Environ. Sci. Technol. 2009, 43, 5952–5958
Metallic Ca-Rh/C-Methanol, A High-Performing System for the Hydrodechlorination/Ring Reduction of Mono- And Poly Chlorinated Aromatic Substrates Y O S H I H A R U M I T O M A , * ,† MITSUNORI KAKEDA,† ALINA MARIETA SIMION,‡ NAOYOSHI EGASHIRA,† AND CRISTIAN SIMION‡ Department of Environmental Sciences, Faculty of Life and Environmental Sciences, Prefectural University of Hiroshima, 562 Nanatsuka-Cho, Shobara City, Hiroshima, 727-0023, Japan, and Department of Organic Chemistry, Spl. “Politehnica” University of Bucharest, Independentei 313, 060042 Bucharest, Romania
Received February 13, 2009. Accepted June 16, 2009.. Revised manuscript received June 14, 2009
We investigated the reduction of some substituted monoand poly chlorobenzenes bearing functional groups such as methyl, methoxy, hydroxyl, and amino, under mild conditions (80 °C and magnetic stirring, for 2 h) using a system consisting of metallic calcium and methanol (as hydrogen donor system) and 5% wt. Rh/C (as hydrodechlorination/ring reduction catalyst). Hydrodechlorination easily took place for methoxyand alkyl-chlorobenzenes, yielding the corresponding hydrodechlorinated compounds (57-76%) and affording as secondary reaction products the ring-reduced compounds (16-43%). Treatment of hydroxy- and amino-chlorobenzenes under the same conditions, respectively, gave corresponding hydrodechlorinated compounds (over 60%) along with the ringreduced compounds. Results show that the reaction of substituted polychlorinated benzenes needs a longer reaction time (6 h), the transformation being nevertheless complete.
Introduction Because of their importance and versatility as starting materials, solvents, reagents, intermediates, and final products, various chlorinated compounds have been produced industrially in enormous quantities since the beginning of the industrial era. Chlorinated derivatives have been praised for their usefulness (as drugs, pesticides, monomers for plastics, or as inert nonflammable solvents) or blamed for their toxicity (asphyxiating, vesicant, or lachrymatory gases) (1-5). However, in the past half-century, some categories of chlorinated compounds have earned the despicable reputation of being the worst contaminants ever; one such category is generically known as “polychlorinated-dibenzo-p-dioxins” (6-9), which have proved to be highly toxic, carcinogenic, teratogenic, and mutagenic chemicals, posed as a threat to both the environment and human health (10-13). * Corresponding author phone/fax: 81-824-74-1748; e-mail:
[email protected]. † Prefectural University of Hiroshima. ‡ “Politehnica” University of Bucharest. 5952
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Scientists worldwide have mounted a strong campaign of developing new methods of detoxification through decomposition or hydrodechlorination of these harmful compounds. Most methods are classified as reductive dechlorination or hydrodechlorination processes, mediated by metals such as alkaline and alkaline-earth metals, principal group metals, or transition metals (14). Although several reports in the literature describe the use of calcium salts in hydrodechlorination procedures (mainly in mechanochemical processes) (15-17), we are today, to the best of our knowledge, the only team that uses metallic calcium, especially for its specific reactivity. Although not as reactive as a group I metal (which would enable substitution of chlorine with the formation of an organometallic aromatic derivative), it is sufficiently reactive in promoting the hydrodechlorination process according to a reductive protocol. There was a previous attempt of using metallic calcium from Rieke and co-workers, but it implied a special and reactive form of metallic calcium, obtained in situ by the reduction of calcium halides with lithium biphenylide in THF (18, 19). The use of simple metallic calcium instead of an alkali metal as a promoter for the proton generation, aside from allowing effective degradation at room temperature by ensuring the reductive media, also offers the merit of scavenging the chlorine, which would otherwise poison the noble metal catalyst. Among the numerous methods that have been proposed for such a degradation (20-25), some interesting studies of liquid-phase hydrodechlorination of chlorinated dioxin-like compounds have been conducted by Ukisu and co-workers (26-32). Based on a similar general pattern (a system acting as hydrogen donor, in this case NaOH + alcohol, in the presence of a noble metal catalyst deposed on charcoal), this team has investigated catalytic degradation of dioxins and dioxin-like compounds using NaOH in 2-propanol, which serves as a hydrogen source, in the presence of Rh/C or Pd/C. In one of the first investigation of the use of rhodium catalysts in a hydrodechlorination process (33), catalysts such as Rh/Al2O3 or Rh/SiO2 seemed to be effective for the transformation of chlorobenzene to chlorocyclohexane and benzene. Such simple catalysts surrendered quickly to more complex rhodium species. For example, various chlorinated aromatic