The Nature of Furfurvl Alcohol J
A. P. DUNLOP AND FREDUS N. PETERS, JR. The Quaker Oats Company, Chicago, Ill.
ONSIDERABLE work has been reported in the
C
f o r 10 m i n u t e s , a n d t h e n with ‘Odium carbonate; (e) dissolved in a n equal volume of distilled water and stored at room temperature for approximately 3 months. The resulting products were in but On tilling under vacuum, varying amounts of unchanged furfuryl alcohol were recovered. After removal of the furfuryl alcohol, a dark viscous liquid remained which on further distillation was separated in each case into the followina fractions: A. 100-160° C. at 6 mm.: B, 160-210O C. at 4 &.; C, black residue which decomposed on further heating.
The transformation of furfuryl alcohol into the so-called insoluble form is due, at least in part, to intermolecular dehydration. Under normal storage conditions O n l y a small percentage of the original furfuryl alcohol is involved, high yields of the latter being recovered on distillation. The condensation reaction is greatly accelerated by heat and is retarded by the presence of any one of a variety of organic and inorganic bases.
literature regarding the changes which furfuryl alcohol undergoes when stored in contact with water in the presence or absence of various acidic reagents. Under such conditions it appears that furfuryl alcohol is first insolubilized and f i n a l l y resinified. T h i s is shown by Wissell and Tollens (7) who warmed the alcohol with dilute hydrochloric, acetic, and sulfurous acids, and obtained a water-insoluble “oil” Drior to resinification. Umpricht (4) found that this transformation took place Teadily with dilute hydrochloric acid and with explosive violence when the concentrated acid was used. Erdmann (a) confirmed these findings and, in an effort to explain .the phenomenon, postulated the formation of an unsaturated, open-chain aldehyde due t o ring scission with the addition of water. A comparatively recent study by Pummerer and Gump (6) led t o the conclusion that the so-called insoluble form of furfuryl alcohol is not a chemical individual but consists essentially of furfuryl alcohol which is removed from the water phase by the presence of a small amount of transformation product. These workers also state that the insoluble oil shows no aldehyde reaction and that it appears 60 have a higher carbon content than furfuryl alcohol. The present study was undertaken t o throw some light on the nature of the water-insoluble products formed from furfuryl alcohol and t o investigate means of retarding or preventing their formation. The solution of these problems is important from a commercial standpoint since furfuryl alcohol is sometimes stored for many months prior to use and, during this period, frequently becomes water insoluble. The furfuryl alcohol used in this investigation was prepared by fractionating the commercial grade three times under a vacuum of 15 mm., using a %foot Hempel column packed with 9-mm. porcelain Raschig rings. Discards of 10 per cent of the total were made at the beginning and end of each distillation, and the mid-fraction used was completely miscible with water. The following constants were determined:
EXAMINATION OF FRACTION A. Careful fractionation gave a pale yellow product I, insoluble in water; soluble in acetone, benzene and nitrobenzene; boiling a t 131-3” C. a t 2.5 mm.; d:: 1.178-9; n% 1.5290, n y 1.5270. The molecular weight (in nitrobenzene) was found to be 180 (calculated, 178) which, with the combustion analysis, fixed the molecular formula as C10H1008. The latter analysis showed 67.57-67.85 per cent carbon and 5.77-5.78 per cent hydrogen, compared to calculated values of 67.42 and 5.62 per cent, respectively. A rough bromine absorption test indicated four double bonds in the molecule. Tests for -CHO, >CO, and -COOH were negative, but the presence of one hydroxyl group was shown by the preparation of a-naphthylurethan and benzoate derivatives. The former, which melted at 107-8” C., showed 4.30 per cent nitrogen compared to the calculated value of 4.03. Combustion analysis of the benzoate ester (melting point 70-71 C.) gave 72.23-72.24 per cent carbon and 5.02-5.00 per cent hydrogen (calculated, 72.34 per cent carbon, 4.97 per cent hydrogen), and the saponification equivalent was determined to be 278-279 (calculated, 282). EXAMINATION OF FRACTION B. On distillation a yellow colored liquid, 11, was obtained which exhibited the same solubility characteristics as product I: It boiled a t 199-202’ C. a t 3 mm.; d;; 1.192; ng 1.5428, ng 1.5411. The molecular weight (nitrobenzene) was determined to be 266 (calculated, 258), which after combustion analysis, indicated a molecular formula of C,,k1,0,. The latter analysis showed 69.25-69.60 per cent carbon and 5.53-5.55 per cent hydrogen, compared to calculated values of 69.74and5.46per cent, respectively. Tests by bromine absorption indicated six double bonds in the molecule and, as in the case of product I, no -CHO, CO, or -COOH groups-could be detected. A gummy pro uct was obtained when an attempt was Boiling point, C. at 16 rnm. 73-4 made to