Determination of Unsaponifiable Matter in Rosin I. E. KNAPP,' Newport Industries, Inc., Pensacola, Fla.
P
solution add 6.0 ml. of 50 per cent sodium hydroxide solution (sp. gr. 1.52). Boil gently under a reflux condenser for 1.5 hours and then add 150 ml. of water together with an ebullition tube. Set the flask in an oil or glycerol bath and connect it to a condenser. Hold the tem erature in the bath at 120" to 130' C. until the total volume ofthe distillate amounts to 210 ml. Transfer the rosin soa solution quantitatively to a 250-ml. volumetric flask, cool, and &lute to the mark with distilled water. To obtain the unsaponifiable matter, pipet a 50-ml. ali uot into the extractor. Place 100 ml. of ethyl ether in the E3enmeyer flask, connect it to the extractor, and set it in a water bath which is maintained at 50" to 55" C. by an electric hot plate. Continue the extraction for 6 hours with the reflux rate approximately 3 drops per second. Pour the ether solution into a 500-ml. Squibb separatory funnel and rinse out the flask with two 15-ml. portions of fresh ether. Shake thoroughly with 50 ml. of 1 per cent sodium hydroxide solution. Draw off the aqueous layer into a second sepsiratory funnel and to it add 30 ml. of fresh ether; shake thoroughly and discard the aqueous layer. Run the ether back into the first separatory funnel and wash the combined ether solutions three times with 50-ml. portions of distilled water. Run the washed ether solution into a carefully tared 250-ml. flask, rinsing the separatory funnel with 15 ml. of fresh ether. Immerse the flask in a water bath and distill off the ether. Then raise the temperature of the water t o 67" to 70" C . and maintain a vacuum of 20 to 25 mm. of mercury for 30 minutes. Remove the flask, cool, and weigh. The material recovered is the '[net washed extract." Dissolve
UBLISHED methods for determining the unsaponifiable matter in rosin are few in number and of doubtful accuracy. Both Griffin's method (2) and the proposed A. S. T. M. method (1) call for the ether extraction of a dilute (2.5 to 5.0 per cent) solution of the saponified rosin soap. Rosin soap is strongly hydrolyzed in aqueous solution, and ether extracts appreciable quantities of resin acids and/or rosin soap from such a solution. The above methods make no attempt to remove these impurities from the ether solution. Moreover, the final residue is dried under conditions which cause serious losses by volatilization. Matlack and Palkin (3) recognized the presence of both resin acids and soaps in the residue obtained by the A. S. T. M. method. They washed the ether solution with dilute alkali and water until the wash water showed no cloudiness on acidifying, thus ensuring the absence of rosin soap. They also recognized the volatility of the unsaponifiable matter and dried the final residue in a vacuum a t 70" c. I n the present study it has been found that even with the procedure of Matlack and Palkin the final residue contains an appreciable quantity of titratable acidity. On an average rosin this is equivalent to from 0.3 to 0.6 per cent of resin acids (calculated as abietic acid). In the method described below, the final residue, after weighing, is dissolved in neutral alcohol and titrated with standard alcoholic caustic alkali. The equivalent quantity of resin acid, calculated as abietic acid, is then deducted from the final residue to yield the net unsaponifiable matter in the rosin. This correction is similar to that recommended in the determination of the unsaponifiable matter in soap (5). I n order to ensure complete extraction of the unsaponifiable matter a continuous extractor was designed as shown in Figure 1. (This special piece was constructed from Pyrex glass by the Scientific Class Apparatus Go., Bloomfield, N. J. The Erlenmeyer flask and reflux condenser, shown in Figure 2, each with a standard-taper ground-glass connection, were stockitems obtained from the same company.) This is similar to the apparatus described by Palkin, Murray, and Watkins (41, with the following modifications: 1. The construction of the inner tube or solvent distributor is simplified by having only three small holes in the bulb. 2. The depth of the soap layer is increased so that the droplets of solvent travel further and are therefore in longer contact with the soap solution. 3. The use of standard-taper ground-glass joints is advantageous in preventing contamination and loss of solvent.
8-
The operation of the extractor needs little explanation. As shown in Figure 2, the solvent (ether) is placed in the Erlenmeyer flask which is set in a beaker of warm water. The condensate collects in the inner tube until the "head" becomes sufficient to force the solvent out through the small holes a t the bottom of the tube. The droplets of solvent then rise through the aqueous rosin soap solution, collect in a layer above it, and overflow back into the flask. Thus the rosin soap is continuously brought into contact with fresh solvent.