substrates could be successfully hydrodechlorinated using a complex catalyst with pentamethylcyclopetadienyl (Cp*) ligands, [Cp*RhCl2]2, in boiling 2-butanol and in the presence of KOH, for 17 h (34). Another direction was the use of nanoparticles of complex rhodium or palladium catalysts, in a colloidal system and using a high pressure of gaseous H2 (35). In that case, a mixture of hydrodechlorinated/ring reduced reaction products was obtained. In a previous study, we have described an effective and convenient method for hydrodechlorination of chlorinated aromatic compounds (36), that uses metallic calcium and an alcohol. Paradoxically, this system afforded only monohydrodechlorination when applied to dichlorobenzene and afforded no hydrodechlorinated reaction products when chlorophenol or chloroaniline was used as substrate, but it proved to be effective when applied to several classes of harmful compounds, such as coplanar polychlorinated biphenyls (co-PCBs), polychlorinated dibenzo-dioxins (PCDDs), and polychlorinated dibenzo-furans (PCDFs) (37). In the search for useful application of the hydrodechlorination process, we have managed to improve the efficiency of our method further by combining the Ca/methanol mixture’s properties with the reducing capacity of the Rh/C catalyst. 10.1021/es9004587 CCC: $40.75
2009 American Chemical Society
Published on Web 07/01/2009
Thus, such a system became extremely efficient for the degradation of PCDDs, PCDFs, and co-PCBs inside both fly ash and contaminated soils (38-40). Consequently, our idea was to combine the reductive power of the calcium/methanol system with the catalytic activity of Rh/C, a simple rhodium catalyst, instead of the more sophisticated (and expensive) complex ones, in a process that does not require harsh conditions, a long reaction time, or a high pressure of molecular hydrogen, returning to our first attempts for which the simple metallic Ca/alcohol system was inefficient (36). Beside using commercially available and easy-to-handle reagent (Ca), solvent (methanol), and catalyst (Rh/C), our method has the benefit of not needing, as other catalytic hydrodechlorination procedures, molecular hydrogen (always a risk), harsh operating conditions (e.g., high pressure or high temperature), or long reaction-time, proving itself to be a rapid, effective, low-cost and energy-saving process. The present study refers to the investigation of different aromatic substrates in such a hydrodechlorination process in order to assess its scope and limitations and to determine a possible reaction pathway.
Experimental Section Materials. Distilled water was used for all reactions. Commercially available alcohols were used (Wako Pure Chemical Industries Ltd.). Granular particles of metallic calcium were purchased from Kishida Chemical Co. Ltd., (99%, particle size distribution: 2-2.5 mm, surface area: 0.43-0.48 m2/g). The 5% Rh/C was acquired from Aldrich Chemical Co., (particle size distribution: 3.0-271 µm, average of distribution: 40.1 µm, surface area: 542 m2/g, BET). Calcium and Rh/C catalyst were used directly, with no pretreatment. Chlorinated compounds (>99.0%, GC) were purchased from Aldrich Chemical Co. Sealed and pressure resistant tubes of 35 mL volume from Ace Glass, Inc. were used in these experiments. For some experiments, we used a portable reactor (38 mL internal volume TVS-1 type from Taiatsu Techno Corp.), which permitted the measure of the variations of the internal pressure, respectively the temperature, with a pressure gauge and a thermocouple thermometer. On a typical procedure all components were loaded into the reaction tubes; the reaction mixture was stirred magnetically and kept at the right temperature for the duration of the experiment. General Procedure. A mixture of chlorinated substrate (1 mmol), metallic calcium (0.40 g, 10 mmol or 0.80 g, 20 mmol (from a freshly opened flask)), and 5 wt.% of Rh/C (0.1 g) in methyl alcohol (5 mL) was stirred in a sealed tube at 80 °C. After 2 h, 20 mL of 1 M nitric acid was added and the reaction mixture was subsequently extracted several times using diethyl ether. Combined organic layers were washed, dried on MgSO4, and evaporated. The obtained compounds in the crude reaction mixture were identified using GC and GC-MS analyses. The GC-MS analyses were conducted using a gas chromatograph (HP 6890 series) equipped with a 30 m of DB-5 ms column (i.d. 0.25 mm) (J&W Scientific Inc.) and a quadrupole mass spectrometer (JMSAM II series; JEOL). Ionization was performed under 70 eV electron-impact conditions. Assignment of structures was performed through a search of the GC-MS library. Another gas chromatograph (30 m DB-1 and FID detection, GC-2010; Shimadzu Corp.), provided with a recorder (C-R6A Chromatopac; Shimadzu Corp.), was used for routine work and yield determination. Both GC programs were identical, and the initial temperature of the column was 40 °C, maintained for 3 min; then the temperature was first increased with a rate of 15 °C/min up to 150 °C and next with 40 °C/min up to 250 °C, where the temperature was maintained for 4 min.
