AW.2 1914
TIIE JOURS.! L OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
Both potash (KzO) a n d phosphoric acid (P205) were determined b y t h e official method for fertilizers, t h e former b y treatment with concentrated sulfuric acid, ignition a n d extraction with dilute hydrochloric acid; t h e latter b y treatment with a solution of magnesium nitrate, evaporation, ignition a n d a similar extraction. A glance a t t h e table shows t h a t a wide variation exists, not only i n t h e percentages of t h e fertilizer constituents present, b u t also in t h e ratios of nitrogen t o phosphoric acid, nitrogen t o potash or phosphoric acid t o potash. This large variation is attributable t o either one, or both of two things: ( I ) T h e presence of considerable extraneous matter such a s rock dkbris, etc., or ( 2 ) t h e removal of some of t h e more available constituents b y leaching, or, i n t h e case of nitrogen, b y decomposition of t h e material and subsequent volatilization as ammonia. I t may be said in this connection, t h a t in t h e more recent deposits, nitrogen is t h e most valuable constituent, phosphoric acid a n d potash following in t h e order given; b u t on “aging,” t h e nitrogen content decreases very rapidly since most of i t is present in a n available form.’ The writer wishes t o place particular stress on t h e sample from Haiti as i t represents uncontaminated a n d practically undecomposed b a t guano which is very likely of recent origin, since thousands of bats2 spend their days in t h e cave at t h e present time. As received in t h e laboratory, i t consists of a dry, dark brown powder, in which t h e wings a n d other parts of insects can be seen b y t h e naked eye.3 Over 90 per cent of t h e phosphoric acid present is water-soluble as is also t h e greater part of t h e potash; a n d if t h e high percentage of nitrogen, together with t h e large amount of organic matter (as shown b y t h e volatile determination), are reckoned with these facts, i t is evident t h a t t h e substance is very valuable. It has been calculated from d a t a concerning t h e Haitian cave (which had not been fully explored a t t h e time) t h a t i t contains approximately seven hundred tons of b a t guano. Based on t h e market prices of 2 0 cents per pound for nitrogen,‘ a n d j cents per pound for phosphoric acid a n d potash, t h e material is worth (not considering t h e organic matter, which is a big factor) very close t o $40 per ton, or approximately $30,000 for the entire deposit. Whether or not this is a representative example is a matter for conjecture, b u t very likely it is above t h e average in quantity a n d i t certainly is in quality. N o specific d a t a on t h e extent of t h e American deposits already discovered, are available. I n several instances, however, they were reported as being of considerable size. The facts given in this paper warrant t h e suggestion t h a t a further search for bat guano be made, since 1 Thompstone. E , “ B a t Guano in Burma,’’ A g r . J . Indra, 4 (1909). 379-81 1 I t has been reported that the “flight of the bats on leaving the cave, in rope-like formation, as large in diameter as an ordinary street car, requires over an hour, by actual timing.” 3 For further description see, Tod, W., “Ueber Fledermausguano,“ L a d w . ners Slalton, 1 (1859). 264-268. 4 “Quotation on Nitrogen of Bat Guano,” Bull. Texas E x $ . Stolion, 160, July, 1913, p 10
66 j
there is a possibility, or even a probability, of the existence of other valuable, a n d as yet undiscovered deposits in this country. BUREAUOF SOILS
u. s. DEPARTMENT OF AGRICULTURE WASHINGTON
STUDIES IN SYNTHETIC DRUG ANALYSIS-I. ESTIMATION OF ACETANILIDE AND PHENACETIN IN ADMIXTURE By W. 0 . E M E R Y ~ Received April 30, 1914 INTRODUCTIOS
During t h e past few years, more particularly since :he inceptiTn of both federal and State drug enactments, attent’on has been directed repeatedly t o t h e dearth of c,dequately tested methods for detecting a n d estimating medicinal agents. The need of these methods was most keenly felt in connection with certain iiiliibited substancc-s of synthetic character like acetanilide a n d i t s derivatives, antipyrin, cocaine, codeine, heroin a n d other similarly potent drugs, which find extended application in many of our proprietary medicines. .4side from these considerations, hon-ever, there existed in t h e case of acetanilide a n d phenacetin (acetphenetidin) additional cause, on the part of drug analysts a t least, for desiring quantitative methods. The relatively low cost of acetanilide, taken in connection with its pronounced physical resemblance t o phenacetin, has already suggested t o t h e unscrupulous t h e possibility of partial or even complete substitution of‘the former drug for t h e latter, a n d indeed several flagrant instances of such practice are on record. Accordingly, much time and effort have been expended in various quarters in t h e hope of devising a quantitative separation, though hitherto apparently without marked success. It is evident, however. t h a t any procedure, calculated t o determine even approximately t h e relative proportions of acetanilide and phenacetin in admixture, t h u s blocking t h e ways of t h e sophisticator, must prove welcome t o officials a n d chemists engaged in drug control. Ordinarily, t h e preliminary or gross separation of these two drugs from complex mixtures presents no unusual difficulties. being easily effected b y extraction with chloroform. I t is i n the subsequent quantitative partition of t h e mixture t h u s isolated where t h e real problem begins, since no purely physical method, involving, for example, water or a n y of t h e commonly available, organic solvents. lends itself t o a sharp separation. A partial separation may indeed be effected according t o Will2 with water about as follows: If I gram of a mixture of equal parts of acetanilide and phenacetin be shaken with zoo cc. of water, all of t h e acetanilide goes into solution together with 0.13 g. of phenacetin, t h e remainder being unaffected. T h i s latter portion is then filtered and weighed. Its weight, corrected b y t h e addition of 0.13, represents t h e phenacetin originally present in this particular 1 2
Chief, Synthetic Products Laboratory Pharm. J.. [ 3 ] 21, (1890), 377.
