Semimicro Techniques Employing Small Sealed Vessels for Determination of Acids, Bases, and Esters DONALD MILTON SMITH, JOHN MITCHELL, JR., AND ANNETTE M. BILLMEYER Polyehemieals Department, E. I. du Pont de Nernours & Co., h e . , Wilmington, Del.
HE equipment for chemical antnslyses of organic compounds Ttends to be bulky, and the macromethods require relatively large amounts of sample. Preliminary studies in the authors' laboratory have indicated that many functional group analyses may be made in small sealed vessels. Use of these standardized containers permits saving of considerable space and simplification of many techniques, while the semimicro scale requires only small amounts of reagents and sample. The basic tools of this system of analysis are phannaceuticaltype serum bottles with pressure seal stoppers, hypodermic syringes and needles, and a mpid-weighing analytical balance. The balance replaces the buret for most measurements. Weighiugs acourate to a few tenths of % milligram may be obtained readily, while volumetric measurements of comparable accuracy can be made only with special equipment. The pressure seal feature of the stoppers permits addition and removal of solutions through hypodermic needles without exposure to the atmosphere. Hypodermic equipment has been used to 8ome extent in analysis aud in small scale organic syntheses. For Karl Fischer reagent titrations Levy, Murtaugh, and Rosenblstt (IO) employed small tubes with tightly fitting serum bottle sleeved rubber stoppers. Hypodermic needles were used to introduce solvents, sample, and reagents. These authors also recommended the standard serum bottle as titrating vessel for the determination of moisture in penicillin sodium d t . Dean and Hawley (4, 6) described a novel field kit for use in the determination of chloride and oxygen in pond waters. A micrometer-syringe buret was employed. Some of the reagent bottles were fitted with rubber disks from 10-ml. penicillin vials. The disks, held in place by plastic Screw caps drilled with 0.25-inch holes, could be perforated repeatedly by hypodermic needles during withdrawal of the solutions. Harrison and Meincke (7) employed puncture sealing gaskets far polymerimtions in bottles, and Houston ( 8 ) devised a modified syringe for sampling latex during polymerization. Miscellaueous laboratory applications of hypodermic syringes were reported by Dunn (6),Kress (9),and Scallet ( I S ) . The present paper describes applications of these tools to the determination of acids, bases, and esters. The cylindrical serum bottles &reof 10- or 25-ml. capacity with a neck opening of about &mm. inside diameter (Figure 1 ) (see also B). The red rubber stoppers are provided with a hole closed by a I-mm. rubber membrane and a retractable flap which covers the entire neck of the bottle (these are standard stock items with many laboratory supply houses-e.g., Crttdog No. 2319, A. H. Thomas Co., Philadelphia, Pa.). One- and 2-mI. hypodermic syringes are employed, preferably equipped with Luer-Lok adapters for the 25- or 27-gage 0.75to I-inch needles. A rapid weighing balance is desirable, such as the Gram-atic balance stocked Figure 1. by Fisher Scientific Co. Hypode r Where feasible, the reagents required for indimio Syrvidual analyses are delivered through hypodermic inge and needles into the sealed vessels. Since the stoppers S e r u m Bottle are self-sealing, losses and Contamination are
-
oliminated. The effectiveness of the seal was demonstrated as follows: A weighed quantity of methanol was introduced through a stopper into a 10-ml. vessel. The stopper was pierced four times with the needle. After 4 hours on a steam bath, the vessel was removed and allowed to cool to room t.emperature. No weighable lass of methanol wm evident. Consequently, safe storage of reagents can be made in the exact quantities required for single determinations. DETERMINATION O F ACIDS AND BAS
