198
INDUSTRIAL AND ENGINEERING CHEMISTRY
and ores should always be tested by a sample representative of the type to be analyzed. The apparatus required for the oxalate method can be found in almost every analytical laboratory. Any type of centrifuge tube which allows the use of a large enough volume can be used, The centrifugal method.of separation of precipitates is as rapid or more rapid than filtration, but washing by the centrifugal method is much easier and more complete. I n many cases two washings are sufficient to remove all excess ammonium oxalate.
Vol. 16, No. 3
L. Smith of the Polytechnic Institute of Brooklyn for furnishing some of the zinc samples used. LITERATURE CITED
(1) Am. SOC.Testing Materials, “Methods of Chemical Analysis of Metals”, Designation B45-36T, pp. 117-18, Philadelphia, 1939. (2) Am. SOC. Testing Materials, “1Method of Test for Water and Sediment in Petroleum Products by Means of a Centrifuge”, Designation D96-40. (3) Classen, A., Z.a d . Chem., 16,470-2 (1877). (4) Ibid., 18,373-99 (1879). (5) Coleman, S. A,, and Smith, G . B. L., IND. ENQ.CHEM.,ANAL. ED.,13, 377-9 (1941). (6) Elving, P. J., and Caley, E. R., Ibid., 9,558-62 (1937). (7) Fales, H. A., and Wares, G . M., J . Am. Chon. SOC.,41,487-97 (1919). (8) Fowler, R. M.,and Bright, H. A., J . Research Nutl. Bur. StandUT&, 15, 493-501 (1935). (9) Furman, N. H.,ed., “Scott’s Standard Methods of Chemic4 Analysis”, Vol. I, pp. 1057 and 1060, New York, D. Van Nostrand Co., 1939. (10) Jefferson, C. E. P., and Swift, E. H., J . A m . Chem. Soc., 54, 3219-28 (1932). (11) Lundell, G.E.F., Hoffman, J. I., and Bright, H. A., “Chemical Analysis of Iron and Steel”, p. 388,New York, John Wiley & Sons, 1931. (12) Mayr, C.,Z.anal. Chem., 92, 166-74 (1933). (13) Nass, G.,2. angew. Chem., 7 , 501 (1894). (14) Reis, M.A,, Ber., 14,1172-9 (1881). (15) Ward, H. L.,Am. J . Sci., 33, 334-8 (1912).
SUMMARY
Zinc can be completely precipitated as the oxalate in a 70% acetic acid medium. The zinc oxalate can be separated by use of a centrifuge or by filtration and dissolved in sulfuric acid. The oxalic acid formed can be titrated with a standard potassium permanganate solution. Ammonium nitrate and ammonium sulfate do not interfere with the precipitation, but ammonium chloride does. Elements which form oxalate precipitates in 70% acetic acid solution interfere. A procedure waa developed for the determination of zinc in brasses and bronzes. Four Bureau of Standards alloys were analyzed for zinc and favorable results were obtained. A procedure was attempted for aluminum-base alloys, but the high concentration of aluminum salts made the method unfeasible. An attempt was made to determine zinc in an ore but the sample which waa available was of such an unusual composition that further work was inadvisable. A procedure for the determination of zinc in a zinc concentrate was developed and favorable results were obtained on a National Bureau of Standards sample.
PRESENTED before the Division of Analytical 5nd ,Micro Chemistry a t the 105th Meeting of the AMERICANCHEMICAL SOCIETY, Detroit, Mich. Abstracted from a thesis presented by John C. Lamkin to the Graduate School of Purdue University in partial fulfillment of the requirements for the degree of master of science, April, 1943.
