Studies of the Catalytic Activity of Iron (III) Porphyrins for the Protection of Carbonyl Groups in Homogeneous Media

Abstract

The protection of carbonyl groups that produce acetal products is a key reaction in fine chemistry due to the high reactivity of aldehydes and ketones in certain media. This process can be catalyzed by protic or Lewis acids. Since metalloporphyrins often possess free axial positions in the central metal, they can be applied as Lewis acid catalysts, allowing the additional coordination of substrates. Therefore, three ferric complexes were selected to be evaluated as catalysts for the acetalization of benzaldehyde with ethanol and triethyl orthoformate (TEOF) in the homogeneous phase: (i) 5,10,15,20-tetrakis(phenylporphyrin) iron (III) chloride (Fe0F); (ii) 5,10,15,20-tetrakis(2,6-difluorphenylporphyrin) iron (III) chloride (Fe2F); and (iii) 5,10,15,20-tetrakis(pentafluorphenylporphyrin) iron (III) chloride (Fe5F). The complex Fe5F showed the highest catalytic activity, and kinetic parameters were evaluated for this reaction, exhibiting an increasing rate of reaction of about 550-fold in comparison with the non-catalyzed reaction. The reaction scope was also investigated, and Fe5F was found to be active for the acetalization of benzaldehyde and acetophenone, with different protective agents such as alcohols, glycols, glycerol, and epoxide being selective for the formation of cyclic acetals. The protection of benzaldehyde with ethylene glycol and propylene glycol were also studied at different temperatures, and turnover frequency (TOF) values of up to 360 h−1 were determined at 40 °C in homogenous media without the need for solvent or drying agents.

An Efficient Acetalization Method for Biomass‐Derived Furfural with Ethanol Using γ‐Al2O3‐Supported Catalysts

“…The protonated carbonyl group undergoes the nucleophilic attack of O atom of the ethanol and subsequently, a second molecule of ethanol is added to the rhodium center (Step 3, Figure ). This last species releases the FDEA and a water molecule (Step 4, Figure ) that can thus star another catalytic cycle.…”

Copper Sulfate-Induced Diphenylamine for Rapid Colorimetric Point-of-Care Detection of Contagious Pathogens Combined with Loop-Mediated Isothermal Amplification

“…However, only low quantities of keto aldehydes were formed in the negative sample when compared with those obtained in the positive sample, and they can be inactivated by protecting groups. 39,40 The protected forms of carbonyl groups known as cyclic acetals are developed when aldehydes (R-CHO) or ketones (RCOR) react with a diol (e.g., ethylene glycol) in the presence of an acid catalyst. 39,40 Based on this phenomenon, we used ethylene glycol for protecting keto aldehyde, which is formed after DNA hydrolysis.…”

Versatile Coordination Polymer Catalyst for Acid Reactions Involving Biobased Heterocyclic Chemicals

“…The reactions of Gly with aromatic aldehydes such as furfural (Fur) and benzaldehyde (Bza)-derived from lignocellulosic biomass (Fur) [104], pyrolysis of vegetable biomass (Fur and Bza) [105] or oil (Bza)-may give cyclic acetals (Scheme 1) as fuel additives [77,101,106] with antioxidant, non-toxic and renewable features [84]. Different types of acid catalysts were studied for the Bza/Gly reaction (organic acids [107], metal chlorides [108], ionic liquids [109], Keggin-tungstophosphoric acid-based [92], acid resins [77,79,110] and organic polymers [84], metal or mixed metal oxides [82,111], sulfated metal oxides [33], zeolites [19,79,82], functionalized silicas [93,102,112], mesoporous silicas or aluminosilicates [19,31,32,83,88,113] and silesquioxanes [80]), and for the Fur/Gly reaction (metal chlorides [114], resins [77,106] and organic polymer [84], metal or mixed metal oxides [78,81,99], mesoporous silicas or aluminosilicate (bulk and supported) catalysts [31,32,101,[113][114]…”