Am peromet ric Determinutio n of Aceta I de hyde with Hydroxylamine Hydrochloride R. E. VAN ATTA, W. W. HARRISON,' and D. E. SELLERS Department o f Chemistry, Southern lllinois University, Carbondale, 111.
b The oxime produced by the reaction of acetaldehyde with hydroxylamine hydrochloride yields a polarographic reduction wave ideally suited for the amperometric titration of the aldehyde in aqueous solutions. The polarographic current is measured at a constant potential of - 1 .?5 volts vs. the saturated calomel electrode, using a dropping mercury electrode. The method is convenient and rapid, requiring no more than 10 minutes for completion after initial preparation of the test solution. Aqueous solutions of CHsCHO in the range of 1 i o lOOmM may be titrated with the 0.1 M reagent 1 of with an average accuracy of =t the amount of acetaldehyde taken; the concentration range may be extended by increasing or decreasing the concentration of the titrant. Impurities, such as ethyl alcohol, ethyl acetate, or acetic acid, do not interfere in concentrations as great as five times the concentration of the aldehyde; acetone interferes at concentrations greater than 40% of the acetaldehyde concentration. The technique has been applied successfully to the analysis of commercial acetaldehyde preparations.
yo
S
visual and potentiometric titration techniques for the determiriation of acetaldehyde in aqueous media have been reported in the literature (1, 2, 8 ) . I n general, these methods are time-consuming and, in some cases, relatively inaccurate. Visual titration with hydroxylamine (2) appears t'o be the most reliable and accurate, although it is difficult to perform in the presence of ethyl alcohol and certain other organic solvents. Elving and Rutner ( 4 ) reported a polarographic method for the determination of acetaldehyde in liquefied Ca fractions, obtained by the fractionation of butadiene-containing samples, which is not subject to interference b y considerable amounts of ethyl alcohol. Other polarographic methods for the determination of acetaldehyde have been reported by S!iikata and his coEVERAL
1 Present address, 1)epartment of Chemistr?, University of Illinois: Urbana,
111.
1548
ANALYTICAL CHEMISTRY
workcrs (9, I O ) , as w l l as by Smoler (11).
The object of this investigation was the development of a titrimetric tcchnique capable of the determination of acetaldehjde in aqurous solutions in the presence of ethyl alrohol, ethyl acetate, acetic acid, and a t least limited nmounts of acetone. respectively. It \vas further desired that the ultimate mctliotl be suitable for adaptation t o inexpensive apparatus, while capable of routine performance by nontechnical personnel. Inasmuch as the polarographic behavior of various oximes has been reported ( 3 , 6, IZ),the drvcxlopment of an amperometric titration technique, based on the measurement of the polarographic current resulting from the reduction of acctaldoxime, appeared possible. It seemed probable that such a technique might result in a rapid, yet relatively precise and accurate, method for the analysis required. EXPERIMENTAL
Apparatus. Polarogranis we're recorded n i t h a Leeds &! Korthrup Electro-Chemograph, T y p e E, while amperometric measurements were made ~ i t ha Sargent Model I11 Polarograph. T h e titration cell consisted of a Laitinen-Burdett r.lcc-trolysis vessel ( 6 ) connected with a conventional saturated calomel refcrcnce electrode by means of a n agar-saturated KC1 salt bridge. The capillary used as t,he dropping mercury electrode in the amperometric measurements was constructed of Corning marine barometer tubing; the drop life was 6.3 seconds. measured at open circuit in distilled water. The nitrogen used for purging was preconditioned with concentrated II,SO, and alkaline pyrogallol. -4211 pH measurements were made with a I k k man Zeromatic pH inrater. A 10-ml. Schellharh semimicroburet with capillary tip wis used t o drliver the titrant into the titration vessel. Reagents. A4cetaldchyde (Eastm a n Kotlak White Laliel Grade) stock solutions WI'C prepared hy dilution of t h t s re q u i r r ~ l a c c u ra t cl y nica sur cld volumr of t h e reagcnt with distillcd ivatrr. Hytlroxylnminc hydrochloritlc (Fisher CcLrtifid Kr,agrrit) s solutions \vorc prepared b>- di the requisite weight of the dried rengcmt i n tli~tilled\\.:iter, follo\vrd hy tliluticin t o the proper volunic~. .\I1 other chcm-
i d s and reagents u m l were anal>.tiral reagent grade or equivalent. Procedure. P r e p a w t h r trst solution h y transf(,rring (pipet) the tlrsirctl volunic of ac~taltleliydesolution t o a 100-ml. volunir,tric flask containing 0.7 gram of KC'I dissolved in a frw milliliters of tli~tillctl water. Dilute thv resulting solution t o v d u m e and mix propcrlj., :tdjwting t o pH 7: if n( ?;try, by the c:irrful adtlition of rlilutc~ HCI or S a O H . Transfer 7.5 nil. of the prepared tost solution t o the titration vessel and purge ivith riitrogrii for 5 minutes. Set the manual Polarograph at - 1.25 volts z's. S.C.E. a i d t h c current multiplier a t 100 (full scale galvanometer tleflwtion approxiniatcly 2 pa.), anrl titratc, the sample colution with 0.141 hytlroxylamine hydrochloridc reagcmt. Plot the indicated current 2's. the titrant volunit~at 1.0-nil. incrrnicnts and tietermin(. the end point ti>- the intersection of the two straight lines obt'ained. RESULTS A N D DISCUSSION
Preliminary Polarographic Investigation. 'Yo determine the feasibility of the a m p n o m e t r i c titration approach, it was necessary t o invcstigate first t h e polarographic characteristics of the reagent, t h e medium, t h e individual components measured, and posaihle interfering conipounds. ConstqucntlJ-, polarograms were recorded. after nitrogen purging and in 0.1M KCI as supporting elrctrolyte, for 5ni.U solutions of acetaldehyde, acetone. hydroxylamine hydrochloride, acetaldosime, dimethyl ketoxinie, ethyl alcohol, ethyl acetate. anrl acetic acid. The speries giving rise to polarographic reduction waves are listed in Tablc I, along with potential and geometrical descriptions of the wave.:; all other species checked did not produce polarographic n-avep. The twt solutions containing the oximcs wcre preparrd by mixing equimolar quantities of the parent carhonyl compound and tlic hytirosylaniine liydrochlorirlr~ rcngent. I n such casw, no tr:m of the original rvavcs duc t o either rt,agcrit or purcnt cnrlxmyl c~oiiipound n a:: found. Since ampr:rometrica titratioiii involve onlj. the location of polsro~raphicI Y ~ V O Sm t l :ire not conc.rriirr1 ivitli currcsiit niagnitutlw. crirrcnt m:ignitLitics s t w not t ~luatcd. ~ j
' i Table I. Potential and Geometrical Descriptions of Reducible Species I1
-
-
I* I
-
Investigated
-
1
I 1I
,
End point volume 3.74ml.
