Name: making alcohols by carbonyl reduction
Uploaded: 2025-05-22T09:05:35.000Z
Duration: 2 min 23 s
Channel: JoVE

Alcohols can be prepared from carbonyl compounds by adding two hydrogen atoms across the double bond.
This reduction is important in the synthesis of essential molecules like the perfume ingredient muscone and the antidepressant drug Prozac.
While aldehydes, carboxylic acids, and esters are reduced to primary alcohols, ketones are reduced to secondary alcohols.
The classical method involves catalytic hydrogenation using hydrogen and transition-metal catalysts. However, this requires high temperature and pressure and also reduces any carbon&#8211;carbon multiple bonds present in the molecule.
The laboratory method involves the stepwise addition of nucleophilic hydride ions from sodium borohydride, lithium aluminum hydride, and their derivatives, in an irreversible reaction, followed by protonation with solvent or acid. This method selectively reduces the carbonyl group in comparison to hydrogenation.
In unsymmetrical ketones, the planar carbonyl group can undergo a nucleophilic hydride attack from either face with equal probability. This generates a chiral tetrahedral intermediate, giving a pair of enantiomeric products. 
Reduction by sodium borohydride is carried out in polar protic solve

alcohols from carbonyl compounds: reduction

Alcohols from Carbonyl Compounds: Reduction

Reduction is a simple strategy to convert a carbonyl group to a hydroxyl group. The three major pathways to reduce carbonyls to alcohols are catalytic hydrogenation, hydride reduction, and borane reduction.
Catalytic hydrogenation is similar to the reduction of an alkene or alkyne by adding H2 across the pi bond in the presence of transition metal catalysts like Raney Ni, Pd&#8211;C, Pt, or Ru. Aldehydes and ketones can be reduced by this method, often under mild to moderate heat (25&#8211;100&#176;C) and pressure (1&#8211;5 atm H2), to yield 1&#176; and 2&#176; alcohols, respectively.
<img alt="Cyclohexanone to cyclohexanol conversion, H2, catalyst (Pt, Pd, Ni), reaction yield 90-95%, diagram." src="/files/ftp_upload/11925/11925_PT_Figure_1.svg" style="text-align: center; height: 90px;" data-altupdatedat="1754904545000" data-alt="Hydrogenation reaction diagram; cyclohexanone to cyclohexanol using H&#8322;/Pt, Pd, Ni catalyst, 90&#8211;95% yield." />
Figure 1. Catalytic hydrogenation can be suitable for industrial applications when harsh conditions are not required, but unsaturated carbon&#8211;carbon bonds are also reduced.
Hydride reduction can be achieved by hydride transfer reagents, like sodium borohydride (NaBH4) and lithium aluminum hydride (LiAlH4, or LAH), as nucleophilic attack by a free hydride ion, <img alt="Lewis structure of hydride ion H&#8315;; diagram showing electron configuration and charge." src="/files/ftp_upload/11925/11925_PT_Figure_2.svg" style="height: 18px;" data-altupdatedat="1754904545000" data-alt="Lewis structure of hydride ion, H&#8315;, showing a hydrogen atom with a lone pair and a negative charge." />, is almost unknown for NaH salts due to its high charge density, making it a strong base. The hydrogen atoms of LAH and NaBH4, being covalently bonded to boron and aluminum atoms, have partial negative charges, thereby enhancing their nucleophilicity at the cost of basicity. The first step of nucleophilic addition leads to the formation of alkoxide ions. The byproduct alkoxyborohydride or alkoxyaluminate reduces three more carbonyl molecules, successively transferring all their hydrogen atoms. Since hydride is a poor leaving group, the hydride transfer steps are irreversible, and therefore the reaction proceeds to completion. Lastly, the reaction mixture is worked up with solvent (i.e., water or alcohol in the case of NaBH4 and dilute acid in the case of LAH).
<img alt="Chemical reduction of ester to alcohol using LiAlH4, reaction equation." src="/files/ftp_upload/11925/11925_PT_Figure_3.svg" style="text-align: center; height:55px;" data-altupdatedat="1754904545000" data-alt="Chemical reaction diagram: ester reduction by LiAlH4 to form alcohols, showcasing reduction process." />
Figure 2. Aldehydes and symmetrical esters produce one 1&#176; alcohol product. Unsymmetrical esters produce a mixture of 1&#176; alcohols.
LAH, NaBH4, and their derivatives are highly useful in the reduction of aldehydes and ketones. LAH, a powerful reducing agent, can also reduce carbonyl compounds like acids, esters, acyl chlorides, and amides. LAH reacts violently with water and other protic solvents, liberating hydrogen gas and forming metal hydroxides/alkoxides. Hence, LAH reductions are typically carried out in aprotic solvents like anhydrous diethyl ether and THF.
<img alt="Organic reaction diagram, reduction of ester to alcohol via LiBH4 in EtOH." src="/files/ftp_upload/11925/11925_PT_Figure_4.svg" style="text-align: center; height: 45px;" data-altupdatedat="1754904545000" data-alt="Organic reduction reaction equation, LiBH4/EtOH, carboxylic acid to alcohol conversion, chemical synthesis." />
Figure 3. An alcoholic solution of lithium borohydride is a non-hazardous alternative to LAH in selectively reducing esters over acids.
On the other hand, NaBH4 is of a milder nature and generally reduces only in protic solvents like ethanol or methanol. Therefore, NaBH4 can be used to reduce aldehydes and ketones in the presence of functional groups like alkyl halides, esters, alkyl tosylates, and nitro groups. Diisobutylaluminum hydride (DIBAL-H) can also convert carbonyls to alcohols at room temperature by two successive additions of hydride ions. However, when reacted with esters at low temperatures, this reaction can be stopped at the aldehyde stage by adding only one equivalent of hydride ion.
Borane reduction uses a borane (BH3) solution in diethyl ether, THF, or Me2S to selectively reduce electron-rich carbonyl groups like carboxylic acids in the presence of other reducible functional groups such as esters and even ketones.
<img alt="Organic synthesis reaction, borane reduction of carboxylic acid to alcohol, chemical equation." src="/files/ftp_upload/11925/11925_PT_Figure_5.svg" style="text-align: center; height: 65px;" data-altupdatedat="1754904545000" data-alt="Hydroboration-oxidation reaction equation; organic chemistry; synthesis of alcohols; reaction diagram." />
Figure 4. The formation of a reactive triacylborate intermediate with a more electrophilic carbonyl group than the starting ester molecule drives the reduction reaction forward.
For living organisms, reduced coenzyme NADH or its phosphoester NADPH is equivalent to laboratory hydride reagents in enzyme catalysis of similar biological reductions.

