Benzene and its Derivatives along with its structure and uses
- 1. BENZENE AND ITS DERIVATIVES PREPARED BY: Ms. Kadam A. J. Dept: Pharmaceutical Chemistry PRES’s Institute of Pharmacy, Loni 1
- 2. UNIT I Benzene and its derivatives A. Analytical, synthetic and other evidences in the derivation of structure of benzene, Orbital picture, resonance in benzene, aromatic characters, Huckel’s rule B. Reactions of benzene - nitration, sulphonation, halogenation reactivity, Friedelcrafts alkylation- reactivity, limitations, Friedelcrafts acylation. C. Substituents, effect of substituents on reactivity and orientation of mono substituted benzene compounds towards electrophilic substitution reaction D. Structure and uses of DDT, Saccharin, BHC and Chloramine
- 3. Content: • Physicai Properties Of Benzene • Nomenclature • Structure Of Benzene • Molecular Formula • Resonance Hybrid Structure Of Benzene • Huckel’s Rule And Aromaticity • Reactions Of Benzene • Friedal Craft Acylation • Friedal Craft Alkylation
- 8. Physicai properties of Benzene Benzene is a colourless or light yellow It is liquid at room temperature. It has a sweet odour and is highly flammable. Natural sources of benzene include volcanoes and forest fires. Benzene is also a natural part of crude oil, gasoline, and cigarette smoke. IUPAC name Benzene Cyclohexa-1,3,5-triene;1,3,5- Cyclohexatriene 2 Space-filling model Ball and stick model
- 9. Benzene is an organic chemical compound consisting of carbon and hydrogen atoms with alternating double bonds. As it contains only carbon and hydrogen atoms, benzene is classed as a hydrocarbon. The chemical formula of benzene is C6H6 , so it consists of six carbon atoms and six hydrogen atoms. joined in a ring with one hydrogen atom attached to each.
- 10. NOMENCLATURE Monosubstituted alkylbenzenes are named as derivatives of benzene. For example, ethylbenzene. The IUPAC system retains certain common names for several of the simpler monosubstituted alkyl benzenes CH2CH3 CH3 CH=CH2 Toluene Ethylbenzene Styrene
- 11. Common names for some monosubstituted benzenes are as follows P h e n o l A n is o le A n ilin e B e n z a ld e h y d e B e n z o ic a c id Phenyl group (C6H5- or Ph-): Derived by loss of an H from benzene, O C H 3 O C -O H N H 2 O H O C - H C H 6 5 1-Phenylcyclohexene 4-Phenyl-1-butene Phenyl group 1 2 4 3
- 12. • When two substituents occur on a benzene ring, three isomers are possible, they may be located by 1. numbering the atoms of the ring or 2. using the locators ortho (o), meta (m), and para (p) COOH Br CH3 CH3 CH2 CH3 1 2-Bromobenzoic acid (o-Bromobenzoic acid) 1,3-Dimethylbenzene (m-Xylene) 1-Chloro-4-ethylbenzene (p-Chloroethylbenzene) 1 2 2 2 3 3 4 1 Cl
- 13. STRUCTURE OF BENZENE Facts that supported Kekule Formula 1) Molecular formula 2) Open Chain Structure not accepted 3) Evidences in favor of Ring Structure a) Catalytic Hydrogenation of benzene yields cyclohexane b) Benzene yields one mono substitution product: c) Benzene forms 3-di and trisubstituted product which can be explained on basic of ring structure. 4) Resonance hybrid Structure 5) Molecular Orbital Structure 8
- 14. MOLECULAR FORMULA 1)Benzene has molecular formula- C6H6. From its elemental composition and molecular weight, benzene was known to contain 6-C and 6-H atoms. Benzene has molecular formula C6H6 as compared to hexane C6H12 which confirms that benzene is highly unsaturated than hexane.From this, it was concluded that 6-C atoms in the benzene were linked by double or triple bonds so as to form a straight chain or closed ring as proposed by Kekulè. C C C C C H H C H H H H A K e k u l ŭ s t r u c t u r e s h o w i n g a l l a t o m s A K e k u l ŭ s t r u c t u re a s a l i n e - a n g l e f o r m u l a
- 16. 2) OPEN CHAIN STRUCTURE NOTACCEPTED 16 The possible open chain structure for benzene could have been CH2 = CH − C ≡ C − CH = CH2 CH3 − C ≡ C − C ≡ C − CH3 CH ≡ C − CH2 − CH2 − C ≡ CH - structure I - structure II - structure III All this structures were ruled out because benzene didn’t give the usual reactions of alkenes, alkynes
- 18. For example 18 when above open chain structured compounds containing double and triple bonds are added to tetrachloride solution of bromine in which is red in colour carbon becomes colourless but benzene do not give this reactions benzene can not have open chain structure .
