MUCIC ACID FROM ARABINOGALACTAN GEORGE
T .
A U S T I N
College of Engineering Research Division, Washington State University, Pullman, Wash. 99163 Mucic acid was prepared by oxidizing commercially produced arabinogalactan with nitric acid. Optimum yields of 5 8 grams of mucic acid per 100 grams of arabinogalactan fed were obtained using 3 hours' heating a t 93OC. starting with 60% "01. The distribution of H N O i as evolved oxides and residual mother liquor was determined. Chromatographic studies of impurities were made. Cost estimates for raw materials for commercial production are included.
MUCIC, acid, the six-carbon dibasic
tetrahydroxy acid obtained by the oxidation of lactose, galactose, or galactans with nitric acid, was discovered and studied a t a very early date. Liebig (1847) describes prior work done by Berzelius, Hagen, and Guckelberger. Because of the wide range of usefulness of similar dibasic acids such as oxalic and tartaric, it seems that mucic should be a commercially valuable substance, but the high cost of the lactose and galactose used for its manufacture has OH
OHH I
/
I
HOOC-C-C-C-C-COOH I
I
I
I
H OHOHH
kept it too expensive to be industrially interesting. Acree (1921) and Schorger (1921, 1929) patented methods for manufacturing mucic acid from larch sawdust, which is high in arabinogalactan and can be oxidized to mucic acid with nitric acid, but nitration-oxidation in the presence of cellulosic materials is most hazardous. Whittier (1924) studied the catalyzed oxidation of galactose to mucic acid and found that 3570 nitric acid a t 85" C. produced optimum yields. Tollens (1885) describes purification methods. Arabinogalactan has recently appeared as a commercial product (STRactan, St. Regis Corp., Libby, Mont.), available in large quantity a t prices that have been estimated (Adams, 1967) as low as 20 cents per pound, which makes it an interesting raw material for mucic acid production. Attempts t o oxidize arabinogalactan to mucic acid using bromate, iodate, hypochlorite, permanganate, chromate, and air with catalysts were all unsuccessful. Conversion by oxidation with nitric acid is extremely simple. The effects of time, temperature, and concentration of nitric acid on the oxidation of arabinogalactan were studied. Because a considerable amount of nitric acid is lost in the mother liquor and as fumes, attempts to devise satisfactory methods to recover part of the nitric values thus lost are also reported. Methods of purifying the crude mucic acid obtained are described and a thinlayer chromatographic study of the contents of the mother liquor and precipitates was made. Apparatus and Procedure
Arabinogalactan used for these studies was commercial STRactan-10 obtained from the St. Regis Corp. This material is approximately 98% arabinogalactan, with some minor brown colored impurities of tsnnin-like substances. 424
I & E C PRODUCT RESEARCH A N D DEVELOPMENT
Twenty-five grams of arabinogalactan were added t o a 1-liter, three-necked flask equipped with a reflux condenser, the requisite quantity of water was added, and the mixture was heated in a constant temperature bath in a fume hood. Concentrated nitric acid (7OCc) was added to the solution in one installment and 2 to 4 drops of Dow-Corning antifoam B were added to control persistent foaming. Vigorous evolution of oxides of nitrogen began quickly, but had largely subsided in about 1 hour. The induction period rarely exceeded 5 minutes and the reaction was always controllable. The vessel was held a t constant temperature for the reaction time noted, allowed to sit overnight a t room temperature, then the product was filtered through a medium porosity sintered glass crucible, washed with $0 to 80 ml. of iced distilled water and 20 ml. of alcohol, dried for 24 hours a t 90°C., and weighed. Mucic acid is only slightly water-soluble (0.33 gram per 100 grams of H,O), so very little should be lost in washing. An experimental wash of 15 grams of dried product with 70 ml. of water a t room temperature produced a loss in weight under l ' c . A similar wash with 95'c ethanol produced a negligible weight loss, indicating the almost complete absence of oxalic acid in the product. Expected impurities in the acid included oxalic, saccharic, a b - and t a b mucic acids, etc., but these substances are water- and/or alcohol-soluble and should be reduced to low