Determination of Furfural Produced from Hardwoods HAROLD A. TDDLES
AND
PAULJ. ROBBINS, TJniversity of New Hampshire, D u r h a m , N. H. VOLUMETRIC POTASSIUM BROMATE-BROMIDB MXTHOD.Following the method suggested by Powell arid Whittaker and since used by others, 25-cc. portions of approximately 0.1 N potassium bromatebromide were pipetted into four glass-stoppered bottles. Into two of these the samples made up to 200 cc. with 12 per cent hydrochloric acid were added and into the other two, 200 cc. of 12 per cent hydrochloric acid were added for blank runs. After standing for one hour in the dark, 10 cc. of 10 per cent potassium iodide were added and the liberated iodine was titrated with 0.1 N sodium thiosulfate. The number of cubic centimeters required by the sample subtracted from the number required for the blank was a measure of the furfural present.
T
HE standard method for the determination of pentoses and pentosans in plant materials (I, 6, 6) involves the distillation of the sample with 12 per cent hydro-
chloric acid until no more furfural is produced, as indicated by the absence of a pink coloration with aniline acetate. The distillate is treated with phloroglucinol to produce a precipitate of indefinite composition which may be determined gravimetrically. Because of the empirical nature of this method and the length of time consumed in its operation, several alternative methods have been suggested. The use of thiobarbituric acid as a precipitant has been studied by Dox and Plaisance ( 2 ) ; the potentiometric titration of the furfural in acidified potassium bromide solution with potassium bromate has been proposed by Pervier and Gortner (7'); and the use of excess bromine t o react with the furfural and subsequent estimation of the unused bromine was studied by Powell and Whittaker (8) and recently used by Kline and Acree (4). The primary object of the work recorded in this paper was the determination of the quantity of furfural produced from six species of American hardwoods. Preliminary t o these determinations, a comparison of the four above-mentioned methods for the estimation of furfural was made on pure furfural samples. And further, distillations of pure furfural by means of the standard method with 12 per cent hydrochloric acid and also with 12 per cent hydrochloric acid and steam were made to contrast the relative amount of destruction in these procedures. On the basis of these comparisons the furfural produced by acid-steam distillation of the hardwood samples has been determined by the volumetric potassium bromate-bromide method of Powell and Whittaker (8).
I n an attempt to employ the potentiometric method proposed by Pervier and Gortner great difficulty was found in determining the end point, and erratic and often high results were obtained. This observation has been made also by Youngburg and Pucher (1%'). Consequently it was not used in further work. A comparison of the averages of results for the three methods given in Table I (100.17, 102.0 and 102.88 per cent) shows that the standard phloroglucinol method gave practically theoretical results, while the latter two were slightly above the theoretical which is in close agreement with the results for these methods recorded by the original authors (9, 8). The widest variations in the errors observed in the different methods of analyzing weighed portions of furfural were about 2 per cent with phloroglucinol, 1 per cent with thiobarbituric acid, and 1.2 per cent with potassium bromate-bromide. If in contrasting these three methods the advantages of greater simplicity, economy of time, and equal constancy of results are considered, then the volumetric method seems to be superior to either of the gravimetric methods. TABLEI
DETERMINATION OF FURFURAL In comparing the quantitative methods of estimation, the furfural was purified by distilling technical furfural a t a pressure of 16 t o 20 mm. four or five times until an almost colorless distillate was obtained. Five-gram samples were immediately dissolved in water and made up t o 500 cc. from which 5-0~.aliquot portions were used in the following determinations: PHLOBOQLUCINOL OR A. 0. A. C. METHOD.A quantit of phloroglucinolabout double the amount necessary for the furrural present w~tsdissolved in 12 per cent hydrochloric acid and added to the sample with stirring. The solution turned yellow and then a green preci itate appeared which grew darker until it became nearly blac% After making the solution up to 400 cc. with 12 r cent hydrochloric acid and allowing it to stand overnight, precipitate was collected on a tared Gooch, washed with 150 cc. of water, and dried a t 100' C. for 4 hours. After weighing the precipitate, the amount of furfural recovered was calculated by means of Krober's (5, 6) formulas. THIOBARBITURIC ACID METHOD,To the sample of pure furfural, made up to 200 cc. with 12 per cent hydrochloric acid, was added the precipitant consisting of thiobarbituric acid, slightly in excess of the equivalent amount, also dissolved in 12 per cent hydrochloric arid. The final volume was made up to 400 cc. with 12 per cent hydrochloric acid and allowed t o stand overnight to insure complete recipitation. The precipitate, which filtered slowly, was colgcted on a tared Gooch and dried at 100" C. The weight of furfural was calculated on the basis of a reaction ratio of one molecule of furfural to one of thiobarbituric acid.
