Chloroferrates

The pyrylium cation possesses, according to the substituents in positions 2, 4, and 6, a more or less pronounced electrophilic reactivity which enables it to add nucleophiles in these positions. According to the nucleophilic reactivity and the carbon basicity " of the anions, an ion pair (a substituted pyrylium cation and an anion halide, perchlorate, sulfate, fluoroborate, chloroferrate, etc.), or a covalently bonded 2H- or 4//-pyran may be formed. With the more basic anions... 

First, mention should be made of the metathetical reaction, replacing an anion of a pyrylium salt by another-, when the solubility of the latter salt is lower than that of the former, the conversion is easy. In the opposite case, one has to find a solvent in which the solubilities are reversed (perchlorates are less soluble in water than chloroferrates or iodides, but in concentrated hydrochloric or hydroidic acids, respectively, the situation is reversed For preparing chlorides which are usually readily soluble salts, one can treat the less soluble chloroferrates with hydrogen sulfide or hydroxylamine. Another method is to obtain the pseudo base in an organic solvent and to treat it with an anhydrous acid. 

More serious limitations and precautions apply to compounds in which not all three R, R, and R" groups are aromatic. Autocondensation of benzylideneacetone (111) yields an unstable chloroferrate which may be 113 or 115, according to whether a Michael addition to 112 or a crotonic condensation to 114 is first involved. Since compound 113 could readily be prepared from 2,6-dimethyl-4-phenylpyrylium and benzaldehyde, the structure of the reaction product should be easily soluble. Another equivocal product is formed from two moles of benzylideneacetone, but a definite structure (116) results from chalcone and benzylideneacetone. ... 

A few systems obtained by the ECD method comprise polyacetylene tetra-chloroferrate [87] [CH(FeCl4)y]x and tetrachloroaluminate [CH(A1C14)X], Li+ doping (LiC104 in propylene carbonate) [86] or [(CH)x(SbF6)y] (anodic oxidation in a solution of [CH3(CH2)3]4 N+ SbFg in dry CH2C12) [92]. 

Seddon and co-workers described the Friedel-Crafts acylation reaction of benzene with ace-tylchloride using acidic chloroferrate ionic liquids as catalysts [38], In contrast to the same reaction in presence of acidic chloroaluminate systems the ketone product could be separated from the ionic liquid by solvent extraction, provided that the molar ratio of FeCl3 is in the range 0.51-0.55 in the applied ionic liquid catalyst (Scheme 1). 

Scheme 1. Friedel-Crafts acetylation using an acidic chloroferrate ionic liquid.

Chlorostannate and chloroferrate [110] systems have been characterized but these metals are of little use for electrodeposition and hence no concerted studies have been made of their electrochemical properties. The electrochemical windows of the Lewis acidic mixtures of FeCh and SnCh have been characterized with ChCl (both in a 2 1 molar ratio) and it was found that the potential windows were similar to those predicted from the standard aqueous reduction potentials [110]. The ferric chloride system was studied by Katayama et al. for battery application [111], The redox reaction between divalent and trivalent iron species in binary and ternary molten salt systems consisting of 1-ethyl-3-methylimidazolium chloride ([EMIMJC1) with iron chlorides, FeCb and FeCl j, was investigated as possible half-cell reactions for novel rechargeable redox batteries. A reversible one-electron redox reaction was observed on a platinum electrode at 130 °C. 

The most simple anion exchange reaction is the metathesis reaction it can be conveniently applied when the solubility of the desired salt is lower than that of the starting one. For example, since thiopyrylium chlorides are usually readily soluble, they can be easily converted into iodides, chloroferrates, and perchlorates (70KGS900). 

A novel imidazole synthesis utilizes the salt IV-isopropylacetonitrilium tetra-chloroferrate (8) in condensation with an amino acid ester. The salt is readily made from acetonitrile, ferric chloride and isopropyl chloride. For example, with norvaUne methyl ester a 40% yield of 5-hydroxy-l-isopropyl-2-methyl-4-propylimidazole results. The reaction is believed to proceed via an intermediate amidine. Similarly, 1-isopropyl-2,5-dimethylimidazole is formed when (8) reacts with propargylamine (Scheme 4.1.5) [43, 44). 

The reactions of a-aminocarbonyl compounds (and their acetals) with cyanamide continue to provide an attractive route to 2-aminoimidazoles. A 40% yield of the 5-hydroxyimidazole derivative 29 was obtained from the interaction of norvaline methyl ester and JV-isopropylacetonitrilium tetra-chloroferrate (28). ... 

Chen X F, Peng Y Q. Chloroferrate(III) ionic liquid Efficient and recyclable catalyst for solvent-free synthesis of 3,4-dihydropyrimi-din-2(lH)-ones. Catalysis Letters. 2008. 122, 310-313. 

The oxidation of 2,3-diaminocyclopropenethiones 41 with iron(III) chloride afforded the bis(2,3-diaminocyclopropcnyliumyl) disulfide dications which were isolated as the bisftetra-chloroferrate) salts 46. °... 

By the condensation of ethylideneacetophcnone (109, It — Ph, R — Me) with acetophenone (110, R" = Ph), the first unambiguous synthesis of 2,6-diphenyl-4-methylpyrylium chloroferrate was effected by Schneider and Ross,49 elucidating the course of reaction in Section II,D,2,a. 

---