662
V O L U M E 19, N O . 9
Color. I n acid solution, the condensation product is capable of resonance without separation of charge after the addition of a proton to the carbonyl osygen:
I n support of this view, benzyl chloride, aldol conderisation products, and ketones (as dinitrophenylhydrazones) hsor been isolated from the reaction between benzaldehyde and higher aliphatic alcohols in high concentrations of hydrogen ion. -1mechanism for the oxidation is proposed, which ip supported by the formation of dibcnzalacetonc f om benzaldehyde ani1 isopropyl chloride under anhydrous conditions.
T h i s type of resonance undoubtedly accounts for ,he color.
LITERATURE CITED
IT.E., ISD.EX. C H m f . , -4x.k~.ED., 14, 20 (1942). Fellenberg, Th. von, Chon.-Zfg.. 34, 7 9 1 (1910). Fellenberg, Th. von, M i f f .Lebensm. Hyg., 1, 3 1 1 (1910). Komarowski, C h e m - Z f g . ,27, 807, 1806 (1903). Penniman, W. B. D., S:nith, D. C., and Lawshe, E. I., IND. ENO. CHEM.,ANAL.ED.,9, 9 1 ( 1 9 3 7 ) . Coles, H. W., and
SUMMARY
Experiments have been performed which indicate that the color produced in the Iiomarowski reaction is due to aldol condensation products which are formed through the two consecutive reactions:
+ RzCHOH +C,H,CH?OH + RzC 0 R,C = 0 + CsHjCHO +condensation products
Tournay,
PRESENTED before t h e Divieion oi .Inalytical and hlicro Chemist,ry a t t h e 108th Meeting of the .IJIERIC.AN CHEMICAL SOCIETY, rltlantic City, pi. J K o r k done in part in Frick Chemical Laboratory, Princeton, N . J.
CeHjCHO
Analysis of Hypochlor ite-Hypo bromite Sohtions LADISLAUS FARKAS
AND
I)I@NhCHERI LEWIN
Department of Physical C h e m i s t r y , T h e Hebrew C'niversity, Jerusalem
A method for the simultaneous determination of sodium hypochlorite and hypobromite, without and in the presence of bromide, chloride, bromate, and chlorate, is based on the selective reduction of hypobromite under certain conditions with alkali phenol solution; the sum of hj-pochlorite and hypobromite is estimated by arsenite and iodine in the usual way. The most suitable conditions for the analytical procedure are given, and the influence of various salts and other factors on the accuracy of the determination is described.
I
S T H E course of a n investigation carried out in this laboratory on the reaction between sodium hypochlorite and bromides ( I ) , an analytical procedure was required for the determination of sodium hypochlorite and sodium hypobromite separately in the presence of chloride, bromide, chlorate, and bromate ions. Various methods for determining hypochlorite in the presence of chlorite, chlorate, and hypobromite in the presence of bromite and bromate are described in the literature. (2, 3). T h e methods a r e based on the different osidation potentials and oxidative capacities of the substances in these two series of osyhalogen acids. Hair-ever, the system containing bo! h series of oxyhalogen acids has not yet been sufficiently investigated. The only publication on this subject is in the book of de Konirlcli and lleineke (If), b u t their procedure does not differentiate between bromide and hypobromite ions and allows only the total bromine to be estimated. Similar difficulties are encountered in the estimation of hypobromite by oxidizing it t o bromate, since the bromide present would also be oxidized t o bromate (10, 12). The method presented in this paper is based on the different' rates a t which phenol reacts in alkaline solution with hypochlorite and h>-pobroniite. T h e bromination of various phenols has been thoroughly investigated by Francis and Hill (6, 7 ) . These authors and Sprung (15) used this reaction for the quantitative determination of phenols. The brominating agent used was elementary bromine in acid solution obtained by acidifying a bromide-bromate mixture and estimating the excess bromine iodometri::illy. In a similar way, Kolthoff (8) used the bromination method for determining salicylic acid and Iiolthoff and Lingane (9)extended this method to the determination of other phenol deriyatives. They worked with a large excess of bromine water and converted phenol into trihromophenol bromide which was detrrniiiied either gravimetrically or iodometrically. Pollak ( I S ) u s d phenol in order to determine bromine in acid solutions.
