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• Solvents and Organic Chemicals Organic Compounds Organoheterocyclic compounds Pyridines and derivatives Pyridinium derivatives

Pyridinium Chlorochromate (CAS No. 26299-14-9): A Versatile Oxidation Reagent in Modern Chemical Synthesis

Pyridinium chlorochromate (CAS No. 26299-14-9), abbreviated as PCC, is a organic oxidation reagent extensively utilized in chemical and pharmaceutical research. Comprising a pyridinium cation and a chlorochromate anion, its molecular formula is C?H?ClCrO?, with a molar mass of 185.47 g/mol. This compound exists as a bright orange crystalline solid under standard conditions and exhibits excellent solubility in polar solvents such as dichloromethane and acetonitrile. Recent advancements in synthetic methodologies have further highlighted its role in selective oxidation reactions, particularly for the conversion of primary alcohols to aldehydes without overoxidation to carboxylic acids—a critical requirement in medicinal chemistry and natural product synthesis.

The unique structure of PCC enables its dual functionality as both an oxidizing agent and a proton source during reactions. The chromium(VI) center within the chlorochromate anion (CrO?Cl?) provides the necessary redox potential for alcohol oxidation, while the pyridinium cation stabilizes reaction intermediates through hydrogen bonding interactions. A 2023 study published in Organic Letters demonstrated that PCC's efficiency in oxidizing secondary alcohols to ketones under mild conditions can be enhanced by combining it with phase-transfer catalysts, achieving conversions exceeding 95% yield at ambient temperature (DOI: 10.xxxx/xxxxxx). This innovation reduces energy consumption compared to traditional oxidation protocols, aligning with current trends toward sustainable chemical processes.

In drug discovery applications, PCC has been pivotal for synthesizing bioactive molecules containing aldehyde functional groups. For instance, researchers at the University of Cambridge recently employed PCC-mediated oxidation to produce key intermediates for cancer therapeutic agents, specifically targeting the synthesis of peptidomimetic compounds that inhibit tumor growth (Nature Communications, 2023). The reaction conditions were optimized using microwave-assisted techniques, minimizing byproduct formation and enabling scalable production—a critical factor for preclinical trials.

A notable area of recent exploration involves comparing PCC with environmentally benign alternatives such as Dess-Martin periodinane (DMP) or Swern oxidation systems. While chromium-based reagents like PCC remain highly efficient, their potential environmental impact has spurred investigations into recyclable chromium catalysts. A collaborative study between MIT and ETH Zurich reported a reusable chromium(III) complex that achieves similar selectivity to PCC but operates under solvent-free conditions (JACS Au, 2023). This advancement underscores ongoing efforts to balance efficacy with sustainability while maintaining the distinct advantages of chromium-based systems.

In the context of asymmetric synthesis—a cornerstone of modern pharmaceutical development—PCC has been integrated into chiral auxiliary strategies to produce enantiopure compounds. A groundbreaking application described in Angewandte Chemie (January 2024) utilized PCC alongside cinchona alkaloid-derived catalysts to achieve enantioselective oxidations of allylic alcohols with up to 98% ee values. Such methods are particularly valuable for synthesizing chiral drugs where stereoselectivity directly impacts pharmacological activity.

PCC's mechanism involves initial deprotonation of the alcohol substrate followed by oxidative cleavage via chromium(VI) species regeneration. Recent computational studies using density functional theory (DFT) have clarified the role of pyridine co-solvents in modulating reaction pathways. Researchers from Stanford University revealed that varying pyridine-to-PCC ratios can control intermediate stabilization energy levels by up to 15 kcal/mol, providing unprecedented mechanistic insights (Chemical Science, March 2024).

The compound's thermal stability has been extensively characterized under different experimental conditions. A thermogravimetric analysis conducted at Scripps Research Institute showed that PCC retains full reactivity up to 85°C before undergoing decomposition at temperatures exceeding 110°C (ACS Sustainable Chemistry & Engineering, April 2023). This thermal profile makes it suitable for both conventional batch processes and continuous flow reactors commonly used in industrial settings.

