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Volume 35, 1902
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Art. LVIII.—A Contribution to the Chemistry of Colophony.

By T. H. Easterfield and G. Bagley.

[Read before the Wellington Philosophical Society, 18th March, 1903.]

Colophony, or common rosin, is one of the cheapest of all organic preparations. It is the residue which remains in the still when crude turpentine is being worked into oil or spirit.

Colophony has been investigated by numerous chemists; nevertheless, many points in the chemistry of the substance remain to be cleared up. It is, moreover, unfortunate that several investigators have published statements which have not been confirmed by subsequent workers, so that a mere perusal of the literature is not sufficient to separate the facts from the fiction.

The following facts are in general accepted amongst chemists:—

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  • (1.)

    Colophony consists principally of organic acids, of which one, abietic acid, is in preponderating proportion. The use of rosin in soap-making depends upon its acidic nature.

  • (2.)

    Rosin, when distilled at ordinary pressures, yields a very composite mixture of substances, consisting chiefly of hydrocarbons, the more volatile portions of which are known as “rosin-spirit,” the less volatile as “rosin-oil.” The oil is largely used in the preparation of lubricants for heavy machinery. Rosin-oil consists very largely, according to Deville, of a hydrocarbon the percentage composition of which approximates to that of turpentine, but the molecular weight of which is much greater. It is generally regarded as a diterpene.

  • (3.)

    When distilled under diminished pressure, rosin is said to yield an anhydride of an acid isomeric with abietic or sylvic acid, together with a hydrocarbon, probably the “colophene” of Deville. This statement is due to Bischoff and Nastvogel. The authors greatly regret that their work has led them to conclusions of a totally different nature.

Put shortly, the results of the present investigation may be thus stated:—

  • (1.)

    When colophony is fractionally distilled under diminished pressure a small quantity of turpentine and other hydrocarbons distil first. The greater part of the rosin then comes over in an unchanged state, between 260-285° C., at 15 mm. pressure. This is nearly pure abietic acid. Lastly, there is a small quantity of pitch, which has so far defied all attempts at investigation. The distillation of colophony under diminished pressure is an excellent method of obtaining crude abietic acid; for the middle portion of the distillate, when twice crystallized from alcohol, yields practically pure abietic acid melting at 163-165° C.

  • (2.)

    If the distillation be conducted slowly, the early portion of the distillate increases in quantity, whilst the second portion diminishes. The pitch increases at the same time. Careful examination of these facts has shown the authors that this change in the yield, with the altered conditions, is due to the fact that the hydrocarbon is produced from abietic acid according to the equation—

    C19H28O2 = C18H28 + CO2.

    This hydrocarbon, though evidently identical with that found by Deville in 1841 amongst the products of the distillation of colophony,* is not, as has hitherto been supposed, a diterpene, but appears to be a member of a special series. The name abietene is proposed for this compound. The authors have

[Footnote] * See Liebig's “Annalen,” 37, 193.

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  • little doubt that the so-called diterpene obtained by Lieber-mann* and by Haller† by the action of hydriodic acid on abietic acid is dihydro-abietene.

The results obtained by the vacuum distillation led to the belief that similar results would be obtained by the distillation of colophony with superheated steam. A patent for the purification of colophony by this process was taken out by Hunt and Pochin in 1858; but no account has been published of the chemistry of the process, if, indeed, it has ever been the subject of investigation.

Experiments on the steam distillation of rosin were therefore carried out at Kaiwarra by the kind permission of the directors of the New Zealand Candle Company. The results were completely as anticipated, water-white rosin, heavy hydrocarbon, and a small quantity of pitch being practically the only substances produced by the process.

Experimental.

Preliminary Experiment.

105 grms. of rosin (N quality) was distilled under diminished pressure (18 mm. approximately). The course of distillation was as follows: Up to 270° C., 23 grms.; 270-285° C., 67 grms.; pitch, 12 grms.; loss, 3 grms.

The portion distilling at 270-285° was refractionated. About 70 per cent. of it passed over between 262-268° C. as a light-yellow oil, which when rapidly cooled set to a hard transparent resin; but which when cooled slowly became opaque, owing to the formation of crystals, which gradually increased in quantity until the whole mass was crystalline.

This substance was analysed, and gave numbers agreeing closely for those required for abietic acid, but not for those required by the “isosylvic anhydride” of Bischoff and Nastvogel.