- 19. 3) EVIDENCE IN FAVOR OF RING STRUCTURE 19 a) Catalytic Hydrogenation of benzene yields Cyclohexane + 3H2 Since, hydrogenation is not bringing about any major structural change in carbon frame. It proves the presence of closed ring of 6-C atoms in Benzene molecule. Pt/Ni Δ Benzene Cyclohexane
- 20. b) Benzene yields one mono substitution product: If bromination is done, only one bromobenzene is obtained because 1-H atom is replaced by bromine. It is same in the case of Chlorobenzene and Nitrobenzene. This proves that each Hydrogen must be exactly equidistant to other hydrogen since the replacement of any Hydrogen gives the same product and suppose we consider the open chain structure it would yield the isomeric monoderivetives, as all the Hydrogen atoms are not equal as shown in struters I,II & III This could be possible only if 6 carbons in benzene are joined to each other to form a closed ring and one hydrogen atom is attached to each carbon. 20
- 21. C) Benzene Forms 3-di And 3-trisubstituted Products Which Can Be Explained On Basic Of Ring Structure. Positions 2And 6Are Same (Ortho Product) Positions 3And 5Are Same (Meta Product) Position 4 is Para Position 21
- 22. Benzene forms 3-di and trisubstituted product which can be explained on basic of ring structure. + 3Br2 FeBr3 Br Positions 2 and 6 are same (ortho product) Positions 3 and 5 are same (meta product) therefore only three dibromobenzene are possible. Straight Chain structure will give more than 3 di or trisubstituted products. Br Br Br Br Br
- 23. RESONANCE HYBRID STRUCTURE OF BENZENE The above Kekulè structures of benzene differ in position of electrons.Benzene is a hybrid of structures I & II are exactly equivalent and have same stability and they make equal contribution to the hybrid structure . The resonance stabilization energy which is responsible for the unusual stability of benzene can be calculated from the measurement of heat of combustion or heat of hydrogenation 16 H C C C C C C H H H C C C C C H C H H H H H H H
- 24. STABILITY OF BENZENE Stability of benzene can be explained in the following way Heat of Hydrogenation is the quantity of heat evolved when mole of an unsaturated compound is hydrogenated.Addition of Hydrogen to a double bond is an exothermic reaction. As heat is given out in hydrogenation means the product in each case is more stable than the original one. + H2 + 28.6 kcal/mol + 2H2 + 55 kcal/mol + 3H2 + 50 kcal/mol 17 Cyclohexane Cyclohexadiene Cyclohexane Cyclohexene Cyclohexane Benzene
- 25. MOLECULAR ORBITAL STRUCTURE By the X ray diffraction mechanism ,it is proved that benzene consists of planar hexagon of 6-c atoms havinh all c-c bonds equal in length i.e. 1.4 Angstron c-c-c bond angle is 120 degrees. Therefore, it can be proved that each of this 6-c in benzene ring is in the state of trigonal hybridization.The ring system is costructed from six sp2-hybridized carbons by the overlapping of two hybrid orbitals each to form sigma bonds. 25
- 26. The structure of benzene molecule is best described in terms of molecular orbital treatment theory. According to this theory, all the C-atoms in benzene are sp2-hybridized. Remaining six sp2-orbital of six C-atoms overlap with 1s orbital of six H-atoms individually to form six sigma bonds. 26
- 27. HUCKEL’S RULE AND AROMATICITY 27 The complete delocalization of π electrons caused by side-side overlapping gives benzene aromatic character.An aromatic compound must contain 4n+2 electrons (n=0, 1, 2, and so forth). Cyclic, planar and completely conjugated compounds that contain 4n π electrons are especially unstable, and are said to be antiaromatic. Benzene is aromatic and especially stable because it contains 6 π electrons. Cyclobutadiene is antiaromatic and especially unstable because it contains 4π electrons.
