ANALYTICAL CHEMISTRY
730 precipitate is filtered off and dissolved in 3 S hydrochloric acid. One gram of tartaric acid, 10 ml. of magnesia mixture, and an excess of ammonia are added to the solution. After shaking for 2 hours the precipitate is filtered and washed with dilute ammonia (1 to 20). The precipitate is dissolved in 3 S hydrochloric acid and the arsenat,e determined as described previously. When t.he amount of arsenic is small (of the order of 0.1 mg.) the titration is carried out with 0.005 iodine added from a microburet,. A blank is run following the same procedure, except that no steel is added. The amount of iodine required in the blank is subtracted from t,hat used in the det,ermination. The method was checked ivith a Bureau of Standards sample of ingot iron, 90.55, containing 0.012$, of arsenic. The results in cight determinations varied between 0.011 and 0.14Yc, n-ith a n average of 0.012%. K h e n the amount of arsenic in the steel \vas lcss than O . O l % ,
the blank was so large compared t o the amount of iodine used in the determination, that the resultswere not satisfactory. LITERMTURE CITED
(1) .Jssoc. Official d g r . Chem.. Official and Teiitative Methods of Analysis, 4th ed., p. 2 5 2 , 1935. ( 2 ) Beriitrop, Tudschrift 1'001'toeycpaste Scheikunde e n Hugiene, 4, 112
(1900-01).
IT.F., and Lundell, G. E. F., "Applied Inorganic Analysis," pp. 211, 509. Sew Tork, John Wiley &Sons, 1929. (4) Kolthoff, I. -M., "J-olunieti.ic Analysis," by N. H. Furman, Yol. 11,p. 410, New York. John Jl-iley Br Sons, 1929. ( 5 ) Mellor, J. IJ-,, "Coiiipreliensive Treatise on Inorganic and TheoVol. I V , p. 584, Val. IX, p. 177, London, Longmans, Green and Co., 1923. ( 3 ) Hillebraiid,
From a master's thesis submitted by C. \I-. Cam to the Graduate School, Uni\-ersity of Alinnesota, 1939.
RECEIVEDFebruary 5 , 1048.
Determination of Diphenyl Carbonate JEROME GOLDENSON AND SAMUEL SASS Chemical Corps, Technical Command, Army Chemical Center, .Wd. Three analytical methods are described for estimating diphen11 carbonate in cloth: bromination of the phenol produced by alkaline decomposition, estimation of the blue indophenol color formed by the phenol decomposition product with 2,6-dibromoquinone chloroimide, and ultraviolet absorption nieasurements. A modification of the colorimetric indophenol method markedly stabilizes the color and is applicable to determinations of small amounts of phenol as well as diphenyl carbonate.
D
I P H E S l L carbonate, one of the new industrial chemicals available in commercial quantities, is being used for pharmaceutical manufacturing purposes. It has been found, by the U. S. Department of Agiiculture, Bureau of Entomology, Orlando, Fla., to be a promising miticide and larvacide, and is permitted for restricted use on the skin by the Division of Pharmacology of the Food and Drug Administration. I n connection with the study of miticides for impregnation in clothing being conducted a t the Army Chemical Center, it became necessary to devise methods of analysis foi this compound applicable t o clothing impregnated a ith the compound. h divcrsity of methods is desirable during development itages. The methods described in this paper involve broniinatiiig the phenol produced by alkaline decomposition of the compound; estimating the blue color formed by phenol 11 ith 2,6-dibromoquinone chloroimide by tpiansmittance measurements a t 565 to 630 millimicronq, using a photoelectric colorimeter; and measur ing ultiaviolet absorption. They xere found satisfactory for estimating various amounts of the compound in cloth and with niinoi changes may be of value in othei applications of diphen>l carbonate. APPARATUS
Soshlet typc extraction apparatus with standard-taper Erlenineyer flask. Beckiiian quartz spectrophotometer, AIodel CUV, range 220 to 1000 millimicrons, with interchangeable hydrogen discharge lamp in housing, and a pair of fused silica absorption cells with Pyrex covers. Nett-Summerson photoelectric colorimeter, 3lodel900-3, with brown color filter No. 59 with maximum transmittance a t 565 to G30 millimicrons, and calibrated test tubes. REAGEYTS A\D MMTERIALS
Cndyed pure-finish cotton herringbone twill, undyed, sized cutton herringbone tjvill, and olive drab cotton herringhone twill cloth.
