Carbonylation reactions in supercritical carbon dioxide

Identificador:  TDX:870

Handle: https://hdl.handle.net/20.500.11797/TDX870

Autores:  Tortosa Estorach, Clara

Resumen:
Homogeneous catalysis has achieved an important role in chemical industries in the last decades. A recent aspect of this role that is receiving increasing attention is the use of alternative reaction media that solve the environmental problems associated with many of the traditional volatile organic solvents. The use of non-conventional reaction media also provides opportunities for facilitating the recovery and recycling of the catalyst. Among these reaction media, supercritical carbon dioxide(scCO2) is an interesting solvent in the context of green chemistry and catalysis in several mono- and biphasic systems.<br/>The use of scCO2 as a solvent, a part it is economic, non-toxic, non-flammable, has the advantage to recycle easily the catalyst, has high miscibility with gases and it is easy change its properties changing temperature or pressure. The main limitation is the low polarity of the media which lead to low solubility of the catalytic systems. <br/><br/>The aim of the present thesis is to use supercritical carbon dioxide as alternative solvent for different catalytic carbonylation reactions such as hydroformylation, hydrocarboxylation, hydroesterification of long chain alkenes and copolymerisation of carbon monoxide and tert-butylstyrene. To afford solubility in that system, different attempts have been used: synthesis of perfluorinated phosphorus or nitrogen donor ligand or the use of acetylated cyclodextrin or perfluoropolyether molecules as solubilizer agents.<br/>The hydrocarboxylation of linear alkenes using scCO2 as a solvent has been studied. It was used a palladium (II) precursor with fluorinated phosphines (Figure 1).<br/> <br/>Figure 1<br/>The solubility of the systems in supercritical carbon dioxide was studied. The best system for the reaction was [PdCl2(PhCN)2]/1 at non-soluble conditions, obtaining 55% of conversion, 90% of selectivity and l/b =3. The activity of the system adding an ammonium salt of Krytox as a surfactant. It showed an increase in the conversion (93%) and in the regioselectivity (l/b=4.5) although the selectivity decrease(77%).<br/>By HPNMR spectroscopy, the species formed at similar conditions than hydrocarboxylation were studied observing the formation of Pd(0) species which by reacting with an acid could produce the hydride active species of the mechanism.<br/><br/>The hydroesterification of 1-hexene was studied using the same Pd-systems. The best conditions were obtained with system was [PdCl2(PhCN)2]/2/MeOH at non-soluble conditions.<br/><br/>Regarding to CO/tertbutylstyrene copolymerisation in scCO2, different palladium bischelated complexes were synthesised and characterised [Pd(5,6,7,8)2]X2. All of this complexes were soluble in liquid and supercritical carbon dioxide.<br/> <br/>Figure 2<br/>The best result was obtain in liquid expanded CO2, using [Pd(5)2](BArF)2, obtaining 1.4 Kg copolymer/g Pd, 167000 of molecular weight and 90% of syndiotacticity.<br/><br/>Finally the hydroformylation of 1-octene was studied in scCO2. CF3-groups phosphites were synthetised from phenol (9-10) and from benzylalcohol (11-12) (Figure 3).<br/> <br/>Figure 3<br/><br/>The reactivity of them with CO/H2 were studied by HPNMR and by HPIR, observing as a major species formed [HRh(9-12)3(CO)]. <br/>The catalytic experiments were carried out in toluene and in scCO2. Comparing both solvents, the conversion were better then toluene or similar for the systems Rh/9,10,12 although the selectivity decrease. However, for Rh/11 the selectivity obtained in scCO2 was higher then in toluene. <br/><br/>The effect of addition a peracetylated cyclodextrine (Figure 4, 16) to increase the solubility of a non-soluble rhodium system Rh/13-15 (Figure 4) was studied.<br/><br/> <br/>Figure 4<br/>The system became soluble at 250 atm and 80 ºC. The addition of the cyclodextrine increase the conversion and the l/b ratio of the hydroformylation of 1-octene although the selectivity decrease, probably Per-Ac-&#946;-CD may favour the dissociation of the ligand 13-15 from the catalytic species. In the scCO2 medium, this dissociation could be very high and would lead to free ligand catalytic species which favour the isomerisation.