Ind. Eng. Chem. Res. 1995,34, 3766-3770
3766
Mechanism Study of Sugar and Sugar Alcohol Hydrogenolysis Using 1,3-Diol Model Compounds Keyi Wang, Martin C. Hawley,* and Todd D. Furney Department of Chemical Engineering, Michigan State University, East Lansing, Michigan 48824
Knowledge of the bond cleavage mechanism governing sugar and sugar alcohol hydrogenolysis is important to control of the selectivity of sugar and sugar alcohol hydrogenolysis. Previous work by others has resulted in the suggestion of a variety of mechanisms to explain the C-C cleavage in sugar and sugar alcohol hydrogenolysis, and has not provided any definitive evidence to elucidate either the C-C or C - 0 cleavage mechanism. In this work, we present a mechanism study carried out using 1,3-diol model compounds. Our experimental results indicate that cleavage of the C-C and C - 0 bonds in hydrogenolysis is through retro-aldolization and dehydration of a B-hydroxyl carbonyl, respectively. The structure of this ,&hydroxyl carbonyl is already contained in a n open-chain sugar molecule, and is generated from the sugar alcohol molecule by dehydrogenation. The intermediates from both C-C and C - 0 cleavage are subsequently hydrogenated to yield alcohols or polyols. This mechanism of sugar and sugar alcohol hydrogenolysis provides us a good background to understand factors that control the selectivity in sugar and sugar alcohol hydrogenolysis. Based on this understanding, a rational approach to control of the selectivity of sugar and sugar alcohol hydrogenolysis may be developed.
Introduction Under high temperature and high hydrogen pressure, sugars and sugar alcohols can be catalytically hydrogenolyzed to give various polyols. This process has been explored since the 1950's as a potential means to produce glycerol, ethylene glycol and propylene glycol from renewable biomass resources (Clark, 1958;Arena, 1983; Dubeck and Knapp, 1984; van Ling et. al. 1970, 1969, 1967; Tronconi, et al.). Hydrogenolysis of sugars and sugar alcohols is catalyzed by transition metal catalysts and enhanced by addition of bases. In this process, both C-C and C-0 bonds are susceptible t o cleavage: R3C-CR3
+ H,
R3C -OH
+
H2
-
-
R,CH+HCR', R&H+ H20
One interesting question is how are the C-C and C-0 bonds of the sugar and sugar alcohol molecules broken in hydrogenolysis? This question is important to selectivity control in sugar and sugar alcohol hydrogenolysis. Cleavage of C-0 bonds, as Montassier et al. (1988, 1989) proposed, is through dehydration of a ,&hydroxyl carbonyl: on on I
/
RCHCHCHR'
-Hz
on
7 TH
RCCHCHR' I
on
.Hz0
0
//
RCC=CHR' I
on
+HZ
on
o
OH
OH
-
0
0
-
1 1 -H 11 I I1 I1 +"z RCHCHCHR' 3 RCCHCHR' 1 RCCH20H + HCR' I OH Re1ro.aldol on
OH I
RCHCH2OH + HOCH2R'
Andrews and Klaeren (1989) suggested the same mechanism, based on their observation that the primary C-C cleavage site is /3 to the carbonyl group in sugar hydrogenolysis. According to this mechanism, the C-C cleavage precursor is again a P-hydroxyl carbonyl. Cleavage of this ,&hydroxyl carbonyl leads to an aldehyde and a ketone, which are subsequently hydrogenated to alcohols. Later, however, Montassier et al. (1988) found that it was difficult to explain the absence of methanol and the presence of COz in the hydrogenolysis products of glycerol and other sugar alcohols with the retro-aldol mechanism. Therefore, they proposed another mechanism, namely, the retro-Claisen reaction, for the C-C cleavage in glycerol hydrogenolysis:
on 1
RCHCHCH2R'
I
on
The structure of this ,%hydroxyl carbonyl is already contained in an open-chain sugar molecule, and it may be generated from a sugar alcohol molecule by dehydrogenation. The direct product from dehydration of the j3-hydroxyl carbonyl is an a,/?-unsaturated carbonyl, which yields a polyhydric alcohol upon hydrogenation. In the reaction scheme just discussed, the dehydration step is catalyzed by bases, and the dehydrogenation and hydrogenation steps are catalyzed by transition metal catalysts.
