APRIL, 1938
INDUSTRIAL AND ENGINEERING CHEMISTRY
Literature Cited (1) Bhattacharva. J . SOC.Chem. Id.,54,82T (1935). (2j Zbid., 55,309T (1936). (3) Bougault and Cattelain, Compt. rend., 186, 1746 (1928). (4) Carothers, J . A m . Chem. Soc., 51, 2548 (1929); Chem. Rev., 8, 359 (1931). (5) Carothers et al., J . A m . Chem. SOC.,52,314. 711, 3292, 5289, 5307 (1930). (6) Gardner et al., IND.ENQ.CHEM.,Anal. Ed., 4, 48 (1932). (7) Harries, C., and Nagel, W., Ber., 55B,3833 (1922).
(8) Harries, C., and Nagel, W., Wiss. VerQfent. Siemens-Konzern, 3, 12 (1924). (9) Kerschbaum, Ber., 60, 902 (1927). (10) Kionle, IND.ENQ.CHEM.,22, 590 (1930). (11) Lvcan and Adams. J. A m . Chem. Soc., 51, 625, 3450 (1929). (12) Nagel, Ber., 60B, 605 (1927).
45 1
(13) Nagel and Mertens, Zbid., 69, 2050 (1936). (14) Ibid., 70,2173 (1937). (15) Ranganathan and Aldis, Indian Lac Research Inst., Bull. 14 (1936). (16) Raudnitz, Schindler, and Pet& Ber., 68B, 1675 (1935). (17) Ruzicka et al. Helv. Chim. Acta, 9, 230, 249, 339, 399, 499, 715, 1008 (1926); 10, 695 (1927); 11, 496, 670, 686, 1159, 1174 (1928). (18) Schiemann, Chem-Ztg., 58,740, 749 (1934). (19) Tschirch, A., and Farner, A., Arch. Pharm., 237, 35 (1899); abstracted in J . Chem. Soc., 76 (I), 446 (1899). (20) Tschirch et al., Helv. Chim. Acta, 6, 994 (1923); Chem. Umschau Fette, Oele, Wachse Harze, 32, 309 (1925). (21) Weinberger and Gardrier, IND.ENG.CHEM.,30, 454 (1938). RECEIVED October 28, 1937.
Nature and Constitution of Shellac’
Fractionation of Shellac by Solvents BENJAMIN B. SCHAEFFER,* HAROLD WEINBERGER,S AND WM. HOWLETT GARDNER Polytechnic Institute of Brooklyn, Brooklyn, N. Y.
H E forces responsible for the amorphous character of resins contribute materially to the difficultiesencountered in their chemical examination. This fact has not always been clearly recognized. Investigators have sometimes been misled to believe with Nagel (1.6) that the “criteria of organic chemistry have no place in resin chemistry]” whereas the inapplicability of customary methods of analysis can be traced invariably to complications of a physico-chemical nature. These disturbing influences can often be eliminated, either by a careful purification of the resin to remove sqbstances which have a predominant peptizing action, or by a fractionation of the material into simpler chemical mixtures.
The latter can be readily accomplished by the use of organic liquids which preferentially dissolve (8) individual components. This paper describes a method for fractionating shellac in this manner.
Phenomena Which Affect Analysis Some resins, including shellac, contain several constituents which are very similar in both their physical and chemical properties. These constituents tend to form solid solutions of a resinous character which render them difficult to analyze. Subdivision of the original material into several characteristic groups does not always eliminate this difficulty. This was found to be the case when the constituent acids obtained upon saponification of shellac were so divided (21).
The physico-chemical phenomena which interfere with the analysis of resins can often be eliminated by initially fractionating the material with solvents. I n this way simpler and purer substances are obtained for the subsequent chemical examination. This paper describes a solvent scheme for dividing shellac into several component parts. The results seem to show that shellac owes its resinous properties to a solid solution of the several components. The fractions obtained showed only limited film-forming characteristics in contrast to the original material.
These analytical difficulties may be further increased by minute traces of naturally occurring peptizing agents which lend stability to the solid solution formed and aid in solvate formation. Their presence is not always easy to detect and their removal frequently requires special treatment of the resin. Colophony, for example, contains small quantities of resenes which prevent the crystallization of the rosin acids. In one investigation, Seidel (22) showed that resenes even prevented the precipitation of the lead salts of abietic acid, but when removed by volatilization with diethyl ether under reduced pressure, precipitation took place normally. Ruzicka and Hoskings’ success in the investigation of the copal and kauri resins (19) was accomplished by early removal of the terpenic substances by extraction with solvents. They were then able to obtain pure crystals of agathic 1 Other articles in this series appeared in this journal in 1929, 1931, 1933, 1935, 1936, and March, 1938, and in the Analytical Edition of INDUSTRIAL AND ENQINEERINQ CHEMISTRY in 1929, 1932, 1933. and 1934. 2 Shellao Research Fellow, 1934-1936: present address, United Cas Improvement Company, Philadelphia, Pa. 8 Shellac Research Fellow, 1935-1936: present address, Long Island University, Brooklyn, N. Y.
