Application of pyridinium chlorochromate PCC [Background and Overview]
Pyridinium chlorochromate, molecular formula C5H4N·HCrO3Cl, abbreviated as PCC, the abbreviation of Pyridinium chlorochromate, Chinese Also known as Sarrett’s reagent. PCC was first discovered as a new selective oxidant by E.J. Corey in 1975 after conducting developmental research. Mainly used for the oxidation of alcohols into aldehydes/ketones, selective oxidation of local radicals in carbohydrates, oxidation of borane and oxime (deoxime reaction) into carboxyl compounds, 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. If PCC is inhaled, move the patient to fresh air; if skin contact occurs, take off contaminated clothing and wash the skin thoroughly with soap and water. If you feel uncomfortable, seek medical attention; if contact with eyes occurs, separate the eyelids and apply Rinse with running water or saline and seek medical attention immediately. If ingested, rinse mouth immediately. Do not induce vomiting and seek medical attention immediately.
Application of pyridinium chlorochromate PCC [Synthesis]
Usually, chromium trioxide is reacted with hydrochloric acid to form chloropyridine into chlorochromic acid, and then pyridine is added at 0°C to obtain an orange-yellow stable pyridine chlorochromate solid:
Specific reaction steps: quickly add chromium trioxide (100 g, 1 mol) to 6 N hydrochloric acid (184 ml, 1.1 mol) under stirring. After 5 minutes, wait until the uniform solution is cooled to 0 At ℃, add pyridine (79.1 g, 1 mol) carefully over 10 minutes. The solution is cooled to 0 ℃ again to obtain an orange solid. The solid is collected on a sintered glass funnel, filtered, and vacuum dried for 1 hour. The yield 250.5 grams, 54%.
Application of pyridinium chlorochromate PCC [Application]
Adsorb PCC on alumina, or support PCC anions on the polymer skeleton to produce polyvinylpyridine chlorochromate (PVPCC), which is very convenient to use in synthesis. The resin consumed during the reaction can be quantitatively recovered and reused after regeneration. Therefore, PCC is a valuable selective oxidant in organic synthesis, especially in fine organic synthesis. PCC is a mild oxidizing agent used to oxidize alcohols to aldehydes in a limited manner. Application examples are as follows:
1. Chain alkynes: For example, 6-heptynal is a useful intermediate for constructing long-chain compounds and has important application value in drug synthesis. In general, acetylenic compounds can be prepared using carboxylic acid under the action of an appropriate reducing agent, without affecting the carbon-carbon triple bond, but the yield is not high; if dimethyl sulfoxide or oxalyl chloride is used for oxidation, higher yields can be obtained. The yield is high, but it needs to be carried out at a low temperature of -78°C, and the reaction conditions are harsh. Sarrett’s reagent (Sarrett), that is, PCC, can oxidize alcohols to aldehydes at room temperature without affecting unsaturated bonds and is convenient for industrial production. 3-heptyne-1- can be first oxidized in ethylenediamine under the action of sodium hydride. The rearrangement reaction of alcohol gives 6-heptyn-1-aldehyde, which is then oxidized at room temperature using Sarit reagent. After completion, the reaction solution is purified through a silica gel column to obtain 6-heptyn-1-aldehyde, yield is 93.2%. This method is relatively simple and easy to prepare 6-heptyn-1-aldehyde, and is suitable for scale-up production. The reaction process is as follows:
2. Synthesis of 10-HDA, including the following steps:
1) Using toluene as the solvent, 8-bromo-1-octanol is obtained from 1,8-octanediol and hydrobromic acid under the action of a catalyst; where the mole of 1,8-octanediol and hydrobromic acid The ratio is 1:1-1:1.6;
2) Oxidize the 8-bromo-1-octanol obtained in step 1) with pyridinium chlorochromate (PCC) in dichloromethane to 8-bromooctanal; wherein 8-bromo-1-octanol and chlorochromium The molar ratio of acid pyridine is 1:1.1-1:1.6;
3) React 8-bromooctanal obtained in step 2) with phosphorus ylide reagent (triethyl phosphoryl acetate) to obtain (2E)-10-bromo-2-decenoic acid; wherein 8-bromooctanal and The molar ratio of phosphorus ylide reagent is 1:1-1:1.6; the obtained (2E)-10-bromo-2-decenoic acid is hydrolyzed under alkaline conditions and then acidified to obtain (2E)-10-hydroxy-2-decenoic acid. olefinic acid (10‑HDA).
Application of pyridinium chlorochromate PCC [Main reference materials]
[1] Song Yang; Zhang Lijun. Synthesis of 6-heptylenal from stannous fluoroborate using Sarit reagent. Synthetic Chemistry, 2010, 18.B09: 142-142.
[2] Xiao Yanhua. Synthesis process of 10-HDA. CN201210033170.0, application date 2012-02-15
[3] Zhong Qi; Shao Jianguo. A new selective oxidant-pyridinium chlorochromate. Journal of Yangzhou University (Natural Science Edition), 1986, 1: 012.
[4] Pyridinium chlorochromate-a universal oxidant in organic synthesis. Journal of Yangzhou University (Natural Science Edition), 1984.