* To whom
The original mechanism proposed by the Montassier group (Sohounloue, 1983) to explain the C-C cleavage in sugar and sugar alcohol hydrogenolysis is the retroaldol reaction:
correspondence should be addressed. E-mail:
[email protected].
This mechanism allows formation of formic acid which decomposes under the hydrogenolysis conditions to form COz. The mechanism based on the retro-aldol reaction allows formation of formaldehyde rather than formic acid. Upon hydrogenation, formaldehyde yields methanol. To explain the C-C cleavage in the hydrogenolysis of xylitol and sorbitol, Montassier et al. (1988) also proposed the retro-Michael reaction as the mechanism: on
P"
I RCHCHCHCHCHR'
I
l
l
ononon
-2"z
0
0
0
11 I1 RCCHCHCHCR'
I
l
l
ononon
il
0
I1
RCC = CH + OHCH2CR' Reoo-Michael
Q888-5885l95/2634-3766$Q9.QQIQ 0 1995 American Chemical Society
I 1 OH OH
Ind. Eng. Chem. Res., Vol. 34,No. 11, 1995 3767
Scheme 1. Mechanism of Sugar and Sugar Alcohol Hydrogenolysis 0
0
I/
I/
RCCHZOH + HCR' I11 IV
OH
OH
I
I
I
-H2
OH
I
RCHCHzOH + HOCHzR'
V
1
rctro-aldol
RCHCHCHR'
+h
VI
OH
0
I
I/
RCCHCHR'
I
OH
OH
I dehydration
1
I1 .H$J
0 I1 RCC =CHR' I
OH
VI1
"2
OH
1
RCHCHCH2R' 1
OH
VI11
This mechanism requires a 6-dicarbonyl as the bond cleavage precursor. However, two theoretical considerations prevent us from believing that either retro-Claisen or retro-Michael is a dominating C-C cleavage mechanism over the retro-aldol in hydrogenolysis. First, both the retroClaisen and retro-Michael mechanisms require a dicarbony1 precursor. The formation of a dicarbonyl presumedly occurs through further dehydrogenation of a monocarbonyl. As the dehydrogenation is thermodynamically unfavorable, the dicarbonyl formed is unlikely to be significant relative to the monocarbonyl, the precursor of the retro-aldol reaction. Second, the dehydrogenation of the monocarbonyl is in competition with dehydration, the C-0 cleavage reaction. Since the dehydration is both thermodynamically and kinetically (in the presence of bases) much more favorable than the dehydrogenation, the hydrogenolysis products would have exclusively resulted from C-0 cleavage, had either the retro-Claisen or the retro-Michael been the dominating mechanism of C-C cleavage in hydrogenolysis. In contrast, the retro-aldol reaction shares the same precusor as the dehydration, and has the ability to compete with the dehydration. On the basis of these reasons, we tend to believe that the C-C cleavage occurs through the retro-aldol reaction. Thus,the bondcleaving processes in the hydrogenolysis of sugars and sugar alcohols can be pictured as Scheme 1. As for the formic acid in the hydrogenolysis of glycerol, it may be produced from the Cannizzaro reaction of formaldehyde. In the Cannizzaro reaction, formaldehyde is oxidized to formic acid while other carbonyl compounds are reduced to alcohols. This reaction is catalyzed by bases but has been reported t o be greatly enhanced by transition metal cocatalysts (Cook and Mailis, 1981). The Cannizzaro reaction enhanced by the transition metal is likely t o be the side reaction competing with the hydrogenation of formaldehyde in the hydrogenolysis of glycerol and other sugar alcohols, which is responsible for the absence of methanol and the presence of COz in the hydrogenolysis product. The reaction mechanism described in Scheme 1 can explain all the reaction products found so far in the hydrogenolysis of sugars and sugar alcohols. Other than that, the results from the hydrogenolysis of sugars and sugar alcohols provide no clue that the C-0 bond is broken through dehydration of a /?-hydroxylcarbonyl. Experimental evidence that dehydrogenation is a necessary step in the hydrogenolysis of sugar alcohols is also unavailable, and no sugar intermediate has been identi-
