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Boletín de la Sociedad Chilena de Química

versão impressa ISSN 0366-1644

Bol. Soc. Chil. Quím. v.45 n.3 Concepción set. 2000

http://dx.doi.org/10.4067/S0366-16442000000300008 

HOMOGENEOUS CATALYSIS REACTION OF FORMALDEHYDE
WITH SYNTHESIS GAS USING RHODIUM COMPLEXES.

P.J. BARICELLI1*, R.E. LUJANO1, L. MEDINA2, C. LONGO3,
A.J. PARDEY4, R. PASTENE5, S.A. MOYA5.

1Centro de Investigaciones Químicas, Facultad de Ingeniería, Universidad de Carabobo,
Valencia, Venezuela. E-mail: pbaricel@thor.uc.edu.ve
2Escuela de Química, Facultad Experimental de Ciencias y Tecnología,
Universidad de Carabobo, Valencia, Venezuela.
3Centro de Investigación y Desarrollo de Radiofármacos Facultad de Farmacia,
Universidad Central de Venezuela, Caracas, Venezuela.
4Escuela de Química, Facultad de Ciencias, Universidad Central de Venezuela,
Caracas, Venezuela.
5Departamento de Química Aplicada, Facultad de Química y Biología,
Universidad de Santiago de Chile, Santiago, Chile.
(Received: April 26, 2000 - Accepted: May 24, 2000)

In memorian of Dr. Guido S. Canessa C.

ABSTRACT

In the present work, we report the homogeneous catalytic hydroformylation reaction of formaldehyde with rhodium complexes like [Rh(CO)2L2](PF6) with L = pyridine (1) or 4-picoline (2), using different solvents such as toluene, acetone, N,N-dimethylformamide, and 4-picoline. The experiments were carried out in an autoclave (Parr, 100 mL), 10 atm, CO/H2 = 1 and ratio catalyst/substrate 1/100. Preliminary kinetics parameters show a high catalytic activity of these complexes to the formation of methanol and methyl formate.

Key Words: hydroformylation, formaldehyde, rhodium complexes, methyl formate.

RESUMEN

En el presente trabajo, reportamos la catálisis homogénea de la reacción de hidroformilación de formaldehído con complejos de rodio del tipo [Rh(CO)2L2](PF6) con L = piridina (1) o 4-picolina (2), utilizando diferentes solventes tales como tolueno, acetona, N,N-dimetilformamida y 4-picolina. Los experimentos fueron llevados a cabo en un autoclave (Parr, 100 mL), 10 atm, CO/H2 = 1, relación catalizador/sustrato 1/100. Parámetros cinéticos preliminares muestran una alta actividad catalítica de estos complejos, a la formación de metanol y formato de metilo.

Palabras Claves: hidroformilación, formaldehído, complejos de rodio, formato de metilo.

The reaction of formaldehyde using transition metal complexes is an important step in production of ethylene glycol from syngas (CO/H2 1/1) (Eq. 1).

H2CO + 2H2 + CO ® HOCH2CH2OH
(1)

The ethylene glycol is an important chemical compound, which is used in the chemical industry as component in the resins of polyesters, fibers and antifreeze additive. At this moment the ethylene glycol is prepared from the ethylene. However, the syngas is a material potentially less expensive. Although different methods exist to obtain ethylene glycol starting from the syngas mixture1), the direct route (Eq. 2) it is theorically the simplest and the most efficient2).

2 CO + 3 H2 ®HOCH2CH2OH
(2)

The reaction of syngas with different organic substrates using a wide variety of transition metal complexes has been reported. Spencer3), has studied the conversion of formaldehyde to ethylene glycol by use of RhCl(CO)(PPh3)2, Chang et al.2) have reported an active and selective system of cationic complexes of rhodium(I) [Rh(COD)(PPh3)2]BF4 and [HRh(COD)(PPh3)3] with high conversion of formaldehyde to ethylene glycol, Okano et al.1) have reported that the use of pyridines increases the catalytic activity of [HRh(CO)(PPh3)3] in the hydroformylation reaction. In this paper we are reporting the results obtained from the studies of complexes like [Rh(CO)2L2]PF6 (with L = pyridine (1) or 4-picoline (2) in the reaction of formaldehyde with syngas mixture and its preliminary kinetic parameters.

All manipulations were carried out under N2 atmosphere by using standard Schlenk techniques4). Solvents were purified by known procedures and saturated with nitrogen prior to use. The infrared spectra were recorded in a Perkin Elmer FTIR 1725X using samples as KBr disks. Analyses by NMR were obtained on a Varian EM-60 spectrometer. The UV-Visible spectra were taken in a diode array Hewlett Packard 8452 spectrometer. GC analysis were performed on a Hewlett Packard 5890 Series II chromatograph with a flame ionization detector and 5% methyl phenyl silicone, 25m, 0.32 mm column. Acetonitrile, ethylene glycol, 4-methyl-pyridine, pentane, pyridine, 1,5-cyclooctadiene and RhCl3 • 3H2O were obtained from Aldrich Chemicals. N,N-dimethylformamide, sulfuric acid and p-formaldehyde were obtained from Riedel-de-Haën. All gases were purchased from AGA gas of Venezuela. All other chemicals were commercial products and were used without further purification. The complexes [RhCl(COD)]2, [Rh(COD)(Py)2]PF6, [Rh(CO)2(4-pic)2]PF6 were synthesized by known procedures5,6).