FIGURE 1. Hydrodechlorination and ring reduction of compound 1.
Results and Discussion For a rapid monitoring and assessment of reduction trends as the primary objective, the reaction mixture was stirred for only 2 h at a constant temperature of 80 °C, in a sealed tube, followed by rapid extraction, filtration, drying, and subsequent GC-MS analysis. In a previous study (36), we ascertained that the success of a hydrodechlorination process carried out in the presence of only Ca and ethanol might depend on the nature of the substituent; indeed, when electron-withdrawing substituents were present, the yield was almost quantitative, whereas the presence of an electron-donating substituent inhibited the hydrodehalogenation. For example, we found out that when 4-chlorotoluene or 4-chloroanisole was submitted to the dechlorination process, a total recovery of the starting material was recorded. In order to demonstrate the superiority of our new hydrodechlorination process carried out in the presence of a system formed of Ca and Rh/C in alcohol, we started our experiments working with substituted chlorobenzenes bearing electron-donating substituents of several types such as chlorotoluenes 1a, chloroanisoles 1b-1e, chlorophenols 1f-1g, chloroanilines 1 h-i, as well as di- and trichlorobenzenes 1j-1k, since our first method (36) allowed only monohydrodechlorination to occur (e.g., dichlorobenzene afforded after treatment monochlorobenzene). All results are summarized in Table 1 The treatment of 2-, 3-, and 4-chlorotoluenes 1aa-1ac with metallic calcium and Rh/C in methanol afforded toluene 2 in good yield (57-75%) along with methylcyclohexane 3a (25-43%). Most notably, the amount of methylcyclohexane 3a is lowest when the starting material is 4-chlorotoluene 1ab. We previously observed that for chlorotoluene no hydrodechlorination occurred when using metallic calcium alone in ethanol (36). This outlines the major role played by Rh/C catalyst both in the hydrodechlorination as well as in the reduction of the aromatic ring, although when used alone, in the absence of metallic Ca, it has no activity (38). Thus, the reductive capacity of the system metallic Ca/alcohol is enhanced by the catalytic presence of Rh/C. For sake of comparison of the reductive power of the metallic calciumRh/C catalyst, we submitted toluene 2 to the same process; in the same conditions (2 h process at 80 °C, in a sealed tube), beside a 70% recovery of the starting toluene, the remainder of 30% was represented by methylcyclohexane 3a. Similarly, 4-chlorophenol and 4-chloroaniline, which previously were unable to be hydrodechlorinated solely by Ca in ethanol (without Rh/C), were now transformed in the corresponding phenol 2f (69%), respectively, aniline 2h (66%), along with the secondary hydrodechlorination/ring reduction reaction products, cyclohexanol 3f (13%) and cyclohexylamine 3h (11%). It is noteworthy that, in the case of a polysubstituted phenol, the conversion of the starting material is almost similar, the difference being in the ratio of resulting compounds 2 (hydrodechlorination) and3 (hydrodechlorination/ring reduction), paradoxically, a monosubstituted phenol generates less hydrodechlorination/ring reduction than hydrodechlorination products; however, for the higher substituted phenol an opposite situation is recorded. In the case of anilines, it is worth mentioning the other byproduct: two secondary amines (dicyclohexylamine VOL. 43, NO. 15, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 1. Hydrodechlorination Resultsa
a Chlorinated substrate (1 mmol), Ca (0.4 g), ratio substrate:Ca ) 1:10, Rh/C (0.1 g), MeOH (5 mL) stirred at 80 °C for 2 h, in a sealed tube; yields, determined by GC-MS analysis, represent average values of 3 consecutive and identical experiments. b “-” ) the compound was not recorded, or only traces of it appeared in the GC-MS analysis.
and N-cyclohexylaniline), whose formation is possible in similar reaction conditions, as demonstrated by Olah and Tashiro (41). 5954
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The case of chloroanisoles is revealing for the behavior of such substituted chlorinated substrates toward hydrodechlorination: the higher the chlorine atoms concentration,
TABLE 2. Conversion Results after 2 and 6 ha total conversion, %b run
no.
X
n
compound
2h
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
1aa 1ab 1ac 1ba 1bb 1bc 1ca 1cb 1cc 1d 1e 1f 1g 1h 1i 1ja 1jb 1jc 1ka 1kb 1kc
CH3 CH3 CH3 OCH3 OCH3 OCH3 OCH3 OCH3 OCH3 OCH3 OCH3 OH OH NH2 NH2 Cl Cl Cl Cl Cl Cl
1 1 1 1 1 1 2 2 2 3 4 1 3 1 2 1 1 1 2 2 2
2-chlorotoluene 3-chlorotoluene 4-chlorotoluene 2-chloroanisole 3-chloroanisole 4-chloroanisole 2,3-dichloroanisole 2,4-dichloroanisole 3,5-dichloroanisole 2,4,6-trichloroanisole 2,3,4,5-tetrachloroanisole 4-chlorophenol 2,4,6-trichlorophenol 4-chloroaniline 3,5-dichloroaniline 2-dichlorobenzene 3-dichlorobenzene 4-dichlorobenzene 1,2,3-trichlorobenzene 1,2,4-Trichlorobenzene 1,3,5-trichlorobenzene
100 100 100 97 98 93 87 91 82 77 59 82 86 100 52 99.5 99 100 90 90 83
6h na na na 100 100 100 95 100 90 83 76 100 67 na 77 na 100 na 100 100 100
a Chlorinated substrate (1 mmol), Ca (0.4 g), ratio substrate: Ca ) 1:10, Rh/C (0.1 g), MeOH (5 mL) stirred at 80 °C for 6 h, in a sealed tube. b “na”, The experiment was not attempted, since a complete conversion was attained after 2 h.
the lower the hydrodechlorination yield. All three chloroanisoles 1b presented similar behavior: an almost total transformation with the formation in good yields of anisoles 2b (72-74%) along with cyclohexyl methyl ether 3b (16-25%), and occurrence of cyclohexanone 7 as a side-product (4-8%). Although dichlorobenzenes 1j previously afforded only monochlorobenzene when submitted to the simple hydrodechlorination process (Ca/ethanol) (36), this time the hydrodechlorination was complete: benzene 6 was the major reaction product and cyclohexane6 was the secondary product. For their part, monochlorobenzenes were recorded only as traces. The same situation (although with an enhancement in the concentration of monochlorobenzene) was recorded when using trichlorobenzenes as starting materials. Starting from the 1985 observation that, when submitted to reduction/hydrodechlorination with simple rhodium catalysts, chlorobenzene afforded a mixture of chlorocyclohexane and benzene (33), and from our 2001 report that metallic calcium in an alcohol is a suitable system for hydrodechlorination (36), the fact the no reduced ring bears chlorine atoms is an indication the hydrodechlorination process is prior to the reduction of the aromatic ring. Observing and comparing the results obtained for these different classes of chlorinated substrate, it is noticeable that lower transformation yields were obtained for substrates having the chlorine atom(s) in meta-positions. It is known that when the degradation of PCDDs occurs in solution (e.g., under photoirradiation), the replacement of a Cl atom by an H atom occurred more readily at the lateral position (2,3,7,8) than at the longitudinal position (1,4,6,9) (42-44). However, different results have been reported for surface reactions (43, 45) or in the presence of hydrogen donors (46). This is a clue for the double role played by Rh/C: it offers a suitable surface for the hydrodechlorination process and in the same time it catalyzes the ring reduction process. When prolonging the reaction time up to 6 h, the conversion of the starting poly chlorinated (mono-, di-, tri-, or tetra-) is higher or almost complete (except for 2,4,6trichlorophenol, when conversion is lower after 6 h), and the yields in the hydrodechlorination/ring reduction reaction product are sensibly improved.