fied so far in any of the sugar alcohol hydrogenolysis experiments (Clark, 1953; Sohounloue et al., 1983; Motassier et al., 1988, 1989; Chang et al., 1985). Andrew and Maeren's (1989) observation that the primary C-C cleavage site is /3 to the carbonyl group in sugar hydrogenolysis may be a strong suggestion that the C-C cleavage has occurred through the retro-aldol reaction. However, bond breakage at this site is also expected by the retro-Claisen mechanism. Clearly, more evidence is required to validate the mechanism described in Scheme 1. In this work, we attempt t o verify the reaction mechanism in Scheme 1 using 1,3-diol model compounds. According to Scheme 1,a 1,3-diol or its dehydrogenation product is the basic structural unit giving the reactivity to sugar and sugar alcohol molecules. Therefore, a mechanism study of the hydrogenolysis of sugars and sugar alcohols can be pursued with these compounds. Using 1,3-diol model compounds in the mechanism study has several advantages over direct use of the sugar or sugar alcohol compounds. First, the bond cleavage pattern is indicated by the reaction products, since the starting molecule undergoes only one bond-cleavingreaction in the hydrogenolysis of 1,3-diols. In the hydrogenolysis of sugars and sugar alcohols, the starting molecule can undergo a chain of bond-cleaving reactions before further hydrogenolysis is impossible. As a result, the bond cleavage pattern is difficult to recognize based on the final products in the sugar and sugar alcohol hydrogenolysis. Second, sugar and sugar alcohol molecules have too many functional groups, which makes it possible to interpret the experimental results in a variety of ways. In contrast, 1,3-diols possess only the functional groups necessary for the hydrogenolysis to occur, which minimizes the ways t o interpret the results. The retro-Michael mechanism is excluded from the hydrogenolysis of 1,3-diols, for instance, because 1,3-diols are incapable of forming the 6-dicarbonyl as required by the mechanism. Last and the most important, 1,3-diols with special structural features can be used to verify the role played by a single reaction in the hydrogenolysis.
Experimental Section In this work, 1,3-diolswith various structural features were hydrogenolyzed with Raney Cu and Raney Ni as catalysts, t o provide experimental evidence for the mechanism described in Scheme 1. All the 1,3-diols used in this work were purchased from Aldrich and were used as received. The Raney Cu and Raney Ni catalysts were also purchased from Aldrich and were received as 50% slurry in water. The hydrogen (99.9% pure) was obtained from Purity Cylinder Gases. The hydrogenolysis experiments were performed in a specially designed, stainless steel reactor with a capacity of 50 mL. To carry out the reaction, about 1g of the starting diol, 8-12 g of Raney Cu or Ni slurry, 0.4 mL of 1 N sodium hydroxide, and proper amounts of distilled water were placed in the reactor, giving a total volume of about 40 mL. The reactor was purged by alternately connecting it to nitrogen and vacuum, and then was heated in a silicone oil bath. As soon as the temperature of the reactor reached 210 "C, the hydrogen pressure was applied to the reactor and was controlled at 5 MPa. During the reaction course, the reaction medium was constantly stirred by a magnetic stirring bar and its composition was monitored using high-performance liquid chromatography (HPLC). The HPLC samples were taken via a sampling port on the reactor every 30 min.
3768 Ind. Eng. Chem. Res., Vol. 34, No. 11, 1995 Table 1. Structures of the 1,3-Diols Used in the Current Work name
2,4-dimethyl-2,4pentanediol (1) 2-methyl-2,4-pentanediol(2) 2,2,4-trimethyl-1,3-pentanediol (3) 2,2-dimethyl-l,3-propanediol(4) 2,4-~entanediol(5)
Ri CH3 CH3 H H CH3 H H
R2
R3
R4
R5
CH3 CH3 H H H H H
H H CH3 CH3 H H H
H H CH3
CH3 H H
Rs CH3 CH3 CH(CHd2
H
H
H
The hydrogenolysis products were analyzed by reverse phase HPLC and were confirmed by normal phase HPLC. The column used for reverse phase HPLC was a 25 x 0.46 cm C18 column obtained from Whatman (Catalog No. 4621-1502), and the column used for normal phase HPLC was a 25 x 0.46 cm amino column obtained from Aldrich (Catalog No. 2226122). The detector used was a differential refractometer. During the performance of reverse phase HPLC, the samples taken from the reactor were injected without any preparation; during the performance of normal phase HPLC, the hydrogenolysis products were transferred by extraction from the water phase to methylene chloride before injection. To differentiate the peaks resulting from the impurities introduced into the reaction medium with the Raney catalysts from those for hydrogenolysis products, an experiment without any 1,3-diolsubstrate was performed and samples were collected. Chromatograms for these samples were obtained to compare with those for impurity-containing hydrogenolysis products.