- 28. Characteristic reaction of benzene involves substitution in which resonance stabilized ring is preserved.This reaction is calledAromatic Substitution. Compared to sigma bonds pi electrons are loosely held and are available to the reagent i.e. seeking electrons.So typical reaction of benzene is electrophilic substitution reaction, where hydrogen of aromatic ring is substituted by an atom or group Ar-H Ar-X Reactions of Benzene 28
- 29. GENERAL MECHANISM OF ELECTROPHILIC SUBSTITUTION REACTIONS. Aromatic substitution reactions are initiated by the attack of electrophile on the ring followed by the elimination of proton.Such reactions are called electrophilic substitution reactions. Benzene with its pi electrons behaves as an electron rich system.Electrons in the pi clouds are readily available to form a new bond with electron deficient species,i.e. the electrophile.Electrophilic substitution reactions folows the following mechanism 29
- 30. Step-1:Generation of electrophile either by spontaneous dissociation of reagent or by acid catalyzed dissociation E-Nu E+ +Nu E-Nu +A- E-Nu+-A- E+ +Nu-A- Step-2:Formation of the -complex first then -complex -complex forms by association of electrophile with the aromatic ring .In this -complex,an electrophile is not attached to any specific position of ring but later it rearranges to give -complex. -complex is a resonance hybrid of stabilized carbonium (arenium) ion produced by the attack of electrophile on benzene ring Step-3:A proton H + is then eliminated from -complex by the base to yield the final substitution product. 30
- 31. 31
- 32. HALOGENATION NITRATION AND SULFONATION 32 Nitration and sulfonation of benzene are two examples of electrophilic aromatic substitution. The nitronium ion (NO2 +) and sulfur trioxide (SO3) are the electrophiles and individually react with benzene to give nitrobenzene and benzenesulfonic acid respectively.
- 33. NITRATION OF BENZENE Mechanism Step-1- Generation of electrophile HNO3 is activated with sulfuric acid through protonation which then causes the loss of a water molecule and forms a nitronium ion,which is a stronger electrophile,. H HNO3 H2SO4 NO2 + H2O Nitrobenzene +
- 34. Step-2 & Step-3- Formation of the -complex and then elimination of proton H + from -complex takes place to get the final product
- 35. SULFONATION Sulfonation is a reversible reaction that produces benzenesulfonic acid by adding sulfur trioxide and fuming sulfuric acid. The reaction is reversed by adding hot aqueous acid to benzenesulfonic acid to produce benzene. 35
- 36. MECHANISM OF SULFONATION 36 Step-1-Generation of electrophile The sulfur in sulfur trioxide is electrophilic because the oxygens pull electrons away from it as oxygen is very electronegative.To produce benzenesulfonic acid from benzene, fuming sulfuric acid and sulfur trioxide are added. Fuming sulfuric acid, also refered to as oleum, is a concentrated solution of dissolved sulfur trioxide in sulfuric acid.
- 37. THE SULFUR AND STEP-2 & STEP-3- THE SUBSEQUENT PROTON 37 BENZENE TRANSFERS ATTACKS OCCUR TO PRODUCE BENZENESULFONIC ACID. I.E. FORMATION OF THE -COMPLEX AND THEN ELIMINATION OF PROTON H + FROM -COMPLEX TAKES PLACE TO GET THE FINAL PRODUCT
- 38. FRIEDEL CRAFTS ACYLATION This reaction involves the introduction of RCO (acyl) group in the aromatic ring in presence of AlCl3,BF3, FeCl3 etc 38
- 39. MECHANISM Step 1- The very first step involves the generation of the electrophile i.e. the acylium ion 39
- 40. Step 2- The second step involves the attack of the acylium ion on benzene as a new electrophile to form one complex: 40
- 41. Step 3- The third step involves the departure of the proton in order for aromaticity to return to benzene 41
- 42. FRIEDEL CRAFTS ALKYLATION 42 This reaction involves the attack of an alkyl group in benzene in presence of anhydrous aluminum chloride.This reaction is called Overall the Friedel‐Crafts alkylation reaction. transformation: Ar-H to Ar-R The mechanism for this reaction begins with the generation of a methyl carbocation from methylbromide. The carbocation then reacts with the π electron system of the benzene to form a nonaromatic carbocation that loses a proton to reestablish the aromaticity of the system.
- 43. 43 1. Step 1- The first step involves the generation of the electrophile methyl carbocation by the reaction of methylchloride with aluminum chloride. 2. Step 2- The electrophile attacks the π electron system of the benzene ring to form a nonaromatic carbocation.
- 44. 44 The positive charge on the carbocation that is formed is delocalized throughout the molecule. Step 3- The aromaticity is restored by the loss of a proton from the atom to which the methyl group has bonded.
- 45. Step 4- Finally, the proton reacts with the AlCl 4 − to regenerate the AlCl 3 catalyst and form the product HCl. Carbocations can rearrange during the Friedel‐Crafts alkylation reaction, leading to the formation of unpredicted products. One example is the formation of isopropyl benzene by the reaction of propyl chloride with benzene.