.
W
'
T H E J O U R N A L OF I N D C S T R I A L A N D ENGINEERING C H E M I S T R Y
66 6
mixture. I n two similar experiments, but involving slightly different proportions of t h e two constituents, it was found t h a t the weight of the undissolved phenacetin augmented b y 0.13 corresponded t o t h e quantity of this drug present in the mixture. It is quite evident, however, t h a t such a procedure, while having a legitimate place in proximate determinations, could hardly form the basis for t h e quantitative separation of unknown mixtures. I n t h e method presently t o be described. advantage is t a k e n of the fact t h a t , when a n aqueous solution of phenacetin is added t o a solution, of iodine a n d potassium iodide containing a mineral acid, a n iodine addition product or periodide separates, a t first in a n apparently emulsified condition, later assuming with greater or less rapidity-depending on temperature! concentration, a n d other undetermined factorst h e form of brilliant bronze-colored leaflets, practically insoluble in t h e resulting menstruum, a n d having t h e composition ( C2 Hs 0 .CsH4NH. COC H3) 2 . H I . 14.
Vol. 6 , KO. 8
is a matter requiring very nice manipulation, since a n y premature separation of phenacetin as such from the resulting menstruum would necessarily lead t o a corresponding loss in periodide formation a n d thus vititate the determination. T h e small quantity of acetic acid employed not only facilitates solution of both phenacetin a n d acetanilide, b u t also inhibits latent hydrolytic tendencies affecting the acetyl group. Now it so happens t h a t phenacetin yields with iodine a n d hydriodic acid not only t h e periodide. (C~OHI~NOZ)Z.HI.I~ (1) on the formation of which the separation of acetanilide a n d phenacetin is based, b u t under certain conditions also a less insoluble addition product, containing one-half as much iodine,
EXPERIMEXTAL
(C~OH~~NO~)Z.HI.I~ (2) While t h e former of these t w o periodides represents t h e optimum in iodine addition, constituting as it does t h e sole or major portion of the addition product as ordinarily obtained, t h e more the iodine content of t h e reacting medium is reduced by t h e separation of t h e favored type ( I ) , t h e greater t h e tendency for t h e formation of type (2). Furthermore, since the separation of a n y periodide of t h e phenacetin type is conditioned on t h e presence of 'free hydriodic acid (or what amounts t o t h e same thing, potassium iodide a n d hydrochloric acid), i t is quite evident that a maxim u m homogeneity in t h e precipitated product can result only by first bringing the phenacetin, iodine a n d potassium iodide into such uniform distribution a n d intimate relationship t h a t , on the rapid addition of hydrochloric acid, a n immediate liberation of hydriodic acid required t o complete the combination will take place simultaneously throughout t h e entire mass. With due regard, therefore, for the conditions set forth above, as also for errors naturally inherent in iodometric operations, it becomes possible t o reduce t o a minimum certain of these disturbing elements which might otherwise seriously impair the efficiency of the method.
I n practice, the mixture of acetanilide a n d phenacetin dissolved in very dilute acetic acid is added t o standard iodine contained in a graduated glass-stoppered flask, in preference t o the reverse operation, t h e resulting liquid being then acidified with hydrochloric acid. This order of procedure is the outcome of results obtained in a variety of experiments a n d based o n the following considerations:
I n order t o determine experimentally the most favorable conditions under which t o operate, in any analytical procedure, i t became necessary t o carry through several hundred estimations, both singly a n d in series, a few of which appear below. With exception of Series 2, in which 2 j , 30, a n d 3 j cc. of standard iodine were, respectively, used in the three determinations, z j cc. of iodine were invariably employed.