The prolongation of the reaction time offered different patterns according to the substrates: on the three isomers of trichlorobenzene, 1,3,5-trichlorobenzene 1kc presented after 2 h the lowest conversion (having meta-positioning of the substituents). After 6 h, all three isomers are completely stripped of their chlorine atoms. Therefore, we can assume that for the more “resisting” chlorinated compounds, a longer reaction time is needed. In the same time, 3,5-dichloroanisole 1cc (another compound with a di-meta- positioning of the chlorine atoms) and 4-chlorophenol 1f, whom after 2 h presented a similar conversion that of 1,3,5-trichlorobenzene (∼82-83%), showed after 6 h conversions of 90 and 100%, respectively. The nature of the substituent (electro-donor -OCH3), along with the 3,5-positions occupied by chlorine atoms could explain why the conversion is not complete for 3,5-dichloroanisole, even after a 6 h treatment. On the other hand, complete hydrodechlorination of 4-chlorophenol could be explained by the fact that the phenol can act both as a substrate and a hydrogen donor (pKa ) 9.38), enhancing thus the production of nascent hydrogen in the reaction media. We assumed that the quantity of Ca introduced into the process is an important factor, since its presence permits the release of active species of hydrogen. Therefore, our next step was to increase (for starting materials presenting lower conversions, even after 6 h of treatment) the initial quantity of Ca, from simple to double, for a 2 h reaction time. The obtained conversions were usually higher, with an accessory increased amount of hydrodechlorination/ring reduction product 3 (cyclohexane 5 for the trichlorobenzene species). Again, a diverging note was made by 2,4,6trichlorophenol; when most of total conversions are heading toward a clean 100%, 2,4,6-trichlorophenol suffered a reverse process, the conversion dropping to merely a third of the initial amount of the poly chlorinated compound. This rather odd behavior could be explained through the roles that trichlorophenol can play in the process. Its low pKa of only 6.23 (47) makes it unrivaled by methanol (pKa ) 15.2) in the competition for metallic Ca. Nevertheless, the higher quantity of methanol (0.125 mols) compared to that of 2,4,6-trichlorophenol (0.001 mols) insures a considerable amount of nascent hydrogen to be formed in the reaction mixture. VOL. 43, NO. 15, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 3. Hydrodechlorination and Hydrodechlorination/Ring Reduction Results with Ratio Substrate: Ca = 1:20a
a Chlorinated substrate (1 mmol), Ca (0.8 g), Rh/C (0.1 g), MeOH (5 mL) stirred at 80 °C for 2 h, in a sealed tube. The compound was not recorded, or only traces of it appeared in the GC-MS analysis.
b
“-”,
FIGURE 2. Possible dechlorination pathway. However, even if nascent hydrogen is also generated in the reaction between 2,4,6-trichlorophenol and metallic calcium, the lowest conversion of the phenolic species to hydrodechlorinated ones could be explained by the different rates in the hydrodechlorination of 2,4,6-trichlorophenol and calcium 2,4,6-trichlorophenolate. Another process that is possible to occur and explain the lower conversion of trichlorophenol is its sorption capacity related to its hydrophobicity. It is known that 2,4,6-trichlorophenol have such a strong sorption capacity on montmorillonite Ca clays (48, 49). In the presence of a higher amount of metallic Ca, a similar process could occur, the Rh/C playing the role of adsorbant. The oily sludge thus formed could inhibit the generation of nascent hydrogen as well as its migration, rendering thus inoperative the hydrodechlorination process. Considering the results of this hydrodechlorination/ring reduction process, some assumptions can be made regarding to the possible reaction pathway. (1) Since the yields of hydrodehalogenated aromatic products are always higher than those for the hydrodechlorination/ring reduction products, it is probable that hydrodehalogenation occurs prior to ring reduction. Also, (2) because some of these 5956
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reactions could not happen using only metallic calcium in ethanol (e.g., chlorotoluene or chloroanisole (36)) and they are effective in the presence of Rh/C, we can assume that hydrodehalogenation takes place partly in solution and partly on the catalyst surface, whereas ring reduction must take place on the catalyst surface. In our opinion, the hydrodechlorination reaction occurs not through an organocalcium intermediate, as postulated by Rieke (18, 19), but rather with a radical mechanism, as proposed by Walborsky (50), the active species being nascent hydrogen, slowly formed by the interaction of metallic calcium with methanol. One proposal of the overall reaction pathway of the dechlorination step might be that shown in Figure 2. For the second step of the process, the aromatic ring reduction, we first assumed that the reaction pathway would probably depend on the quantity of molecular hydrogen formed through combination of the atomic hydrogen on the metal surface. When enough amount of molecular hydrogen is present on the Rh/C surface, corroborated with the presence of a hydrodechlorinated substrate adsorbed on the same surface, the reduction of the aromatic ring occurs. Nevertheless, release of the molecular hydrogen from the
Literature Cited
FIGURE 3. Possible ring-reduction pathways: hydrogenation (A) or Birch reduction (B).
