July 15, 1931
INDUSTRIAL AND ENGINEERING CHEMISTRY
per cent is probably nearer to the true value than is the theoretical 100 per cent. This idea is substantiated by the fact that, if 97.4 per cent is taken in calculating the theoretical per cent of methane in the hydrogen and methane mixture, it gives a value of 49.6 per cent, which is only 0.1 per cent lower than the mean of 49.7 per cent experimentally determined for this. The theoretical purities of the other gases are considered to be correct. The authors believe that Table I is representative of the degree of precision which is to be expected from this type of microanalysis. It is of the same general order as that of macroanalysis.
269
Acknolyledgment
The first named author was the holder of the du Pont fellowship of the Department of Chemistry while this research was in progress and wishes to express his appreciation for this substantial aid. Literature Cited (1) Christiansen, J . A m Chem. Soc., 47, 109 (1925); 2. anal. Chem , 80, 435 (1930). (2) Dennis, “Gas Analysis,” p. 371, Macmillan, 1920. (3) Gbye and Germann, J . chim. phys., 14, 194 (1916). (4) Langmuir, J . Am. Chem. Soc ,34,1310 (1912). ( 5 ) Reeve, J. Chem. Soc., 126, 1946 (1924). (6) Ryder, J . Am. Chem. Soc., 40,1656 (1918).
Acid Value of Cellulose Fatty Acid Esters and
Rapid Analysis of Certain Cellulose Acetates’ T. F. Murray, Jr., C. J. Staud, and H. LeB. Gray EASTMAN KODAK Co., ROCHESTER, N Y.
Some of the more important methods to be found in and Singer (14) published a INCE cellulose acetate the literature for the determination of the acetyl value modification of it. was first prepared, and of acetylated compounds have been critically reviewed. Cross and B e v a n (1) proe s p e c i a l l y when celluThe method of Eberstadt has been found to be basically posed the use of sodium ethlose acetates became of techthe best suited for work with acetylated cellulose, but oxide for saponification, pernical importance, the question it has been modified slightly in the !nterests of economy mitting the sample to stand of determining the acid values of material and time. a t room temperature for 12 of the esters p r o d u c e d has A method is described for the determination of acetic hours. Wood b r i d g e ( I 5 ) been the subject of numerous acid and formic acid in the presence of each other and found that best results were investigations. The methods in the presence of one or more acids not volatile with obtained on standing for 16 employed have fallen into two steam. hours, and &fork (Q), on atgeneral classes : acid hydrolyA method is proposed for the analysis of cellulose tempting to use higher temsis and saponification with acetate by means of which the saponification time is peratures to increase the rate alkali. hour, and the time of pretreatcut from 24 hours to of saponification, found that T h e a c i d hydrolysis was ment is cut from 30 to 15 minutes. The results obthe effect of sodium ethylate p r o p o s e d b y O s t in 1906 tained by the method are in close agreement with those as ordinarily used a t refluxing ( I O ) , and in the same year obtained by the slower method. temperatures, was to produce by G r e e n a n d P e r k i n (4) Suggestions are made for a method of precipitating acid groups in the cellulose who added alcohol, removed the cellulose acetate in order to render it readily soluble residue, thus causing high apthe ethyl ester by distillain warm pyridine. parent acetic acid values. He t i o n , and saponified it with Some of the limitations of the pyridine method are proposed the use of a 0.5 N alkali. indicated. The acid method has two solution of sodium hydroxide major disadvantages: It is in which the solvent is a mixtime-consuming and its accuracy is subject to question. The ture of equal parts of water and ethyl alcohol. various processes calling for the distillation of ethyl acetate I n 1909, too, Eberstadt (2), working under Knoevenagel, instead of acetic acid (3,4) were devised to increase the speed prepared a dissertation in which he showed that preliminary of the determination. Inaccuracies were due to the large swelling of the acetate in alcohol-water or alcohol-acetone amount of distillate that was required and the indefiniteness mixtures increased its porosity and facilitated saponification of the end point of the hydrolysis and distillation. Fre- with 0.5 N potassium hydroxide. After that time, Knoevenaquently the action of the strong acid on the cellulose residue gel (6) and his pupils did considerable work on the analysis produced formic acid which distilled with and was titrated of cellulose acetates. T o r i (IS) compared the methods of Green and Perkin, Ost, as acetic acid. Sulfuric acid was commonly used to hydrolyze the cellulose ester, and the organic matter often resulted in Woodbridge, Barthelemy, Eberstadt, and Barnett. He the reduction of part of it to sulfur dioxide, causing high concludes that Eberstadt’s method is best in principle, but he recommends saponification with 1 N alkali for 1 hour a t results. Hess (6) continued to support the acid hydrolysis method room temperature, a period which has been found to be far and with some of his pupils has devised an elaborate system too short for some cellulose acetates. for buffering his sulfuric acid before distilling, and then Kruger (8) again reviewed the literature on the determinacarrying out the distillation under reduced pressure and also tion of the acetyl values of cellulose acetates and pointed employing steam and hydrogen (6). There were, however, out that for technical purposes the alkaline saponification is objections to the method, and the following year Weltzien favored. Technical control in the production of cellulose acetate 1 Received March 7. 1931. Communication 461 from the Rodak Remade it necessary to select a method which would first give search Laboratories.
