Shella.c OSCARM. OLSEN, William Zinsser 8 Co., Inc., New York, N. Y. DETERMINATION O F COLD INSOLUBLE, WAX, AND ASH HE term "insoluble," when used in connection with shellac, is understood to mean that material which is insoluble in ethyl alcohol, consisting usually of sand, insect remains, and arsenious sulfide, exclusive of wax. Occasionally there may be present insoluble (polymerized) shellac resin, insoluble in cold but partially soluble in boiling alcohol, If so, determination by the hot-alcohol method ( I ) would therefore yield inaccurate results. The official cold-alcohol method (11),which is recommended for the determination of polymerized shellac, specifies the use of 124-mesh silk as the filtering medium, and the results obtained are always lower than actuality because of the passage of small particles of insoluble matter through the +0.120-mm. openings. Shellac wax is also insoluble in cold alcohol and soluble in boiling alcohol, chloroform, or carbon tetrachloride. As it is considered to be a normal constituent of shellac up to 5.5 per cent, it is determined and reported separately (2). However, by retaining cold alcohol as the solvent, filtering through paper or alundum crucibles, and extracting the wax with hot chloroform, accurate determinations of the insoluble matter and polymerized resin can readily be made. METHOD. The sample of shellac should be ground to pass 100 per cent through a No. 30 sieve, and thoroughly mixed to insure uniformity. Place 5 grams in a 200-cc. lipped beaker, and add 100 cc. of 95 per cent alcohol (No. 1 or 30 specially denatured). Stir frequently for 2 hours to dissolve all the soluble matter. Next stand the beaker in an ice-water bath, a t 5" C., for 2 hours without stirring. A low temperature facilitates settling and filtration.
Some typical comparative results by this method are shown in Table I.
T
SPECIFICGRAVITY
Oberdoerffer (IO) gives a specific gravity value of 1.205 for "pure" shellac. Coffignier ( 5 ) found values of 1.009, 1.036, and less than 1 a t 16" C., for sticklac, pale orange, and bleached shellac, respectively. Booper (7) reports 1.139 for lac resin. Langmuir (9), Olsen (12) ,Thorpe ( I S ) , and Hodgman and Lange (6) publish values of 1.08 to 1.13 for shellac. Hurst (8) states that lac has a specific gravity of 1.113 to 1.214, the darker varieties being the heavier. Wolff ( I d ) found values of 1.035 to 1.14 a t 15" C. for shellac. The method employed is not stated by any of the authors. I n only two instances is the temperature reported and in only one instance is the grade of shellac reported on clearly stated. The values reported show an evident lack of agreement. Bradley (4) found values of 1.152 for orange superfine, and 1,110 for bleached dry shellac at 20" C., by displacement of water. As shellac adsorbs water to some extent and swells, determination in water may influence the accuracy of the results. As previous experiments had shown that shellac was insoluble in and unaffected by kerosene, the specific gravities of three common varieties of shellac were determined in this liquid. A convenient method which specifies the use of kerosene as the displacement medium is Standard Methods of Test for Specific Gravity of Pigments, A. S. T. M., D 153-27, Method A, and after proper preparation of the shellac this method (3) was followed. The three varieties selected were T N pure orange, containTABLE I. INSOLUBLES, WAX, AND ASH,IN SHELLACS ing 2.75 per cent insoluble, dry bleached 0.6 per cent insoluble, BLEACHED and dry bleached refined 0.4 per cent insoluble. ORANGE DRY Each sample was ground t o pass 100 per cent through a T N P U R E ORANQETN USSA BLEACHED DRY REFINPD 