Diphenyl carbonate, prepared by Chemical Division, Army Chemical Center, and recrystallized three times from ethanol, melting point 79 "-80' C. Reagents for Bromination Method. C.P. ethyl ether; potassium hydroxide solution approximately 0.2 IT; C.P. hydrochloric acid, concentrated; potassium bromate-potassium bromide solution of 3.5 grams of C.P. potassium bromate, and 13.0 grams of C.P. potassium bromide, made up to 1 liter with water; potassium iodide solution, 10%; sodium thiosulfate solution, 0.1 S ; and starch indicator solution, 1%. Reagents for Colorimetric Indophenol Method. Buffer solution of 28.4 grams of C.P. sodium tetraborate (?ITa2B107.10HnO1, and 5.9 grams of C.P. sodium hydroxide, made up to 1 liter with boiled and cooled distilled water ; 2,6-dibromoquinone chloroiniide (Eastman Kodak KO. 2304) solution prepared by dissolving 0.08 gram of the compound in 50 ml. of 95% ethanol and filtering into a dark brown bottle: and 0.3 S sodium hydroxide solution. The 2,6-dibromoquinone chloroimide solution should be kept in a cool, dark place and made up fresh a t least every second day. Thc buffer solution should be adjusted to a p H of 10 n i t h boric acid or sodium hydroxide, so that a solution of 0.20 ml. of thc buffer and 10 ml. of distilled water will have a p H of 9.8. DEVELOPMEVT OF METHODS
Ultraviolet Absorption Measurement. 9ome preliminary work vias done to make ultraviolet absorption measurements the basis of a n analytical method. The procedure applied was essentially the same as described by Gibb (-5) and KIotz (9). In order to obtain the optimum Xvave length, which is regarded as the wavc length of maximum absorption, the absorption spectra of diphenyl carbonate in concentrations of 0.01, 0.10, and 0.80mg. per nil. in 95Yc ethanol were determined. I t was indicated that the most, pronounced absorption of diphenyl carbonate in 95c70 ethanol solution occurs in a wave band somewhere below 210 to 220 millimicrons, which is the lower limit of the Beckman quartz spectrophotometer used for this work. -knother lesser absorption peak for this compound occurs a t about 256 millimicrons, and it was found that concentrations of diphenyl carbonate in the range of 0.05 to 0.8 gram per liter of 95% ethanol may be estimated by
V O L U M E 2 0 , ' N O . 8, A U G U S T 1 9 4 8 absorption iiieasuremciits at 256 niilliinicrons in the absencc of interfering material. Much greater sensitivity was obtained by breaking the compound don-n to phcnol and carbon dioside by alkali and applying ultraviolet absorption measurcnieiits to the estimation of the phenol. Phenol in ethanol has a pronounced absorption band a t about 274 millimicrons ( 8 ) and can be estimated by a nicthod indicatcd hy Klotz (9). Both methods based on ult raviolet absorption nieasurcnic.nts were rapid and accurate for purc-finish cloth samples impregnated with diphenyl cai,bonate, but inarked interfcrencc was esprrienced in chstiinating small percent ages of the compound in cloth containing largo amounts of ulti.avivlr.t-absorbing material such as sizing preservatives. Slight iriterferc~iiwsmay tic compensated by use of suitable blanks, if they are availahlt,, or by a nicthoti of some inhiliitors in such as the one used for dt~termii~ation rubber bl- ultraviolet absorption (1). Bromination Method. .ittempts to hroininatc diphc,riyl carbonate directly in alcohol, cartion tetrachloride, or :wetic acid solutions (14) were unsuccessful: the carbonate group evitlently inhibited the bromination of the phenyl groups in this casc. Ho~vever, no difficulty was esperienced when the compound \\-as decomposed by alkali t o phenol, which is readily brominated in aqueous solution to 2,4,6-tribroinophenol by niethods described in the literature ( 4 , 10, 22). Recoveries of 99.8, 99.6, and 9 9 . 