FURFURAL PRECIPITAXT SAMPLE
USED
USED
Gram
Gram
FURFURALFURFURAL RECOVERED
PRECIPITATE FOUND [Gram
%
Gram
PHLOROQLUCINOL METHOD
1 2 3 4
0.0574 0.0574 0.0574 0.0574
0.1054 0.1050 0.1074 0.1051
0.390 0,389 0.390 0.390
0.0573 0.0571 0.0584 0.0972
99.82 99.48 101.74 99.65
Av. 100.17 THIOBARBITURIC ACID METHOD
1 2 3 4
0.0575 0.0575 0.0575 0.0575
0.132 0.132 0.132 0.132
0.1367 0.1352 0.1353 0.1356
0.0591 0.0585 0.0585 0.0586
102.78 101.73 101.73 101.91
Av. 102.04 VOLUMETRIC POTASSIUM BROMATE-BROYIDE
SAMPLE
tg
FURFURAL USED
Gram 0.0508 0.0508 0.0508 0.0508 0.0508 0.0508 0.0508 0.0508
0.1 N NazSeOs
cc.
21.69 21.67 21.82 21,67 21.77 21.77 21,84 21.92
METHOD
FURFURAL FURFURAL FOUXD RECOVERED Gram % 0.0521 102.55 0.0520 102.36 0.0524 103.15 0.0520 102.36 0.0523 102.95 0.0523 102.95 0.0524 103.15 0.0526 103.54
Av. 102.88
COMPARISON OF DISTILLATION PROCEDURES The standard procedure for the distillation of pentoses produces low results, nrhich may be attributed to the destruc55
56
ANALYTICAL EDITION
'
Vol. 5 , No. 1
tion of the furfural by the acid upon long exposure. To overcome this difficulty Jolles (3) and Pervier and Gortner (7) have used steam distillation on xylose and arabinose and report practically complete recovery of the furfural based on the pentose used, whereas Kline and Acree (4)find that steam distillation does not improve the yield over that from the standard distillation when xylose was being determined. It has been shown by Youngburg (11) that various pentoses and pentosans give by all known methods of distillation from 50 to 100 per cent yields of furfural, so that the furfural yield is not an accurate measure of the pentosan content of vegetable materials.
the first with 12 per cent hydrochloric acid alone. The greatest variations in furfural recovered by distilling pure furfural were 5.5 per cent with 12 per cent hydrochloric acid alone and 5 per cent with steam and 12 per cent hydrochloric acid.