benzoylate product I1 by the Schotten-Baumann reacSpecific gravity, daf 1.1321-2 tion, but it did not lend itself to purification by the usual methods. Refractive index, ng 1.4843-5 EXAYIXATION OF FRACTION C. A small quantity of the black Refractive index, ng 1.4868-71 residue was sealed in a glass tube and heated a t 100-110’ C. Moisture (1) Yo 0.00-0.03 0.002-0.003 After approximately 4 days it had been transformed into a hard, Acidity (calcb. &8 acetic), $6 black resin, and water had condensed on the sides of the tube (a”,”1.3336). Combustion analysis of the resin showed 70.33‘‘Insoluble Form” of Furfuryl Alcohol 70.73 aer cent carbon and 5.30-5.30 Der cent hvdroaen. IITPERMOLECULAR DEHYDRATION O F FURFURYL ALCOHOL. The object of this study was to examine “insoluble” furfuryl 45.2 grams (0.461 mole) of furfuryl alcohol were heated in a alcohol with a view toward the isolation and characterization sealed glass tube at 100-110” C. for approximately 6 weeks. of transformation Products. Furfuryl alcohol was treated During this period the alcohol became progressively more viscous, and a separation into two liquid phases occurred; the lower under the following conditions: (a) refluxed alone for 7 (organic) layer eventually solidified to a brittle black resin. hours; (b) heated alone in a sealed glass tube at 150” C. for 7 When opened, the tube was found to be under a slight pressure. hours; ( c ) refluxed with a n equal volume of distilled water On distillation, the liquid layer (n%1.3390) yielded 5.9 grams of for 3 hours; (d) dissolved in an equal volume of distilled water (ng 1,3334), leaving a small amount of viscous brown residue. water containing a trace of hydrochloric acid, held at 80’ C. 814
b
July, 1942
INDUSTRIAL AND ENGINEERING CHEMISTRY
When furfuryl alcohol is heated alone in a sealed tube, water is split out and a dark colored, water-insoluble liquid is formed. On continued heating more water is liberated, the organic layer gradually becoming more and more viscous until finally a brittle black resin results. It may also be demonstrated that aqueous solutions of furfuryl alcohol undergo similar transformation, the change being accelerated by heat and by the presence of acids and acid salts. I n addition, there is some evidence to indicate that exposure to ultraviolet light speeds up the reaction. On distilling the insolubilieed furfuryl alcohol, water, furfuryl alcohol, and a viscous black product are obtained; the relative amounts of each component vary with the conditions under which insolubilization occurs. Examination of the viscous residue has led to the isolation of two comparatively pure liquid products, I and 11, having the molecular formulas C ~ ~ I I Sand O SC I ~ H H ~respectively. ~O~, These products are light yellow when freshly distilled but darken rapidly on exposure to light and air. The formation of I and I1 can be explained by postulating an intermolecular dehydration, compound I resulting from the condensation of two molecules of furfuryl alcohol with the elimination of one molecule of water. This reaction is probably progressive so that I1 is produced by the further condensation of I with furfuryl alcohol, another molecule of water being split out. The undistillable viscous residue remaining after the removal of I and I1 probably consists of higher molecular weight compounds of the same type, although the final solidification step may involve cross linkages between the condensation products. The elucidation of the structures of products I and I1 is beyond the scope Of this study, but a theory wiu be presented with the hope that it may be helpful to some future investigator. We have shown that compound I (CIOHlOOd contains one hydroxy1 group and, since tests for and -cOOH were negative, the other two oxygen must be €inked in the form of ethers. The observed molecular refraction of product I is MRD 46.7, compared to the CdCUlated value of 46.9,when allowance is made for four double bonds. If the latter are conjugated as they are in furfuryl alcohol, then the identity of the observed and calculated molecular refractions can be explained by assuming two furan rings in the molecule, since the depressant effect of ring strain in the furan nucleus almost exactly neutralizes the exaltation due to conjugated double bonds. We believe, therefore, that furfuryl alcohol is insolubilized by intermolecular dehydration in the following manner: HC-CH
815
the most part, compounds I and I1 and higher molecular weight products of the same type. I n other words, when furfuryl alcohol is treated with dilute acids, there are two competitive reactions-ring splitting to levulinic acid and intermolecular dehydration. On the other hand, Teunissen (6) reported that ring cleavage of 2-hydroxymethyl-5-furfural to levulinic and formic acids takes place almost quantitatively. This would seem to indicate that, by replacing the hydrogen atom in the 5 position in furfuryl alcohol with a n aldehyde group, condensation to form compounds of type I and I1 was blocked, thereby allowing the ring splitting reaction to proceed with little or no side reaction products.
