ANALYTICAL EDITION
January 15, 1941
gas phase than for the other three materials is not clear. It presumably points to a large “internal” surface area in cracks or crevices that are inaccessible to large organic molecules in solution and yet are covered by nitrogen molecules during the low-temperature gaseous adsorption measurements. The areas calculated from the butane isotherms are usually considerably smaller than those obtained from nitrogen isotherms. This is consistent with previous experience with this gas (2, 3, 6); the explanation of the smaller values is not yet certain. Small symmetrical molecules appear in general to be preferable to large long molecules for surface area measurements. The area of the standard sample of cement had been determined by the usual liquid flotation method and was given to the authors as 0.1890 sq. meters per gram. This is smaller by a factor of about 6 than the value 1.08 sq. meters per gram obtained in the present adsorption studies. The authors prefer not to discuss the possible causes of this discrepancy until more work has been done comparing the two methods. However, in view of the general agreement of the nitrogen adsorption method with ultramicroscopic methods for carbon black and zinc oxide, the error is probably to be looked for in some of the assumptions made in the standard determinations by elutriation methods. Close examination of the adsorption isotherms on the zinc oxide samples and on acetylene black will reveal some shape peculiarities analogous to those noted previously for certain iron synthetic ammonia catalysts ( 2 ) . The linear portion of the isotherm whose lower extremity is about 100 mm. in all the present work extends a few hundred millimeters only and then either increases or decreases in slope abruptly before joining the higher pressure part of the curve that is convex to the pressure axis near the saturation pressure. It is not possible to state as yet the cause of these shape irregularities above 400 mm. However, on all of these materials the VcT, values obtained from plots of Equation 1 are in good agreement with the point B values. The runs on lithopone, paper, and cuprene merely serve to illustrate the possible utility of the new method for measuring surface areas of miscellaneous industrial materials. Although due caution should be observed in interpreting the results of similar surface area measurements on materials on which the method has not yet been tried, the authors see no reason to doubt the wide applicability of the low-temperature adsorption method in determining the relative and even the absolute surface areas of a variety of materials [for a critical discussion of the method see (41. So far, out of the several hundred different materials studied only charcoal (2) and dehydrated chabazite give other than the S-shaped a d s o r p tionisotherm. For reasons that are not entirely clear but appear to be concerned with pore diameters, the one sample of charcoal and the numerous samples of chabazite that have been tried yield Langmuir-type adsorption curves that do not become convex to the pressure axis as pressure a p proaches the liquefaction value but approach asymptotically a limiting adsorption value.
Acknowledgment The authors wish to extend their thanks to B. L. Harris for his assistance in making the experimental adsorption measurements on the zinc oxide samples.
Literature Cited (1) Brunauer, S., and Emmett, P. H., J . Am. Chem. SOC., 57, 1754 (1935). ( 2 ) Ibid., 59, 2682 (1937). (3) Bruuauer, S., Emmett, P. H., and Teller, E., Ibid., 60, 309 (1938). (4) Committee on Contact Catalysis, National Research Council, 12th Report, Chap. V, Ken, York, John Wiley & Sons, 1939.
33
Dodge, B. F., and Dunbar, A. K., J . Am. Chem. SOC.,49, 591 (1927). Emmett, P. H., and Brunauer, S., Ibid., 59, 1553 (1937). Emmett, P. H., and Brunauer, S., Trans. Electrochem. Soc., 71, 383 (1937). Emmett, P. H., Brunauer, S., and Love, K., Soil Sci., 45, 57 (1938). Ewing, W. W., J . Am. Chem. SOC., 61, 1317 (1939). Gehman, S. C., and Morris, T. C., IND.ENQ.CHEM.,Anal. Ed., 4, 157 (1932). Giauque, W. F., Johnston, H. L., and Kelley, K. K., J . Am. Chem. SOC., 49, 2367 (1927). Green, H., J . Franklin Inst., 204, 713 (1927). Lineweaver, Hans, J . Biol. Chem., 122, 549 (1938). News E d . (Am. Chem. S O C . )18, , 492 (1940).
Colorimetric Method for Determination of Nitrite MARTHA B. SHINY Renziehausen Diabetic Foundation, Children’s Hospital of Pittsburgh, Pittsburgh, Penna.
A method employing sulfanilamide and N-(1-naphthyl)-ethylenediamine dihydrochloride for the determination of nitrite is proposed. These reagents have been found superior to sulfanilic acid and a-naphthylamine, formerly employed, in that the color developed is clearer, reaches its maximum intensity more rapidly, and remains stable for a longer time. A standardized solution of sulfanilamide is substituted for sodium nitrite as a primary standard to obviate the difficulties arising from the instability of the latter.
