Organic Chemistry II: Raney Nickel and Hydrogenation
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Questions and Answers

What is the product of the reaction between hydroxylamine and ketones or aldehydes?

  • Imine
  • Oxime (correct)
  • Hydrazone
  • Semicarbazone

    • What is the product of the reaction between hydrazine and ketones or aldehydes?

  • Oxime
  • Imine
  • Hydrazone (correct)
  • Semicarbazone

    • What is the product of the reaction between semicarbazide and ketones or aldehydes?

  • Semicarbazone (correct)
  • Hydrazone
  • Imine
  • Oxime

    • What is the purpose of excluding air from aldehyde containers?

    <p>To avoid slow oxidation by atmospheric oxygen</p> Signup and view all the answers

    What is the oxidizing agent used in the Tollens test?

    <p>Silver ion Ag+</p> Signup and view all the answers

    What is the purpose of the Tollens test?

    <p>To test for aldehydes</p> Signup and view all the answers

    What is the most common reagent used to reduce ketones and aldehydes?

    <p>Sodium borohydride</p> Signup and view all the answers

    When is the suffix carbaldehyde used in naming?

    <p>When the aldehyde group is a substituent of a large unit</p> Signup and view all the answers

    What are the products of reducing ketones and aldehydes with sodium borohydride?

    <p>Primary and secondary alcohols</p> Signup and view all the answers

    How is a ketone or aldehyde group named as a substituent on a molecule with a higher priority functional group?

    <p>By the prefix oxo-</p> Signup and view all the answers

    What is the common name of the ketone with the formula (CH3)2CO?

    <p>Acetone</p> Signup and view all the answers

    How are substituent locations given in common names of ketones and aldehydes?

    <p>Using Greek letters</p> Signup and view all the answers

    How are common names of aldehydes derived?

    <p>From the common names of the corresponding carboxylic acids</p> Signup and view all the answers

    What makes aldehydes and ketones polar compounds?

    <p>The polar carbonyl group</p> Signup and view all the answers

    Why do aldehydes and ketones have higher boiling points than non-polar compounds of comparable molecular weight?

    <p>Because of their polar carbonyl group</p> Signup and view all the answers

    What is the term given to the carbon atom next to the carbonyl group in common names of aldehydes?

    <p>α carbon</p> Signup and view all the answers

    What is the primary function of sodium borohydride in organic chemistry?

    <p>To reduce ketones and aldehydes</p> Signup and view all the answers

    What is the advantage of using sodium borohydride over catalytic hydrogenation in a laboratory setting?

    <p>It reduces ketones and aldehydes faster than olefins</p> Signup and view all the answers

    What is the catalyst commonly used in catalytic hydrogenation of ketones and aldehydes?

    <p>Raney nickel</p> Signup and view all the answers

    Why is lithium aluminum hydride not preferred for simple reductions of ketones and aldehydes?

    <p>It is more difficult to work with</p> Signup and view all the answers

    What is the product of reducing a ketone with sodium borohydride?

    <p>Secondary alcohol</p> Signup and view all the answers

    What is Raney nickel?

    <p>A finely divided hydrogen-bearing form of nickel</p> Signup and view all the answers

    Why is catalytic hydrogenation still widely used in industry?

    <p>Hydrogen is cheaper than sodium borohydride</p> Signup and view all the answers

    What is the function of sodium triacetoxyborohydride?

    <p>To selectively reduce aldehydes</p> Signup and view all the answers

    What is the result of treating a nickel-aluminum alloy with a strong sodium hydroxide solution?

    <p>A finely divided nickel powder saturated with hydrogen</p> Signup and view all the answers

    What is the disadvantage of using catalytic hydrogenation in a laboratory setting?

    <p>It requires special equipment</p> Signup and view all the answers

    What is the purpose of deoxygenation of ketones and aldehydes?

    <p>To replace the carbonyl oxygen atom with two hydrogen atoms</p> Signup and view all the answers

    What is the number of electrons involved in a deoxygenation reaction?

    <p>Four electrons</p> Signup and view all the answers

    What is the role of H2 in deoxygenation reactions?

    <p>It is used to symbolize the actual reducing agents</p> Signup and view all the answers

    What is the name of the reduction reaction used for deoxygenation under acidic conditions?

    <p>Clemmensen reduction</p> Signup and view all the answers

    What is the purpose of amalgamated zinc in the Clemmensen reduction?

    <p>To provide a surface for the reduction to occur</p> Signup and view all the answers

    What type of compounds can be deoxygenated using the Wolff-Kishner reduction?

    <p>Compounds that cannot survive treatment with hot acid</p> Signup and view all the answers

    What is the purpose of using ethylene glycol or diethylene glycol in the aldol condensation reaction?

    <p>To facilitate the high temperature needed in the reaction</p> Signup and view all the answers

    What is the result of the nucleophilic addition of an enolate ion to another carbonyl group?

    <p>Formation of an aldol</p> Signup and view all the answers

    What is the product of an aldol condensation reaction?

    <p>A β-hydroxy ketone or aldehyde</p> Signup and view all the answers

    What is the result of the dehydration of an aldol product?

    <p>Formation of an α,β-unsaturated carbonyl compound</p> Signup and view all the answers

    What is a crossed aldol condensation?

