Organic Chemistry - Heterocyclic Compounds - Azoles PDF

Organic Chemistry Heterocyclic Compounds Five membered rings heterocyclic with two hetero atoms (1,2-azoles) | Lec.17 Azoles Contents : General features 3 Physical properties 5 1,2-azoles synthesis 7 Pyrazole 8 Industrial methods for pyrazole synthesis 11 Novel pyrazole synthesis method 12 Pyrazole...

Organic Chemistry Heterocyclic Compounds Five membered rings heterocyclic with two hetero atoms (1,2-azoles) | Lec.17 Azoles Contents : General features 3 Physical properties 5 1,2-azoles synthesis 7 Pyrazole 8 Industrial methods for pyrazole synthesis 11 Novel pyrazole synthesis method 12 Pyrazole and its reduced forms 13 Physical properties of pyrazole 14 Chemical properties of pyrazole 15 Chemical reactions of pyrazole 16 Azoles General features: Five member ring contain two hetero atoms one of which is nitrogen. The other hetero atoms are N, O & S. All have a characterization of aromatic compound. Like 1,3-azole, N carries lone pair of electrons. 1,2 azoles are basic compounds due to the lone pair of electrons on nitrogen atom of C=N- group but it is less basic than 1,3 azoles. Azoles Numbering of the ring start from the heteroatom with higher atomic no. All these rings are aromatics, like the 1,3-azoles. Azoles Physical properties: 1- Basicity Pyrazole is the most basic compounds pKa= 2.5 Isoxazole = -3.0 Isothiazole = -0.5 Owing to the electron with drawing effect of the adjacent hetero atom of the 1,2 azoles. The 1,3 azole are more basic than 1,2 azoles. Azoles 2- Boiling point Pyrazole 186-188°C Isoxazole 95°C Isothiazole 114°C Azoles 1,2- azoles synthesis: Synthesis of Pyrazoles/lsoxazoles from 1,3-Dicarbonyl Compounds and Hydrazines or Hydroxylamines. This is the most widely used route to pyrazoles and isoxazoles. The dicarbonyl component can be a β-keto ester or a β-keto aldehyde. Pyrazole Azoles Pyrazole: Pyrazole refers to the class of simple aromatic ring organic compounds of the heterocyclic series characterized by a 5membered ring structure composed of three carbon atoms and two nitrogen atoms in adjacent positions. It has pharmacological effects on humans, they are classified as alkaloids, although they are rare in nature. Pyrazoles are produced synthetically through the reaction of α,β-unsaturated aldehydes with hydrazine and subsequent dehydrogenation. Azoles Azoles Industrial methods for pyrazole synthesis: 1. In the industry pyrazole also produces by interaction of diazoalkans with acetylene. 2. And by interaction hydrazine, alkylhydrazine or arylhydrazine with 1,3-dicarbonyl compounds. As mentioned in slide 7. Azoles Novel pyrazole synthesis method: Heterocycle formation from 1,3-dinitroalkanes. A novel pyrazole synthesis method. Azoles Pyrazole and its reduced forms: Azoles Physical properties: Pyrazole is a colorless crystal compound with weak pyridine smell, which is soluble in water, ethanol and ether. In nonpolar solvents like benzene, pyrazole forms dimers and trimers through formation intermolecular hydrogen bonds. Azoles Chemical properties of pyrazole: Pyrazole is amphoteric compound, like imidazole. It has pyrrole type nitrogen atom, it has weak acidic properties, also it has pyridine type nitrogen atom basic properties. Hence, pyrazole can react with acids and bases. Azoles Chemical reactions: Interaction with alkyl halides: Azoles Nitration and sulfonation: Azoles Halogenation of pyrazole: Reduction: