Chapter 22
Development of Hydrotalcite Catalysts in Heterogeneous Baeyer—Villiger Oxidation
Downloaded by STANFORD UNIV GREEN LIBR on October 8, 2012 | http://pubs.acs.org Publication Date: August 13, 1996 | doi: 10.1021/bk-1996-0638.ch022
Kiyotomi Kaneda and Shinji Ueno Department of Chemical Engineering, Faculty of Engineering Science, Osaka University, Toyonaka, Osaka 560, Japan
Hydrotalcites catalyze the Baeyer-Villiger oxidation of various ketones using a combination oxidant system composed of molecular oxygen and benzaldehyde to give high yields of lactones and esters. The catalytic reaction depends on the basic character of the hydrotalcites. Multi-metallic hydrotalcites having the elements Fe, Ni, or Cu in the Brucite-like layers of the hydrotalcites give the highest yields of oxidation products.
In 1990, we reported that Ru compounds in the presence of molecular oxygen and aldehyde catalytically cleaved carbon-carbon double bonds of terminal olefins to give the corresponding carboxylic acids and ketones. We also showed that peracids and/or peroxyaldehydes generated in situ from the reaction of molecular oxygen with aldehyde oxidize Ru0 to higher oxidation states of ruthenium, e.g., Ru0 . (7) Using the above combined oxidant of molecular oxygen and aldehyde, many selective oxidations catalyzed metal compounds have been explored. • Epoxidation (2-18) • Baeyer-Villiger oxidation (77,16,19-22) • Oxidation of alkanes and aromatic compounds (77,16,18, 23-28) • Oxidation of aldehydes, alcohols and sulfides (16,29-31) We also found that the combined oxidant has potential for the epoxidation of olefins and the Baeyer-Villiger oxidation of ketones (Eq.l) even in the absence of metal catalysts. (32, 33) 2
4
Ο CHO
Ο 11
Ο
C-OH
+
(1)
0097-6156/96/0638-0300$15.00/0 © 1996 American Chemical Society In Heterogeneous Hydrocarbon Oxidation; Warren, B., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1996.
22. KANEDA & UENO
Hydrotalcite Catalysts in Baeyer-Villiger Oxidation
Hydrotalcites consist of Brucite-like layers (34) with positive charge and anionic compounds in the interlayer to form neutral materials. Mg Al (OH) C0 , a prototype of the hydrotalcites was originally found as a mineral clay. Recently, many kinds of hydrotalcites have been synthesized using various elements in the Brucite-like layer, e.g., Al, Mg, Fe, and Ni, and anionic compounds in the interlayer, e.g. halogenated, metal complex, organic acid, and heteropolyacid anion. (34) Combination of the elements, change of element ratios in the Brucite-like layer, and selection of anionic compounds can tune the basicity of the hydrotalcites and the interlayer distance. (35) It has been known that base and acid compounds acted as promoters of the BaeyerVilliger oxidation of ketones with organic peracids. (36, 37) The tunable basic character of the hydrotalcites has attracted considerable interest and the effect on the Baeyer-Villiger oxidation is the subject of this paper. The oxidation of various ketones in the presence of the combined oxidant is reported with emphasis on the following three cases. • Baeyer-Villiger oxidation in the absence of metal catalysts. (33) • Baeyer-Villiger oxidation using various kinds of hydrotalcites with different ratios of the Mg/Al and interlayer anions. (38) • Catalysis of functionalyzed hydrotalcites containing various transition metal elements, e.g., Ni, Fe, and Cu. (39)
Downloaded by STANFORD UNIV GREEN LIBR on October 8, 2012 | http://pubs.acs.org Publication Date: August 13, 1996 | doi: 10.1021/bk-1996-0638.ch022
6
2
16
3
Experimental 1) General NMR spectra were obtained at JNM GSX270 with tetramethyisilane as an internal standard. IR spectra were recorded on a Hitachi EPI-G. Analytical GLC was performed with OV-17, Silicone SE-30 and SPB™-l(Fused Silica Capillary, l.Oumdf) columns on an instrument equipped with a flame ionization detector. Powder X-ray diffraction patterns were obtained using a Shimazu VD-1 diffractmeter using Cu K a radiation. Aldehydes were purified according to the literature (40) and stored under an argon atmosphere. Solvents, such as carbon tetrachloride and 1,2-dichloroethane etc., were purchased from Wako Chemicals as special grade and dried with MgSO^ followed by distillation under a nitrogen atmosphere. Ketones were also purchased from Wako Chemicals and dried with MgS0 , followed by distillation. Ketones of 4-terf-butylcyclohexanone, norcamphor, 2-adamantanone, p-methoxyacetophenone, and benzylphenylketone were recrystallized before use. m-CPBA was purchased from Nacalai tesque and used without further purification. A1(N0 ) 9H 0, Al(OH) , Mg(NC>3) -6H 0, Mg(OH) , N K N O ^ H j O , Cu(NC>3) 3H 0, and Fe(N0 ) 9H 0 were purchased from Wako Chemicals as special grade. 4
3
2
2
2
2
3
2
3
2
3
3
2
2) Preparation of various hydrotalcites Mg Al (OH) C0 , Mg Al(OH) Cl, Mg Al (OH) (C H (C0 ) ), and M Al(OH) (p-S0 CH C H ) were prepared by literature procedures. (34,41-43) Various multimetallic hydrotalcites were prepared by a modification of the above method. (34) A 6
3
2
16
3
6
3
3
8
4
2
12
6
4
2
2
g2
4
In Heterogeneous Hydrocarbon Oxidation; Warren, B., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1996.