T h e chemical a n d physical properties of t h e periodide are such t h a t t h e determination t o be quantitative must be made in a relatively restricted volume, t h a t is, 'in rather concentrated solution, b u t on the other hand, owing t o t h e very slight solubility of phenacetin in aqueous media, t h e transfer of this substance in solution t o t h a t of iodine in t h e graduated flask, as also its retention therein in dissolved condition,
Series 1
Acetanilide under like treatment yields no insoluble periodide, though there may be a n d doubtless is present in the resulting solution a n iodine addition product of corresponding form, ( CsH6NH.COCH3)z.H I . Id. If, therefore, t h e precipitation of the periodide is effected in a measured volume of standard iodine a n d the insoluble addition product then removed by filtration, i t readily becomes possible t o determine volumetrically the quantity of iodine t h u s withdrawn from solution and, by means of appropriate factors, calculate the phenacetin present in t h e mixture. The phenacetin may also be determined gravimetrically after liberation from its periodide a n d subsequent extcaction with chloroform. The acetanilide is estimated in a n aliquot of t h e filtrate from the insoluble periodide b y extraction with chloroform-the free iodine having been first discharged with a sulfite-followed by hydrolysis with dilute sulfuric acid a n d final titration of the resulting aniline sulfate with standard potassium bromide-bromate.
1
A more detailed description of t h e properties of this addition p r o d u c t
-which
was first described, though incorrectly interpreted, b y Scholvien,
Pharm. Zentralhalle, 32 (1891), 311-will appear shortly in a paper entitled "Periodides of Phenacetln, Methacetin a n d Triphenin." 2 Wheeler a n d U'alden. A m . Chem. J . , 18, 89
No. 1. . . . . . . . . . . 2 , . . . ., , , , , , 3........... 4. . . . . .. , , .. 5 , . . . . .. . . , , Series2
Phenacetin Phen- Glacial Iodin acetin AcOH Cone. Excess Expended recovery Gram Cc. HC1 Cc. Cc. G r a m P e r cent 97.95 19.23 2 1 . 8 4 ' 0 . 1 9 5 9 0.2000 1.00 3 c c . 1 9 . 2 0 2 1 . 9 0 0.1964 9 8 . 2 0 0 , 2 0 0 0 0 . 7 5 3 cc. 19.20 2 1 . 9 0 0.1964 9 8 . 2 0 0,2000 0.50 3 c c . HzSOa 1 9 . 1 5 2 2 . 0 0 0 . 1 9 7 3 98.65 0 , 2 0 0 0 1.00 2 cc. HaPOi 1 9 . 4 5 2 1 . 4 0 0.1932 9 6 . 6 0 0 , 2 0 0 0 1 . 0 0 2 cc.
Iodin Phenacetin PhenAcet- Glacial Cone. Ex- Ex- recovery acetin anilide AcOH HC1 cess pended Per No. Gram Gram cc, cc, cc, cc, Gram cent 5 2 0 . 9 0 1 1 . 2 5 0 , 1 1 9 7 99.75 l . , , o , 1200 o,0960 2 . . . . 0 . 1 2 0 0 0.0960 3 5 2 5 . 8 1 1 1 . 0 8 0.1179 98.25 3 . . . . 0,1200 0,0960 3 5 3 1 . 0 2 1 1 . 1 1 0,1182 9 8 . 5 0
.
-4cetanilide recovery Per Gram cent 0 0940 97.92 0.0944 98.33 0,0952 99.17
Aug., 1914
T H E J0CR.A-AL O F I A V D C S T R I A L A Y D E L V G I N E E R I S G C H E M I S T R Y
Series 3 GlaPhenacetin Phenhcetcia1 Conc. recovery acetin anilide AcOH HC1 Per Gram G r a m R a t i o Cc. Cc. G r a m cent 3 1 9 . 0 2 21.83 0.2000 0 , 2000 3 1 9 . 2 5 21.37 0.2000 0 . 0300 4 ' : ' l 3 19.18 21.51 0,2000 0,1000 2 : l 3 19.10 21.67 0.2000 0 . I500 4 : 3 3 1 8 . 9 8 21.91 0.2000 0 . 2000 1 : 1 3 18.90 22.07 0.1500 0.2000 3 : 4 3 2 1 . 7 6 16.35 0.1000 0 , 2 0 0 0 1 : 2 3 2 4 . 5 0 10.87 0.0500 0 , 2 0 0 0 1 : 4 3 27.60 4.67 Series 4 l . . . . . 0.2000 2 . . . . . 0.2000 3 . . . . . 0.2000 4..... 0.2000 5..... 0 . 2 0 0 0 6 . . . . . 0,2000 0.2000 i . . . . . 8 . . . . . 0.1000 9 . . . . . 0.0667 10 . . . . . 0.0500 11 . . . . . 0,0400 Series 5 1 . . . . . 0.'000 2 . . . . . 0.2000 3 , . . . . 0.2000 4 . . . , , 0.2000 5 , . , . . 0.2000 9 . . . . . 0.2000 , . . . , . 0.2000 8 . . , .. 0.1000 9 . . . . . 0.0500 Series 6 l..... I..... 3..... 4..... 3 . . . . .