Results and Discussion In order to verify the mechanism described in Scheme 1, hydrogenolysis experiments have been performed with 1,3-diols of various structures, including 2,4dimethy1-2,4-pentanediol(l),2-methyl-2,4-pentanediol (2),2,2,4-trimethyl-1,3-pentanediol(3), 2,2-dimethyl-1,3propanediol(4), 2,4-pentanediol(5), 1,3-butanediol (61, and 1,3-propanediol (7). The structures of these compounds are provided in Table 1. The experimental results are summarized in Table 2, together with a documentation of the expected products from each 1,3diol based on Scheme 1. All the experiments in this work have been performed at 210 "C and 5 MPa hydrogen pressure in aqueous phase. NaOH was added to promote the reaction. The transition catalysts used in this work are Raney Cu and Raney Ni, two of the typical catalysts used in sugar and sugar alcohol hydrogenolysis (Montassier et al., 1988; Changet al., 1985; Sohounloue et al., 1983). The yields presented in Table 2 are based on the reacted 1,3-diols. The mass is not balanced perfectly, but is within the experimental error. In all the experiments where methanol is an expected product, it is found only in a trace amount. The reason is attributed to the transition-metal-catalyzed Cannizzaro reaction, which intercepts formaldehyde, the hydrogenation precusor to methanol, as discussed earlier. According t o Scheme 1, the hydrogenolysis of a 1,3diol is initiated by dehydrogenating one of its hydroxyl groups. This postulation is strongly supported by the results from hydrogenolysis of 1. Because of the absence of a hydrogen atom on both the a and y carbons, 1 is incapable of undergoing dehydrogenation, and thus is expected to be inactive under the hydrogenolysis conditions. As indicated in Table 2, 1 is indeed found to be inactive. The hydrogenolysis of 1 has been carried out for 6 h with Raney Cu as a catalyst (run 1)and for 4 h with Raney Ni as a catalyst (run 8). No reaction products have been identified at the end of either
1,3-diol OH I
Rq
l
OH l
reaction. For comparison, other 1,3-diols used in this work are all found to be reactive under the same conditions, because they can undergo the dehydrogenation reaction. That dehydrogenation is a necessary step for hydrogenolysis is additionally supported by the results from hydrogenolysis of 2. As 2 cannot be dehydrogenated at the a carbon, the C-C and C - 0 bonds of 2 are not expected to be broken between the p and y carbons and at the y carbon, respectively, during hydrogenolysis, although they may be broken between the a and carbons and at the a carbon, respectively. The experimental results turned out again exactly as expected (runs 2 and 9). The results from hydrogenolysis of 2 (runs 2 and 9) also provide good evidence against the retro-Claisen as the dominating C-C cleavage mechanism. The retroClaisen reaction requires a dicarbonyl precursor. Since 2 is incapable of forming such a dicarbonyl, the retroClaisen mechanism predicts that the C-C bonds of 2 are unbreakable in hydrogenolysis. However, the experimental results show otherwise: the hydrogenolysis rate of 2 is not impaired by its incapability of undergoing the retro-Claisen reaction, as shown by the conversion data in Table 2. In contrast to the retro-Claisen mechanism, the retroaldol mechanism predicts that the C-C bond of 2 may be broken between the a and p carbons to form two 2-propanol molecules, as 2 can be dehydrogenated a t the y carbon. The retro-aldol mechanism also predicts that the 2-propanol is formed through an acetone intermediate. As seen in Table 2,2-propanol is not only found at the end of the reaction (runs 2 and 91, but is a dominating product of 2-methyl-2,4-pentanediol hydrogenolysis. Furthermore, acetone is identified in the reaction when Raney Cu is used as the hydrogenolysis catalyst (run 2). Acetone is not detected in the reaction when Raney Ni is used as the catalyst, because Raney Ni is a more efficient hydrogenation catalyst than Raney Cu. The acetone formed in the hydrogenolysis of 2 may be quickly hydrogenated to 2-propanol. The results from hydrogenolysis of 2 is very supportive of the retroaldol mechanism. The results from hydrogenolysis of 3-7 are also supportive of the retro-aldol mechanism. In all these experiments, the C-C bond cleavage