Rita Kovács

Green chemical tools in organophosphorus chemistry-organophosphorus tools in green chemistry

Abstract A variety of reactions including esterifications, alkylations, additions, cycloadditions, fragmentations, and condensations were carried out under microwave MW-assisted and solventless conditions, occasionally in ionic liquids (ILs). In a few cases, MW was synergic with phase transfer catalysis or could substitute it. A variety of P(III) ligands were developed and converted to Pt(II) complexes that can be used as catalysts. Finally, phosphorylations and the Kabachnik–Fields reaction were monitored and optimized by an on-line method, in situ Fourier transform IR spectroscopy.

Diels–Alder Cycloadditions of 1,2-Dihydrophosphinine Oxides and Fragmentation-Related Phosphorylations with 2-Phosphabicyclo[2.2.2]Octadiene Oxides Under Green Chemical Conditions—The Role of Microwave and Ionic Liquids

Abstract The effect of the use of microwave (MW) and solvents including ionic liquids on the Diels–Alder reaction of 1,2-dihydrophosphinine oxides (1) and fragmentation-related phosphorylation of phenols with 2-phosphabicyclo[2.2.2]octadiene oxides (4) was studied. The MW-assisted Diels–Alder reaction of dihydrophosphinine oxides (1) with N-phenylmaleimide may be advantageous to carry out in [bmim][BF4] due to shorter reaction times, but the dimerization of the double-bond isomers (A and B) of the dihydrophosphinine oxides (1) may be best accomplished under MW in the absence of any solvent. The fragmentation-related phosphorylations may also be carried out under MW, which with the P-phenyl precursor (4a) became more efficient in [bmim][BF4]. GRAPHICAL ABSTRACT

Microwave Irradiation as a Useful Tool in Organophosphorus Syntheses

Application of the microwave technique offers advantages in organophosphorus chemistry, such as in the Kabachnik–Fields reaction, in Diels–Alder cycloadditions, in an inverse Wittig-type reaction, and in fragmentation-related phosphorylations.

Optimized Synthesis of Etidronate

The synthesis of Etidronate (as the disodium salt) by the reaction of acetic acid with phosphorus trichloride/ phosphorus acid in methanesulfonic acid was studied and optimized. We showed that it is enough to use 3.2 equivalents of the phosphorus trichloride and there is no need to apply phosphorus acid. In the two-step variation of the synthesis, the acetyl chloride was formed by the reaction of acetic acid with phosphorus trichloride, thionyl chloride or triphosgene, then the intermediate was converted to etidronate by reaction with 2.2 equivalents of phosphorus trichloride. The work-up included in all cases hydrolysis and pH adjustment.

Environmentally friendly syntheses and tools

Abstract Recent results obtained by our group on MW-assisted reactions, such as the alkylation of P˭O-functionalized CH-acidic compounds and the addition of dialkyl phosphites to α-ketophosphonates, are summarized together with the rational synthesis of hydroxy-methylene bis(phosphinic acids). GRAPHICAL ABSTRACT

Green Chemical Synthesis of Bisphosphonic/Dronic Acid Derivatives

GRAPHICAL ABSTRACT Abstract Our recent results on the synthesis of dronates/dronic acids have been summarized.

A Study on the Reduction of 4-Chloro-1,2-Dihydrophosphinine Oxides by Transfer Hydrogenation

Abstract Under the conditions of transfer hydrogenation by ammonium formate, the title compounds (6) were converted to a mixture of the corresponding 1,2,3,6-tetrahyidrophosphinine oxide (7), its dechlorinated derivative (8) and the respective 1,2,3,4,5,6-hexahydrophosphinine oxide (9). In the phenyl-substituted instance, the ratios of the components depended on the mode of heating (traditional heating or microwave irradiation), temperature, and the solvent (toluene or [bmim][BF4]) used. In the ethoxy-substituted series, the dechlorinated 1,2-dihydrophosphinine oxide (10b) was detected as an intermediate. GRAPHICAL ABSTRACT

Greener synthesis of bisphosphonic/dronic acid derivatives

Abstract According to literature, the synthesis of dronic acid derivatives from the corresponding carboxylic acids using phosphorus trichloride and phosphorous acid as the P-reactants is controversial, due to the wide range of molar ratios and diverse conditions. In this minireview, we summarize our results on the clarification of these problems. For example, with zoledronic acid and risedronic acid, we found that, using methanesulfonic acid (MSA) as the solvent, 3.2 equivalents of phosphorus trichloride was enough. Generalizing this optimized method, etidronate, fenidronate, ibandronate and alendronate were obtained in yields of 38%–57%, which is reasonable for valuable dronates, and in most cases, with high purities. Mechanistic aspects are also discussed.

Synthesis of Organophosphorus Compounds under Microwave Conditions

A variety of reactions including esterifications, alkylations, additions, cycloadditions, fragmentations and condensations were carried out under microwave (MW) and solventless conditions, occasionally in IL-s. In a few cases, the reactions could only be accomplished only under MW conditions, but not on traditional heating. In certain instances, MW could substitute phase transfer catalysis, in other cases MW was synergetic with it.