8 5 were obtained \Then weighed amounts of diphenyl carbonate wwc decomposed wit,h 0.2 iV potassium hydroside, followcd by brornination with a solution of potassium bromide and potassium bromate. K h e n the method was applied to cloth inipregnated with diphenyl carbonate, the first trials were run by extracting the cloth with ethyl or methyl alcohol, deconiposing the extracted compound in alcohol solution by addition of 0.1 S potassium hydroxide solution, and reflusing, follo\vd by bromination. I n the presence of alcohol, unless thc bromination was carried out under carefully controlled conditions of temperature and time, side reactions took place between the bromine and alcohol, giving variable results. But xhen the cloth was estracted with ethyl ether, followed by evaporation of the ether, decomposition with 0.1 S potassium hydi,osidc solution, and bromination, the I'Csults were uniform and recoveries of 99.8, 99.8, and 100.Oyc \yere obtaiiied with samples coiitairiing as little as 5 mg. of the compound. Several trials also indicated that there was no loss of t h e compound ivhcn the ether was r.vapoi,ated from the rstract. When blanks were run using pure-finish cloth and chloriiiat(d paraffin, no iritei fcrcncc \vas found. \Vlien blanks iverv run using sized cloth, :t very slight blank titration was ubtaiiitd. This hhould he indiratvd 1 hat, for g r e a t c ~accul'ac.?., a blank cori~c~ction made. I t \vas also found that thc dctcrniirintion can be iiiadc tiy hvatiiig a wighed sample of cloth i m p i ~ g ~ i a t ctvith d dipheiiyl car'bonate directly with 0.1 potassiuiii hydrosidcx solutioii, folloivcd by filtration of the resultant phenol solution and bromination. I n this case, higher blanks wercx obtained, but in all casrs the blank c low conip:wd to the titration of thtt titrations ~ e r relativcly sample.
731 Cool, transfer to a 500-nil. iodine flask, add a measured amount of potassium bromate-bromide solution (25 to 35 ml., depending on the amount needed to have, at least 2 to 5 ml. excess over that rcquired for bromination), arid add 4 ml. of concentrated hydrochloric acid (if the volumes of th(x potassium hydroxide and potassium bromate-bromide solutions are changed, use an amount of hydrochloric acid to have an acidity between 0.7 and 0.8 -V). Insert the stopper qui( and shake intrrmittently for 5 minutes. Add 10 ml. of 1 potassium iodide solution, taking rare to avoid loss of bromine while the stopper is being lifted. \Vash don-n the stopper and sides of the flask with water and titrate the liberated iodine with 0.1 Ssodiuni thiosulfato sblution, using starch indicator at thr ciid of th(, titiation. Run a cloth blank under thc same cwnditions. Thcb tlifft~ri~nce hc~t~veen the titration volunic~ of the hlaiik arid that of thti ramplc al'tcr b~.omirlationis the, ncit titi,ation. Thcn:
