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Chapter 8: Problem 147

When aniline is treated with acetyl chloride in presence of anhydrous aluminium chloride, the main product is (a) o-aminoacetophenone (b) \(\mathrm{p}\) -aminoacetophenone (c) Both (a) and (b) (d) m-aminoacetophenone

Short Answer

Expert verified
The main product is (b) p-aminoacetophenone.

Step by step solution

01

Understand the Reaction

The reaction involves aniline (C鈧咹鈧匩H鈧�) reacting with acetyl chloride (CH鈧僀OCl) in the presence of anhydrous aluminium chloride (AlCl鈧�). This is a type of Friedel-Crafts acylation reaction, where the acyl group (COCH鈧�) is added to the aromatic ring of aniline.
02

Consider Friedel-Crafts Acylation

Friedel-Crafts acylation typically introduces an acyl group to the benzene ring, creating a carbonyl group bonded to the ring. Aluminium chloride (AlCl鈧�) acts as a catalyst to facilitate the formation of the acylium ion from acetyl chloride, which then attacks the aromatic ring.
03

Influence of Amino Group

Aniline contains an amino group (NH鈧�) which is ortho-para directing due to its electron-donating nature. This directs the incoming acyl group to the ortho and para positions of the benzene ring. However, aniline itself can react with AlCl鈧�, forming a complex that typically inhibits its reactivity.
04

Predict the Main Product

Despite the formation of a complex, when the reaction proceeds, the para position is less hindered and more stabilizing due to steric and electronic factors. Hence, the para-aminoacetophenone (p-aminophenyl acetate) is the predominant product.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Aniline: The Starting Material
Aniline, written as \( C_6H_5NH_2 \), is an aromatic amine, which means it consists of a benzene ring attached to an amino group \( (NH_2) \). This structure gives aniline unique chemical properties. Being an amine, it is a basic compound and can form hydrogen bonds, which has implications on its reactivity.
  • Aniline is known for its distinct feature of an electron-donating amino group.
  • This electron-donation activates the benzene ring towards electrophilic substitution reactions.
  • It is due to this property that aniline often undergoes reactions like the Friedel-Crafts acylation.
Understanding these properties allows us to predict how it will behave in reactions and why certain products are favored, especially in the context of its reactivity with acetyl chloride.
Acetyl Chloride: The Acylating Agent
Acetyl chloride, \( CH_3COCl \), is an acyl chloride used in Friedel-Crafts acylation reactions. This compound is highly reactive due to the presence of the chlorine atom, which is a good leaving group.
  • When acetyl chloride reacts, it forms the highly electrophilic acylium ion \( (CH_3CO^+) \) in the presence of a Lewis acid like aluminium chloride \( (AlCl_3) \).
  • The acylium ion is the active species that attacks the activated benzene ring of aniline.
The formation of this ion is crucial for the reaction to take place and determines where the acyl group will be added on the benzene ring, largely influenced by the directing effects of other groups present on the ring, such as the amino group in aniline.
Ortho-Para Directing: Guiding Electrophiles
In organic chemistry, certain groups attached to a benzene ring can influence the position where additional substituents are added during electrophilic aromatic substitution. This is known as "directing" power. The amino group \( (NH_2) \) in aniline is a strong example of an ortho-para directing group.
  • The amino group donates electrons into the benzene ring, enhancing the electron density especially at the ortho and para positions.
  • This enhancement stabilizes the intermediates (carbocations) that would form if an electrophile attacks these positions.
  • In the case of Friedel-Crafts acylation, this directing effect leads the acyl group to preferentially attach to either the ortho or para position.
  • However, due to steric and other factors, the para position is often more accessible and less hindered, resulting in the major product being substituted at the para position.
Understanding this concept is essential for predicting which products will form in reactions involving substituted benzene rings.
Para-Aminoacetophenone: The Main Product
Para-aminoacetophenone is the main product in the given Friedel-Crafts acylation of aniline with acetyl chloride. Its name derives from the position of the acetyl group relative to the amino group on the benzene ring.
  • The term "para" indicates that the acetyl group \( (COCH_3) \) is situated opposite to the amino group, or positioned 180 degrees away.
  • This arrangement is favored due to reduced steric hindrance compared to the ortho position.
  • In addition, electronic factors such as the stabilization of the aromatic system also play a role.
The production of para-aminoacetophenone illustrates the practical application of directing effects and regioselectivity in electrophilic aromatic substitution reactions, and highlights the influence of both steric and electronic factors in determining the outcome of chemical reactions.

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Most popular questions from this chapter

Grignard reagents \((\mathrm{RMg} X)\) are prepared by the reaction of an organic halide and magnesium metal is in ether solvent. $$\mathrm{R}-\mathrm{X}+\mathrm{Mg} \stackrel{\mathrm{R}-\mathrm{O}-\mathrm{R}}{\longrightarrow} \mathrm{R}-\mathrm{Mg} \mathrm{X}=$$ The solvent (usually diethyl ether or tetrahydrofuran) plays a crucial role in the formation of a Grignard reagent. Alkyl halides are more reactive than aryl and vinyl halides. Indeed, aryl and vinyl chlorides do not form Grignard reagent in diethyl ether. However, an alkyl halide containing an alcoholic -OH group can be converted to Grignard reagent by first protecting the -OH group to tert-butyldimethylsilyl ether which is inert to Grignard reagent. The protecting group is finally liberated by treatment with fluoride ion. The function of tetrahydrofuran in the preparation of Grignard reagent is that it (a) Acts as a solvent (b) Helps in maintaning the reactivity of magnesium (c) Both (a) and (b) (d) None of the these

\(2,4,6\) -Trinitrophenol can be prepared in good yield (a) by the nitration of 2,4 -dinitrochlorobenzene (b) by the nitration of 2,4 -dinitrophenol (c) by both (a) and (b) (d) neither by (a) nor by (b)

When the following three different types of esters are hydrolyzed in a basic medium, the hydroxide anion attacks the acyl carbon in carboxylates while it attacks the alkyl carbon in sulphonates leading to a difference in the site of cleavage. More interestingly, phosphate esters lie somewhat in between carboxylates and sulphonates in that cleavage can occur in either direction. In an acidic solution, all the three types of phosphates (monoalkyl, dialkyl and trialkyl) are hydrolyzed to phosphoric acid, while in a basic solution only trialkyl phosphates undergo hydrolysis and only one alkoxy group is removed. In an aqueous solution, a monoalkylphosphate ester can exist as (a) A neutral ester (b) A monoanion and dianion (c) A monoanion, dianion and protonated ester (d) A monoanion, dianion, protonated ester and neutral ester

Hydrolysis of esters in presence of an acid is a reversible reaction. What is true about ester hydrolysis in presence of a base? (a) It is irreversible because salts of carboxylic acids are insoluble. (b) It is irreversible because salts of carboxylic acids have high melting points. (c) It is irreversible because carboxylate ion is resonance stabilized. (d) It is a reversible reaction.

Which of the following is not a good reagent in Wittig reaction? (a) \(\mathrm{Ph}_{3} \mathrm{P}=\mathrm{CH}_{2}\) (b) \(\mathrm{Ph}_{3} \stackrel{+}{\mathrm{P}} \overline{\mathrm{C}} \mathrm{HCH}_{2} \mathrm{CH}_{3}\) (c) \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCH}=\mathrm{PPH}_{3}\) (d) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COCH}=\mathrm{PPh}_{3}\)
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