470
ANALYTICAL CHEMISTRY
applied after addition of the phosp’horic acid, a clear solution was still obtained when the ammonia was added. Better colorimetric results were obtained when the solution was heated to drive off the nitric and hydrochloric acids. The colorimetric reference curve obtained using tin samples of known copper content, was a straight line. As excellent results Tvere obt,ained by using a Klett-Summerson filter S o . 59 (6) no spectrophotometric study was made of the blue copper amine color. The spectrophotometric curves published by previous investigators ( 5 ,6, 7 ) may not be applicable to the author’s method, because the hue of the blue copper amine color is changed by the presence of phosphoric acid ( 5 ) . The method described is designed for the routine determination of copper in tin-base alloys that contain 1 to 1 0 5 copper. The blue copper amine color will keep 24 hours without, change if the flasks are tightly stoppered to prevent t’he escape of animonia. Sickel, cobalt, and chromium interfere with t,he blue copper amine color ( 5 ) . These rlrments, however, are rarely present in tin-base alloys. Iron up to 5% was found not, to interfere with the determination, An attempt to hold up the tin in ammoniacal solution nic.rel>-
by the presence of tartaric acid without the presence of phosphates was not successful (3). I t would seem that considerable tin and antimony would be volatilized in driving off the hydrochloric and nit,ric acid-. Actual analysis, however, revealed that, most of the tin and nittimony remained in solution. The author has made a study of the effect, of phosphoric and pyrophosphoric acids on the precipit,at,ion of the common mct,als i n ammoniacal solution. LITERATURE CITED
(1) Ani. SOC.Testing Materials. “Methods of (‘hemica1 . h i l l > Metals,” p. 247, 1946. (2) Ibid., p. 249. (3) Galan, AI., and Schragei., S..Industrial Teat Laborator>-.Pliiladelphia Naval Shipyard, oral communication, 1946. (4) Mchlpine, R. K., and Soule, B. A , , “Prescott and Johnmi’Qualitative Chemical ;inalysis,” p . 497. S e w 1-ork, D. \ ‘ a i l Xostrand C o . , 1933. (5) Mehlig, J. P.. ISD. E s o . C H E M . . SAL. ED., 13, 533-5 (1941’. (6) Milner, 0 . I.,Ibid., 18, 94-6 (1946). (7) Yoe. J. H., and Barton. C . J., I b i d . , 12, 456-9 (1940). RECEIVED September 2 , 1947.
The opinions expressed in this article ai’? those of the author, and are not to be construed as representing the o f f i c i a l views of the Kavy Department.
Analysis of Chloroacetic Acid Determination of Dichloroacetic and Acetic Acids GEORGE 4. DALIN AND JEROAlE N.HAISISOHIV Sturcffer Chemical C o m p a n y , .Yew York Research Laboratory, .Yew I-ork, .Y. Y . The accuracj of the determination of dichloroacetic acid in chloroacetic acid is shown to be dependent on the quantity of reagent used. Regulation of the amount of reagents used and the addition of manganous sulfate bring the accurac) within the range required by material specifications. Determination of the acetic acid content bj difference is shown to be unsatisfactor? and a direct method inbohing titration after distillation M ith an added sol\ent is described.
C
HLOROACETIC acid achieved prominence during World War I as a raiv material in the manufact,ure of chloroacetophenone and analytical methods: were esbdlished for army use ( 2 ) . More recently, chloroacetic acid has become of import,ancc in manufact,uring 2,4-dichlorophenoxyacetic acid and carboxymethylcellulose, products which will be used on a large scale. Specifications for chloroacctic acid have been issued by purchasers and have included analytical methods similar to those described in the army report. This method in turn goes back to work done by Pool (I) and in brief depends on the following procedure: A sample is dissolved in wat,er caustic is added, and the solution is refluxed until the chloride ’is completely hydrolyzed. The monochloroacetic acid yields glycolic acid; dichloroacetic acid yields glyoxylic acid, which in the presence of alkali disproportionates t o sodium glycolate and sodium oxalate. From an ali uot, the oxalate is precipitated out with calcium acetate, and is ?etermined by permanganate titration. This procedure gives t.he dichloroacetic concentration.