ACKNOWLEDGMENT
The authors take this opportunity to thank G. E. F. Lundell and H. A . Bright of the National Bureau of Standards and G. B. I
Determination of Total Phthalic Anhydride in Oil-Modified
Alkyd
Resins
A. I. GOLDBERG, Brooklyn College, Brooklyn, N. Y. Several modifications of the Kappelmeier procedure for the determination of phthalic anhydride in oil-modified alkyd resins are proposed. Anhydrous potassium phthalate is recommended as the weighing form instead of the alcoholate. A simplified saponification procedure is suggested. The adverse effect of water and its elimination are described. A volumetric procedure is offered in place of the gravimetric one.
potassium sulfate (9) has been reported. Most of these methods are laborious, time-consuming, or subject to various errors (9,15). The Kappelmeier method (8), which generally is accepted today, involves hydrolysis of the alkyd resin with alcoholic potassium hydroxide, precipitating potassium phthalate containing one mole of alcohol of crystallization. WEIGHING FORM
T
HIS determination of total phthalic anhydride, free and combined, in oil-modified alkyd resins has been the subject of a number of papers (3,5,8-11,14,16). In the case of the alkyd hypothetically represented below, dipotassium phthalate, potassium linoleate, and glycerol are obtained upon alkaline hydrolysis:
The monomer within the bracket is useful in representing the molecule for analytical purposes but should not be taken as an indication of the actual molecular structure. The analytical problem involved is twofold: (1) to isolate the dibasic acid quantitatively and (2) to determine its quantity. Its determination as phthalic acid (3, I O ) , lead phthalate ( b ) ,potassium carbonate (14), potassium phthalate alcoholate ( 8 ) ,and
The necessity for drying the alcoholate to constant weight over concentrated sulfuric acid in a vacuum desiccator makes this neighing form inconvenient for routine work. Kappelmeier reported (8) that the alcohol is lost with difficulty a t 100’ C., that heating in air results in a brownish discoloration, and that drying the alcoholate in a vacuum between 100” and 120’ C. results in a slow loss of weight until 16% has been lost. which corresponds to exactly one molecule of alcohol. The tenacity with which the alcohol is held was verified. However, the alcoholate was decomposed in air quantitatively without discoloration by heating a t 150” C. for 3 to 4 hours. The theoretical loss is 15.97%; 15.97 * 0.07 was found (Table I). This treatment yields the anhydrous salt which is therefore recommended as the weighing form. METHOD OF SAPONIFICATION
The standard method of saponification requires a preliminary heating below the hoiling temperature, followed by B prolonged
A N A L Y T I C A L EDITION
March, 1944
Table
I. Formation of Anhydrous Dipotassium Phthalate from the Alcoholate
Weight of CsH4(COOK)*.GHsOH Grams 1.676 1.824 1.462 1.162
Weight
of CBHI-
(COOK)a Grams 1.409 1.532 1,226 0.977
Table ----Resin Temp. C.
50
Hr. 1
2 4 8 40
30
1
2 4 8 1 2 4
a
CnHsOH Lost
% 15.90 16.01 16.14 15.92
Weight of C6H4Weight (COOK)2.- of C s H c CnHrOH (COOKh Gram6 Grams 1.634 1.374 1.579 1.879 1.772 2.110 1.272 1.512
CaHlOH Lost
% 15.92 15.97 16.02 15.87
II. Rate of Hydrolysis of A l k y d Resins ----Resin
--1 Phthalic anhydride
Hydrol-
7c
R
28.0 36.0 36.2 36.0 19.3 29.3 35.3 36.5 13.6 22.0 30.0 35.3
77.4 100.0 100.0 100.0 53.4 80.9 97.5 100.0 37.6 60.9 82.8 97.5
ysis
Temp. C. 60
50
40
2 Phthalic anhydride Hr. 1 2 4 8 1 2 4 8
1 2 4 8
Hydfolysis
7c
70
41.5 42.0 42.0 42.0 42.0 42.0 42.0 42.0 28.0 42.0 42.0 42.0
100 100 100
100 100 100
100 100 66.7 100 100
100
