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Ch. 19 - Amines
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728당신이 사용하는 게 아니라요?교과서 변경
모든 교과서Wade 9th EditionCh. 19 - Amines문제 24
19장, 문제 24

Propose a mechanism for the synthesis of methyl orange.

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Step 1: Begin by identifying the two reactants in the synthesis of methyl orange. The first reactant is dimethylaniline (N(CH3)2 group attached to a benzene ring), and the second reactant is a diazonium salt derived from sulfanilic acid (COOH group and diazonium group attached to a benzene ring). This reaction is an example of an azo coupling reaction.
Step 2: Prepare the diazonium salt. Sulfanilic acid is treated with sodium nitrite (NaNO2) and hydrochloric acid (HCl) under cold conditions to form the diazonium salt. The reaction involves the formation of nitrous acid (HNO2), which reacts with the amine group (-NH2) of sulfanilic acid to produce the diazonium ion (-N≡N⁺).
Step 3: Activate the dimethylaniline for electrophilic substitution. The dimethylaniline acts as the nucleophile in the azo coupling reaction. The electron-donating dimethylamino group (-N(CH3)2) increases the electron density on the benzene ring, making it more reactive toward the electrophilic diazonium ion.
Step 4: Perform the azo coupling reaction. The diazonium ion reacts with the dimethylaniline at the para position relative to the dimethylamino group. This position is favored due to steric and electronic effects. The reaction forms a new azo bond (-N=N-) between the two aromatic rings.
Step 5: Finalize the product. The resulting compound is methyl orange, an azo dye. It contains the dimethylaniline moiety connected to the sulfanilic acid moiety via the azo bond. The structure includes the -N=N- linkage, the dimethylamino group, and the sulfonic acid group (-SO3H) from sulfanilic acid.

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Diazo Compounds

Diazo compounds are organic compounds containing two nitrogen atoms connected by a double bond (N=N). They are typically generated from primary amines and are highly reactive, often used in coupling reactions to form azo compounds. In the synthesis of methyl orange, diazo compounds play a crucial role in the formation of the azo linkage that characterizes the dye.

Azo Coupling Reaction

Azo coupling is a reaction between a diazonium salt and an activated aromatic compound, leading to the formation of azo compounds, which contain the -N=N- functional group. This reaction is essential in dye chemistry, as it allows for the creation of vibrant colors. In the case of methyl orange, the coupling of a diazonium salt with an aromatic amine is a key step in its synthesis.

Electrophilic Aromatic Substitution

Electrophilic aromatic substitution (EAS) is a fundamental reaction in organic chemistry where an electrophile replaces a hydrogen atom on an aromatic ring. This mechanism is vital for introducing functional groups into aromatic compounds. In the synthesis of methyl orange, EAS is involved when the diazonium salt acts as the electrophile, reacting with the aromatic amine to form the final product.
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