Pyrazole refers both to the class of
simple aromatic ringSimple aromatic rings, also known as simple arenes or simple aromatics, are aromatic organic compounds that consist only of a conjugated planar ring system with delocalized pi electron clouds. Many simple aromatic rings have trivial names. They are usually found as substructures of more complex...
organic compounds of the heterocyclic
diazoleDiazole refers to either one of a pair of isomeric chemical compounds with molecular formula C3H4N2, having a five-membered ring consisting of three carbon atoms and two nitrogen atoms.The two isomers are:...
series characterized by a 5-membered ring structure composed of three
carbonCarbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
atoms and two
nitrogenNitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
atoms in adjacent positions, and to the unsubstituted parent compound. Being so composed and having pharmacological effects on humans, they are classified as
alkaloidAlkaloids are a group of naturally occurring chemical compounds that contain mostly basic nitrogen atoms. This group also includes some related compounds with neutral and even weakly acidic properties. Also some synthetic compounds of similar structure are attributed to alkaloids...
s, although they are rare in nature. In 1959, the first natural pyrazole, 1-pyrazolyl-alanine, was isolated from seeds of
watermelonWatermelon is a vine-like flowering plant originally from southern Africa. Its fruit, which is also called watermelon, is a special kind referred to by botanists as a pepo, a berry which has a thick rind and fleshy center...
s. The term pyrazole was given to this class of compounds by
Ludwig Knorr Ludwig Knorr was a German chemist. Together with Carl Paal, he discovered the Paal-Knorr synthesis, and the Knorr quinoline synthesis and Knorr pyrrole synthesis are also named after him. The synthesis in 1883 of the analgesic drug Antipyrin, now called Phenazone, was a commercial success...
in 1883.
Reactions
- In a classical method developed by H. Pechmann
Hans von Pechmann was a German chemist, renowned for his discovery of diazomethane in 1894. , Pechmann condensation and Pechmann pyrazole synthesis...
in 1898, pyrazole can be synthesized from acetyleneAcetylene is the chemical compound with the formula C2H2. It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in pure form and thus is usually handled as a solution.As an alkyne, acetylene is unsaturated because...
and diazomethaneDiazomethane is the chemical compound CH2N2. It is the simplest of diazo compounds. In the pure form at room temperature, it is a extremely sensitive explosive yellow gas, thus it is almost universally used as a solution in diethyl ether...
.
- Pyrazoles are produced synthetically through the reaction of α,β-unsaturated aldehyde
An aldehyde is an organic compound containing a formyl group. This functional group, with the structure R-CHO, consists of a carbonyl center bonded to hydrogen and an R group....
s with hydrazineHydrazine is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. Approximately 260,000 tons are manufactured annually...
and subsequent dehydrogenationDehydrogenation is a chemical reaction that involves the elimination of hydrogen . It is the reverse process of hydrogenation. Dehydrogenation reactions may be either large scale industrial processes or smaller scale laboratory procedures....
:
- Pyrazoles react with potassium borohydride to form a class of ligands known as scorpionate
The term scorpionate ligand refers to a tridentate ligand which would bind to a metal in a fac manner. The most popular class of scorpionates are the hydrotrisborates or Tp ligands. These were also the first to become popular. These ligands first appeared in journals in 1966 from the then...
. Pyrazole itself reacts with potassium borohydride to form a tridentate ligand known as Tp ligand.
Uses
In medicine, derivatives of pyrazoles are used for their analgesic, anti-inflammatory, antipyretic, antiarrhythmic, tranquilizing, muscle relaxing,
psychoanalepticIn pharmacology, a psychoanaleptic is a medication that produces an arousing effect upon the patient.Antidepressants, psychostimulants, agents used for ADHD and nootropics, and Anti-dementia drugs are all psychoanaleptics....
, anticonvulsant, monoamineoxidase inhibiting, antidiabetic and antibacterial activities.
See also
- Imidazole
Imidazole is an organic compound with the formula C3H4N2. This aromatic heterocyclic is a diazole and is classified as an alkaloid. Imidazole refers to the parent compound, whereas imidazoles are a class of heterocycles with similar ring structure, but varying substituents...
, an analog with two non-adjacent nitrogenNitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
atoms
- Isoxazole
Isoxazole is an azole with an oxygen atom next to the nitrogen. It is also the class of compounds containing this ring.Isoxazole rings are found in some natural products, such as ibotenic acid. Isoxazoles also form the basis for a number of drugs, including the COX-2 inhibitor valdecoxib...
, an analog with the nitrogen atom in position 1 replaced by oxygenOxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
- Pyrrole
Pyrrole is a heterocyclic aromatic organic compound, a five-membered ring with the formula C4H4NH. It is a colourless volatile liquid that darkens readily upon exposure to air. Substituted derivatives are also called pyrroles, e.g., N-methylpyrrole, C4H4NCH3...
, an analog with only one nitrogenNitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
atomThe atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...
, in position 1
- Pyrazolone
Pyrazolone, a five-membered-ring lactam, is a derivative of pyrazole that has an additional keto group.It has a molecular formula of C3H4N2O.Examples of derivatives include:* Ampyrone* Metamizole* Phenazone-External links:* *...
- Simple aromatic rings
- Triazole
Triazole refers to either one of a pair of isomeric chemical compounds with molecular formula C2H3N3, having a five-membered ring of two carbon atoms and three nitrogen atoms.The two isomers are:*1,2,3-Triazole 100px*1,2,4-Triazole 100px...
s, analogs with three nitrogen atoms
External links
- Review article (properties, biological activities, syntheses of pyrazoles):