Consequently, in order to contrast the procedures under comparable conditions, furfural samples were subjected to the two types of distillation and the recovery measured by the same method of analysis in both cases. Samples of about 5 grams of freshly distilled furfural were distilled by the A. 0. A. C. method and the distillate was made up to 500 cc. from which 5-cc. aliquots were analyzed by the volumetric potassium bromate-bromide method. I n all cases the solution being distilled turned dark and a brownish precipitate separated out as the distillation proceeded. Samples were also distilled from 12 per cent hydrochloric acid using the steam distillation method, in which a slow stream of steam was led into the distilling flask while it was maintained at 103' to 105' C. When no further test for furfural was obtained, the distillate was analyzed volumetrically. The results appearing in Table I1 (98.83 per cent recovery when ordinary distillation is employed and 101.54 per cent when steam distillation is used) indicate an average furfural recovery in the second method 2.71 per cent higher than in
COKCLUSIOWS The volumetric method of determination of furfural as proposed by Powell and Whittaker gave consistent results which compare favorably with the gravimetric methods with either phloroglucinol or thiobarbituric acid. The widest variations observed in the different methods of analyzing weighed portions of furfural were about 2 per cent with phloroglucinol, 1 per cent with thiobarbituric acid, and 1.2 per cent with potassium bromate-bromide. By the volumetric procedure the whole determination may be made in one day whereas the A. 0. A. C. method requires a longer time. The steam distillation of furfural from a 12 per cent hydrochloric acid solution led to a recovery which was 2.71 per cent higher than in the ordinary distillation with 12 per cent hydrochloric acid. This would indicate less destruction of the furfural during the time of distillation. Six species of hardwoods have been distilled with steam and 12 per cent hydrochloric acid to yield furfural which has been determined volumetrically. This method gave
FURFURAL PRODUCTION FROM HARDWOODS
Only a limited amount of data is available on the pentosan content or furfural yield of American hardwoods, the available data being the results of investigations carried on a t the U. S. Forest Products Laboratory (10) by using the standard A. 0. A. C. method of determination. I n the present work, samples of six species of air-dried TABLE11. METHODSOF DISTILLATION APPLIEDTO FURFURALwood were prepared by filing an entire cross section with a THEORETICAL coarse wood rasp and the filings were used which would pass WEIOHTOF through a 40-mesh sieve but would be retained by an 80FURFURAL IN FURFURAL FOUND BY FURFURAL mesh sieve. The moisture content of each sample was deSERIEB AND DISTILLATE 0.1 N TITRATION R ~ C O V E R Y NarSaOa NUMBER SAMPLE termined by drying it to constant weight at 105' C. and Gram CC . Gram % STANDARD M l T H O D all results are based on the dried sample. One-gram sam0.0491 95.16 lA 0.0516 20 48 ples were distilled by the 12 per cent hydrochloric acid0,0496 96.12 B 0.0516 20.66 0.0495 95 93 steam distillation method a t a rate which produced slightly C 0.0516 20.61 0 0493 95.54 D 0.0516 20.56 less than 500 cc. in 4 to 5 hours. At the end of this time 0,0496 96.12 E 0.0516 20 66 no further test for furfural was obtained with aniline acetate. 