S
ANALYTICAL EDITION
270
reasonably accurate results, and second, would allow as large a number of samples as possible to be analyzed in a specified time. Experimental Procedure
For the purpose of evaluating more critically the methods available at that time, the following experiments were carried out. Refluxing the sample with 0.5 N sodium hydroxide for various lengths of time was tried, but the results obt?ined were irregular and unsatisfactory, as shown in Table I. Table I-Acetyl
Values Obtained b y Refluxing Cellulose Acetate with 0-5 N Sodium Hydroxide CHaCO
HOURS
% 2 3 4
4a.8 43.1 44 6 43.5. av.43.5 43.9: 44.9: 45'0: 45.1; av. 44.7 44 S 44 4. av 44 6 46.4:46 51 av: 45.9 46.2 43.0
6
8 9
The same was true when the samples were saponified on a steam bath, indicated by the results given in Table 11. Table 11-Acetyl Values Obtained by Heating Cellulose Acetate on S t e a m Bath with 0.5 N Sodium Hydroxide HOURS CHaCO G7"
,Y
2 21/2 3 5
42.6,41.4; av. 42.0 43.0,42.1; av. 42.5 AX 3
8
iz:s, 42.0: av. 43.3 42.4
16 24 30 48
47.5 48.4,47.9; av. 48.1 49.1 55.8, 54.6; av. 55.2
Experiments were run in which the sample, after refluxing in alkali for varying lengths of time, was acidified, the carbon dioxide boiled out, and the excess acid retitrated. The results so obtained also varied as Table 111 shows. Table 111-Acetyl Values Obtained by Refluxing Cellulose Acetate with 0.5 N Sodium Hydroxide a n d Correcting for Absorbed Carbon Dioxide HOURS CHiCO
2 3
4 6 9
%
41.1 42.4.43.8.43.2.40.7: av. 42.5 41.0' ' 43.6,42.2: av. 42.9 41.9
These data seemed to point to a reaction between cellulose and air, giving a compound which neutralized part of the sodium hydroxide. To investigate this, runs were made with filter paper and with cotton in which 0.5-gram samples of the material were refluxed for 3 hours with 20 cc. 0.5 N sodium hydroxide. One experiment with each material was refluxed in the usual way, a second was refluxed with an introduction into the reaction flask of a slow current of air, and a third was similarly treated but with hydrogen substituted for the air. The excess alkali was titrated back, and then the solution was acidified, the carbon dioxide boiled out under reflux, and the excess acid titrated back, giving the acetyl value corrected for carbon dioxide. The results are given in Table IV. Table IV-Acetyl
Values Obtained b y Refluxing Filter Paper a n d Cotton with 0.5 N Sodium Hydroxide Time, 3 hours: cotton, 99.5per cent alpha cellulose APPARENT ACETYL VALUE PROCEDURE Uncorrected Corrected for COi % ' CHaCO % ' CHaCO FILTER PAPER
Regular With air With hydrogen
3.4 4.6 2.7
2.6 3.5 2.5
6.2 11.3
5.4 9.0 5.7
COTTON
Regular With air With hydrogen
...
Several runs were made in which cellulose acetate was saponified with 2 per cent sodium hydroxide] acidified with
Vol. 3, No, 3
phosphoric acid, alcohol added, the ester distilled into standard alkali, and the amount of acetate in the original sample determined. The apparent acetyl values thus found varied and increased when darkening took place during distillation, as shown in Table V. Table V-Acetyl Values Obtained by Refluxing Cellulose Acetate with 0.5 N Sodium Hydroxide, Adding Methanol a n d 10 CC.of 85 per c e n t Phosphoric Acid Distilling into 0.5 N Sodium Hydroxide, Saponifying aGd Titrating Excess Sodium Hydroxide METHANOL USED ACETYL VALUE cc. % CHsCO 35 75 65 115 225 125 43.4 200 43 9 46 6, 41,O; av. 43.8 250 44.9 150 46.6 300 49.5 250 47.6b 150 47.8b 1500 0 oc 150a 3.2b a Purified Peruvian sliver. b Darkened. 0 Not healed to darkening
Eberstadt's method was investigated and found to be the most satisfactory. For convenience the proportions used were modified somewhat. Thus, instead of a 1.0-gram sample and 50 cc. of 0.5 N potassium hydroxide, a 0.5-gram sample and 20 cc. of 0.5 N sodium hydroxide were used. While this smaller sample gave a slightly larger margin of error, this was more than outweighed by the convenience gained. With the above proportions, duplicate runs can be made using no more of the cellulose acetate than would be required for a single determination by the original Eberstadt method, a given quantity of standard solutions would serve for two and one-half times as many determinations, and in the case of all technically usable cellulose acetates thus far examined, four samples can behitrated back with one fdling of a 50-cc. buret. These time economies are important where a great many samples are being analyzed each day. Details of Present Method for Use with Cellulose Acetate
The material to be analyzed is dried to constant weight a t 105" C., and a 0.5-gram sample of the cellulose acetate is accurately weighed and put into a 250-cc. Erlenmeyer flask. To this are added 20 cc. of 75 per cent aqueous ethyl alcohol and the flask kept at 50" to 60" C for */2 hour.2 To each Aask are then added 20 cc. of 0.5 sodium hydroxide, the flasks tightly closed with rubber stoppers and kept in the bath for 15 minutes longer, then a t room temperature, with occasional shaking, for 24 hours, or 48 hours if the material is hard and horny. At the end of this time the sides of the flask are washed with 50 to 75 cc. of distilled water, 2 drops of 1per cent phenolphthalein solution are added, and the excess alkali is titrated back. With some samples there is a tendency for the cellulose to retain some of the alkali after the solution becomes colorless. I n such cases it is necessary to stopper the flask again and allow it to stand, adding standard acid from time to time until the solution shows no further tendency to become red. The acetyl (CH3CO-) value of the sample is calculated from the fdlowing formula:
.
% CHaCO =
0.0215 X cc. 0.5 NaOH X 100 weight of sample
Table VI gives the analysis of several samples of cellulose acetate using the above method. The results were taken from among a great many analyses of commercial and experimental cellulose acetates with a maximum range of acetyl content. 9 I t has been found convenient to use a double-walled bath in which acetone is kept refluxing. In this way a temperature of 53 O C. is maintained with a variation of not more than l o C.
INDUSTRIAL AND ENGINEERING CHEMISTRY
July 15, 1931
of Cellulose Acetate Using Method Described ACETYL SAMPLE ACETYL % CHsCO% CHaCO44 6 to 44 6 I 32 9 to 33 1 44 5 to 44 6 22 7 to 22 s 42 6 to 42 8 13 2 to 13 2 39 8 to 40 1 L 11 4 t o 11 8
Table VI-Analysis
SAMPLE A
H
B
C D E F G H
39 38 37 37
4 to 0 to 7 to 0 to
34 38 37 37
M N 0
4 1 9 0
4 8to5 0
3 7to3 9 16tol 7
The completeness of the saponification by this method is indicated by the following experiments: Two 25-gram samples of cellulose acetates A and B were saponified by the above method and the residues filtered off, washed, and dried. Samples of this recovered material were then analyzed for acetyl by the above method with the results shown in Table VII. Table VII-Analysis of Residue for Acetyl Weight of sample. 0 5 gram SODIUM HYDROCHLORIC ACID HYDROXIDE REQUIRED FOR RESIDUE USED BACKTITRATION Sample from A Sample from B Tissue paper control
cc.
cc.