gentle refluxing. This involves the use of water baths, air-cooled condensers, and the likelihood of violent bumping. A simplified method was investigated in view of the exceptionally rapid rate of hydrolysis of alkyd resins (16 ) . Similar-sized samples of a given resin were weighed into a series of corked Erlenmeyers. A solution of 0.5 A' otassium hydroxide in absolute alcohol was prepared and e q u 3 volumes were added to each flask. They were then set in ovens maintained a t the given temperature 1 2 " C. for varying periods of time. At the end of this time they were placed in a water bath and cooled rapidly to room temperature, ether was added, and they were filtered into Gooch crucibles within ,10 minutes after removal from the oven. The weight of phthalic anhydride was calculated on the resin solids baais, using the dipotassium phthalate alcoholate as the weighing form (15). The extent of hydrolysis as a function of time may be calculated by considering the reaction complete a t the point where maximum and constant value is obtained. The data in Table I1 indicated that refluxing is unnecessary. Indeed, saponification has been found to be complete in flasks which have been allowed to stand 18 hours at 25' C. I t is recommended that saponification be carried out a t 55' C. for 4 to 6 hours. I t may be necessary to heat difficultly saponifiable resins overnight. Higher temperatures may result in building up excessive pressures within the flask and it is advisable to stopper the flask loosely. This modification was tested upon two commercially prepared alkyd resins, using the customary reflux procedure as a control. Both the above weighing forms were used to secure the data in Table 111. The modified saponification procedure gave results agreeing to * o.3570. This less drastic saponification procedure has been used successfully on hundreds of samples of oil-modified alkyd resins of the type of Rezyl 7818-1 (American Cyanamid & Chemical Corp.), Beckosol 1334 (Reichhold Chemicals, Inc.), Falkyd A-4-D (Falk and Co.), Glyptal ZV-1125 (General Electric Company), etc. EFFECT O F WATER
The necessity of precipitating the dipotassium phthalate under anhydrous conditions has been noted (9). The quantitative effect of known quantities of water on the precipitation of dipotassium phthalate was observed. The alcoholic potassium hydroxide was prepared by drying .commercial absolute alcohol over lime for 48 hours, followed by
199
distillation over sodium. The fraction distilling over a t 78-79 'C was used t o prepare the 0.5 N alcohohc potassium hydroxide. The C.P. potassium hydroxide contained 13% water and thus introduced 0.5% of water into the alcoholic potassium hydroxide solution. Solutions containing up t o 8% more water were prepared by adding calculated quantities of water to this stock solution. Table I V shows a maximum of 37.4% phthalic anhydride obtained where no water was added. An error of 1%is introduced in the presence of 2% added water. A further increase in water content leads to large errors. In another series of determinations where the same alkyd resin was analyzed using commercial absolute alcohol and c.P.' potassium hydroxide the average of six determinations was 37.05 * 0.05%. PREPARATION OF LIMEDALCOHOLIC POTASSIUM HYDROXIDE. For each determination 4.5 grams of C.P. potassium hydroxide are added to 125 ml. of absolute alcohol, 10 grams of calcium oxide, to remove a maximum of 2.5% of water, are added, and the solution is refluxed for 20 minutes. The warm solution is filtered rapidly with suction, a minimum of air being sucked through to avoid absorption of carbon dioxide. To observe the effect of lime in the preparation of the alcoholic potassium hydroxide, two commercial resins were analyzed. Table V shows that the use of lime results in an increase of about 1% in the determination of phthalic anhydride. A comparison of columns A and C shows that the effect of the addition of ether is negligible. Apparently, only in the presence of an appreciable quantity of water does the ether decrease the solubility of the salt sufficiently to warrant its use (8). VOLUMETRIC PROCEDURE
The advantages of the Kappelmeier procedure in isolating the phthalic anhydride as the dipotassium salt would be best realized if a convenient and accurate volumetric procedure could be developed. A volumetric procedure which partially fulfills these
Table
Ill. Phthalic Anhydride by Kappelmeier Reflux and Modified Kappelmeier (55' C.) Methods Resin 3
.4
B
A Resin
B
%
%
%
%
Reflux
35.67 35.69 35.53 35.56 35.57 35.56 35.63 35.69 Weighing form. A = CaHl(COOK)a.CzHsOH. Duplicate results listed. 550 c.
Table
IV.
36.43 36.45 36.42 36.42 36.60 36.33 36.31 36.31 B = C~HI(COOK)~.
Effect of Water on Quantitative Precipitation of Dipotassium Phthalate
HzO Added
Phthalic Anhydride
Lossa
%
70
7%
Hi0 Added
Phthalic Anhydride
Loss*
% 2.0
%
%
37.0 35.1 29.6 added.
