August, 1925
IiVD USTRIAL A X D ELVGIXEERILVGCHEiWSTRY
851
The Highly Reducing Substances in Fresh Wood Distillate' By R. J. Williams, P. A. Lasselle, and H. A. Reed UNXVERSITY OF OREGON,EUGENE,ORE.
The high reducing power of fresh wood distillate cannot be accounted for on the basis of any of the numerous substances that have been isolated from it. The reducing power is due largely to the presence of phenolic compounds rather than aldehydes, as the high-boiling oils have the highest reducing power. From 2 liters of fresh distillate including the tar, most of which was a t first in suspension, as much as 200 grams of oil boiling from 130" to 205" C. a t 20 mm. pressure have been recovered. Most of this material is phenolic, with some paraffin in the highest fraction. Experimental evidence makes it practically certain t h a t the reducing power of this oil is not due to the presence of pyrogallol in any appreciable amount.
From 12 to 16 per cent of this high-boiling oil from fresh wood distillate consists of a very high reducing oil, which is precipitated by lead acetate and is a mixture of substances that have never before been reported as isolated fram wood distillate. This corresponds roughly to 1 per cent of t h e total weight of distillate, and to about 40 per cent of the reducing power of the oil. One of the important c m s t i t u ents of this oil appears to be 1-monomethyl ether of pyrogallol, and the homologs of pyrocatechol, as well a s other 0-dihydroxy phenols, are probably present. Old pyroligneous acid and tar contain very Iittle of these highly reducing oils which are precipitated by lead acetate and on heating the original high-boiling oils, condensation takes place and the amount of these substances present decreases.
.. .. ..
\HE total distillate Qbtained from distillation of wood separates on standing into an aqueous layer known as pyroligneous acid and a layer of settled tar. Aside from the material that settles out on long standing, there is a so-called "soluble tar," which remains as a pitchy residue when the clear aqueous layer is distilled. Much of the same material precipitates when the clear solution is made alkali. It was thought desirable to study in fresh condition the materials that make up this pitchy residue obtainable from the clear pyroligneous acid. Pyroligneous acid, however, is known to age on standing, and it was found impracticable to obtain the fresh liquor clear and free from the material that would eventually settle and form the settled tar, because this material is finely divided and the upper layer may require days or weeks to become clear. During this time the composition of the soluble material which it was desired to study might easily be altered materially and partially precipitated as part of the settled tar. . Therefore the whole fresh distillate was studied and work concentrated on the substances present in the fresh liquor but absent from liquor that has stood for some time. The highly reactive substances present in the fresh liquor are the ones that are most likely to disappear on standing, and since the fresh distillate does contain substances capable of taking up atmospheric oxygen and in other ways shows high reducing powers, it was decided to study the substances responsible for the high reducing power. Reducing Power of Various Fractions Titration of samples against Fehling's solution was used in the following manner to determine quantitatively the reducing power of various fractions.2 Ordinarily, 10 cc. of Fehling's solution are accurately measured into a flask and about 40 cc. of water added. This is heated to boiling and the sample to be tested added, from a graduated pipet, in the form of a solution of known strength. After 3 minutes' boiling a small amount is pipetted out and filtered on a spot plate, acidiiied with acetic acid, and a drop of potassium ferrocyanide added. As long as any reduced copper is present a brown precipitate will develop, in which case the operation is repeated until 1 2
Received March 9, 1923 Leach, "Food Inspection and Analysts," p 615.
all the copper is reduced. The disappearance of the blue color cannot be used, as in the titration of sugar solutions, because the solution turns dark brown. A preliminary distillation showed that the highly reducing substances are those with high boiling points (Table I). Table I Cc. t o reduce 10 cc. Fehling's soh. Or36 1.21 1.28
FRACTION Original fresh distillate I ( to 1000 e.) I1 (1000 t o 105" C . ) I11 (lOS5' t o 115' C . ) I V (115'to 130' C.) V (150'to 250' C.)
0.76
0.25 0.16
On the basis of these results it was decided to confine the study to the higher boiling fractions. Subsequent results showed that the substances with the highest reducing powers had boiling points above 230' C. The investigation was therefore limited to the material boiling above this point. Reducing Powers of Phenolic Compounds The phenolic compounds are the only substances having high reducing powers and boiling points as high as that given above, which have been isolated from pyroligneous acid or tar. The phenolic compounds listed by Hawley3 a 5 having been isolated from this source are as follows: Table I1 BoiliEg poinh
c.
o-, Phenol m-, and $-Cresols Guaiacol *1, 3-Xylenol-4 *I, 3-Xylenol-5 *Phlorol (o-ethyl phenol) *Coerulignol (3-methyl ether of 1, 3, 4-propyl catechol) Pyrocatechol Pyrogallol dimethyl ether *Propyl pyrogallol dimethyl ether Pyrorrallol . Known to occur in wood tar.
*
183 191 to 2 0 3
206 211.5
219.5
207 210 to
,%F
240 t o 2 4 5 265 286 293 (decemposed,d
The occurrence of pyrogallol is based, according t O this author, upon the statement of Beilstein. In the third edition of Beilstein there is a statement that pyrogallol has been obtained "from beechwood," but no reference is given to a n y original work on this point, and this statement is followed by 8
Hawley, "Wood Distillation," p. 66.
INDUSTRIAL AND ENGINEERING CHEMISTRY
852
one to the effect that pyrogallol dimethyl ether was found by Hoffman in beechwood creosote. It is true that Hoffman obtained pyrogallol from beechwood creosote by breaking down the dimethyl ether of pyrogallol, but the statement that pyrogallol itself has been found in wood tar is apparently an error. The latest edition of Beilstein makes no mention of pyrogallol itself as coming from wood tar. Whether or not pyrogallol is actually present in the wood distillate is another question, which will be discussed later. The reducing powers of the phenolic substances known to occur in the distillate (except those indicated by an asterisk, Table 11) were determined, as well as those of some others which have bearing on the later discussion (Table 111). Table 111
High boiling oil (140' to 190' C. at 16 mm.) *Pyrocatechol *o-Cresol *m-Cresol * p - Creiol "Pyrogallol dimethyl ether "Guaiacol Eugenol Resorcinol Orcinol Hydroquinol Pyrogallol Phloroglucinol Pyrogallol monomethyl ether Pyrogallol monoethyl ether *Pyrogallol trimethyl ether Isohomopyrocatechol Known t o occur in wood tar,
Cc. Fehling's soln. to oxidize 1 eram substance 60-77 Ahout 5 . 0 1.3
