Preparing Cuprammonium Solvent and Cellulose Solutions HERBERT F. LAUNER' A N D WILLIAM K. WILSON 'Vational Bureau of Standards, Washington, D . C . A critical review of the literature suggested the possibility of preparing cuprammonium reagent by dissolving solid cupric hydroxide in ammonium hydroxide and of protecting the cellulose from oxidation during dispersion by the addition of metallic copper or cuprous chloride. This simple method of protection makes possible the use of Erlenmeyer flasks as dissolving vessels instead of more complicated equipment. The following very simple procedure was devised. The cuprammonium reagent was prepared by dissolving solid cupric hydroxide in
T
HE cuprammonium test is frequently used to estimate the extent of degradation of cellulose, and has been set up in a variety of standard methods (1, 7 , 10, I S , S6, S9) for use here and abroad. These methods are based upon the investigations of Schweizer (SO), Ost ( Z 4 ) , Gibson, Spencer, and McCall (14), Joyner (19), Farrow and Seale ( 1 2 ) , Small (Si),Clibbens and Geake (6), and others. Because the process employed in the standard methods for the preparation of the cuprammonium reagent by bubbling air over copper metal in ammonium hydroxide is tedious and timeconsuming, the reagent is usually prepared in large batches aBd elaborate precautions are taken for storage. The procedures specified in these methods for the nondegradative dispersion of cellulose in the cuprammonium reagent require specialized equipment. These are strong deterrents to the use of the test. The difficulties involved in the preparation and use of cupramnionium have been extensively recognized, and partially explain the search for other reagents, such as cupri-ethylenediamine (4,34) and dimethyldibenzyl ammonium hydroxide (Triton F) (4,22, 26), foliowing the pioneer work of Traube ( 3 7 ) on the substituted amines. Strauss and Levy (34) claim that substituted amine-type solvents offer the advantages of rapid dispersion and slight degradation of cellulose during dispersion. The latter has been questioned by Clibbens ( 5 ) and the former appears to be true only under certain conditions, as shown by Jolley ( 1 8 ) . These substituted amines are rather costly and vary considerably from one batch to another, and the viscosity values obtained with them differ from those obtained with cuprammonium; therefore much confusion would result in the years required to change standard methods. Rather than a complete change to another method, an attempt to improve the cuprammonium procedure would seem preferable. This article describes a very simple procedure for the preparation of cuprammonium reagent and for the dispersion of cellulose therein, requiring no special equipment. This procedure merely constitutes an amalgamation of techniques already described in the literature, resulting in considerable saving of time and effort without sacrifice of precision.
ammonium hydroxide in an ice bath. The solution of cellulose in cuprammonium was prepared in rubber-stoppered Erlenmeyer flasks by mechanical agitation of the cellulose and the cuprammonium solution, to which cuprous chloride and copper wire had been added. The time of flow of the solution was measured in a viscometer enclosed in a glass jacket thermostated by water pumped from a constant temperature water bath. This procedure saved time, and the results compared favorably with those obtained with a more orthodox method.