I ! I O . I O O M N H 8 0 H HCI, M I
Figure 1. A typical amperometric titration plot for acetaldehyde with hydroxylamine hydrochloride
-1s a re-ult of tlic prcS1iniin:iry polarographic nie~isurcnionts:.a potential of - 1.25 volts 2's. S.C.E. was scllccted as the onr a t wliich am~ioromctrietitrations of acct:ildehytlr with hytlroxylaminc liytlrochloritlr might IJC pcrfornictl, since this value. lirs Iwtn-ern the limiting potcnti:il of the acctaltloxinic w v c and the initial I)otc,nti:d for t h r reagent wave. Effect of Nitrogen Purging. -41t li 011 g Ii a ni pc'ro nic t ri titrations of :i(T t alt l (lhy t l \\-ith 11 y(1 rosy la niir I e h ytlroc*liloritle :ire p o s ~ i l ) l (in~ t h e pres( ~ I ( Y of ~ dissolved o s y g r n , b c t t r r repro(lii(~il)ilityis obtained after osygen rcmowl h). riitrogon purging. Further, tho v o i i h t rwtioii of the, 1,aitini~ri-Hurtlt~tt c.1 ~ ~ e r m initrogen ts I J L I ~ ~ iug Eiiiel siiiiultnnc~~u.: Iiolarogrnphic c.urrcnt nicx>urmicnt, thus ac*complishirig cviitinuous agitation of th(9 solution tliroughoiit tlic titration, Oit-iiig t o the. volatilit!. of acetaldel i > d c s it I\ :i. c~on~idorctidcsiratile t o iiiv(s-tig:itt, tlicx effract of purging time on tlic. (~onst:ui(~>. of curwnt~nicarureintwts :it - 1.25 volts. Thercforc. a ,writ'> of nie:isiircnients was contiuctctl to tl(~tc~rniinc I~ohsiblcrffccts of variable purging tiin(, 011 the measured current. .I . i . O O m . l ~twt solution of acetaldehyde i n 0.l.U K('1 \vas prcparrd and used for suc*li iiic:ih~irc,iii(~iits. PLirgiiig periods of 5 , 10. 15. :inti 20 minutes were used; tn.o tl~~tc~rtiiiiintiolin e r c made at each purging 1 )c>riotl. l i c ~ i l t siii(licatcc1 no >ignifiwiit vari:ition i t i thcs nicnsurctl liniiting currcwt. ('onsequontl!., the mow cnn~c~iiic~iit 5-niiniitc ~ ~ r i r g i ntime g a. u w l in all s u b ~ c q u ~ ~nicasurcnt mc~ntq. Effect of pH. .ic~uroiissolutions of :ic'c't:iltit~h?-el(~ in 0 . 1 X KCI cdiil)itrd a slightly :ii.iilic. n:ituw, t h r 1'1% v d u c s i x n g i i i p f r o m 5 t o 6. 3Icasurc,nicuts c~oiicluc~tc~tl oil such colutiuns yielrlctl itlo:il :iiii!Jc't,omc'ti.ir. titration curvcs ( l ~ i g u i ~1i)~. O t l i i x i , siniilai~ solutions (w titr:itrtl, a f t w prcliiiiiii:ir>. :idjuxtmrnt of thc'ir 1iH v:iluc~ 1). the c.arcfii1 :id~litionof 0.1.11 IIC'I or 0.1.11 S a O I I . 'I'ht, rcwlts of tlicw mra-urrn i r i i t . :iw..IIIJ\VII i n 'I.:il)lv 11. 111 riii~rliu e1
(s
Approsimat?
-E1,*us.
Potential Range of \T:tve, Volts
S.C.E., Volts
('HICHO
- 1 . 7 t,o - 1 . 9
1.8
SHzOH. HCI
- 1 ,?I
CH:ICH=h-OH
- 0 . 8 t>o- 1 . 2
1.0
(CH1)?C=SOH
-1.2to -1.5
1. 3
Compound
to
- 1 .(i
foulld to iJCsapprosir!!:itcly 0.10.11.