0.0499 100.60 2A 0.0496 20.77 0,0495 99.80 The distillate, which was protected by passing it into the B 0.0496 20.63 0.0498 100.40 C 0.0496 20.75 receiver through a small filter, was then made up to 500 0.0496 100.00 D 0.0496 20.67 0.0494 99.60 E 0.0496 20.60 cc., the acidity of the solution was determined, and sufficient 100.18 23.71 0.0569 3A 0.0568 concentrated hydrochloric acid was added to bring the con0.0568 100.00 B 0.0568 23.67 centration up to 12 per cent hydrochloric acid. The furfural 0.0572 100,70 C 0.0568 23.83 0.0572 100.70 D 0.0568 23.85 content was then determined by the volumetric method 0.0571 100.53 E 0.0568 23.77 by using 200-cc. aliquots and an accompanying check by 4A 0.0504 20.65 0.0499 99.01 the phloroglucinol precipitation method was run on a 3000.0498 98.81 B 0.0504 20.63 0.0499 99.01 C 0.0504 20.67 cc. aliquot. 0.0523 99.05 5A 0.0528 21.65 The results recorded in Table I11 show a close agreement 0.0524 99.24 B 0.0528 21.69 between the two methods of determination, the volumetric 0,0523 99.05 c 0.0628 21.67 being slightly higher here as in the determination of pure Av. 98.83 furfural. In the analysis of six woods the volumetric broBTEAM DISTILLATION M E T H O D mate-bromide titration gave from 0.2 to 0.86 per cent higher 0.0516 101.58 1,4 0.0508 21.51 0.0515 101.48 B 0.0508 21.46 furfural yields than the phloroglucinol method, or a difference 0.0518 101.97 C 0.0508 21.56 D 0.0508 21.59 0.0518 101.97 of 1.5 to 5.0 per cent of the furfural itself. The widest 102.17 21.62 0.0519 E 0.0508 variations in several determinations of furfural from each 0.0519 102.37 2A 0.0507 21.62 of the six woods were, respectively, 2.3, 2.2, 1.5, 1.2, 0.77, 0,0520 102.56 B 0.0507 21.69 0.0521 102.76 C 0.0507 21,73 and 2.3 per cent of the furfural by the bromate-bromide 0.0523 103.15 D 0.0507 21.79 method, and with phloroglucinol they were approximately 21.73 0.0521 102.76 E 0.0507 3.7, 0.8, 4.4, and 2.4 per cent with four of these woods. 98.37 22.44 0,0542 3.4 0.0661 0.0541 98.19 B 0.0551 22.41 I n the precipitation method other compounds such as methyl 0.0542 98.37 C 0.0551 22.04 furfural and hydroxymethyl furfural enter into reaction and 0.0558 102.20 46 0,0546 23.09 are determined with the furfural. Undoubtedly these com0.0559 102.38 B 0.0546 23.14 102.38, 23.21 0,0559 C 0.0546 pounds may have an effect in the volumetric procedure, although this possible effect has not been determined. Av. 101.54
January 15, 1933
INDUSTRIAL AND ENGIXEEKING CHEMISTRY
57
TABLE111. DETERMINATION BY VOLUMETRICAND PHLOROGLUCINOL METHODS VOLUMETRIC METHOD Sample
Weight Gram
1A
B
C
2A
B
C
3A
B C
1A
B
C 2A
B C
3A
B C
0.1939 0.1939 0.1939 0.1936 0.1936 0.1936 0.1936 0.1936 0.1936
0.1917 0.1917 0.1917 0.1917 0,1917 0.1917 0.1917 0.1917 0.1917
0.1 N NazSzOa cc
.
Weight of furfural Gram
14.92 14.86 14.88 14.86 14.72 14.79 14.55 14.58 14.58
16.23 15.17 15.20 16.05 15.00 15.03 14.88 14.93 14.92
0.0361 n nmn
PHLOROQLUCINOL METHOD Weight of Weight of Weight of precipitant precipitate furfural
7
Furfural %
Weight
18.46 18.46 18.41 18.39 18.23 18.34 18.03 18.08 18.08
.... ....
Gram YELLOR ' BIRCH-EetUla lutea . . I .
Gram
Gram
.... .... ....
....
....
0.2904
0,3990
....
0.0948
....
....
0 4002
....
0.0910
....
0.2904
....
.... .... I
....
....
Av. 18.27 PAPER BIRCH-BetUla papyrifera 19.04 0.2875 18.99 .... 19.04 .... 18.83 .... 18.78 .... 18.83 18.62 0.1917 18.67 .... 18.67 .... . . t .
Gram
..... ... 0.0518
.... .... 0.0499 .... ....
1A
B
C 2A
B
C 3A
B C
46 B C
1A
B C
2A
B C
3A
B C
0.1911 0.1911 0.1911 0.1910 0.1910 0.1910 0.1912 0.1912 0.1912 0.1911 0.1911 0.1911
0.1924 0.1924 0.1924 0.1925 0.1925 0.1925 0.1923 0.1923 0.1923
11.51 11.48 11.61 11.68 11.70 11.68 11.62 11.50 11.65 11.64 11.49 11.51
11.15 11.16 11.14 11.30 11.35 11.33 11.21 11.25 11.26
0.0956
0.4003
....
.... .... .. .. .. ..
saccharum
....
.... .... ....
.. .. .. ..
.... .... ....
0.4000
0.0615
.... ....
.... .... ..,.. ... ....
... ... ... ... ....
.... .... .... 0,4004 .... ....
..I.
0.2867
.... ....
Av. 14.50 WHITE As=-Fraxinus americana 13.93 .... 13.93 0.2886 13.86 ... 14.08 14.13 0 ~2888 14.13 .... 13.99 14.04 0 :is85 14.04 ....
