Noah Vinter
Pyridinium chlorochromate (PCC) is a highly effective oxidizing agent for primary and secondary alcohols, converting them into aldehydes and ketones, respectively. This selective oxidation process is a vital tool in organic chemistry, allowing chemists to achieve desired oxidation states without over-oxidation. The mild nature of PCC compared to stronger oxidizing agents like chromic acid makes it particularly useful in organic synthesis, as it does not oxidize aldehydes to carboxylic acids. This specificity is due to the absence of water during the reaction, preventing unwanted side reactions and ensuring a cleaner product.
| Characteristics | Values |
|---|---|
| What is PCC | Pyridinium Chlorochromate |
| Formula | [C5H5NH]+[CrO3Cl]− |
| Use | Used as an oxidant |
| Effect on primary alcohol | Oxidises primary alcohol to aldehydes |
| Effect on secondary alcohol | Oxidises secondary alcohol to ketones |
| Effect on tertiary alcohol | Tertiary alcohols do not oxidise |
| Compared to other oxidising agents | Mild oxidising agent |
| Water presence | Water presence can lead to over-oxidation |
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What You'll Learn
PCC is a selective oxidizing agent
Pyridinium chlorochromate (PCC) is a yellow-orange salt with the formula [C5H5NH]+[CrO3Cl]−. It is a reagent in organic synthesis used primarily for the oxidation of alcohols to form carbonyls. It is a selective oxidizing agent that is used to oxidize primary alcohols to aldehydes and secondary alcohols to ketones.
PCC is a milder version of chromic acid. It is a chromium-based oxidizing agent, similar to CrO3, Na2Cr2O7, and chromic acid, collectively known as Jones oxidation. However, unlike these other agents, PCC is a mild oxidizing agent that will not oxidize aldehydes to carboxylic acids. This is because PCC oxidations involve a transfer of 2 electrons from the Cr to the substrate, and there is no water to turn the aldehyde into an aldehyde hydrate.
The oxidation reaction involves converting the alcohol to its corresponding chromate ester, which then undergoes deprotonation by a base to form a C=O double bond. The chloride ion or the alcohol can serve as a base to remove the hydrogen. The outcome of the oxidation depends on the presence or absence of water. If water is present, it can add to the aldehyde to make the 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.
PCC is commercially available and is used as an oxidant in various applications. It is highly effective in oxidizing primary and secondary alcohols, and it is more selective than the related Jones' Reagent. This makes it a useful reagent for the selective oxidation of alcohols, as it offers a lower chance of over-oxidation compared to other reagents.
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PCC is a mild oxidizing agent
Pyridinium chlorochromate (PCC) is a mild oxidizing agent that is often used in organic synthesis. It is a milder version of chromic acid and is used to oxidize alcohols. The oxidation of primary alcohols using PCC results in the formation of aldehydes, while the oxidation of secondary alcohols results in ketones.
PCC is a yellow-orange salt with the formula [C5H5NH]+[CrO3Cl]−. It is commercially available and was discovered accidentally by Prof. Suggs. The reagent is highly effective in oxidizing primary and secondary alcohols, and it offers the advantage of selective oxidation. This means that, unlike other oxidizing agents, it will not over-oxidize aldehydes to form carboxylic acids.
The reaction mechanism involves the addition of an alcohol to a suspension of PCC in dichloromethane. The first step is the attack of oxygen on chromium to form a Cr-O bond. This is followed by the transfer of a proton on the (now positive) OH group to one of the oxygens of chromium, possibly through the intermediacy of the pyridinium salt. A chloride ion is then displaced, forming a chromate ester. Finally, a base removes the proton on the carbon adjacent to the oxygen, resulting in the formation of a C-O double bond.
It is important to note that PCC is mildly acidic, and in rare cases, it can cause protonation when there is a highly substituted electron-rich alkene present. Additionally, when using PCC in a laboratory setting, it is crucial to add molecular sieves, Celite, or another solid to the bottom of the flask to avoid the formation of a difficult-to-clean brown tar.
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PCC is commercially available
Pyridinium chlorochromate (PCC) is commercially available. It is a yellow-orange salt with the formula [C5H5NH]+[CrO3Cl]−. It is a reagent in organic synthesis used primarily for the oxidation of alcohols to form carbonyls.
