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Chapter - 18 Chemistry of Imidazole Oxazole
Chapter - 18 Chemistry of Imidazole Oxazole
Course
Pharma Organic Chemistry (POC 01)
121 Documents
Students shared 121 documents in this course
Academic year: 2016/2017
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Chemistry of Imidazole & Oxazole
Session Objectives
By the end of this session, students will be able to:
- Discuss the various method of synthesis of Imidazole and Oxazole
- Discuss the chemistry, reactivity, properties of Imidazole and Oxazole
Chemistry of Imidazole
- Imidazole is isomeric with pyrazole or azapyrrole
- Also called as glyoxaline, as it was first prepared in 1858 from glyoxal and ammonia
- Imino nitrogen is assigned position-1 while tertiary nitrogen atom position-
- Imidiazole nucleus is found in number of naturally occurring compounds such as histamine, histidine, pilocarpine and allantoin, purine nucleus, vitamin B
- Since imidazole also exists in tautomeric forms, either of the nitrogen can bear the hydrogen atom and two nitrogen become indistinguishable
- Numbering becomes rather complex for mono substitution
- For example, 4-methylimidazole is identical with 5-methylimidazole and depending on the position of imino hydrogen compound can be designated
- Such compound is designated as 4(5)-methyl imidazole
Physical properties:
- Imidazole is colorless liquid with boiling point 256 0C and is high boiling point among all other five membered heterocyclic compounds
- Shows that hydrogen bonding exists in imidazole ring
- More basic with pka 7 than pyridine (pka 5)
Page 1 of 4
- Imidazole has increased reactivity toward electrophilic attack and more susceptible than other five membered heterocycles
- From the resonance structures, electrophilic attack is preferred at 4(5) position in imidazole
- Halogenation: very complex and depends upon type of substrate, reagents and reaction conditions
- Bromination (Br2/CHCl3) yields 2,4,5-tribromoderivative
- Iodination (alkaline conditions) yields 2,4,5-triiodoimidazole
Page 2 of 4
Chemistry of Oxazole
- Oxazole is a 1,3-azole having an oxygen atom and a pyridine type nitrogen atom at 3-position in a five membered ring
- First introduced by Hantzsch in 1887 but was not synthesized until 1947
- Does not occur in nature and does not play any part in fundamental metabolism like imidazole or thiazole
- Partially reduced oxazoles are called oxazolines
- Three types are possible depending on position of double bond
- 2-oxazoline, 3-oxazoline and 4-oxazoline
- Fully saturated system is called oxazolidine- solids
Physical properties:
- Oxazole is a liquid with boiling point 69 0C
- Odor resembling that of pyridine
- Miscible with water and many organic solvents
- Weakly basic (pka 0)
- Possess a sextet of π-electrons, delocalization is incomplete and has little aromatic character
- Function as dienes in the Diels-Alder reaction and electrophilic substitution is rare
Synthetic methods:
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Chapter - 18 Chemistry of Imidazole Oxazole
Course: Pharma Organic Chemistry (POC 01)
121 Documents
Students shared 121 documents in this course
University: The Maharaja Sayajirao University of Baroda
Was this document helpful?
Chemistry of Imidazole & Oxazole
Session Objectives
By the end of this session, students will be able to:
• Discuss the various method of synthesis of Imidazole and Oxazole
• Discuss the chemistry, reactivity, properties of Imidazole and Oxazole
Chemistry of Imidazole
• Imidazole is isomeric with pyrazole or azapyrrole
• Also called as glyoxaline, as it was first prepared in 1858 from glyoxal and ammonia
• Imino nitrogen is assigned position-1 while tertiary nitrogen atom position-3
• Imidiazole nucleus is found in number of naturally occurring compounds such as histamine, histidine, pilocarpine and
allantoin, purine nucleus, vitamin B12
• Since imidazole also exists in tautomeric forms, either of the nitrogen can bear the hydrogen atom and two nitrogen
become indistinguishable
• Numbering becomes rather complex for mono substitution
• For example, 4-methylimidazole is identical with 5-methylimidazole and depending on the position of imino hydrogen
compound can be designated
• Such compound is designated as 4(5)-methyl imidazole
Physical properties:
