LITERATURE CITED
G. H., .44sa~.CHEXI.25, 1622 i 1953). ( 2 j Ai;&, A y e k , G. H., Meyer, A. S., Jr., Ibid., 23, 299 (1951). ( 3 ) RPami' Beamish, F. E., McBryde, W.A., I b i d . , 25, I1613 L.2) V 1 3 ((1953). lYdr3 J. ( 4 ) Conrad, A . L., Evans, J. K., Gaylor, V. F., Ibid.,31, 422 (1959). IT. ( 5 ) Furman. Furman, K. H.. H., Mason. Mason, i\-. B., B.. Pekola, J. S.,Ibid., 21, 1325 (1949). ( 6 ) Gilchrist, R.,J . Research A'atl. B u r . Standards 20, 745 (1938). (1) hyers,
( 7 ) Gilchrist, R., Kichers, E., J . Am. Chem. Sac. 57, 2565 (1935). ( 8 ) Gordon, C. L., Schlecht, K. G , Wichers, E., Bur. Standards J . Research 6 , 421 (1931). ( 9 ) Xixon, TI-. S.(to Cniversal Oil Products Co.), U. s. Patent 2,828,200 (?riarch 25, 1958). (10) Ryan, D. E., Analyst 76, 167 (1951). ( 1 1 ) Seath, J., Beamish, F. E., IND.ESG. CHEII., A s a ~ ED. . 12, 169 (1940). (12) Smith, 31. E., A s . 4 ~ . CHEM. 30, 912 (1958).
(13) Swisher, Ll. C., I N D Esc. . CHEJI., ANAL. ED. 1 1 , 162 (1937). (14) Vonossi, R., A n d e s asoc. guim. Arg. 38. 117 11950). (15) 'Westland, k. D.. Bemnish, F. E., ASAL. CHEX 30, 414 (1958). (16) Wichers, E., Pchlecht, JY. G., Gordon, C. L., Bur. Standards J . Research 6 , 421 (1931). (17) Yoe, J. H., Kirkland, J. J., i 2 s . 4 ~ . CHEW26, 1335-40 (1954).
RECEIVEDfor review June 15, 1959. Accepted September 25, 19-59.
Volumetric Determination of Isophthalic and Other Dicarboxylic Acids in Modified Alkyd Resins G. G. ESPOSITO and M.
H. SWANN
Coating and Chemical laboratory, Aberdeen Proving Ground, Md.
b A volumetric method involving nonaqueous titration was developed for general application to the determination of single dicarboxylic acids in all types of modified alkyd resins. Gravimetric methods are unsuitable for measuring isophthalic acid and are rarely adaptable to modified alkyd resins of any type. The volumetric method is more rapid than the ultraviolet method and requires no special equipment.
A
of dicarboxylic ncids are used in the manufacture of alkyd resins, polyesters, and plasticizers and riiinierous analytical mc.thods are availnlile for detecting and measuring these acids. M?th the exreption of the chlorinatrd a i d liydrogc~natedphthalates and possibl) azelaic and maleic acids (j),all of thcse acids can be separated as their dipotassium salts by saponification in anhydrous medium. This technique is the first step in most of the analytical procedures. Calculation of phthalic anhydride from the \\-eight of the precipitated salts ( 2 ) was the fastest and most popular method for a number of years but \Tas unsuitable for alkyds modified n ith polystyrene, vinyl chloride-acetate, epoxy, and other resins. The introduction of isophthalic acid resulted in high yields by the gravimetric method due to coprecipitation of alkali and fatty acid soaps with the salts. This acid must be determined spectrophotometrically (8). A certain amount of potassium carbonate always precipitates with the dipotassium salts, so that even in the analysis of pure phthalate alkyds, a correction by titration with acid has to be applied. Other volumetric methods ( 3 , 6) have been proposed for o-phthalic anhjdride in alkyd KUMBEE
resins but are subject to error from the coprecipitated carbonate and free alkali. Recent methods (1, 4) provide for the rapid identification of dicarboxylic acids in alkyds and, for those containing single acids, the volumetric procedure described in this paper is rapid and generally applicable. I t s time-saving features include the elimination of the need for drying, m-eighing, and cooling filtration crucibles and the subsequent application of instrumental measurement. The acids are measured by nonaqueous titration in ethylene glycolethyl alcohol medium. I n Table I, the values resulting from the analysis of a variety of modified alkyds by gravimetric and volumetric methods are compared to the values obtained by the ultraviolet procedure ( 7 ) . Volumetric and spectrophotometric ( 8 ) analyses on five isophthalic alkyds are compared in Table 11. EXPERIMENTAL
Reagents. Potassium hydroside in methanol, 0 . 2 s . Dissolve 6.5 grams of potassium hydroxide in 100 ml. of absolute methanol, filter, and dilute t o 500 ml. with methanol. Hydrochloric acid in ethyl alcohol, 1.0s. Dilute 10 ml. of concentrated hydrochloric acid t o 120 ml. with absolute ethyl alcohol. Hydrochloric acid in ethyl alcohol, 0.024N. Dilute 1 ml. of concentrated hydrochloric acid to 500 ml. with absolute ethyl alcohol. Table 1.
