1446
ANALYTICAL CHEMISTRY
'
solutions. Proceed in this way until the value of I z / I 1equals 0.37. This means that,the transmittance of the solution being examined is only 0.135 with respect to the solvent although it is 0.37 with respect to a solution whose own transmittance is only 0.37. Again p is evaluated by changing our standard so that it is identical with the one already in the other cuvette. Taking this as the second reference point, 12/11values may be measured for the more concentrated solutions. In this way if the absorption law applies, the precision of measuring the slope relating A to c will be kept at the maximum value possible for the instrument and the absorbance range chosen. When measurements for the entire concentration range which the instrument can handle have been made, the value of p will be finally evaluated and with maximum precision using the solution of highest concentration. LITERATURE CITED (1) Ayres, G. H., ANAL.CHEM., 21,652 (1949). (2) Bastian, R., Ibid., 21,972 (1949). (3) ChBveneau, C., Ann. chim. p h y s . , 12, 155 (1907). (4) Halban, H. von, and Ebert, L., 2. physilz. Chem., A112, 321 (1924). (5) H' yon+ and Eisenb'and, J.* Ibid.*A132, 401 ( l 9 2 8 ) ; A170, 212 (1934). (6) Halban, H., von, and Geigel, H., Ibid., A96,214 (1920) (7) Halban, H. von, and Siedentopf, K., Ibid., A100, 208 (1922).
Hamilton, H. H., IND.ESG.CHEM.,ANAL.ED., 16,123 (1944). Klota, I. hl., and Dole, M., I b i d . , 18, 741 (1946). Korttim, G., Angew. Chem., 50, 193 (1937). Korttim, G., Metallwirtschaft, 23,350 (1944). (12) Lothian, G. F., "Absorption Spectrophotometry," London, Hilgw and Watts. 1949. (13) Rabinowitch, E., and Lehmann, H. L., Trans. Faraday Soc., 31, 689 (1935). (14) (15) (16)
Rabinowitch, E., and Wood, W .C., I b i d . , 32, 547 (19361. Ringbom, A , , Z.anal. Chem., 115,332 (1939). Ringbom, A, and Sundman, F., Ibid., 115, 402 (1939) ; 116,104
(1939). (17) Soc. for .Ipplied Spectrosropy, Bull. 4, S o . 2 ( I 949). (18) Twyman, F., and Lothian, G. F., Proc. Phys. SOC.London, 45. 645 (1933). ( I S ) Willard, H. H., and .Iyres, G. H., IND.EKG.CHEM.,ANAL.ED.. 12,287 (1940). (20) W'inn,A . G., Trans. Faraday SOC.,29, 689 (1933). (21) Withrow, R. B., Shrewsbury, C. L., and Krayhill, H. L., IND. ENG.CHEM.,ASAL.ED.,8, 214 (1936). ( 2 2 ) Y o e , J. H., and Crumpler, T. B., I b i d . , 7, 281 (1935). (23) Zinsadze, C. H., Ibid., 7, 280 (1936). (24) Zscheile, F. P., Hogness, T. R., and Young, T, P., ,J. Phys. Chem., 38, 1 (1934).
RECEIVEDMarch 16, 1949.
Amides of Saturated Aliphatic Acids A n X - R a y Di'raction
Study
DOROTHY H. WURZ A N D NORMAN E. SHARPLESS Kational Institutes of Health, Bethesda, Md. X-ray diffraction data for the amides of the saturated aliphatic acids (CI to Ci4) are presented. Isostructuralism among the even members and also among the odd members of the series above CSis shown.