19 90 19 90 19 90
19 90 19 86 19 91
271
Rates of Acetone-Soluble Cellulose Acetate ACETYL ELIMINATED TIMEOF SAPONIFICATIONWithout preWith treatment pretreatment Hours Minutes % CHsCO % CHICO 1 15 36.7 1 25 33: 6 .. 2 35 37.2 .. 37.2 5 15 17 30 39:7 23 39:s 24 .. 39:6
Table IX-Dl'ksteriecation
These results are shown graphically in Figure 2.
I
0
R A T E O F SAPONIFICATION O F C O M M E R C I A L C E L L U L O S E ACETATE. (ACETONE. SOLUBLE)
I
SOLID L I N E - A L C O W O L TRETATEDI TREATED.
While satisfactory results can be obtained in the analysis of acetone-soluble cellulose acetates by the alkaline saponification without a preliminary treatment with alcohol, this is not true of the triacetate, as the following results indicate. Figure 2 T 0 3 fl
45.-
u
RATE O F S A P O N I F I C A T I O N O F FINELY DIVIDED CELLULOSE ACETATE.
. .
-
r
u
A
ALCOHOL T R E A T E D . B-CELLULOSE TRI-ACETATE. N O T ALCOHOL TREATED. C- ACETONC SOLUBLE. CELLULOSE ACETATE WITH O R WITHOUT A L C O H O L TRERTMENT.
"'k
8
1;
h8 &
1 6 O; 24 db HOURS IN A L K A L I
& 4k
i 8
'
Figure 1
I n Table VI11 (see Figure 1) are given the rates of deesterification of very finely divided cellulose triacetate and of acetone-soluble cellulose acetate, both when pretreated with 75 per cent aqueous ethyl alcohol a t 53" C., and when such treatment is omitted. Saponification was carried out a t room temperature. Rates of Finely Divided Materials ACETONE-SOLUBLE CELLULOSE TRIACRTATE CELLULOSE ACETATE TIMEOF Without With Without With SAPOXIFICATION alcohol alcohol alcohol alcohol Hours % CHsCO % CHICO 74 CHsCO 74 . _ CHsCO 38.5 38.3 38.5 38.5 38.5 38.3 38.3 38.1 38.1 38.1 38.1 38.1 Table VIII-De&terification
When acetone-soluble cellulose acetate in the form in which it is usually employed in technical operations was used instead of the finely divided material on which Table VI11 is based, saponification was very much slower, owing to the much smaller surface area exposed. Table I X gives the results of these analyses both when the sample is pretreated with 75 per cent alcohol and when this treatment is not used.
The saponification can be brought t o completion more quickly if the samples are allowed to remain for a longer period a t 53" C., as indicated by the fact that 39.1 per cent acetyl was eliminated in 1.5 hours a t this temperature following pretreatment with alcohol. Long treatment a t elevated temperatures is not recommended, however, owing t o the tendency of the alkali to attack the cellulose under these conditions. In the case of acetylated sugars, acetylated degradation products of cellulose, and cellulose mixed esters where one of the acid residues is formic or an acid not volatile with steam and the other is acetic or some other steam distillable acid, a modification of the above procedure may be successfully used. Direct titration of the excess alkali would not give a measure of the ester content in the case of esters of degraded cellulose and some sugar acetates, either because of the pronounced color developed in the presence of the alkali, or because of a reaction between the carbohydrate residue and the alkali which would give a high acid value. I n the case of mixed esters, it is obvious that direct titration would not show the relative amounts of the various esters. In such cases the saponification is carried on as above, and for mixed esters total acidity is determined by back titration. Any insoluble matter is filtered off, an excess of 30 per cent tartaric acid solution is added, the solution is transferred to a boiling flask connected for steam distillation, and the volatile acid or acids are distilled. By maintaining a small volume, and therefore a high salt concentration in the distilling flask, the amount of distillate necessary to carry over all of the volatile acids is reduced to 2 liters as against 4 or 5 liters when considerable water accumulates. When 2 liters of distillate have been obtained, if no formic acid is present the distillate is boiled under reflux to free it of carbon dioxide, cooled with a soda lime tube in the condenser, the condenser washed out with distilled water, and the whole titrated to neutrality using phenolphthalein and standard alkali. A non-volatile acid would be obtained by difference. I n cases where formic and one other volatile acid are present together, the distillate is made alkaline with sodium
272
ANALYTICAL EDITION
