Textbook Question
Rank the compounds in each set in order of increasing acid strength.
(a) CH3CH2COOH, CH3CHBrCOOH, CH3CBr2COOH
2
views
Ch. 20 - Carboxylic Acids
Wade9th EditionOrganic ChemistryISBN: 9780135213728
Not the one you use?Change textbookSelect a different textbook
Table of contents
- Ch.1 - Structure and Bonding107
- Ch. 2 - Acids and Bases; Functional Groups115
- Ch.3 - Structure and Stereochemistry of Alkanes100
- Ch.4 - The Study of Chemical Reactions99
- Ch.5 - Stereochemistry93
- Ch.6 - Alkyl Halides; Nucleophilic Substitution118
- Ch. 7 - Structure and Synthesis of Alkenes; Elimination158
- Ch.8 - Reactions of Alkenes171
- Ch.9 - Alkynes91
- Ch.10 - Structure and Synthesis of Alcohols143
- Ch.11 - Reactions of Alcohols104
- Ch. 12 - Infrared Spectroscopy and Mass Spectrometry22
- Ch. 13 - Nuclear Magnetic Resonance Spectroscopy45
- Ch. 14 - Ethers, Epoxides, and Thioethers72
- Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy89
- Ch. 16 - Aromatic Compounds74
- Ch. 17 - Reactions of Aromatic Compounds126
- Ch. 18 - Ketones and Aldehydes193
- Ch. 19 - Amines129
- Ch. 20 - Carboxylic Acids77
- Ch. 21 - Carboxylic Acid Derivatives141
- Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds175
- Ch. 23 - Carbohydrates and Nucleic Acids93
- Ch. 24 - Amino Acids, Peptides, and Proteins54
Chapter 20, Problem 4
Suppose you have just synthesized heptanoic acid from heptan-1-ol. The product is contaminated by sodium dichromate, sulfuric acid, heptan-1-ol, and possibly heptanal. Explain how you would use acid–base extractions to purify the heptanoic acid. Use a chart, like that in Figure 20-3, to show where the impurities are at each stage.
Verified step by step guidance1
Step 1: Dissolve the mixture containing heptanoic acid, sodium dichromate, sulfuric acid, heptan-1-ol, and heptanal in a solvent like diethyl ether. This will separate the organic impurities (heptan-1-ol and heptanal) into the ether phase, while the inorganic impurities (sodium dichromate and sulfuric acid) will remain in the aqueous phase.
Step 2: Separate the ether phase from the aqueous phase using a separatory funnel. The ether phase contains heptanoic acid and organic impurities, while the aqueous phase contains inorganic impurities.
Step 3: Add dilute sodium hydroxide (NaOH) or sodium bicarbonate (NaHCO₃) to the ether phase. This will convert heptanoic acid into its water-soluble carboxylate salt (RCOO⁻ Na⁺), which will move into the aqueous phase, leaving the organic impurities in the ether phase.
Step 4: Separate the aqueous phase (containing RCOO⁻ Na⁺) from the ether phase (containing organic impurities). Acidify the aqueous phase with hydrochloric acid (HCl) to regenerate heptanoic acid (RCOOH), which is now insoluble in water.
Step 5: Extract the regenerated heptanoic acid into fresh ether. This final ether phase contains purified heptanoic acid, free from both organic and inorganic impurities.
Verified video answer for a similar problem:
This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
8mWas this helpful?
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Acid-Base Extraction
Acid-base extraction is a technique used to separate compounds based on their acidity or basicity. In this process, an organic compound (like heptanoic acid) is converted into its ionic form by reacting with a base, making it soluble in the aqueous phase. This allows for the separation of the organic acid from neutral organic impurities, which remain in the organic solvent (ether).
Recommended video:
Guided course
02:49
The Lewis definition of acids and bases.
Solubility Principles
Understanding solubility is crucial in acid-base extraction. Organic acids, such as heptanoic acid, are typically soluble in organic solvents like ether but can be made soluble in water when converted to their ionic forms. Conversely, neutral organic compounds and inorganic salts have different solubility profiles, allowing for effective separation during the extraction process.
Recommended video:
Guided course
02:01Introducing common solvents and other molecules in organic chemistry.
Phase Separation
Phase separation refers to the division of a mixture into distinct layers based on differences in solubility and density. In the context of acid-base extraction, after mixing the organic and aqueous phases, the two layers can be separated. The aqueous phase contains the ionic form of the acid and any soluble impurities, while the organic phase retains non-polar compounds, facilitating the purification of the desired product.
Recommended video:
1:53Merrifield Solid-Phase Peptide Synthesis Concept 1
Related Practice
Textbook Question
Oxidation of a primary alcohol to an aldehyde usually gives some over-oxidation to the carboxylic acid. Assume you have used PCC to oxidize pentan-1-ol to pentanal.
(a) Show how you would use acid–base extraction to purify the pentanal.
(b) Which of the expected impurities cannot be removed from pentanal by acid–base extractions? How would you remove this impurity?
16
views
Textbook Question
Phenols are less acidic than carboxylic acids, with values of pKa around 10. Phenols are deprotonated by (and therefore soluble in) solutions of sodium hydroxide but not by solutions of sodium bicarbonate. Explain how you would use extractions to isolate the three pure compounds from a mixture of p-cresol (p-methylphenol), cyclohexanone, and benzoic acid.
2
views
Textbook Question
Rank the compounds in each set in order of increasing acid strength.
(c)
1
views
Textbook Question
Rank the compounds in each set in order of increasing acid strength.
(b) CH3CH2CH2CHBrCOOH, CH3CH2CHBrCH2COOH, CH3CHBrCH2CH2COOH
1
views
Textbook Question
The IR spectrum of trans-oct-2-enoic acid is shown. Point out the spectral characteristics that allow you to tell that this is a carboxylic acid, and show which features lead you to conclude that the acid is unsaturated and conjugated.
<IMAGE>
2
views