T~~~ 1. E~~~~ OF H~~~ ON F~~~~~ ALCOHOL IN CONTACT WITH GLASS Tzmz.,
100
150
2 0 ~
To i; 0.0 5.5 10.5 20.5 30.6
o.o
1.5 5.5 10.5 0.0 1.0 2.0 3.0
Refractive Index, ng 1.4871 1.4868 1.4874 1.4878 1.4893 1.4870 1.4875 1.4890 1.4944 1.4~71 1.4882 1.4900 1.4904
Density,
Cloud Point,
Water (f),
1.1322 1.1328 1.1334 1.1339 1.1372
6.0 10.0 14.5 19.5 44.0 6.5 13.5 36.0 Inaol.atlOO°C. 6.0 31.5 57.0 65.0
0.00 0.11 0.21 0.29 0.92 0.03 0.18 0.67 3.05 0.00 0.64 1.37 1.73
dii
1.1333 1.1356 1.1428 1.1322 1.1343 1.1365 1.1373
c.
%
Comparatively low concentrations (o.5-1.0 per cent) of compounds 1 and 11 in furfuryl alcohol render the Iatter incompletely soluble in water. That fact is significant. For instance, after long storage periods it is generally found that furfurylalcohol is no longer miscible with water, T K ~is evidenced by the formation of a distinct cloudiness on dilution with water or, in more advanced cases, by a separation into two layers. distillation, however, the alcohol may be recovered in high yields, leaving only a small amount of residue. other words, only a small percentageof the initial furfuryl alcohol is involved in the transformation which takes place under normalstorageconditions,
on
Thermal Stability of Furfuryl Alcohol This portion of the work was devoted to a study of the influence of time and temperature on the properties of furfuryl alcohol. To our knowledge, no data are available in the literature on this subject. I n each case approximately 40 cc. of furfuryl alcohol were placed in a Pyrex glass tube which was
iron pipe previously described (2), and then placed in an oven at the desired temperature for a definite Product I period of time. The cloud point of each sample HC-CH HC-CH HC-CH HC-CH was determined by diluting 2 cc. with 2 cc. of water and cooling I1 11 b-CH-4 b-CH@H the clear solution until it beI EL! C - c H , O- H O AH came definitely c l o u d y . T h e 'O/ 'O\ '0' solution was then allowed to Product I1 warm up with stirring until it was just clear. At this point, cooling produced an immediate cloudiness, and the temperaI n support of the suggested mechanism is the comprehenture was taken and recorded as the cloud point. sive study of Pummerer and Gump (6) regarding the splitting Moisture determinations were made by distillation with of furfuryl alcohol to form levulinic acid. Under the most toluene (1) in a distilling tube receiver which could be read in favorable conditions these workers obtained a yield of only hundredths and estimated to thousandths of a cubic centi3040 per cent of levulinic acid and found that more than half meter. I n each case 35-40 grams of the sample were used for of the original furfuryl alcohol underwent resinification. It analysis. seems probable that the resinification products comprise, for +
&
b
INDUSTRIAL AND ENGINEERING CHEMISTRY
816
Vol. 34, No. 1
TABLE 11. STABILIZATION OF FURFURYL ALCOHOL AT 150" C. CONTACT WITH GLASS Stabilizer Iione
0.1%n-butyl amine
Time,
Hours
,
I
, I
Hour3 of Heating
I
Water (f),
c.