carbonate, evaporated on a steam bath to small volume, and the formic acid determined according to the method of Ost (11) in which an excess of standard potassium permanganate is added to the alkaline solution which is then heated to 60" C . for 5 minutes. It is acidified with dilute sulfuric acid, an excess of oxalic acid solution, which has been recently standardized against the potassium permanganate, is added, and the excess oxalic acid titrated back with standard potassium permanganate. After the formic acid has been oxidized, the solution is made slightly alkaline with sodium hydroxide, an excess of tartaric acid solution is added, and the solution is again distilled at high concentration, collecting 2 liters. The carbon dioxide is boiled out as before and the other volatile acid is determined in the cooled solution. The results so obtained are accurate to within 0.6 per cent and easily reproducible. Rapid Method for Acetyl Determination While the method for acetyl determination given above is perfectly satisfactory for routine determinations, there are times when a much more rapid method would be desirable. In the majority of methods proposed heretofore for the , determination of acetyl content, it is apparent that the limiting factor in the rate of saponification of the cellulose acetate is the rate of diffusion of the alkali into the mass and the diffusion out of the saponification products. It has therefore appeared desirable to attempt determinations in highly dispersed phase systems. To this end a sample was dissolved in 20 cc. of acetone and to this were added 20 cc. of 0.5 N sodium hydroxide with gentle agitation. The sample was then let stand at room temperature. Table X gives the results obtained b y this procedure. Table X-Determination i n Acetone TIMEOF SAPONIFICATIONACETYL ELIMINATED % CHsCO 45 minutes 39.6 2 hours 39.4
250 cc. capacity. To each are added 20 cc. of Eastman pyridine. The flasks are covered with an inverted beaker, or loosely stoppered and warmed on a steam bath or in the 53 O C. constant-temperature bath with occasional shaking until the cellulose acetate has completely, dissolved. This should not require more than 15 minutes. To each flask are then added 20 cc. of 0.5 N sodium hydroxide, while shaking gently to disintegrate any precipitate that forms. The flasks are tightly stoppered with rubber stoppers and placed in the 53" C. constant-temperature bath for hour. At the end of this time the sides of the flask are washed with about 25 cc. of distilled water, two drops of phenolphthalein are added, and the excess alkali is titrated back with standard acid until the solution becomes just colorless. Using the pyridine method the tendency of the cellulose to retain alkali which diffuses out of the material slowly, thus delaying final back titration, is eliminated. This fact also increases the speed of the determination. The acetyl value is calculated according to the formula given above. Table X I gives the results obtained when the pyridine method of analysis is used, as compared with the results obtained with 75 per cent alcohol pretreatment method and allowing the samples to stand at room temperature for 24 hours. Table XI-Comparison
of Acetyl Values Obtained by Pyridine and
Eberstadt Methods SAMPLE MODIFIED DESIGNATED EBERSTADT METHOD PYRIDINE METHOD % CHaCO % CHnCO 39.3, 39.7, 39.6, 3 9 . 3 39.8 39.8 38C-41 43.5,43.7 43.4:42.8 13770 40.4, 40.4 40.2,40.2 14770 D 35.7,35.9 14770K 35 9 35 7 50C-41 44:9: 4 4 : 7 44.7 44.7 44.7 5597 38 9 38 7 38 7: 3 8 . j 5633 37.8: 37:S, 3 7 . 8 , 3 8 . 1 3 8 . 5 , 38.1, 38.3, 38 1 5635 38 3 3 8 . 3 38 1, 3 8 . 1 15881A 41: 3: 4 1 . 3 41.1, 4 1 . 1 15881B 41.3, 41.3 41.3.41.3
-
The range of acetyl values used with the pyridine method has been from the triacetate with an acetyl value of about A sample of the cellulose acetate was dissolved in acetone, 44.8 to an acetate which contained 35.8 per cent CH3C0. and after the alkali was added the sample was held at 53" C. On all of these materials covering a range of nearly 10 per cent for hour. The acetyl value so obtained was 39.8 per cent. CH&O, the method worked satisfactorily provided the From the above data i t would appear that determinations conditions prescribed were rigidly adhered to. An important factor in the procedure is that the cellulose made in acetone might be satisfactory for the purpose of plant control. The range