INDUSTRIAL AND ENGINEERING CHEMISTRY
452
acid as the major constituent of several of these resins after a subsequent separation with ammonium carbonate solution. It is interesting to note that twenty-eight other acids have been isolated from these resins (11, 17, 18, 23-26). These acids, Ruzicka and Hoskings consider, may have been either impure forms of agathic acid or products formed from it during the analyses.
FIQURE 1. APPARATUS Still 2. Extractor 3. Condensers 1.
4. Electric hot plate 5. Iron ring 6. Three-way stopcock
Even when definite peptizing agents are absent, irregular results may arise from the colloidal character of the solutions of resin themselves. The degree of aggregation has a considerable influence upon the solubility behavior of these substances. Harries and Nagel (10) obtained the resin from shellac in three distinct physical modifications in their attempts to purify it. These modifications consisted of the normal resin which can readily be dissolved in alcohol and easily saponified; of a resin intermediate in degree of aggregation which was soluble in alcohol, but was only partially affected by saponification; and of a resin which was practically entirely insoluble in alcohol and largely unsaponifiable. No chemical reaction could be detected in changing from one form to another. This is a phenomenon which has also been observed to take place with caoutchouc (10). Conversion of the normal type of resin to one of the unsaponifiable varieties is always liable to occur when shellac is recovered from nonaqueous solutions unless special precautions are taken both in the extraction and in the recovery.
Extraction Apparatus The use of solvents for dividing shellac into its possible components had not been previously employed except by one of the authors (6). I n the purification of shellac, Harries and Nagel (9) had used diethyl ether to obtain their socalled Tehharz but had made no further attempt to subdivide this fraction of the resin with solvents. The process developed by Verman and Bhattacharya (28, 2Q) for the same purpose did not meet all of the present requirements. The method which they used was laborious and required considerable time, so that in this investigation it was necessary iirst to develop a continuous extractor which would be suitable. Previous study (6) had shown that aggregation could be avoided when using immiscible liquids by keeping the sol-
VOL. 30, NO. 4
vent saturated with water wherever possible. It was also desirable to extract the shellac at room temperatures. APPARATUS. The new apparatus (Figure 1) was therefore a modification of the small-size glass extractor previously described (8). It consisted of an extraction vessel, constructed from a 5-gallon varnish pail with a special baked varnish inner coating which was, in general, fairly resistant to solvents. A short piece of half-inch copper tubing was soldered to the center of the bottom of the pail for an outlet. A coarse wire screen placed inside supported a canvas bag containing the shellac admixed with filter aid. This permitted a free drainage of the extract from the vessel. The extractor was supported on a wooden stand at a sufficient height for gravity Row of the solution through a lass tube to a 12-liter round-bottom flask. %his round-bottom flask was placed over an electric hot plate and so served as a still. A 15-mm. glass tube insulated with lead foil was inserted into the neck of the flask and carried the vapors of the solvent from the boiling solution to a nearly horizontal water condenser. The outlet of this condenser was placed above the extractor so that the condensed liquid would flow directly into it through a copper tube inserted throuKh the cover of the extractor. A short water-cooled condenser inserted vertically through the neck of the flask served to keep the system at atmospheric pressure. The liquid in the flask was kept at a constant level during operation by regulating the rate at which the extract was returned to the still. This was controlled by means of a three-way stopcock placed in the return line from the extractor. This arrangement also permitted sampling of the extract at this oint. PROCEDURE. One kilogram of shellac whicf had been ground to ass a 30-mesh sieve was mixed thoroughly with 2 kg. of SuperCefannd placed in a canvas bag in the extractor. The friction top of the extractor was then sealed by means of the patented clamping device which came with the pail. Eight liters of solvent were then poured into the extractor through the copper opening in the top and allowed to flow through the extraction. Four liters of this extract were allowed to drain into the empty still. The flask was then heated so that 12 to 15 ml. of distillate were obtained per minute. At the end of 8 hours, 3 liters of the concentrated extract were siphoned from the still, and an equal amount of fresh solvent was added to the extractor. This was always done just before leaving the apparatus for the night when it was not in operation. To obtain the material from the extract, the solvent was removed by steam distillation until no traces were left in the resin, This ensured the obtaining of a soluble product (4, IS). The molten material was then removed and spread out upon a glass plate by rollin it into a thin sheet to dry. It was then broken up either by han$ or by grinding, depending upon its character.