1 2 3 4 5a 6 No. 120 sieve (0.125-mm. openings), and dried a t 42" C., in % % % % % % an air-bath for 18 hours t o eliminate adsorbed moisture and Cold insoluble, gases. It was then re-sieved, and from 0.300 t o 0.600 gram 0.34 3.06 2.48 2.59 0.6s newmethod 3.77 4.80 4.00 3.98 4.20 0.20 wax 4.18 was filled into a weighed 25-cc. pycnometer in the air-bath. 0.10 0.64 0.93 0.26 0.05 Ash 0.75 0.38 3.06 2.82 0.56 0.37 Hotinsoluble 3.65 After weighing the pycnometer and shellac a t room temperaCold insoluble ture, the shellac was completely covered with kerosene. 0.05 1.65 0.00 05ioialmethAd 1.37 1.40 1.30 Iodine value 17.20 22.90 20.70 7.70 7.60 6.30 Thereafter the method was followed in detail. The results Contained polymerized shellao. are shown in Table 11. Q
Meanwhile, ignite an RA-98 porous alundum thimble at low red heat for about 15 minutes, cool, and weigh. Place the thimble in a carbon filter-tube, 32 mm. in diameter and 70 mm. in depth, whose stem passes through B rubber stopper in the neck of a 500-cc. filter flask. Decant the shellac solution into the thimble, washing the insoluble from the beaker with about 100 cc. of cold alcohol and using a policeman. Apply a moderate vacuum, if necessary. Next extract the thimble containing the insoluble and wax with hot chloroform in a Soxhlet extractor for 1 hour to extract all of the wax. Dry the thimble a t 105' C. for 2 hours or more to constant weight, and the percentage of cold alcoholinsoluble matter can be calculated. The amount of ash can be determined by igniting the thimble until the carbon is destroyed, cooling, and weighing. After distilling off most of the chloroform from the wax extract in a weighed flask, the wax can be dried at 105" C. to constant weight.
TABLE11. SPECIFIC GRAVITY OF SHELLACS ORANGE TN PUR^ 1.196 1.199 1.212 1.216 1.212
... ...
Av. 1.207
(At 16.6°/16.50 C.; moisture-free) BLPACHED DRY BLEACHED DRYREFINED 1.198 1.214 1.194 1.226 1.199 1.223 1.193 1.207 1.190 1.187 1.211 1.196 1.217
... ... ...
As shellac wax is soluble in kerosene, the specific gravity of a sample of known purity, unbleached, was determined in 95 per cent alcohol instead, by the same method. Moisture-free, a t 15.5"/15.5" the specific gravity of shellac wax was found to average 1.028.
e.,
ACKNOWLEDGMENT The author desires to acknowledge invaluable assistance from H. E. Wolff during the course of this work. 47
48
Vol. 4, No. 1
ANALYTICAL EDITION
LITERATURE CITED (1) Am. SOC.Testing Materials, “Tentative Standards,” pp. 296-9 (1930). (2) Am. Soc. Testing Materials, Ibid., pp. 303-5 (1930). (3) Am. Soc. Testing Materials, “Standards,” pp. 345-8 (1930). (4) Bradley, IND. ENQ.CHEM.,Anal. Ed., 3, 306 (1931). (5) Coffignier, “Varnishes,” pp. 86-7, Scott, Greenwood, 1923. (6) Hodgman and Lange, “Handbook of Chemistry and Physics,” p 478, Chemical Rubber Publishing Co., 1930. (7) Hooper, “Agricultural Ledger No. 9,” G. Watt; Government Printing, India, reprinted, 1921. (8) Hurst (N. Heaton), “Painters’ Colours, Oils, and Varnishes,” p. 429, Griffin, 1922. (9) L ~ ~,gIndustrial ~ Chemistry,,, ~ p, ~ 822, Van ~Nostrand, 1921.
(10) Oberdoerffer, Arch. Pharm., 153, 13 (1860). (11) Official Methods Of hdYSiS approved by U. S. Shellac Im-
porters Assocn. and American Bleached Shellac Mfrs. Assocn.. 1929. (12) OlSen, “Van Nostrand’s Chemical Annual,” p. 482, Van No+ trand, 1926. (13) Thorpe, “Dictionary of Applied Chemistry,” Vol. VI, Longmans, 1926. (14) Wolff, “Die Naturlichen Harze,” p. 363, Wissenschaftliche Verlag, 1928. RnosIvmD 1931. Presented before the Division of Paint and Varnish, Chemistry at the 82nd Meeting of the American Chemical ~ Society, Buffalo. N. Y.,August 31 to September 4, 1931.