patterns are found t o be consistent with the retro-aldol mechanism. In hydrogenolysis of 6 (run 6), acetone is again identified as an intermediate predicted by the retro-aldol mechanism. Hydrogenolysis of 2,6,and 7 has been carried out by Conner and Adkins (1932) with a catalyst prepared by precipitation of nickel carbonates. However, in hydrogenolysis of 2, they identified only the end products, as in our 2-propanol (11) and 4-methyl-2-pentanol(19), experiment with Raney Ni as the catalyst. In hydrogenolysis of 6 and 7, they did not report the C-C cleavage a t all. The successful identification of C-C bond cleavage in hydrogenolysis of 6 and 7 and of the retro-aldol intermediates in hydrogenolysis of 2 and 6
Ind. Eng. Chem. Res., Vol. 34, No. 11, 1995 3769
*2
in this work strengthens the theory that the C-C cleavage is through the retro-aldol reaction. Also according t o Scheme 1,the dehydration reaction is responsible for the C-0 cleavage in hydrogenolysis. This postulation is strongly supported by the results from hydrogenolysis of 3 and 4. Based on the dehydration mechanism, a hydrogen atom attached t o the p carbon is necessary for the hydrogenolysis of C-0 bonds t o occur. Since such a hydrogen does not exist in 3 and 4,cleavage of the C-0 bonds is not expected t o occur in the hydrogenolysis of these compounds. Indeed, as indicated in Table 2, no C-0 cleavage is found in hydrogenolysis of either 3 or 4. The dehydration mechanism is also supported by the C-0 cleavage pattern found in the hydrogenolysis of 2 (runs 2 and 9). The dehydration mechanism expects the C-0 bond t o be broken only a t the a carbon in hydrogenolysis of 2, as 2 can be dehydrogenated only a t the y carbon. The results from hydrogenolysis of 2 shows that this expectation is correct. The additional products 2-pentanone (18)and 2-butanone (16)identified in the hydrogenolysis of 5 (runs 5 and 12) and 6 (run 61,respectively, provide additional evidence to the dehydration mechanism. These compounds are not the direct products of dehydration, or VI1 in Scheme 1,but intermediates from VI1 t o VIII. The hydrogenation of VI1 t o VI11 is believed to take place in two sequential steps, as shown in the following with hydrogenolysis of 5 as an example:
W
9 2
2
0
2
0 11
CH,CH=CHCCH,
0
VI1 = 3-pentene-2-one
2
> oooo DYTOCOQ,
2
*
0 0 0 0 YTYTU) r ) N N * r l N N N 3
22
0 00
4
0 0 0
*corn
N 3 N
+H
11
-
2 CH~CH,CH~CCH, 2-pentanone
+H2
PH
CH,CH,CH~CHCH, VI11 = 2-pentanol
The accumulation of 2-pentanone in hydrogenolysis of 5 and of 2-butanone in hydrogenolysis of 6 suggests that, with Raney Cu and Ni as catalysts, the hydrogenation of C-C double bonds is faster than the hydrogenation of C-0 double bonds. As discussed above, the hydrogenolysis mechanism described in Scheme 1 is strongly supported by the results from hydrogenolysis of the various 1,3-diolmodel compounds. In no reaction has a product other than the expected been found, and in no reaction has an expected product not been found. The experiments in this work have been done with two different catalysts. The reaction patterns are not affected by the change of catalysts. Compared to Raney Cu, Raney Ni is a more efficient hydrogenolysis catalyst, as shown by the conversion data in Table 2. In addition to the bond cleavage mechanism, selectivity control is another important issue concerning sugar and sugar alcohol hydrogenolysis, and thus is also a concern of the current work. In hydrogenolysis of a 1,3diol, typically four bond cleavage selectivities can be defined, namely, Ca-CP vs Ca-0, Cp-C, vs Cy-0, C,-Cp vs Cp-C,, and Ca-0 vs Cy-0. According to Scheme 1, the retro-aldol reaction responsible for the C -C cleavage and the dehydration reaction responsible for the C - 0 cleavage share the same precursor. Compared to the hydrogenation reactions catalyzed by Raney Cu and Raney Ni, the retro-aldol and dehydration reactions require only moderate reaction conditions. It is believed that, in hydrogenolysis of 1,3-diols, the retro-aldol and dehydration reactions are basically in an equilibrium state. Therefore, the C-C vs C-0 selectivities are determined by the equilibrium constants between the retro-aldol products (111and rv)and the dehydration products (VII) and by the relative hydrogenation rates of them.