B
C
2A
B
C 3A
B C
.... 0.2834
12.10 12.11 12.09 12.06 12.11 12.08 12.03 12.11 12.08
boredis
18.19
.... ....
. . ..
..,.
....
0.0346
....
....
B 2A B C
36
B C 4A B C
0,1928 0.1928 0.1928 0.1928 0.1928 0.1932 0.1932 0.1932 0.1928 0.1928 0.1928
.. .. ..
....
.... ....
0.3998
... ... ...
0.0391
13164
.
.
I
.
....
....
.... ....
.... ....
0.0389
.... 0.0733 .... ....
0.4010
.... ....
0 : 0703
....
....
.
...
0.0698
0.0719
....
.... .... .... 0.0756
....
0.4005
0.2837
0.4011
0.2834
0.4001
0.0744
.... ....
.. .. .. .. ....
12.86 12.89 12.67 12.62 12.67 12.75 12.72 12.77 12.69 12.77 12.76
1i:05
.... ....
....
....
I
....
.... .... 0.0407 .... .... 0.0400
.... ....
....
....
0.0764
....
....
....
0.0413
.... .... 0.0419 ....
....
0.0423
...
...
..
13:4s
... ...
14:09 13: 87
...
14157
...
14:77
...
14:93
Av. 14.76
Av. 15.35
1A
...
... ... ... ...
0.4003
....
....
BmcH-Fagus
. .
Av. 13.81
NORTHERN R E D OAK--&Ue?CUS
0.1889 0.1889 0.1889 0.1891 0.1891 0.1891 0,1889 0.1889 0.1889
...
ii:is
0.0523
Av. 14.01 1A
17: 84
Av. 18.12
MAPLE-ACIr
14.44 14.44 14.44 14.66 14.66 14.66 14.44 14.44 14.49 14.50 14.44 14.44
,..
...
Av. 17.51
Av. 18.83 SO'QAR
Furfural %
graitdifolia
... ... ... ... .. .. .. ..
.... ... ... ... ... .... .... ....
0.2892
0.4006
. .
. I
I .
. .
.... ....
.... .... ....
....
.... .... .... ....
. . I .
0,0811
....
....
....
....
... ... ... ... ... ...
.... .... ....
...
0.0447
15.47
....
.... ....
. I .
...
Av. 15.84
results which were 0.2 to 0.86 per cent higher than by the phloroglucinol method or a difference of 1.5 to 5.0 per cent of the furfural itself. The widest variations in several determinations of furfural from each of the six woods were,, respectively, 2.3, 2.2, 1.5, 1.2, 0.77, and 2.3 per cent of the furfural by the bromate-bromide method, and with phloroglucinol they were approximately 3.7, 0.8, 4.4, and 2.4 per cent with four of these woods. LITERATURE CITED (1) Assoc. Official Agr. Chem.. Methods, p. 120 (1925). (2) Dox and Plaisance, J. Am. Chem. Soc., 38, 2156 (1916).
(3) JolleR, Sittber. Akad. Wiss. W i e n Math.-nuturw. Klasse, Abt. 11. 114. 1191 (1905). (4) Kline and Acree, Bur. Standards J . Research, 8, 25 (1932). (5) Krober, J . Landw., 48, 537 (1900); 49, 7 (1901). (6) . . Krober, Reinbach, and Tollens, Z. angew. Chem., 15, 477, 508 (1902). (7) Pervier and Gortner, IKD. ENG.CHEIM., 15, 1167, 1255 (1923). (8) Powell and Whittaker, J. SOC.Chem. Ind., 43, 35T (1924). ENG.CHEIM., 14, 1050 (1922); 15, 1056 " (9) Ritter and Fleck, J. IND. (1923); 18, 608 (1926). (10) Schorger, Ibid., 9, 556 (1917). (11) Youngburg, J. Biol. Chem., 73, 603 (1927). (12) Youngburg and Pucher, Ibid., 61, 741 (1924).
--.
~~
,
I
RECEIVED August 2, 1932.
