Chromium-based oxidizing agents

Using chromium-based oxidants 2,4-Dimethylpentane-2,4-diol chromate(VI) diester, 122 Trimethylsilyl chlorochromate, 327 Using other oxidizing agents... 

Using chromium-based oxidants 2,4-Dimethylpentane-2,4-diol chromate(VI) diester, 122 Trimethylsilyl chlorochromate, 327 Using other oxidizing agents Bis(tributyltin) oxide, 41 Hydrogen hexachloroplatinate(IV)-Copper(II) chloride, 145 4-Methoxy-2,2,6,6-tetramethyl-1 -oxopiperidinium chloride, 183 Osmium tetroxide, 222 Potassium nitrosodisulfonate, 258 Samarium(II) iodide, 270 From alkenes by addition or cleavage reactions... 

Chromium-based oxidants are probably the most widely used of all oxidizing agents. Over the years they have been continually developed and modified to overcome the typical problems that occur during oxidation and to accept wider ranges of substrates with improved selectivities. They have been accepted readily by synthesis chemists since they are easy to handle and are often off the shelf reagents . However, they are not without their problems worit-up can be problematical overoxidation can occur, and, at all times, removal of the product from toxic chromium contaminants is a concern, especially with respect to large scale preparations. In an attempt to circumvent these problems the trend has been to develop the use of catalytic and/or supported reagents. Hiis review is concerned for the most part with the ai lica-tions and limitations of more recent chromium(VI) oxidants. Several other comprehensive reviews have appeared in this area and should be consulted for more detailed descriptions of older methods, chro-mium(V) oxidants, mechanism of oxidation and for typical experimental procedures. 

Various oxidizing agents based on chromium(VI) have been used to oxidize 2° alcohols to ketones. 

A variety of methods have been described to solve the task in solution.16 Common oxidative agents for this transformation include various heavy-metal reagents such as chromium-or ruthenium-based oxides, pyri-dine-S03, and dimethylsulfoxide (DMSO) in combination with acetic anhydride, carbodiimide, or oxalyl chloride for activation. One of the most prominent methods for the reliable conversion of sensitive compounds is the Dess-Martin reagent or its nonacetylated equivalent, 1-hydroxy-(17/)-benzo-l,2-iodoxol-3-one-l-oxide (2-iodoxybenzoic acid, IBX). 

Chromium(VI) oxide in various solvent systems provides an excellent oxidizing agent for alcohols, since it rapidly forms chromate esters which are intermediates in the oxidation of alcohols to aldehydes and ketones. The oxidation of [2- H]propan-2-ol showed a significant isotope effect when compared to propan-2-ol. Hence the abstraction of a proton by a base in the fragmentation of these esters is the rate-determining step in the reaction (Scheme 2.19). 

Chromium(vi). This inorganic pollutant can be determined by a whole range of analytical techniques, e.g. FAAS, ICP-AES/MS or XRF. However, in this situation the requirement is to determine a particular oxidation state of chromium. While not mentioned specifically in the list of analytical techniques above, a method does exist for the spectrophotometric determination of hexavalent chromium based on extraction with a chelating agent (see Chapter 5 for details). 

CHROMIUM LITHIUM OXIDE (14307-35-8) Aqueous solution is a base. An oxidizer. Reacts with many substances, including reducing agents, combustible materials, organic substances, strong acids. Incompatible with zirconium. Aqueous solution is a base. Aqueous solution is incompatible with alcohols, aldehydes, alkylene oxides, cresols, caprolactam solution, epichlorohydrin, organic anhydrides, glycols, maleic anhydride, phenols. 

HAZARD RISK Moderate explosion hazard when exposed to flame incompatible with strong oxidizing agents and strong bases hazardous combustion products are carbon monoxide and carbon dioxide ignites on contact with chromium trioxide, potassium permanganate and sodium peroxide NFPA code H 1 F 1 R 0. 

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