Noah Vinter
PCC (Pyridinium Chlorochromate) is a versatile oxidant in organic synthesis, often used to oxidize primary and secondary alcohols to carbonyl compounds. It is a milder version of chromic acid, and its oxidation of alcohols yields aldehydes and ketones, respectively. The presence of water can impact the outcome of the reaction, and PCC is considered a mild oxidizing agent compared to other reagents. Following the PCC reaction, the subsequent use of the oxidizing agent Br2 (bromine) further oxidizes the aldehyde to a carboxylic acid. This two-step process allows for the conversion of primary alcohols to carboxylic acids, showcasing the versatility of PCC and Br2 in alcohol oxidation and organic synthesis.
| Characteristics | Values |
|---|---|
| What is PCC | Pyridinium Chlorochromate |
| Type of Reagent | Milder version of chromic acid |
| What it does to Alcohol | Oxidizes alcohols one rung up the oxidation ladder |
| Primary Alcohol | Converts to aldehydes |
| Secondary Alcohol | Converts to ketones |
| Tertiary Alcohol | Will not be oxidized |
| Byproducts | Cr(IV) and pyridinium hydrochloride |
| Water in the reaction | Can add to the aldehyde to make the hydrate |
| What is BR2 | Bromine Radical |
| Reaction with Alcohol | Replaces OH group with Br group |
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What You'll Learn
PCC is a milder version of chromic acid
Pyridinium chlorochromate (PCC) is a milder version of chromic acid. It is a versatile oxidant in organic synthesis, often used to oxidize primary and secondary alcohols to carbonyl compounds.
PCC oxidizes alcohols one rung up the oxidation ladder. It can convert primary alcohols to aldehydes and secondary alcohols to ketones. However, unlike chromic acid, PCC does not oxidize aldehydes further to form carboxylic acids. This makes it a milder oxidizing agent.
For example, if you add one equivalent of PCC to a primary alcohol, the oxidized version, an aldehyde, will be produced. The byproducts of this reaction are Cr(IV) and pyridinium hydrochloride. The presence of water in the reaction can impact the outcome. If water is present, it can add to the aldehyde to create a hydrate, which could be further oxidized by a second equivalent of PCC. However, this is not a concern with ketones, as there is no H directly bonded to C.
The mechanism of PCC oxidation involves the transfer of two electrons from Cr to the substrate. The C-O double bond forms when a base removes the proton on the carbon adjacent to the oxygen. The electrons from the C-H bond then move to form the C-O bond, breaking the O-Cr bond, and Cr(VI) becomes Cr(IV) (O=Cr(OH)2).
PCC is a useful reagent for selectively oxidizing alcohols without over-oxidation to carboxylic acids. It is important to note that PCC is mildly acidic, and in rare cases, it can protonate highly substituted electron-rich alkenes.
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It oxidises primary alcohols to aldehydes
Pyridinium chlorochromate (PCC) is a versatile oxidant in organic synthesis. It is a milder version of chromic acid and acts as an oxidizing agent. It converts alcohols to carbonyls, but it is not strong enough to convert primary alcohols to carboxylic acids.
PCC oxidizes alcohols one rung up the oxidation ladder. It oxidizes primary alcohols to aldehydes and secondary alcohols to ketones. This is because, unlike chromic acid, PCC does not oxidize aldehydes to carboxylic acids.
The oxidation of a primary alcohol by PCC in a dichloromethane solvent yields an aldehyde. This is an oxidation-reduction reaction, where the alcohol is oxidized to a carbonyl, and the Cr6+ is reduced to the corresponding Cr4+ species. The C-O double bond is formed when a base removes the proton on the carbon adjacent to the oxygen. The electrons from the C-H bond move to form the C-O bond, and in the process, the O-Cr bond is broken, and Cr(VI) becomes Cr(IV).
The reaction is often carried out in the absence of water. If water is present, it can add to the aldehyde to create the hydrate, which could be further oxidized by a second equivalent of PCC. This is not a concern with ketones because there is no H directly bonded to C.
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It oxidises secondary alcohols to ketones
Alcohol oxidation is a collection of oxidation reactions in organic chemistry that convert alcohols to aldehydes, ketones, carboxylic acids, and esters. The reaction primarily applies to primary and secondary alcohols. Secondary alcohols form ketones, while primary alcohols form aldehydes or carboxylic acids. Tertiary alcohols, on the other hand, cannot be oxidised without breaking the C-C bonds of the molecule.
