with (iPr)2NMgCl, which has been shown to add to the variety of iodobenzenes.
Isoquinoline being basic reacts with acids to form salts. 
Protonation usually takes place under strong acidic conditions at position 5. 

When isoquinoline is exposed to strong acidic conditions, reduction of the benzene ring takes place.
This compound belongs to the class of organic compounds known as isoquinolines and derivatives. 
These are aromatic polycyclic compounds containing an isoquinoline moiety, which consists of a benzene ring fused to a pyridine ring and forming benzo[c]pyridine.

Isoquinoline is a bicyclic heteroaromatic compound with the molecular formula C₉H₇N, consisting of a benzene ring fused to a pyridine ring in which the nitrogen occupies the 2-position relative to the fusion.
Isoquinoline is a structural isomer of quinoline, and this positional change of the nitrogen atom leads to distinct chemical behavior and reactivity.
Isoquinoline is typically a colorless to pale yellow liquid or low-melting solid with a sharp, unpleasant odor.

From a structural and electronic standpoint, isoquinoline is aromatic and planar, with a delocalized π-electron system extending across both rings.
The nitrogen atom contributes a lone pair that is not part of the aromatic sextet, making the molecule a weak base.
This lone pair is available for protonation, coordination to metals, and participation in substitution reactions.

Chemical reactivity of isoquinoline reflects both its aromaticity and the presence of the ring nitrogen.
It undergoes electrophilic substitution reactions preferentially on the benzene ring, while nucleophilic substitution and addition reactions tend to occur near the nitrogen-containing ring under appropriate conditions.
Isoquinoline readily forms salts with acids and can be quaternized to give isoquinolinium salts.

Physical properties include low solubility in water and good solubility in most organic solvents such as ethanol, ether, chloroform, and benzene.
Isoquinoline has a relatively high boiling point compared to monocyclic aromatic heterocycles, reflecting its fused-ring structure.
These properties make it easy to handle and purify in laboratory and industrial synthesis.

In synthetic organic chemistry, isoquinoline is an important heterocyclic building block.
Isoquinoline serves as a precursor for a wide variety of substituted isoquinolines prepared through reactions such as the Pomeranz–Fritsch, Bischler–Napieralski, and Pictet–Spengler pathways.
These transformations are central to heterocyclic and medicinal chemistry.

In pharmaceutical science, the isoquinoline scaffold is found in many natural alkaloids and synthetic drug candidates.
Isoquinoline and its derivatives appear in compounds with antispasmodic, antihypertensive, anticancer, antimicrobial, and neuroactive properties.
As a result, isoquinoline is frequently used as a reference compound and impurity standard in drug discovery and quality control.

In coordination and organometallic chemistry, isoquinoline acts as a neutral nitrogen donor ligand.
Isoquinoline can bind to transition metals through its ring nitrogen, influencing electronic properties and catalytic behavior.
Such complexes are studied in homogeneous catalysis and mechanistic research.

Toxicological properties indicate that isoquinoline is an irritant.
Exposure can cause irritation to the skin, eyes, and respiratory tract, and inhalation of vapors may lead to headache or dizziness.
Although not used in consumer products, standard laboratory safety practices are required during handling.

Environmental considerations suggest limited water solubility and potential toxicity to aquatic organisms at higher concentrations.
Isoquinoline is expected to degrade biologically over time, but uncontrolled release should be avoided.
Waste disposal must follow chemical and environmental safety regulations.

Regulatory and industrial status classifies isoquinoline as a research and industrial chemical.
Isoquinoline is listed under CAS No. 119-65-3 and appears in chemical inventories, toxicological databases, and pharmacopoeial references.
Its use is generally restricted to laboratories, pharmaceutical development, and specialty chemical manufacturing.

Isoquinoline is a fundamental nitrogen-containing heteroaromatic compound with broad importance in chemistry.
Its rigid aromatic framework, basic nitrogen atom, and synthetic versatility make it indispensable in heterocyclic synthesis and medicinal chemistry.
At the same time, its irritant nature requires careful handling under controlled conditions.

Uses Of Isoquinoline:
Isoquinolines are used in the manufacture of dyes, paints, insecticides and antifungals. 
It is also used as a solvent for the extraction of resins and terpenes, and as a corrosion inhibitor.
Isoquinoline (isq) has been used: in the preparation of cis-[(dcbH2)2Ru(isq)2](ClO4)2 [dcbH2 = 4,4′-(CO2H)2-2,2′-bipyridine] to investigate the toxicity of three two-ring and five three-ring azaarenes to the green alga Scenedesmus acuminatus and its relationship with molecular structure.

Isoquinoline is primarily used as a chemical intermediate in organic synthesis, especially for the preparation of substituted isoquinolines and other heterocyclic compounds.
Isoquinoline serves as a starting material in classic heterocycle-forming reactions such as the Pomeranz–Fritsch, Bischler–Napieralski, and Pictet–Spengler syntheses.
These reactions are fundamental in academic research and industrial fine-chemical production.