m-Cresol Purple indicator. Dissolve 0.025 gram of m-Cresol Purple in 100 ml. of absolute ethyl alcohol. Isolation of Dipotassium Salts. ISOPHTHALIC ACID. -4 sample containing 0.05 to 0.15 gram of isophthalic acid is weighed into a 1-liter Erlenmeyer flask and dissolved in 50 ml. of benzene. Two hundred milliliters of 0.5N alcoholic potassium hydroxide (made with absolute ethyl alcohol and filtered) are added and the sample is refluxed in a water bath for I'/z hours. Benzene (270 ml.) is added and the sample is cooled to room temprmture and allowed to stand for 1 1 2 hour. It is then filtered through a fritted-glass crucible of coarse porosity, prc,ferably one prepared with a mat of filtering asbestos. The prwipitatcd salt is transferred and washed with about 150 ml. of 2 to 1 benzenr-ethyl alcohol mixture and air is drawn through the crucible for about 1 minute. It is then reserved for nonaqueous titration. In the cas? of isophthalic acid only, it is advantageous to warm the crucible for about 15 minutes in an oven a t 105' C. just before dissolving the salts. Table II.
Analysis of lsophthalic Alkyds
Isophthalic Acid, 7 Ultraviolet Volumetric 19.0 59.8 36.7 27.6 19.9
19.0; 59.6; 35.9: 27.4: 19.9:
19.3 59.8 36.2 37.8 20.1
Analysis of Some Modified Alkyds
Type of XIodification
Ultraviolet
Found, 7G Gravimetric
Volumetric
Styrenated alkyd Epoxy ester modified alkyd Poly(vinylto!uene) alkyd
19 9 25 7 20 0
23 6 ; 24 8 28 7; 30 8 22 7 ; 23 1
1') 6 ; 19 7 25 7 ; 26 0 19 7 : I n 9
VOL. 32, NO. 1, JANUARY 1960
49
OTHERACIDS. X sample of the resin solution, usually 1 or 2 grams, is weighed into a 500-ml. Erlenmeyer flask and dissolved in 150 ml. of benzene. Sixty milliliters of 1 N alcoholic potassium hydroxide (made with absolute ethyl alcohol and filtered) are added and the sample is refluxed for 1 hour. It is then filtered through the fritted-glass crucible described above. The precipitated salt is transferred and m-ashed with a mixture of 3 to 1 benzene-ethyl alcohol. Air is drawn through the crucible for 1 minute and it is then reserved for nonaqueous titration. Nonaqueous Titration of Isolated Acids. T o the crucible retained from above, 10 ml. of warm ethylene glycol (60’ C.) are poured down the inside surface. After a 2-minute stand, suction is applied and the glycol is collected in a clean, dry filter flask. The suction is released and an additional 10 ml. of warm glycol are added. -4fter draining the crucible, a third addition of 5 ml. of warm glycol is made and drarw through. Finally, 100 ml. of the 0.0245 hydrochloric acid in ethyl alcohol are added and drawn through the crucible. Three milliliters of the m-Cresol Purple indicator are added to the flask. If the solution is not red, 1.0A- hydrochloric acid (in ethyl alcohol) is added until a definite red color appears and then 3 drops are added in excess. The sample is agitated constantly for 1 minute then titrated with the 0.2N potassium
hydroxide in methanol from a 10-ml. buret. The volume is recorded when the color changes from red t o yellow and the titration is continued to the violet end point. I n case of doubt or overtitration, the sample can be retitrated by adding the 1N hydrochloric acid (in alcohol) until the red color reappears and retitrating in the manner described. Per cent dicarboxylic acid
- (Vp - Vi) X iV
X F X 100
wxs
where
VI
= volume of alkali a t first color
change volume of alkali a t second color change ‘V = normality of standard potassium hvdroxide solution W = weight of resin sample S = nonvolatile vehicle fraction F = factor (0.08301 for isophthalic acid, 0.07406 for o-phthalic anhydride)
TIZ
preparing and without drying, provided they are thoroughly rinsed with alcohol and benzene. Of all the indicators in the loR-er pH range, only m-Cresol Purple performed satisfactorily. It is advisable during the first trial with this method to titrate standard potassium biphthalate in glycol-ethyl alcohol as described to establish the end points accurately. ACKNOWLEDGMENT
The advisory assistance of C. F. Pickett, director of the laboratory, is acknon-ledged and appreciated.
