Benzene Reactions (PDF) - Organic Chemistry Notes

Okay, here's the conversion of the image into a structured markdown format. ### lec./ << Benzene reactions >>> **Benzene** * Cyclic * Conjugated * Planar * Obeys Hückel's rule * \[aromatic] Benzene reacts with substitution, not addition, due to delocalization of $\pi$. **Electrophilic...

Okay, here's the conversion of the image into a structured markdown format. ### lec./ << Benzene reactions >>> **Benzene** * Cyclic * Conjugated * Planar * Obeys Hückel's rule * \[aromatic] Benzene reacts with substitution, not addition, due to delocalization of $\pi$. **Electrophilic Substitution Reactions (EAS / $S_EAr$)** Mechanism of action including 3 steps: 1. Formation of $E^+$ 2. Add $E^+$ to form intermediate carbocation ($\sigma$-complex). (Rate determining step). *af System خطوة صعبة علشان بكسر الـ* 3. Deprotonation to regenerate aromatic system * addition $$ +y^{+} \longrightarrow \begin{array}{c} H \\\\ \end{array} \longrightarrow \text{product} + HB \\\\ $$ * Poor لا resonance rich بفضل : * *بتحرك الـ - ناحية أقرب* * = ناخد الـbases * تتكون علشان تستعيد ال aromatiaty * خطوة ازالة الـ H **Halogenation** \[halogen + lewis $A$] Polarize halogen mol. * Catalyst: $Br_2/AlCl_3$ (Bromination) $\longrightarrow Cl_2/AlCl_3$(Chlorination) $$ Cl-Cl +AlCl_3 \longrightarrow [Cl^+\rightarrow AlCl_3]^{-} \longrightarrow Cl^+ +AlCl_4^{-}\\ Cl-Cl +AlCl_3 \longrightarrow HCl + AlCl_3 $$ **Nitration** \[$HNO_3 + H_2SO_4$] $$ H-\ddot{O}-NO_2 + H - \ddot{O} - SO_3H \longrightarrow [H-\ddot{O}H]^++ \ddot{O}-NO_2 \longrightarrow NO_2^+ + HSO_4^-\\ Catalyst \hspace{1cm} E^+ \hspace{1cm} lewis B $$ $$ + NO_2^+ \longrightarrow \begin{array}{c} NO_2 \\\\ \end{array} \rightarrow \text{product} \text {Nitrobenzene} $$ * Reaction is irreversible * Overall reaction is exothermic --- ### Sulfonation & desulphonation Add $SO_3H$ to benzene. * Fuming mixture: conc. $H_2SO_4 + SO_3$ (Provide fast reaction) * Conc. $H_2SO_4$ (Slow reaction) $$ H-\ddot{O}-S\overset{\normalsize \oplus}{O}OH + H-OSO_3H \longrightarrow +\\Xss. \text{Sulfuric} \text{\`a}\rightarrow \text{product}- H_2 O\\ \text{Base}+HSO_4 $$ $$ + \begin{array}{c} \underset{SO_3H}{\ominus} \\\\ \end{array} \longrightarrow \text{product Sulfonic acid} +SO_3H \longrightarrow + H_2SO_4 \text{Benzene \\\\ sulfonc acid} $$ * Reaction is reversible * Sulfonation: Fuming mix * Desulfonation: dil .H2SO4/ H20 ### Friedel Crafts acylation $$ R-Cl + AlCl_3 \longrightarrow R-\overset{\normalsize \oplus}{C} \overset{\normalsize \oplus}{O}+ AlCl_4 \longrightarrow R-C=O+AlCl_4 $$ ### Friedel crafts alkylation $$ + R-C \longrightarrow product $$ $$ R-Cl+ AlCl_3 \text{react to break the R-X bond}\text{reaction} \longrightarrow R^++ AlCl_4 $$ $$ +\begin{array}{c} H-\ddot{O}-S\\\\ \end{array}+ \begin{array}{c} R\\\\ \end{array}alkyl groups \longrightarrow продукт $$ * Disadvantages of alkylation(عيب علشان مش بقدر أحصل * polyalkylation $$ + \begin{array}{c} CH3-CH_3Cl\\\\ \end{array} \longrightarrow \text {product على mono بسهولة} +AlCl_3 \text{+ HCL} $$ * Rearrangement $$ CH_3-CH_2-CH_2Cl-+ AlCl_3 \longrightarrow \text { product benzene} CH_2 - \underset{+ CH_3} CH +AlCl_3 $$ $$ H-CH_3-CL+ AlCl_3 \longrightarrow \text { N- propyl benzene -AlCl3 Isopropy} +alcl3 - $$ ### EWD (NO2, SO3H,CooH.CHO) * Need e rich ring $$\rightarrow \text{No reaction} +$$ ### Strong ED (NH2 ,:ÖH) $$\rightarrow \text {Complex doesn't undergo F.C} -$$ Advantages of acylation 1. No Polyalkylation 2. No Rearrangement 3. Used to obtain monoalkyl benzene $$ \text{convert benzene N, propyl benzene 100%} $$ *علشان acylation هحل مشكلة alkylation * 1. +C-C Followed by Reduction 2. Zn/Hg/Hel 3. 100% 4. N- propyl 5. علشان acylation هحل مشكلة ال alkylation ومحقق الغرض*