-
The reactions involved are:
+ 6NaOH 2CH(OH)2C02Ka+ 4NaC1 + 2 H 2 0 2CH(OH)&02Ka + S a O H S a 2 C 2 0 4+ CH2(0H)CO2Na+ 2H20 CH&1CO2H + 2NaOH CH20HCOZXa*+NaCl + HzO 2CHClZCOzH
(1)
+
(2)
(3) A second aliquot is taken and the total chlorine is determined by the Volhard method. The chlorine as dichloroacetic acid is subtracted from the total chlorine to give the amount as monochloroacetic acid and thus the monochloroacetic acid concentra-+
tion. -4nother portion of the sample is dissolved in water and is titrated with standard alkali. Subtraction of the monochloioacetic and dichloroacetic acid values from the total acid, as determined with standard alkali, gives the acetic acid concent ration. The determination of trichloroacetic acid is not involved because the concentration i y negligible under the usual conditions of preparation. In order to test the method for the determination of dicliloi,oacetic acid, samples were prepared and analyzed. The r t w l r i were invariably low by factors ranging from 15 t,o 857,. Becauw calcium oxalate is soluble to the extent of approximately 7 mg. per liter a t 25” C. it seemed likely that, part of the discrepan(*\was due to the use of too much water during the procedure. It was noted that. when the tot,al quantity of permanganate used was small, it was very difficult to recognize the end point. Satisfactory titrat.ion with permanganate requires that manganouion be present. When the titer is large, this ion is produced during the first of the titration. In the revised procedure, as described below, these difficulties lvere satisfactorily eliminated by scaling down the quantities of reagents and vash liquids used, and t)y adding manganous sulfate immediately before the titration. DETERMINATION OF DICHLOROACETIC ACID I h iMONOCHLOROACETIC ACID
A sample weighing from 2 to 3 grams is dissolved in 40 ml. of water, and 14 grams of sodium hydroxide pellets are added. The mixture is refluxed, under a water-cooled condenser, for 1 hour. After cooling, the solution is made acid with concentrated hydrochloric acid, then neutralized with concentrated aqueous ammonia, and 3 ml. of eycess ammonia are added. The silica which
471
V O L U M E 20, N O . 5, M A Y 1 9 4 8 is precipitated a t this point can be filtered off, but' this was found to be unnecessary. The solution (or filtrate) is concentrated t o the saturation point, using glass beads to prevent bumping. After concentrating, and while the solution is still hot, 11 nil. of freshly prepared 5% calcium acetate solution are added, followed by 5 ml. of concentrated aqueous ammonia. The mixture is allovied t o stand, with intermittent stirring, for 1 hour, after which time the precipitate is filtered off by gravit,y on No. 40 Whatman paper. The flask and the precipitate are then washed successively with 20 nil. of dilute ammonia (1 t o lo), 20 ml. of 1 5 calcium acetate, and 20 ml. of water, following which the filter paper and precipitate are returned t o the flask. S o attempt is made to remove the last traces of precipitate from the flask, as it is subsequently used for the titration. Just before the titration of each sample 200 ml. of 1 t o 10 sulfuric acid are added, the mixture is heated to 70' C., and then 3 ml. of manganous sulfate solution (containing 2 grams per liter) are added. Standard pt'rmanganate (approximately 0.1 N ) is used for the titration. A buret of 5-ml. volume, graduated in 0.01 ml. and fitted ivith a wservoir, has been found convenient. Blank determinations are simultaneously carried through the entire procedure, with the same amounts of reagents. If there is any delay between the addition of the sulfuric acid and the titration, excessive attack on the filter paper takes place, resulting in a n irregular blank. The concent,ration of dichloroacetic acid is calculated as follows:
.
. 1
(nil. of t,it,er - ml. of blank) normal factor X 12.895
x
Table I shorn a comparison of results when varying quantities of reagents arc: used. In this procedure, approximatelj- 30 mg. of calcium oxalate would bcx formed from a 3-gram sample containing 2YGof dichloroacetic acid. JTlth 100 grams of water used as solvent and for washing, the loss of calcium oxalate would be approximately 0.7 nig. If the army method n-ere used, the loss would he about 3 mg., which is about 10cc of the total oxalate present. If an
/25
Quantity of Reapentsa 1 I 1 1 1 1 4.5 4.5 6 4c
Effect of Quantitj of Reagents Used on Dichloroacetic 4cid Results Dichloroacetic Acid Concentration Found,
x o . of
Known,
6 4. 5 5 4 3 4
2.40 2 06 100 b 2.4 2.05 3.50 2 05 3 00 2 OF
Replicates
5
2 3
52
:3,50
To
2.38 2.09 I102 2.30 2.05 3.48 1.76 2.52 0.72 0.5
i 0.02 I O . 0 1 i l', =t 0 09 0 02 0 02 i 0 04 =t0.13 i 0.04
**
Llultiples of amounts given in method. A160 inellides diliient and liquids. b Anrtlysiq of recrystallized dichloroacetic x i d c Result obtained in another laboratory. 0
c.xcessive amount of \\-ash wati,r is usid thc loss could prater.