[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

Calculated for Abietic Acid—C19H28O2. Found. Calculated for Isosylvic Anhydride—C40H58O8
C = 79-16 78-88 78-86 81-9
H = 9–72 9-77 9-80 9-9

Confirmatory Experiment.

As it appeared possible that the difference between these results and those recorded by Bischoff and Nastvogel might be due to the fact that their distillations were carried out under higher pressure, and that their distillates were more frequently fractionated, a fresh set of experiments was made.

[Footnote] * Berichte, 17, 18841.

[Footnote] † Berichte, 18, 2165.

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(a.) Four hundred grams of colophony was distilled with a rod and disc fractionation column at a pressure of 31mm. The portion distilling between 270-290 weighed 222 grms. This was redistilled five times, at pressures varying from 27-35 mm. The second, fourth, fifth, and sixth distillates were analysed, but the results only confirm the conclusion arrived at in the preliminary experiment. The numbers obtained were as follows:—

[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

Calculated for Isosylvic Anhyd. Calculated for Abietic Acid 2nd Distillate. Found 4th Distillate. 5th Distillate. 6th Distillate.
C = 81-9 C = 79-16 78-8 78-7 78-8 78-9
H = 9–9 H = 9–72 9-6 9-5 9-8 9-7

As the composition of the distillate had not changed during six distillations, it was evidently useless to continue the fractionation further.

According to Bischoff and Nastvogel, the “anhydride” dissolves in alkali, and when reprecipitated by dilute acetic acid yields isosylvic acid melting at 61-63° C., and isomeric with sylvic or abietic acid. The sixth distillate was accordingly dissolved in potash, shaken out with ether to remove any oily impurities, and reprecipitated according to Bischoff's and Nastvogel's directions. Two preparations melted respectively at 65-73 and 67-80. The latter was recrystallized from 80 per cent. alcohol, from which it separated in crystals, having the characteristic crystalline form and melting-point (160-165) of abietic acid. The evidence is thus complete for the non-existence of isosylvic acid and its anhydride.

The low melting-point of the precipitated acid, as compared with the crystalline acid is easily understood. The precipitated acid is amorphous, and has no definite melting-point. When once melted and kept a few degrees above its melting-point it crystallizes. The crystals must then be raised to a higher temperature before they melt. A number of analogous cases might be quoted.

Abietene.

In the series of fractionations above described a small quantity of low boiling-point material was invariably observed, even in the last distillation. This indicated that even under the most favourable circumstances a slow decomposition was taking place, a conclusion that was supported by the fact that even when the pressure was reduced to 11 mm. the liquid in the distilling-flask did not bump. The most evident reaction which might explain this phenomenon is that abietic acid is losing carbon-dioxide and yielding the corresponding hydrocarbon, the name of which should be “abietene,” from analogy in the case of benzoic acid and benzene.

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To test this conclusion 36 grms. of crystallized abietic acid was heated in a four-bulb Ladenburg flask at 30 mm. pressure, the temperature in the uppermost bulb being maintained at 210-220°C. Under these circumstances an almost colourless distillate was obtained, and this consisted of an oil which did not solidify on cooling. After five hours' heating the contents of the distilling-flask had become so pitchy that the heating was discontinued. The distillate amounted to 44 percent, of the acid taken, and consisted of an almost colourless faintly florescent viscous oil, which still contained some abietic acid. The oil was dissolved in toluene, freed from acids by washing with caustic soda, and dried, first over calcium-chloride and afterwards by sodium. Finally, the toluene was removed by distillation, and the residue distilled at 19 mm. pressure. Practically the whole came over between 300-315° C. The product was redistilled over sodium at 82 mm. pressure, when the greater portion distilled at 247-250° C. This was analysed, with the following results:—

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Calculated for C18H28 Found.
C=88-5 88-3
H=11-5 11-7

The molecular weight was kindly determined by Mr. P. W. Robertson in phenol solution.

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Found. Calculated for C18H28
244
249 244

taking 72 as the depression constant of phenol. (Eykman.)

It is worthy of note that, though a second receiver was attached and kept in a freezing mixture during the whole distillation, no volatile products, except a few drops of water slightly discoloured by oil, could be detected. The same hydrocarbon is easily obtained by the slow distillation of common colophony.

