636
Ind. Eng. Chem. Res. 1992,31,636-638
Metal-Catalyzed Carbonylation of Acetamide: Homogeneous-Phase Recovery of Cobalt from a Water-Soluble Amino Acid The cobalt catalyst from the production of iminodiacetic acid (IDA) was recovered in excellent yield using ion-pair extractant Alamine 304 (solvent extraction hydrometallurgy). The Co(II) solid, believed to consist primarily of C o c o 3 and CO(OH)~, contained 99.5% of the cobalt used in the reaction. On ) ~ , is the the basis of precedent, this cobalt species can be converted in high yield to C O ~ ( C O which starting catalyst for IDA production. Scheme I Introduction The synthetic procedure for generating N-acyl-a-amino acids from amides via cobalt-catalyzed amidocarbonylation CH3CNH, has been available for many years (Wakamatsu et al., 1971). Our interest in this methodology resulted from the need to establish a commercial process for manufacturing iminodiacetic acid (IDA), which is a key intermediate in many industrial processes. The issues regarding the development of a commercial IDA process were (1)production of the desired compound in high yield and (2) recovery of the metal catalyst. The synthesis of IDA in good yield has been performed via the acid hydrolysis of N-acetyl-IDA which was generated (Stern et al., 1982) by the reaction of acetamide and CH20 with CO/H2 in the presence of HCO(CO)~ (generated in situ from Co,(CO),). However, a method for catalyst recovery had not been established. A procedure was required for recovering the active cobalt catalyst, HCO(CO)~ (Parnaud et al., 1979), from the Nacetyl-IDA precursor to IDA. The separation of the cobalt catalyst from N-acetyl-IDA was particularly challenging since the process required the separation of the metal from a water-soluble, strongly chelating amino acid. Several methods for recovering HCO(CO)~ from chemical processes have been practiced commercially. One method involves the conversion of HCO(CO)~ to its sodium salt followed by separation of the water-soluble N ~ C O ( C O ) ~ from the organic-soluble products (Lemke, 1965, 1966). Other methods for cobalt recovery require the conversion of the Co(0) present in HCO(CO)~ to the Co(I1) valence state followed by separation of the water-soluble cobalt species from the organic-soluble product (Kummer et al., 1974). A method for cobalt recovery via generation followed by separation of the cobalt metal from the product mixture has also been reported (Mertzweiller and Watts, 1965). These methods were not applicable to cobalt recovery from the N-acetyl-IDA water solution. Presented in this paper is a potentially commercial viable method for separating the cobalt catalyst from a water-soluble, strongly chelating amino acid N-acetyl-IDA.
Results and Discussion Synthesis of Iminodiacetic Acid (IDA). N-AcetylIDA was produced from acetamide, CH20,CO/H2 (95:5), and C O ~ ( C Oas) ~catalyst (Scheme I). After removal of the 1,4-dioxane solvent, acid hydrolysis of N-acetyl-IDA with HC1 provided iminodiacetic acid (IDA) in 94% pptimized yield. Stern et al. (1982) reported only a 61% veld of N-acetyl-IDA. To utilize the IDA for further downstream processing, solvent extraction hydrometallurgy (Hudson, 1982) involving ion-pair extractant Alamine 304 (available from Henkel Corporation-Minerals Industry Division, Tucson, AZ) was used as a method for removing cobalt from the water-soluble N-acetyl-IDA product mixture (House, 1984). Recovery of Cobalt Catalyst from N-Acetyl-IDA Product Mixture. The approach undertaken to recover the cobalt from the N-acetyl-IDA solution was to convert the remaining HCO(CO)~ (15% of total cobalt) to the Co(I1)-N-acetyl-IDA complex followed by further con-
cn,o ,
H,O
1.4-DIOXANE
N-ACEM-IDA
HC1
7
"
+
CH3C02H
H02C---/ IDA (94 70YIELD FROM ACETAMIDE)
t' [ Co-(N-Acetyl-IDA)l(,) \\
version of the latter to an organic-soluble cobalt complex. The cobalt could then be stripped from the organic solution using water followed by precipitation of a cobalt species. Solvent extraction hydrometallurgy using an ion-pair extradant was successfully used to recover 99.5% of the initial charged cobalt (Scheme 11). The conversion of the remaining HCO(CO)~ to the Co(I1)-N-acetyl-IDA complex was performed by slowly distilling the 1,4dioxane from the product mixture. This procedure minimized loss of the volatile HCO(CO)~ (Roth and Orchin, 1980) from the reaction mixture. Analysis of the distillate indicated the presence of only 0.1% of the total cobalt used in the reaction. Following removal of the 1,4-dioxane, the Nacetyl-IDA was dissolved in 36% HC1. It was during this stage of the process that the Co(I1)-N-acetyl-IDA complex was converted into C O C ~ ~ Analysis ~-. by UV-vis spectroscopy supported the formation of this complex (Brode,
0 1992 American Chemical Society QS~S-58S5/92/2631-Q636$03.QQ/Q
Ind. Eng. Chem. Res., Vol. 31, No. 2, 1992 637 1928). After formation of the CoC12- complex, the cobalt species underwent an ion-exchange reaction with the hydrochloride salt of Alamine 304 (trilaurylamine; R = CH3(CHJ11-) contained in an organic solution. The resulting complex (R3NH+)2CoC142(Sato, 1966) was then extracted into the organic phase (extraction step). The solvent containing the trilaurylamine was petroleum-based (paraffins 3470, naphthenes 49%, aromatics 17%) and is completely immiscible with the water solution containing the N-acetyl-IDA. After completion of the cobalt extraction, the cobalt was stripped from the organic phase with H 2 0 (stripping step). The water solution contained the cobalt as CO(H~O),~+ (Ophardt, 1980). Treatment of the water solution from the stripping step with 50% water-soluble NaOH followed by 1.0 M water-soluble Na2C03resulted in the precipitation of a solid believed to be a mixture of Coco3 and CO(OH)~ (99.5% of initial cobalt). Although not demonstrated in our laboratory, ample precedent exists for converting the CoC03/Co(OH), mixture to Co2(CO), (Kato et al., 1960; Knap et al., 1967; Medvedeva, 1976). Solvent extraction hydrometallurgy involving the ionpair extractant Alamine 304 provided excellent recovery of the cobalt from a water solution of the chelating amino acid N-acetyl-IDA. Both the organic solution containing the (R3NH+),CoC12- and the water solution containing the C0(H20)2+can be continually recycled with minimum loss of material. It was also important to maintain the highest HC1 concentration in the N-acetyl-IDA solution to obtain the maximum concentration of CoCl,” since it is this species which is extracted by the Alamine 304 extractant from the N-acetyl-IDA solution.