6
301
302
HETEROGENEOUS HYDROCARBON OXIDATION
typical example is for Mg Al M (OH) CO . Ni(NO^) -6H O (0.003mol), Mg(NC>3) -6H 0 (0.03mol), and A1(N0 ) 9H 6 (O.Olmol) were dissolved in water (100ml). A second water solution (60 ml) of Na C0 (0.03mol) and NaOH (0.07mol) was prepared. The first solution was slowly added to the second. The resulting mixture was heated at 65°C for about 18 h with good mixing. The greenish slurry was then cooled to room temperature, filtered, washed with a large amount of water and dried overnight at 110°C. From the XRD spectrum, the basal spacing was 7.82A. 6
2
2
2
0L6
172
3
3
3
2
Downloaded by STANFORD UNIV GREEN LIBR on October 8, 2012 | http://pubs.acs.org Publication Date: August 13, 1996 | doi: 10.1021/bk-1996-0638.ch022
a
a
2
3
3) General procedure for the Baeyer-Villiger oxidation Into a three necked flask with a reflux condenser cooled at -15°C were placed hydrotalcite (25mg), benzaldehyde (12mmol), and 1,2-dichloroethane (15ml). Oxygen was bubbled into the stirred heterogeneous mixture at 40°C for 30 min. A 1,2dichloroethane solution (5ml) of ketone (4mmol) was added and the resulting mixture was stirred with bubbling of oxygen at 40°C for 4.5h. Hydrotalcite was separated by filtration and the filtrate was treated with Na S0 and NaHC0 . Removal of the solvent under reduced pressure afforded a clear liquid, which was subjected to column chromatography on silica gel (hexane / ethyl acetate, 3:1 ) giving the corresponding pure ester. 2
3
3
4) Baeyer-Villiger oxidation using m-CPBA A typical example of the title reaction is for 2-methylcyclopentanone. Into a three necked flask with a reflux condenser cooled at -15°C were placed Mg Al (OH) CO (25mg), 2-methylcyclopentanone (2mmol), m-chloroperbenzoic acid (3mmol), and 1,2-dichloroethane (15ml). The resulting mixture was stirred at room temperature for 5 h. GLC analysis of the reaction mixture showed 94% yield of 5methylvalerolactone. A similar reaction procedure was operated in the absence of the hydrotalcite and the lactone was formed in 12% yield after 5 h. l0
2
7A
3
5) Reuse experiments of various hydrotalcites Into a three necked flask with a reflux condenser cooled at -15°C were placed Mg Al j OH) C0 (25mg), benzaldehyde (12mmol), and 1,2-dichloroethane (15ml). Oxygen was bubbled into the stirred mixture at 40°C for 30 min. A 1,2-dichloroethane solution (5ml) of cyclopentanone (4mmol) was added and the resulting mixture was stirred with bubbling of oxygen at 40°C for 4.5h. GLC analysis of the reaction mixture showed 90% yield of 6-valerolactone. The hydrotalcite was washed with 3x10ml saturated NajCX^ solution and 5x10ml of water, and dried at 50°C in vacuum overnight. IR and XRD spectra of the washed hydrotalcite did not change appreciably. For a reuse experiment of the hydrotalcite catalyst, a half scale mole reaction of cyclopentanone (2mmol) with benzaldehyde (6mmol) in 1,2-dichloroethane (10ml) was carried out in the presence of the spent hydrotalcite (12.5mg). After 5 h, the lactone was formed in 80% yield. On the other hand, the spent Mg-Al-Fe-C0 hydrotalcite was used without the above aqueous Na C0 treatment for the BaeyerVilliger oxidation of cyclopentanone and gave 81% yield of 6-valerolactone without appreciable loss of catalytic activity, viz. 83% yield for fresh catalyst. 10