\Vel1 defined, limiting current coalesces with electrolyte discharge Well defined b u t unsymmetrical, slight maximum )Yell defined, with large maximum from -1.1 t>o - 1 . 2 volts Well !defined, with shsrp maximum about - 1.4 volt::
1. 5
more aridic than pH 5, no definite deflection point is observed in the titration plot; at pH values greater than 10, no current changc is otiserved on the addition of the titrant. Satisfactory analytical results are obtained in the pH rangc of 5 t o 9. Consequently, sample solutions more acidic than pH 5 or morr alkaline than pH 9 must be adjusted t o within the prescrilitd range prior t,o amperometric titration. Optimum Conditions. T h e most favorable acetaldehyde concentration in t h e test solution n'as found to be approximatrly 5mM. Twt solution concenti~ations in t h e rangc of 1 t o l 0 m M 1 r - c stutlicd. ~ H o w v e r . using t h e 0.10OM t i t r a n t , thr lower value (1m;lf) required an end point volume, of less than 1 ml., while the upper (10mM) required nearly 10 nil. (the capacity of the h r e t ) . An intermediate concrntration-i .e,, approximately 5m.Wyirlded a11 end point of approxiniatclv 4 ml. and an ideal titration plot. T h sentration of acetaldehyde t o he aiialyzcd i.5 known tain limith, a n appropriate the unknoivii is transferred to the 100-ml. volumetric flask and the t r s t solution ]irepareti as descrihed in the Procedure. K h e n the concentration of the acetaldehyde in the sample to he analyzed is conipl&ly unknown: a n intrrmediatt voluint of samplc ( 5 t o 10 ml.) is tranqfmred t o the 100-nil. flask and th(1 tcst solution prepared as described in thc Procidurc. preliminary titration is then conipletcd. If the rnd point volumv is less than 1 or greater than 9 ml.: a nrw test solution is p r e p a i d following appropriate adjustment of thc, raniplc ~ ~ o l u mtaken, r and thr titration is r ( ~ p c a t ( d . Thr itir~nl r c q c ~ n t concrlntration required for the titration of ac~~tnldrhytlr solutions ranging from 1 to 1000ni.lP w a . ~ tictt~rmincd. l'hc c,oncwitration miiiirriizc tlilutiori errors., ing sufficbirnt mpa(holes
S o titration
break 3 98
4 39 4 60 4 97, 4 93 4 93. 5 06
5 0 5 , 4 97 5 03,4 98 4 9 4 , 4 93 4 81
-20.4
-12.2 - 6.2 -0.6, - 1 . 4
-1.4, + 1 . ? +1.0, - 0 . 6 + O . G , -0.4
-1.2, - 1 A - 3.8
s o titration break
Table 111. Amperometric Analysis of Pure Aqueous Acetaldehyde Solutions
Conditions: hydroxylamine hydrochloride, 0.1OOJI: potassium chloridc (supporting electrolyte), 0.1JI; applied potrntiaI; -1.25 &Its os. S.C.E.: Sargent 51odel 111 current multiplier, 100 hcetalAcetaldehyde dehyde Taken, Found, Relative RImoles Nnioles Error, $1 1 .00
2.50 5 00
0 .07 1.02 0,08 2 .50 2.46 2 52 4 06
5 07 4 98
10 00 25.00
50 00 100.(JO
9 94 9 85 10.00 24.60 24 85
24.75 50 65 50 75 49 80 on. 4 os.0 101.5
VOL. 32, NO. 1 2 , NOVEMBER 1960
- 3 .0 +2 0 -2,o 0.0
-1.6
+o
.8 -0 8 +1 . 4 -0 4 -0.6 -1.5
0 0 -1.6 -0 (i
-1.0
+1 3 +1 5
-0 4 -0.G -2.0 +1 . 5
1549
Table IV.
EfFect of Impurities on Determination of Acetaldehyde
Conditions: acetaldehyde, 10.00mM; hydroxylaxhine hydrochloride, 0.100M; potassium chloride (supporting electrolyte), 0.1M; applied potential, - 1.25 volts us. S.C.E.; Sargent Model I11 current multiplier, 100 Concentration, Acetaldehyde Relative Impurity mM Found, Mmoles Error, % CHsCOOH 5 9.91 -0.9 10 10.09 +0.9 20 9.87 -1.3 50 9.90 -1.0 5 10.01 +0.1 CHiCHlOH 10 9.92 -0.8 0.0 20 10.00 -1.3 50 9.87 9.85 -1.5 5 10.09 10 $0.9 -1.2 9.88 20 9.90 -1.0 50 2 9.93 -0.7 10.13 3 +1.3 10.94 5 $9.4 11.61 10 +IS. 1 0 Acetaldehyde concentrations of 5, 20, and 50mM in the presence of acetone (2-50 m M ) were also investigated. In all such cases, the error became significantly high as the acetone concentration exceeded 40yothat of the aldehyde.
