STU DIES UPON RESINS. BY L. H. FRIEDBURG, PH. D. Resins have, at different times, been subjected t o chemical treatment and as far as some of them are concerned, we have quite valuable knowledge of the same. We know of abietinic acid in rosin, we know of a peculiar facility of reaction between some of them with phenol, b u t still, if asked, what is a resin, chemically speaking, cannot give an explanation. I.-COPAL
RESIN.
I have begun to study, qualitatively, a resin of great practical importance in the manufacture of varnishes, the so called copal. T h e difficulty which meets us a t the outset of such researches is this : Are we always sure of finding the same raw material under such a name, for example, as copal ? What is copal, not chemically but commercially ? We find soft copals, such as damar, which is Boluble in ether, but there are other half hard, and still other perfectly liard copals which only partially dissolve in different solvents, b u t which can be made soluble by allowing them to suffer previously a chemical change. After this, however, we have no longer to do with the raw product “copal,” but with a product of decomposition of the same. T h e soft copals are said to be found mainly on the islands of Sumatra, Java, Molucca and the Philippines, also in Australia. T h e hard copals are imported via Calcutta and Bombay from some places in Africa. All of these have very different appearance and different physical properties, so different t h a t i t seems almost impossible to attribute the same name to them. Their origin is not very clear. T h e hard copal is called hard animi in England ; it is imported into Europe via Calcuttaand brought there by African 285
STUDIES UPOX ILESINS.
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We know from the above t h a t copal suffers decomposition by heat in such a m a n n e r as to leave a residue soluble in boiling oil uI' turpentine to a varnish. Consequently the exact conditions of this decomposition sliould be ascertsined. Heating copal slowly i : k a flask connected with a Liebig's condenser, a light flowing disti Ihte which has an agreeable odor, suggestive of terpenes, even O F lemon, passes over a t first, T'liis odor indicates t h e presence of the li7ilo?l.e?~,of Wnllnch. ( = 1 1 ~ 7 1 . Cheix,, Liebig, %j2, 10s.) Shortly after this, vapors arise wliicli cannot be condensed and which are of an irritating nature, the mass turns darker brown, and the boiling continues in this way until almost all of the copal is destroyed. Performing this experiment with the itid of a tliermometer in a fraction flask, we see the aromatic oil distil a t temperatures above 100" C. u p to 170" C. or 155" C. * The niass boils quietly, then the wliite vapors, which partially condense to a liquid of empyreumatic odor, begin to :tppcar wheii tlie temperature of 215" C. is reached, the mass turns very dark, boils quietly witliont sending OR visible v:ipors and t h o thermometer f a l l s suddenly and rapidly to 170" C., or even below that tempemtnrc. It seenis to follow from this, t h a t wiiilc u p to 215" a fi*:ictional separation of a mistiire is going on, when this temptmtnre is renclictl tlic heat applied is partly used for more proioiind inlier decomposition of the residue in t h e flask. If, therefore, the copal be only 1ic:tted to 152" C. until n o more distillate is ol.)titiiied, :nid then allowed to cool, we avoid this latter decomposition. C o p 1 t h u s heated to IS.!" C., when allowed t o cool, yields n cry brilliant glass-l~ard,tninslucent resin, ivliich is solablt? with tile greittest facility in cold or warm oil of turpentine. 'J'lie distillate obtained forms Q of weight of the ~ * a ~ v c o pused. al In order to obtain the first yolatile oil of agreeable odor in purer * I n all the data given in this paper i n regard to teinperatui*t~s, tlie thermometer is always supposed to be in tlie w p w above tlie li(1iiitl and never immersed in t h e liquid. In a siihsequent paper esperiments will be reported which I have made with L: view to dete::tline both temperatures siinultnneoiisly, those of tlic melttd gum ns well as of the vapors fornied.