values by the simple wash purification. A sample of the product was converted to sodium mucate, recrystallized several times from hot water, then reconverted to mucic acid by acidification. The melting point remained constant a t 205" to 210°C. (with decomposition), the infrared absorption spectrum remained unaltered, and the thin-layer chromatograms of the precipitate remained substantially identical. Melting point is not a good criterion for purity of mucic acid, but the once-washed material has a neutral equivalent of 105 (theoretical, 105) and is believed to be pure. Figure 1 shows TLC chromatograms of the washed mucic acid solid, recrystallized washed mucic acid solid, oxalic acid, and the mother liquor from oxidations of arabinogalactan, arabinose, and galactose with nitric acid under similar conditions. Small samples of D-arabinose (Mann), L(+)-arabinose (Fisher), D(-)-arabinose (Eastman), D(+)-galactose (Eastman), lactose, and commercial arabinogalactan were oxidized with nitric acid under identical conditions. D ( + ) galactose, lactose, and arabinogalactan reaction products
Figure 1. Thin-layer chromatogram of oxidation product solids and mother liquors
Nitric Acid Consumption. The nitric acid used is either evolved as oxides of nitrogen or remains behind as nitric acid in the mother liquor; only a small amount is destroyed. Figure 4 shows the apparatus used to determine the evolved oxides of nitrogen by absorption in sodium hydroxide, reoxidation with air, and hack titration. The nitrate in the spent liquor was determined gravimetrically by precipitation with nitron following removal of interfering organic substances by oxidation with permanganate. Nitric acid balances obtained in this manner check within 670, which can he taken as the upper limit of the loss to he expected.
R,Voluer
1 . Mother liquor-D-arabinose oxidized wilh HNOl 2. Mother liquor-L(+)-orabinore oxidized with "Os 3. Mother liqu~r-D(-)-orobinore oxidized with
"08
4. Mother liquor-D(+)-galoaore oxidized with HN03 5. Mother liquor-lactose 6. Mother liquor-STRoOon-2
7. Precipitole-D(+)-saloctore 8. Precipitole-loclore 9. Piecipitote-STRocton-2 10. Oxalic acid 1 I . TEA and woter only
0.65,0.52.0.43 0.66,0.48, 0.43 0.67,0.49, 0.42 0.67,0.53, 0.46 0.67,0.53,0.45 0.67,0.52, 0.43 0.45 0.40 0.50 0.43 0.44
contained solid mucic acid; the other materials yielded clear solutions only. These small samples were used for the chromatographic studies. The chromatographic medium used was Mallinckrodt CHRomar-500 silicacontaining sheet. Two-microliter spots of triethylamine salt solutions were used with the composition 0.1 gram of salt plus 4 ml. of H,O plus 1 ml. of triethylamine. These were developed ascending with 60/20/20 v./v./v. 1hntinol-olsrii m-ot.ir erirl-arat.er mirtnre and viu~alizod ~_____. lll". l .^...._I_ _ ._I
with ninhydrin. I t has not proved possible to separate oxaiic from mucitc acid chromatographically, but several unidentified impu rities, a t least part of them oxidation products from arahin ose, exist in the mother liquor and are absent from th,e washed precipitate. Reaction products from arabinose ani1 galactose afe shown to he similar, with impurity levelS : .. 'L^ 111 Ll't:
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C_^_-. llV'll
. . : J " & : . .
"AluaLlVII
^C -","-a,.""I 6dl"L.'VUZ,
lactose, and arabinogalactan all low and similar. Oxidation of arabinose [D, L(+), and D(-)] produced no precipitate, while o(+)-galactose, lactose, and arahinogalactan all gave precipitates of a similar nature, but in varying quantity as shown by melting point, infrared spectrum, and neutral equivalent. Effect of Time of Redion.. Arahinogalactan was oxidized starting with 41.1 and 54.6% nitric acid a t 9 2 C . and with 41.1% acid a t 9YC. for varying periods (Figure 2). Periods beyond 3 hours bring decreased yields in all cases, probably due to continued oxidation of the products formed. All later studies were made with 3 hours' heating time. Effect of Initial Acid Concentration and Temperature. A comprehensive series of tests with initial nitric acid concentrations of 30, 40, 50, and 60% resulted in the values shown in Figure 3. These tests show that optimum yields of 58 grams of mucic acid per 100 grams of arahinogalactan charged occur when, the initial nitric acid concentration is 60% and the reaction is allowed to run 3 hours a t 94°C.