Reagents. Standard 1 M aqueous sodium byL aqueous hydrochloric acid is used as reagent for acids or bases, respectively. Phenolphthalein, thymolphthalein, and thymol blue me suitable indicators for acid determinations. Bromophenol blue and thymol blue w e satisfactory for base anslyses. Procedure. One drop of indicator solutiou is added to each of several 10-ml. ~ e r u mbottles. The bottles are stoppered and weighed, To prepare for acid determinations, standard 1 M sodium hydroxide reagent (usually about 1 ml.) is added t o the vessel through a hypodermic syringe fitted with a 25- or 27-gage needle. A second needle is inserted through the stopper t o serve as a vent. To prepare for the determination of bases, standard 1 M hydrochloric acid reagent is added to the sealed vessels. The bottles are weighed to determine the esact amount of reagent added. These preparations can be made a t any time prior to the analysis, and the bottles can be stored until ready for use. A portion of the sample tc be analyzed is transferred to a 2-ml. hypodermic syringe. The needle of this syringe is inserted through the rubber stopper of a vessel containing the desired reagent, and t,he sample is added esrefully until the end point has been reached. A second hypodermic needle may be used as a vent. However, if volatile liquids are present, potential losses
_I_ I _ ___"
qurtntiby of reagent in the 'small 'sealed vessel. The technique WAR illustrated in a previous publication (8). DETERMINATION O F ESTERS
The saponification procedure for esters was adapted from the macro and semimicro volumetric methods reported previously (1,9). Reagents. Approximately 2 N sodium hydroxide in 90% methanol is used BS saponification reagent. Phenolphthalein, thymol blue, or thymolphthalein serve8 as indicator. Standard 0.5 )VI aqueous hydrochloric acid is employed far backt,itratition. Procedure. Approximately 1 ml. of 2 N alkali reagent is weighed into CT 10-ml. sealed vessel containing 1 drop of indicator solution. Then 1 ml. or less of sample, containing up to 1 milliequivalent of acid plus ester, is weighed into the reagent, The vessel is placed in a 60' f 1" C. water bath for 30 minutes, after which it is removed and coaled in an ice bath. Excess alkali is ddermined by titration with standard 0.5 J4 hydrochloric acid, ANALYTICAL RESULTS
In those procedures employing caustic as a standard reagent an indicator was desired which would retain its color in the alkaline solution. The results of color stability tests on four indicators are shown in Table I. In all ca8es 1 drop of indicator solution was added to 1 ml. of caustic solutiou. In all alkaline solutions containing phenolphthalein the pink color returned during titration with hydrochloric acid. The end point appeared normal, even though the caustic containing this indicator had stood for as muoh as 8; week. Solutions of representative acids were analyzed by the small sealed vessels technique. Results are given in Table 11. 1847
ANALYTICAL CHEMISTRY
1848
Table I.
Color Stability of Indicators :in Caustic Solution -I-.
lllllr
Alkali Conon., N 2.0 1.0 0.5 2.0 2.0 2.0
Indioztor Phenolphthalein Phenolphthalein Phenolphthzlein ThyrnolDhtirslein Thymol blue Trutest
r *"..!>.n'"Urn6
I.
of Indioator 30'seoonds 1 minute >10 minutes >1 week > 1 week 1 day
With the exception of beneaic and p-toluene sulfonic acids, which weredissolved inethanol, the acids were prepared in aqueous solutions. In preparing for boric acid analyses about 0.7 gram of mannitol was weighed into the vessel before addition of the sodium hydroxide reagent. The averages of triplicate determinations, as shown in column 3 of Table 11, compared favorably with the concentrations measured by macro volumetric titrations in calibrated burets, as shown in column 2. Based on the total number of determinations reported in Table 11, the relative precision to be expected in analyses for acids is *O.l%.
Table 11. Analytioal Data for Acids
-Borio "....." Formic
Concn., Wt. %" 4.65 0.01 RR 3.64 A 0 + 0.01 0 "9 11.03 3z 0.02 10.24 10.01 55.20 f 0.02 8 . 2 1 f 0.01
BenSOio
12.06b 12.06 j; 0.01
Acid Hydrochlorio Pnrmin
Aoetio Aoetio Butyric Adipic
p-Toluene sulfonic
+ + -
1.45b
Acid Found. Wt. % 4.65 f 0.01
**3.65 7" f i n 0.00 11
11.07 f 0 . 0 3 10.26 f 0.01 55.19 10.04 8 . 1 8 10.01 1 . 4 5 +oo.oo 12.06 10.01 12.07 f 0.01
Unless otherwise indioated coneentmtiaa. were bssed on triplicate titrations 01 5 t o 10 milliequivalents of sample with atandaid 0.1 N sodium hya
droxide. b Crarimetric wepsr8tion.
Similar data for bases analyzed in triplicate are presented in Table 111. The inorganic compounds and methylamine were prepared in aqueous solution; methanol was used as solvent for the remaining amines. Thymolphthalein was used an indicator for the sodium hydroxide sample and thymol blue or bromophenol blue for the remaining materials. The relative precision averaged 0.2%.
