Simple Iron Salts

Iron-catalyzed Allylic Oxidations 3.2.2.1 Simple Iron Salts 

Porphyrin complexes, however, are prone to oxidative decomposition and therefore synthetic applications are hampered by rapid catalyst deactivation. This problem can be overcome by attaching electron-withdrawing groups to the periphery of the porphyrin system. Another problem is the poor chemoselectivity. In many cases, addition to the C=C double bond and formation of the epoxide are much faster than the corresponding hydrogen abstraction, which leads to the allylic alcohols. This is 

The prevalence for epoxidation seems to be independent of the electronic structure of the porphyrin or the type of oxidant. For example, the catalytic oxidation of cyclohexene la with molecular oxygen and isobutyraldehyde in the presence of Fe3+(TPP)C1 (TPP = tetraphenylporphyrin) in 1,2-dichloroethane yielded exclusively the epoxide 4a and only trace amounts of the allylic alcohol 2a or ketone 3a, as demonstrated by Nam et al. [111]. 

A PFeCI, K(18-crown-6)N02,NMP, HOAc (1%), Ar, r.t., 1 h B F20TPPFeCI, fBuOOH, CH2CI2-MeOH, 30 min C F20TPPFeCI, ffiuOOH, CH3CN H20, 10 min 

Exclusive enone formation could be achieved by electrocatalytic oxygenation of 2-cyclopentene-l-acetic acid in the presence of a water-soluble iron(III) porphyrin (2-TMPyP)Fe [2-TMPyP =tetrakis(N-methyl-2-pyridyl)porphyrin]. Unfortunately, neither yields nor TONs are given [116]. 

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Therapy is perfectly adequate with simple iron salts (Table 2). In adults ferrous gluconate, fumarate or sulphate are all of proven equal efficiency. Approximately 50 mg of iron is present in each tablet with the remaining 300 mg made up with an inert filler. These are given on an empty stomach at least twice a day but should nausea prevail they can be taken with food. Absorption of slow release preparations is not recommended since iron is detached from the carrier beyond the main areas of absorption in the duodenum or jejunum. Stools turn black in all cases and this is a useful index of patient compliance. In 25% of individuals gastrointestinal tract side effects are encountered in the form of diarrhoea or constipation and patients will often spontaneously discontinue medication. It is therefore essential that a tablet-count be carried out on a regular basis with a substitute being provided when this first-line medication is intolerable. In children the same preparations are favoured as syrups these are given twice... 

In aqueous solutions at low pH, simple iron salts dissociate to give the fully aquated ions. As the pH is raised, these hydrolyze and polymerize to yield insoluble oxyhydroxide precipitates (7, 15, 48, 120). The solubility product of Fe(OH)a is —10 -, so that at pH 5 the maximum concentration of soluble Fe in aqueous solution, and without a competing ligand for OH, is 10 M. By contrast, the solubility product of Fe(OH)2 is Thus in aqueous and aei obic environments at... 

Iron Oxides and Simple Iron Salt-based Catalysis... 

An iron-catalyzed double hydrophosphination of alkynes generated 1,2-bisphosphines in excellent yields (Scheme 4.16 and Example 4.16) [58], A range of iron compounds were screened for activity, and CpFe(CO)jMe was found to be the most effective. Simple iron salts such as ferrous or ferric chloride did not catalyze the reaction. The reaction was... 

It is found that catalysts prepared from precursors that do not easily crystallize, such as the above mentioned chelated iron compounds, contain high quantities of small, highly active iron oxide particles (2-5 nm). However, catalysts prepared with precursors that crystallize readily, like most of the simple iron salts, contain large iron oxide particles (>20 nm). Catalysts containing small iron oxide particles exhibit higher activities and selectivides. 

DRlt i S proved to be an appropriate technique to determine the bare part of the silica surface. It is found at the silica is most completely covered by the iron oxide, when iron citrate is used as a precursor (table ni). Very stinct is the difference between catalysts prepared from the chelating iron compounds and frtun the simple iron salts. Also the influence of the of die Ffe EDTA solution on the coverage of the silica can be seeru... 

Therefore impregnation with solutions of chelated iron compounds leads to highly dispersed active components and thus to highly active catalysts. These results could not be obtained by impregnation with simple iron salts. 

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