P
ROCEDURES for the colorimetric determination of nitrite in foods, water, and sewage have been based on the diazotization of sulfanilic acid by the available nitrite and the subsequent coupling with an agent such as a-naphthylamine ( I , 2, 6). As employed, these methods are open to two objections: (1) The coupling of diazotized sulfanilic acid with a-naphthylamine is relatively slow, requiring from 10 to 30 minutes for full color development ( 2 ) . With anaphthylamine acetate the color must be read within 30 minutes ( I ) . ( 2 ) Primary nitrite standards are unstable and difficult to prepare. It has been found possible to circumvent. these difficulties in part by replacing a-naphthylamine with N-( 1-naphthyl)ethylenediamine dihydrochloride, the coupling component suggested by Bratton and Marshall ( 3 ) for sulfanilamide determinations. It has the advantage of being water soluble, decreases the time required for color development to 2 minutes, gives a final color that remains constant for several hours, and is less sensitive t o variations in pH, reacting equally well in acid concentrations ranging from 0.1 to 1 Y. I n place of sulfanilic acid, sulfanilamide (p-aminobenzenesulfonamide) has been used. Sulfanilamide of a high degree
INDUSTRIAL AND ENGINEERING CHEMISTRY
34
TABLE I. RECOVERY OF KITRITE (Color developed in a final volume of 50 ml.) Nitrite Content Nitrite Content by by Assay Sulfanilamide Standard Recovery
MQ.
Mv.
70
0.0515 0.0424 0.0258 0.0241 0,0241 0.0212 0.0129 0.0071 0.0052 0.0028 0.0026 0.0014 0.0013 0.0006
0.0516 0.0423 0.0258 0.0242 0.0240 0,0210 0,0130 0.0070 0.0053 0.0026 0.0025 0.0013 0.0013 0.0005
100.2 99.8 100.0 100.4 99.6 99.1 100.8 98.6 101.9 100.0 96.2 92.9 100.0 83.3
of purity can be obtained; it is more stable than sulfanilic acid both in the dry state and in solution, and it reacts more rapidly in the coupling process. Finally, inasmuch as the methods for the colorimetric determination of nitrite and of sulfanilamide (3, 4)employ the same fundamental reactions of diazotization and coupling and the concentrations analyzed lie in a comparable range, the substitution of a standardized stock solution of sulfanilamide for the primary nitrite standard was considered practical. Experiments have shown that sulfanilamide and nitrite react stoichiometrically in the presence of a suitable excess of either, The following method is proposed for the determination of nitrite.
Reagents SULFANILAMIDE, 0.2 per cent solution in water. This will keep for a t least one month in a refrigerator. Winthrop’s “Prontylin, sulfanilamide powder repurified for injection” has been found satisfactory. HYDROCHLORIC ACID, 1 to 1 dilution of the concentrated acid. SODIUMNITRITE,0.1 per cent solution (approximate). This solution will keep for one week or longer in a refrigerator. AMMONIUM SULFAMATE, 0.5 per cent solution in water, obtained from LaMotte Chemical Products Company, Baltimore, Md., Marshall and Litchfield (4) have shown that excess nitrite remaining after diazotization of sulfanilamide interferes markedly with the coupling process. To ameliorate this condition they recommend the use of ammonium sulfamate to remove residual nitrite before the addition of the coupling agent. N-(~-NAPHTHYL)-ETHYLENEDIAMINE DIHYDROCHLORIDE, 0.1 cent solution in water, kept in dark bottle. Obtained from aMotte Chemical Products Company, Baltimore. This is referred to below as the “coupling agent”.
