Determination of Diglycols in Mixtures of Ethylene and Propylene Glycols C. V. FRANCIS IVyandotte Chemicals Corporation, Wyandotte, Mich.
A method for the determination of diethylene glycol or dipropylene glycol as contaminant in monoglycols is presented. The monoglycols are removed by reaction with periodic acid and distillation. Excess periodic acid is reduced to iodic acid, and the remaining diglycols are oxidized with potassium dichromate. The excess dichromate is measured with a polarograph.
I
x' THE manufacture of a refined grade oi monoglycolshaving a diglycol content of less than 1%,it becomesnecessary to have a rapid and accurate method for the direct determination of the diglycol content. Methods for the estimation of ethylene and propylene glycols (1-4) h a w a precision and accuracy of only 1 to 2%, and, therefore, the diglycol cannot be estimated by difference. This paper proposes a method for determining dlethylene glycol or dipropylene glycol, or both, present in quantities less than 1% in mixtures of ethylene glycol and propylene glycol. The method, however, is not limited to small quantities; diglycols can be determined in a refined grade of monogl) cols with an accuracy of 1 0 . 1 to *0.2% when 0 to 3% diglycols are present. The monoglycols are removed by reaction with periodic acid and distillation. The excess periodic acid is removed by reduction to iodic acid, and the remaining diglycols are oxidized with potassium dichromate. The dichromate is measured with a polarograph before and after the oxidation reaction.
Record a polarogram w k h the instrument set as fo1lon.s: D.C. e.ni.f. Span Initial Damping Drop time DropRing mercury electrode Sensitivity
1 . 5 volts 1 . 5 volts Zero
Off
hpproximatels- 3 svconds Negative
0 , 0 1 mirroampere per
Record only the range of 30 to 60% of the voltage applied. Record a polarogram of 20 ml. of 0.1 X potassium dichromate carried through the procedure beginning wit,h the refluxing with sulfuric acid, but without sample added to determine weight of potassium dichromate per microampere recorded. Factor A. Record a polarogram of a known weight of diglycols beginning with the dichromate oxidation t,o det,ermine the weight of diglycol equivalent to 1 gram of potassium dichromate. Factor
B.
CALCULATION
(Microamperes for blank - microamperes for sumple) X factor A X factor B X 100 Weight of sample diglycol, % by \\eight
REAGENTS A N U EQLIIP3ZI EAT
l'eriodic acid, G. F. Smith Chenlic.al ('ompiny. Fuchsin-aldehyde reagent. Sodium carbonate, C.P. anhydrous. Hydrogen peroxide, 3% solution. Sulfuric acid, 1 to 1 aqueous solution. Potassium dichromate, 0.1 N, accurately standardized, Sodium hydroxide, 1.0 N . Diethylene glycol standard, redistilled and dried 6,P-dihydroxyethyl ether, Eastman Kodak KO.20.11. Kjeldahl distilling unit, 250-ml. flask, trap, and vertical cow denser. Reflux condensers with ground-glass connect,ions, and fitted with 500-ml. Erlenmeyer flasks. Polarograph. The model used in this laboratory is the Sargc.ut-Heyrovsk4 recording polarograph, >lode1 XXI.
Inin
i Y 4LYTlCAL RESULTS
Experimental samples were prepared containing various amounts of diglycols as contaminants, the major portion of each sample being a mixture of ethylene and propylene glycol in an approximate 60 to 40 ratio. These samples were carried through the procedure outlined above. Some typical results are shown in Table I. DlSCUSSIOh
In the distillation t o remove aldehydes formed from monoglycols, it Ras noted that the more dilute the aldehyde solution, the more efficiently the aldehydes were removed. If very small
PROCEDURE
Weigh and dilute the sample with distilled water so that the aliquot taken for analysis contains about 5 to 10 m g . of diglycols. Transfer the aliquot to a 250-ml. Kjeldahl flask, and add 2 grams of periodic acid dissolved in about 50 ml. of water and a few glass beads. If more than 0.5 gram of monoglycol is present, use a correspondingly larger amount of periodic acid. Dilute with distilled water to about 200 ml. Connect the flask to thc distillation unit and distill until the distillate no longer shows an aldehyde reaction with fuchsin-aldehyde reagent. If the residue is reduced to 15 ml. and aldehydes are not removed, add 50 ml. of water to the flask and continue the distillation. Cool the residue and dilute to 50 ml. Make alkaline with dry sotlium carbonate and add 15 ml. of 3% hydrogen peroxide. Distill until the volume of residue is again reduced to about 20 ml. Cool, transfer to a 500-ml. Erlenmeyer flask, and add 100 ml. of 1 t o 1 sulfuric acid. If a yellow color appears, boil until it is reniuved. Add 20 ml. of 0.1 A' potassium dichromate and reflux 45 minutes. Transfer the cooled refluxed mixture to a 1-liter volumetric flask and dilute to the mark. Transfer a 10-ml. aliquot to a 100-ml. flask and dilute to the mark with 1.0 S sodium hyJrositle.