%
1.4870 1,4875 1.4890 1.4944
1.1322 1.1333 1.1356 1.1428
5.5 13.5 36.0 Insol. a t 100' C.
0.03 0.18 0.67 3.05
0.0
1.1318 1.1317 1.1318 1.1321
7.0
6.5
7.0 7.5
0.07 0.05 0.09 0.11
10.5
1.4870 1.4868 1.4870 1.4871
0.3%,n-butyl amine
0.0 1 5 5.5 10.5
1.4868 1.4870 1.4869 1.4871
1.1308 1,1309 1.1310 1.1311
8.5 8.5 8.5 9.0
0.09 0.06 0.16 0.19
3.07,,n-butyl amine
0.0 1.5 5.5 10.5
1.4845 1.4844 1.4844 1.4844
1.1177 1.1181 1.1181 1.1183
18.5 19.0 19.0 19.5
0.11 0.14 0.22 0.17
0.1% piperidine
0.0 1.5 5 .6 10.5
1.4870
1.1320 6.0 Sample broken 1,1324 8.0 1.1330 10.0
0.06
0.3% piperidine
0.0 1.5 5.5 10.5
1.4868 T o o dark T o o dark Too d a r k
1.1318 1.1321 1.1324 1.1330
7.0 8.5 T o o dark Too dark
0.05 0.04 0.14 0.20
3.0y0piperidine
0.0 1.5 5.5 10.5
1.4863 1.4867 Too dark Too dark
1.1251 1.1253 1.1255 1.1261
16.5 17.0 Too dark Too dark
0.11 0.17 0.15 0.19
1
I
c l o u d point,
0.0 1.5 5.5 10.5
!.?
S . J
w o r ,
Refractive Density, Index, n g dzz
1.4870 1.4872
IN
0.10 0.16
OF TEMPERATURE ON RATEOF FIGURE 2. INFLUENCE INTERMOLECULAR DEHYDRlTION O F FURFURYL ALCOHOL
FIGURE1. EFFECTOF HEAT ON FURFURYL ALCOHOL IN CONTACT WITH GLASS
The data obtained are presented in Table I and Figure 1. The rate of change of the various properties of furfuryl alcohol is greatly increased by raising the temperature. For instance, treatment for only about 2 hours at 200" C. will produce changes equivalent to those obtained after 30 hours a t
looo c.
The rate of water formation is a measure of the rate of intermolecular dehydration as described in the section on "Insoluble Form" of Furfuryl Alcohol. In interpreting the data in terms of the latter reaction, it is perhaps most convenient to do so on the supposition that compound I, C10H1003, is the only end product. For this reason in Figure 2 we have recalculated the amount of water split out in terms of the per cent transformation of furfuryl alcohol to C~OHIOO~; 100 per
cent transformation represents 9 grams water split out per mole of furfuryl alcohol. The values obtained are not strictly true since we have reason t o believe that higher molecular weight condensation products are also formed. n'evertheless, they do offer to some extent a convenient measure of the rate of condensation of furfuryl alcohol under the described conditions. Figure 2 illustrates how this rate varies with temperature, the values a t 100' and 150'' C. being obtained by interpolation from Figure 1. In ascertaining the quality of the furfuryl alcohol produced commercially, the cloud point temperature is of considerable value, This determination can be made quickly and conveniently with comparatively little material, and the result is probably less affected by traces of impurities and varying moisture content of the furfuryl alcohol than is the refractive index.