Procedure The necessary preliminary saponification of the rosin is conducted as follows: Dissolve 30.00 grams of rosin in 200 ml. of anhydrous alcohol in a 500-ml. round-bottomed flask, and to the slightly cooled 1
1I
0
k
_-
4 - /mm. holes
Preseut address, Goodyear Yellow Pine Co., Picayune, Miss.
315
fiyure 1 KXTRACTOR All dimensions in rnillimeters
316
INDUSTRIAL AND ENGlNEERlNG CHEMISTRY
VOL. 9, NO, 7
the special d e s i g n a t i o n “ B wood resin.”) -RosinNet Washed Loss on The time required for comNo. Kind Apparatus Solvent Gross Extract Extract Washing plete extraction varies someCrams Grams % Grama % % 2,303 23,03 1.817 18,17 4.86 what with the kind of rosin. 1902 B wood 10.00 Funnels 6X Ethyl ether 4910 B wood 10.00 Continuous Ethyl ether 2.569 25.69 2.030 20,30 5.39 Tests made with WW gum and 4911 B wood 10.00 Continuous Ethyl ether 2.652 26.52 2.066 20.66 5.86 5915 B wood 10.00 Continuous Petroleum ether 1.295 12.95 1.165 11.65 1.30 Wood rosins showed prac1904 B wood 10.00 Continuous Toluene 2.230 22.30 871 18.71 3*59 tically complete extraction in 3 hours: Eontinued e x t r a c tion with fresh ether for an adit in about 40 ml. of neutral alcohol and titrate with standard ditional 8 hours showed only 0.10 to 0.15 per cent net extract. alcoholic potassium hydroxide (preferably 0.1 N), to a phenolBut with B wood resin this additional extraction time yielded phthalein end point. more than 1.0 per cent net extract. With this special resin (Weight of net washed extract) X 100 = % of extract, E the extraction should be run for a t least 10 hours. Weight of rosin in aliquot (= 6.00) As to the choice of solvent, Tables I and I1show unmistaka(Ml. of standard alkali) x normality X 30.2 bly that ethyl ether is superior to petroleum ether. While = % of abietic acid, A Weight of rosin in aliquot ( = 6.00) petroleum ether does not extract as large a proportion of resin Then acids and/or soaps as does ethyl ether, it does not extract E - A = % of unsaponifiable matter all of the unsaponifiable matter, especially from the lower grades of rosin such as FF rosin and B wood resin. Ethyl Discussion I ether appears t o be generally applicable to all kinds of rosin. A few extractions were made with benzene. This solvent It was very difficult to obtain satisfactory results when inappears to be satisfactory on dark rosin, but on the pale grades dividual samples were saponified and extracted, chiefly beit yields low results and produces troublesome emulsions. came of the difficulty of transferring the rosin soap solution into The necessity for washing the ether extract to remove resin the extractor quantitatively without using too large a volume acids and/or soaps is shown by Table I. In these runs the of water. The procedure was greatly simplified by saponiether solution was evaporated directly and weighed to give fying a large sample and transferring aliquot portions of the the gross extract (column 5). This was then redissolved soap solution to the extractor by means of a pipet. This proin ether and the solution was washed with dilute alkali and cedure also provides sufficient rosin soap solution for check water (as described above) and again evaporated and dried determinations. to give the net washed extract (column 6). It is evident The removal of the alcohol from the soap solution is likely from these results that the omission of the washing yields to be accompanied by severe bumping and foaming unless extremely high results. the foregoing directions are followed in detail. It appears to Very little trouble has been experienced with emulsions in be necessary to distill practically all the alcohol out of the the washing of these ether solutions. I n those few cases soap solution, for if this is not done a considerable volume of where an emulsion was formed, the addition of a few cubic ether will dissolve in the soap layer during the extraction centimeters of 1 per cent sodium hydroxide solution caused step. The result may be that the soap solution will overflow the emulsion to break quickly and completely. into the ether reservoir. The data show that the separatory-funnel method does not exNumerous attempts were made to increase the size of the sample so that t h e 50-ml. aliquots would contain the equivalent of 10.00 grams of rosin. TABLE11. UNSAPONIFIABLE MATTERIN VARIOUS ROSINS However, when the concenTitratable Net tration was appreciably greater Acids Unsa oni -Net Washed (Calcd. as fia6e ------Rosinthan 12 per cent t h e r e was Abietic) Matter Solvent Extract Apparatus Kind NO. considerable separation of rosin Crams % Grams % % ... ... soap. Even the 12 per cent 1.488 18.60 Ethyl ether 8.00 Funnels 3X 2SA B wood ... 