Reduction is a simple strategy to convert a carbonyl group to a hydroxyl group. The three major pathways to reduce carbonyls to alcohols are catalytic ...

alcohols-from-carbonyl-compounds-reduction

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Organic Chemistry

Unit 1

Alcohols and Phenols

KEY TERMS AND CONCEPTS

making alcohols by carbonyl reduction

Making alcohols by carbonyl reduction is a key reaction in organic chemistry. It converts a carbonyl group into a hydroxyl group. The main routes are catalytic hydrogenation, hydride reduction, and borane reduction.

Catalytic hydrogenation works by adding H2 across the pi bond of the carbonyl group. It uses transition metal catalysts such as Raney Ni, Pd-C, Pt, or Ru. Aldehydes and ketones can be reduced this way under mild to moderate heat, usually 25–100°C, and H2 pressure of about 1–5 atm. Aldehydes form 1° alcohols, and ketones form 2° alcohols. This method can suit industrial use when harsh conditions are not needed, but it can also reduce unsaturated carbon-carbon bonds.

Hydride reduction uses reagents that transfer hydride, which is a hydrogen atom with extra electron density, to the carbonyl carbon. Common examples are sodium borohydride, NaBH4, and lithium aluminum hydride, LiAlH4, or LAH. Their hydrogens are bonded to boron or aluminum, so they act as nucleophiles rather than strong bases. The first step forms an alkoxide ion, and the resulting alkoxyborohydride or alkoxyaluminate can reduce three more carbonyl molecules by passing along its hydrogen atoms.

Because hydride is a poor leaving group, these transfer steps do not reverse easily. The reaction is then finished with a workup step using water or alcohol for NaBH4, or dilute acid for LAH. Aldehydes and symmetrical esters give one 1° alcohol product, while unsymmetrical esters can give a mixture of 1° alcohols. LAH is a strong reducing agent and can also reduce acids, esters, acyl chlorides, and amides. It reacts violently with water and other protic solvents, so these reductions are usually done in aprotic solvents such as anhydrous diethyl ether and THF.

