COAL BY-PRODUCTS Properties of Hydrogenated Indene-Coumarone Resins' WILLIAM H. CARMODY AND HAROLD E. KELLY Carmody Research Laboratories, Inc., Springfield, Ohio exposed for a 15-minute interval, and then an additional length was withdrawn from the case for exposure. This exposure echelon gave a means of following the fulvene structure development in indene resins and of comparing other resin types in a convenient manner. Evaluation of the finished strips with a colorimeter and comparison with the original gave comparative figures for each section exposed. The yellowing developed by commercial indene resin in a %hour exposure was termed 100 per cent. I n the majority of cases the developed yellow or brown color could be compared with the standard with no difficulty. I t is recognized that the color formation in the different resins examined is not all due t o one cause, and only comparative results are offered. Figure 1 illustrates the drum and end covers in which the resins were exposed. It is 30 inches (76.2 cm.) in diameter, with the mercury vapor lamp fixed in the axis; samples were distributed around the sides. Figure 2 gives comparative results on other commercial resins. Curves 1 and 2 indicate the extent of the improvement hydrogenation confers upon indene resin when exposed to ultraviolet light. This new resin is resistant to oxidation and discoloration to an extent which is superior to most of the synthetic resins now available. It appears to outrank ester gum and the alkyds in the matter of color permanency.
The hydrogenation of commercial indene resins has given rise to a new line of polymers which are extremely resistant to ultraviolet light and atmospheric oxidation, and show reduced discoloration on exposure to weathering conditions. Their thermal decomposition further distinguishes them and indicates that saturation improves their heat resistance; they maintain their original molecular weight values and melting points under severe heating conditions. -411-round chemical resistance is improved by the saturating reaction, and products are obtained that are suitable for the manufacture of tank and can linings, food containers. or other articles which must withstand mineral acids or salt solutions. They are compatible with a wide number of recent synthetic materials and with rubberlike materials or with Vistanex and ethylcellulose.
T
HE properties of indene-coumarone resins have been the subject of many investigations. Their principal uses are determined by their main properties and to a smaller extent by the fact that their color instability is of no objection in the specific use. They are permanently excluded from the coatings field because of unfailing color instability and because expensive aromatic solvents must be used in the preparation of h i s h e d coating materials. Hydrogenation has developed new and valuable properties. These new characteristics have placed them in an envied position, and the purely chemical aspects of their production and properties are of assistance in elucidating the structures of such polymers before and after hydrogenation treatment. The major properties have been examined and are outlined.
Solubility of Hydrogenated Resins The solubility of these new resins is directly related to the percentage of hydrogen and carbon comprising them, and this composition is an important factor in determining solubility. The influence of molecular weight is of minor importance, as later publication will show. The presence of the aromatic group and unsaturation are factors determining the solvency of the resin in any given solvent for it. Hydrogenation destroys the aromatic nature and converts the resin into a cycloparaffin type. This newly acquired similarity is one reason for the marked improvement of resin solubility in all ranges of petroleum cuts, without exception. Previous tendency of the polymers to associate in solution is reduced or eliminated by the hydrogenation treatment, The reduction in viscosity of solutions of this resin as compared with the old readily demonstrates the decrease in association tendency. In addition to their color stability, the unusual solvency is their next distinguishing characteristic. Hydrogenated indene resins dissolve completely in all petroleum cuts, from the light ethers to heavy mineral oils or waxes. The majority of the vegetable oils serve as good solvents, with only a few minor exceptions. More powerful solvents, such as the ethers, esters, ketones, chlorinated solvents, and all the aromatics, dissolve the resins with ease a t room
Behavior under Ultraviolet Light Fulvenation (1, 4) is the most logical explanation for the growth and development of color when exposed to favorable conditions. Outdoor exposure tests have as main objects the simultaneous contact of sunlight and oxygen to provide breakdown and weathering possibilities. Ultraviolet light greatly accelerates the yellowing of indene resins, and a test can be completed in 5 or 6 hours which is equivalent to approximately 3 months of exposure under normal conditions. Strips of glass coated with the resin to be examined were placed in a long light-tight metal shield, and about one inch of the test panel was exposed a t a time. The piece was 1
Previous papers in this series appeared in April (page 525), and May
(page 684), 1940.
