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Chapter 22: Problem 526

Explain the feature of amine basicity.

Short Answer

Expert verified
Amine basicity refers to an amine's ability to act as a Lewis base, accepting a proton (H+) from a Lewis acid, forming an ammonium ion. The basicity is influenced by factors such as electron donating or withdrawing groups (inductive effects), resonance effects, solvent effects, and steric factors. Electron-donating groups increase basicity, while electron-withdrawing groups decrease it. Resonance stabilizes the positive charge on the nitrogen atom, decreasing basicity in aromatic amines. Solvent properties, such as hydrogen bonding, can also affect basicity. Finally, steric hindrance can limit the approach of a proton donor, affecting basicity.

Step by step solution

01

1. Define Amines

Amines are organic compounds derived from ammonia (NH3) by replacing one or more hydrogen atoms with alkyl (R) or aryl groups (Ar). They can be classified as primary (1°), secondary (2°), or tertiary (3°) amines depending on the number of alkyl/aryl groups attached to the nitrogen atom. The general formula for amines is RnNH(3-n), where n is the number of alkyl/aryl groups.
02

2. Define Basicity

Basicity, in the context of amines, refers to the ability of an amine to act as a Lewis base, accepting a proton (H+) from a Lewis acid (proton donor) to form a positively charged ammonium ion (RnNH(3-n)+). The strength of an amine's basicity is often measured using the pKa value of its conjugate acid, which is the ammonium ion formed after the amine accepts a proton. A higher pKa value indicates a stronger base.
03

3. Factors Affecting Amine Basicity

The basicity of amines is influenced by several factors, including: 1. Electron donating or withdrawing groups (inductive effects) 2. Resonance effects 3. Solvent effects 4. Steric factors
04

4. Inductive Effects on Basicity

Electron-donating groups (EDG) increase the electron density on the nitrogen atom, making it more available to accept a proton and hence increasing its basicity. In contrast, electron-withdrawing groups (EWG) decrease the electron density on the nitrogen atom, making it less available to accept a proton and hence decreasing its basicity.
05

5. Resonance Effects on Basicity

Resonance stabilizes the positive charge on the nitrogen atom by delocalizing it throughout the molecule. In aromatic amines, the lone pair of electrons on the nitrogen atom is involved in resonance with the aromatic ring, which decreases the basicity of the amine. This effect is more relevant in anilines (aromatic amines) than in aliphatic amines.
06

6. Solvent Effects on Basicity

The basicity of an amine can be influenced by the solvent in which it is measured. In protic solvents (e.g., water), hydrogen bonding between the solvent and the nitrogen atom can stabilize the amine, thereby increasing its basicity. In aprotic solvents (e.g., DMSO), hydrogen bonding is absent, and the basicity is mostly determined by the inherent electron density on the nitrogen atom.
07

7. Steric Factors on Basicity

Steric hindrance can affect the basicity of amines by limiting the approach of the proton donor to the nitrogen atom. Tertiary amines are less basic than secondary and primary amines due to the presence of bulky alkyl groups, which create steric hindrance and make it more difficult for the amine to accept a proton. In summary, amine basicity is influenced by factors including inductive effects, resonance effects, solvent effects, and steric factors. By understanding these factors, one can better predict and explain the basicity of amines.

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Most popular questions from this chapter

Provide an acceptable name for each of the following. Indicate whether the amino groups in these compounds are primary, secondary or tertiary (a) \(\mathrm{CH}_{2}=\mathrm{CHCH}_{2} \mathrm{NH}_{2}\) (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CHNHCH}_{3}\) (c) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}\) (d) \(\mathrm{H}_{2} \mathrm{NCH}_{2} \mathrm{CO}_{2} \mathrm{H}\)

A colorless basic liquid \(\mathrm{C}_{7} \mathrm{H}_{9} \mathrm{~N}(\mathrm{~A})\) reacts immediately with sodium nitrite in cold dilute sulfuric acid to give a neutral yellow oil (B) . Reaction of A with acetic anhydride in pyridine solution gives a neutral white solid (C), the nmr spectrum of which shows a singlet at \(\delta 1.9\), a singlet at \(\delta 3.5\), and a multiplet at \(\delta 7.3\) with intensities of \(1: 1: 1.67\), respectively. Assign structures to \(\mathrm{A}, \mathrm{B}\), and \(\mathrm{C}\).