Standardization of Sulfanilamide Solution Dry analytical reagent grade sodium nitrite for 24 hours in a desiccator. Dilute a weighed sample of about 1 gram to 100 ml. in a volumetric flask and assay by titration with potassium permanganate according to the U. S. P. XI method (6). A. Employing the assayed sodium nitrite, prepare an accurately known solution containing about 0.005 mg. of nitrite per ml. With a transfer pipet measure 5 ml. of this into each of two 50-ml. volumetric flasks, add 1 ml. of 50 per cent hydrochloric acid and 5 ml. of the 0.2 per cent sulfanilamide solution, and after 3 minutes add 1 ml. of the ammonium sulfamate reagent. (The sulfamate plays no part here but is added t o ensure uniformity of treatment.) Two minutes later add 1 ml. of the coupling agent and dilute to volume with water. B. A t the same time into two other 50-ml. volumetric flasks measure 5 ml. of an accurately prepared 1 to 100 dilution of the 0.2 per cent sulfanilamide solution. Add 1 ml. of 50 per cent hydrochloric acid, 1 ml. of 0.1 per cent sodium nitrite, and about 5 ml. of water. Allow t o stand 3 minutes, add 1 ml. of ammonium sulfamate solution to destroy excess nitrite, let stand 3 minutes, add 1 ml. of the coupling agent, and dilute to volume. Samples A and B prepared as above are read against each other in a colorimeter. K i t h a Duboscq-type colorimeter the nitrite equivalent value of the sulfanilamide solution is calc u l a t d from the equation:
Vol. 13, No. 1
Reading of A x mg. of NO^- in A x 20 = mg. of NO*- repreReading of B sented by 1 ml. of 0.2% sulfanilamide solution
Procedure The solution taken for analysis should be either neutral or acid. Variations in acid concentration between 0.1 and 1 N at the time of coupling do not influence the final color. The unknown should contain no more than 0.05 mg. of nitrite and should be limited in volume to no more than 35 ml. To the unknown sample add 1 ml. of 50 per cent hydrochloric acid, 5 ml. of 0.2 per cent sulfanilamide solution, and let stand for 3 minutes. Add 1ml. of ammonium sulfamate solution. After 2 minutes add 1 ml. of coupling reagent and dilute to volume. A t the same t’imeprepare a nitrite standard from the sulfanilamide solution according to the procedure outlined in B. The unknown is read against the standard and the nitrite present in the sample taken is calculated by the equation: Reading of standard Reading of unknown
NO%-value of 1ml. 0.2% sulfanilamide 20 mg. of NO*- in sample
Precision Known samples of sodium nitrite in water were analyzed according to the method described. Beer’s law was found to hold throughout the useful range of color intensity. The proposed procedure gave results as shown in Table I. It was found that samples containing less than 0.0025 mg. of nitrite in a final volume of 50 ml. gave colors too faint to be read in a photoelectric colorimeter with a reasonable degree of accuracy. If the final volume can be decreased, the sensitivity of the method will be correspondingly greater. Samples containing more than 0.05 mg. of nitrite in 50 ml. should be diluted before analysis, as this represents a color near the upper limits of desirable intensity.
Time Required for Color Development Color development of aqueous solutions of sodium nitrite subjected to analysis by the method proposed was followed on a Klett-Summerson photoelectric colorimeter a t 5-minute intervals for 1.5 hours. The color attained its maximum intensity within 2 minutes and remained constant for 90 minut’es. By the end of 3 hours slight fading had occurred.
TABLE 11. EFFECTO F VARYING QUANTITIES O F SULFANILAMIDE ON RECOVERY OF NITRITE (0.0241 mg. of nitrite taken.
Sulfanilamide Added
Color developed in a final volume of 50 ml.) Nitrite Found Recovery
MQ.
MQ.
%
0.10 0.20 0.30 0.50 1.00 2.00 5.00 10.00 50.00
0.0173 0.0231 0.0233 0.0241 0,0240 0.0240 0.0242 0.0242 0.0244
71.8 95.8 96.7 100.0 99.6 99.6 100.4 100.4 101.2
Stability of Sulfanilamide Solution The nitrite value for a 0.2 per cent solution of sulfanilamide has been found to remain constant for a t least one month. To investigate further the stability of sulfanilamide in water a 0.2 per cent solution was divided into two portions, one of which was analyzed immediately while Jhe other was subjected to ultraviolet irradiation (2537 A.) to the point of marked discoloration. This mas considered an artificial aging well beyond the point a t which the solution would normally be discarded. A loss of 1.9 per cent was detected in the discolored portion. Solutions which have been kept a t room temperature for more than a year have failed to show
ANALYTICAL EDITION
January 15, 1941
35
any trace of discoloration, b u t accurate analytical figures over such a period are not available.
is thus satisfactory for all concentrations of nitrite within the practical range.
Amount of Excess Sulfanilamide Required The method proposed depends upon the addition of a sufficient excess of sulfanilamide t o assure complete utilization of order to ascertain the permissible all the nitrite present,
Literature Cited
upper and lower limits Of concentration,v a r g n g quantities were used for the analysis of a constant amount of nitrite. The results obtained are given in Table 11. Approximately 20 mg. of sulfanilamide per mg. of nitrite were required for complete recovery and 2000 mg. per mg. of nitrite do not interfere. The amount chosen in the method
(1) Am. Pub. Health Assoc., “Standard Methods of Water Analysis”, 8th ed., pp. 46, 133, New York, 1936. (2) Assoc. Official Agr. Chem., Official and Tentative Methods of Analysis, 4th ed., pp. 216, 506 (1935). (3) Bratton, A. C., and Marshall, E. K., Jr., J . Bio2. Chem., 128, 537 (1939). (4) Marshall, E. K., Jr., and Litchfield, J. T., Jr., Science, 88, 85 (1938). (5) Scott, W. W., “Standard Methods of Chemical Analysis”, 5th ed., Vol. 11, p. 2052, New York, D. Van Nostrand Co., 1939. (6) United States Pharmacopoeia XI, p. 344, 1936.