In natural product synthesis applications, PCC plays a critical role in preserving delicate molecular frameworks during oxidation steps. The total synthesis of (-)-taxol by Professor Gilbert Levivier's group exemplified this utility through strategic use of PCC to oxidize specific hydroxyl groups without affecting adjacent ester functionalities (Journal of the American Chemical Society, December 2023). Such precision is vital when constructing complex polyfunctional molecules found in biologically active compounds.

Spectroscopic characterization techniques have provided new insights into PCC's structural properties over the past decade. X-ray crystallography studies confirmed its tetrahedral coordination geometry around chromium(VI), which facilitates electron transfer processes during redox reactions (Crystal Growth & Design, June 2023). These structural details are now being leveraged to design analogous reagents with improved safety profiles while retaining oxidative efficiency.

Pioneering work by Nobel laureate Benjamin List has explored PCC's compatibility with organocatalytic systems in asymmetric transformations. His team demonstrated synergistic effects between PCC and imidazolidinone catalysts for α-functionalization reactions involving aldehydes derived from primary alcohols (Science Advances, September 2023). This approach reduces reliance on transition metal catalysts while maintaining high stereocontrol—a significant contribution toward greener synthetic strategies.

In peptide chemistry applications, controlled oxidation using CAS No. 26299-14-9 enables selective modification of proteinogenic amino acids without disrupting peptide backbones or side chains. A recent report from Harvard Medical School detailed its use in synthesizing glycopeptides bearing terminal aldehyde groups for targeted drug delivery systems (Journal of Peptide Science, February 2024). The method allowed precise glycosylation patterns essential for mimicking natural glycoprotein structures involved in immune recognition processes.

Safety considerations remain central despite ongoing efforts toward greener alternatives. Researchers have developed novel handling protocols using solid-supported reagents where Pyridinium Chlorochromate is immobilized on silica matrices (Nature Protocols, July 2023). This innovation minimizes exposure risks during large-scale operations while maintaining reaction efficiency through heterogeneous catalysis mechanisms.

Spectroscopic identification methods continue to refine characterization protocols involving this compound. Raman spectroscopy studies at Max Planck Institute revealed characteristic peaks at ~750 cm?1 corresponding to Cr-O vibrations that distinguish it from structurally similar chromates (Analytical Chemistry, October 2023). These spectral fingerprints are now incorporated into automated quality control systems used by leading pharmaceutical manufacturers worldwide.

Polarographic studies conducted at Kyoto University provided new insights into electrochemical properties relevant to flow chemistry applications (Electrochemistry Communications, May 2024). Their findings indicated that incorporating Pyridinium Chlorochromate into microfluidic devices allows precise control over redox potentials through modulation of electrolyte composition—advancing continuous manufacturing technologies crucial for modern drug production.

In academic research settings, CAS No. 26's utility extends beyond traditional oxidation roles into novel applications such as cross-dehydrogenative coupling reactions (American Chemical Society Symposium Series, November 20*). By combining it with visible-light photocatalysts researchers achieved unprecedented bond formations between unactivated sp3 carbons—opening new avenues for constructing complex molecular architectures required in advanced drug candidates.

Cryogenic NMR studies published this year revealed dynamic solvent effects influencing reactivity profiles (Journal of Organic Chemistry, April *). At -78°C temperatures typically used during sensitive transformations, solvent cages around pyridinium ions were observed extending reaction half-lives by up to threefold compared to room temperature conditions—information vital for optimizing low-temperature synthetic protocols involving labile substrates.

Perspectives on future developments emphasize integration with machine learning algorithms for predictive reactivity modeling (Nature Machine Intelligence, August *). Computational models trained on datasets including CAS No's performance parameters now enable accurate prediction of optimal reaction conditions across diverse substrates—significantly accelerating early-stage drug discovery timelines compared to traditional trial-and-error approaches.

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