Theo Nash
Jones oxidation is an organic reaction used for the oxidation of primary and secondary alcohols to carboxylic acids and ketones, respectively. The oxidation process is not an equilibrium process, and once the carboxylic acid stage is reached, there is no reversing the reaction. The Jones oxidation reaction is named after its discoverer, Sir Ewart Jones, and involves the use of a solution called the Jones reagent, which is prepared by dissolving chromium trioxide in aqueous sulfuric acid. This acidic mixture is then added to an acetone solution of the substrate. The oxidation reaction is rapid, exothermic, and typically yields high results.
| Characteristics | Values |
|---|---|
| Name | Jones oxidation |
| Named After | Sir Ewart Jones |
| Type of Reaction | Organic reaction |
| Reactants | Primary and secondary alcohols |
| Products | Carboxylic acids, ketones, aldehydes |
| Reagent | Jones reagent, chromium trioxide, potassium dichromate |
| Reaction Conditions | Strongly acidic, high yields, rapid and exothermic |
| Drawbacks | Carcinogenic compounds (Cr(VI)), aldehyde isolation challenge |
| Alternatives | Collins reagent, chromium (VI) reagents (PCC, PDC) |
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What You'll Learn
Jones oxidation of primary alcohols
Jones oxidation is a chemical reaction involving the oxidation of primary and secondary alcohols to carboxylic acids and ketones, respectively. It is named after its discoverer, Sir Ewart Jones. The oxidation step is not an equilibrium process, so once the carboxylic acid stage is reached, the reaction cannot go back.
The traditional Jones oxidation is a reaction of an alcohol with a mixture of chromium oxide (CrO3). The reaction is very rapid and quite exothermic, with typically high yields. The reagent is convenient and cheap. However, Cr(VI) compounds are carcinogenic, which has reduced the use of this methodology.
Jones oxidation can be used to selectively oxidize benzylic and allylic alcohols to aldehydes, which do not form hydrates in significant amounts. The reagent is very acidic, and the substrate in acetone is essentially titrated with the oxidant solution. The concentration of sulfuric acid can be decreased to minimize side reactions, although the oxidation power increases too.
For oxidation to aldehydes and ketones, two equivalents of chromic acid oxidize three equivalents of the alcohol. For oxidation of primary alcohols to carboxylic acids, four equivalents of chromic acid oxidize three equivalents of the alcohol. The aldehyde is an intermediate. The inorganic products are green, characteristic of chromium(III) aquo complexes.
The Jones oxidation is a common protocol for the synthesis of carboxylic acids from primary alcohols in the presence of a wide variety of functional groups. It is one of the oldest and most common methods for converting alcohols to aldehydes or carboxylic acids.
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Jones oxidation of secondary alcohols
Jones oxidation is a chemical reaction involving the oxidation of primary and secondary alcohols to carbonyl compounds. It is named after its discoverer, Sir Ewart Jones.
Jones oxidation is a common protocol for the synthesis of carboxylic acids from primary alcohols in the presence of a wide variety of functional groups. The reaction is carried out by titrating chromic acid against the substrate dissolved in acetone. Acetone helps in the dissolution of the substrate and prevents epimerization by acid-catalyzed enolization of the α-center in the ketones during oxidation of the secondary alcohols. The resulting carboxylic acids often react with the starting alcohols to give the corresponding ester as a side product. To avoid this side reaction, an inverse addition protocol can be used, wherein the alcohol is added dropwise to the Jones reagent.
Jones reagent is a solution prepared by dissolving chromium trioxide in aqueous sulfuric acid. The oxidation is very rapid and quite exothermic, with typically high yields. The reagent is convenient and cheap. However, Cr(VI) compounds are carcinogenic, which has reduced the use of this methodology.
The oxidation of secondary alcohols using Jones oxidation efficiently produces their respective ketones. The silyl protection and the acyclic ketal protections were found to be less tolerant of Jones oxidation conditions, while the cyclic ketal protecting groups were able to withstand the acidic conditions.
Jones oxidation has been used for the synthesis of amino acids from the corresponding amino alcohols in high enantiomeric purity, without racemization of the α-center of the amino acid. The use of an acid-labile protecting group for alcohols facilitates simultaneous deprotection followed by oxidation to the desired acids.
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Jones oxidation of aldehydes
Jones oxidation is a chemical reaction involving the oxidation of primary and secondary alcohols to yield carbonyl compounds, such as carboxylic acids and ketones. The reaction was discovered by Sir Ewart Jones and is particularly useful for the synthesis of carboxylic acids from primary alcohols.
The Jones oxidation reaction is carried out under specific conditions, typically at 0 °C, using chromic acid as the oxidizing agent. The chromic acid is formed by dissolving chromium trioxide in aqueous sulfuric acid, creating an acidic mixture. This mixture is then added to an acetone solution of the substrate, resulting in a very rapid and exothermic reaction with typically high yields.