Results obtained on pilot-plant-iiiil)rcgnatcd batches of cloth, some of nhich had been aged outdoors and some aged in simulated tropical storage for varying lengths of timcx, are given in Table I. The cloth used was either purtl-finish or sized undyed cotton herringbone twill and some of thc sainples \vert: impregnated wit,h chlorinated paraffin as a fixative in addition to the diphenyl carbonate. Colorimetric Indophenol Method. This, method was selected for estimating smaller amounts of the compound, as Snell and Riffin ( 1 1 ) reported it to be very satisfactory and the best available, I t involves decomposition of diphenyl carbonate by alkali to phenol, formation of a blue color by treating a buffered solution (pH 9.4 t o 9.8) of the phenol with a solution of 2,6-dibronioquiiione chloroimide, and estimation of the amounts of phenol by light transmittance measurements a t 610 millimicrons (6, I S ) . U'hen the method was applied as described by Snell (11) and ti,ansmittancies were read on a photoelcctric colorimeter, satisfactory results could be obtained under carefully controlled conditions of time and pH, but some inaccuracy was found because thr sample and blank transmittaricy readings increased in a variable manner with time. Gibha (6, 7 ) and others ( 2 , 3) reported t hat the 2,6-dibromoquinone chloroiniide decomposes slo\vly in alkaline buffers, giving rise t o discoloration of the wlutions, and it is thought that the variable transniittancy readings are due chiefly to the decompositioii of the excess 2,6-tlibromoquinone chloroimidr over that rtquircd to form the colored indophcmol compound. Bwausc an excess of the chloroimitle ovtir phcnol must br uscd (61, sonic nicaiis of removing o r tklstroying this escc~ssafter formation of the color was indicated as a possibility i n increasing thc stability of tht. color. Be Gieeiie, and Stmgcr (21, in o d e r to inci
A\-
D ETA1LEU BROhII R ' A TI 0 PROCEUVRE. Cut the cloth sample into 1-em. squares and ni to make the saniple more homogeneous. Estract a weighed sample of the cloth containing about 50 m g . of diphenyl carbonate for 1.5 hours with ethyl ether in a Soshlet type estractor with a paper thimble. (If Soxhlet equipment is not available, the cloth may be heated directly with the potassium hydroxide solution and the extract separated by filtration. Blanks will be slightly higher if this is done.) Evaporate tho ether carefully from the extract in the flask of the extractor and add 25 nil. of aqueous 0.2 S potassium hydroxide solution. (If a sample containing about 200 mg. or more of diphenyl carbonate is used, 0.5 S potassium hydroxide solution should be used in place of 0.2 S potassium hvdroxide and an aliquot portion should be used in place of the"entire extract.) Attach a reflux condenser to the flask and heat to boiling until the compound is saponified and in solution (requires from 20 to 30 minutes).
Table I. Comparison of Bromination and Colorimetric Indophenol \lethods for Determination of Diphen>l Carbonate in Cloth Impregnated in a Pilot-Plant 1 m pregnator
8ariiples w i t h chlorinatpd paraffin as tixatire
Sariiples ~\-itiioutfixative 8 9 10 11
i 4 , 3 .3 2 8 , 2.9 0.9 , o 9 0.04. 0 . 0 6
5 5 2.9 0.9 0.05
5.47
2.75 0.78 0.055
732
ANALYTICAL CHEMISTRY
diphenJ-l cartmiate will be present. If the amount of diphenyl carbonate is completely unknown, prepare several dilutions until the right range is obtained. I n each case, place 10 nil. of the diluted solution in a calibrated Klett test tube, add 0.20 nil. of the borate buffer solution, and mis well. Add 0.20 ml. of the 2,6dibronioquinone chloroimide solution, mix well, and allow t'o stand for 10 minutes. After 10 minutw, add 0.10 ml. of 0.3 .Y sodium tiydrosidrb solution :ind a l l o ~to stand for another 10 minutes. Prepare a blank solution undei, thrb sanie conditions, starting ivith 10 nil. (if distillrd 1vatc.r. Using the blank solution to adjust the inrti.unit:nt to 1007; transniit.tancay, read the transniittancy of tht. .;olution in a ~prctropti~)tomet('r at a wave length of 610 colorinic~tei~ such as the Klettmillimicrons 01' iir a pliotor~lr~ctric* . 