6..... /...._
s.....
Y..... 10... .. I1.....
0.2000 0,2000 0.2000 0.2000 0.2000 0.2000 0,2000 0.2000 0 . I500 0.1000 0.0500
.. 0 .o i 0 0 0.0500 0.0667 0.1000 0.2000 0.2000 0.2000 0.2000 0.2000
A,, 0.oi00 0.0500 0.066i 0.1000 0.2000 0.2000 0.2000
1
..
4
5 : 1 4 : 1
3 2 1 1 1
: : : : :
l l l 2 3
4 4 4 4 4
l : 5
4 4 4 4
, .
1
1 :4
19.00 19.25 19.06 19.05 19.06 18.94 18.70 24.38 26.+2 27.36 28.13
21.8; 0.1977 21.37 0.1932 21.75 0 , 1 9 6 6 2 1 . 7 7 0.I968 2 1 . 7 5 0 . I966 2 1 . 9 9 0.1988 22.47 0.2028 11.11 0 . I004 i . 0 3 0.0636 5 . 1 5 0.0466 3.61 0,0326
19.01 19.22 19.10 19.02 19.02 18.91 18.75 24.37 L'i . 4 0
21 85 21.43 21.67 21.83 21.83 22.05 22.37 11.23 5.07
0,1975 0,1937 0 . 1959 0 . 1973 0.1973 0.1993 0,2022 0.lOl5 0.0458
96.86 9i.95 98.67 98.67 99.67 101.11 101.52 91.55
3 3 3 3 3 3 3 3 3 3 3
19.02 19.15 19.10 18.98 18.95 18.90 18.76 18.60 21.25 24.25 2i.60
21.83 2l.5i 21.67 21.91 21.97 22.07 22.35 22.67 lT.3i 11.3i 4.67
0,1973 0.1950 (1.1959 0.1981 0.1986 0.1995 0.2020 0.2049 0.15i0 0.1028 C.0422
98.67 97.50 97.95 99.05 99.30 99.75 101.02 102.46 104.67 102.78 84.43
3 3 3 3 3 3 3 3 3 3 3
16.12 16.22 1i.08 18.02 18.94 19.93 20.90 21.80 22.80 24.02 25.31
19.26 19.06 17.34 15.46 13.62 11.64 9.70 i.90 5.90 3.46 0.86
( I . lYi8 0 . 1957 0.1781 0 . 1588 (1, 1399 ( I . I I95 ( I , 0996 (I ,081 1 ( I , 06d6 0.0355 (I 0088
98.90 9 7 . 85 98.93 99.23 99.93 99.62 99.62 101.41 100.99 88.83 44.16
2
16.30 16.40 1i.15 17.30 18.12 18.20 18.93 19.12 19.93 20.02 20.98 21.00 21.90 22.05 22.95 23.04
18.90 18.70 17.20 16.90 15.26 15.10 13.64 13.26 11.64 11.46 9,54 9.50 i.70 i.40 560
0 1941 0.1921 0,1766 0 . I756 (1. 1567 0.1551 ( I . 1401 0 . 1362 0 . 1195 0.1177 0.0980 0.0976 0.0791 0.0760 0.05i.5
5.42
0,055i
97.05 96.05 9 8 . I3 97.53 97.95 96.92 100.06 97.2i 99.62 98.08 97.98 97.57 98.85 94.99 95.85
16.20 16 22 1 1i.30 3 li.05 1 18.18 3 17.98 1 19 17 3 18.96 1 20.00 3 19.90 1 20.92 3 20.90 1 22.12 3 21.90 1 23 00 3 22.90 1 24.85 3 24.22
19 10 19.06 16.90 11.40 15.14 15.54 13.16 13.58 11.50 11.i0 9.66 9.70 7.26 7.70
3 3 3 3 3 3 3 3 3 3 3
.. 3 5 : 1 3 4 : 1 3 3 :1 3 2 :1 3 1:1 3 1 :2 3 1 :4 3 , .
