With this experiment, students clearly understand the mechanism underlying the nitration reaction in one laboratory session. The mechanism for the nitrobenzene reaction occurs in six steps. Nitration of benzene mechanism electrophilic aromatic. Microsoft word phenol reactivity toward electrophilic aromatic substitution. Phenols are potentially very reactive towards electrophilic aromatic substitution. The rest is according to the general mechanism of electrophilic aromatic substitution.
Were going to substitute the electrophile for a proton on our benzene ring. Electrophilic aromatic substitution reactions are univer sal to most undergraduate organic chemistry laboratory courses. In the second part of the laboratory experiment you will perform an electrophilic nitration on two. Electrophilic substitution of benzene is the one where an electrophile substitutes the hydrogen atom of benzene. The electrophilic substitution reaction between benzene and nitric acid. May 06, 2018 friedel crafts alkylation and acylation reaction mechanism electrophilic aromatic substitution duration. The first shows the friedelcrafts synthesis of the food preservative bht from paracresol. The nitration of aromatic compounds via electrophilic aromatic substitution is a fundamental. Electrophilic substitution reactions of phenols nitration. Friedel crafts alkylation and acylation reaction mechanism electrophilic aromatic substitution duration. However, this reaction proceeds slowly, which is inconvenient dangerous since hot, conc. Electrophilic aromatic substitution halogenation of benzene is one of many electrophilic aromatic substitution reactions. Nitrationofsubstitutedaromaticringsandrate analysiskayladiemozdr. Thus, it stabilizes the arenium ion through resonance.
Because of their high nucleophilic reactivity, aniline and phenol undergo substitution reactions with iodine, a halogen that is normally unreactive with benzene derivatives. Phenol is also very reactive in other electrophilic substitution reactions, such as nitration. The first difference of benzene being less reactive brings the need for using a lewis acid febr 3 which turns the br 2 into a stronger electrophile and makes the reaction possible. Mechanism and regioselectivity of electrophilic aromatic. The facility with which the aromatic ring of phenols and phenol ethers undergoes electrophilic substitution has been noted. The quantitative mononitration of phenol and o, m, and pcresol by nitric acid in 5880% sulphuric acid involves reaction with the nitronium ion at or very close to the encountercontrolled rate. The overall reaction for the nitration of methyl benzoate.
Notice that h 2so 4 is not present as it is in the nitration of benzene. Example nitration of methyl benzoate c o no 2 ome reacts slower than benzene meta hno 3 h2so 4. A new method for nitration of phenolic compounds wiley online. Choose from 500 different sets of electrophilic aromatic substitution flashcards on quizlet. The electrophilic nitronium ion reacts with the nucleophilic cc of the arene. The mechanism for the substitution of atoms like chlorine and bromine. This is the rate determining step as it destroys the aromaticity of the arene. In the first step, the addition of an electrophile yields a highenergy carbocation in which the aromatic. Electrophilic aromatic substitution nitration aims of the experiment perform an electrophilic aromatic substitution.
Aromaticity and electrophilic aromatic substitution. The nitration of benzene is an important reaction since nitrobenzene is an essential precursor for the synthesis of aniline which is used in many other reactions, including the one we have just seen for the synthesis of fluorobenzene. Catalytic mononitration of phenol using isopropyl nitrate. The reaction involves formylation of phenol and analogues using chloroform in the. An easytocomplete, microwaveassisted, green chemistry, electrophilic nitration method for phenol using cuno32 in acetic acid is discussed. Experiment 16 electrophilic aromatic substitution page 5 of 8 acetanilide under electrophilic nitration conditions to determine experimentally which of the two substrates is more reactive. Regioselectivity of the nitration of phenol by acetyl nitrate adsorbed. Phenol 1 and different types of 4substituted phenols 4 were subjected to a. Aromatic nitration of benzene derivatives with electron donating substituent leads to. Results efficiency % yield % recovery discussion predicted rankings steric effects bromine would most likely add to the 4 position before any other position because of the steric clashes between bromines substitution and the substituent present aniline experimental boiling. Activating substituents all activating substituents increase the rate of electrophilic aromatic substitution and are orthopara directors. Electrophilic aromatic substitution electrophilic substitution is the typical reaction type for aromatic rings. Electrophilic aromatic substitution of benzene with. Electrophilic aromatic substitution video khan academy.
The traditional method of phenol nitration involves the use of a mixture of nitric and. Nitration reactions in the manufacture of pharmaceutical. Electrophilic aromatic substitution is an organic reaction in which an atom that is attached to an aromatic system usually hydrogen is replaced by an electrophile. Ultimately the product is at a meta position since the compound contains metadirecting. The hydroxyl group attached to the aromatic ring in phenol facilitates the effective. In another example of an electrophilic aromatic substitution reaction, benzene reacts with a mixture of concentrated nitric and sulfuric acids to create nitrobenzene. Electrophilic aromatic substitution reactions are the reactions where an electrophile replaces one or more hydrogen atoms attached to the aromatic ring. The bromination of benzene, for example, is an aromatic substitution because a hydrogen of benzene the aromatic compound that undergoes substitution is replaced by another group bromine. The general mechanism for all electrophilic aromatic substitutions is summarized below. Electrophilic aromatic substitution reactions of phenols. The hydroxyl group attached to the aromatic ring in phenol facilitates the effective delocalization of the charge in the aromatic ring. Electrophilic aromatic substitution mechanism video khan. The potential energy surfaces in gas phase and in aqueous solution for the nitration of benzene, chlorobenzene, and phenol have been elucidated with density functional theory at the m062x6311gd,p level combined with the polarizable continuum solvent model pcm. If a sulfonic acid is fused with solid koh, the so 3h group is replaced by oh.