amount of added persulfate roughly equivalent to 0.26 ml. of air. Some investigators have sought to avoid the effect of oxygen during dispersion by the use of hydrogen or nitrogen as a displacing gas (12, 14). Others (1, 6, 7 , 10, $1, $8, 29, 56, 56) completely filled the mixing vessel, either the viscometer tube itself, or a bottle, with the reagent. Entirely different methods of protecting the cellulose against oxidation during dispersion have been described by Scheller (as), Doering (11), and Battista ( 2 ) . Scheller added cuprous chloride powder, and Doering added copper metal, to the cuprammonium a t the outset of the mixing process, with the result that the deteriorative effect of the air present w-as greatly diminished or entirely eliminated. Doering showed, from viscosity measurement, that the presence of pieces of metallic copper prevented oxidation of the cellulose as effectively as displacing the air with nitrogen. The protection afforded by metallic copper has recently been confirmed by Hisey and Brandon (16) for cotton. Scheller showed that 0.1 gram of cuprous chloride in 100 ml. of cuprammonium reagent afforded considerable protection for cotton cellulose; without the cuprous chloride the viscosity values decreased by two thirds (28). These results are of great importance to the test, for they suggest that a very simple technique of mixing, using commonplace equipment, will suffice. A confirmation was desirable, and accordingly experiments were performed using a high-grade cellulose derived from unused cotton fabric. Rubber-stoppered, 125-ml. Erlenmeyer flasks, charged with 0.231 gram of cellulose (dry weight), 50.0 ml. of cuprammonium reagent, and varying amounts (0 to 0.5 gram) of cuprous chloride, were shaken mechanically until dissolved and tested in a capillary viscometer of the type described in the A.S.T.M. standard method (1). Two series were run, one with air and one with tank nitrogen, probably containing oxygen as an impurity. The results in Figure 1 show that the deteriorative effect of atmospheric oxygen was eliminated by the use of 0.7 gram or more of cuprous chloride per 100 ml. of cuprammonium reagent, and that the degree of polymerization values approached those of tank nitrogen systems containing much less oxygen. Values for the degree of polymerization were taken from a practically straight line relating log (time of flow) to degree of polymerization from DP = 300 to D P = 3000. Values for degree of polymerization were calculated using the expression derived by Battista ( Z ) , D P = 2160 [log (relative viscosity 1) - 0.2671 Relative viscosity is the viscosity of the solution divided by that of the solvent (the viscosity of the solvents used in this work was 1.46 cp. a t 20" C.). These viscosities were related to time of flow, t , as follows: Viscosity = density of solvent (0.925 gram per ml. a t 20" C.) X (0.000698 t - 0.176/t)
INVESTIGATION OF TECHVIQUES
The two principal sources of difficulty in the cuprammonium test are the oxidation of cellulose during the dispersion process and the preparation of the reagent. Avoidance of Oxidative Degradation during Dispersion. Scheller (28) has shown that a 10% decrease in the viscosity of a cuprammonium dispersion of cellulose resulted from an
+
Present address, Western Regional Research Laboratory, U. S. Depart. ment of Agriculture, Albany, Calif.
455
ANALYTICAL CHEMISTRY
456
The tkvo constants were obtained for the particular viscometer tube from time of flow measurements of two or more standard liquids of known viscosities obtainable a t the Kational Bureau of St andards. The upper curve also shows that the effect of the impurity of oxygen in the nitrogen, which must have been small in view of Scheller's results ( 2 8 ) , was offset by small amounts of cuprous chloride. Similar experiments were performed without cuprous chloride, but ( a ) with copper metal and tank nitrogen, ( b ) with highly purified nitrogen giving no test for oxygen in a mass spectrometer, using special glass-stoppered flasks with inlet and outlet tubes to permit rigid exclusion of air, and (c) with special mixing vials completely filled with the cuprammonium reagent, to exclude air. All these nieasurements gave results essentially equal to those obtained using cuprous chloride.
