Table
Sample A
B C D
Vol. 16, No. 7
INDUSTRIAL AND ENGINEERING CHEMISTRY
432 111.
Typical Analyses of Commercial aminopentane I (Precipitstea dried 16 hourd Found, % Sample 8 4 . 1 , 8 3 6.83.7 E F 96.8,96 h 9 6 . 7 80.7.80.5 86.2,86 2
G
H
1 -Diethylamino-4Found, g, 78 1 78 1 7 7 . 9 96'3'98.3'96.6 53 8:83.8:83 9 81.5,Sl.O.81.8
The gravimetric determination of 1-diethylamino-4-aminopentane consists of precipitating it as the dithiocarbamate from aqueous acetone solution containing about 2% water, collecting the precipitate on a tared filtering crucible, washing with acetone, and drying in vacuum over calcium chloride. The acetone used in the following procedure was dried ovw potassium carbonate and filtered. PROCEDURE.About 1 gram of the amine sample was weighed to the nearest 0.1 mg. into a 1OO-ml. beaker. Without delay, 20 ml. of acetone wcre added by washing down the sides of the beaker, and this was followed by 0.75 ml. (I5 drops) of water T o the resulting solution were added 10 ml. of a 15% (by volume) solution of carbon disulfide in acetone. The mixture turned light brown, and after a few seconds a white crystalline precipitate began to appear. The mixture was stirred with a small glass rod for about one minute or until precipitation was largely complete, and then it was allowed 40 stand. After 0 Fi hour, 25 mi. of acetonc were added, and the mixture was well stirred and allowed to stand for an additional 0.5 hour. The precipitate was loosened From the walls of the beaker with a rubber-tipped rod, and the acetone solution was decanted through 8 tared filtering crucible. The precipitate was washed by decantation with two 10 to 15-ml. portions of acetone and then transferred to the crucible with acetone.
After the precipitate had been sucked as dry as possible, the crucible was placed over anhydrous calcium chloride in a vacuum desiccator which wm evacuated to 5 to 10 mm and allowed to stand a t room temperature. The precipitate was weighed after drying for at least 5 hours and preferably longer. As obtained by the above procedure, the precipitate had the The effect of the length of time formula CIOH?ZN~S~.~/~HIO. of drying the precipitate in vacuum over calcium chloride is indicated in Table I. The weights remain constant between 16 and 25 hours, but a t 46 hours some loss becomes apparent. In later determinations on commercial samples, the weight became almost constant after drying about 5 to 8 hours. The optimum time for drying is, therefore, probably between 5 and 46 hours. Analyses of mixtures containing known quantities of I-diethylamino-4aminopcntane are presented in Table 11. Two of the compounds used in the mixtures, B-diethylaminoethanol and 1-diethylaminopentanone-4, are commonly present as impurities in I-diethylamino-4-aminopentane. The analysis is unsatisfactorv only in the case (No. 6 ) in which 1-diethylarnino-4aminopentane is a minor constituent of the mixture. In Table I11 are listed some typical analyses on commercial samples of 1-diethylamino-4-aminopentane. The agreement between duplicate and triplicate determinations is cousidercd highly satisfactory for a method of this kind. LITERATURE UTED
(1) Hofmann, Ber., 5, 241 (1872). (2) Ristenpart, Ibid., 29, 2527 (1896). (3) Strack, 2.physiol. Chem.,180,198 (1929). (4) Zahlova, Collation Czechoslov. Chem. Commun., 2, 108 (1930) I
Analysis of Solutions of Ethyl Ether, Benzene, Ethyl Alcohol, and W a t e r WILLIAM E. SHAEFER Hercules Experiment Station, Hercules Powder Company, Wilmington, Del.
A method for the analysis of mixtures of ethyl ether, benzene, ethyl alcohol, and water has been developed It has been applied to three synthetic mixtures containing 1 to 1 5 % ethyl ether, 1 to 30% benzene 5 3 to 84% ethyl alcohol, and 7 to 15% water and shown to yield ierults which, when expressed as per cent of a component present, have an accuracy and a precision of about 1%.