Table 1. Tj pica1 inalyses of Diglycols a s Contaminant in Monoglycols Containinant
Contaminant Present 0.
1 .i
1.3 0.7; (1.77 2.3
Dipropylrne glycol
1.4 1.0
0.75 0.52
Diethylene glycol pluc diuropylene glycol, 60/40 ratio Triethylme glycol Sone None
1238
Containinant Found C'
1.7 1.3 0.70 0.73 2.4 1.3 1.0 0.81 !.60
2.5
-.7
1 .; 1.1
1.5 1.0 1.2 0.9 0.05
1.3 0.8 0
0
-0.1
1239
V O L U M E 21, NO. 10, O C T O B E R 1 9 4 9 anlourits of diglycols are present, it may be rieccssary to add water to the rcsidue and redistill to remove the aldehydes completely. This process does not appreciably affwt the diglycol determinatioii. The tiiiie specified for refluxing with dichromate is about the niiiiinium time but additional refluxing does not alter results. h i unsuccessful attempt was made to remove the iodine conipounds by precipitation as metal salts (6, 6 ) , using lead, barium, bismuth, and other metals so that the dichromate could he tit rated with sodium thiosulfate. For the oxidation of diethylene glycol by potassium dichromate, tlir following reaction is usually given: XC'4H,oOa 10K2Cr20, 40H2SO4+ 10K2S04 10Cr2(SO& 12C02 55H20 13y thi+ rt::tction. factor €3 should t,e 0.1082. This factor. as dr-
+
+
+
+
+
terinined by the above method, was 0.1381 which is roughly equivalent to 8 moles of potassium dichromate to 3 mnlc3.s of diethylene glycol. This factor is reproducible and was used iri this work. The reason for this deviation from the theorc,tic.:il is not known. Y . , and C'olenian, K. h I . , 1 s ~ I.:TGI. . AXAL.El>., 12, 884-7 (1940). ( 3 ) Iteinke. 11. C . , and Luce. E. N., Ibid., 18, 244-5 (1946). ( 3 ) Shupe, I. S.,J. Assoc. O f i c . A g i . Chemists, 26, 249-55 (1'3431. (1) Warshowsky, B., and Elving, P. J., IND. E m . CHenr., AKZL ED..18,253-4 (1946). ( 5 ) TT'illard, H. H., and Thompson, J. J.. .J. A m . C ' h m t . ,Sot.. 56, 1827-
(1) .4lle11, N..('liarbolinier, H. (.'HFx.,
8 (1934). (6) I h i d . , 56, 1828-30 (1934). R W ~ . I ~ P.I;tntiary :D 1 2 , l!l49.
Determination of Microgram Amounts of Thorium A Colorimetric Method 1'. F. THOiMASON, 11. A. PERKYI, A N D W. M. BYEKI,Yz
Oak Ridge .Vational Laboratory, Oak Ridge, T e n n . A method for determining thorium in the range .5 to 80 micrograms has been developed, using l-(o-arsonophenylazo)-2-naphthol-3,6-disulfonic acid. Uranium and the rare earths do not interfere in amounts less than 1000 micrograms and interference from iron can be lessened by reduction to the ferrous state.
