Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

28. Carbohydrates

Monosaccharides - Kiliani-Fischer

Organic Chemistry

28. Carbohydrates

Monosaccharides - Kiliani-Fischer

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Problem 52j

Textbook Question

Predict the products obtained when D-galactose reacts with each reagent.
(j) (1) KCN/HCN; (2) H₂, Pd/BaSO₄; (3) H₃O⁺

Verified step by step guidance

Step 1: Understand the structure of D-galactose. D-galactose is an aldohexose, meaning it contains six carbons and an aldehyde functional group at the first carbon. The reaction will primarily involve the aldehyde group.

Step 2: Analyze the first reagent, KCN/HCN. This is a cyanohydrin formation reaction. The aldehyde group of D-galactose reacts with HCN to form a cyanohydrin. The cyanide ion (CN⁻) attacks the carbonyl carbon of the aldehyde, forming a new carbon-carbon bond and resulting in a hydroxyl group (-OH) at the former carbonyl carbon.

Step 3: Examine the second reagent, H₂ with Pd/BaSO₄. This is a partial reduction step. The nitrile group (-C≡N) formed in the previous step is reduced to an imine (-C=NH) under these conditions. The BaSO₄ acts as a poison to prevent over-reduction.

Step 4: Consider the third reagent, H₃O⁺. The imine group formed in the previous step undergoes hydrolysis in the presence of acid (H₃O⁺), converting it into a primary amine (-NH₂) and a carboxylic acid (-COOH) group. This results in the formation of an amino acid derivative.

Step 5: Summarize the overall transformation. The reaction sequence converts the aldehyde group of D-galactose into a cyanohydrin, then into an imine, and finally into an amino acid derivative with both an amine (-NH₂) and a carboxylic acid (-COOH) group at the former aldehyde carbon.

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Key Concepts

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

Monosaccharide Reactivity

Monosaccharides like d-galactose can undergo various chemical reactions due to their functional groups, primarily the aldehyde or ketone group. Understanding the reactivity of these groups is crucial for predicting the products of reactions with different reagents, such as nucleophiles or reducing agents.

Nucleophilic Addition

In the presence of KCN or HCN, the nucleophilic cyanide ion can attack the carbonyl carbon of d-galactose, leading to the formation of cyanohydrin. This reaction exemplifies nucleophilic addition, where a nucleophile adds to a carbonyl compound, altering its structure and introducing new functional groups.

Reduction Reactions

The reaction of d-galactose with H2 in the presence of a catalyst like Pd/BaSO4 represents a reduction process. This reaction typically converts the carbonyl group of the sugar into an alcohol, resulting in the formation of a sugar alcohol, which is an important transformation in organic chemistry.

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