Nitration of bromobenzene by electrophilic aromatic. The second difference is that the br in the electrophilic aromatic substitution reaction replaces the hydrogen while both hydrogens are still there when they are on the alkene. Benzene is treated with a mixture of concentrated nitric acid and concentrated sulphuric acid at a temperature not exceeding 50c. Additionally, most deactivating groups direct the incoming electrophile to the meta. Iodination of vanillin and subsequent suzukimiyaura coupling. Electrophilic aromatic substitution of benzene with mechanism. Electrophilic aromatic substitution mechanism video.
King chapter 18 electrophilic aromatic substitution i. Electrophilic aromatic substitution is a multistep process. Three reaction intermediates have been identified along both surfaces. Water functions as a base to remove the proton from the sp 3 c bearing the nitro group and. This page gives you the facts and a simple, uncluttered mechanism for the electrophilic substitution reaction between benzene and a mixture of concentrated nitric acid and concentrated sulphuric acid. The lab follows the reaction of nitration, an electrophilic aromatic substitution reaction in which methyl benzoate is added with concentrated sulfuric acid to produce a nitronium carbocation. Electrophilic substitution involves the attack of a electrophile which is deficit of electrons. Method for the nitration of phenolic compounds download pdf. Because phenol is activated toward electrophilic substitution, it is also possible to nitrate phe. For product ratios, the two easiest peaks to use are at 4. We call the methy group and alkyl groups in general an activating group for electrophilic aromatic substitution. As the aromaticity of benzene is not disturbed in the reaction, these reactions are highly spontaneous in nature.
Basic examples of electrophilic substitution reaction of benzene are nitration, sulfonation, halogenation, friedel. Dec 18, 2017 the potential energy surfaces in gas phase and in aqueous solution for the nitration of benzene, chlorobenzene, and phenol have been elucidated with density functional theory at the m062x6311gd,p level combined with the polarizable continuum solvent model pcm. And what happens in electrophilic aromatic substitution. Thus, the nitro group is a metadirecting group because all electrophilic substitution reactions of nitrobenzene occur at the meta position. Lets begin by recalling the key steps in an electrophilic aromatic substitution mechanism.
Lets look at the general reaction for electrophilic aromatic substitution. Electrophilic aromatic substitution chapter describes the. When two substituents direct to the same position o ch3 no 2 mdirector o,p director hno 3 h2so 4. Phenols are highly prone to electrophilic substitution reactions due to rich electron density. If you want the nitration mechanism explained to you in detail, there is a link at the bottom of the page. Electrophilic substitution of phenols chemistry libretexts. The lab follows the reaction of nitration an electrophilic. Pdf nitration of phenols under mild and heterogeneous conditions. For ocresol the ratio of 2methyl6nitrophenol to the 4nitro isomer changes from 1. Valerieburkeseptember,2010abstract thisprojectstudiedtheelectrophilic.
Phenol reactivity toward electrophilic aromatic substitution. Electrophilic nitration of acetanilide meta selectivity with a deactivating group when a deactivating group is present on the aromatic ring, the electrophilic aromatic substitution takes place at a much slower rate than with an activating group. Nitration of bromobenzene by electrophilic aromatic substitution important concepts electrophilic aromatic substitution reactions nitronium ion as an electrophile activating vs deactivating groups o,pdirectors vs meta directors using resonance structures to predict substitution pattern part a, p. Experiment 16 electrophilic aromatic substitution page 1 of 8 16. Electrophilic aromatic substitution the most characteristic reaction of aromatic compounds is electrophilic aromatic substitution, in which one of the ring hydrogens is substituted by a halogen, nitro group, sulfonic acid group, alkyl or acyl group. What is the increasing rate of electrophilic substitution in. The nitration of pcresol in 6872% sulphuric acid involves ca. Ex nitration, sulphonation, halogenation, acylation, alkylation of aromatic ring. Additionally, most deactivating groups direct the incoming electrophile to the meta position. Common reactions that proceed by electrophilic aromatic substitution include the nitration and sulfonation of benzene, hydration of benzene, friedelcrafts acylation and friedelcrafts alkylation. Nitration lab 2 general mechanism for an electrophilic aromatic substitution. So, benzene becomes less reactive in eas when deactivating groups are present on it.
Deactivating groups are often good electronwithdrawing groups ewgs. There is no such structure in the intermediate for nitration of benzene, so the intermediate for toluene nitration is more stable and the reaction which goes through it is faster. This experiment had many virtues in that the white crystalline product methyl metanitrobenzoate was ideal for learning the technique of recrystallization, and its 1h nuclear magnetic resonance nmr spectrum featured wellresolved meta and ortho aromatic. The catalysts and coreagents serve to generate the strong electrophilic species needed to effect the initial step of the substitution. The mixed halogen iodine chloride icl provides a more electrophilic iodine moiety, and is effective in iodinating aromatic rings having. The mechanism for the substitution of an alkyl group such as ch 3 ch 2 into benzene, by a reaction involving an alkene such as ethene. What is the increasing rate of electrophilic substitution. Electrophilic aromatic substitution by cassidy walker on prezi. Iodination of vanillin and subsequent suzukimiyaura.
Learn electrophilic aromatic substitution with free interactive flashcards. Water functions as a base to remove the proton from the sp 3 c bearing the nitro group and reforms the cc and the aromatic system. Reactions of aromatic compounds rutgers university. The nitration of a benzene ring is an electrophilic aromatic substitution reaction, andits general mechanism is summarized in figure 2. The nitration of aromatic compounds may be achieved with many nitrating. That is, benzene needs to donate electrons from inside the ring. Ionic nitration, though, is not limited to the electrophilic mechanism. The carbocation is then deprotonated to finish the substitution of the hydrogen with an electrophile. The most common method used for bonding nitrogen to aromatic system is nitration.
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