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rubber-derived film-forming materials, styrene polymers, white mineral oils, olefin polymers, and certain of the glyptal resins. These are all clear and show evidence of good compatibility characteristics. Hydrogenation does not improve tolerance with cellulose derivatives, except with alkyl cellulose materials to a somewhat limited degree. With ethylcellulose, hydrogenated resin is compatible to the extent of about 25-30 per cent, but the melting point of the resin used and the presence or absence of other materials will influence this value either way. Various hot melt compositions can be produced consisting largely of resin with plasticizer, wax, ethylcellulose, etc., to suit the problem ( 8 ) .
Thermal Characteristics of Hydroindene Resin
FIGURE 1. DRUMIN WHICHTHE SAMPLES UNDERGOING YELLOWING TESTWEREEXPOSED TO ULTRAVIOLET LIGHT
THE
temperature. They are insoluble in alcohols and in mixtures containing appreciable percentages of an alcohol ( 3 ) .
Hydrogenated indene resins are distinguished from the unhydrogenated variety in a striking manner by being subjected to destructive distillation, and by the proportions and composition of the resulting cracked fragments. Each of the two resins has its particular critical temperature a t which it begins to depolymerize and distill. Under milder exposure to heat some depolymerization can also take place, with lowering of molecular weight and without loss of material as a lowboiling fraction. The usual indene resin breaks down r a p idly a t about 380' C.; hydrogenated indene resin under identical treatment requires 410 O C. to begin active distillation. During thermal decomposition of ordinary indene resin there is no formation of gas, and only a trace of material with a boiling point below indene is formed. Scission occurs mainly in such a way as to produce entire units of original indene in more or less modified form. During cracking some autohydrogenation occurs, and a considerable amount of
Chemical Resistance Hydrogenated indene resins have remarkable resistance to chemical deterioration. They are fully saturated with hydrogen and are fortified against all kinds of chemical attack except thermal decomposition. Being wholly hydrocarbon in composition, all parts of the molecule may be considered to have identical chemical reactivity or lack of activity. They do not possess functional groups in their structure; this property further distinguishes them from other resins which respond to certain identification tests. KO test or reaction can readily identify them as being of coal by-product origin, except possibly the multiplicity of six-membered rings in their composition, and their skeletal arrangement. They are resistant to mineral acids in concentrated form and, apart from a slight superficial effect from the oxidizing mineral acids, will remain in their original state after long immersion. Salt solutions or alkalies have no effect on them. Solutions subject to chemical action resist change, and the resin can be recovered in unaltered form. This inertness towards all ordinary reagents makes them ideal materials for coatings, linings, etc., which have to withstand the action of acids, alkali solutions, fruit juices, and alcoholic beverages
($1 * Compatibility with Other Solid Materials Hydrogenation changes the compatibility characteristics of indene resins. A few of the lower polymers in the unhydrogenated state are found to be compatible, and as the molecular weight increases, this compatibility diminishes. It is now possible to hydrogenate the highest available commercial polymers and improve their characteristics. New blends can be made with hydrocoumarone-indene resins and
MINUTES EXPOSURE
FIGURE 2.
COMPARATIVE DISCOLORATION OF COMMERCIAL RESINSUNDER ULTRAVIOLET LIGHT
nonvolatile residue deficient in hydrogen is formed. These cracked products of intermediate boiling range give clues as to the manner of decomposition. The aromatic rings maintain their identity and resist cracking or destruction. The bonds joining the adjacent indene units in the polymer chain are relatively the weaker bonds, and they are severed to produce a maximum of low-boiling indene containing distillate; some hydroindene also is formed during the cracking. In hydrogenated resins the aromatic rings have been converted to a naphthene type structure, with the bonds joining the adjacent units in strengthened condition; and they resist cracking down to the parent unit. As a result, increased
