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| Names | |||
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| Preferred IUPAC name Isoquinoline[1] | |||
| Other names Benzo[c]pyridine 2-benzazine | |||
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3D model (JSmol) | |||
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| ECHA InfoCard | 100.003.947 | ||
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| Properties | |||
| C9H7N | |||
| Molar mass | 129.162 g·mol−1 | ||
| Appearance | Colorless oily liquid; hygroscopic platelets when solid | ||
| Density | 1.099 g/cm3 | ||
| Melting point | 26–28 °C (79–82 °F; 299–301 K) | ||
| Boiling point | 242 °C (468 °F; 515 K) | ||
| Acidity (pKa) | pKBH+ = 5.14[2] | ||
| −83.9·10−6 cm3/mol | |||
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |||
Isoquinoline is an individual chemical specimen - aheterocyclicaromaticorganic 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 astructural isomer ofquinoline. Isoquinoline and quinoline arebenzopyridines, which are composed of abenzene ring fused to apyridine ring. In a broader sense, the term isoquinoline is used to make reference to isoquinolinederivatives.1-Benzylisoquinoline is the structural backbone in many naturally occurringalkaloids such aspapaverine. The isoquinoline ring in these natural compound derives from the aromaticamino acidtyrosine.[3][4][5][6][7][8]
Isoquinoline is a colorlesshygroscopic liquid at temperatures above its melting point with a penetrating,unpleasant odor. Impure samples can appear brownish, as is typical for nitrogen heterocycles. It crystallizes in form of platelets that have a lowsolubility in water but dissolve well inethanol,acetone,diethyl ether,carbon disulfide, and other commonorganic solvents. It is also soluble in diluteacids as the protonated derivative.
Being ananalog of pyridine, isoquinoline is a weakbase, with apKa of 5.14.[2] It protonates to formsalts upon treatment withstrong acids, such as HCl. It formsadducts withLewis acids, such as BF3.
Isoquinoline was first isolated fromcoal tar in 1885 by Hoogewerf and van Dorp.[9] They isolated it byfractional crystallization of the acid sulfate. Weissgerber developed a more rapid route in 1914 by selective extraction of coal tar, exploiting the fact that isoquinoline is more basic than quinoline. Isoquinoline can then be isolated from the mixture by fractional crystallization of the acid sulfate.
Although isoquinoline derivatives can be synthesized by several methods, relatively few direct methods deliver the unsubstituted isoquinoline. ThePomeranz–Fritsch reaction provides an efficient method for the preparation of isoquinoline. This reaction uses abenzaldehyde and aminoacetoaldehyde diethyl acetal, which in anacidmedium react to form isoquinoline.[10] Alternatively,benzylamine and aglyoxalacetal can be used, to produce the same result using the Schlittler-Müller modification.[11]
Several other methods are useful for the preparation of various isoquinoline derivatives.
In theBischler–Napieralski reaction an β-phenylethylamine is acylated and cyclodehydrated by a Lewis acid, such asphosphoryl chloride orphosphorus pentoxide. The resulting 1-substituted 3,4-dihydroisoquinoline can then be dehydrogenated using palladium. The following Bischler–Napieralski reaction produces papaverine.
ThePictet–Gams reaction and thePictet–Spengler reaction are both variations on the Bischler–Napieralski reaction. A Pictet–Gams reaction works similarly to the Bischler–Napieralski reaction; the only difference being that an additional hydroxy group in the reactant provides a site for dehydration under the same reaction conditions as the cyclization to give the isoquinoline rather than requiring a separate reaction to convert a dihydroisoquinoline intermediate.
In a Pictet–Spengler reaction, a condensation of a β-phenylethylamine and analdehyde forms an imine, which undergoes a cyclization to form atetrahydroisoquinoline instead of thedihydroisoquinoline. Inenzymology, the(S)-norcoclaurine synthase (EC4.2.1.78) is anenzyme thatcatalyzes a biological Pictect-Spengler synthesis:
-norcoclaurine_synthesis.svg)
Intramolecular aza Wittig reactions also afford isoquinolines.
Isoquinolines find many applications, including:
Parkinson's disease, a slowly progressing movement disorder, is thought to be caused by certainneurotoxins. A neurotoxin calledMPTP (1[N]-methyl-4-phenyl-1,2,3,6-tetrahydropyridine), the precursor to MPP+, was found and linked to Parkinson's disease in the 1980s. The active neurotoxins destroydopaminergic neurons, leading to parkinsonism and Parkinson's disease. Severaltetrahydroisoquinoline derivatives have been found to have the same neurochemical properties as MPTP. These derivatives may act as precursors to active neurotoxins.[13]
Isoquinolines are used in the manufacture ofdyes,paints,insecticides andfungicides. It is also used as asolvent for theliquid–liquid extraction ofresins andterpenes, and as acorrosion inhibitor.
"Quinoline" .Encyclopædia Britannica. Vol. 22 (11th ed.). 1911. pp. 758–759.
| Authority control databases: National |
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