Solvent Scheme for Fractionation Many solvents will dissolve definite portions of shellac. The quantitative amount (6) which can be extracted by some of these is shown in Table I. By subsequent extractions it should be possible therefore to divide shellac into a number of parts which might contain either a single component or a simpler mixture of components.
TABLEI.
SOLUBILITY OF SHELLAC IN ORGANIC SOLVENTS
Solvent Benzene Benzene Carbon tetrachloride Ethyl ether Ethyl ether Chloroform Chloroform Acetone Acetone (boiling)
Per InvestiCent gator 6.0 20.0 6.8 20-25 23.7
33.9 52.0 62.3 92-95
Solvent Ethyl methyl ketone Methyl butyl ketone Ethyl acetate Amyl acetate Amyl acetate Ethyl oxybutyrate Ethyl lactate Butyl lactate
Per InveatiCent gator 72.8 84.4 71.0 67.5 93.4 87.0 99.2 99.5
(8)
The scheme of solvent extractions shown in Figure 2 was selected after studying several possible combinations (20). Preference was given to those liquids which are immiscible in water, because of the advantage in solvent recovery when steam distillation is used. Chloroform proved to be an excellent solvent for the initial fractionation, since it extracted approximately 40 per cent of the material, thus
INDUSTRIAL AND ENGINEERING CHEMISTRY
APRIL, 1938
dividing the lac into two nearly equal portions. The soluble resinous product from the chloroform extract was then sub. divided, as indicated, with diethyl ether. The insoluble portion from this extraction was shown in a later investigation to be an individual compound, so that the use of chloroform as indicated proved to be one of the simplest procedures which might be outlined for a solvent fractionation. I n a similar manner, subsequent extraction with ethyl acetate of the portion which was insoluble in chloroform and subdivision of the extracted resin with diethyl ether gave another individual component. The wax which is a natural constituent of most lacs was found almost entirely in the fraot,ions soluble in diethyl ether. It was removed from these quantitatively with warm petroleum ether along with a small amount (2 per cent) of soluble resin. The procedure thus yielded six purified fractions of lac resin.
453
Characteristics of the Fractions
The individual fractions differ markedly in their physical and chemical properties. Fractions K I B and K I I B (Figure 2) were hard brittle products which could be readily ground to fine powders. Their light tan color was due to a slight contamination with unextracted dye. Thin films from concentrated alcohol solutions left amorphous white deposits which could be easily rubbed off when the solvent had been evaporated, showing that these products lacked resinous properties. The diethyl-ether-soluble fractions, K I D and KIID, were plastic semiliquid masses which were almost red from a concentration of erythrolaccin, the yellow dyestuff present. Their intensity of color appeared to increase with time as if some constituent were being oxidized to produce more dye. Even when completely freed from solvents by prolonged treatment with steam, they gave soft tacky nondrying films. Fraction K I I I showed a number of peculiarities which disTABLE 11. FRACTIONS OBTAINED WITH SOLVENTS tinguished it from the other fractions. Acetone solutions TN KusmiTN Kusmiwere dark when first obtained upon extraction but deposited Shellac, Khair Shellac Khair Fraction" % Shellac, % Fraction" % Shellac, % a deep brown resin on standing and left a pale yellow solu12 16.0 16 15.5 KIII KIB tion. This solution tended to superheat when the acetone KIV 4 7.0 KID 20 14.7 was evaporated. When treated with steam and air-dried, 26 32.5 KIC + KIIC 7 5.6 KIIB 3 0.4 12 8.0 Dirt KIID the dark precipitated resin was insoluble in solvents. Frac" Figure 2 explains the designation of the fractions. tion KIV also showed a tendency to give an insoluble form of product. The first four fractions were either completely soluble or unaffected by the eleven liquids shown in Table 111. The A comparison of the yields for each fraction for two difliquids represented distinctly different chemical types of ferent samples of shellac which were investigated are shown in solvents, and it is unlikely that any of these fractions can be Table 11. The T N shellac was a composite sample of comfurther