1700
5
1600
i=
Q
2
1500
:6
1400
n
b
1300
Y Y B2
sn
1900
1100
as well as by air oxidation of copper, but preferred the former because of its much greater simplicity. Others have prepared the reagent by dissolving copper hydroxide, Cu( OH)?, in amrnoniuni hydroxide (9, 14). The solubility of copper hydroxide in ammonium hydroxide is limited, corresponding to 11 to 12 grams per liter of copper. For this reason several investigators ( 7 , 3 1 )have objected to this procedure on the assuniption that the resulting cupramnionium mould be inferior for dispersing high-grade cellulose, and higher copper concentrations have been recommended, such as 30 (7, S l ) , 20 ( I S ) , and 15 grams per liter. Evidence against the greater effectiveness of high concentration of copper has been presented by Hisey and Brandon ( 1 6 ) , who showed that the time required to disperse a cotton cellulose in reagents containing 10, 15, 20, and 22.4 grams per liter of copper increased systematically over this range by a factor of 2. They ascribed this effect to a decrease in the surface area of the cotton by gel formation a t higher copper concentrations. .4 similar opinion has been expressed by Joyner (19j, who reconimends 13 grams per liter of copper. Both Sakurada (27) and Kuniichel (20) reported that all the types of cellulose except raw, untreated cotton were dispersible in cuprammonium containing 7 grams per liter of copper. The solubility (11 to 12 grams per liter of copper) of copper hydroxide in ammonium hydroxide s h o w that cuprammonium, with a copper content (15 to 40 grams or more per liter) above its equilibrium concentration, as prepared by air oxidation of metallic copper, is unstablp. The attainment of unstable systems is probably due to the partially colloidal condition of such cuprammonium, as shown by the work of Bhatnagar, Goyle, and Prasad ( 3 ) .and Stamm ( 3 3 ) . Such cupramnionium solutions can be expected to be less duplicable than those prepared from copper hydroxide. The fact t,hat the limited solubility of copper hydroxide is of
1000 0
P
4
6
8
10
CUPROUS CHLORIDE, GRAMS PER LITER
Figure 1. Effect of Cuprous Chlorideon Depolymerization of Cellulose by Oxygen dufing Dispersion in Cuprammonium
There seems to have been no experimental investigation of the mechanism involved in these very simple methods of solving the problem of cellulose oxidation during dispersion. Simple Preparation of Cuprammonium Reagent. The usual method of preparing the cuprammonium reagent by bubbling air through iced ammonium hydroxide containing copper turnings, as first proposed by Ost (%$), is considered by some-for example, Hatch, Hammond, and McSair (15)-to be simple, but most investigations recorded in the literature do not appear to bear out this contention. The use of sucrose to facilitate dissolution of copper is almost always reconiniended. Experiences in three laboratories at the Sational Bureau of Standards indicate that, the process is highly variable in facility of execution. The method of preparing the cupraninioniuni reagent by oxidation of copper by air is cornplicated by the simultaneous oxidation of ammonia to nitrite ion. Sitrite ion, according to Clihberis and Gealre ( 6 ) , prevents the dispersion of higher grades of cellulose. Jollcy (18) found that cupramnioniurn prepared by oxidizing copper metal with air, anti ront:tining nitrite (and sucrose), dispersed somewhat less cellulose than cuprammonium produccd, without these contaminants, from copper hydroxide. This fact is reflected in all met,hods of this type by specifications for upper limits of the nitrite concentration ( 1 , 2, 6, 7 , 16, 36), which, if exceeded, call for discarding the hatch. These difficulties were recognized by Ost (24j,who prepared cupranimonium reagent from basic copper sulfate, CU~SOI-
Table I. Degrees of Polymerization"'h and of Fluidity Values Obtained Using CuprammoniumCReagents Prepared in Various Ways Type of Cellulose Pnrified cottond
Means Rag paperj
Means
Copper Hydroxide DP Fluidity 2040 4.51 2035 4.54 2015 4.63
-2nlA ..
4.. 62 .-
2050 2031
4.46 4.55
1795 1795 1795 1785 1775g 1789
5.98 5.96 5.96 6.05 6.12 6.01
Oxidation of Copper DP Fluidity 2110 4.15 2075 4.33 2100 4.21 2085 4.29 -. 2105 4.18 2095 4.23
1795 1805 1810 1810 1795 1803
5.98 5.91 5.89 5.89 5.98 5.93
,
Basic Copper Carbonate DP Fluidity Incompletely dispersede
1875 1885 1870 1850 1876 1871
5.43 5.39 5.47 5.61 5.45 5.47
Sulfite paperh
590 27.7 590 27.7 590 27.7 600 27.2 585 28.1 610 27.0 590 27.7 590 27.7 610 27.0 595 27.5 590 27.7 615 26.7 600 27.5 590 27.7 610 27.0 Means 595 27.5 589 27.8 607 2i.l a See text for method of calculating D P from time of flow. b Cellulose dispersions prepared according t o method suggested in Procedure. grams per liter of ammonia C Cuprarnmonium reagents contained 24 and 15 grams per liter of copper except t h a t prepared from copper hydroxide which contained 1 1 t o 12 g d m s per liter of copper. T h e reagent pre: pared by oxidizing copper metal with air also contained 1 gram per liter of sucrose and approximately 0 3 gram per liter of nitrite expressed as nitrous acid. d Raw cotton purified by method of Corey and Gray (8). 6 Undispersed masses of gel could be seen in purified cotton in cuprammonium made from basic copper carbonate. Periods of shaking were 16, 2,a n d 0.5 hour for purified cotton, rag paper, and sulfite pulp, respectively. j Made in bureau paper mill from unused cotton fabric without bleachin or other serious degradative action. I t probably represents highest type cellulose encountered in marhine-made paper. I t was made wlthout alum, sizing, or filler. 0 D P values in Table I for rag paper cellulose are higher t h a n those in Figure 1, which were obtained on paper stored for 8.years in a chemical laboratory, subject t o higher room temperatures and infrequent and short daylight exposures. Values in table were obtained on paper stored in dark in a relatively cool place. h Ordinary commercial sulfite pulp used in paper industry.