NaBH4 is milder and usually works in protic solvents like ethanol or methanol. That makes it useful for reducing aldehydes and ketones while leaving groups such as alkyl halides, esters, alkyl tosylates, and nitro groups in place. Diisobutylaluminum hydride, or DIBAL-H, can also reduce carbonyls to alcohols at room temperature through two hydride additions. At low temperature, however, ester reduction can be stopped at the aldehyde stage by using only one equivalent of hydride.

Borane reduction uses BH3 in diethyl ether, THF, or Me2S. It can selectively reduce electron-rich carbonyl groups such as carboxylic acids, even when other reducible groups like esters or ketones are present. The reaction is driven by a reactive triacylborate intermediate, which makes the carbonyl more electrophilic than the starting ester. In living systems, NADH and NADPH serve a similar role to laboratory hydride reagents during enzyme-catalyzed reductions.

Making Alcohols by Carbonyl Reduction

structure and nomenclature of alcohols and phenols

structure-and-nomenclature-of-alcohols-and-phenols

Alcohols and Phenols: Naming Basics

Alcohols and phenols are important organic compounds with simple naming rules. Alcohols contain a hydroxyl group, or –OH group, directly bonded to carbon. Phenols also contain an OH group, but it is attached directly to a benzene ring. Alcohols are usually colorless. Phenol is a white crystalline compound with a characteristic hospital smell. These compounds are named using formal and standard systems. The most widely used system is the International Union of Pure and Applied Chemistry, or...

physical properties of alcohols and phenols

physical-properties-of-alcohols-and-phenols

Alcohols and Phenols: Boiling Point Trends

Alcohols and phenols are organic compounds whose physical properties depend on structure. In alcohols, a hydroxy group is attached to a saturated carbon. In phenols, the hydroxy group is attached to an aromatic ring. Their boiling points and water solubility are shaped by hydrogen bonding and dispersion forces. The oxygen-hydrogen dipole in the hydroxy group allows intermolecular hydrogen bonding. This gives alcohols a higher boiling point than aliphatic hydrocarbons with similar molecular...

acidity and basicity of alcohols and phenols

acidity-and-basicity-of-alcohols-and-phenols

Why Phenols Are More Acidic Than Alcohols

Alcohols are weak acids and weak bases because the O–H bond is polar and the oxygen atom has lone pairs. The partially positive hydrogen can be lost as a proton, and the oxygen can also accept a proton. When an alcohol is protonated, hydroxide changes into water, which is a much better leaving group. Alcohols vary a little in acidity. Methanol, with a pKa of 15.5, is slightly stronger as an acid than water, which has a pKa of 15.7. Ethanol, tert-butanol, and many other alcohols are weaker...

preparation of alcohols via addition reactions

preparation-of-alcohols-via-addition-reactions

Alcohol Synthesis from Alkenes

Alcohol synthesis from alkenes can follow three addition reactions: acid-catalyzed hydration, oxymercuration-demercuration, and hydroboration-oxidation. These methods all add across the double bond, but they give different alcohol products from the same alkene. In acid-catalyzed hydration, water adds to the double bond in an acidic atmosphere. The acid lets the hydrogen in water act as an electrophile and attack the alkene. A proton first adds to the double bond and forms a carbocation, which...

acid-catalyzed dehydration of alcohols to alkenes

acid-catalyzed-dehydration-of-alcohols-to-alkenes

Alcohol Dehydration Pathways to Alkene Products

Alcohol dehydration forms alkenes and water by removing a hydroxyl group and a hydrogen from a neighboring carbon. This reaction is usually done by heating the alcohol with an acid catalyst. Primary alcohols need higher temperatures and stronger acid conditions, while secondary and tertiary alcohols can react under milder conditions. Secondary and tertiary alcohols usually dehydrate through an E1 mechanism. In the first fast step, the alcohol is protonated and becomes an alkyloxonium ion. Then...