3770 Ind. Eng. Chem. Res., Vol. 34, No. 11, 1995 Generally speaking, for straight-chain 1,3-diols, the equilibrium favors the dehydration product, while for branched-chain 1,3-diols, the equilibrium favors the retro-aldol product (Neilson and Houlihan, 1968). With Raney Cu as the catalyst, the C-C vs C-0 selectivity is basically controlled by the equilibrium between the retro-aldol and the dehydration products, as shown by the C-C vs C-0 selectivity data in Table 2. In hydrogenolysis of 2 (a branched-chain 1,3-diol), the reaction favors the C-C cleavage; in hydrogenolysis of 5 and 7 (straight-chain 1,3-diols), the reaction favors the C - 0 cleavage. Compared to the Raney Cu catalyst, Raney Ni seems to direct the reaction more toward the C-C cleavage. In hydrogenolysis of 2, the C-C vs C-0 selectivity is further enhanced; in hydrogenolysis of 5 and 7 , the C-C and C-0 cleavage are equally favored, although the equilibrium between the retro-aldol and dehydration products still favors the later. On the basis of the above results, Raney Ni must hydrogenate the retro-aldol products faster than it hydrogenates the dehydration products. In dealing with the Ca-Cb vs Cb-C, and the Ca-0 vs Cy-0 selectivities, an additional factor, the dehydrogenation, must be considered, besides the retro-aldol and dehydration reactions. In hydrogenolysis of 3,the C,-Cb vs Cb-C, selectivity seems to be controlled by the retro-aldol reaction, when Raney Cu is used as the hydrogenolysis catalyst. The retro-aldol reaction favors the Ca-Cy cleavage substantially over the Ca-Cp cleavage in this case. When Raney Ni is used as the catalyst, this selectivity cannot be explained purely based on the retro-aldol reaction, because cleavage of the two carbon bonds is almost equally favored. A logical conclusion seems that with Raney Ni as the catalyst the dehydrogenation of a secondary hydroxyl group is favored over that of a primary hydroxyl group. The selectivity pattern shown in hydrogenolysis of 6 (run 6) is more complex and is more difficult to rationalize. When the retro-aldol reaction occurs, the aldol reaction is also possible, which often leads to scrambling of the retro-aldol fragments. Thus, in the hydrogenolysis of 1,3-diols, one might expect 1,3-diols other than the starting ones to be formed as the result of the scrambling aldol reaction. However, no such byproducts have been observed in any experiment carried out in this work. The reason is attributed to the fast hydrogenation of aldehydes under the hydrogenolysis conditions and the unfavorable condensation between ketones, which minimize the formation of any new 1,3-diols.