the sum of the other three components. The method is a simple one which requires no expensive equipment. Benzene may also be determiued on an original sample by using the recent,ly published colorimetric methods of Dolin (a) or Baernstein (9), which were not available a t the time the method described in this paper waa being developed. DETERMINATION
V
ARIOUS methods are in use for the determination of ethyl ether, benzene, and ethyl alcohol individuzlly in the presence of water. Although Masson and McEwan (IO),Desmaroux ( 4 ) . and Kubias (?) studied ternary mixtures of certain of these components with water, no rapid procedure has been available for the complete analysis of quaternary mixtures of water and sppreriable quantities of each of these solvents. The method described in this paper WFS developed for control purposes only and cannot be used for the analysis of mixtures of unknown composition. In the following method the ether is driven off and determined by loss in weight; the benzene is determined by measuring (a) the water-insoluble portion of the residue and ( b ) the water-immiscible portion that remains in a distillate from this ether-free residue after removing the alcohol from the distillate by oxidation. Alcohol and water are determined on original samples-alcohol by acetylation and water by the Karl Fischer method. Any one of the four components not present in a small quantity, can be satisfactorily determined by the difference between 100% and
OF ETHER
Preliminary experiments showed that ether could not be separated easily and sharply from benzene and alcohol by distillation through a simple column having a minimum holdup. However, it can be separated well from the other components if the sample is first treated with an equal volume of water, regardless of the fact that a two-phase system may thus be formed.
PROCEDURE. A sample of approximately 100 ml. is weighed in a 300-ml. round-bottomed flask containing a few particles of Carborundum, about 100 ml. of water are added to the flask, and the whole is weighed again. The flask is attached to a %bulb Snyder column (IS) as indicated in Figure 1. A rather strong current of air is directed against the lower bulb of the column t o ensure adequate refluxing, then the flask is heated gently with a flame until the distillation starts. The precautions which make this operat,ion a safe one are shown in Figure 1. The heating must be conducted cautiously in case there are two liquid layers in the flask. The flask is heated until the thermometer shows a vapor temperature of 52' C., and the temperature is maintained as close as possible to 52' for 3 minutes. The column is allowed to drain for 1 minute; the flask is removed and weighed again. The decrease in weight is the weight of ether in the sample.
433
ANALYTICAL EDITION
July, 1944
The distillation is continued until a volume of 20 to 25 ml. has been collected in an Eggertz tube or in a 5o-ml. buret a t the rate of 1.0 to 1.5 ml. a minute. Fifteen milliliters of 3'7 potassium dichromate solution and 2 of concentrated hydrochloric acid are added to the distillate. The mixture is shaken vigorously and allowed to stand for a t least 15 minutes. Exactly 10.0 ml. of gasoline or ne htha are added with a n accurate pipet or &.met. The mixture is again shaken and allowed to stand until the la e n separate. The volume of the upper %yer is read. This volume, less 10.0 ml., is the volume of benzene in the benzene-alcohol wat,er distillate. From the total volume of benzene found in the two fractions, the per cent of benzene in the sample is calculated. To facilitate this calculation, it may be stated that the density of benzene varies from 0.878 a t 20" to 0.868 a t 30'.
A.
..
Specimeii No.
I.
Acetylrtion of Ethyl A l c o h o l Alcohol Water, by Present, Karl Fischer by Alcohol Found Method Difference by Acetylation) Table
% 1
2
DETERMINATION OF ALCOHOL
%
7.22 7.24 Av. 7.23 7.80 7.70
92.77
Av. 7.75
92.25
% 90.77 90.79 90.78 90.45 90.59 90.78 90.61
Extent of Acetylation of Alcohol
% 97.9
98.2 Av. 98.1
DETERMINATION OF BENZENE
When a considerable proportion of benzene is present, it has been found advisable to determine it by measuring (a) the waterinsoluble portion of the residue from the ether distillation and ( b ) the fraction of the water-soluble portion of a distillate from this residue that is not oxidized by 3% potassium dichromate and concentrated hydrochloric acid. These reagents oxidize the alcohol in the distillate. This procedure was developed by Babington and Tingle (8). I n case only a little benzene is present, there will be no water-insoluble portion in the residue from the ether distillation, and the determination will consist only of measuring fraction b i . e . , the benzene dissolved in the residue.
The original sample is analyzed for alcohol by the usual pyridine acetylation method ( I d , 16). I n applying thie method, particular attention must be given to the size of the samples taken. If more than 30% water is present, i t is advisable to determine the alcohol by some other method. To make this reaction proceed to the maximum extent, B large excess (at learrt 300%) of acetic anhydride is required. The acetylation of ethyl alcohol haa been found to be 99.1% complete when acetyl chloride is used arr the reagent (14), and Moore and Blank ( 1 1 ) recently found that glycerol is acetylated to the extent of 99.3% by acetic anhydride in pyridine. Under the usual analytical conditions of using acetic anhydride in pyridine, the degree of acetylation of two specimens of 95%-bcy volume ethyl alcohol was determined. Assuming that the alrohol contained no appreciable impurity other than water, the results in Table I show acetylation to 98% of the stoichiometicvalue; therefore a correction factor of 1.02 was applied in calculating the results for ethyl alcohol in the quaternary mixtures reported in Table 11.