Chapin ( 2 ) was the first to usti phenol for the reduction of sodium hypobromite. He found that phenol reacts selectively with sodium hypobromite, but not n.ith sodium bromite, and dweloped a method for the determination of bromite in alkaline solution in the presence of hypobromite. The chlorination of phcnol by hypochlorous acid was studied by Soper and Smith (Id), who found that the rate of reaction is proportional t o the concentrations of the free hypochlorous acid and the phenoxide ion. Esperiments on the reaction of phenol n.ith hypohromite-hypochlorite mixtures are described below, and an analytical method for the simultaneous estimation of both the hypochlorite and the hypobromite is given.
Table I. Influence of Salts and of the pH of Hypobromite Solution on Reduction of H\pobromite with a n ilLaline Phenol Solution ( I n each PH
experiment
12.1 12.1 12.1 12.1 12.1 12.1.
9.2 8.6 9.2
0 5975 millimole oi sodiuni h ~ p o b r o m i t etnben)
Salts Added Giam 0.2 SaCl 0.6 SaCl 1.0 SaCl 2.0 SaCl 0 . 2 CaCh
SaBrO Error llzllzmoie 0 0000 0 0005 0 000x 0 0036 0 0047 0 0060
., . . . . .
0 0000 0 0005 0 0000
+ 0 . 2 lrgcil 0 2 CaCh - 0 . 2 3IgC19
. . ..
-0
0 2 CaCh
2 NaClr
663
SEPTEMBER 1947 Table 11. Influence of Time of Phenol Action on -4ccuracy of Hypochlorite Determination ( I n each experiment, 0.7705 millimole of S a C l O dissolved in 15 nil. of distilled water, 5 nil. of 0.5% phenol solution, 5 ml. of 2 S sodium hydroxide, and 2 5 ml. of 0.1 .V arsenite were used) Time of Phenol Action S a C l O Error See. Millimole 15 -0,0008 -0 0012 30 60 -0.0045 120 - 0.0063
Table 111. Influence of Alkali Concentration on riccuracg of Hypochlorite Determination (Experimental conditions except addition of alkali same a s in Table 11. Time of phenul action 7 t o 10 seconds Initial volume of sample 25 nil ) Final Alkali 2 .V NaOH Concentration S a C l O Error .Wl .\ Mdlamole 3 0.27 -0.0005 2 -0.0015 0.19 1 -0.0120 0.11 0.5 -0,0320 0.07 0.0 -0.0717 0.03
REAGENTS USED
T h e sodium hypobromite solution was prepared by weighing o u t purified, chlorine-free, liquid bromine in ampoules and breaking them at 0" C. below the surface of an excess of 0.5 A' sodium hydroxide. T h e excess of sodium hydroxide was sufficiently great t o yield a solution having a p H greater than 12.0. Under these conditions, no bromite and bromate are formed, and the solution is stable at 0" C. for at least several hours. T h e sodium hypobromite solution thus obtained was 0.07965 S. T h e sodium hypochlorite solution was prepared by bubbling 70 grams of chlorine slowly through 1 liter of a 9 % solution of sodium hydroxide a t 0" to 2" C. The solution was diluted to give a n approximate 0.1 S solution of sodium hypochlorite and had a p H of 12.15. This solution was practically free of chlorite and chlorate, and was kept in glass-stoppered dark bottles in the refrigerator. T h e concentration of the solution was determined daily. Sodium arsenite, 0.1 S, and 0.05 .\r iodine were prepared according t o Clowes and Coleman ( 4 ) . Aqueous solutions of 0.57, phenol, 2 A' sodium hydroxide, 2 A' acetic acid, 5% sodium bicdroonate, 20% calcium chloride, 20% magnesium chloride, and 5 s boric acid were prepared from analytical reagents. REACTION OF HYPOBROMITE WITH PHENOL
'
T h e experiments were carried out by closely following Chapin's ( d ) procedure. Measured quantities of hypobromite solution were pipetted into Erlenmeyer flasks of 200- to 300-ml. capacity, requisite amounts of the 0.5yGphenol solution and the 2 9 sodium hydroxide were added, and the mixture was stirred vigorously. After a predetermined time (measured with a stop watch) a known quantity ol' excess 0.1 5- arsenite solution was quickly added. The arsenite was oxidized by any hypobromite remaining. After 5 minutes, 75 ml. of SCyGsodium bicarbonate, a fex drops of starch solution, and about 4 ml. of 2 S acetic acid \\-ere added slowly with vigorous shaking, until carbon dioxide began to be evolved. T h e solution was finally titrated with 0.05 -\-iodine. I n the experiments with sodium hypobromite, 15 ml. of a 0.07965 S solution, 25 nil. of 0.1 -V arsenite, and varying quantities of phenol a n d alkali (usually mixed before addition) were used. T h e volume of each sample before the addition of phenol and alkali was 25 mi. T h e sodium hypobromite solutions were freshly prepared, in order to avoid the presence of small quantities of sodium bromite 1%-hichare s l o ~ l yproduced on standing. Sodium bromite is not attacked by phenol, but is reduced by arsenite. I n the temperature range of 0' to 35' C., r i t h an alkali concentration ranging from 0.02 t o 0.7 and a 1.2- t o 7-fold excess of phenol, it v a s found t h a t the reaction bet.men sodium hypobromite and phenol is completed in less than 3 seconds. A reaction time u p t o 1 to 2 minutes does not affect the results. I n Table I the influence of p H a n d of the addition of neutral salts in various concentrations on the reaction b e t w e n sodium hypobromite and phenol is given. For each experiment, 0.5975 millimole of sodium hypobromite dissolved in 25 nil. of n-ater, 5 ml. of 0.5% phenol, 5 ml. of 2 -V sodium hydroxide, and 25 ml. of A\-,