07
V O L U M E 2 2 , NO. 3, M A R C H 1 9 5 0
457
Table 11. Degrees of Polymerization and Fluidity Values of a Cellulose" in Cuprammonium* Reagents Containing Yarying Amounts of Nitrite, Sucrose, and Copper, and Prepared hp T w o Processesc 1.
Prepared from air a n d copper metal. Xitrite as HKO?, 3.2 grams per liter; sucrose, 1 gram per liter; copper, 15 grams per liter
1.
Prrpared from cupric hydroxide. Nitrite as " 0 2 , 3.2 grams per liter; sucrose, 1 graiii per liter; copper, 12.1 grams per liter
3.
Prepared from cupric hydroxide. Nitrite as HNO?, 3.2 grams per liter; eucroye, none; copper, 11.0 grams per litpr
Means
Meuns
AIeans
DP 2535 2500 2505 2535 2515 2515
Fluidity 2.58 2.68 2.67 2.58 2.64 2.63
2460 2420 2420 2425 2470 244
1.81 2.92 2.94 2.92 2.77 2.87
2405 2455 2515 2465 2440 2455
3.03 2.82 2.64 2.80 2.88 2.83
Prepared from cupric hydroxide. S i t r i t e , none; aurrose, none; copper, 11. grams per liter
2425 2.91 2410 2.96 2475 2.77 2490 2.71 Means 2450 2.84 a Purified cellulose from different source, not t o be compared x i t h purified cellulose in Table I. b All reagents contained 236 t o 240 grams per liter of XHs. C Cellulose dispersions prepared according t o Procedure. For all other details see footnotes t o Table I. 4.
little consequence is due to vii,tual independence of degree of polymerization values on ropper concentration in this range. This is shown most convincingly by the work of Hisey and Brandon ( 1 6 ) , who found no significant difference in viscosity between cotton cellulose dispersions containing 10 and 15 grams per liter of copper; even those containing 22.4 grains per liter of copper Iwre only slightly different. This was also shown by the work of Joyner (19), who found only slight differences at 29 and 10 grams per liter of copper, and by Seale and Waite (25). The writers confirmed these findings: using the rag paper cellulose described in Table I, found no differences in degree of polymerization in cuprammonium containing 10, 12, 14, 15, 16, 17, and 18 grams per liter of copper. The range of the data was of the same order of magnitude as the data in Table I. The experiments performed b y the writers, and by others, all refer to dispersions of 0.5 gram of cellulose, the usual amount, per 100 ml. of cupramnionium. rlt higher concentrations of cellulosr, the effect of copper concentration is appreciable. The writers have found that all grades of cellulose studied are as effectively dispersed in cupranimonium prepared from rupric hydroxide as in that prepared by air oxidation of copper and having a higher copper concentration. There is a definite, but small, difference in the degree of polymerization and fluidity values for purified cotton with the two reagents as shown in Table I ; for the other celluloses studied the differences are negligible. .&pplication of the "Student's t" test ( 3 2 )shows that this difference in behavior of purified cotton ton-ard the two reagents is large enough to be significant. For most purposes, horever, t,hese differences are negligible. I n columris 6 and 7 of Table I are also shown some results obtained using a cuprammonium reagent prepared by dissolving basic copper carbonate, Cu&Os(OH),, in ammonium hydroxide. This is simi1:ir to the reagent used by Ost ( 2 4 ) ; i t does not disperse purified cotton completely. The difference in degree of polymerization values for purified cotton in Tahle I was often confirmed in the course of this work, and found not to be due to differences in copper concentration. T o ascertain whether it might be due to the nitrite present in the rragent prepared by the air osidation of copper, experiments were performed in which ammonium nitrite was added to a cuprarnmonium solution prepared fi,oni copper hydroxide, and the