PROCEDURE. In preparing 2.4 N acetylation reagent, pyridine containing about 0.35% water is used to prevent the resin formation that would otherwise occur when the reagent is heated (16). Malm, Genung, and Williams (9) have shown that the addition of water is unnecessary when the reaction is conducted a t a lower temperature and with a less concentrated reagent. Twentyfive-milliliter portions of reagent are placed in each of a number of Erlenmeyer flasks. Assuming the water content of the material analyzed to be 15% or less, samples of approximately 0.8 gram are weighed directly into the reagent from a Smith weighing buret. If a greater proportion of water is present, the sample must be correspondingly smaller. I t is helpful to place a few particles of Carbolvndum in each flask. The flasks containing reagent only, for blank determinations, and those containing reagent plus samples are attached to water condensers whose inner surfaces are dry and refluxed for a t least
PROCEDURE.The residue left aftfr the distillation of ether is cooled. If this cooled residue consists of two layers, they are separated and the benzene is determined in each of them separately as follows: The contents of the h s k are poured into a 250ml. separatory funnel, and 10 ml. of saturated sodium chloride solution are added. The flask need not be rinsed. The mixture is shaken vigorously. The lower layer is transferred to the distillation flask Dreviouslv used. The upper 'layer in "the separatory funnel is washed twice with an approximately equal amount of water, and the Table II. Analysis of Synthetic Mixtures Synthetic wash water is transferred each time to LMixture Analysis Ether Beneene Alcohol Water the distillation flask. This treatment No. No. Present Found Present Found Present Found Present Found Total removes alcohol from the benzene. % % % % % % % % The benzene is then transferred either 1 1 1.5 1.6 30.2 29.9 52.7 53.2 15.6 15.7 to a dry 50-ml. Eggertz tube or to a buret 2 1.3 29.5 54.4 15.8 which has previously been filled with 3 1.5 .. 53.5 15.4 .. 53.1 4 benzene to the lowest graduation mark. Av. 1.5 29.7 53.6 15.6 100.4 The volume of the benzene is read. The separatory funnel is rinsed with 2 1 14.8 15.1 14.7 14.9 56.3 56.8 14.2 14.3 2 14.1 15.3 55.2 14.2 benzene-free ethyl alcohol into the dis3 14.4 14.6 58.3 14.3 tillation flask which contains water, Av. 14.5 14.9 56.1 14.8 99.8 alcohol, and a small amount of dissolved 3 1 7.5 $.: 1.0 2.: 84.a g.? 7.2 0 benzene. The flask is attached to the .c ".s . ." 8.4 0.7 85.6 7.1 5 Snyder column and condenser, and the 8.1 0.8 85.2 7.2 101.3 Av. solution is heated gently, so that the 0.4 0.3 0.7 0.1 Average error distillation will start slowly. A n air 1.7 0 . 2 Maximum error 0.9 0.7 current is not directed against the lower bulb of the column in this distillation.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
434
15 minutes. The condensers are rinsed with water and the solutions are cooled below 20" C . and titrated with approximately N sodium hydroxide. During this titration, the solution should be shaken vigorously and care should be taken not to overstep the end point. As an additional precaution against sa onification of ethyl aretate (luring titration, it is well to add the aliali slowly. DETERMINATION OF WATER
Regardless of the amount of water present in a solution, its water content may best be determined by the use of Karl Fischer reagent (1, 6). In applying this method, samples containing about 150mg. of water should be measured from a Smith weighing buret and placed directly in freshly dried 150-ml. balloon flasks containing 25 ml. of anhydrous methanol. It is preferable to make the tit,rations electrometrically, using a dead-stop end point (8). ANALYSIS OF SYNTHETIC MIXTURES
The results of a number of analyses of three synthetic mixtures, shown in Table 11, are considered sufficiently accurate for a routine ront rol method. ACKNOWLEDGMENT
The author wishes to acknowledge the wistance of the late Walter Giinther in making many of the analyses.