Nature and Constitution of Shellac IV. A Study of the Saponification Number WILLETF. WITITMORE AND HAROLD WEINBERGER WITH WM.HOWLETT GARDNER, Polytechnic Institute of Brooklyn, Brooklyn, N . Y. A D E T A I L E D S T U D Y has been made of the shows that shellac contains two types of ester linkmethod of determining the saponification number of ages. Potentiometric-titration curves of saponified shellac shellac. I t has been shown that the usually employed method of rejuxing with 0.5 N alkali for solutions show that all the constituent hydroxyhalf a n hour does not give complete saponification. acids are weakly ionized in alcohol, since their For a n accurate saponification number, the solu- soluble potash salts can be completely titrated with tion must be refluxed f o r at least 2 hours. Aqueous a strong acid, such as hydrochloric acid. The true saponijcation numbers of different hydrochloric acid may be used f o r back titrating with varieties of lac are given. Fairly uniform ester thymol blue as outside indicator. The results of this study indicate that the numbers are obtained for shellac when these values saponijication takes place in three stages, which are computed on the basis of true resin content. HOCHy (CHz)ICHOH*CH(CHz)~.CO HELLAC may be considered to be an ester condensation product in which the ester linkages represent elimination of water from the hydroxyl group of one constituent hydroxy-acid and the carboxyl group of another. When O b (CH47. ~HCHOH.(CH~)&HTOH shellac is saponified with alkali, these ester bonds are broken and the alkali salts of the constituent hydroxy-acids are Undoubtedly what they obtained was an intra-ester type formed. It can be seen from this that in any extensive in- similar to those described by Carothers (1): vestigation of the constitution of shellac (4)an accurate knowlHOCHz(CH2)b.CHOH. CHOH. (CHn),. COO. CHr edge of its saponification is important. (CH2)a.CHOH . CHOH. (CH2)7.COOH Whether these ester linkages are all of the lactide type, as On the other hand, there is no reason to suppose that the postulated by Harries and Nagel (6), is questionable. These authors were led to believe that shellac was a lactide, not only original shellac does not contain several ester types. Its from the fact that they were able to isolate aleuritic acid, synthesis probably takes place in the body of the insect Trachardia lacca Kerr. We may expect lactides, lactones, C16H28(OH)3COOH, and shelloic acid, C ~ ~ H H ( O (COOH)2, H)~ from the saponified product, but also because they were able anhydrides, and intra-esters. The first three of these types to synthesize resins resembling shellac from these acids (7) we might expect to be more readily hydrolyzed than the latter. by heating them under reduced pressure. Since various investigations have used different methods However, from the work of Carothers ( 2 ) ,Kerschbaum (9), and Ruzicka ( I S ) , it is clear that in the case of the resin syn- for determining the saponification number of shellac with thesized from aleuritic acid, Harries and Nagel certainly did varying results, it was felt that a careful and detailed study of not obtain a lactide, since these more recent workers have the saponification of this resin might add further valuable shown that ring structures containing more than seven atoms information to our knowledge of its constitution, and at the cannot be obtained by the method employed in this synthesis. same time contribute to the analytical methods of the identifiHarries and Nagel (8), themselves, have shown that aleuritic cation of resins. The saponification number is defined as the number of acid has the structure, HOCH2(CH2)+CHOH.CHOH.(CH~)~.COOH. The smallest ring structure possible for lactide for- milligrams of potassium hydroxide consumed by one gram of substance during saponification (3). For resins in general, mation with this acid would contain 20 atoms:
S
d
b