PCC is a milder version of chromic acid. It is used to oxidize primary alcohols to aldehydes and secondary alcohols to ketones. It is more selective than other oxidizing agents, such as Jones' Reagent, and does not cause over-oxidation to form carboxylic acids. This makes it a useful reagent for oxidizing alcohols, particularly when compared to other options such as dimethyl sulfoxide and hypervalent iodine compounds.
However, one disadvantage of PCC is its toxicity, which it shares with other hexavalent chromium compounds. It is important to carefully control the amount of water present in the reaction, as the presence of water can lead to the oxidation of aldehydes to carboxylic acids.
A typical PCC oxidation involves the addition of an alcohol to a suspension of PCC in dichloromethane. This reaction can be used to oxidize a wide variety of alcohols, including primary and secondary alcohols, to form aldehydes and ketones, respectively.
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PCC is soluble in halogenated organic solvents
Pyridinium chlorochromate (PCC) is a yellow-orange salt with the formula [C5H5NH]+[CrO3Cl]−. It is a reagent in organic synthesis used primarily for the oxidation of alcohols to form carbonyls. PCC is a milder version of chromic acid and is used to oxidize primary alcohols to aldehydes and secondary alcohols to ketones. It is a highly efficient reagent for the oxidation of primary and secondary alcohols to carbonyl compounds.
The oxidation reactions of this sort are a kind of elimination reaction, where a carbon-oxygen single bond is converted to a carbon-oxygen double bond. The elimination reaction occurs because we're putting a good leaving group on the oxygen, namely the chromium, which will be displaced when the neighbouring C-H bond is broken with a base. The first step is the attack of oxygen on the chromium to form the Cr-O bond. Subsequently, a proton on the (now positive) OH is transferred to one of the oxygens of the chromium, possibly through the intermediacy of the pyridinium salt.
In the acid-base step, either the chloride ion or the alcohol can serve as a base to remove the hydrogen. Using other common oxidants in place of PCC usually leads to dehydration because such alcohols cannot be oxidized directly. PCC also converts suitable unsaturated alcohols and aldehydes to cyclohexenones.
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PCC is used to oxidize secondary alcohols to ketones
Pyridinium chlorochromate (PCC) is a yellow-orange salt with the formula [C5H5NH]+[CrO3Cl]−. It is a reagent in organic synthesis used primarily for the oxidation of alcohols to form carbonyls. PCC is a milder version of chromic acid and is used to oxidize alcohols one rung up the oxidation ladder.
When used with secondary alcohols, PCC oxidizes them to ketones. This is because the carbon atom with the -OH group does not have a bond with hydrogen. This reaction is an elimination reaction, going from a carbon-oxygen single bond to a carbon-oxygen double bond. The elimination reaction occurs because we're putting a good leaving group on the oxygen, namely chromium, which will be displaced when the neighbouring C-H bond is broken with a base.
The first step is the attack of oxygen on the chromium to form the Cr-O bond. Secondly, a proton on the (now positive) OH is transferred to one of the oxygens of the chromium, possibly through the intermediacy of the pyridinium salt. A chloride ion is then displaced to form what is known as a chromate ester. The C-O double bond is formed when a base removes the proton on the carbon adjacent to the oxygen.
It is important to note that the amount of water present in the reaction must be carefully considered. If water is present, it can add to the aldehyde to make the hydrate, which could be further oxidized by a second equivalent of PCC. This is not a concern with ketones, as there is no H directly bonded to C.
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Frequently asked questions
PPC oxidizes secondary alcohols to ketones without further oxidation.
Pyridinium chlorochromate (PCC) is a yellow-orange salt with the formula [C5H5NH]+[CrO3Cl]−.
The oxidation reaction of PPC with secondary alcohols involves the removal of hydrogens from the alcohol functional group to form a ketone.
PPC is a milder oxidizing agent compared to chromic acid and other strong oxidizers, which can continue to oxidize aldehydes to carboxylic acids.
PPC provides a reliable method for directly oxidizing secondary alcohols to ketones without over-oxidation, enabling diverse applications in organic synthesis and research.