=
DISCUSSION
Precipitated salts from some systems, notably styrenated alkyds and those containing isophthalic acid, are not easily filtered and tend to clog crucibles. The use of filter asbestos in frittedglass crucibles helps prevent filtration difficulties. The asbestos matted crucibles can be used immediately after
LITERATURE CITED
(1) Adams, M. L., Swann, M. H., ANAL. CHEM.30, 1322 (1958). (2) Am. SOC. Testing Materials, Phila-
delphia, Pa., “ASTM Standards,” Designation D 563-52, p. 355, 1955. ( 3 ) Brink, A., J. Oil & Colour Chemists’
Assoc. 40, 361 (1957). (4) Esposito, G. G., Swann, M. H., O$c. Dig. Federation Paint & Varnish Production Clubs 30, 1059 (1958).
( 5 ) G u n , P. D., Gilroy, H. M , A N ~ L . CHEM.30, 1663-5 (1958). ( 6 ) Goldberg, A. I., IND.ENG. CHEM., AXAL.ED. 16, 198 (1944). ( 7 ) Shreve, 0. D., Heether, M. R., A x . 4 ~ . CREM. 23,441 (1951). ( 8 ) Swann, M. H., Adams, M. L., \Veil, D. J., Ibid., 27, 1604 (1955).
for review July 30, 1959. RECEIVED cepted October 27, 1959.
Ac-
An Indirect Absorptiometric Method for the Determination of Boron ROBERT H. CAMPBELL with M. G. MELLON Purdue University, lafayefte, Ind.
b A new indirect absorptiometric method for boron, based on the fluoride complexes of molybdate and boric acid has a molar absorptivity of 7000 and a determination range from 0.1 to 2.5 mg. of boron per 50 ml. The method is subject to interferences from elements forming strong fluoride complexes or heteropoly acids. If the method is used with the methyl borate separation technique, all these interferences are eliminated. The variables affecting the method were investigated, and the optimum working conditions determined.
C
reactions of borate, fluoride, and molybdate ions suggested the possibility of an indirect absorptiometric method for boron based on the reduction 50
ERTAIN
0
ANALYTICAL CHEMISTRY
of an acidified molybdate solution to molybdenum blue. Molybdate alone, a t a suitable pH, can be reduced t o molybdenum blue. Borate has little or no direct effect on this reduction. Kurtz (12) reported that boric acid eliminated the interference of fluoride ion in the determination of phosphorus. It is known that fluoride ions react with molybdate to form several oxyfluomolybdate salts (NH4)&003F3 (14) and KzMoOzF4 (16). Borate forms strong complex anions of tetrafluoborate, BFa-, and oxytrifluoborate, BF30H- (17). Therefore, it seemed that borate might successfully compete with molybdate for the fluoride ion. If so, the boron concentration should be related to the amount of molybdate available for reduction to molybdenum blue. Several indirect methods are based on
the tetrafluoborate complex. Monnier, Rusconi, and Kenger ( I S ) measured the color developed from interactions among iron(III), sulfosalicylic acid, and fluoride. In a recent critical evaluation of their method, Beck ( 2 ) reported the procedure unsatisfactory because sulfosalicylic acid has interfering indicator properties and the unbuffered solution is pH sensitive. He also found that, when the pH was kept constant, the change in absorbance was insufficient for a successful method. Fukamauchi, Sekiguchi, and Kazuko (9) developed an indirect method based on the yellow color of pertitanate when boric acid is added to a fluotitanic acid solution. I n view of the indirect methods cited, this investigation was directed t o the possibility of basing one upon reactions