Fig mu
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n
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020
70
75
80
85
95
90
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100
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J OIL B A T H
Figure 4. Apparatus for oxidation of arabinogalactan with nitric aicd VOL. 8 N O , 4 DECEMBER 1 9 6 9
425
Table 1. Distribution and Consumption of Nitric Acid
Run No.
Initial HNO, Con.cn., 5;
"0,
Evolved, Grams
"03
Mother, Grams
HXO', in Mother Liquor
Grams HNOI" G r a m M.4
50 45 35 35 29
3.89 3.91 3.60 3.68 3.45
2.10 1.88 1.64 1.52 0.91
61 55 39 42 39 32 32
4.24 3.92 3.63 3.63 3.60 3.50 3.64
2.53 2.15 1.42 1.52 1.41 1.12 1.16
ic
Grams HiVOID Grams M A
Temperature 88' C.
0
35.3 38.0 44.8 49.3 61.5
22.8 25.8 27.0 29.2 36.5
6 7 8 9 10 11 12
29.1 35.3 41.2 44.8 49.3 54.8 61.5
20.0 22.5 30.2 28.8 30.3 33.8 33.8
1 2 3 4
24.6 22.4 17.3 17.4 9.3 Temperature 93s C. 29.7' 27.2' 19.jc 20.9' 19.4 15.9' 15.9
Assumes no HiVO, recover?., acid fed M A produced. 'Assumes all HNO, vapors evolved recocerable, (acid fed-acid evolved) M A produced Estimated by difference.
I
0.5
L 20
I 30
I 40
I
I I 50 60 I N I T I A L C O N C E N T R A T I O N OF N I T R I C A C I D - O/o
I
1
70
Figure 5 . Effect of initial nitric acid concentration on nitric acid utilization U p p e r . 88°C. Lower. 93°C.
The absorption of the evolved oxides of nitrogen in fresh arabinogalactan solutions has been tried and found feasible, although foaming is a persistent problem. T h e concentration of nitric acid in the mother liquor is between 10 and 24% and represents nearly half of the acid fed, so this material cannot be wasted if the process is to be economic. A small amount can be utilized as dilution water in making up reactant solutions and tests have shown that the impurities do not build up in the system, causing difficulties. The remainder must be recovered by distillation, but no experiments on the recovery problems have been made. Table I and Figure 5 summarize the results obtained from a series of experiments designed to study nitric acid distribution and consumption.
426
I & E C PRODUCT RESEARCH A N D DEVELOPMENT
Taking a price of 20 cents per pound for arabinogalactan and technical 6 8 5 nitric acid a t 5 cents per pound, the raw material costs for mucic acid, made under optimum observed conditions, are: if evolved gases are wasted, $0.60; if evolved gases are recovered, $0.43; if evolved gases and HNOi in mother liquor are recovered ( 6 5 loss), $0.36. In view of the extra equipment required for the recovery of the mother liquor, this step would probably be economically unsound unless a waste-disposal problem made it essential. Optimum conditions for manufacture thus appear to be 3 hours' reaction time a t 94°C. with an initial 6 0 5 concentration of nitric acid. High temperatures (90" to l0O'C.) are also essential if the precipitate obtained is to be filterable. At temperatures below 90'C. the acid lives up to its German name, "Schleimsaure." Product color is also much improved by high temperature oxidation. Acknowledgment
S. M. Jain made most of the oxidation runs as part of an M. S.thesis problem at Washington State University (1961). Other students contributing significantly to this work include: Maurice Hedlund, Donald Bea, Karl Berntsen, Don Ennis, Dave Larsen, and Ibrahim Kellizy. Literature Cited
Acree, S.F., Brit. Patent 160,777 (March 18, 1921). Adams, M. F., Washington State University, Pullman, Wash., private correspondence, 1967.t Liebig, J., Ann. 63, 347 (1847). Schorger, A. W., Can. Patent 213,175 (Aug. 30, 1921); U. S. Patent 1,718,837 (June 25, 1929). Tollens, G., Ann. 227, 222 (1885). Whittier, E. O., Ind. Eng. Chem. 16, 745 (1924). RECEIVED for review March 17, 1969 ACCEPTED July 22, 1969