0.0100 1 0 ' : ' l 0 0400 5 : l 0,0500 4 : 1 0.0667 3 : 1 0.1000 2 : l 0.2000 1 . 1 0.2000 3 : 4 0 . 2000 I : 2 0 2000 1 . 4
I 2 2 2 2 2 7
2 2 2 2
Acetanilide recovery Per Gram cent 0.1976 98.83 0.1934 96.70 0.194i 97.35 0.1961 98.50 99.15 0,1983 0.1994 99.70 0.1480 98.67 0.0984 98.40 0.0423 84.60 98.85 96.60 98.30 98.40 98.30 99.40 101.40 100.43 95.30 93.20 81.50 98.i5
Series 7 0.2000 0.2000 0.1800 0.1600 0.1400 0.1200 0.1000 0,0800 0.0600 0.0400 0 .0200 Series 8 l . . . . . 0.2000 L..... 0,2000 3 . . . . . 0.1800 4..... 0.1800 5 . . . . . 0.1600 6 . . . . . 0 , I600 0.1400 I . . . . . s . . . . . 0.1400 Y..... 0.1200 1 0 . .. . . 0.1200 I1 . . . . . 0.1000 1 2 . . , . . 0.1000 1 3 . . , . . 0.0800 1 4 . . . . . 0.0800 15 . . . . . 0 , 0 6 0 0 16 . . . . . 0.0600 Series 9 I..... 2..... 3..... 4..... J..
...
6..... I . . . .
.
s.....
9..... 10 . . . . . 11 . . . . . 12 . . . . . 13.. , . . 14 . . . . . 15 . . . . 16 . . . . . 17 . . . . , 18 . . . . .
.
0,2000 0.2000 0.1800 0.1800 0.1600 0 . 1600 0 . I400 0.1400 0.1200 0.1200 0.1000 0.1000 0,0800 0.0800 0.0600 0,0600 0.0400 0.0400
.. 0 . or00
Y ':' 1 0.0~004 : 1 0.0h00 7 : 3 0.0800 3 : 2 0.1000 1 : l 0.1200 2 ' 3 0 . 1400 3 : , 0,1600 1 : 4 0,1800 1 : 9
.. 0 . oi00 0.0100 0.0400 0.0400 0.0600 0,0600 0.0800 0,0800 0.1000 0.1000 0.1200 0.1200 0.1400 0,1400
9 ':' 1 9 : 1
..
..
0 .oi00 0.0200 0.0400 0.0400 0,0600 0.0600 0,0800 0.0800 0,1000 0.1000 0.1200 0.1200 0.1400 0.1400 0.1600 0.1600
4 : 1
4 ' 1 i : 3 7 : 3 3 : 2 3 : 2 I : 1 1 : l 2 : 3 2:3 3:7 3::
9':' 1 9 : l
I 2 2 2 2 2 2 >
2 7
2
> 2 2 2 2 2 2 2 2 7
2 2 1
2 2 2 1 1 2 7
4 : 1
2
4 : l 7:3
2
i : 3
3 : 2 3 : 2 1 : l 1 : l 2 : 3 2 : 3 3 : i 3 : i 1 : 4 1:4
2 2 2 2 2 2
2 2 2 2 2 2
1
2 1 2 1 I 1 2 1 2 1 2 1 2 1
3 3
0.1962 0.195; 0.1736 0 . 1787 0 . 1555 0 . 1596 0.1352 0.1395 0.1181 0.1202 0.0992 0.0996 0.0746 0.079 1 5 . 5 0 0.0566 5 . 7 0 0.0585 1 . 8 0 0.0185 3 06 0 . 0 3 14
92.7i
98.10 97.85 96.42 99.28 97.17 99.75 96.54 99.62 98.42 100.13 99.21 99.62 93.20 98.85 94.14 9 i . 56 46.21 78.56
I N T E R P R E T A T I O N O F RESULTS
As t h e title of this paper implies, t h e procedure comprehends in it.s entirety not only t h e separation b u t t h e estimation as well of both acetanilide a n d phen-
acetin. Accordingly, several of t h e mixtures examined were treated with this object in view, namely, t h e recovery of both ingredients, as embodied in Series 2. A s a rule, however, analysis ended with t h e recovery of phenacetin, since this was believed t o represent t h e more important phase of t h e problem under investigation. Examination of t h e d a t a presented in t h e several series. as also t h a t of other series not here shown, leads t o t h e following conclusions: ;iny mineral acid unaffected b y iodine or hydriodic acid under the conditions of t h e experiment can apparently be employed, although hydroch!oric acid is perhaps, o n account of its physical properties. t h e one best suited t o t h e purpose in hand. I t will be noted t h a t a n increase of this acid within reasonable limits operates favorably on phenacetin recovery. I n t h e estimation of this substance alone, not more t h a n 2 0 0 mg. should be taken for every 2 j cc. of standard iodine of specified strength, while the amount of acetic acid used in each determination should not exceed I cc., in which event t h e recovery will fall within 3 t o j mg. of t h e quantity taken or actually present. I n admixture with acetanilide, however, the total amount of both ingredients taken for analysis should likewise not exceed 2 0 0 mg., b u t more acetic acid may be advantageously employed, since such increase tends t o counteract a n apparent tendency on t h e part of acetanilide t o augment unduly the quantity of phenacetin recovered. Whatever t h e cause of such excess recovery, whether due t o occlusion or adsorption of iodine as such or in form of acetanilide periodide on t h e part of phenacetin periodide, t h e limit of usefulness of the method appears t o lie bet\Yeen the ratios I : 3 a n d I : 4 