In order to prepare a quantity of the hydrocarbon, a kilogram of common rosin was distilled from a cast-iron retort, provided by means of a stuffing-box, with a rod and disc fractionating column. With a little care it was easy to maintain the still-head at 215-230°C., the pressure being kept at 15-35 mm. 100 grms. of the oily distillate was dissolved in 300 c.c. of light petroleum, thoroughly agitated with 400 c.c. of 1 per cent. soda-solution, and sufficient alcohol to prevent the formation of a permanent emulsion. The soap-solution was shaken out with a second quantity of petroleum. The hydrocarbon was dried by calcium-chloride, the light petroleum removed by distillation, and the heavy oil fractionated in vacuo. The following fractions were obtained:—

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Boiling-point. Pressure. Weight of Distillate.
241-250° 80-85 mm. 8-3 per cent.
250-253 81 mm. 63-7 "
256-272 81 mm. 6-9 "

Residue = 3–9 per cent.

Acid recovered from washings = 14 per cent.

Loss = 3–2 per cent.

The fraction boiling at 250-253 was redistilled several times over sodium. When analysed different samples gave numbers agreeing with those already given for the compound prepared from crystallized abietic acid. Different specimens gave:—

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Calculated for C18H28. I. II. III.
C = 88-5 88-3 88-2 88-5 88-7
H = 11-5 11-1 10-9 11-0 11-3

Further evidence of the identity of the two substances is shown by the similarity of their physical constants.

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Hydrocarbon from Abietic Acid. Hydrocarbon from Crude Rosin.
Specific gravity 0–9728 at 19° C. 0-9727 at 18° C
Refractive index 1–537 " 20° C. 1-538 " 12° C.
{199-200 " 13 mm.
Boiling-point 247-250 " 82 mm. 253-255 " 82-85 mm.
340-345 " 760 mm.

The hydrocarbon from crude rosin is optically active. It gave the value [a]d = 92-9.

In 1884 Liebermann* obtained a hydrocarbon approximating in composition to that of a terpene by heating abietic acid with hydriodic acid and phosphorus at a temperature of 240° C. It appeared of great interest to learn whether the formation of this hydrocarbon was due to the reducing-action of hydriodic acid, or, as it appeared more probable, to the splitting-off of carbon-dioxide. Experiment showed that the latter hypothesis was the corrct one.

Five grams of abietic acid was heated in a sealed tube with 20 c.c. of fuming hydriodic acid for six hours at a temperature of 210-230° C. The gas which collected in the tube consisted largely of carbon-dioxide, and the abietic acid was transformed into a hydrocarbon. This was purified in the usual way. It was then found to boil for the most part at 245-255°C. at 84 mm. pressure. The quantity of material was insufficient for a complete purification; but the analytical results and physical constants leave little doubt that the product of the action of hydriodic acid is identical with that formed by the distillation under diminished pressure. The analyses gave:—

[Footnote] *Berichte, 17, 1885.

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Calculated for C18H28. Found.
C = 88-5 88-2
H = 11-5 10-9
Specific gravity = 0–962.
Refractive index = 1–5817.
Boiling-point = 245-255.

Liebermann's hydrocarbon boiled at 330°-340° (at ordinary pressure), and contained 1 per cent. more hydrogen than the compound here described—it was probably dihydroabietene produced by the reducing-action of the hydriodic acid and phosphorus at the higher temperature.

Distillation of Rosin with Superhebated Steam.
Preliminary Report.

Sixteen hundred and fifty-five pounds weight of rosin (N quality) was placed in a 3-ton stearine still, melted, and superheated steam blown through the mass. When the temperature of the still-head had risen to 268° C. an oily distillate began to come over. The temperature gradually rose to 299° C. The distillate was almost colourless, and set upon cooling to an almost colourless resin. At 305° C. the distillate was water-white. At 310° C. it began to darken, and came over more slowly. The temperature was accordingly raised, until at 332° C. the distillation was stopped, and the pitch blown out by the pitch-pipe. During the whole distillation the third, fourth, and fifth coils of the still yielded a viscous distillate which did not set on cooling. The quantities obtained were as follows:—

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Lb. Per Cent.
Hard distillate 1,052 68-6
Soft " 424 25-6
Pitch and loss 179 10-8

The pitch being very hard a great portion of it refused to leave the still, a fact that made itself abundantly evident the next time the still was used.

Hitherto only the light-coloured portion of the distillate has been analysed. It contained C = 79-7; H = 9–7; and thus consisted principally of abietic acid. The other portions of the distillate are under examination.

In conclusion, the authors desire to express their indebtedness to Messrs. Newton and Son and to the directors and secretary of the New Zealand Candle Company for the assistance they have given in the carrying-out of the above investigation.

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