results were compared with those using a cuprammoniuni soliltiori containing an equivalent amount of nitrite by oxidation. Remembering that copper content in this range is unimportant, the results given in Table I1 indicate that no difference, either in degree of polymerization or dispersibility, was ascribable t,o nitrite o r to sucrose. Colloidally dispersed copper, present in exress of the amount corresponding to the solubility of cupric hydroxide \Then euprammonium is prepared by oxidizing metallic copper'. appears to be the factor responsible for the difference in degree of polymerization values and fluidity which are obtained by the use of the two solutions. It appears likely, therefore, that a cuprammonium reagent, prepared by simply stirring an escess of copper hydroxide with cold ammonium hydroside, will adequately replace the rwigmt uwilly pi'e'pared in mucli niorp complicated procedures. PROCEDURE
'Thc cupranimoniuni rragent is prepared from conr~'ntrat,t:d, 29.0c;, C.P. ammonium hydroxide, specific gravity 0.90, and c.17. copper hydroxide. The copper hydroxide is added to the ammonium hydroxide while stirring rapidly in an ice 1)ath. [Cloliper hydroside may be obtained from Eimer & Amend, S e w Yoi,Ii, S. Y., or i t may be prepared hy Bottger's method given hy Uawson (9) or Van Bemmelen (38). The writers fo.ind the commercial product) to be equivalent' to that prepared using Biittger's directions.] I t is important that the amnioiiiuni hydroxide be cooled to at least 2' C. or below before adding the cupric hydroxide. T o prevent undue loss of ammonia, t,he animonium hydroxide solution should he chilled before it is poured from the reagent bottle. The escape of ammonia during mixing is diminished by stirring in a rubber-stoppered flask through a greased glass sleeve. After stirring about 15 minutes, the excesR cupric hydroxide is allowed to settle. The concentration of ammonia is then usually u p w ~ r dof 240 grams per liter, a t which point standardization may he desirable, as its concentration does affect the degree of polymerization values appreciably (21, 29). Analysis of the reagent for copper is not necessary after the first few trials. The cellulose dispersions are pivp:tiwf tiy adding, in order, 0.231 gram (dry weight) of cellulose. cwrwted for moisture content,, 10 to 20 1-cm. pieces of clean copper wire, 2- to 4-mni. diameter, ahout 0.4 gram of powdered C.P. cuprous chloride, and 50.0 ml. of the cupramnionium reagent, to a 125-Erlenme>-er flask. During the addition of these materials it is desirable, but not essential, to displace the air in the flask with t,ank nitrogen. The flasks are then rubber-stoppercti and shaken, either by hand or mechanically, depending upon the quality of the cellulose, until dispersion is complete. ( A commercial "wrist-action" shaker servc=s the purpose. Rubber stoppers offer a simple means of stoppering against the slight pressure of ammonia developed during the shaking, and were found to introduce no error.) The most convenient procedure is t o leave the flasks on the shaker overnight and perform the viscosity rneasuremcnt the next morning. Rich ( 2 5 ) and Howlett and Belward ( 1 7 ) have developed techniques which may prove advantageous when rapid dispersion is desired. After dispersion, the viscosity may be measured by any one of a variety of techniques (1, 6, 7 , 10, 13, 21, 34, 59). The authors used a very simple device where the viscometer was set in a glass jacket through which water from a constant temperature bath was pumped continuously by a small centrifugal pump. The tip of the viscometer projected through a rubber stopper in the bottom of the jacket. A fluorescent lamp, with proper shading, behind the jacket made it easy to rend the menisci. The importance of good temperature control of the viscomet,er is shown by the fact that evaporation while pouring the sollition into the viscometer can loner the temperature as much as 1 O C. Therefore, it is best to allow the solution to stand in the viscometer about 3 minutes before starting the measurement. A CK h OW LEDGM ENT
The authors gratefully acknowledge the assistance of Alice J. Padgett in the analytical determinations. LITERATURE CITED i 1) .irn. SOC. Testing
Materiitls, Standard D 539-40T.