59 (niasimum transmi4on 566 Pumnit~i~ion with l)roIvn t i l t r ~ i So. to 630 millimicrons). The rtwlinp ghould t)tl taken within 2 Tahlc 11. Effect of 4dtlitioii of Sodium I I > t l r o x i d e on hourb, nz the c,)lor l a t i t ~ sgradually with tinw aftcsr this period. Stahilit? of liidopheriol Color Reading9 of Nett-Summerson C D I U ~ ~ I I I at P I P ~ Preparc, ti curvc rdating colorimetei, readings with diphenyl carbonate conwntration, using known solutions treated as described Various Time Interval\ ~_ -~ abovt., and make the quantitative dcxtermination of tho unknon-n 1.5 2.0 30 4.3 60 90 140 l$0 Sainule min. niin. iiiin. inin, niin. m n . Inin. i m n . nun. by applying the reading obtained to the rurve. The curve readings should be checked with known solutione 0.01inp. of diphenyl cerbonate 142 146 147 150 1.33 153 136 I56 1.37 each time a ne\v buffer solution is prepared, as a slight change in Blank 36 41 43 45 48 49 52 51 54 pH may mnkc it necessary to prepare a new curve. Net reading 106 105 104 105 103 104 104 105 103 0.01 mg. of diphenyl carbonate + 0.1 m!. of 0.3 N KaOH after DI scu SSION 10 rmn. 144 144 143 143 143 143 143 142 140 Blank + 0.1 1111 of 0.3 S XaOH after 10 The best niethods evolved for diphenyl carbonate determinatiori min. 37 36 36 37 37 37 37 37 37 N e t rrading 107 108 107 106 106 106 106 103 103 are the bromination method for larger amounts (down to 20 mg.) and the colorimetric indophenol method for small amounts (20 tiown to 0.01 mg.). The method based on ultraviolet absorption measurements of diphenyl carbonate solution in 95% Some efforts xere made t,o find a suitable reagent which could ethanol or of ph(Lno1 solutions is offered only as an alt,ernate or be added to the solution to destroy the excess of 2,6-dibroniocheck method. I n the bromination and colorimetric indophenol methods for quinone chloroimide after formation of t'he blue indophenol coloi,. Reducing agents such as sodium sulfite, hydrazine, and hydrosyldiphenyl carbonate, the phenol liberated on alkaline decomposit,ion of the compound is estimated. Any free phenol present' a8 aniine destroyed t,he blue color. Ammonium hydroxide, which an impurity or from a prior breakdown of the compound would reacts with chloramides, and triethanolamine did not decolorize give high results. However, in the many samples of impregnated the blank solut,ion, but had a pronounced stabilizing effect on the colors of the sample and blank solutions; reagents such as anicloth handled which had been stored outdoors, or in tropical monium acetate, ammonium carbonate, ammonium oxalate, and storage, or had undergone launderings, t,he odor of free phenol wae not detectable. If phenol is found to be present in any samples; urea did not. This indicated that increasing the p H after de,it mal- hit determined separately by the bromination procedure, velopment of the color had a stabilizing action, and sodium alkalinr. decomposition of the diphenyl carbonate is omitted, as hydroxide, which was tried next, gave good results (Table 11). diphr~nylcarbonate will not brominate without prior alkaline deIt may also be observed ill Table I1 that, the net readings Cor composition. The free phenol can also be removed b?; ext,raction the unt,reated sample are fairly const,ant alt,hough t,he blank anti with a.atrlr, in which the diphenyl carbonate is insolpble. saiiiple readings increase with time. But if the times of the blank ;ilthough 110 appreciable interfprences Jwre encountered in deand sample readings \vert%not carefully controllvd (which is inttxrinining diphenyl carbonate in cloth by either the bromination convenient when many sirniplw ai'e run), large variations in thv or colorimetric. indophr.no1 methods, the phenol could be sepanet readings occurred. rat,ed froin nonvolatilt~intcLrfc,ring matrrials by distillation ( 2 ) . Trials with 0.1 nil. of 0.2 -\, 0.3 ,\-,and 0.6 .