Secondary alcohols (OH is on a carbon that is attached to two other carbons) can be oxidised to ketones (OH turns into a =O) using a variety of reagents, including PCC with CH2Cl2. PCC, or pyridinium chlorochromate, is a milder version of chromic acid. It oxidises primary alcohols to aldehydes and secondary alcohols to ketones. It is an efficient reagent for the oxidation of primary and secondary alcohols to carbonyl compounds.
The oxidation of secondary alcohols to ketones is an important reaction in organic chemistry. It is converted to a ketone as a secondary alcohol is oxidised. Along with the hydrogen bound to the second carbon, the hydrogen from the hydroxyl group is lost.
A common method for oxidising secondary alcohols to ketones uses chromic acid (H2CrO4) as the oxidising agent. Chromic acid, also known as Jones reagent, is prepared by adding chromium trioxide (CrO3) to aqueous sulfuric acid. Other commonly used oxidising agents include potassium permanganate (KMnO4) and sodium dichromate (Na2Cr2O7).
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It is a chromium-based oxidising agent
Pyridinium chlorochromate (PCC) is a chromium-based oxidising agent. It is a milder version of chromic acid and is used to oxidise alcohols. PCC oxidises primary alcohols to aldehydes and secondary alcohols to ketones. It is an efficient reagent for the oxidation of primary and secondary alcohols to carbonyl compounds. The oxidation process involves the transfer of two electrons from the Cr to the substrate.
The C-O double bond is formed when a base removes the proton on the carbon adjacent to the oxygen. The electrons from the C-H bond move to form the C-O bond, and the O-Cr bond is broken, resulting in Cr(VI) becoming Cr(IV). PCC is mildly acidic, and in rare cases, it can cause protonation when there is a highly substituted electron-rich alkene present.
Chromium trioxide, another chromium-based compound, is a strong oxidising agent that is not soluble in most organic solvents. It forms chromic acid and anhydrides in water, from which commercially available salts such as sodium dichromate and pyridinium dichromate are derived. A solution of chromium trioxide in aqueous sulfuric acid, when mixed with acetone, can be used to isolate oxidation products such as carbonyl compounds and carboxylic acids.
Chromium-based reagents, such as those discussed above, are commonly used in the oxidation of alcohols to aldehydes and ketones. These reactions are detailed in the book "Oxidation of Alcohols to Aldehydes and Ketones" by Tojo and Fernández.
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It is a weak oxidising agent
Pyridinium chlorochromate (PCC) is a weak oxidising agent. It is a milder version of chromic acid. It is used to oxidise alcohols one rung up the oxidation ladder. In other words, it converts primary alcohols to aldehydes and secondary alcohols to ketones.
PCC is a chromium-based oxidising agent, most of which are CrO3, Na2Cr2O7, and chromic acid. It is a Cr6+ salt formed between pyridine (C6H5N), HCl, and CrO3. It is soluble in halogenated organic solvents such as dichloromethane, which allows the reaction to be carried out in the absence of water.
The oxidation of a primary alcohol by PCC in a dichloromethane solvent yields an aldehyde. However, it is important to note that PCC will not oxidise aldehydes to carboxylic acids. This is in contrast to chromic acid, which is a harsher oxidant and will perform this reaction.
The mechanism of PCC oxidation involves the transfer of two electrons from the Cr to the substrate. The C-O double bond is formed when a base removes the proton on the carbon adjacent to the oxygen. The electrons from the C-H bond move to form the C-O bond, and in the process, the O-Cr bond is broken, and Cr(VI) becomes Cr(IV).
Overall, while PCC is a weak oxidising agent, it is an efficient reagent for the oxidation of primary and secondary alcohols to carbonyl compounds.
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Frequently asked questions
PCC (Pyridinium Chlorochromate) is a milder version of chromic acid. It oxidizes alcohols one rung up the oxidation ladder, from primary alcohols to aldehydes and from secondary alcohols to ketones.
The C-O double bond is formed when a base removes the proton on the carbon adjacent to the oxygen. The electrons from the C-H bond move to form the C-O bond, and in the process, the O-Cr bond is broken, and Cr(VI) becomes Cr(IV).
The byproducts of the reaction are Cr(IV) and pyridinium hydrochloride.
PCC is a mild oxidizing agent. Unlike chromic acid, it will not oxidize aldehydes to carboxylic acids.