VoL 16, No. 7
LITERATURE CITED
(1) Alniy, E. G., Griffin, W. C., and Wilcox, C. S., IND.ENQ.CHBY., ANAL.ED., 12,392-6 (1940). (2) Babington, F. W., and Tingle, A., J. IND.ENQ.C ~ M .11, , 666-6 (1919). (3) Baernstein, H. D.,IND. ENQ. CHBM.,ANAL. ED., 15, 251-3 (1943). (4) Desmaroux, hl., A f h . poudres, 23,285-99 (1928). (5) D o h , B. H., IND.ENQ.CHEM.,ANAL.ED., 15,242-7 (1943). (6) Fischer, K.,Angew. C h a . , 48,394-6 (1935). (7) Kubins, J., Chem. Ohror, 12,543(1937). (8) McKinney, C.D.,Jr., and Hall, R . T.,IND.ENG.CHEM.,ANAL. ED.,15,460-2 (1943). (9) Malm, C.J., Genung. L. B..and IYilliams. R. F., Jr., Zhid.. 14, 93540 (1942). (10) Masson, I.. and MrEwan. T. L., .I. SOC. Chem. Z n d . , 40,2932T (1921). (11) Moore, J. C.,and Blank, E. W., Oil and Soup, 20, 178 (1943). (12) Shaefer, W. E., IND.ENG.CHEM., ANAL.ED.,9,449-60(1937). (13) Simons, J. K., and Wagner, E . C., J . Chem. Education, 9, 12241 (1932). (14) Smith, D.M.,and Bryant. U'. M . D.,J . Am. Chem. Soc., 57, 61-5 (1935). (16) Verley, A,, and Bolsing, F., Be?., 34,3354-8 (1901). (16) Wilson, H.N.,and Hughes. W. C., .I. SOC.Chem. Id., 58, 747T (1939).
Determination of Carbon-Linked Methyl Groups W. U. S.
F. BARTHEL AND F. B. LAFORGE
Department of Agriculture, Bureau of Entomology and Plant Quarantine, Washington,
IK
COXXECTIOK Kith investigations of pyrethrolonc (4) the authors have drawn important conclusions from the carbon-linked methyl content'of various fractions and derivatives. For the determination of this grouping they have employed the method described by Pregl ( 5 ) , which is essentially that of Kuhn and L'Orsa (9), based on chromic acid oxidation of the sample and titration of the resulting acetic acid. Since many determinations were required, some modifications and simplifications in the original method were introduced. I n general, little use has been made of terminal-methyl determinations in analytical studies of organic compounds, perhaps because theoretical values are seldom obtained except with certain types of groupings. Although in general straight-chain compounds furnish the theoretical yield of acetic acid with great precision, other groupings, such as a single methyl group attached to an aliphatic ring, usually yield somewhat less than loo%, and the result must be considered in connection with that furnished by a reference compound. I n many cases where more than one methyl group on the same carbon atom is involved, or where methyl groups are attached to aromatic rings, this method seems to be of doubtful value. The special problem was to distinguish between the two formulas for pyrethrolone-formula I (or similar compounds with the grouping C=CH-CHa) and formula 11-and to estimate the proportions of earh in mixtures. CHI
H2-~ ~ - c H = c = c H - - C H s HO---
L
I
CHa
H
D. C,
The terminal-methyl determination of Pregl for carbon-linked methyl groups has been modified for more rapid determinations. The terminal-methyl number, or the number of mole equivalents of acetic acid produced from a mole equivalent of substance, has been determined for certain reference compounds.
In both formulas the methyl group attached to the pentenolone ring would, from analogy with similar known structures, furnish about 0.8 mole of acetic acid per mole of compound, which is about the value that should correspond t o formula 11. Formula I should furnish a value of about 1.8, because of the second terminal methyl. I n the special case of pyrethrolone and its derivatives very sharp and reproducible results were obtained, as is shown in Table I. In addition to making changes in the method, the authors have determined the amount of acetic acid furnished by a number of structures, especially of cyclic compounds. EXPERIMENTAL
The changes made in the original directions consist in employing the apparatus (Figure 1) designed. by Clark (1) for use in acetyl semimicrodeterminations, and in eliminating the redurtion of the excess chromic acid with hydrazine. From 20 to 30 mg. of sample are weighed on a iece of cigaret r p e r in the case of solids or, if a liquid, in a s m a t glass capsule. he sample is placed in the oxidation flask, A , together with 5 ml. of cold oxidizing mixture made by adding 20 ml. of concentrated sulfuric acid to 16.8 grams of chromic anhydride dissolved in 100 ml. of water. The finger condenser, R, is put in the neck of the flask, and the mixture is refluxed over a microflame for 1.5 hours. The finger condenser is then removed and washed free of acid with as little water as possible, the washings being allowed to run into the flask. Seven grams of magnesium sulfate are added, and the fiask is set up for steam distillatmion. The b e is replaced under the flask durin the distillation in order to concentrate the contentg of the flas! while 50 rnl. of distillate are being collected. The distillation is then titrated with a 0.05 N barium hydroxide solution to the neutral point of phenolphthalein.