of acetone solubility is, however, acetate used must be in such a physical condition that it is rather restricted, and a solvent which would have a wider easily and readily dissolved in warm pyridine. To accomplish range of solubility and which would not be affected by the this, the acetylation solution on which the analysis is to be alkali appeared to be more desirable. Pyridine answered made is diluted with two to four volumes of acetone and prethe requirement of greater solubility range. To study the cipitated by pouring it, in a small stream, into six or eight effect of alkali on acetone and on pyridine, 20-cc. portions of volumes of hot water (85" to 95" C.), This gives a finely alkali were pipetted into each of six flasks. To two of these divided or fluffy precipitate, which dissolves readily and comnothing was added, to two were added 20-cc. portions of pletely in pyridine even in the case of cellulose triacetate acetone, and to the remaining two were added 20-cc. portions acetylation solutions. If the precipitate consists of large, of pyridine (Eastman white label). After standing stop- hard nodules, the pyridine gelatinizes them without bringing pered at room temperature for 11/2 hours, the alkali was ti- them into solution and the results are low. This is illustrated by the results obtained on a sample of trated with 0.5 N hydrochloric acid, using phenolphthalein as an indicator. The amount of acid used was exactly equal precipitated cellulose triacetate. This acetate, by the modito the amount of alkali in the blank and when pyridine was fied Eberstadt method, gave values of 44.5, 44.7, 44.7, and added, but the acetone samples required 0.10 cc. less acid 44.7 per cent CH,CO. Samples of the same material heated than did the checks. To investigate further the effect of with pyridine for 30 minutes on a steam bath then held a t hour after the addition of the 0.5 N alkali gave alkali on pyridine, 20 cc. of 0.5 N alkali were added to 20 CC. 53" C. for of pyridine and the solution was kept at 53" C. for 2 hours. 43.9 to 43.5 per cent CHaCO. A sample given a pretreatment The alkali was then titrated back and required 20 cc. of 0.5 N in pyridine for only 15 minutes gave a value of 42.8 per cent. Upon long contact pyridine appears to react with the celluacid. *From the foregoing results it appeared that pyridine would lose acetate, especially in the presence of sodium hydroxide. be an ideal medium in which to carry out acetyl determina- A sample treated as for the above method of analysis was tions. The method suggested below is devised for rapid saponified a t 53" C. for 48 hours. The sample became brown determinations of acetyl content of cellulose acetate contain- and the end point was indefinite. A second sample of cellulose acetate was dissolved in pyridine and the solution held ing between 44 and 35 per cent CHICO. The cellulose acetate is weighed out, using 0.5-gram por- at 53 C. for 48 hours. The alkali was then added and saponihour at 55" C. The acetyl tions, and transferred to Erlenmeyer flasks of 200 CC. or fication was carried on for O
July 15, 1931
INDUSTRIAL AND ENGINEERIN% CHEMISTRY
value SO obtained was 40.4 per cent, an increase of 0.6 per cent over the value obtained when the analytical procedure given was strictly followed.3
273
(4) Green and Perkin, J . Chem. Soc., 89,811 (1906). Weltzien*and Messmer#Ann.*4359 e4 (1924). , (6) Knoevenagel, Chem.-Zlg, 39, 248-9 (1922) (7) Knoevenagel and Konig, Cellulosechemie, 3, 113-21 (1922), (8) Kruger. Farben-Zlg , 36,2032 (1930). Literature Cited (9) Mork, J . A m . Chem. Soc., 31, 1069 (1909). (10) Ost, 2. angew. Chem , 19,993 (1906). (1) Cross and Bevan, Worden Tech. Cellulose Esters VIII, 2 (11) Ost. Chem.-Ztg, 32, 815 (1908). (2) Eberstadt, Dissertation, Heidelberg, “uber Acetylcellulo Schultze and Hew, Ann , 490, 65 (1925) (3) Freudenberg, Ann., 433,230 (1923). - (12) (13) Torii,’J. C h x . I n d . (Japan),25, 118-31 (1921). ’ a Subsequent to the carrying out of this work, a procedure using pyri(14) Weltzien and Singer, Ann., 443, 71 (1925). dine was published by Battegay and Penche, Bull. SOC. chim., 46, 132 (J929). (15) Woodbridge, J . Ana Chena. Soc ,31, 1068 (1909). Hessp
L
Determination of Phenols in Water Solution Adaptation of Bromine Method to Include Range of 1 to 75 p. p. m.‘ J. A. Shaw2 MELLON INSTITUTE
OF
INDUSTRIALRESEARCH, UNIVERSITY OF PITTSBURGH, PITTSBURGH, PA.
