BENZENE AND ITS DERIVATIVES.pptx

This presantation is beneficial for B pharmacy students who will reading in 3rd semester as per pci syllabush

1. BENZENE AND ITS DERIVATIVES PREPARED BY- KRISHN KUMAR BARMASE ASSISTANCE PROFESSOR DEPARTMENT OF PHARMACEUTICAL CHEMISTRY S.D.COLLEGE OF PHARMACY,BETUL

2. BENZENE

3. BENZENE Benzene is the simplest organic,  aromatic hydrocarbon . Benzene is a volatile, clear, colorless, and flammable liquid aromatic hydrocarbon possessing a distinct, characteristic odor. Benzene is the simplest aromatic compound, with a six carbon ring, a hydrogen atom attached to each carbon atom, and alternating double bonds in the ring structure Benzene is a naturally occurring substance produced by volcanoes and forest fires and present in many plants and animals, but benzene is also a major industrial chemical made from coal and oil. Benzene is one of the elementary petrochemicals and a natural constituent of crude oil. Benzene is highly toxic and carcinogenic in nature .

4. MOLECULAR FORMULA C 6 H 6 The benzene  molecule  is composed of six  carbon  atoms joined in a planar  ring  with one  hydrogen  atom attached to each. Because it contains only carbon and hydrogen atoms, benzene is classed as a  hydrocarbon .

5. History of Benzene The word "benzene" derives historically from "gum benzoin ", sometimes called " benjamin " an aromatic resin known to European pharmacists and perfumers since the 15th century as a product of southeast Asia. • Michael Faraday first isolated and identified benzene in 1825 from the oily residue derived from the production of illuminating gas, giving it the name bicarburet of hydrogen.

6. Nomenclature of BENZENE Benzol  (historic/German) IUPAC Name- - Cyclohexa-1,3,5-triene - 1,3,5-Cyclohexatriene 

7. DERIVATIVES OF BENZENE Monosubstituted derivatives of bezene - Toluene,Cumene , Phenol, Aniline, Benzoic acid, Benzaldehyde , styrene. Disubstituted derivatives of benzene- Xylene , Phthalic acid , Isophthlic acid , Cresol, salicylic acid

8. MONOSUBSTITUTION OF BENZENE When one of the positions on the ring has been substituted with another atom or group of atoms, the compound is a  monosubstituted  benzene.

9. DISUBSTITUTION OF BENZENE When two of the positions on the ring has been substituted with another atom or group of atoms, the compound is a  Disubstituted  benzene.   the Toluene with another methyl group is called “ xylene ”. Depending on the positions of the methyl groups, we have ortho , meta, and para-Xylenes :

10. Other disubstituted derivatives of benzene

11. STRUCTURE OF BENZENE MOLECULAR FORMULA STRAIGHT-CHAIN STRUCTURE NOT POSSIBLE EVIDENCE OF CYCLIC STRUCTURE KEKULE’S STRUCTURE RESONANCE DISCRIPTION MOLECULAR ORBITAL STRUCTURE

12. MOLECULAR FORMULA O F BENZENE Elemental analysis and molecular weight determination showed that benzene had the molecular formula- C 6 H 6 This indicated that benzene was a highly unsaturated compound.

13. STRAIGHT –CHAIN STRUCTURE NOT POSSIBLE Benzene constructed as a straight chain or ring compound having double (C=C) and or (C=C) bonds But benzene does not behave like alkenes and alkynes.

14. EVIDENCE OF CYCLIC STRUCTURE A) Substitution of benzene:- B enzene reacts with bromine in the presence of FeBr3 to form monobromobenzene . Only one monobromo and no isomeric products obtained, becoz all hydrogens are identical. Benzene had cyclic structure Of six carbons and to each carbon was attach. one hydrogen. Benzene Br2/ Ccl 4 Dilute cold Kmno 4 H2O/H + No reaction Bromobenzene

15. EVIDENCE OF CYCLIC STRUCTURE B) Addition of Hydrogen:- Benzene added three moles of hydrogen in presence of nickel catalyst to give cyclohexane . It porved that presence of three carbon-carbon double bonds.