    <p>A reaction between the enolate of one aldehyde or ketone and the carbonyl group of a different aldehyde or ketone</p> Signup and view all the answers

    What is the importance of selecting the compounds carefully in a crossed aldol condensation reaction?

    <p>To obtain a single product</p> Signup and view all the answers

    What happens when the enolate of one aldehyde or ketone adds to the carbonyl group of a different aldehyde or ketone?

    <p>A mixture of several products is formed</p> Signup and view all the answers

    What is the purpose of converting a ketone or aldehyde to its hydrazone?

    <p>To form an enolate ion</p> Signup and view all the answers

    Study Notes

    Nomenclature of Ketones and Aldehydes

    • Aldehyde groups can be named as substituents on a molecule with a higher priority functional group as its root.
    • The suffix "carbaldehyde" is used when the aldehyde group is a substituent of a large unit (usually a ring).
    • Ketone or aldehyde carbonyl is named by the prefix "oxo-" if it is included as part of the longest chain in the root name.
    • When an aldehyde CHO group is a substituent and not part of the longest chain, it is named by the prefix "formyl".

    Common Names of Ketones and Aldehydes

    • Ketones and aldehydes are often called by common names instead of their systematic IUPAC names.
    • Ketone common names are formed by naming the two alkyl groups bonded to the carbonyl group.
    • Substituent locations are given using Greek letters, beginning with the carbon next to the carbonyl group.
    • Some ketones have historical common names, such as dimethyl ketone (acetone) and alkyl phenyl ketones (acyl group followed by the suffix "-phenone").
    • Common names of aldehydes are derived from the common names of the corresponding carboxylic acids.
    • Greek letters are used with common names of aldehydes to give the locations of substituents.

    Physical Properties of Ketones and Aldehydes

    • The polar carbonyl group makes aldehydes and ketones polar compounds, and hence they have higher boiling points than non-polar compounds or comparable molecular weight.

    Condensations with Hydroxylamine and Hydrazines

    • Ketones and aldehydes condense with other ammonia derivatives, such as hydroxyl amine and substituted hydrazines, to give imine derivatives.
    • The equilibrium constants for these reactions are usually more favorable than for reactions with simple amines.
    • Hydroxylamine reacts with ketones and aldehydes to form oximes; hydrazine and its derivatives react to form hydrazones; and semicarbazide reacts to form semicarbazones.

    Oxidation of Aldehydes

    • Aldehydes are easily oxidized to carboxylic acids by common oxidants such as bleach (sodium hypochlorite), chromic acid, permanganate, and peroxy acids.
    • Aldehydes oxidize so easily that air must be excluded from their containers to avoid slow oxidation by atmospheric oxygen.
    • Mild reagents such as Ag2O can oxidize aldehydes selectively in the presence of other oxidizable functional groups.
    • The Tollens test involves adding a solution of silver-ammonia complex (the Tollens reagent) to the unknown compound, and if an aldehyde is present, its oxidation reduces silver ion to metallic silver.

    Reductions of Ketones and Aldehydes

    • Ketones and aldehydes are most commonly reduced by sodium borohydride.
    • Sodium borohydride (NaBH4) reduces ketones to secondary alcohols and aldehydes to primary alcohols.
    • Lithium aluminum hydride (LiAlH4) also accomplishes these reductions, but it is a more powerful reducing agent and is much more difficult to work with.
    • Sodium triacetoxyborohydride (NaBH(OAc)3) is less reactive than NaBH4, and it selectively reduces aldehydes even in the presence of ketones.

    Catalytic Hydrogenation

    • Like alkene double bonds, carbonyl double bonds can be reduced by catalytic hydrogenation.
    • Catalytic hydrogenation is slower with carbonyl groups than with olefinic double bonds, however.
    • The most common catalyst for catalytic hydrogenation of ketones and aldehydes is Raney nickel.

    Deoxygenation of Ketones and Aldehydes

    • A deoxygenation replaces the carbonyl oxygen atom of a ketone or aldehyde with two hydrogen atoms, reducing the carbonyl group past the alcohol stage all the way to a methylene group.
    • Deoxygenation can be accomplished by either the Clemmensen reduction (under acidic conditions) or the Wolff-Kishner reduction (under basic conditions).
    • The Clemmensen reduction commonly converts acylbenzenes (from Friedel-Crafts acylation) to alkylbenzenes, but it also works with other ketones and aldehydes that are not sensitive to acid.
    • The Wolff-Kishner reduction is used for compounds that cannot survive treatment with hot acid.

    The Aldol Condensation of Ketones and Aldehydes

    • Condensations are some of the most important enolate reactions of carbonyl compounds.
    • The aldol condensation involves the nucleophilic addition of an enolate ion to another carbonyl group under basic conditions.
    • The product, β-hydroxy a ketone or aldehyde, is called an aldol because it contains both an aldehyde group and the hydroxy group of an alcohol.
    • The aldol product may dehydrate to an α,β-unsaturated carbonyl compound.

    Crossed Aldol Condensations

    • When the enolate of one aldehyde (or ketone) adds to the carbonyl group of a different aldehyde or ketone, the result is called a crossed aldol condensation.
    • The compounds used in the reaction must be selected carefully, or a mixture of several products will be formed.

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    Description

    Learn about Raney nickel, a finely divided nickel powder saturated with hydrogen, and its application in hydrogenation reactions of ketones and aldehydes.

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