tit,
V:I-!I
nrurli
J~ETERMINATIOIVOF ACETIC ACID IS CHLOROACETIC ACID
The specifications which have been issued r6cently limit the dichloroacetic acid content to approximately 2% and the acetic acid content to approximatel?; lCc. If t,he error in determining the concentration of acetic chloroacetic acid is of the order of 15, acid as determined by the difference betiwen two quantities, each of which is approximately 1005, (the weight of the sample and t,he combined w i g h t s of the chloroacids), \\-ill be complctely indeterminate. I n fact, it is surprising that negative values f o ~the , aretic acid content have never been reported. Obviously, acetic acid must be determined directly and not by difference. I t \?-asdecided to investigate separation hy distillat ion, but the comparative1)- large holdup in any sort of column and distilling head rulcd out the use of any of the standard tcxcli11 iques. -1s an alternative, thc, effect of adding an inert, interniediatc3\,oiling material was investigated. Xylene (boiling point 137" to 140' C.), methyl n-amyl ketonc (boiling point 150" C.), and di-n-butyl pther (boiling point 142" C.) were selected for study because their boiling points are well removed from those of acetic acid (boiling point 118" C.) and chloroacetic acid (boiling point 189 O (3.). Synthetic mixturee were prepared and distilled through a column 60 em. (2 fect) long and 10 nim. in inside diameter, packed with 'II6inch helices. The reflux ratio \\-as held constant at approximately 10 to 1. The distillate was collected in small fractions (rach of which was extracted with water if the inert material \vas water-immiscible). Thc fractions n-err titrated with standard alkali, and the acid was calculated as acetic acid. Fraction were collected until the ratio of acid value t o size of fraction bei me constant. The cumulative. arid values were then graphed against the cumulative distillatcx.
/ 00
2 2 c3
d
a
Table I.
0.75
u
5 0
a
w 0.50
z Q A
3
f
V
0.25
0
5
/O
CUMULATIVE
IS
20
25
DISTILLATE, ML.
Figure 1
K i t h xylc~neand the ketone as additives, the pot residues ~ I Y ~ I ~ L ~ discolorcd and the distillates fumrd on exposure to air, indicating that decomposition had taken place during t,he distillation. Since the pot temperature rose to approximately 170' C. in each case, decomposition was iuevit able. The ether was added i n much larger quant,ity, as a result of which the pot t,emperature rose only to 150" C.; the residue was colorless and no fuming was noted. Undoubtedly the same wsult could have been obtained by using about the same proportion of xylene or the ketone. Graphs of the xylene and ketone runs (Figure 1) showed that acid is cont,inuousl,v evolved. If the assumption is made that acid (other than the original acetic acid) vias evolved at a constant rate t,hroughout the distillation, the effect of the additional acid can be eliminated by extrapolating the straight portion of the curves back to zero distillate.. Table I1 gives the results obtained in this way. The value obtained nit,h xylene as the additive is someivhat low, but i t is likely that in thie, t,he first such experiment run, the distillat,ion should have been carried further. I t is also possible
ANALYTICAL CHEMISTRY
472 Table I I. Added Solvent ,\.I1.
50 Xylene
40 RIethyl n-amyl ketone 100 Di-n-butyl ether
.+cetic Acid Determination Acetic Acid Known Found Gram Gram 0.993
0.905
0.564
0.564
0.497
0,485
Chlorinated Acid Content Grams (50 RIonocliloroacetic acid 11 Dichloroacetic acid 50 RIonochloroacetic acid 50 RIonochloroacetic acid
impossible to prepare a completely neutral sample of the ketone by distillation from calcium oxide. -4pparently the precision of the method can be improved to any estrnt desired by increasing the size of the sample and amount of additive, as the acetic acid is very easily separated. T h r method should be capable of application to any series of homologous compounds for which a series of inert additives can hrl found. I t n-ould have to be established that relative volatilitics w r e not too much altcrrd. LITER-ITCRE CITED
that the acid was not completely extracted from the syl(,ne. The> procedure using the ket,one is t,he simplest in that the Icctorir~ i i soluble in a reasonable quantity of Tvater, and extraction i q thtsi~bi t \v:i,fore unnecessary. This is c q x ~ i a l l yintrresting k~c~~:iiisc~
(1) Pool, J. 1;. A , , Pharm. Teekblad'. 42, No. 8 , 16.5 (190.5) ( 2 ) U. S.. k m y Specifiratioris 4-503-15 (May 9, 1924).