Table 111. i(nalytiea1 Data for Bases Base Conon., Wt. %" Base Found. Wt. % Sodium hydroxide 3 . 6 7 10.01 3.67 f 0.01 Sodium carbonate 8.12 f 0 . 1 2 8.12 f 0.03 Methylamine 30.05 =t 0.05 30.09 =k 0.15 n-Butylsmine 19.86 f 0 . 0 2 19.83 0.06 Pyridine 95.25 =t 0 . 0 8 95.21 3z 0 . 1 9 " Pyridine . . : - .> 2$.0$ 0.02 :?.go 9.03 DeY'Ylllllllle *,.o+ I " . " O ',..5i)T"."~ Hexam?thrlenedia.mine 33.31 -t 0.10 33.22 10.05 PiperhZlne 12.47 =% 0.02 12.47 f 0.03 Tri-n-butylamine 23.57 +O.OO 23.54 0.04 Triethanolamine 27.46 =% 0.03 27.44 f 0.02 Results me average of duplimte or trlplica>e titrations of 5 t o 10 m i l k equivalents of sample with0.l N hydrochlorx a c d
+
+
+ +
A further indication of the precision of acid-base titrations a n the small sealed vessels scale was given by the titration of 1 gram ofO.1 M hydrochloricacid withO.l M sodium hydroxide. Aseries of five successive determinations showed a maximum relative deviation of *0.0670. The reverse titration technique could not be used conveniently for sodium carbonate analyses because of the liberation of carbon dioxide. Reliable results were obtained by titration of standard hydrochloric acid into the small sealed vmsel containiig the sodium carbonate solution plus phenolphthalein indicator,
Figure 2.
Modified Small Sealed Vessels
provided the titration was not carried beyond the bicarbonate stage. The titration was more easily controlled when 1 molar aqueous acetic acid was substituted for the hydrochloric acid and thymol blue indicator was used. Result8 from the analysis for sodium carbonate by titration with acetic acid are shown in Table 111. Results obtained on a variety of esters are given in Table IV. Most of the compounds were purified by distillation pfior to analysis. The data indicate a precision and accuracy of about *O.Z%, comparing favorably with other methods for the determination of esters. DISCUSSION
Preliminary data, have indicated that the small sealed vessel technique is also applicable to other analyses of organic compounds. Experiments in progress should lead to reliable pracedures for carbonyl compounds and acetals by oximation, and for alcohols by acetylation. The small sealed vessel technique should be readily adaptable to a micro scale. Probably less concentrated reagents and smaller vessels would be desirable for microanalyses. These versatile bottles also can be used as separatory funnels. The vessels permit easy separation of liquid layers. In the upright position the upper layer can be removed through a hypw dermic. By reversing the tube, the lower layer can be separated e,onveuiently. A double-necked flask with or without a sintered-
Ester iter Found. Wt. % Triacetin (9 6 99 6 f 0 . 2 Ethyl n-butyrst 99:s f 0 . 2 Ethyl isobutura. Isobutyl acetate Isobutyl isobutx Cyeloheryl isob (3) 99.9 1 0 . 3 Cyoloheryl valerate Distilled Cyolohcxyl isov~lerate~ Distilled m-Bntyl phthalate EastmanKodak 3) 99.7 0.1 a Ten determinations by macro a n d aemimiorornethods (I, 11) gave resultsof99.8 f O . 3 % . 6 Figures in parentheses represent number of individual determinations.
4y3 .E=;!;; p
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V O L U M E 24, NO. 11, NOVEMBER 1 9 5 2
1849
glass separator (Figure 2 ) serves as a convenient gas scrubber in a continuous system. The single-necked flask also can be used by employing two needles, one of which dips below the surface of the scrubbing liquid. Both types of tubes can serve as centrifuge vessels. For this purpose the double-necked tube permits direct removal of a lower liquid layer without disturbing the system. Also for these purposes a vessel with an elongated neck (Figure 2) often is useful. After suitable calibration, the long-necked flask becomes a pycnometer of the Reischauer type The information reported in this paper is intended to indicate that preliminary “mass” preparation of the bottles containing the required amounts of reagents permits significant savings of time, both over-all and during the actual analyses. Where analytical activities are spread over a considerable area, these reagent preparations may be made advantageously in one central location. The techniques offer a means for carrying an organic analytical laboratory to the source of the samples.