Novocaine, a local anesthetic, is a compound of formula \(\mathrm{C}_{13} \mathrm{H}_{20} \mathrm{O}_{2} \mathrm{~N}_{2}\). It is insoluble in water and dilute \(\mathrm{NaOH}\), but soluble in dilute HC1. Upon treatment with \(\mathrm{NaNO}_{2}\) and \(\mathrm{HCl}\) and then with \(\beta\) -naphthol, a highly colored solid is formed. When Novocaine is boiled with aqueous \(\mathrm{NaOH}\), it slowly dissolves. The alkaline solution is shaken with ether and the layers are separated. Acidification of the aqueous layer causes the precipitation of a white solid A; continued addition of acid causes \(A\) to redissolve. Upon isolation \(A\) is found to have a melting point of \(185-6^{\circ}\) and the formula \(\mathrm{C}_{7} \mathrm{H}_{7} \mathrm{O}_{2} \mathrm{~N}\). Evaporation of the ether layer leaves a liquid \(\mathrm{B}\) of formula \(\mathrm{C}_{6} \mathrm{H}_{15} \mathrm{ON}\). B dissolves in water to give a solution that turns litmus blue. Treatment of \(B\) with acetic anhydride gives C, \(\mathrm{C}_{8} \mathrm{H}_{17} \mathrm{O}_{2} \mathrm{~N}\), which is insoluble in water and dilute base, but soluble in dilute HCl. \(\mathrm{B}\) is found to be identical with the compound formed by the action of diethylamine on ethylene oxide. (a) What is the structure of Novocaine? (b) Outline all steps in a complete synthesis of Novocaine from toluene and readily available aliphatic and inorganic reagents. $$ \begin{array}{|l|l|l|} \hline {\text { CARBOXYLIC ACIDS }} \\ \hline \text { Name } & \text { Formula } & \begin{array}{c} \text { M.p. } \\ { }^{\circ} \mathrm{C} \end{array} \\ \hline \text { o-Nitrobenzoic } & \circ-\mathrm{O}_{2} \mathrm{NC}_{6} \mathrm{H}_{4} \mathrm{COOH} & 147 \\ \hline \text { m-Nitrobenzoic } & \mathrm{m}-\mathrm{O}_{2} \mathrm{NC}_{6} \mathrm{H}_{4} \mathrm{COOH} & 141 \\ \hline \text { p-Nitrobenzoic } & \mathrm{p}-\mathrm{O}_{2} \mathrm{NC}_{6} \mathrm{H}_{4} \mathrm{COOH} & 242 \\ \hline \text { Phthalic } & \mathrm{o}-\mathrm{C}_{6} \mathrm{H}_{4}(\mathrm{COOH})_{2} & 231 \\ \hline \text { Isophthalic } & \mathrm{m}-\mathrm{C}_{6} \mathrm{H}_{4}(\mathrm{COOH})_{2} & 348 \\ \hline \text { Terephthalic } & \mathrm{p}-\mathrm{C}_{6} \mathrm{H}_{4}(\mathrm{COOH})_{2} & 300 \text { sub1. } \\ \hline \text { Salicylic } & \mathrm{o}-\mathrm{HOC}_{6} \mathrm{H}_{4} \mathrm{COOH} & 159 \\ \hline \text { p-Hydroxybenzoic } & \mathrm{p}-\mathrm{HOC}_{6} \mathrm{H}_{4} \mathrm{COOH} & 213 \\ \hline \text { Anthranilic } & \mathrm{o}-\mathrm{H}_{2} \mathrm{NC}_{6} \mathrm{H}_{4} \mathrm{COOH} & 146 \\ \hline \text { m-Aminobenzoic } & \mathrm{m}-\mathrm{H}_{2} \mathrm{NC}_{6} \mathrm{H}_{4} \mathrm{COOH} & 179 \\ \hline \text { p-Aminobenzoic } & \mathrm{p}-\mathrm{H}_{2} \mathrm{NC}_{6} \mathrm{H}_{4} \mathrm{COOH} & 187 \\ \hline \text { o-Methoxybenzoic } & \mathrm{o}-\mathrm{CH}_{3} \mathrm{OC}_{6} \mathrm{H}_{4} \mathrm{COOH} & 101 \\ \hline \text { m-Methoxybenzoic } & \mathrm{m}-\mathrm{CH}_{3} \mathrm{OC}_{6} \mathrm{H}_{4} \mathrm{COOH} & 110 \\ \hline \text { p-Methoxybenzoic(Anisic) } & \mathrm{p}-\mathrm{CH}_{3} \mathrm{OC}_{6} \mathrm{H}_{4} \mathrm{COOH} & 184 \\ \hline \end{array} $$

Describe exactly how you would go about separating a mixture of the three water-insoluble liquids, aniline (b. p. \(\left.184^{\circ}\right), \mathrm{n}\) -butylbenzene (b. p. \(183^{\circ}\) ), and n-valeric acid (b. p. \(187^{\circ}\) ), recovering each compound pure and in essentially quantitative yield. Do the same for a mixture of the three water-insoluble solids, \(p\) -toluidine, o-bromobenzoic acid, and \(\mathrm{p}\) -nitroanisole.

Propose a method for separating a mixture of cyclohexane- carboxylic acid, tri-t-butylamine, and decane.
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