Perhaps the most frequently used method for deRAPID m e t h o d for stand 2 or 3 minutes. Sepatermining phenols in coke-plant effluents and similar the determination of rate the two layers. Wash process liquors is the bromine method. This method the aqueous layer twice more phenols in solutions was not readily applicable to samples containing much with 75-ml. portions of ether such as gas liquor was publess than 75 p. p. m. phenol. The present article delished by the writer in 1929 a n d combine t h e e t h e r scribes a simple procedure making it appliczable to washes. Now discard the (1) and, from the testimony the analysis of samples having a concentration of 1 a q u e o u s l a y e r a n d place of many c h e m i s t s usingit, p. p. m . phenols or even less. Lower concentrations the ether in the separatory it a p p e a r s to h a v e given than this in plant liquors are usually of little imfunnel. e n t i r e s a t i s f a c t ion when Wash the ether three times applied within t h e l i m i t s portance. with 8-ml. p o r t i o n s of 10 specified. However, the method without modification was not applicable to a sample per cent sodium hydroxide solution and finally with one containing less than 75 p. p. m. phenols. It is therefore 10-ml. portion of distilled water, combining these aqueous evident that it is applicable to the most important of the alkaline washes. Boil gently to remove most of the ether, phenol-bearing plant effluents, but that it is not satisfactory cool, and dilute to a volume of 50 ml. in a small graduated for the analysis of a large number of plant effluents con- cylinder. I n removing the ether from the caustic by boiling, taining perhaps only a few parts per million of phenols. the solution becomes first turbid and then clear, indicating At the present time the methods employed in analyzing these the disappearance of most of the ether. All of the phenol in the sample has now been concentrated effluents for phenols are time-consuming and in some cases actually grossly inaccurate. For this reason it is believed into the 50 ml. of caustic solution. This may now be analyzed that a real need exists for a rapid and reasonably accurate according to the previously published method if the concenmethod for determining phenols in liquors having a tar tration of phenol in the original sample was not less than acid concentration between 1 and 75 p. p. m. I n the course 5 p, p. m. To save time it is well to take a few milliliters of some work done in The Koppers Research Corporation of the caustic solution, make just acid to methyl orange Laboratories, this need became acute and a variation of the with sulfuric acid, and add two volumes of distilled water previously published method was developed to meet this and a slight excess of bromine water in a small test tube. If a distinct turbidity is not produced, the phenol must be situation. The variation in procedure consists simply in concentrating further concentrated. To do this, note the volume of the the phenols into caustic soda solution by means of ether3 caustic solution, acidify with sulfuric acid, and repeat the [ (C2H&O ] washes, heating the sodium hydroxide solution previous procedure for concentrating with ether. In this to drive off the ether (and certain other impurities) and then case the small separatory funnel should be employed. Use applying the previously published method of Shaw (1) three 10-ml. portions of ether and three 3-ml. portions of to the acidified caustic solution. caustic, supplementing the caustic washes with one water wash of 3 ml. volume. The aqueous alkaline washes should Apparatus and Reagents . be dropped directly into the 8 X 1 inch (20.3 X 2.5 cm.) In addition t o the apparatus and reagents originally test tube in which the final phenol distillation is to be made. specified, a separatory funnel for 1000 ml., and one for 100 Calculations ml., and U. S. P. ethyl ether (C2H&0 are required. Assume only one series of ether washes to have been made. Procedure Then By means of a graduated cylinder, measure 800 ml. of p. P . m. phenol in standard matched X dilution factor sample into the large separatory funnel. Acidify with sulconcentration factor furic acid. Add 125 ml. of ether, shake well, and allow to = p. p. m. phenol in sample 1 Received March 10,1931. For example, a 750-ml. sample was washed with ether and 2 Industrial fellow, Multiple Fellowship of The Koppers Research caustic solution as above described and the caustic diluted Cocp., Mellon Institute, Pittsburgh, Pa. * The chemists of the U. S Steel Corp. use ether for this purpose in a to exactly 50 ml. Ten milliliters were acidified and distilled, and 25 ml. of distillate were caught. When 10 ml. of dissomewhat different connection.
A