1.568 19.60 Ethyl ether 8.00 Funnels 3X 29A B wood solution may become cloudy on 0.67 20:80 1.718 21.47 Funnels 6X Ethyl ether 8.00 B wood 28B 0.67 20 89 1.725 21.56 Ethyl ether Funnels 6X 8.00 29B B wood standing overnight a t a tem1.00 21.60 1.808 22.60 Ethyl ether Continuous 8.00 19 B wood 0.79 21.71 1.800 22.50 p e r a t u r e as low as 20” C., Ethyl ether Continuous 8.00 B wood 24 0.88 21.74 1.840 22.62 Ethyl ether 8.00 Continuous B wood 30 but it will again become homo0.50 16.12 1.330 16.62 Petroleum ether Contrnuous 8.00 B wood 37 0.40 16.25 1.332 15.65 Petroleum ether Continuous 8.00 B wood 38 geneous on warming slightly. 0.70 21.60 1.784 22.30 Benzene Continuous 8.00 B wood 35 0.80 21.66 These statements a p p l y t o 1.777 22.46 Benzene Continuous 8.00 B wood 36 gum rosins and to decolorized 0.76 13.00 1,100 13.75 Continuous Ethyl ether 8.00 14 FF wood 0.67 13.00 13.67 1.094 Continuous Ethyl ether 8.00 15 FF wood wood rosins. I n the special 0 . 1 1 10.34 0.836 10.45 Petroleum ether Continuous 8.00 16 FF wood 0.06 10.50 Petroleum ether 0,845 10.56 case of rosins of abnormally Continuous 8.00 FF wood 17 high unsaponifiable c o n t e n t , 0.27 8.98 0.555 9.25 Continuous Ethyl ether WW wood 8.00 01 0.18 8.82 0.540 9.00 Continuous Ethyl ether 6.00 02 WW wood such as B wood resin, the size 0.10 8.83 8.93 Continuous Petroleum ether 0.536 6.00 03 WW wood 0.09 8 68 8.77 of the sample may be increased Petroleum ether 0.526 Continuous W W wood 6.00 04 0.09 8.09 0.491 8.18 Continuous Benzene 6.00 WW wood 05 t o 40.00 grams-i. e., 8.00 0.31 11.53 0.888 11.84 Continuous Ethyl ether 06 WW gum No. 1 7.50 grams in the 50-ml. aliquot0.34 11.50 0.888 11.84 Continuous Ethyl ether WW gum No. 1 7.50 13 without separation or clouding. 0.31 10.64 0,657 10.95 Continuous Ethyl ether 8.00 26 WW gum No. 2 (The U. S. Department of Agri0.45 10.80 11.25 0.675 Ethyl ether Continuous WW gum No. 2 6.00 27 0.15 8.52 8 . 6 7 0.520 Benzene 6.00 Continuous No. 2 WW gum 39 c u l t u r e has ruled that the 0.10 8.30 8.40 0.504 Continuous Benzene 6.00 WW gum No. 2 40 dark-colored resinous material 0.36 9.79 0.609 10.15 Ethyl ether Continuous 6.00 20 N gum w h i c h i s o b t a i n e d as a by0.52 9.68 0.612 10.20 Continuous Ethyl ether 6.00 N gum 22 product in the decolorization of 0.89 10.53 0.685 11.42 Ethyl ether 6.00 Continuous 31 H gum 0.59 10.66 0.675 11.25 Continuous FF wood rosin shall not be sold Ethyl ether 6.00 32 H gum as a “rosin” but shall carry
TABLE I. EFFECTOF WASHING THE ETREREXTRACT
ww
JULY 15, 1937
v
ANALYTICAL EDITION
ASSEMBLY
€the,.
tract all the unsaponifia b l e m a t t e r . Even w h e n t h e r o s i n soap solution is shaken out with ether six times, i n s t e a d of t h e customary three times, the q u a n t i t y of neutral material extracted (Nos. 28B and 29B in Table 11) is distinctlv lower t h a n that 06tained by the continuous extractor (No. 30) on an aliquot of the same soap solution. T h e unsaponifiable matter in rosin is distinctly volatile at 100" C., and special precautions must be taken in drying it. The data in T a b l e I11 show the losses on drying various samples under different conditions. The loss i n t h e oven at 105" C. (No. 78) is obv i o u s 1y excessive. A m o d e r a t e vacuum a t 100" C. (No. 11) produces a s i m i l a r loss i n weight. A h i g h v a c u u m a t temperatures above 75" C. (No. 14) is also too severe. The best results were obtained with a vacuum of 23 mm. a t a tem-
317
differences do not appear to be related either to the source or the grade of the rosin. It is possible that in certain rosins the presence of resin acids having a molecular weight lower than that of abietic acid may be partly responsible. This is not the whole explanation, however, for if it were, B wood resin should show the greatest difference; actually it shows the least. Matlack and Palkin (3) found a somewhat similar anomaly which they could not explain.