The oxidation process can be represented by the following chemical equation:
2 HCrO4− + 3 RR'C(OH)H + 8 H+ + 4 H2O → 2 [Cr(H2O)6]3+ + 3 RR'CO ·
In this equation, two equivalents of chromic acid (HCrO4-) oxidize three equivalents of the alcohol (RR'C(OH)H), leading to the formation of aldehydes or ketones. The aldehydes produced may undergo further oxidation to carboxylic acids, particularly in the presence of water, as they can form hydrates that facilitate this additional oxidation.
It is important to note that the Jones oxidation reagent is very acidic, and only specific functional groups are compatible with this reaction. For example, esters and tert-butyl esters generally remain unchanged during the reaction. Additionally, the concentration of sulfuric acid can be adjusted to minimize side reactions, although this modification increases oxidation power.
While the Jones oxidation is a convenient and inexpensive method, the use of Cr(VI) compounds, such as chromium trioxide, has raised concerns due to their carcinogenic nature. As a result, milder and more selective reagents, such as the Collins reagent, have been developed for oxidation reactions.
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Jones oxidation: alternative methods
Jones oxidation is a classic organic chemistry oxidation reaction, mainly used to oxidize primary alcohols to carboxylic acids and secondary alcohols to ketones. The oxidation step, however, is not an equilibrium process. So, once we reach the stage of carboxylic acid, the reaction cannot be reversed.
The Jones Reagent is a mixture of chromic trioxide or sodium dichromate in diluted sulfuric acid, which forms chromic acid in situ. The oxidation is very rapid and quite exothermic. Yields are typically high. The reagent is convenient and cheap. However, Cr(VI) compounds are carcinogenic, which deters the use of this methodology.
Alternative Methods
There are some alternative methods to the Jones oxidation. The use of Jones oxidation has decreased over time due to the development of milder, more selective reagents. Some of these alternatives include:
- Collins reagent or chromium (VI) reagents such as PCC and PDC can be used for the synthesis of aldehydes.
- Molecular oxygen can be used in the presence of palladium as a catalyst for the synthesis of aldehydes, ketones, and carboxylic acids.
- Catalytic amounts of CrO3 in aqueous solution can be used in tandem with a strong stoichiometric oxidant that can reoxidize Cr(IV) but does not interfere with organic compounds.
- Pyridinium chlorochromate (PCC) is a milder version of chromic acid. It oxidizes primary alcohols to aldehydes and secondary alcohols to ketones.
- Dess-Martin periodinane is another milder oxidant that can be used to oxidize primary alcohols to aldehydes.
- Potassium dichromate (K2Cr2O7) can be used instead of chromium trioxide.
- Potassium permanganate (KMnO4) can be used as an oxidizing agent.
- Sodium dichromate (Na2Cr2O7) can be used as an oxidizing agent.
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Jones oxidation: safety considerations
Jones oxidation is a widely used method in organic synthesis for the oxidation of primary alcohols to carboxylic acids and secondary alcohols to ketones. It is named after its developer, Sir Ewart Jones, and has been a cornerstone in various synthetic pathways due to its relatively straightforward procedure and the availability of the required reagents. However, its use has decreased with the development of milder, more selective reagents, such as the Collins reagent.
The Jones reagent is a solution prepared by dissolving chromium trioxide in aqueous sulfuric acid. This mixture is then added to an acetone solution of the substrate to initiate the oxidation reaction. The process is very rapid and exothermic, with typically high yields. Despite its convenience and low cost, the carcinogenic nature of Cr(VI) compounds has deterred its use.
Safety considerations for the Jones oxidation are crucial due to the hazardous nature of the reagents and the potential for side reactions. When working with large-scale reactions, specialized equipment is necessary, including reactors designed for corrosive and hazardous materials, along with safety gear such as personal protective equipment and ventilation systems. Proper training in handling these reagents and equipment is essential for safe operations.
To minimize side reactions, the concentration of sulfuric acid can be decreased. However, this also increases oxidation power, so it is a careful balance. Any toxic residues of Cr(V) and Cr(VI) compounds should be destroyed by adding an excess of 2-propanol once the reaction is complete.
Alternative solvents can be used with the Jones oxidation, offering advantages like improved solubility of reactants and reduced reaction times. However, this also introduces the possibility of side reactions with the solvent and the need for additional safety precautions due to the potential use of more hazardous solvents. The Jones reagent can be modified to suit specific applications, such as adjusting the ratio of chromium trioxide to sulfuric acid to influence its oxidizing power.
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Frequently asked questions
Jones oxidation is an organic reaction for the oxidation of primary and secondary alcohols to carboxylic acids and ketones, respectively. It is named after its discoverer, Sir Ewart Jones.
Jones reagent will convert primary and secondary alcohols to aldehydes and ketones, respectively. Depending on the reaction conditions, the aldehydes may then be converted to carboxylic acids.
Jones reagent is a solution prepared by dissolving chromium trioxide in aqueous sulfuric acid. Alternatively, potassium dichromate can be used in place of chromium trioxide.