( 2 ) Battista, 0. A , . IND.FINO.( 7 1 i m i . , ANAL.ED., 16, 351 (1944). (3) Bhatnagar, S.S.,Goyle, D. X., and Prasad, Mata, Kolloid Z . , 44, 79 (1928).
ANALYTICAL CHEMISTRY
458
’
(4) Brownsett, T., and Clibbens, D. A,, J . Textile Inst., 32, T32 (22) Mease, R. T., and Gleysteen, L. F., Ibid., 27, 543 (1941). (1941). (23) Neale, S. M., and Waite, R., T r a n s . Faraday Soc., 37, 261 (1941). (5) Clibbens, D., Tech. Assoc. Papers, 25, 734 (1942). (24) Ost, H., 2. angew. Chem., 24, 1892 (1911). (6) Clibbens, D,A., and Geake, A,, J . TextileInst., 19, T77 (1928). (25) Rich, E. D., Paper Trade J., 112, 35 (Feb. 6, 1941). (7) Committee on Viscosity of Cellulose, AM. CHEx SOC., IND. (26) Russell, W. W., and Woodberry, N. T., IXD. EXG. CHEM., EXG.CHEM., AN.4L. ED.. 1, 49 (1929). ANAL. ED., 12, 151 (1940). (8) Corey, A. B., and Gray, H. L., I n d . Eng. Chem., 16, 853, 1130 (27) Sakurada, I., B e r . , 63, 2027 (1930). (1924). -(28) Scheller, E., Melliand Textilber., 16, 787 (1935); in Tech. Assoc (9) Dawson, H. M., J . Chem. Soc., 95, 370 (1909). Papers, 25, 551 (1942). (10) Dept. of Scientific and Industrial Research, Fabrics Research (29) Schtltz, F., Klandita, W., and Winterfeld. P., Papier-Fabrikant, Committee, London, 1932. 35, 117 (1937). (11) Doering, H., Papier-Fabrikant, 38, 80 (1940). (30) Schweieer, Eduard, J . prakt. Chem., 72, 109, 334 (1857). (12) Farrow, F. D., and Neale, S. M.,J . Textile Inst., 15, T157 (31) Small, J. O., I n d . Eng. Chem., 17, 515 (1925). (1924). (32) Snedecor, G. W.,“Statistical Methods,” p. 60, Ames, Iowa, (13) German Association of Pulp and Paper Chemists and En,’Vineers, Iowa State College Press, 1946. Papier-Fabrikant, 34, 113 (1936). (14) Gibson, W. H., Spencer, L., and McCall, R., J . Chem. Soc., (33) Starnm, A J., J . Phgs. Chem., 35, 659 (1931). 117, 493 (1920). (34) Stiauss, F L., and Levy, R. M., Paper Trade J., 114, 31 (Jan. (15) Hatch, R. S.,Hammond, R. N.,and McNair, J. J., Tech. 15, 1942); 118, 29 (Feb. 10, 1944). Assoc. Papers, 25,426 (1942). (35) Tankard, J., and Graham, J., J . TestiZeInst., 21, T260 (1930). (16) Hisey, W. O., andBrandon, C. E., Ibid., 27, 697 (1944). (36) Technical Assoc. of Pulp and Paper Industry, Standard T206m(17) Howlett, F., and Belward, D., J. TextileInst., 40, T399 (1949). 44. (18) Jolley, L. J., Ibid., 30, T4, T22 (1939). (37) Traube, Wilhelrn, Bw., 54, 3220 (1921). (19) Joyner, R. A., J. Chem. Soc., 121, 1511 (1922). (38) Van Bemmelen, J. >I., 2. anorg. Chem., 5, 466 (1894). (20) Kumiohel. W.. Pavier-Fabrikant. 36. 173, 497 (1938). (39) Woolwich Research Dept., Rept. 22 (1923). ( 2 1 ) Mease, R. T., J. Research N a t l . Birr. Standards, 22, 271 (1939); 27, 551 (1941). RECEIVED September 13, 1949.