catalytic
catalyst surface before the rise of enough hydrodechlorinated substrate will slow down the rate of the ring reduction process, resulting in lower yields of reduced aromatic substrates. Indeed, a building up of internal pressure inside the sealed tube was recorded a short while after the start of the process, probably because of the accumulation of molecular hydrogen. However, we cannot completely discard the involvement of nascent hydrogen in the ring-reduction step. Thus, a direct reaction of nascent hydrogen with the aromatic substrate in a Birch-type reduction could also be conceived (51, 52). Finally, a combination of both processes (Birch reduction + molecular hydrogen reduction) could be involved. In order to determine which possibility is most probable, we interrupted some experiments before completion and recorded the presence of partially reduced aromatic rings (cyclohexadienes and cyclohexenes) as well as, in some cases, the presence of 4,4′-disubstituted tetrahydro-biphenyl derivatives as traces, which are an indication of a Birch-type reduction process in a radicalic process. In a previous study, when applying the system metallic calcium/methanol to the hydrodechlorination of 2-chlorobiphenyl, a mixture of biphenyl, phenyl cyclohexadiene, phenyl cyclohexene, and phenylcyclohexane is formed (40). On the other hand, a buildup of the internal pressure is recorded, which indicates the presence of gaseous hydrogen. These facts suggest that in the ring-reduction step both types of reduction are involved, with a predominance of the radical (Birch-type) mechanism. X-ray diffraction analysis (Rigaku, RAD-X system, Cu KR2) of the reaction slurry (filtered prior to the addition of HCl 2N and dried) presented several 2θ peaks at 10.0°, 18.0°, 28.0°, 30.0°, 49.0°, and 51.0°. Similar patterns of X-ray data were obtained for the mechanochemical degradation of PVC (53) or thermal destructive adsorption of chloroform, trichloroethilene, and tetrachloroethane (54), both processes using CaO, and attributed to the CaClOH or Ca(ClO)2 2H2O species. These 2θ peaks were also obtained during an investigation of the reaction mechanism of Ca(OH)2 with gaseous HCl (55). There is though one difference between our data the mentioned ones: we did not recorded a peak at 39.0°, but on the other hand the compound whose formation we have proposed for this mechanism is not CaClOH, but CaClOMe. The reduction of various chlorobenzene derivatives by the calcium/rhodium catalyst system was investigated. In this report, we specifically described reduction of several mono- and poly chlorobenzenes with functional groups, e.g., methyl-, methoxy-, hydroxyl-, and amino-groups. Results show that, in a metallic calcium-rhodium/carbon catalyst reaction, the hydrodechlorination is complete in 2-6 h, a major secondary product being the hydrodechlorination/ ring reduction one. Compared to other existing methods (e.g., ref (34): KOH + 2-BuOH, [Cp*RhCl2]2 catalyst, reflux, 17 h), our method seems to be more convenient: Ca + MeOH, Rh/C catalyst, 80 °C, 2 h.
Acknowledgments We gratefully acknowledge financial support for this study from the Industrial Technology Research Grant Program (04A47002) of the New Energy and Industrial Technology Development Organization (NEDO) of Japan and from a Grant-in-Aid for Scientific Research, no. (B) 20310046.
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