6.2 20.7
37.4 0.0 0.5 37.3 0.2 4.0 1.0 37.3 0.2 8.0 Assunling 100% precipitation where no water was
0.0
Table
A 7%
V.
1.0
Effect of Lime in Preparation ol Alcoholic Potash in Modified Kappelmeier Procedure Resin 3 Resin 4
Phthalic Anhbdride B C
% 35.6 35.5 35.6 35.5
A
Phthalic Anhidride B C
L'i /O % % 70 35.3 36.3 36.9 36.5 35.4 36.3 37.1 36.5 35.3 36.4 36.9 36.5 35.3 36.4 37.5a 36.5 Results listed in quadruplicate A Modified Kappelmeier, using normally prepared alcoholic potasmiurn hydroxide. B Modified Kappelmeier, using "limed" alcoholic potassium hydroxide. C Same a s A except for omission of ether before tiltration of potasiiom phthalate. This sample contained only half the conoenhration of resin used in all the other samples.
35.4 35.3 35.4 35.3
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
200 Table
VI. Titration of Dipotassium Phthalate with Perchloric Acid in Glacial Acetic A c i d
Wei h t of Ci"(8OOK)a Taken
A
Grams 0.928 0.986 1,154
Calod. Wei ht of CsHi CO%K)a from Litration B Grams 0.935 0.995 1.162
Weight
of KC104
Found
C
Grams 1.061 1.131 1.329
Calcd. Weight of CsH4(COOK)r from KClOn D Grama 0.929 0,990 1. I60
requirements is based on the use of sfeebly basic solvent to increase the basicity of the phthalate ion. Hall and Werner (7) have shown that perchloric acid is the most suitable of the common acids for titrimetric purposes in a glacial acetic acid solvent. The use of indicators in titrating amines with perchloric acid in glacial acetic has been reported (a). The titration of dipotassium phthalate or its alcoholate can be followed with several indicators-for example, bromophenol blue, bromocresol purple, and methyl violet-the latter was very satisfactory (1, 4). It is necessary to remove the water present in the solutions to secure quantitative results (6). The addition of acetic anhydride converts the water to acetic acid; excess acetic anhydride has no effect on the titration ( l a ) . The anhydrous perchloric acid solution was standardized by the use of sodium carbonate as a primary standard ( d ) , the end point being taken a t the green-yellow stage. The perchloric acid presents a little danger in handling. The 0.1 N solution should be prepared carefully as indicated below, Once the perchloric acid is present in the dilute solution it is relatively harmless. The glacial acetic solutions are most conveniently used in a wellventilated hood. The standard solution of approximately 0.1 N perchloric acid in glacial acetic acid was prepared by adding 9 ml. of 60% perchloric acid dropwise to 36 ml. of acetic anhydride kept in a chilled glass-stoppered liter Erlenmeyer ( 7 ) . The resultant solution was then diluted with 720 ml. of glacial acetic acid and 24 ml. of acetic anhydride and allowed to stand 2 weeks until the reaction with water was completed (IS). To standardize the solution a definite quantity of sodium carbonate was dissolved u-ith gentle warming in a solution of 20 ml. of glacial acetic acid and 2 ml. of acetic anhydride and brought to boiling (hood) in order to react with any water. Upon cooling, this solution was titrated with the above perchloric acid solution using methyl violet indicator, 2 drops per 10 cc. of 0.2yomethyl violet in glacial acetic acid. The results obtained by titrating dipotassium phthalate isolated by the modified Kappelmeier procedure are given in Table VI. A comparison of columns A and B shows that the volumetric procedure gives results that are 0.8% high. A white precipitate, formed upon addition of the perchloric acid, contained potassium and was soluble in hot water and insoluble in cold water. The precipitation of potassium perchlorate under these conditions has been noted ( 7 ) . The precipitate was filtered off, dried to constant weight, and used as a basis for calculating the weight of dipotassium phthalate. A comparison of columns A and D indicates that precipitation is quantitative. Sodium perchlorate is soluble in glacial acetic acid while the potassium salt is insoluble. A procedure for determining both potassium and sodium simultaneously under certain limited conditions is indicated. Semiquantitative results were secured on mixtures of potassium acetate and sodium carbonate. ACKNOWLEDGMENT
The author wishes to express his gratitude to the Paint and Automotive Chemical Laboratory of the Army Ordnance Department now located in the Proving Center, Aberdeen Proving Ground, Md., where the laboratory work was performed. LITERATURE CITED
(1) Adams, E. Q., and Rosenstein, L., J . Am. Chem. SOC.,36, 1452 (1914).