- 46. Structure and uses of Following compounds: • DDT • Saccharin • BHC • Chloramine
- 47. DDT: Dichlorodiphenyltrichloroethane DDT (Dichlorodiphenyltrichloroethane) is a synthetic organic compound with the chemical formula C14H9Cl5. Its molecular structure consists of: 1. Two benzene rings (phenyl groups) connected by a central carbon atom 2. Three chlorine atoms attached to the central carbon atom 3. Two additional chlorine atoms attached to each benzene ring
- 48. Method of Preparation : DDT is prepared by heating chlorobenzene with Chloral in presence of conc. H₂SO4
- 49. • Uses of DDT • DDT was widely used in the past for: • Insecticide: DDT was used to control mosquitoes, flies, and other insects that spread diseases like malaria, typhus, and yellow fever. • Agriculture: DDT was used to control pests that damaged crops, such as insects, mites, and ticks. • Public health: DDT was used to control disease-carrying insects in homes, schools, and public areas. • Veterinary medicine: DDT was used to control external parasites on animals, such as ticks and lice. • However, due to its environmental and health risks, the use of DDT has been largely banned or restricted in many countries since the 1970s. • Environmental and Health Risks • Persistence in the environment • Bioaccumulation in wildlife • Toxicity to aquatic life • Potential human health risks, including cancer and neurological effects
- 50. Saccharin: Saccharin is an artificial sweetener with the chemical formula C7H5NO3S. Its molecular structure consists of: 1. A benzene ring with a sulfonamide group (-SO2NH2) attached to it 2. A nitrogen atom bonded to the sulfonamide group 3. A carboxyl group (-COOH) attached to the nitrogen atom
- 51. Method of Preparation: It is prepared by sulfonation of toluene, followed by reaction with ammonia to form sulphonamide and then, oxidation of sulphonamide to form saccharin. - The para isomer formed after the sulfonation of toluene is not considered since it cannot form saccharin.
- 52. • Uses of Saccharin • Saccharin is commonly used as a: • Artificial sweetener: Saccharin is 300-400 times sweeter than sugar and is used in: • Diet foods and beverages • Sugar-free gum and candy • Low-calorie desserts • Food additive: Saccharin is used as a sweetening agent in: • Baked goods • Soft drinks • Fruit juices • Canned goods • Pharmaceutical applications: Saccharin is used as a: • Sweetening agent in cough drops and syrups • Excipient in tablet and capsule formulations • Research applications: Saccharin is used in: • Biochemical research as a sweetening agent • Toxicological studies as a control substance
- 53. BHC: Benzene Hexachloride: BHC, also known as Lindane, is an organochlorine compound with the chemical formula C6H6Cl6. Its molecular structure consists of: 1. A benzene ring with six chlorine atoms attached to it 2. The chlorine atoms are arranged in a specific geometric pattern, resulting in different isomers (alpha, beta, gamma, delta, epsilon, and zeta)
- 54. Preparation of Benzene hexachloride Chlorine combines with benzene, in the presence of UVlight and in the absence of oxygen as well as substitution catalysts, to form hexachlorocyclohexane.
- 55. • Uses of BHC • BHC is used as: • Insecticide: BHC is used to control insects, such as: • Lice and scabies in humans • Fleas and ticks in animals • Agricultural pests, like wheat and rice borers • Fungicide: BHC is used to control fungal diseases in: • Crops, like wheat, barley, and oats • Seeds, like wheat and rice • Pharmaceutical applications: BHC is used in: • Topical creams and lotions for skin conditions, like eczema and dermatitis • Shampoos for lice and dandruff • Veterinary medicine: BHC is used to control: • External parasites, like ticks and lice, in animals • Fungal infections in animals • Other uses • BHC is used in some industrial applications, like: • Wood preservation • Leather treatment
- 56. Chloramine: Chloramine is a chemical compound with the formula NH2Cl. Its molecular structure consists of: 1. A nitrogen atom bonded to two hydrogen atoms and one chlorine atom 2. The nitrogen atom has a lone pair of electrons, making chloramine a polar
- 57. Method of preparation: • chloramine is prepared by the reaction of ammonia with sodium hypochlorite: NH3 + NaOCl → NH2Cl + NaOH. • Gaseous chloramine can be obtained from the reaction of gaseous ammonia with chlorine gas (diluted with nitrogen gas): 2 NH3 + Cl2 ⇌ NH2Cl + NH4Cl • Pure chloramine can be prepared by passing fluoroamine through calcium chloride: 2 NH2F + CaCl2 → 2 NH2Cl + CaF2
- 58. • Uses of Chloramine • Chloramine is used as: • Disinfectant: Chloramine is used to disinfect: • Water treatment plants • Swimming pools • Wastewater treatment plants • Bleaching agent: Chloramine is used as a bleaching agent in: • Textile industry • Paper industry • Pharmaceutical applications: Chloramine is used as: • An antiseptic in wound care products • A preservative in eye drops and contact lens solutions • Laboratory reagent: Chloramine is used as a reagent in: • Organic synthesis • Analytical chemistry • Other uses • Chloramine is used in some industrial applications, like: • Cleaning and sanitizing surfaces • Controlling algae growth in cooling towers