H. R. Roe, who aided in some of the experimental work reported
ACK-OB LEDGRIEYT
RECEIVED for review April 2 , 1952. Accepted June 30, 1952. Presented in part before the Division of Analytical Chemistry at the 118th 3leeting of the AYERICAX C n E M I c . 4 L SOCIETY. Chicago. Ill.
The authors are grateful to Walter Hawkins, G. E. Moore, and
in this paper. LITERATURE CITED
(1)
Bryant, W.AI. D., and Smith, D. AI., J . Am. Chem. Soc., 58, 1014-17 (1936).
( 2 ) Chem. Eng. S e w s , 29, 2282-4 (1951). (3) Chem. Week, 68,No. 20,24-5 (1951). (4) Dean, R. B., and Hawley, R. L., ANAL.CHEW.,19,841--2 (1947). ( 5 ) Dean, R. B., and Hawley, R. L., Pacific Sci., 1, 108-15 (1947). (6) Dunn, H. J., Chemist-Analyst, 39, 15 (1950). (7) Harrison, S. A, and Meincke, E. R., d ~ a CHEM.. ~ . 20, 47-8 (1948). (8) Houston, R. J.,Ibid., 20,49-51 (1948). (9) Kress, K. E., Chemist-Analust, 39, 17-18 (1950). 110) Levy, G. B., Murtaugh, J., Jr.. and Rosenblatt, M.,ISD. ESG. CHEM.,, ~ N A L .ED..17,193-5 (1945). (11) Mitchell, J., Jr.. Smith, D. hl., and Money, F. S.,I h i d . , 16, 410-12 (1944). (12) Scallet, B. L., Chem. Eng. S e w s , 29, 2983 (1951).
Separation and Analysis of Tar Bases by Countercurrent Distribution CALVIN GOLUMBIC Synthetic Fuels Research Branch, Bureau of Mines, Bruceton, Pa. OUSTERCURRENT distribution ( 3 , 6, has been emC ployed a i t h considerable success in the determination of the composition of the phenolic fraction (tar acids) of coal hydro12)
genation oils (9). Since homologous and isomeric pyridines, anilines, and quinolines usually have significantly different partition properties ( 7 , 8), the distribution method should also be applicable t o the separation and analysis of tar bases derived from coal by hydrogenation or carbonization processes, In this note, the experience gained in the analysis of known tar base mixtures is briefly summarized.
elsewhere (11, 12). In these calculations, optical densities of the organic layers in peak tubes free from overlapping band &-ere converted to weights by means of the known extinction coefficients of the bases. RESULTS AND DISCUSSION
The distribution patterns obtained for mixtures of picolines, toluidines, and quinolines are shown in Figures 1 to 3. These
MATERIALS AND PROCEDURE
The source and purity of the bases investigated have been recorded in previous publications ( 7 , 8). The distributions were performed in the 54-tube cylindrical instrument of Craig and Post (4). The solvent pair consisted of chloroform or cyclohexane and a citrate-phosphate buffer (2). The distributed samples were analyzed by ultraviolet absorption measurements a t wave lengths of maximal absorption, employing the Cary recording spectrophotometer. The composition of the mixtures was then determined by the requisite calculations, described in detail
Figure 2. Distribution Pattern of a Toluidine Mixture 1. p-Toluidine 2. m-Toluidine 3. o-Toluidine Solid circle represents theoretical
Table I. Analysis of Tar Base Mixtures by Countercurrent Distribution
Figure 1. Distribution Pattern of a Mixture of 3- and 4-Methylpyridine 1. 3-Methylpyridine
2. 4-Methylpyridine Solid circle represents theoretical
Mixture System 3-Methylpyridjne CHCla, 4-Methylpyridlne aq. PH 4 o-Toluidine m-Toluidine Cyclohexane, aq. pH 3.6 p-Toluidine 2-Methylquinoline Cyclohexane, 8-Methylquinoline aq. pH 3.4
Amount Trans- Present, fers Mg. 53 20 20 90
53
2o 20 2o 15 10
Amount Found, Mg.
20.7 21.2 19.2 19.9 19.0
14.5 9.7
Error, 3.5 6.0 -4.0 -0.5
-5.0 -3.3 -3.0
