What Is Isoquinoline?
Isoquinoline (chemical formula: C9H7N) is a heterocyclic aromatic compound consisting of a benzene ring fused to a pyridine ring.
It is an isomer of the chemical compound quinoline, which is also called 2-azanaphthalene or 2-benzazine because of its structure. Many naturally occurring organic compounds containing nitrogen atoms, and alkanides, have the structural skeleton of isoquinoline. In a broad sense, isoquinoline refers to a variety of substances with this skeleton.
In Japan, isoquinoline is not designated as a substance under the Fire Service Law or the Poisonous and Deleterious Substances Control Law.
| Chemical Formula | C9H7N |
| English Name | Isoquinoline |
| Molecular Weight | 129.16 |
| CAS No. | 119-65-3 |
Uses of Isoquinoline
1. Pharmaceuticals
Isoquinoline and its derivatives are mainly used in the pharmaceutical field. Examples of specific uses include use in anesthetics, antihypertensives, and vasodilators.
Anesthetics
Chemicals such as quinisocaine are in practical use and exert local anesthetic effects by blocking nerve sodium channels.
Antihypertensives
Drugs such as quinapril are in practical use. This drug lowers blood pressure by disabling the enzyme that synthesizes angiotensin, a substance that induces high blood pressure.
Vasodilators
A drug called papaverine is used. This drug dilates blood vessels by acting on receptors such as acetylcholine receptors that exist in the smooth muscles controlling blood vessel and intestinal movements. Its main mechanism of action is by blocking the influx of calcium ions into vascular smooth muscle.
Other pharmaceutical uses include antimalarial, antifungal, and antiseptic.
2. Dyes
Isoquinolines are also used as raw materials in the synthesis of dyes, and many substances such as isoquinoline dyes have an isoquinoline skeleton. Isoquinolines absorb the appropriate wavelength of light and are easily synthesized into a wide variety of derivatives, resulting in the synthesis of a wide variety of dyes.
In addition, isoquinolines are used as synthetic raw materials in the manufacture of pesticides for insecticidal applications. Isoquinoline has a tertiary amine moiety, which acts by inhibiting cholinesterase in insects and significantly increasing their acetylcholine levels.
Other uses of isoquinoline are in the manufacturing industry, where it is useful as a catalyst in the manufacture of polyimide film and as a corrosion inhibitor.
Properties of Isoquinoline
Isoquinoline has a melting point of about 26°C. When melted, isoquinoline is in a colorless oily state, but less pure samples may have a brown color. Like many nitrogen-containing compounds, it has a strong odor. Because of its pyridine ring, it is weakly basic, with a pKb of approximately 8.6.
Isoquinoline is insoluble in water but has high solubility in ordinary organic solvents such as ethanol, diethyl ether, and carbon disulfide. However, it can dissolve well in dilute acids because the nitrogen atoms in the molecule are protonated.
Structure of Isoquinoline
Isoquinolines have a structure that contains a nitrogen atom in the aromatic ring. Therefore, like pyridine, which also has a nitrogen atom in the aromatic ring, the carbon at position 2 is more susceptible to electrophilic substitution reactions.
It also has a higher electron density than the benzene and naphthalene rings, making it more reactive to electrophilic substitution reactions than these molecules.
Other Information on Isoquinoline
Synthesis of Isoquinoline
Isoquinolines are obtained industrially by extraction from coal tar, but in the laboratory, there are various synthetic methods.
The first is synthesized by reacting benzylamine with glyoxal acetal using the Pomeranz-Fritsch reaction. This method is a very good way to obtain unsubstituted isoquinolines.
The second is the Pictet-Spengler reaction to synthesize tetrahydroisoquinoline derivatives from various benzylamine derivatives and aldehydes, followed by dehydrogenation.