Chromium reagents reaction with acids

HP IR cells need to exhibit high mechanical strength and resistance to corrosion by solvents and reagents. They are often fabricated from austenitic steels (e. g. type 316) which are satisfactory for relatively mild temperatures and pressures but can be corroded by acid or form [Fe(CO)5] and [Ni(CO)4] by reaction with CO. Alternative materials for construction include some titanium alloys (which can be vulnerable to primary alcohols at high temperature) and nickel-molybdenum-chromium alloys (e. g. Hastelloy C-276, Hastelloy B2) which are highly resistant to reducing, oxidising and acidic conditions. 

The oxidation of alcohols to aldehydes or ketones by periodane has several advantages over chromium and DMSO-based oxidants because of its shorter reaction times, higher yields and simplified work up. There is very little overoxidation to the carboxylic acid. It is a practical reagent for the facile and efficient oxidation of benzylic and allylic alcohols. Saturated alcohols are slow in their reactions with it. It oxidizes alcohols in the presence of non-hydroxylic functional groups such as sulfides, enols, ethers, furans and 2°-amides. An example of the DMP oxidation is the oxidation of 3,4,5-trimethoxybenzyl alcohol (7.17) with 7.16 in CH2CI2 to give 94% yield of 3,4,5-trimethoxybenzaldehyde (7.18). 

Generation of the Enolate and Reactions with Electrophiles. The enolate of the title reagent (1) is generated with lithium amide bases and reacts with electrophiles such as benzylic bromides or tricarbonyl(fluorobenzene)chromium to give the corresponding 4,4-disubstituted derivatives of type (2), which are hydrolyzed under acidic conditions " to, for instance, the amino... 

Thus, in general catalytic oxidations with molecular oxygen are not applicable to more complicated, less volatile molecules. For reactions in the liquid phase catalytic oxygen transfer constitutes a useful alternative that combines the advantages of stoichiometric oxidants (high selectivities and broad scope) with those of catalytic oxidation with 02 (inexpensive reagent and environmentally acceptable) [3,4], A reaction of commercial interest, to illustrate the point, is the oxidation of 2-methylnaphthalene to 2-methyl-l,4-naphthoquinone (menadione), an intermediate for vitamin K. Traditionally this oxidation was carried out with stoichiometric quantities of chromium trioxide in sulfuric acid and produced 18 kg... 

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