16. KEKULE’S STRUCTURE German chemist Friedrich August Kekulé von Stradonitz • A structure of benzene, containing 3 cyclic conjugated double bonds which systematically called 1,3,5-cyclohexatriene.

17. KEKULE’S STRUCTURE   • The true structure of benzene is a resonance hybrid of the two Lewis structures, with the dashed lines of the hybrid indicating the position of the π bonds.

18. RESONANCE DISCRIPTION the phenomenon in which two or more structures can be written for a substance which involve identical positions of atoms is called as resonance. Actual structure is called as resonance hybrid. Alternating structure is called as resonance structure.

19. RESONANCE DISCRIPTION Resonance energy:- Resonance energy is a measure of how much more stable a resonance hybrid structure than extreme resonance structures

20. MOLECULAR ORBITAL STRUCTURE 1.all carbons are sp2 hybridized 2. Carbons linked together with sigma linkage 3. Carbon and hydrogen linked by sigma linkage 4. The bond angle present is 120° 5. The distance between carbon and hydrogen is 1.34A°

21. Resonance Energy of Benzene

22. Resonance Energy of Benzene

23. AROMATICITY OF BENZENE (HUCKEL RULE) THE CRITERIA FOR AROMATICITY—  Four structural criteria must be satisfied for a compound to be aromatic. Hückel’s Rule: [1] A molecule must be cyclic. To be aromatic, each p orbital must overlap with p orbitals on adjacent atoms. [2] A molecule must be planar. All adjacent p orbitals must be aligned so that the electron density can be delocalized. [3] Each atom in an aromatic ring has a p orbital. These p orbitals must be parallel so that a continuous overlap is possible around the ring. [4] A molecule must satisfy Hückel’s rule, and contain a particular number of electrons. Benzene is aromatic and especially stable because it contains 6 electrons.

24. Method of Preparation Large scale preparation:- From Petroleum(By Aromatisation ):- Substrate - C6-C8 fraction of petroleum neptha Reactant - Pt/Al2O3 Temperature - 500 C Products - Mixture of Benzene,Toluene and Xylenes Isolation - By fractional Distillation at 81 C

25. Fractional distilation

26. Method of Preparation Small scale preparation:- 1.  Heating Phenol with Zinc : To make Benzene from Phenol, Phenol reacts with Zinc dust at a higher temperature, the phenol, is converted to a phenoxide ion and a proton, which accepts an electron from Zn forming an H radical. Which results in the formation of ZnO and the phenoxide ion that was formed, converts itself into Benzene.

27. Method of Preparation 2.   Polymerization of Ethyne : To produce Benzene from Ethyne (acetylene), it has to undergo cyclic polymerization. For this, Ethyne is made to pass through a red hot tube at a temperature of 873K, which in turn, converts itself into Benzene.

28. Physical properties of benzene colourless liquid compound in room temperature Melting point : 5.5 C Boiling point : 80 C There is a harsh smell Burns with high smoke A good solution for non-polar substances such as I 2

29. Chemical Properties of Benzene

30. USES OF BENZENE Benzene is an industrial chemical which is widely used in the production of pesticides, resins, detergents, synthetic fibers, plastics, drugs, dyes. Benzene can be naturally produced from volcanoes and forest fires. It evaporates rapidly from soil and water, if it leaks from storage tanks it can lead to the contamination of water wells and water sources situated close by. Benzene also has household uses too, but the extent of its use is limited due to its toxic and carcinogenic nature. In homes, Benzene is used in glue, adhesive, cleaning products, tobacco smoke, etc. • It is also used to prepare phenol and aniline which is used in dyes. • It is used to manufacture nylon fibers. • Degreasing metals. • One of the most important uses of benzene is to manufacture different chemicals such as ethylbenzene , cyclohexane , cumene , nitrobenzene, etc.

31. END