0.1 S arsenite solutions were used. T h e time of interactiun x i s 7 seconds.
It is seen from Table I that in the presence of sodium chloride in concentrations u p t o 40 grams per liter the reaction 01"sodium hypobromite with phenol is complete. A t higher concentrations, the reaction is not quantitative. Calcium and magnesium chlorides interfcre \\-ith the reaction. On addition of either of these salts to the alkaline sodium hypobromite solution, a precipitate is formed which appears to consist of calcium or magnesium hydroside with adsorbed hypobromite. This effect is of no practical importance at low concentrations of calcium and magnesium, provided the solution is buffered to p H 8.5 l o !1.5, but at higher concentrations the error becomes appreciable. ESTIJIATION O F HYPOCHLORITE WITH ARSEXITE A Y D IODINE IR- PRESENCE O F PHENOL
The reaction of phenol ivith hypochlorite was investigated only in so far as it was of interest for t h e present analytical procedure. The influence of the time of interaction, the alkali concentration, and the addition of neutral salts on the accuracy of the analysis were determined. The experimental procedure !vas similar to that used in the case of hypobromite. It is seen from Table I1 that during the first 15 seconds sodium hypochlorite does not react with plieriol, and the arsenite-iodine analysis gives theoretical results. ;\ppreciable errors occur, hoivever, if the time of interaction is oiie niinilte or more. The results are then too low. I n Table I11 the influence of the alkali concentration on the reaction is summarized. .It concentrations lower than 0.2 .Y hydroxide, the hvpochlorite reacts with phenol and the r:tte of this reaction increases with decreasing alkali concentratici:i. This is in accordance with the views of Soper and Smith (1;). The addition of a fourfold excess of phenol, an increase of the and a variation of the teniperature of alkali concentration t o 1 &I-, the solution b e t w e n 0' and 3.5' C. introduce no error i n the estimation of the hypochlorite. Cliapin ( 2 ) made a certain correction in the iodometric estimation of bromite in the presence of phenol, since undzr his conditions iodine reacts slowly with phenol. The authors fouiid that if the temperature is below 20" C. during the iodorrietric titration, correct results are obtained. I n Table IV a number of experiments are listed iii which the p H of the hypochlorite solution and the concentration of neutral salts were varied. T h e p H of the solution was adjusted by addition of suitable amounts of boric acid and measured v i t h a glass electrode. The boric acid and the neutral salts were added to the hypochlorite solution immediately before the analysis, followed b?- the niixture of phenol and alkali. Tat& IS- shows that above pH 8.5 the hypochlorite estimation is quantitative. Sodium chloride in a concentration up to 100 grams per liter a:id calcibin chloride and magnesium chloride up to a conceiitration of 10 granis per liter do not impair the accuracy of the anal:;ai-.
Table IT. Influence of Salts and pH of Sodium Hl-pochlorite Solution on Determination of Sodium Hypochlorite in Presence of Phenol (Eacli sample contained O.iiO5 millimole of S a C i O ) S n C l O Solution, PH Stilts Added SaClO Error Gram Md11 m o l r 12 0 0 5 snC'1 12.0 1 0 sac1 i2.0 1 5 SaCl 2 0 s:,c'1 12.0 12.0 0 . 1 CJi'lt 0 . 1 LigClt 12.0 0 . 1 5 CaClt f - 0 0002 0.15 MgC12 12 0 0 . 1 CaCIt -0 0002 0 . 2 11pClp - 0 CIOOL' 10 0 ......., -O.O(I0L' 9 2 ........ - 0 000" 9 0 ..... .. , - 0,0015 8.5 ........