\ sodium hydloxidi~ solutions gave, like results, and it \vas decided to us(8 thr 0.3 nstrength. The addition of 0.1 nil. of 3 S sodiuni hydroxide changes LLTEKATURE CITED the p B from 9.8 to 10.9. Using 0.3 S sodium hydrosidc as described in the procedure bclow, a curve was prepared rclating Bailie;.. F.Ll-., arid Elbg, L. T . . I s r i . Erc;. CHEY...&NAL. ED.,18, 5:x5 (1946). Klett-Summerson co1oihr.tr.r wadirigs (logarithmic scal(a), using Beshgetoor, A . IT., Greene, L. >I., and Stenger, V. h.,Ibid.. filter S o . 59, with diphenyl carbonate concentrations. A straight 16,694 (1944). line was obtained up to a concvntration of 0.004 gram per liter Fulpniers, T., Chem. Weekblad, 31, 330 (1934). R-ith a reading of about 400; this cvncentration alsci applirs to Fraucis, d. W., and Hill, A. J., J . Am. Chem. Soc., 46, 2498 (1924). phenol. I n applying t h r nwthotl to elrith samplw w n t aining Gihh. T. R . P., Jr., "Optical Methods of Chemical Analysis," kn0u.n amounts of tiiplicnyl carbonate, no interf'ttrcwcw \vert1 ex1st ed., pp. 79, 113, New York, McGraw-Hill Book Co., 1942. perirnced in analyzing both purr-finish arid siz;cid cloth with and Gibbs, H. D., J . Biol. Chem., 72, 649 (1927). without chlorinatrd paraffin fixative. The method was found Gibhb. H. D.. J . Phgs. Chem., 31, 1053 (1927). "International Critical Tables," Vol. V,p. 361, 1st ed., McGrawt f i t w satisfactory for small aniounts of compound down t o 0.01 Hill Book Co., Yew York, 1929 nig,, but large aniounts involved the cryor uf large dilution. Klot,z. I. >I., J . ('hem. Education, 22, 328 (1945). Some results in comparison with the bromination met hod are Rudemian, I. IT,, ISD.EXG.CHEM.,- 4 ~ 4ED., ~ .18, 753 (1946). given in Table I. Siiell, F. D., and Biffen, F. M., "Commercial Methods of Analysis," p. 484, 1at ed., Sew York, McGraw-Hill Book CO.. 1941. DETAILED IP~DOPHENOL COLORIMETRIC PROCEUKRE. Cut the Sprung. M. M.,IXD.ENG.CHEM.,ASAL. ED., 13, 35 (1941). cloth sample into 1-cm. squares and mix. Extract a weighed Theriault, E. J., I n d . Eng. Chem., 21, 343 (1929). sample and saponify the extract as directed in the bromination K a u g h . T. D., Harbottle, G., and Noh-ea, R. M., IND. ENQ. procedure. Keutralize the resultant alkaline solution with CHEM.,ANAL.ED., 18, 636 (1946). dilute hydrochloric acid to a pH of about 7 and make up to a knoyn volume with distilled water. Dilute portions of this soluRECEIVED.Tanliar)- 29, 1848 tion to such a volume that not mure than 0.0025 mg. per ml. of the termining mere traces of phenol, corweritrated the colored conipound by acidifying the colored solution with hydrochloric acid, extracting M-ith chloroform, separating the chloroform extract, adding alcohol to the ext,ract, and finally making alkaline with sodium hydroxide. Although this procedure (a)is also reported to increase the stability of the color, it was desired to avoid the increased number of steps in the determination and the amount of handling of the colored compound for the authors' applicatioii which bivolved much 1argt.r ani(i~nitsof phenol.
