Georges Gelbard

Transesterification of soybean oil catalyzed by alkylguanidines heterogenized on different substituted polystyrenes

1,5,7-Triazabicyclo[4.4.0]dec-5-ene and 1,1,3,3-tetramethylguanidine were heterogenized on different chloromethylated poly(styrene/divinylbenzene), as well as on linear polystyrene after introduction of a ‘spacer-arm’. Furthermore, polymeric 2,3-dicyclohexylguanidines were synthesized by the reaction of 1,3-dicyclohexylcarbodiimide with p-(6-aminohexyl)polystyrenes. The guanidine-containing polymers were used in the transesterification of soybean oil with methanol in several consecutive catalytic cycles. The guanidines heterogenized on gel-type poly(styrene/divinylbenzene) with 1 meq Cl/g showed a slightly lower activity than their homogeneous analogous but reached the same high conversions after prolonged reaction time. On the other hand, they slowly leached from the polymers, allowing only nine catalytic cycles. The guanidines heterogenized on linear polystyrene with the use of a ‘spacer-arm’ were less active. Furthermore, they suffered substitution reactions during the recycling experiments to form inactive hexasubstituted guanidinium compounds.

Alkylguanidines as catalysts for the transesterification of rapeseed oil

Abstract The transesterification of rapeseed oil with methanol has been studied in the presence of eight substituted cyclic and acyclic guanidines and compared with unsubstituted guanidine. The catalytic activity of the guanidines depends mainly on their intrinsic base strength. With a long alkyl chain on the guanidine, no lipophilic effect is observed. The best catalyst found is commercial 1,5,7-triazabicyclo[4.4.0] dec-5-ene which, when used at 1 mol%, produces a 90% yield of methyl esters with 1 h of reaction time.

POLYNITROGEN STRONG BASES : 1- NEW SYNTHESES OF BIGUANIDES AND THEIR CATALYTIC PROPERTIES IN TRANSESTERIFICATION REACTIONS

Abstract A new and convenient method has been developed for the synthesis of soluble and polystyrene-supported biguanides by the nucleophilic addition of guanidines such as TMG and TDB to diisopropyl-, dicyclohexyl- and polymericarbodi-imide. These biguanides are excellent catalysts for the transesterification.

Epoxidation of cyclohexene with polymethacrylate-based peroxotungstic catalysts

Amino and ammonium groups have been introduced into polyglycidylmethacrylate (PGMA) resins by reaction of trimethylamine either by opening the epoxide ring of PGMA or by reaction with methyl iodide followed by amination. The aminoalky derivatives were phosphorylated to afford grafted phosphotriamides; when loaded with tungsten species in their peroxo form, these polymeric carriers exhibited excellent properties as catalysts for the epoxidation of cyclohexene with hydrogen peroxide.

Polynitrogen strong bases as immobilized catalysts

Guanidines and biguanides are strong bases which are convenient to use as catalysts due to their solubility in organic media; as their basicities are in the range of the common inorganic bases such as alkaline hydroxides and carbonates, they are suitable for a wide range of base- directed reactions such as Michael addition, esterification and transesterification. New syntheses of poly-N-alkylated biguanides have been devised from carbodiimides and recent examples of catalyses with soluble and immobilised guanidines and biguanides are given with emphasis on the transesterification of triglycerides from vegetable oils.

Exclusive 1-4 reduction of conjugated ketones by sodium dithionite

Abstract α - β unsaturated aldehyde and ketones were exclusively reduced to the corresponding saturated aldehyde and ketones by the use of sodium dithionite under phase- transfer catalysis conditions. Neither allylic nor saturated alcohols are formed.

Epoxidation of olefins by hydrogen peroxide catalyzed by phosphonotungstic complexes

Abstract The highest turnovers reported so far in the epoxidation of olefins with hydrogen peroxide are obtained under homogeneous conditions with trioctylmethylammonium tungstate complexed by lipophilic neutral or anionic phosphorus ligands containing the PO subunit.

Epoxidation with peroxotungstic acid immobilised onto silica-grafted phosphoramides

Abstract Epoxidation of alkenes with hydrogen peroxide was catalysed with peroxotungstic acid complexed to immobilised mono- and bisphosphotriamides. Several silica-based materials such as amorphous silica, K10 montmorillonite and hectorite were used as carriers; these were first aminated with methylaminopropyl-trimethoxysilane and phosphorylated to the required phosphotriamides. Styrene, α-methylstyrene, indene, cyclohexene and cyclooctene were used as substrates and repeated uses of catalysts were performed to test the stability of the metal complexes.

Polynitrogen strong bases as immobilized catalysts for the transesterification of vegetable oils

Abstract A new and convenient method has been developed for the synthesis of soluble and polystyrene-supported biguanides by the nucleophilic addition of guanidines to soluble and polymeric carbodiimides. These biguanides are excellent recyclable catalysts for the transesterification of triglycerides.

Epoxidation with polystyrene-supported phosphonotungstic complexes

Abstract Epoxidation of alkenes with hydrogen peroxide was performed with polystyrene-supported peroxotungstiic catalytic species. These peroxo species were complexed by several phosphorus(V) ligands such as phosphine oxides, phosphonic acids and their related amides grafted onto the polymeric matrices through sequential reactions. The efficiencies and the possibilities of repeated uses of these catalysts are related to the kind of the macroligand and its polymeric backbone.