T
Hli colorimetric determinatiou of thoriuiii oii the idcrograin level has received little consideration in the literature, 1 1 0 tlouht because of the absence of characteristic colored conipleses o f thorium. Survey tests in this laboratory with alizarin and other rc!agaiit:: that are known t,o complex thorium (1, IO) have nnt iiidicatetl aiiy stable complex that might he used as a basis for a wtory colorimetric nucrom~ttioti. Recently, however, it wah reported by Kuznetsov ( 7 ) that 1-(o-arsonopheny1azo)-2ii;ipht~ioI-X,~-disulfonic acid formed a specific red precipitate with thoriuin in hydrochloric acid. I t was st,ated that by visual coniparisoil 1 n ~ c r o g r a ~ofi i thoriuni per niillilit,ctr could h r detectrri, ai111:I ,qJiilt ( ~ ttcv~liriiqut.nxs t l t ~ s c i i t ~ i ~ l . .LSO.,H!
€10
S0,II
/'
hi
vicbiv or the ~ i w dfor a rapid micronlethod for tliv tlrtcriiiiiiit-
sinal1 w,inount,sof thorium, the reagent \va the posd)ilities of developing n spectrophoto werc. irivcstiyatwl. 22s a result, a method has been developed for the dr:teriiiiriatiou of thorium iri the range of 5 to 80 microgranir pri' 10 nil. of final volume. Thc method consists of the following steps: adjustiiiolit of pH, addition of the orgaiiic reagerit, dilution iieasurement of the optical density in :L spcctrolis LL rrfrrencr solution of the reagent. tioii
I)(
EXPERIIIENTAL
Synthesis of Organic Reagent. The l-(o-arsonopheii~I~~o)-2-
11aphthol-3,6-disulfoiiic avid tions given by Kuziictsov.
\v:t-
syntht~sizcdaccording to dircc-
To 2.17 grams of o-aniinophenyl:trsonic acid (0.01 molar) dissolved in 40 ml. of m-atei.,add 3 mi. of hydrochloric acid (spcxific gravity 1.12), cool, and diazotize by adding 5.0 ml. of a 2 N solutiou of sodium nitrite. Filter the diazo compound away from (,he accidental dirt and rapidly mix with a filtered solution of' 4.2 grams of the sodium salt of 2,3,6-1iaphtholsulfonic acid ( R s:tlt,) and 4 grams of anhydrous sodium carbonate in 40 ml. of water, The mixture immediately becomes red, and after some seconds a precipitate fornls. Let stand for 2 to 3 hours, then slowly warn1 (the precipitate dissolves) and add 14 grams of cleari, solid sodium chloride. Ori cooling, the mass thickens. Filter, squeoze out the liquid, and wash wit,li oold water. Ruby red crystals :tIe produced. -4solutioii iii water arid dilute acid is orange coloitd, in alkali is orangered, in concc!ntr:tteti sulfuric acid is rose colorcd. It, is not soluble in alcohol. The required o-aniinophenylarsoiii~~ acid was ohtained by r+ ducing o-nitrophen?.larsoiiic acid 1))' treatment with ferrous sulfate (better ferrous chloride) and sodium hydroxide (2-4). o-Sitrophenylarsoiiic acid is readily prepared by the reaction o f Hart. bv t,he interaction of diazotizotl o-uiti~o:tniliricwith an a k a line soiutiori of arsriiic trioxidc (.F, A, $). 135' analysis tlie arsenic rwritent of the recryst,allized orgaiiic ](,agent was found to hr 13.1%. Theoretical is 13.072 for the disodium d t . A more coiiiplcte and detailed procedure for the syntlirsis of t h c A organic rct~gciitis to br, puhlishrd by Reed arid associates (,'?I. Materials. Reagent grade cheniicab of the common materials were used for testing intcri'crcricc*s. Spectrographic analysis of t h c yttriuin nitrate reagent disclostvl only the rare earths and micium as impurities. Thc zirconyl chloride reagent cont,aiiiod hafnium and t,races of iyon. S o truces of thorium were fount1 in the lanthanum nitrate rc:agent ,
A standard thorium solution was made by dissolving 23.8 grams of chemically pure thorium nitrate tetrahydrate in distilled water and diluting to 1 liter. The thorium nitrate obtained from
