Electrophilic Aromatic Substitution Dr. Anil Waghe University of Oklahoma

Electro philic Aromatic Substitution e- + e- Important components: Aromatic system Electrophile

Electrophilic Aromatic Substitution H H H H H H + NO2

Is it substitution? H A + B C H H C D + E H H H + NO2 Addition : Elimination: C D + E H H H + NO2

Mechanism H H H + + + H H NO2 H

Useful reactions of EAS Nitration HNO3/ H2SO4 Acylation R-COCl /AlCl3 Sulfonation H2SO4 Alkylation R-Cl / AlCl3 Halogenation Br2 / FeBr3

+ -- -- + d - d - d + d + d - d + :OCH3 CHO NO2 Electron Withdrawing Groups Electron Donating Groups Meta directors (NO2, CN, CHO) Ortho, para directors ( R, OH, NR2, Cl, Br, I, F)

Electron Withdrawing groups (EWG) All common EWG will fit in this format. Y is more electronegative than X NO2 N O Y SO3H CN X N O C S = O OH COOR CHO C=O(CH3)

Friedel Craft Alkylation H3C CH3 CH3Cl AlCl3 H3C H CH3 H3C CH3+ Limitations: 1.polyalkylation, 2. rearrangement 3. No reaction for Aryl halide, compounds with active hydrogen and Deactivating groups on aromatic ring

Nitration of Toluene CH3 CH3 HNO3 H NO2 NO2+ H+ H+ + HO---NO2 NO2+ + H2O NO2+ Electrophile Nitric Acid

Application

Aromatic Substitution Products

Typical Proton NMR regions hydrocarbon electronegativity aromatic TMS aldehyde H H H H X C C C C H C=O X X 10 7 6 4 1 deshielding

Aromatic Proton Coupling para coupling 0 to 2 Hz ortho coupling 6 to 10 Hz meta coupling 1 to 4 Hz doublets Singlet ?

Summary Electropholic aromatic reaction mechanism Substituent effect Friedel Craft Alkylation Problem solving using proton NMR

Research Interest Titanium dioxide doped photocatalyst for waste water treatment. (Environmental/Organic) Synthesis of mycosporine-like amino acids (MAAs) for Sunscreen chemicals. (Synthetic Organic/ Bioorganic) Synthesis of polymers for removal of pharmaceutical contaminants from waste water (Polymer/ Environmental)

Electrophile using Nitrating Mixture H+ + HO---NO2 NO2+ + H2O CH3 Electrophile Nitric Acid NO2 O2N H2SO4/SO3 NO2 H2O + SO3 H2SO4 Sulfuric Acid TNT

Typical Proton NMR regions hydrocarbon electronegativity TMS aromatic H aldehyde CH2 CH3 X CHO X X 10 7 6 4 1 deshielding

nitroglycerin, also called GLYCERYL TRINITRATE, a powerful explosive and an important ingredient of most forms of dynamite. It is also used with nitrocellulose in some propellants, especially for rockets and missiles, and it is employed as a vasodilator in the easing of cardiac pain. Pure nitroglycerin is a colourless, oily, somewhat toxic liquid having a sweet, burning taste. It was first prepared in 1846 by the Italian chemist Ascanio Sobrero by adding glycerol to a mixture of concentrated nitric and sulfuric acids. The hazards involved in preparing large quantities of nitroglycerin have been greatly reduced by widespread adoption of continuous nitration processes. Nitroglycerin, with the molecular formula C3H5(ONO2)3, has a high nitrogen content (18.5 percent) and contains sufficient oxygen atoms to oxidize the carbon and hydrogen atoms while nitrogen is being liberated, so that it is one of the most powerful explosives known. Detonation of nitroglycerin generates gases that would occupy more than 1,200 times the original volume at ordinary room temperature and pressure; moreover, the heat liberated raises the temperature to about 5,000 C (9,000 F). The overall effect is the instantaneous development of a pressure of 20,000 atmospheres; the resulting detonation wave moves at approximately 7,700 m per second (more than 17,000 miles/h). Nitroglycerin is extremely sensitive to shock and to rapid heating; it begins to decompose at 50 -60 C (122 -140 F) and explodes at 218 C (424 F). The safe use of nitroglycerin as a blasting explosive became possible after the Swedish chemist Alfred Nobel developed dynamite in the 1860s by combining liquid nitroglycerin with an inert porous material such as charcoal or diatomaceous earth. Nitroglycerin plasticizes collodion (a form of nitrocellulose) to form blasting gelatin, a very powerful explosive. Nobel's discovery of this action led to the development of ballistite, the first double-base propellant and a precursor of cordite. A serious problem in the use of nitroglycerin results from its high freezing point (13 C [55 F]) and the fact that the solid is even more shock-sensitive than the liquid. This disadvantage is overcome by using mixtures of nitroglycerin with other polynitrates; for example, a mixture of nitroglycerin and ethylene glycol dinitrate freezes at -29 C (-20 F).