Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry

Bruice8th EditionOrganic ChemistryISBN: 9780135213711Not the one you use?Change textbook

Bruice 8th Edition

Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry

Problem 15

Chapter 3, Problem 15

Does methanol behave as an acid or a base when it reacts with methylamine?

Verified step by step guidance

Step 1: Begin by identifying the functional groups in methanol and methylamine. Methanol (CH₃OH) contains a hydroxyl (-OH) group, while methylamine (CH₃NH₂) contains an amine (-NH₂) group.

Step 2: Recall the Brønsted-Lowry acid-base theory, which defines acids as proton (H⁺) donors and bases as proton acceptors. Analyze the ability of methanol and methylamine to donate or accept protons.

Step 3: Consider the hydroxyl group in methanol. The oxygen atom in the -OH group is electronegative, making the hydrogen atom slightly positive and capable of being donated as a proton (H⁺). This suggests methanol can act as a Brønsted-Lowry acid.

Step 4: Examine the amine group in methylamine. The nitrogen atom has a lone pair of electrons, which makes it capable of accepting a proton (H⁺). This indicates methylamine can act as a Brønsted-Lowry base.

Step 5: Conclude that when methanol reacts with methylamine, methanol behaves as an acid by donating a proton (H⁺), and methylamine behaves as a base by accepting the proton.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Acid-Base Theory

Acid-base theory explains the behavior of substances in terms of proton (H+) transfer. According to the Brønsted-Lowry theory, acids are proton donors, while bases are proton acceptors. Understanding this theory is crucial for analyzing the interaction between methanol and methylamine, as it determines which compound acts as an acid and which acts as a base in their reaction.

Methanol as a Weak Acid

Methanol (CH3OH) can act as a weak acid due to its ability to donate a proton to a stronger base. In the context of its reaction with methylamine, methanol can lose a proton, forming methoxide (CH3O-) and contributing to the acid-base equilibrium. Recognizing methanol's weak acidic properties is essential for predicting its behavior in this reaction.

Methylamine as a Base

Methylamine (CH3NH2) is a weak base that can accept protons due to the presence of a lone pair of electrons on the nitrogen atom. When reacting with methanol, methylamine can accept a proton, forming methylammonium (CH3NH3+). Understanding the basic nature of methylamine is key to determining the overall acid-base dynamics in their interaction.

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Nitrogenous Bases Example 3

Related Practice

Textbook Question

For each of the acid–base reactions in [Section 2.3], compare the pK_a values of the acids on either side of the equilibrium arrows to prove that the equilibrium lies in the direction indicated.

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Textbook Question

Draw the conjugate acid of each of the following:

a. CH₃CH₂OH

b. CH₃CH₂O⁻

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Textbook Question

For each of the acid–base reactions in [Section 2.3], compare the pK_avalues of the acids on either side of the equilibrium arrows to prove that the equilibrium lies in the direction indicated.

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Textbook Question

Ethyne (HC≡CH) has a pK_a value of 25, water has a pK_a value of 15.7, and ammonia (NH3) has a pKa value of 36. Draw the equation, showing equilibrium arrows that indicate whether reactants or products are favored, for the acid–base reaction of ethyne with

a. HO^-.

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Textbook Question

a. Which is a stronger base: CH₃COO⁻ or HCOO⁻? (The pK_a of CH₃COOH is 4.8; the pK_a of HCOOH is 3.8.)

b. Which is a stronger base: HO⁻ or ^-NH₂? (The pK_a of H2O is 15.7; the pK_a of NH3 is 36.)

c. Which is a stronger base: H₂O or CH₃OH? (The pK_a of H3O+ is −1.7; the pK_a of CH₃O⁺H₂ is −2.5.)

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Textbook Question

Estimate the pKa values of the following compounds:

c. CH₃CH₂COOH

d. CH₃CH₂CH₂N⁺H₃

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