Iron salts as catalysts

Iron. Salts as Catalysts.—Schonbein, in 1857, drew attention to the fact that ferrous salts are capable of acting as oxygen-carriers in certain circumstances,7 but it was not until thirty-seven years had elapsed that... 

Iron Salts as Catalysts. Ferric chloride is employed not only for reactions involving the replacement of hydrogen by chlorine in the aromatic nucleus, but also for accelerating numerous other chlorinations. The preparation of carbon tetrachloride from carbon disulfide is frequently brought about by the catalytic effects of iron. In the absence of iron, perchloro-methyl mercaptan is formed. 

Zhao, H., Sun, W., Miao, C., and Zhao, Q. (2014). Aerobic oxidation of secondary alcohols using NHPI and iron salt as catalyst at room temperature. J. Mol. Catal. A Chem., 393, 62-67. 

The synthesis of thioesters through the coupling aldehydes with thiols has been achieved using common iron salts as catalysts (Scheme 5.33) [54], The reactions required an oxidant, and tert-butyl hydroperoxide was found to be effective tmder the reaction conditions. The reactions were carried out in pure water and afforded moderate to excellent yields of the thioesters. The scope of the chemistry was quite broad as both alkyl and aryl aldehydes as well as alkyl- and arylthiols were successfully coupled as well as several heteroaromatic aldehydes. Overall, this is a practical approach to the preparation of thioesters. 

The first attempts to modify the course of the reaction of Grignard reagents with various substrates by using iron salts as a catalyst were reported by Kharasch and coworkers ... 

Iron Salts as Negative Catalysts.—In certain cases small quantities of ferrous salts act as retarding agents in chemical reactions, and may therefore be termed negative catalysts. For example, ferrous sulphate has long been known 4 to hinder the action of nitric acid on metals. 

Much milder reaction conditions in the Barbier-type reaction can be employed by utilizing iron(III) salts as catalysts. For example, when 2 mol % FeCb is added to Smh, the Barbier reaction between a primary organic iodide and a ketone is complete within 3 h at room temperature (equation 19). The iron(III) is probably reduced by Smh to a low-valent species which serves as an efficient electron transfer catalyst, thus lowering the activation energy for the coupling process vide infra). 

Numerous other examples of this reaction type have been reported with iron(0) or palladium salts as catalyst precursors99-102. 

Ionization potential. See Ionization energy a- and p-lonone, 1049 lonophore, 624,1023 Iron, reduction of nitroarenes by, 878 Iron(III) salts as catalysts in halogenation of arenes, 446, 448—450 Isoamyl acetate, in bananas, 85, 788 Isobutane, 57. See also 2-Methylpropane Isobutene. See 2-Methylpropene... 

While TBHP induces the ketonization of saturated hydrocarbons in the presence of an iron(lll) catalyst, the use of copper(ll) salts as catalysts gives olefination. Differences between the iron-catalyzed and copper-catalyzed reactions support a metal dependent reaction pathway. 

An intriguing approach to the synthesis of pyrroles has been reported using an iron-promoted domino reaction (Scheme 3.54 and Example 3.7) [60]. Starting from cyclopropanes and using a conunon iron salt as the catalyst for the reaction, a series of cyclopropanes were converted into pyrroles in good to excellent yields. One of the more attractive aspects of this chemistry was the ability to carry out the functionalization under air. 

It was reported that iron salts catalyzed the oxidative a-phosphonation of A,A-dimethylanilines with (R0)2P(0)H in the presence of tert-butylhydroperoxide [196]. In the study electrochemical C-H bond activation was utilized to generate iminium species, followed by C-P bond formation. An efficient dehydrogenative coupling reaction involving iminium salt as a possible intermediate was also reported with copper salt as catalyst and molecular oxygen as oxidant [197]. 

Kota 1. If more than 100 mg of the iron salt is used as catalyst for the conversion of lithium, the separation of the layers during the work-up may be difficult, owing to the formation of iron hydroxide gel. 

Other catalyst systems such as iron V2O5-P2O5 over silica alumina are used for the oxidation. In the Monsanto process (Figure 6-4), n-butane and air are fed to a multitube fixed-bed reactor, which is cooled with molten salt. The catalyst used is a proprietary modified vanadium oxide. The exit gas stream is cooled, and crude maleic anhydride is absorbed then recovered from the solvent in the stripper. Maleic anhydride is further purified using a proprietary solvent purification system. ... 

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