form, distiliatioti in a cnrrcnt of steam was resorted to. The oil obtained floated on water, but wis Iiot obtained in quantities sufficiently large. T h e experiment was repeaced on :t Iitrger scale (with the liberal a i d of Dr. Alsberg and in his factory) in a copper still and with 45 pounds of steam pressure.* Then again the cooler was not adequate to allow full condensation, and the room was filled with an agreeable odor suggestive of lemon terpenes. T h e residue i n the still, when cold, was very hard, but porous and conscquently brittle. I t did riot dissolve in oil of turpentine. N e s t it was ascertained what liquids would dissolve copal witho u t prcvious treatment. It is said t h a t t h e distillate obtained from copal b y destructive distillation is a solvent for melted copal. But the evil odor rnakes this unmanageable. It was proved to be correct, :is found by former investigators, that aniline and its homologues dissolved copal very readily. Sitrobenzol o r chloroform dissolved copal, the former better than the latter, which, like almost d l commercial chloroform was riot free from an inflamnirtble admixture, perhaps undecomposed acetone. Phenol dissolves copal well. This is a known and patented fact. 1 found cyneol to be an extremely good solvent for copal. (For Cyneol, see A M L .Chew. Liebig, 826, 295.) A n astonisiiing reaction took place when copal mas treated with benzaldeliytle. This latter dissolves in a most perfect manner a t first. S h o r t l y afterwards thc whole mass thickens to :i light am!Jrsr c:olored jelly, not unlike new peach gum, oiily much softer. I t is ;t11nost impossible to handle this mass. After some experience it is possible to bring it into ii flask arid to subject it to distillation. I k t t e r results w e obtained when ground copal is put into :t flask and the C,jH,COEI added. A perfectly clear solution is obtained. At 80" C. the ,jell?-i'orrri is reached, and care has t o be taken t h a t continued heating does not crack the flask. * I also owe to Dr. tllsberg's kindness a liberal supply of a most tiniforni, rather pale copal (Kauri gum), of a quality superior to that ordinarily used for varnishes.
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Then thick yellowish white fumes are driven through the cooler a n d C,H,COH and some H,O distil off. Later an oil which irritates the eyes follows. Finally a n oil distils which condenses to thick white crystals either in the condensing tube or according t o temperatures in t h e receiver. This crystalline mass is soluble in ether and also in benzaldehyde. When this experiment was performed after prolonged treatment of copal with benzaldehyde, under a n upright conderiser, the result was similar. On distilling, t h e temperature must not rise above 215" C. or more profound decomposition takes place. A peculiar fact connected with this experiment was t h a t a n increase in weight of €$ was noticed, when the quantity of products obtained was compared with the quantity used. This is suggestive of oxidation through atmospheric oxygen, as far as the distillate is concerned. These experiments will be followed u p closely and reported upon later. Ilesnming the study of solvents for crude copal, oil of turpentine was inverted at 870" and seemed to be a solvent. Glacial acetic acid dissolved copal partially. Carbon disulphide is taken up by copal in large quantities, copal being a colloid with the former. On adding more disulphide the plastic mass rises to the surface and on filtering and drying becomes brittle. T h e solution of CS, was evaporated on a water Lath and furnished a gummy, light yellow colored mass of aromatic odor. T h e plastic inass when exposed to air resumes a hard and brittle form. Copal heated together with glycerine without pressure does not form a fatty substance. T h e ex1)eriment in pressure tubes has not yet been perform e d . When conc. H,SO, w t s upon copal, sulphur dioxide is generated and the mass turns dark brown. Chromic acid, even boiling, does u o t act upon copal. When the oxidizing mixture of potiissinm dichromate and H,SO, is used a strong action takes place and a n odor suggestive of t h a t of the dried leaves of A s p e w l a Odorata is noticed. Strong sodium hydrate of 40" Be. does not act appreciably. Potassium permanganate attacks copal on boiling. When boiled with nitrosylsulphiiric acid, a reaction, which is
+
STUDIES UPON RESINS.
291
hyde and that with nitrosylsulphnric m i d to form nitro products a n d the formation of a n ammonium salt which is as volatile as ammoniuni chloride. All these experiments will next be performed quantitatively, and should then allow definite conolusions in regard to my assumption t h a t the crude copal consists of three typical components, a terpene, an easily oxidizable hydrocarbon not a terpene, a n d a n acid which may be homologous with abietinic acid. This acid has t h e peculiarity of being an amorphous, glass-hard and translucent mass. NEWPORT, R. I., Ang. Gth, 1890.