Aclrnowledgment Grateful acknowledgment is made to R. C. Palmer, chief chemist of Newport Industries, Inc., for many helpful suggestions, and also to the management of Newport Industries for permission to publish the results of this investigation.
Summary In determining the unsaponifiable matter in rosin, data show that the results obtained by previously published methods are not accurate. A method is described which eliminates many of the sources of error in these former methods. The use of a continuous extractor of special design, requiring a
TABLE 111. LOSSESON DRYING: No.
78
Drying Time
Temp. Min. C. 20 100 Additional 30 105 Additional 60 105
UNSAPONIFIABLE MATTER
Net Pressure Weight
Mm. Hg 300 762 762
Gram 0.991 0.956 0.919
Loss in Weight During period Total Gram Uram 0:b35 0.037
0:035 0.072
11
20 Additional 30
100 100
300 300
0.825 0.793
0:032
0:032
14
30 Addjt/onal 30 Additional 30 Additional 30
72 77 76 73
23 23 23 23
1.100 1.069 1.056 1.048
0:03l 0.013 0.008
0:03l 0.044 0.052
30 Additional 30 Additional 30 Additional 30
70 68 68 65
23 23 23 23
1.100 1.097 1.095 1.094
01003 0.002 0.001
0:003 0.005 0.006
15
OF FOUND AND CALCULATED VALUE:^ FOR UNSAPONIFIABLE MATTER perature under 70"C. as shown TABLEIV. COMPARISON in No. 15, but even under Abietic Acid Unaaponifiable Matter SaponificaCalculated a8 Calculated by t h e s e conditions the residue Rosin Acid No. tion No. Saponifiable difference Found" Difference could not be dried to a con% % % % stant weight. At lower tem144 77.70 22.30 21.68 0.38 B wood 10s 91.10 8.90 13.00 4.10 169 FF wood 153 peratures (60' C.) there was 91.91 8.09 8.90 0.81 WW wood 168.0 170.6 168.4 90.78 9.22 11.51 2.29 tendency for droplets of water WW gum No. 1 159.8 WW gum No. 2 157.6 167 0 90.03 9.97 10.72 0.75 t o r e m a i n under the residue, N gum 160.3 174.2 93.91 6.09 9.73 3.64 H gum 160.1 168.3 90.68 9.32 10.60 1.28 making it impossible to obtain 5 Mean values from Table I1 obtained with ethyl ether in the continuous extractor. an accurate result. It was finallv decided to drv the residue f;or 30 minutes under a 20minimum of attention during the ether extraction, offers a to 25-mm. vacuum a t a temperature of 67" to 70" C. in the marked improvement over the tedious separatory-funnel water bath. Under these more or less arbitrary conditions method. The method described shows a reproducibility of satisfactory check determinations were obtained, as shown 0.25 per cent or better on check determinations, and appears in Table 11. to be generally applicable to the commercial grades of both The saponification number of a rosin is the number of gum and wood rosin. inilligrams of potassium hydroxide required to saponify one gram of rosin. This can, of course, be expressed as a percentage of abietic acid (molecular weight 302). It would Literature Cited seem RS if the difference between this percentage and 100 (1) Am. Sac. Testing Materials, Proc. 33 (I), 439 (1933). might be a rough approximation of the unsaponifiable matter (2) Griffin, R. C., j'Technioa1 M e t h o d s of Analysis," 2nd ed., pp. in the rosin, but the data presented in Table IV show that 436-7, New York, McGraw-Hill Book Co., 1927. (3) Matlaok a n d Palkin, J. Assoc. Oficial Agr. Chem., 18, 466-71 such a n assumption is incorrect. The saponification number (1935). of each of the rosins used in this study was determined and (4) Palkin, M u r r a y , and Watkins, IND. ENG.CHEM.,17, 612 (1925). then the unsaponifiable matter was calculated by difference (5) Smither, Divine, Long, et al., Ibid., Anal. Ed., 9, 2 (1937). (oolumn 5 ) . The results show very poor correlation with the percentages actually found by analysis (column 6). The R E C ~ I V EFebruary D 23, 1937. I