+
+
V O L U M E 19, " 0 . 9
664
Table V. Determinations of Sodium Hj-pochlorite and €1) pohromite at Different Ratios of Sodium Hypochlorite and Hypobromite and Different Neutral Salt Concentrations XaBrO Present
SaClO SaC'IO 1're:eri t Error .\fdlzmole 0.7705 0.7705 0 Ti05 0 7705 0 , iiO5 0 5135 0 2568 0 1540 0 , 7iO5 0 7705 0 Ti05 0 7705
SaBrO Error
.lIilliinde
0.0 -0,0012 - 0,0005 0.0 0.0 - 0.0005 0.0 -0.0005 -0.0005 -0,0013 0.0 0.0
0.0 0.5975 0.3980 0.1890 0.1195 0.5975 0.5975 0,5975 0.1990 0,1990 0,1990 0.1990
0.0 0,0012 0.0005 0.0 0.0 0.0005 0.0 0.0005 0.0005 0.0013 0.0 0.0
Salts Added Gram
Notes. If magnesium and calcium ions are present in the sample the total alkali added should be sufficient for the precipitation of these ions and a final alkali content of at, least 0.25 N should be reached. If the temperature is over 20" C. the solution should be cooled or cooled bicarbonate solution used. The use of a beaker for the arsenite solution irS recommended, in order t o make the addition of arsenite as rapidly as possible, so as to limit the time of the phenol action t o 7 to 10 seconds. For the low concentrations of hypochlorite 0.04 5 arsenite and odine solution should be used. The amount of hypobromite is given by the difference of the result of titrations 1 and 2.
.... ,...
.... ....
.... ..,. .... 0 . i 'Kcio, 0 . 3 KClOr 0 . 5 NaCl 1.0 SaCI
SI\IULTAVEOUS ESTIMATIOV OF HYPOCIILORITE ANI) HYPOBROLIITE
.
For the siniultaneous estimation of hypochlorite and hypobromite t1i-o titrations are required: determination of the sum of hypochlorite and hypobromite, and determination of the hypochloriti, ~ ( i r i t r n of t the solution after the reduction of hypohromite by phenol. Aiseries of analyses of such mixtures is shoxm in Tahle \-. Solutions of known concentrations of hypochlorite and hypobroniitcl n.c.:.e prepared by mixing sodium hypobromite and sodium hypociilorite solutions inimediately before the analysis. Sincc the hypobromite solution contains bromide ions and these ions react with hypochlorite according to Sac10
+ Br-
=
SaBrO
+ C'l-
The 5p-ml. beaker is rinsed twice with distilled water, and then, 5 minutes later, rinsed again with 75 ml. of 5% sodium bicarbonate solution. .-icetic acid, 2 -Y, is then added dropwise with vigorous shaking until carbon dioxide begins t o be evolved. The titration iodine solution in the is performed, as under ( l ) , with 0.05 -I' presence of starch, until a permanent light blue color appears.
(1)
this precaution is necessary in order to avoid errors due to this reaction. Reaction 1 IW.S investigated a t the authors' laboratory (1) and it n-as found that its rate decreases considerably viith increasing pH. Therefore, the hypobromite solutions rr-ere maintailled sodium hydroxide strongly alkaline by adding t o them 2 nil. of 2 'I' btifore mixing them with the hypochlorite solution. The results shoxn in Table \- are given in millimoles of sodium hypoelllorite and sodium hypobromite. The error does not exceed 0.2' i-i,e,, it is about equal to the usuaI error of titrations. The addition of chloride and chlorate does not impair the accuracy of the analysis. T h e influence of these ions v a s tested, since they are usually formed in hypochlorite solutions on standing. I n v i w of the above i t is not necessary to use freshly prepared hypochlorite solutions for the analyses. A S A L Y T I C i L PROCEDURE
On the basis of the above results, the following procedure for the simultaneous estimation of hypochlorite and hypobromite, chloridr, bromide, chlorate, and bromate is recommended. 1. Estimation of the S u m of Hypochlorite and Hypobromite. I n a 300-1n1. Erlenmeyer flask 25 ml. 0.1 S arsenite and 75 ml. 5C; sodium bicarbonate are mixed and the sample to be analyzed is added to this mixture. Care should be taken that a t least 2 ml. of 0.1 S arsenite remain in excess. =ifter 5 minutes 10 drops of frcshlv prepared lYc starch solution are added and then under vigorourstirring 2 t o 3 ml. of 2 S acetic acid are added dropwise until carbon dioxide begins t o evolve. The excess arsenite is titrated n-ith 0.5 S iodine solution until a permanent light blue color appears. 2 . Estimation of Hypochlorite. T h e sample t o be analyzed, containing about 0.1 t o 0.9 millimole of hypochlorite and 0 to 0.9 millimole of hypobromite, is dissolved in 30 ml. of water. I n case it is buffered. 2 ml. of 2 S sodium hydroxide are added. T o this sample, contained in a 300-ml. Erlenmeyer flask, a mixture of 10 ml. of 0 . 5 5 phenol solution and 10 ml. of 2 A- sodium hydroxide is rapidly added with vigorous shaking. (The amount of alkali added is calculated so as t o bring the final alkalinity t o a t least 0.25 Shaking is continued for 7 t o 10 seconds and then 25 nil. of 0.1 S sodium arsenite are added from a 50-ml. beaker.