of phenacetin t o acetanilide. I n order t o observe what influence! if a n y , freshly boiled distilled water might have on phenacetin recovery, all estimations recorded in Series 9, with the exception of N o . I , were made with water thus treated. A comparison of recoveries noted under estimations 1-0s. I and 2 reveals a slight difference, i t is true, apparent.ly in favor of ordinary distilled water, t h a t is, t h a t from which t h e air had not been expelled, b u t such difference, conceivably due t o the action of dissolved atmospheric oxygen or hydriodic acid, may have been the result of entirely different influences. METHOD
PHENACETIN-Into a small ( j o cc.) lipped Erlenmeyer introduce 0 . z g. of the phenacetin-acetanilide mixture, a d d z cc. of glacial acetic acid, heat gently over wire gauze t o complete solution, then dilute with 4 0 cc. water previously warmed t o 7 0 ° . Transfer t h e clear acetous liquid b y pouring a n d careful washing of flask with two I O cc. portions of warm (40') water t o a glass-.stoppered, graduated I O O cc. flask, into which have been previously r u n from a burette 2 j cc. of standard iodine, of a strength slightly above 0 . 2 X , a n d warmed t o 4 0'. Rotate t h e resulting mens t r u u m t o uniformity, t h e flask being closed meanwhile, then a d d 3 cc. of concentrated hydrochloric acid, close flask anew a n d continue rotation until copious crystallization is apparent, then set the product aside t o cool. If t h e ratio of phenacetin t o acet-
668
T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
anilide is equal t o or greater t h a n I , the formation of crystalline scales will be almost immediate on the addition of acid. As t h e proportion of acetanilide increases, however, the periodide is not only more inclined t o maintain the liquid state, with the rcsu;+ t h a t crystallization ,becomes proportionately slower, b u t its separation also from t h e menstruum itself is in a measure apparently retarded. I n such cases, gentle agitation of the liquid or rotation of t h e flask in water warmed t o 40' or less tends t o promote t h e formation of crystals. When the contents of the flask have assumed t h e room tedperature, fill with water t o within 2 t o 3 cc. OS t h e mark, rotate t o uniformity a n d allow t o stand overnight. Fill t o mark with water, mix thoroughly, then after standing one-half hour withdraw a 50 cc. aliquot of clear liquid by passing through a small ( 5 . 5 cm.) dry, closely-fitted filter into a graduated 50 cc. flask, rejecting, however, about 1 5 cc. of t h e first runnings, t h e latter being received in a n y convenient container for eventual later use, along with addi' tional filtrate, for t h e recovery of acetanilide. Transfer the j o cc. aliquot by pouring and washing t o a 2 0 0 cc. Erlenmeyer a n d titrate with 0.1 N sodium thiosulfate. If reference is had t o t h e composition of the insoluble addition product, constituting the basis for the foregoing separation,
(C2H50.CsH4NH.COCH3)2.HI.L, it will be noted t h a t , for every molecule of phenacetin involved, t w o atoms of iodine are required, hence from a titrimetric standpoint one a t o m of iodine is equivalent t o one-half molecule of phenacetin. If, therefore, t h e quantity of iodine expended in the formation of insoluble periodide is ascertained as the result of such titration, the quantity of phenacetin thereby involved is readily calculated from the expression, phenacetin = I(o.oo88go X N), in which 0.0088go represents the quantity of phenacetin in I cc. of a 0.1 N solution of this substance, N t h e normality of standard thiosulfate employed, while I represents t h e number of cubic centimeters of such thiosulfate corresponding. t o t h e iodine entering into combination with phenacetin isolated as periodide. The gravimetric determination of phenacetin may, if desired, be effected substantially as follows: I n the operation of filtering off the periodide, the latter is collected on t h e filter a n d washed with I O t o I j cc. of standard iodine solution, preferably by suction, then transferred together with filter (likewise a n y particles of precipitate eventually remaining in the graduated flask) t o a separatory funnel, using for t h e purpose not over 5 0 cc. of water. After discharging both free a n d added iodine with a few small crystals of sodium sulfite, the liquid is extracted with three 5 0 cc. portions of chloroform, each portion being subsequently washed in a second separatory funnel with 5 cc. of water. After washing a n d clearing, withdraw solvent through a small ( 5 . 