Bromination of Phenols by Means of Bromide-Bromate Solution J
RIURRAY RI. SPRUNG, General Electric Company, Schenectady, N. Y.
IK
COKNECTIOX with a study of the reactivity of phenols toward paraformaldehyde, it was desirable to have a general method for evaluating the potential reaction capacity towards substitution agents of a phenol or mixture of phenols. A bromination procedure was considered the most likely approach to the problem, since it is generally supposed that aqueous bromine will replace hydrogen atoms ortho and para to a phenolic hydroxyl group rapidly and quantitatively, but will leave unaffected hydrogen atoms not so placed. Bromination has been employed as an analytical tool previously in connection with the problem of the constitution of the phenol-formaldehyde resins by Koebner (1d ) , who thus determined the molecular weights of acid-catalyzed phenolic resins (Kovolaks), apparently assuming that bromine entered quantitatively into free ortho and para positions in the resin molecules, without affecting them at any other points. The method under consideration is essentially that of Koppeschaar ( I S ) . The application of this method to phenol itself was comprehensively examined by Redman, Weith, and Brock (14). Phenol-cresol mixtures and Lysol solutions were studied by Jarvinen ( I I ) , who obtained results consistent to within 0.8 per cent of the theoretical value, assuming a more or less arbitrary value for “cresol”. Day and Taggart (9) found the method to be applicable to several chloro- and nitrophenols, to certain derivatives of salicylic acid, and to resorcinol, p-naphthol, m-cresol, and thymol. They found that it was not applicable to o-cresol, which could, nevertheless, be determined accurately by direct titration with potassium bromate solution. Beukema-Goudsmit (8)also found that m-cresol could be determined accurately by the Koppeschaar method but that o- and p-cresol could not be so determined. The application of this method to various alkylated phenols, and t o certain substituted phenols of particular interest in connection with the problem mentioned above, has apparently not been undertaken previously. Since comparative behaviors were of greatest interest in this connection, a standard analytical procedure was adopted. It soon became evident t h a t the structure of the phenol determined the extent to which i t would react with aqueous bromine under these conditions. The generalizations which were thus disclosed will become evident on examination of the data presented below.
Method Approximately 2 grams of the phenol were weighed into a 125cc. flask, about 50 cc. of water were added, and the phenol was brought into solution by means of 10 to 15 cc. of 10 per cent aqueous sodium hydroxide. The solution was transferred to a 500-cc. quantitative flask and made up to volume with water. A IO-cc. aliquot was transferred to a 250-cc. ground-glass stop-
pered iodination flask. To this were added 25 cc. of 0.1 1%’ potassium bromate (from apipet), 10 cc. of 2 N potassium bromide, 50 cc. of water, and 2 to 3 cc. of concentrated hydrochloric acid, in the order given. The stopper was inserted quickly and the cup was filled with water. The mixture was allowed to stand for 10 minutes with occasional shaking. Ten cubic centimeters of 10 per cent potassium iodide solution were then added (in such a way as to prevent loss of gaseous bromine while the stopper was removed), and the mixture was allowed to stand 10 minutes longer, with occasional shaking. The sides of the flask were washed down with water, and the iodine liberated was titrated with 0.1 N sodium thiosulfate, using starch indicator at the end of the titration. A blank was run on 25 cc. of potassium bromate solution. The “potential reactivity”, T , of the phenol is calculated as follows: r =
0.025 N V M
w
N = normality of Na2S203 V = “net” volume of Xa2SzO3used M = molecular weight of the phenol W = weight of sample TABLE I. REACTIOX WITH BROJIIKE OF PHENOLS WHICH BEHAVE NORM4LIJY Phenol Phenol, U. S. P.. redistilled. water white vi-Cresnla
Reactive Positions per hlole Found % 2.98 99.4
Calcd. 3.00 3.00 3.00 2.00 2.00
2.00 4.00 3.00 2.00 1.00
2.98 2.96 2.01 1.98
2.02 4.09 2.95 2.00 1.018
99.4 98.0 100.5 99.4
101 .o 102.3 98.4 100.0 101.8
p-Bromdphenolb 2,4-Dichlorophenolb a From Eastman Kodak Co. b Furnished by Dow Chemical Co. 0 Commercial sample purified by crystallization from benzene and heptane, then from pure heptane; m p. 50-51’. d Commercial sample purified by crystallization from benzene and dioxane, followed by crystallization from pure benzene; m. p. 157-158’.
Results PHENOLS TTHICH BEHAVESORMALLY. These data are summarized in Table I. Included are all phenols which absorb (within 2 per cent) that quantity of bromine which should be taken u p on the assumption t h a t only free positions ortho or para to the phenolic hydroxyl are reactive. PHENOLS J\-HICH BEH.4VE ABIU‘ORMALLY. The phenols which behave abnormally, with one exception only, give high