July, 1942
INDUSTRIAL AND ENGINEERING CHEMISTRY
Stabilization of Furfuryl Alcohol Many organic and inorganic bases were found to be effective in retarding the rate of change of the various properties of the alcohol, but only n-butyl amine and piperidine will be reported a t this time. To separate samples of furfuryl alcohol were added, by weight, 0.1,0.3,and 3.0 per cent n-butyl amine and piperidine, respectively. As was the case in the thermal stability study, approximately 40 cc. of each sample were then sealed in Pyrex glass tubes, placed in bombs, and heated in an oven a t 150' C . for the indicated period of time. The results obtained are given in Table 11. The differences between the physical properties of the stabilized and control samples, prior to heat treatment, are due to the presence of the stabilizer. It is evident from the data that both n-butyl amine and piperidine greatly retard the rate of intermolecular dehydration of furfuryl alcohol, as measured by the amount of water split out. When calculated (as in Figure 2) in terms of per cent furfuryl alcohol transformed to C10H1003, after 10.5 hours a t 150" C. the alcohol alone is transformed t o the extent of 33 per cent; in the presence of 0.1 per cent of the stabilizers, this value is only 0.4 per cent with n-butyl amine
817
and 1.1 per cent with piperidine. There is no advantage in employing these stabilizers in concentrations higher than 0.1 per cent of the furfuryl aleohol, and there is the disadvantage of discoloring the latter to a greater extent. In hydrogenating furfuryl alcohol to tetrahydrofurfuryl alcohol, a considerable amount of high-boiling residue is obtained. We believe that a sizable proportion of this residue results from the formation of furfuryl alcohol condensation products such as have been described. Use of stabilizers in the hydrogenation process may therefore lead to higher yields of tetrahydrofurfuryl alcohol.
Literature Cited Assoc. Official Agr. Chem., Official and Tentative Methods of Analysis, 3rd ed., p. 277 (1930). Dunlop, A. P., and Peters, F. N., Jr., IND.ENG.CHEM.,32, 1639 (1940).
Erdmann, E., Ber., 35, 1855 (1902). Limpricht, H., Ann., 165,253,300 (1873). Pummerer, R.,and Gump, W., Ber., 56,999 (1923). Teunissen, H.P., Rec. trav. chim., 49, 784 (1930); dissertation, Leiden, 1929. Wissell, L.v., and Tollens, B., Ann., 272,291 (1892).
SOYBEAN PROTEIN ADHESIVE STRENGTH AND COLOR ALLAN K. SMITH AND HERBERT J. MAX U. S. Regional Soybean Industrial Products Laboratory', Urbana, 111.
The adhesive strength, hydrolytic cleavage with sodium hydroxide, and dispersion characteristicsof soybean protein are interrelated. Undenatured soybean protein gives low adhesive values when dispersed in alkaline salts but high adhesive values when dispersed in sodium hydroxide. A mild hydrolytic treatment of soybean protein with sodium hydroxide will change the dispersibility of soybean protein so that it will have good adhesive strength when dispersed in alkaline salts but not so good as the undenatured protein dispersed in sodium hydroxide. The dithionite salts (NaZStOd and ZnSSO4) are the best agents so far discovered for bleaching soybean protein. Coated paper has been prepared in the laboratory which shows the undenatured soybean protein to have higher adhesive strength and a lighter color than a good grade of commercial casein.
P
ROTEINS are used in industry for paper-coating adhesives, tub and beater sizing of paper, molded buttons and buckles, water paints, plywood and furniture glue, insecticide sprays, wax emulsions, leather dressings, fibers, films, and many other less important purposes. Of primary importance in the above uses are adhesive strength, water and oil resistance, color, dispersibility in
water, plasticity, and viscosity, all of which are related to particle or molecular dimensions and complicated structure of the proteins. Proteins from various sources are in competition with one another and, to a certain extent, with starch, gums, and the synthetic resins. The choice for a specific use depends upon the properties desired as well as the cost. The synthetic resins have a great advantage in their superior water resistance and are used where the glued article is exposed to severe moisture conditions. Perhaps it is worth while to point out also that until the recent overproduction of agricultural crops in this country, proteins had been so important in food economy that only waste or by-product proteins could be used economically for industrial purposes. For this reason and also because of their complicated chemistry, comparatively little scientific effort has been expended in their industrial development. While there is a great deal of literature on proteins, very little of i t pertains to industrial utilization or is even helpful a t the present state of development. Soybean protein, while relatively new in the field of proteins, is a primary industrial product. If the entire United States tonnage of soybean meal were considered as a source 1 A cooperative organization participated in by the Bureaus of Agricultural Chemistry and Engineering and of Plant Industry of the U. S. Department of Agriculture, and the Agricultural Experiment Stations of the North Central States of Illinojs, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South Dakota, and Wisconsin.