A series of aqueous acetaldehyde samples ranging from 1 t o lOOmM in the aldehyde was analyzed, utilizing the optimum conditions previously specified. The results of these analyses are shown in Table 111; a n average relative error of =tl%was obtained. Interference Studies. Individual studies on t h e effect of acetone, ethyl alcohol, ethyl acetate, a n d acetic acid BS impurities in t h e presence of acetaldehyde were conducted; these compounds are t h e most probable impurities in commercial acetaldehyde preparations (7). The results of these studies are shown in Table IV. No
significant interference was indicated when acetaldehyde was determined in the presence of ethyl alcohol, ethyl acetate, and acetic acid in concentrations up to 5 times t h a t of the aldehyde. Acetone concentrations less than approximately 40% of the aldehyde concentration produced no significant error while values in excess of this figure yielded progressively higher results. Such interference was anticipated as a result of the potential relations indicated in Table I and the operating potential used. Combinations of the impurities investigated produce analytical results essentially identical with
those indicated for the individual components. ACKNOWLEDGMENl
The authors express their appreciation to the Research Corp. and t o the S a t i o n a l Science Foundation (NSF G11434) for grants which supported the investigation described. LITERATURE CITED
(1) Adams, E. W., Adkins, H., J . Am. Chem. SOC.47, 1358 (1925). 12) Bryant, W. M., Smith, D. M., Ibid., 57, 57 (1935). (3) Calzolari, C., Boll. SOC. adriat. sn'. nat. Trzeste 45. 109 (1949-50): Pubbl. facolta sei. ing.-univ. 'Tnesb Sei. B 81, 1; 82, 3; 83, 3, 116, 171 (1950). (4) Elving, P. J., Rutner, E., IND.ENG. CHEM.,ANAL.ED. 18, 176 (1946). (5) Hartnell, E. D., Bricker, C. E., J . Am. Chem. Sot. 70, 3385 (1948). (6) Laitinen, H. A., Burdett, L. W., ANAL.CHEW22, 833 (1950). (7) Noller, C., "Chemistry of Organic Compounds," 2nd ed., p. 222, Saunders, Philadelphia, 1957. (8) Shaposhnikov, V. G., Makovskaya, Ya. I., Kalinicheva, N. A., Trudy Gosudarst. 0 yt. Zavoda Sintet. Kauchuka Litera $ 3 , 118 (1934). (9) Shikata, M., Shoji, K., Mem. Coll. Agr. Kyoto 4, 75 (1927). (10) Shikata, M., Tachi, I., Proc. Imp. Acad. (Tokyo)2, 226 (1926). (11) Smoler. I.. Collection Czechoslou. ' Chem. C k m u n s . 2, 692 (1930). (12) Souchay, P., Ser, S., J . chim. phys. 49, C172 (1952). RECEIVED fer review May 16, 1960. Accepted August 5, 1960. Division of Analvtical Chemistry, 137th Meeting, ACS, Cleveland, Ohio, April 1960. Taken in part from the M.A. thesis submitted by W. W. Harrison, Southern Illinois UniXrersity.
Dynamic Mechanical Spectrometry by Means of Rolling Friction Measurements D. G. FLOM Generol Electric Research laborafory, Schenecfady,
b Recent success in correlating the rolling frictional properties of polymers with dynamic mechanical losses in these materials has led to a new technique for studying bulk physical properties. Measurements of rolling friction are used to determine dynamic !osses as a function of stress frequency. This inforniation also can be obtained by measuring rolling friction as a function of iemperature because the effects of temperature and frequency on dynamic mechanical properties are
1550
ANALYTICAL CHEMISTRY
N. Y.
usually related. Dynamic mechanical spectra have been obtained for a number of polymers ranging from soft elastomers to relatively hard thermoplastic materials. The range of temperature used has extended from as /ow as -40' to 300" C. The effects of changes in molecular structure on dynamic properties are observed readily in the spectra. In blends of different polymers, dynamic loss peaks chcracteristic of the individual com~onentsalso can be resolved.
T
USE OF dynamic mechanical properties in the study of polymers is now well established. However, the application can be extended further. The changes which accompany structural transitions in these materials at. characteristic temperatures and/or frequencies provide us with an ana!ytical tool which unt>ilnow has received iittle att,ent~ion-namely, dynamic mechanical spectrorr1et)ry. [Although its concept is ncit newv, its importmce n'as recitntly re-emphasized (3).j Also.
HE