5 cm.) dry filter into a 2 0 0 cc. Erlenmeyer, distill off most of t h e chloroform, transferring t h e residual 5 to I O cc. b y pouring a n d washing with fresh solvent t o a small tared beaker
Vol. 6 , No. 8
or crystallizing dish. Evaporate to dryness on steam bath, cool, a n d weigh. ACETANILIDE-should t h e combined weight of the phenacetin-acetanilide mixture be known, t h a t of the latter constituent can be determined by difference, or, if necessary, estimated directly from a second aliquot of filtrate from the phenacetin periodide. T o this end, transfer t o a separatory funnel by means of a pipette 2 5 t o 30 cc. of t h e clear liquid, decolorize with sufficient solid sodium sulfite, a d d solid sodium bicarbonate in slight excess, follow with I to 2 drops of acetic anhydride, then extract with three 60 cc. portions of chloroform, passing solvent when cleared through a small, dry filter into a 2 0 0 cc. Erlenmeyer, from which the chloroform is distilled by the aid of gentle heat down t o about 2 0 cc. Now a d d I O cc. of dilute sulfuric acid ( I cc. of concentrated acid t o I O cc. of water) and digest product on steam bath until the aqueous residue has been reduced one-half, add 2 0 cc. of water a n d continue digestion one hour, add a second 2 0 cc. portion of water and I O cc. of concentrated hydrochloric acid, then titrate very slowly, drop by drop, with standard potassium bromidebromate ( I cc. of which is equivalent t o j to I O mg. of acetanilide), until a faint yellow coloration persists. While adding this reagent, t h e flask should be rotated sufficiently t o agglomerate the precipitated tribromoaniline a n d thus clarify t h e supernatant liquid. The number of cubic centimeters of standard bromide solution required t o complete t h e precipitation, multiplied b y the value of I cc. in terms of acetanilide, will give the quantity of this substance present in t h e aliquot taken. COMMENT AND SUGGESTIONS
T h e preliminary or gross separation of phenacetin a n d acetanilide from complex mixtures is materially lengthened, if the preparation contains, in addition t o those substances, caffeine or antipyrin or both, in which event i t would be necessary first t o subject the mixture of four ingredients t o hot digestion with dilute sulfuric acid in order t o convert phenacetin and acetanilide to phenetidine .and aniline sulfates, respectively, from which caffeine a n d antipyrin may be easily separated by means of chloroform, after which operation phenacetin and acetanilide should be regenerated b y treating the aqueous-acid solution of the corresponding sulfates with solid sodium bicarbonate in slight excess, thereupon with a few drops of acetic anhydride, followed by extraction with chloroform.' I n the operation of transferring t h e acetous solution of phenacetin-acetanilide mixture t o the graduated flask containing standard iodine, great care must be exercised t o the end t h a t none of t h e dissolved substances crystallize out as such during or after the transfer, either in the liquid or about the neck of the Erlenmeyer, since a n y undissolved phenacetin introduced into the iodine reagent would fail in obtaining its full complement of iodine, thus vitiating t h e determination. The necessary transfer is most conveniently effected, and indeed without loss, by the use of a n Erlenmeyer provided with a lip, a form easily 1
PYOC. A 0 A
C ,U S Dept.
A g r , Bur. C h e m , Bull 162 (1912). 197.