The catalytic runs were performed according to the following conditions. The reactors used were two autoclaves from Parr Instruments (4761, 300 mL and 4778, 100 mL) with temperature controlled unit and magnetic stirring. The reaction temperature was varied from 140 to 180 ºC (413 to 453 K); oxygen pressure varied from 100 at 150 atm and the reaction time was varied from 2 to 7 hours.

Two catalytic precursors [Rh(CO)2(py)2]PF6 (1) and [Rh(CO)2(4-pic)2]PF6 (2) were evaluated in the reaction of p-formaldehyde with syngas, in different solvents at 393 K, 10 atm and CO/H2 = 1. The results are summarized in Table I. According to these results, both systems showed approximately the same conversion levels under the reaction conditions. However, the observed products were methanol and methyl formate and none of ethylene glycol was detected presumably due to the hydrogenation reaction of formaldehyde (Eq. 3), which is favored over the hydroformylation reaction under the used reaction conditions7).

Table I. Catalytic for the complexes of rhodium (I) cis-[Ph(CO)2(amine)2](PF)6 with different solvensa.

HCOH + H2 ® CH3OH
(3)

Similar results have been reported in the reaction between p-formaldehyde and syngas in n-butylether using the complex RhCl(CO)(PPh3)2 as catalyst8). Methyl formate and methanol are selectively produced in reaction of formaldehyde with syngas using complexes of cobalt9-12), ruthenium11-14), or iridium11) as a catalyst. In these reactions was observed that methanol is the dominant product with H2-rich syngas, while increasing CO partial pressure increases the yield of HCOOCH3.

From Table I, we decided to investigate with more detail the effect of changes in the temperature, time and pressure on the conversion of formaldehyde.

Effect of temperature. In order to study the temperature influence on this system, the temperature was varied from 413 to 453 K at 10 atm of pressure, during 6 h of reaction. The results are showed in Figure 1.

Fig. 1 A plot of product the composition for the catalytic reaction of formaldehyde catalyzed by cis-[Rh(CO)2(4-pic)2(PF6) as a function of temperature. Experimental conditions: 6.32 g (0.2 mole) of p-formaldehyde, 0.980 g of Rh (0.002 mole), 100 mL of 4-picoline, - formaldehyde/Rh=100/1, P(CO/H2) = 10 atm, time of heating = 6 h. (Line drawn for ilustrative purposes only).

Figure 1 shows an increase of the total conversion to the products of the reaction and also the selectivity to the formation of methanol remains approximately constant and gently decrease in the formation of methyl formate, these observations are presumably because the temperature displace the quilibrium to the formation of formaldehyde 15).

Effect of time. In this case the reaction time was varied from 2 to 7 h, and the temperature was kept at 428 K and the pressure at 10 atm, the ratio CO/H2 = 1/1. The results are displayed in Figure 2.

Fig. 2 A plot of the product composition for the catalytic reaction of formaldehyde catalyzed by cis-[Rh(CO)2(4-pci)2](PF6) as a function of reaction time. Experimental conditions: 6.32 g (0.2 mole) of para-formaldehyde, 0.980 g of Rh (0.002 mole), para-formaldehyde/Rh = 100/1, 100 mL of 4-picoline, P (CO/H2) = 10 atm at 393 K.(Line drawn for ilustrative purposes only).

Figure 2 shows an increase in the total conversion and selectivity in the formation of methanol. Also a slightly increase in the formation of methyl formate with a posterior decrease from 5 h, which presumably increase the methanol concentration due to the hydrogenation reaction of methyl formate16) (Eq. 4).

HCOOCH3 + 2H2 ® 2 CH3OH
(4)

Effect of pressure. Finally it was studied the effect of the variation of pressure on the reaction system at 428 K, 4 h of reaction and ratio CO/H2 = 1/1. The results are shown in Figure 3.

Fig. 3 A plot of the product composition for the catalytic reaction of formaldehyde catalyzed by cis-[Rh(CO)2/(pic-4)2(PF6) as a function of CO/H2 pressure. Experimental conditions: 6.32 g (0.2 mole) of para-formaldehyde, 0.980 g of Rh (0.002 mole), para-formaldehyde/Rh = 100/1, 100 mL of 4-picoline, T = 393 K by 4 h. (Line drawn for ilustrative purposes only).

Figure 3 shows again an increase in the conversion and selectivity in methanol and practically the conversion and selectivity in methyl formate remain constant during the experiment.

The reaction of formaldehyde with syngas using rhodium complexes like cis-[Rh(CO)2L2]PF6 (L = pyridine or 4-picoline) do not showed the formation of any hydroformylation products. However the complex (2) seems to be an excellent catalytical precursor for the formation of methanol under the used reaction conditions.

ACKNOWLEDGMENTS

We thank the financial support of the CODECIHT - UC Venezuela (Proy. 94016); DICYT - USACH and FONDECYT, Chile (SAM); and CDCH - UCV Venezuela (AJP).

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