Determination of Safrole in Soap NORMAN H. ISHLER, EMANUEL BORKER, AND CATHERINE R. GERBER Central Research Laboratories, General Foods Corporation, Hoboken, N . J . An analytical method based on the ultraviolet absorption characteristics of safrole in9.5%aqueousalcohol has been developed for the determination of safrole in soap. The safrole is steam-distilled from the sample after treatment with silver nitrate to precipitate the soap. The distillate is examined in a Beckman DU spectrophotometer and the concentration of safrole is determined from the observed absorbence. Statistical evaluation indicates a reproducibility of results within the range *6970 of the safrole value when dealing with samples containing approximately O.lV0 safrole.
A
S ANALYTICAL method for the determination of sniall amounts of safrole (4-allyl-1,2-methylenedioxybenzene)in soap was needed for production control and t o permit storage studies of its retention in soap. Previously developed gravimetric ( I , 3 , 4 ) and cryoscopic methods ( 7 ) were readily applicable only t o large quantities of safrole. A method based on the ultraviolet absorption characteristics of safrole appeared t o offer a possible solution. These absorption characteristics have been reported in the literature by several investigators (b, 5, 6). A sample of Brazilian safrole of specific gravity (20/4) 1.096 and refractive index (~O/D) 1.538 was used in this investigation. Because safrole is insoluble in water, some suitable solvent was necessary t o enable study of its ultraviolet absorption characteristics. Absorbence-wave-length curves were determined with chloroform, 9.5% aqueous alcohol, and hexane as solvents. Reagent grade chloroform and hexane solutions of safrole gave satisfactory curves. When these organic solvents were saturated with water, the observed absorbence was greater than before saturation and consistent results could not be obtained. A 9.5% aqueous alcohol solution gave a satisfactory absorption curve in the Beckman spectrophotometer with absorption maxima a t 286 and 232 mp with slit widths of 0.80 and 1.6 mm., respectively. Because the 9.5% aqueous alcohol solution of safrole gave such satisfactory results, it was used as a standard solvent in the investigation. To estimate safrole quantitatively, an accurate determination of its absorbence (loglo 100/per cent transmittance) was necessary to calculate a factor. Fifty observations were made t o evaluate the
safrole factor. Solutions of varying concentration from 1.096 to 4.384 mg. of safrole per 100 ml. in 9.5% alcohol-water were prepared and the absorbence a t 285 mp was determined in a Beckman Model DU spectrophotometer. Averages of the data are presented in Table I. The average that best suits the data is an absorbence of 0.207per mg. of safrole per 100 ml. of 9.5% alcohol solution. The data show a satisfactory conformance to the BeerLambert law. Each independent observer should determine the absorbence for the safrole and the instrument used. Separation of safrole from soap by distillation was attempted but only 26% of the oil was recovered. Recovery from 9.5% alcohol by steam distillation was then tried. Various amounts of safrole (2.0t o 9.0 mg.) were steam-distilled with water and 20 ml. of alcohol t o make a 9.5% aqueous alcohol distillate. TWO hundred milliliters of distillate were collected, followed by addition of 20 ml. of alcohol t o the distilling flask and collection of
Table I.
Determination of Safrole Factor in 9.5970 Alcohol Solution
Safrole, RIg./100 M I .
1.096 1.534 2.192
3.288 4.384
No. of Observations 10 10 IO 10 10
Av. Absorbence at 285 mp, Loglo loo/% Trans. 0.226
0.318 0.453 0.678 0,897
4 VI Safrole Factor.
Absorbenae/
Sk./lOO M1. 0.207 0.208 0.207 0.206 0.205