Conclusion A mechanism study has been carried out on the hydrogenolysis of sugars and sugar alcohols using 1,3diols as model compounds. To summarize the experimental results, the hydrogenolysis of 2,4-dimethyl-2,4pentanediol and 2-methyl-2,4-pentanediol demonstrates that the dehydrogenation is a necessary step in the hydrogenolysis of sugar alcohols. The hydrogenolysis of 1,3-dimethyl-l,3-propanediol and 2,2,4-trimethyl-1,3pentanediol demonstrates that the dehydration is responsible for the C - 0 cleavage in hydrogenolysis. The hydrogenolysis of 2-methyl-2,kpentanediol also provides good evidence against the retro-Claisen as the dominating C-C cleavage mechanism. In all the experiments but hydrogenolysis of 2,4-dimethyl-2,4-pentanediol,where no reaction is supposed to occur, the C-C cleavage is found to follow the patterns predicted by the retro-aldol mechanism. In addition, some ketone intermediates expected by Scheme 1are identified in the hydrogenoly-
sis of 2-methyl-2,4-pentanediol, 2,4-pentanediol,and 1,3butanediol. The experiments have been performed with two different catalysts (Raney Cu and Raney Ni); the reaction patterns are not affected by the change of catalysts. All these results suggest that the mechanism described in Scheme 1is correct. With detailed knowledge of the reaction mechanism and an understanding of the factors affecting selectivity, a rational approach to control of the selectivity of sugar hydrogenolysis and thus to economic production of polyols from sugars may now be developed.
Acknowledgment This work was generously supported by the Consortium for Plant Biotechnology Research, the Amoco Foundation, the Michigan State University Crop and Food Bioprocessing Center, and the Department of Chemical Engineering at Michigan State University.
Literature Cited Andrews, M. A.; Klaeren, S. A. Selective Hydrocracking of Monosaccharide Carbon-Carbon Single Bonds under Mild Conditions. Ruthenium Hydride Catalyzed Formation of Glycols. J . Am. Chem. SOC.1989,111, 4131-4133. Arena B.J. Hydrogenolysis of Polyhydroxylated Compounds. US patent 4,401,823, 1983. Chang, F. W.; Kuo, K. T.; Lee, C. N. A Kinetic Study on the Hydrogenolysis of Sorbitol over Raney Nickel Catalysts. J . Chin. Inst. Chem. Eng. 1985,16, 17-23. Clark, I. T. Hydrogenolysis of Sorbitol. Znd. Eng. Chem. 1958,50, 1125-1126. Connor, R.; Adkins, H. Hydrogenolysis of Oxygenated Organic Compounds. J . A m . Chem. SOC.1932,54, 4678-4690. Cook, J ; Mailis, P. M. Formaldehyde as a Hydrogen-donor to Aldehydes and Ketones in Metal-catalyzed Reactions in Water. J . Chem. SOC.,Chem. Commun. 1981, 924-925. Dubeck, M.; Knapp, G. G. Sulfide-Modified Ruthenium Catalyst. US patent 4,430,253, 1984; Chem. Abstr. 102, 167115. Montassier, C.; Giraud, D.; Barbier, J. Poly01 Conversion by Liquid Phase Heterogeneous Catalysis over Metals. In Heterogeneous Catalysis and Fine Chemicals; Guisnet, M., et al., Ed.; Elsevier: Amsterdam, 1988. Neilsen, A. T.; Houlihan, W. J. The Aldol Condensation. In Organic Reactions, Adams, R., et al., Eds.; Wiley: New York, 1968; Vol. 6. Sohounloue, D. K.; Montassier, C.; Barbier, J. Catalytic Hydrogenolysis of Sorbitol. React. Kinet. Catal. Lett. 1983, 391-397. Tronconi, E.; Ferlazzo, N.; Forzatti, P.; Pasquon, I.; Casale, B.; Marini, L. A Mathematical Model for the Catalytic Hydrogenolysis of Carbohydrates. Chem. Eng. Sci. 1992, 47, 24512456. Van Ling, G.; Vlugter, J. C. Catalytic Hydrogenolysis of Saccharides 11. Formation of Glycerol. J . Appl. Chem. 1969, 19, 4345. Van Ling, G.; Ruijterman, G.; Vlugter J . C. Catalytic Hydrogenolysis of Saccharides I. Qualitative and Quantitative Methods for the Identification and Determination of the Reaction Products Carbohydr. Res. 1967, 4 , 380-386. Van Ling, G Driessen, A. J.; Piet, A. C.; Vlugter, J. C. Continuous Production of Glycerol by Catalytic High Pressure Hydrogenolysis of Sucrose. Ind. Eng. Chem. Prod. Res. Dev. 1970, 9 , 210212. Received for review December 2, 1994 Revised manuscript received May 23, 1995 Accepted J u n e 6, 1995@ IE9407130
Abstract published i n Advance A C S Abstracts, August 15, 1995. @