Aug., 1914
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
made in t h e laboratory from t h e ordinary type b y heating t h e neck of flask in a moderate blast flame, t h e n by t h e aid of a file or other suitable instrument pulling down t h e rim t o t h e desired pitch. T h u s modified, the flask delivers aqueous solutions with little or no tendency t o r u n down on t h e outside of neck. T h e standard solution of iodine employed in t h e foregoing separation a n d t h e one giving t h e best results has a strength slightly above 0.2 N , t h a t is, a solution containing 30 g. of iodine a n d 40 g. of potassium iodide to t h e liter. T o prepare, dissolve t h e potassium iodide in t h e least possible quantity of water, a d d t h e iodine a n d after complete solution, dilute to I liter. Twenty-five cc. of this reagent, t h e volume t a k e n for each determination, are standardized with a solution of sodium thiosulfate containing 30 g. t o t h e liter, t h e value of which has in t u r n been ascertained b y titration with very carefully purified iodine. T h e e n d point is best observed b y adding t o t h e liquid toward t h e close of titration I t o 2 drops of freshly prepared starch solution. I n measuring off t h e standard iodine, make readings b y t h e aid of transmitted light. This iS easily done b y holding a n electric bulb just back of t h e burette, t h u s bringing into sharp relief t h e lower meniscus. F o r this a n d similar iodometric operations, very pure iodine was prepared b y dissolving t h e commercial resublimed product in concentrated aqueous potassium iodide, pouring t h e clear liquid into a large volume of water, filtering a n d washing t h e finely precipitated iodine o n a porous plate several times with water, t h e n drying first in t h e air a n d finally in a desiccator over sulfuric acid, where it is kept for future use in a glassstoppered weighing tube. T o standardize t h e sodium thiosulfate, weigh out in a small glass capsule (about ‘/2” high a n d 6/s’’ diameter), provided with a closelyfitting glass cap or stopper, a b o u t 0.3 g. of pure iodine, which together with capsule a n d cover are transferred t o a 2 0 0 cc. Erlenmeyer, containing 0.5 g. of potassium iodide dissolved in I O cc. of water. After complete solution, titrate the iodine with sodium thiosulfate, using I t o z drops of starch solution as indicator. I n t h e qualitative examination of preparations or mixtures, of which phenacetin alone is a known or declared ingredient, suitable tests should be applied in order t o verify the presence or absence of aqetanilide, such as are prescribed in t h e U. S, Pharmacopoeia or described in Allen’s “Commercial Organic Analysis.’’ For the identification of phenacetin, either alone or in admixture with acetanilide, t h e following test i n addition t o those ordinarily employed for this substance will be found of value: T o I t o 2 mg. of sample in a test tube a d d a drop of acetic acid, 0.j cc. of water a n d I cc. of 0.1N iodine, warm mixture t o a b o u t 40°, then a d d a drop of concentrated hydrochloric acid. Almost immediately if phenacetin alone is present, or on cooling a n d agitating t h e liquid if sample consists in large p a r t of acetanilide, t h e iodine addition product of phenacetin separates in t h e form of reddish brown leaflets or needle-like crystals. I n the presence of considerable acetanilide, the periodide first separates as minute oily globules, which on vigorous
669
shaking gradually become crystalline aggregates. This test is so delicate t h a t as little as 0.5 mg. of phenacetin may, if alone, be detected in form of its characteristic periodide. SYNTHETIC PRODUCTS LABORATORY, BUREAUOF CHEMISTRY DEPARTUENT O F AGRICULTURE, WASHINGTON
COMMERCIAL PAPAIN AND ITS ASSAY By H.M. ADAYS Received April 24. 1914
A recent article b y William Mansfield’ gives a clear idea of t h e cultivation, preparation a n d adulteration of t h e commodity papain. T h e adulteration from t h e commercial standpoint is especially interesting, i n view of t h e fact t h a t about 50 per cent of t h e samples received were found t o possess so little digestive power t h a t they are practically worthless. It has long been noticed in this laboratory t h a t t h e dark, l u m p y samples invariably give t h e best digestive strength. It seemed t h a t t h e darker, the more crude t h e appearance, t h e better t h e y were. Occasionally a comparatively light colored sample would show a fair degree of activity, b u t such a n occurrence was very rare indeed. This led t o a n investigation, with t h e result t h a t in t h e poor samples starch was always found t o be present in very marked quantities, while good samples showed no perceptible trace. Mansfield corroborates this with his statement t h a t a large portion of t h e papain on t h e market is adulterated by adding wheat or rye bread crumbs or by pouring t h e papain juice over t h e breads a n d t h e n grinding. This discovery of starch instituted a preliminary test, which was applied t o every sample of papain received. A small portion of t h e finely ground sample was placed on a white porcelain surface a n d a few drops of a weak solution of iodine added. T h e presence of starch was t h u s immediately noted by t h e appearance of a blue color and, with a little experience, a rough estimate could be made, by t h e intensity of this color, as t o t h e digestive value of t h e sample. T o further illustrate this, a few experiments were carried out, showing t h e digestive strength of t h e papain a n d t h e amount of starch present. I n these experiments a high-grade papain was used as a standard a n d called IOO per cent. T h e others are given in t e r m s of this standard. T h e digestion was carried on a t 5 j” C., with frequent shaking for five hours. Finely ground beefsteak was used as t h e material t o be digested a n d distilled water as a medium. residue standing 1 hour
Percentsee as cornpared with standard 100
12.5 13 13 13 6 5.25
35 42 40 40 40 85.7 100
Cc. of -.
SAMPLE Standard.. . . . . . . . . . . . . . . . . . 5 . 2 5 1 .......................... 15 2 .......................... 3 ..........................
........................... 5 . ......................... 6 .......................... 7 ..........................
Percentage starch 5;:4
57.1 58.7 58.3 55 20
..
It was observed in t h e above experiments t h a t when large amounts of starch were present, t h e lower portion of t h e residue was white in color instead of having a greenish tinge as in t h e good samples. Besides starch, pepsin is sometimes used as a n adul1
J. A m . Pharm. Assoc., 1914, p .
169.