subdivided by this means. It is interesting to note mercial blends of this grade of lac; the kusmi-khair shellac that ethyl acetate is also a solvent for the chloroform-soluble was a special sample prepared for this work by the Indian products, indicating a possible similarity in the manner in Lac Research Institute. The lac for the latter sample was which the constituent acids are chemically combined in produced by the insects on the khair (Acacia catechu) host these components. trees on their plantation a t Namkum, India, after a life Their chemical composition and molecular weights, howcycle on the kusum (Schleichera trijuga) host. The shellac ever, are different, as can be seen from Table IV. The values was manufactured in their experimental factory. Table for acid and saponification numbers were obtained by methods I1 shows that the composition of the two samples is somewhich have been previously recommended for shellac (27, what similar in the general proportions of the different 80, 31). The end points in all titrations were determined fractions which are present. p o t e n t iometrically using t h e lithium SHEtLAF ohloridekalomel and CHLOROFORM the antimony elecI t r o d e s (IS). T h i s K I - 30% was done in order to SOLUBLE I N CHLOROFORM eliminate any doubt in regard to the proper indicator. The standard microK I A -.I 6.5% " K I B - 13.52 combustion p r o c e INSOLUBLE SOLUB L F dure was used for the IN IN elementary analyses, ETHER F T,H E R I and a modification (7) BOlLlNQ of the macromethod of Rast for the molecular weights. * K I D - 12.7% KIC-3.8Z *KIIB-301 KnA-9-51 *Km-I5Z *Kl3!-7% INSOLUBLE SOLUBLE INSOLUBLC SOLUBLF SOLU BLC INSOLUBI F All of the fractions IN IN IN IN IN e x c e p t K I I D have LIGROIN LIGROIN ETHER f+\ER ACETONF ACETONE an ester number. BOlLlNQ T h e y also have a g r e a t e r molecular weight, with the ex*KIID- SO KIIC - 3.5 Z ception of the same INSOLUBLE SOLUBLE fraction, than any of IN IN LlGROW LIGROIN the constituents FIQURE 2. SCHBME OF FRACTIONATION OF LACBY SOLVENTS 4 Ninety-five per cent
+
I
* Fractions produoing the resinous portion of lac.
alcohol.
INDUSTRIAL AND ENGINEERING CHEMISTRY
454
TABLE111.
a
Nagel, W., Angew. Chem., 46, 576 (1933). Nagel, W.,Wiss. Ver6,fent. Siemens-Konzern, 10, 108 (1931). Nagel, W.,and Kornchen, M., Ibid., 6, 235 (1923). Rackwitz, M., Arch. Pharm., 245,415 (1907). Richmond, G. F.,Philippine J . Sci., 5A, 177 (1910). Ruzicka, L.,and Hoskings, J. R., Ann., 469, 147 (1929). Schaeffer, B.B.,Ph.D. thesis, Polytechnic Inst. Brooklyn, June, 1936. Schaeffer, B. B.,and Gardner, W. H., IND. ENG.CHEM., 30, 333 (1938). Seidel, “Uber die Darstellung und die Eigenschaften der Abietsauren,” Mannheim, 1913. Tschirch, A., and Engel, A., Arch. Pharm., 246, 293 (1908). Tschirch, A., and Kahan, M., Ibid., 248,433 (1910). (25) Tschirch, A., and Koch, M., Ibid., 240, 202
SOLUBILITY O F FRACTIONS IN ORGANIC LIQUIDS5
Solvent Nitrobenzene Benzene Isopropyl alcohol Octyl alcohols Butyl 2-ethyl acetate Ethyl acetate %-Butylether Methyl ethyl ketone Carbon tetrachloride Chloroform Dioxane
KIB I I S S I S I S I €3 S
KID I I S S I S I I I S S
KIIB I I S S I S I S I I
s
VOL. 30, NO. 4
KIID I I S S I S I I I I S
I = completely insoluble; 8 = completely soluble.
(1902’1. \ - - - - I
(26) Tschirch, A.,and Stephan, Ibid., 234,552(1896). TABLE IV. CHEMICAL COMPOSITION AND MOLECULAR WEIGHTOF FRACTIONS(27) Importers’ Assoc* and Am* Shellac Mfrs.’ Assoc., Official Methods of Mol. Weight Analysis, Specifications and General InformaCalcd. Total No. tion on Shellac and Bleached Shellac, pp. 3G-7, from. COOH New York, 1934. SaponisaponiBy and Acid fication Ester fication Rast COO (28) Verman, L. C., and Bhattacharya, R., London Fraction No. No. No. No. method Groups %C %H Shellac Research Bur.. Tech. Paver 1 (1934). . . Shellac 70.8 231.8 161.8 964 983 4 67.25 9.72 (29) Ibid., 5 (1935). KIB 90.6 255.3 164.7 878 784.5 (30) Weinberger, H.,and Gardner, W. H., IND.ENQ. 126.9 342.4 215.6 654 683 KID CHEM.,Anal. Ed., 5,267 (1933). KIIB 103.6 286.3 182.7 579 565 3 64.76 9.21 147.4 147.2 0.0 380 .. ... (31) Whitmore, W.F.,Weinberger, H., and Gardner, KIID K III .. . 257.1 654 593.6 ... .. W. H., Ibid., 4, 48 (1932);Farhen-Ztg., 8,3456 KIV 70.0 217.8 li7:8 1500 1448 8 ... .. (1933).