Conclusion Feasibility for manufacturing IDA on a commercial scale has been demonstrated by (1) obtaining the product in high yield from acetamide, CH20, and CO/H2 and (2) excellent recovery of the cobalt catalyst (Co2C08). Furthermore, solvent extraction hydrometallurgy has been shown to be a powerful tool in recovering cobalt in excellent yield from a water solution containing a strongly chelating amino acid. This technique for catalyst recovery from water solutions should be applicable to most, if not all, transition metal catalysts. Experimental Section Preparation of Iminodiacetic Acid (IDA) from Acetamide. Acetamide (35.4 g, 0.600 mol), paraformaldehyde (43.2 g, 1.44 mol), H 2 0 (32.4 g, 1.80 mol), Co2(CO), (6.10 g, 0.0178 mol), and 1,4-dioxane (300 mL) were added to a l-L Hastelloy C autoclave. The system was flushed once with argon and then twice with 955 CO/H2. The reaction vessel was then pressurized to 1380 psig with 955 CO/H2. The mixture was then heated to 100 OC. The pressure inside the autoclave increased as the temperature increased. A t 92 OC (P = 1673 psig), the pressure began to decrease rapidly. Due to the exothermic reaction, the system needed to be cooled periodically to maintain a temperature of 100 “C. The mixture was stirred at 100 OC for 2 h, and the gas was then vented from the auklave. After flushing the reaction mixture with argon, the solution was removed from the reaction vessel. The mixture was concentrated under reduced pressure to afford N-acetyliminodiacetic acid as a dark blue resin: ‘H NMR (acet o n e d ) 6 2.07 (s, 3 H, CH3), 4.12 (s, 2 H, CH2),4.24 (8, 2 H, CH2), 8.17-9.03 (br s, 2 H, C02H). The resin was dissolved in 300 mL of 36% HC1 and refluxed for 30 min. Analysis by ‘H NMR indicated the formation of IDA.HC1 along with the complete disappearance of N-acetyl-IDA.
The reaction mixture was prepared for HPLC analysis by adjusting the pH of the solution to 2.9 with 50% NaOH. Analyses by HPLC on a Cation H ion-exchange column and a Zorbax-300 SCX ion-exchange column indicated the presence of IDA (94%) and glycine (1.5%), respectively. Yields were based on acetamide. Cobalt Recovery from N-Acetyl-IDA Mixture Using Ion-Pair Extractant Alamine 304 (Trilaurylamine). Production of N-acetyl-IDA was performed as described (vide supra) using 35.4 g (0.600 mol) of acetamide and 6.16 g (0.0180 mol) of C%(CO)8 (34% Co assay = 2.09 g Co). After the solution containing N-acetyl-IDA was removed from the autoclave and placed in a 2000-mL round-bottomed flask, the mixture was slowly heated to refluxing temperature over a 2-h period and the solution was then distilled under atmospheric pressure over a 2-h 45-min period. The volatiles (1,4-dioxane/H20) were distilled into a flask containing 100 mL of 1.0 M Na2C03(aq). The dark red resin (N-acetyl-IDA) was dissolved in 300 mL of 36% HC1. The mixture was then carefully extracted (3 X 300 mL) with a solution of Alamine 304 (225 g/3000 mL of solution) and isodecanol(180g/3000 mL of solution) in Kermac 470B (obtained from Triangle Refineries, 1nc.-a subsidiary of Kerr-McGee Refining Corporation) so as not to entrain any of the water layer into the organic phase. The extractions were performed in a separatory funnel, and each extraction required 5 min of agitation. The dark blue organic extracts were combined (2600 mL), and the solution was then stirred vigorously for 30 min with 260 mL of H20. The phases were separated and the procedure was repeated three more times. The pink water layers were combined (pH 0) and pH adjusted to 5.0 with 20 mL of 50% NaOH followed by further adjustment to 10.5 with 200 mL of 1.0 M water-soluble Na2C03. A blue precipitate, formed during the pH adjustment, was filtered and dried in a vacuum oven. Analysis of the solid (3.853 g) by ICAP (inductive coupled argon plasma) indicated the presence of 2.08 g of Co (99.5% recovery) and 0.8 wt % Na. Analysis by ICAP of the distillate (l,4-dioxane/H20) indicated the presence of 3.1 mg of Co (0.1% recovery). Elemental analysis (C, H, N) of the solid indicated the presence of carbon (6.4 wt %), hydrogen (2.0 wt %), and nitrogen (