Determination of Alcohol-Insoluble Solids and Sugar Contents of Vegetables J 4 3 I E S C. 3IOYEK -\YD KEA-SETH C . H O L G i T E .Yew Ebrk State .Igriculttcral Experiment Station, Genera, S. 1.. With the aid of a Waring Blendor and 8 5 7 ~alcohol, sugars are extracted froin frozen vegetables. The alcohol-insoluble solids content is determined hj filtering the macerate and drjing the residue. The alcohol in a small aliquot of the filtrate is evaporated and an aqueous solution of the residue is clarified by Somogyi's barium hydroxide-zinc sulfate procedure. For estimation of the total sugar content, an aliquot of the clarified extract is inverted with iniertase. The sugar content before and after in\ersion is determined bj Nelson's colorimetric method, using Somop! i's nelc copper reagent.
D
URISG a study of the losvc~sof soluble constituents in the
processing of vclgdahles, the need arose for a rapid mc~thod of determining the reducing arid total sugar contents. T h r d~ sirability of combining the sugar determinations with that oi alcohol-insoluble solids also became apparent : there w t w indications that the calculation of the constituent losses based o n the dry weight or total solids content would be erroneous becaust' of the altwed composition of the solid material after contact ~ i t h water. T o avoid this error, Lee ( 4 ) suggested that the alcoholinsoluble solids content of a vegetable may be used as a reliahl(~ basis for the computation of vitamin losses during blanching. This investigation was undertaken to devise a proccadurc. whereby the reducing and total sugar contents and alcohol-insoluble solids determinations might be combined and appreciably shortenrd. The formulation of such a procedure requires that consideixtion be given to the rapid and thorough extraction of the supai's from the vegetable, the removal of pigments and interfering cornpounds which vould normalll- react with the chromogen of a colorimetric procedure, the hydrolysis of sucrose for estimation as reducing sugars, and the formation of a reproducible and stahlca color which is proportional in intensity to the sugars present o w r a fairly \vide range. EXTRACTION
Sugars are usually extracted from plant tissues with ethyl alcohol, which, if present in sufficient concentration, precipitate .< polysaccharides and proteinaceous materials and inhibits enzymatic action. Thorough alcoholic estraction is greatly aided hy a maceration of the tissues in a TTaring Bleridor ( 2 , J ) . The following extraction procedure employs the ll-aring Blendor and a resulting alcohol concentration of a t least 75%, depending on the moisture rontcnt of the veyetal,le.
As a means of preserving the samples until a convenient time for analysis, the vegetables are frozen and stored a t -23" C. This also affords an opportunity for obtaining a representative sample for analysis by g1,inding one or more pounds of the frozen material twice in a food chopper at -23" C. Twenty grams of the finely ground vegetable are weighed into a 100-ml. beaker in the cold room. A i troom temperature the ground sample is washed into a Blendor cup (500-nil. capacity, having a rubber gasket under the ,screw top) with 150 nil. of 8 5 5 rthl-1 alcohol (specific gravity 0.850). After 5 minutes of maceration, t,he contents of the Bleridor cup are washed into a 600-ml. beaker with 8jC< ethvl alcohol from a Ivash bottle. The solids are allowed to settle and the contrnts of the bealter are poured onto a weighed 5.5-cni. S o . 40 \I-hatman filter paper in a Ruqhner funnel inserted throukh H two-holed rubber stopper placed in the mouth of a 500-ml. Kohlrausch sugar flask. Khere heavy-walled or Pyres Kohlrausch flasks are not available, a 500-ml. Pyrex volumetric flask can be adapted bl- sealing onto the neck a piece of tubing, 37 mm. in outside diameter and 6 em. long. The use of a Kohlrausch flask and the danger of possible collapse of the flask by the vacuum can be avoided by collecting the filtrate in a 500-ml. volumetric flask under the high-form glass cover of a Fisher Filtrat or. Suction is applied to the interior of the Kohlrausch flask through a small piece of glass tubing bent a t right angles and inserted into the other hole of the rubber stopper. By decanting off most of t,he alcoholic solution before adding the solids to the funnel, the filtration is greatly accelerated. The beaker is then rinsed out with more S5yc ethyl alcohol n-hich is poured into the Biichner funnel. The residue is washed with alcohol three or four times. After each u-ashing the residue is allowed t o become partially dry but care must be taken that t,he precipitate is not too thoroughly dried or the filter paper n-ill pull away from the sides of the funnel and the nest addition of alcohol \vi11 wash the solids into the flask. K h e n the volume of the filtrate approaches the d00-nil. mark. the residue is allowed to dry and carefully removed to a weighing dish for complete drying at 9 5 " C. overnight. The weight of the dried residue represents the alcohol-insoluble solids content of the sample. The volume of the filtrate is then made up to the 500-nil. mark with the 85cr alcohol and the contents of the flask are thoroughly mixed.