Making alcohols by carbonyl reduction is a key reaction in organic chemistry. It converts a carbonyl group into a hydroxyl group. The main routes are catalytic hydrogenation, hydride reduction, and borane reduction. Catalytic hydrogenation works by adding H2 across the pi bond of the carbonyl group. It uses transition metal catalysts such as Raney Ni, Pd-C, Pt, or Ru. Aldehydes and ketones can be reduced this way under mild to moderate heat, usually 25–100°C, and H2 pressure of about 1–5 atm.

alcohols from carbonyl compounds: grignard reaction

alcohols-from-carbonyl-compounds-grignard-reaction

Grignard Reagents in Alcohol Synthesis

Grignard reagents are key tools for making alcohols from carbonyl compounds. They are organomagnesium halides with a highly polar carbon–magnesium bond. Because this bond is partly ionic, the carbon acts as a strong nucleophile. It attacks the carbonyl carbon, which is the electrophilic part of a carbonyl group. Magnesium in the reagent also helps the reaction move forward. It coordinates with the carbonyl oxygen and lowers the electron density on the carbonyl carbon. This makes the carbonyl...

protection of alcohols

Alcohol Protecting Groups in Synthesis

Alcohol protecting groups help control which part of an organic molecule reacts during synthesis. A protecting group is a masking agent that makes a more reactive species inert under a chosen set of conditions. The lesson uses a pipe-flow analogy to show how this improves reaction selectivity. It also shows how protecting an alcohol can allow an organolithium alkylation of a halide to occur when the alcohol would otherwise compete. Common protecting groups for alcohols include trialkylsilyl...

preparation of diols and pinacol rearrangement

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Pinacol Rearrangement of Vicinal Diols

Vicinal diols are compounds with two hydroxyl groups on adjacent carbon atoms. They are also called glycols. Under acidic conditions, these diols can undergo a pinacol rearrangement. The reaction starts when the acid catalyst transfers a proton to one hydroxyl group. This forms an oxonium ion. The oxonium ion then loses water and creates a tertiary carbocation intermediate. Next, a methyl group migrates from one carbon to the neighboring carbon. This step forms a resonance-stabilized cation...

conversion of alcohols to alkyl halides

Alcohols to Halides: Reagents and Mechanisms

Alcohols can be turned into alkyl halides by using reagents that make the hydroxyl group a better leaving group. The hydroxyl group is first protonated, which helps the reaction move forward. From there, the pathway can follow either an SN1 or SN2 substitution, depending on the starting alcohol and the reaction conditions. Tertiary alcohols usually form tertiary alkyl halides through a two-step SN1 mechanism. This route goes through a carbocation intermediate, and hyperconjugation helps...

oxidation of alcohols

Alcohol Oxidation Reagents and Products

Alcohol oxidation changes primary and secondary alcohols into carbonyl compounds. The reaction can mean loss of electrons, loss of hydrogen, or addition of oxygen. Oxidation is the opposite of reduction, so carbonyls can be reduced to alcohols, and alcohols can be oxidized back to carbonyls. The product depends on the alcohol type and the hydrogens on the alpha-carbon, the carbon next to the hydroxyl group. Primary alcohols can become aldehydes and then carboxylic acids. Secondary alcohols can...

preparation of alcohols via substitution reactions

preparation-of-alcohols-via-substitution-reactions

Alcohol Formation from Alkyl Halides

Alcohols can be made from alkyl halides by nucleophilic substitution. In these reactions, the carbon-halogen bond is highly polar, so the halide can leave the molecule. A nucleophile such as hydroxide ion or water then replaces the halide and forms an alcohol. The reaction path depends on the alkyl halide. Primary alkyl halides usually form primary alcohols through the SN2 mechanism. In SN2, the nucleophile attacks the halogen-bearing carbon from the side opposite the carbon-halogen bond. With...

key terms and concepts

Explore how carbonyl compounds are reduced to alcohols using hydrogenation, hydride reagents, and borane. Learn key reagents, products, and conditions.

Making Alcohols by Carbonyl Reduction | JoVE K12

organic chemistry

JoVE Core Organic Chemistry explains basic concepts of stereochemistry, reactions, and mechanisms using concise and easy-to-understand animated video lessons. Additionally, the scientist-in-action videos demonstrate the application of related concepts in classical and original research experiments performed in today's laboratories worldwide.

Making Alcohols by Carbonyl Reduction

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