I
2
E:!;:
i:::
*.
..
isolated from saponified lac. It would thus appear that most of the components of shellac are inter-esters (which includes Iactides) of the constituent polyhydroxy acids. The fact that a large portion of the resin is soluble in ethyl acetate would support this contention. Presumably shellac also contains a small percentage of free acids in fraction KIID, which may constitute the natural plasticizer previously noted (6) to be present. The resin itself is probably a solid solution. This would account for the difference in properties between lac and its components. The data presented show that the individual molecular species are small in comparison with some of the inter-esters which have been prepared synthetically (2), or with the average molecular weight which has been assumed for shellac (1, 15).
RECEIVED November 2, 1937. This paper is based upon part of the these submitted by Benjamin B. Schaeffer and by Harold Weinberger in partial fulfillment of the requirements for the degree of doctor of philosophy at the Polytechnic Institute of Brooklyn, Brooklyn, New York. Contribution 48 from the Shellac Research Bureau and 44 from the Department of Chemistry of the Polytechnic Institute of Brooklyn. This research wa8 sponsored by the United States Shellac Importers’ Association and the Indian Lac Cess Committee.
Acknowledgment
HAROLD WEINBERGER AND WM.HOWLETT GARDNER
The authors wish to express their gratitude to Mrs. D. Norris and to R. W. Aldis for the sample of kusmi-khair shellac used in this investigation, and their appreciation to R. W. Aldis, R. Bhattacharya, and H, K. Sen for their kindness in reviewing this article.
Literature Cited (1) Bhattacharya, R., J . SOC.Chem. Ind., 54, 82 (1935). (2) Carothers, W.H.,and Van Natta, F. J., J . Am. Chem. SOC.,
55, 4714 (1933). (3) Coffignier, C., BUZZ. soc. chim., 7,1049 (1911). (4) Fowler, G.J.. U. S. Patent 975,224(Nov. 19, 1908). (5j Gardner, W. H., Brit. Plastics, 6 , 514 (1935). (6) Gardner, W. H., Shellac Research Bur., Polytech. Inst. Brooklyn, R e m r t s . 1928-34. (7) Gardher, W. H.,Caldwell, B. P., Rurnett, H., and Weinberger, H., Ibid., Research Note 5 (1937). (8) Gardner, W. H., and Harris, H. J., IND. ENG.CHEM.,Anal. Ed., 6,400 (1934). (9) Harries, C., and Nagel, W., Ber., 55,3833 (1922). (10) Ibid., 56, 1048 (1923). (11) Harrmann, P., and Kroll, N., Arch. Pharm., 265, 214 (1927). (12) Madihassan, S.,M. Pidance’s Report on Lac Refining, Osmania Univ. Press, Hyderabad Deccan, India, 1930. (13) Murty, N. N.,Weinberger, H., with Gardner, W. H., Indian Lac Research Inst., Namkum, India, and Shellac Research Bur., Polyteoh. Inst. Brooklyn, Research Note, 1937.
Chemical Composition of Shellac
S
HELLAC has been shown to contain polyhydroxy acids (2, 8,4, 9), and it has been suggested that these might occur as lactides (4) or as other inter-esters‘ (11)in producing the resin. The picture of shellac as consisting only of a mixture of lactides was questioned by the authors when they studied the rates of saponification of shellac (11). A solid solution of chain inter-esters of dissimilar polyhydroxy acids might, however, account for its resinous character. Any method for separating the parent hydroxy acids is limited if it consists in first saponifying the mixture of these naturally occurring condensates (9). Many of the disturbing influences encountered in such procedures can be eliminated if the resin is first fractionated into simpler component mixtures before saponifying and attempting to separate the constituent acids. This paper describes a study of the chemical composition of the several materials obtained by the fractionation of shellac with organic liquids (10). I The terms “intra-ester” and “inter-ester” as used in this article are the same as those employed by W. H. Carothers [J. Am. Chem. Soc.. 51, 2550 (1929)l. An inter-ester denotes that type which would result from a condensation reaction with the loss of water between molecules; a n intra-ester results from the loss of water within z i molecule-e. g,. a lactone.