3. Determination of Bromate. The sum of bromate, hypobromite, and hypochlorite is determined by adding 3 grams of potassium iodide to the sample and acidifying with sulfuric acid, so t h a t the final acid concentration is about 0.5 S. The iodine set frce is titrated in the usual way, and the difference b e t m e n the results of this titration and titration 1 gives the amount of bromate. 4. Determination of Chlorate. The chlorate ion is determined by reducing all the ions-chlorate, bromate, hypochlorite, a n d hypobromite-with ferrous sulfate and by titrating the excess of ferrous ion with potassium permanganate. 5. Estimation of the Sum of Chloride and Bromide Ions. An excess of hydrogen peroxide is added t o the alkaline sample, reducing hypochlorite and hypobromite t o chloride and bromide. After the excess hydrogen peroxide is boiled off, the solution is neutralized with acetic acid and titrated with 0.1 S silver nitrate with potassium chromate as indicator. The difference between this titration and titration 1 indicates the sum of chloride and bromide. 6. Estimation of Bromide. Bromide can be estimated according t o t,he procedure described in (.?'), in another aliquot of the solution which is obtained after boiling off the hydrogen peroxide. Since this estimation gives the sum of hypobromite and bromide, the difference between this titration and t'he amount of hypobromite as determined under ( 2 ) gives the amount of bromide initially present. AC~NOWLEDGLIENT
The authors are grateful to R. Bloch, of Palestine Potash, Ltd., for useful discussions in the course of this investigation. One of the authors (11.L.) is indebted to Palestine Potash, Ltd., Jerusalem, Lodzia Textile Co., Ltd., Tel-Aviv, and .-ita Textile Co., Ltd., Haifa, for a grant which enabled him to carry out this investigation. LITERATURE CITED
(1) Bloch, R., Farkas. L., and Lewin, M., unpublishkd results. (2) Chapin, R.. J . Am. Chem. Soc., 56, 2211 (1934). (3) Clarens, J.! Compt. rend., 157, 216 (1913).
(4) Clowes and Coleman, "Quantitative Chemical hnalysis," 14th ed.. p. 190, London, J. & A. Churchill, 1938. (5) Farkas, L., and Lewin, M..ANAL.CHEM.,19,665 (1947). (6) Francis, A . W., J . A m . Chem. Soc.. 48, 1635 (1926). (7) Francis, A . W,, and Hill, A . J.. I b i d . , 46,2498 (1924). (8) Kolthoff. I . M.,.Pharm. W e e k b l a d , 69, 1159 (1932). (9) Kolthoff, I. >I., and Lingane, J. J., I b i d . , 69,1147 (1932). (10) Kolthoff, I. &I., and Yutzy, H. C., ISD.ESG. CHEM.,4 h - a ~ ED., . 9, 75 (1937). (11) Koninck. J . J. de, and Meineke, C., "Lehrhuch der qualitativen und quantitativen chemischeii Analyse," Vol. 2, p. 345, Berlin, 1904; quoted in "Gmelins Handbuch der anorganischen Chernie," 8th ed., Vol. 7, p. 303, Berlin, Chemie G.m.b.H., (1931). (12) Meulen, J. H., vander, Chem. Weekblad,28,82 (1931). (13) Pollak, F., Z . anorg. Chem., 156,179 (1926). (14) Soper, F. G., and Smith, G. F., J . Chem. Soc., 1926,1582. (15) Sprung, M. M:, I N n . ENG.CHEM.,A x . 4 ~ED., . 13,357 (1941), PARTof a thesis submitted b y Alenachem L e a i n to the Senate of the Hebrew University, Jerusalem, Palestine, for the P h . D . degree.