Vol. 16, No. 3
(2) Blumrich and Bandel, Angew. Chem., 54, 374-5 (1941). (3) Brown, A. E. G., Oil Colour Trades J., 89, 1489 (1936). (4) Conant, J. B., and Werner, T. H., J . Am. Chem. Soc., 52, 4436 (1930). (5) Fonrobert, E., and Munchmeyer, A , , Farben-Ztg., 41, 747-8 (1936). (6) Hall, N. F., and Conant, J. B., J. Am. Chem. SOC.,49, 3065 (1927). (7) Hall, N. F., and Werner, T. H., Zbid., 50, 2367 (1928). (8) Kappelmeier, C. P. A., Farben-Ztg., 40, 1141-3 (1935); 41, 161 (1936). (9) I b i d . , 42,561-3 (1937). (10) Kavanaugh, F., IND.ENG.CHEM.,ANAL.ED., 8, 397-8 (1936). (11) Kerckow, F. W., Farben-Ztg., 44, 33 (1939). (12) Kilpi, S., 2. physik. Chem., A177, 116 (1936). (13) Mitchell, Smith, and Bryant, J . Am. Chem. Sac., 58, H 5 2 (1936). (14) Ruff and Krynicki, Farben-Ztg., 41, 111 (1936). (15) Sanderson, J. McE., A.S.T.M. Bull. 107, 15-16 (December, 1940). (16) Wolff and Zeidler, Farben-Ztg., 41, 1009, 1035 (1936). CONDENBED from a thesis presented to the Department of Chemistry, Brooklyn College, Brooklyn, N. Y . , in partial fulfillment of the requirements for the master of arts degree, June, 1943.
Determination of Total Phthalic Anhydride in Modified A l k y d Resins C. D. DOYLE, Resin and Insulation Meterials Division, General Electric Company, Schenectady, N. Y.
T
HIS paper presents confirmatory evidence of the modified Kappelmeier method ( 3 ) described in the preceding paper
(d), independently obtained during the spring of 1942 by a simi-
lar modification which is used in this laboratory. This modification, which also eliminates the tedious drying of the residual crystals over sulfuric acid, consists in removing the alcohol of crystallization by heating a t 210OC. for one hour. The work done here indicates that the modification is applicable also to alkyd resins complicated by maleic anhydride or fumaric acid.
Table
1. Alkyd Resin Analysis Phthalic Anhydride Btandard Modified method A method B C
RePiin 1 2 3 4 5 6 7 8 9
Other Acids Present Maleic anhydride Maleic anhydride Maleic anhydride Maleic anhydride Rosin Fumaric acid Fumaric acid
10
11
70
70
70
34.10 35.09 34.80 42.05 35,42 34.78 25.95 17.94 28.78 34.32 36.08
34.06 35.17 34.78 42.01 35.43 34.84 25.87 17.87 28.80 34.30 36.06
34.06 35.05 34.80 42.55 36.45 34.65 25.63 17.87 28.88 34.68 35.72
PROCEDURE. The standard Kappelmeier procedure ( 1 ) is followed up to the point of drying the filtration residues over concentrated sulfuric acid in vacuum. The crucibles containing the residues are transferred from the low-temperature oven to a 250" C. oven for one hour. They are then cooled over Dehydrite, weighed, and converted to phthalic anhydride, assuming dipotassium phthalate as the weighing form. Table I lists representative results on the basis of which the two methods may be compared. LITERATURE CITED
(1) Am. Soo. Testing Materials, D563-40T, B.S., 11, p. 1362. (2) Goldberg, A. I., IND. ENQ.CEEM.,ANAL.ED., 16, 198 (1944). (3) Kappelmeier, C. P. A., Farben-Ztg., 40, 1141-3 (1935); 41, 161
(1936).