In pharmaceutical and medicinal chemistry, isoquinoline is an important structural scaffold.
Many natural alkaloids (e.g., papaverine-type and benzylisoquinoline alkaloids) and synthetic drug candidates are based on the isoquinoline nucleus.
It is therefore widely used in drug discovery, lead optimization, and impurity profiling.

Isoquinoline is used as a reference standard and impurity marker in pharmaceutical quality control.
It appears as an impurity or intermediate in the synthesis of several active pharmaceutical ingredients.
Analytical laboratories use it for method development, validation, and regulatory testing.

In coordination and organometallic chemistry, isoquinoline functions as a nitrogen-donor ligand.
It coordinates to transition metals through its ring nitrogen, forming complexes studied for catalytic and mechanistic purposes.
Such complexes are relevant in homogeneous catalysis and materials research.

In dye, pigment, and specialty chemical synthesis, isoquinoline acts as a precursor to nitrogen-containing aromatic compounds.
Its rigid heteroaromatic structure is useful for producing molecules with specific electronic and optical properties.
These applications are typically limited to industrial and research settings.

Isoquinoline is also used in academic research and chemical education as a model heteroaromatic compound.
It is studied to understand aromaticity, basicity, and reactivity of fused nitrogen heterocycles.
This makes it a common reagent in advanced organic chemistry laboratories.

Overall, isoquinoline is used almost exclusively in research, pharmaceutical development, and specialty chemical manufacturing.
It is not employed in consumer products.
Its value lies in its role as a versatile heterocyclic building block rather than as an end-use material.

Isoquinoline is extensively used as a core heterocyclic building block in synthetic organic chemistry.
Its rigid bicyclic aromatic structure makes it ideal for introducing nitrogen functionality into complex molecules.
It is routinely employed in multistep syntheses in both academic and industrial laboratories.

In pharmaceutical research and development, isoquinoline serves as a parent scaffold for a wide range of bioactive molecules.
Numerous drug candidates and natural-product analogues are derived from isoquinoline through substitution and functionalization of the ring system.
This makes it essential in medicinal chemistry, structure–activity relationship (SAR) studies, and lead compound optimization.

Isoquinoline is a key precursor in the synthesis of benzylisoquinoline and tetrahydroisoquinoline derivatives, which are common motifs in natural alkaloids.
These structures are found in compounds with antispasmodic, vasodilatory, analgesic, anticancer, and antimicrobial activities.
As a result, isoquinoline is important in both natural product chemistry and pharmaceutical synthesis.

In pharmaceutical quality control, isoquinoline is used as an analytical reference and impurity standard.
It may appear as a residual intermediate or degradation product in drug manufacturing processes.
Regulatory laboratories use it for impurity profiling and validation of analytical methods.

In coordination chemistry, isoquinoline acts as a neutral nitrogen-donor ligand.
It binds to transition metals such as palladium, platinum, ruthenium, and copper.
These metal–isoquinoline complexes are investigated for catalytic activity and reaction mechanisms.

Isoquinoline is employed in heterogeneous and homogeneous catalysis research as a probe molecule.
Its interaction with metal surfaces and catalysts helps researchers understand adsorption, coordination, and electronic effects.
This is relevant in catalyst design and surface chemistry studies.

In dye, pigment, and advanced material synthesis, isoquinoline derivatives are used to construct conjugated systems.
The fused aromatic framework contributes to electronic and optical properties such as fluorescence and charge transport.
These applications are generally limited to research and high-value specialty materials.

In agrochemical and fine chemical development, isoquinoline is used as an intermediate for nitrogen-containing aromatic compounds.
Such compounds may act as active ingredients or functional additives.
These uses are typically confined to controlled industrial synthesis rather than direct agricultural application.

Safety Profile Of Isoquinoline:
Isoquinoline is harmful and irritating and can cause skin and eye irritation upon direct contact.
Exposure may result in redness, burning sensations, and discomfort, particularly with prolonged or repeated contact.
Protective gloves and eye protection are required when handling.

Inhalation hazards arise from its vapors, especially in poorly ventilated areas.
Breathing isoquinoline vapors may irritate the respiratory tract and cause headache, dizziness, or nausea.
Adequate ventilation or use of a fume hood is recommended during use.

Ingestion hazards include irritation of the gastrointestinal tract and potential systemic toxicity.
Swallowing may cause abdominal pain, nausea, and vomiting.
Ingestion should be treated as a medical emergency.

Chronic exposure may lead to persistent irritation of skin and mucous membranes.
Repeated exposure can cause dermatitis and prolonged respiratory discomfort.
Long-term toxicological data are limited, so minimizing exposure is advised.

Isoquinoline is combustible, though not highly flammable.
It can form combustible mixtures with air at elevated temperatures.
Thermal decomposition during fires may release toxic fumes, including nitrogen oxides.

Isoquinoline environmental hazards include potential toxicity to aquatic organisms at elevated concentrations.
Due to its low water solubility, it may persist in sediments and affect aquatic life.
Release into the environment should be avoided and spills must be contained.