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amounts of higher boiling mat - -T terials are formed; they are mainly dimer and a small amount of very soft resin. The hydrogenated dimer is so stable that when cracking of the resin is in progress a t normal pressure, it volatilizes out of the system and further breakdown is diminished. This is true of the entire range of hydrogenated fragments derived from hydrogenated indene resin. They remain intact as long as possible and can be recovered in essentially the same proportions in which they were formed. The cracking of the usual type of indene polymer is complicated by a number of secondary reactions so that an accurate picture of the depolymerization is remote. Inspection of the various percentages of the cracked materials obtained in the two cases reveals internal distinctions in the stab i l i t y of t h e t w o m a t e r i a l s (Table I). The first effect of depolymerization of a large indene molecule in the polymer is to detach simple fragments such as monomer, dimer, trimer, etc. The more volatile of them escape from the environment, whereas the heavier portions suffer further decomposition. An overlapping or stepwise breakdown of the polymer results. Each fragment is relatively more stable than that from which it was formed, and this resistance progressively diminishes further depolymerization. Raising of the temperature to maintain constant rate of distillate production enables a large part of the product. F I G U R E 3. RELATION BETWEEN I K D E Y E ASD ITSPOLYRIERs, HYDROGEXATED DERIV~TIVES, ASD CRACKED PRODVCTS to avoid secondary breakdown. A definite decolvmerization critical temperature exists for a polymer of any given magnito the extent of 22 and 42 per cent for the hydroresin and the tude, and this is determined mainly by the structural comuntreated resin, respectively. position and the carbon-hydrogen ratio. Further insight into the cracking is to be obtained by Table I illustrates this point clearly. Fragment VI has such comparison of the residues in amounts of 3 and 26 per cent. stability that it distills rather than undergoes further change, First glance seems to contradict the above explanations, but they are in perfect agreement. In the case of the unhydrohence the high recovery of 66 per cent. On the other hand, fragment 11, formed a t lower temperature, cracks a t such a genated resins a complex hydrogenation-dehydrogenation rate that a considerable portion is converted to the monomeric form. The yield is 23 us. 66 per cent. Continued OF Conr~oumsFROM FIGURE 3 TABLE 11. PROPERTIES depolymerization permits the escape of the volatile comMolar Distribution ponents, and thus gives rise to simple and modified monomers Approx. of H into: 1
"
No. of
Compound TABLE
I. EFFECTO F DESTRCCTIVE DISTILLATION .4SD FRACTIOSATION OF 1000 GRAYS OF EACH RESIX
Range,
C.
T o 160 160-178 178-182 182-330
330-3638 Residue Loss
Hydroindene Resin,
5.6
18.7(VIII) 3,4(IX)
1.8 66,4(VI) 3.1 1.0
yo
Original Resin, 5.1
28.0(V) 14.0(IV)
2.0 23.6(11) 26.5 0.d
Yo
Arbitrary Name
Boiling Range
Aromatio rings
Alkene bond
c. I
I1
I11 IV
v
VI VI1
VI11 IX a Melting point.
Indene Indene dimer Indene octamer Indene Hydroindene Satd. dimer Satd. octamer Octahydroindene 1
181-182 345-350 172" 178-182 174-176 340-345 180a
162-164 164-168
3 6 24 3 3 0 0 0 0
1 1 1 0.8 0.1 0 0 0.1 0.93
INDUSTRIAL AND ENGINEERING CHEMISTRY
774
CH
c(
VOL. 32, NO. 6
CH
I I/ ll+oz' C 4 H
cd
\C-CHO
L L
CH
\cn/c\c/cH Hz
Hr
H2
rA
INDENE
P-A
CH
C
i "C-H
C&
I I/
l l + o 4
CH
NCd "\,/" COUMARONE
CH-CH
I/ I
w\,/""
'6-CHO
I/
OR
P-B
E- B
r-ii
CH
\/-
"2
R-
'01 C -R2
KETONE OR ALDEHYE
R-C-R
II
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CHO OXYGEN C ON?Nh'ING POLYMER
o, ,c\c
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n
PRODUCTS FROM CYCLOPENTADIENE FIGURE4. OXIDATION
reaction occurs among the fragments. The liberated hydrogen attaches itself to the indene radical a t the alkene linkage and is continually consumed. The fragments which have donated the hydrogen immediately repolymerize to form residues enriched in carbon, dense in structure, and insoluble. Such an exchange of hydrogen does not take place so readily in the case of the fully hydrogenated resins. Prior introduction of hydrogen stabilizes the polymer against cracking and also diminishes the extent to which such liberated hydrogen might be formed or even accepted by the active fragments. The hydrogenation-dehydrogenation reaction is present to a slight degree only in the case of the cracking of hydrogenated indene resins.
