A mild selective oxidant-pyridinium chlorochromate (PCC)_Industrial additive

Pyridinium chlorochromate, PCC for short, is the abbreviation of pyridinium chlorochromate. A mild oxidizing agent with orange-yellow crystals. It is used to oxidize alcohol to aldehydes to a limited extent. The disadvantages of using PCC are that the reaction time is too long and PCC is toxic. Invented by E.J. Corey. The reagent itself is slightly acidic, so it is often used in conjunction with a buffer such as sodium acetate.

Properties and applications of pyridinium chlorochromate (PCC), a mild selective oxidant

Oxidation of alcohols by pyridinium chlorochromate (PCC), a mild selective oxidant

PCC is an oxidizing agent, particularly efficient in the oxidation of primary and secondary alcohols to aldehydes and ketones. Unlike the related Jones reagent, PCC rarely undergoes peroxidation to form carboxylic acids. A typical PPC oxidation reaction is to add alcohol to PCC suspension in methylene chloride. The simple reaction mechanism is:

C5H5NHCrO3Cl + R2CHOH → C5H5NHCl + H2CrO3+ R2C=O

In actual operation, chromium by-products will precipitate together with pyridine. Inert adsorbents, such as molecular sieves or silica gel, can be added to make the viscous by-products adsorb to the surface and work better.

A mild selective oxidant-pyridinium chlorochromate (PCC) other reactions

In addition to simple hydroxyl oxidation reactions, rearrangement reactions are also feasible. For example: tertiary alcohols cannot be directly oxidized, but in the Babler oxidation reaction, the formation of chromate esters with PCC and allyl tertiary alcohols can pass through [3,3]- before the oxidation step of carbon-based molding. σ migration reaction to perform isomerization. Other common oxidants can usually promote simple dehydration reactions without any oxidation reactions centered on the tertiary hydroxyl group.

Another PCC oxidation reaction is the conversion of unsaturated alcohol or aldehyde into cyclohexenone. This method is a cyclization reaction of oxidative cations, converting (-)-citronellol into (-)-pulegone. PCC will also affect the oxidation reaction of allyl groups, such as the conversion of dihydrofuran into lactone.

Preparation and structure of pyridinium chlorochromate (PCC), a mild selective oxidant

The original preparation method was an accidental discovery. It was prepared by adding pyridine to cold concentrated hydrochloric acid solution of chromium trioxide:

C5H5N + HCl + CrO3→ [C5H5NH][CrO3Cl]

This compound is composed of a pyridine cation ([C5H5NH+]) and a tetrahedral chromium trichloride anion (CrO3Cl-). Related salts available experimentally, such as: 1-butylpyridine chromium trioxide ([C5H5N(C4H9)]+[CrO3Cl]−).

A mild and selective oxidizing agent – pyridinium chlorochromate (PCC) mild oxidizing agent

PCC was first discovered as a new selective oxidant by E.J. Corey in 1975 after conducting developmental research. It is mainly used for the oxidation of alcohols into aldehydes/ketones, the selective oxidation of local radicals in carbohydrates, the oxidation of borane and oxime (deoxime reaction) into carboxyl compounds, and the direct oxidation of alkenyl tertiary alcohols into unsaturated aldehydes; it can also make alkenes Alcohols are directly oxidized to esters or lactones, etc. Compared with other commonly used chromium-containing oxidants such as jons reagent and Colljn reagent, PCC has the characteristics of strong oxidizing ability, good selectivity, the olefinic bonds of the substrate molecules are not affected during the oxidation process, and it is easy to operate.

In addition, the acidity of the subunit P CC is weak, so those groups that are unstable to acid can still be preserved during oxidation. PCC is a mild oxidizing agent with orange-yellow crystals. It is used to oxidize alcohol to aldehydes to a limited extent. The disadvantages of using PCC are that the reaction time is too long and PCC is toxic. The reagent itself is slightly acidic, so it is often used in conjunction with a buffer such as sodium acetate.

A mild selective oxidizing agent – pyridinium chlorochromate (PCC) related reagents

Other transmethylboronic acid reagents that can be used for alcohol oxidation should be more convenient and less toxic include dimethyl sulfoxide-based oxidation reactions (such as Sven oxidation, Pfitzner-Moffat oxidation, trifluoride Boron tetrahydrofuran complex) and hypervalent iodine-based oxidation reaction (such as Dess-Martin oxidant).