Figure 3 is a representation of the relations between indene, its polymers, its hydrogenated derivatives, and its cracked products. Coumarone, a minor polymer constituent, is presumed to act in similar manner. The indene molecule is compound I, which can produce a series of polymers; only the dimer and the octamer are shown as I1 and 111. When depolymerized either of them will result in IV and V. The octamer and dimer when hydrogenated produce compounds VI1 and VI, respectively. They are saturated in all portions of their structures. Thermal decomposition resolves them into compounds VI11 and IX. Each of the end products has been subjected to sufficient identification to establish Table 11. I n the preparation of
INDUSTRIAL AND ENGINEERING CHEMISTRY
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this table hydrogenation methods were used which permitted distinction to be made between that hydrogenation entering the aromatic rings and that saturating the alkene double bond. Cuts IV and V obviously contaminated each other to a slight extent. The balance of Table I1 agrees reasonably well with the expected figures. Substantiation of the mechanism and the identification of the fragments seem satisfactory. Oxidation Products Figure 4 shows the oxidation products resulting when the cyclopentadiene structure is broken down to produce ketones or aldehydes. These hypothetical products are noted as 11, 111, IV, V, and VI. The presence of ketone, aldehyde, and acidic bodies is well established; separation has not yet been accomplished. Indene and coumarone are presumed to produce compounds of the types shown in 11-A, V-A, 11-B, and V-B. A and B represent indene and coumarone, re-
775
spectively, which may polymerize to give the formula of Staudinger shown in X I , and which is now believed to be inadequate in explaining indene polymer properties and reactions. XI1 is the more satisfactory representation which can give rise to XI11 and XV. IX is the fulvenated structure which is the main product resulting from the oxidation reactions. Studies are in progress in this field which have brought new individuals to light, and which promise to have immediate industrial application. Oxidation of indene resins leads to the production of a complex mixture of organic acids whose separation should be of extreme interest. The present papers on hydrogenation and oxidation do not by any means exhaust the possibilities in the field of coal-tar-derived resins.
Literature Cited (1) Carmody, IND.ENG.CHEM., 32,525 (1940). (2) Hercules Powder Co., private communication. (3) Neville Company, "Neville Resins", p. 39 (1938). (4) Thiele, Balhorn, and Albrecht, Ann., 1, 348 (1906).
Liquid-Phase Hydrogenation of p-Cymene KENNETH A. KOBE AND ANTON VITTONE University of Washington, Seattle, Wash. The optimum conditions have been determined for the liquid-phase hydrogenation of p-cymene to p-menthane, with a nickel catalyst. The physical properties of p-menthane have been determined and tabulated.
HE chemical utilization of p-cymene prepared from spruce turpentine has presented an interesting problem because of the quantity of spruce turpentine potentially available which would be recovered if a sufficient market existed (6). Most of this work on p-cymene has been directed toward its oxidation, or a sequence of reactions to produce thymol or carvacrol. The purpose of this series of papers' has been to study the variable factors affecting the organic unit processes applied to p-cymene. The formation of p-cymene in the pulp digester during the sulfite pulping of spruce wood is attributed to the dehydrogenation and rearrangement of various terpenic compounds present in the wood. This paper reports a study of the liquid-phase hydrogenation of p-cymene to p-menthane, which is the parent member of the p-menthane series of terpenic compounds ( 2 ) . This product would be the cheapest starting material for synthesis in the pmenthane series. The earliest work was the vapor-phase hydrogenation by Sabatier and Senderens in 1901 (IO) and by Sabatier and Murat in 1913 (8). The hydrogenated product consisted of 66 per cent menthane with 16 per cent pdimethylcyclohexane and p-methylethylcyclohexane (9). Skita and Schneck (12) studied the stereoisomerism of p-menthane prepared by both vapor-phase hydrogenation over nickel and
T
1
pCymene Studies, V.
Previous articles appeared in J . A m . Chem. Soe.,
57, 1640 (1935),62, 562 (1940),and in IND. ENG.CHEM.,31, 257, 264 (1939).
liquid-phase hydrogenation with platinum catalyst. They state that the former method yielded the trans form and the latter the cis form of p-menthane. Adams and Marshall ( 1 ) hydrogenated p-cymene in glacial acetic acid with platinum oxide catalyst a t room temperature and reported quantitative reduction as measured by hydrogen absorption. Brown, Durand, and Marvel (3) found that reduction by this method is greatly accelerated by small amounts of hydrogen chloride. Shoorel, Tulleners, and Waterman (11) studied the liquid-phase hydrogenation of p-cymene over nickel on kieselguhr a t about 140 atmospheres pressure. Their yield is not stated.
Experimental Procedure P-CYMENE. A technical grade of pcymene was purified by successive shaking with 25-ml. portions of concentrated sulfuric acid per liter of p-cymene until the acid layer remained practically colorless, and then washing with dilute sodium carbonate solution and with water. After being dried over calcium chloride, the p-cymene was refluxed over sodium for 2 hours and fractionally distilled through a Young and Thomas column having 14 disks, 2 cm. in diameter, spaced over a length of 30 cm. The purified product distilled between 175" and 176" C. (di5 = 0.8534,:'n = 1.4878). This p-cymene was used in runs 1 to 6; for runs 7 to 1.5 it was refluxed over the catalyst (2 grams catalyst per 300 ml.) for