S
INCE the simultaneous discovery by Debye and Schemer in Europe and Hull in America of x-ray diffraction powder analysis in 1919, this type of pattern has been found useful in the identification of chemical compounds and minerals. The vast majority of printed data have been limited to inorganic compounds; a very small minority of published patterns are those of organic compounds. Organic compounds, as a rule, have much more complex patterns and exhibit wider diffraction bands than do inorganic compounds, which has made their patterns much more difficult to record. The ease and reliability of this method of identification for organic compounds, however, have increased the amount of research in this field. Several papers on the identification of closely related organic chemical compounds have been published in recent years, including those by Velick (6) and Francis, Collins, and Piper (1). X-ray diffraction powder pattern data, published by Matthews and Michell ( 4 ) for the anilides of the saturated aliphatic acids, demonstrated the ability of this method to distinguish between each member of a homologous series. For the present study, the authors chose the amides of the saturated aliphatic acids. The required amides were synthesized from the corresponding acids essentially by the method of Fuson and Snyder ( 2 ) . One to 2 grams of the acid were refluxed 5 to 10 minutes with 5 ml. of thionyl chloride. The cooled reaction mixture was then poured into 15 mI. of concentrated ammonia a t 0" C., and the resultant amide was filtered. The crude amide was purified by recrystallization from dilute ethanol. With the exception of myristamide ((314) all melting points agreed well with those recorded in the literature. Three recrystallizations of myristamide gave a constant melting point of 94-95" C., which is considerably lower than the value of 103"
given by Kamm ( 3 ) . The melting points of the amides used in this study, as compared with the values in the literature, are given in Table I.
Table I. h-ame
Melting Points of Amides
Content
M.P. Literature (6)
O
Formamide Acetamide Propionamide Butyramide Valeramide Caproamide Heptylamjde Caprylamide Pelargonamide Deoylamide Undecylamide Lauramide Tridecylamide Myristamide
Table 11.
1
2 3 4 5 6 7 8 9 10 11 12 13 14
c.
2 81 (79-80) 114
106 101 96 105 . 89 89 89 I00 100 103
M.P., Experiment O
c.
..
80 (78-79) (115-116) (102-104) 101 96 105 97 99 (97-98) (97-99) (97-88.5) (94-95)
Strongest Line of X-Ray Powder Diffraction Patterns (Flat Cassette)
Name Acetamide Propionamide Butyramide Valeramide Caproamide Heptylamide Caprylamide Pelargonamide Decylamide Undecylamide Lauramide Tridecylamide Myristamide
C Content 2 3 4 5
6 7 8 9 10 11 12 13 14
Strongest Line, A. 3.52 8.3 10.0 11.3
14.5 15.4 18.1 19.6 21.2 21.9
25.7
26.6 31.0
1447 Table IV. Three Strongest Lines of X-Ray Powder Diffraction Patterns ( C Jlindrical Camera) Same
CContent
Formamide Acetamide Propionamide Butyramide Valeramide Caproamide Heptylamide Caprylamide Pelargonamide Dec lamide Undiecylamide Lauramide Tridecylamide &Iyristamide
1
2 3 4 5 6 7 8 9 10 11 12 13 14
Interplanar Spacings First Line Second Line Third LinP
A.
4.
A.
3.41 3.52 8.3 10.1 11.3 4.50 3.72 4.10 3.90 R 7Q 3.92 3.64 3.80 3.94
...
....
5.7 4.70 3.76 4.06 3.64 4.92 4.90 4.42 4.91 4.90 4.50 4.52 4.48
2.84 3.34 4.66 4.78 4.84 4.24 4.36 4.94 4.48 4.38 4.90 4.91 4.90
X
30 T
0
%
5 u)
% *
(3
5 20
x
0
a
4.
Y
u)
I
2
0
0
4 6 8 IO 12 14 NO. OF C A R B O N ATOMS
Figure 1. Largest d Values of Saturated Aliphatic Arid Amides Plotted against Number of Carbon Atoms X
Even amides Odd amides
The x-ray diffraction patterns were made on a General Electiic. Model XRD Type 9 unit utilizing the standard Debye-Scherrer method. The sample amide was finely ground in an agate mortar, tightly packed into a \\-edge-type specimen holder, and mounted in the center of a cylindrical camera of 14.32-em. diameter. Copper radiation filtered through a 0.00035 nickel filter, was used, giving essentially Ko: radiation of wave length 1.537 9. The cutoff due t o the constryction of the cylindrical camera occurred at approximately 12 A. In order to record the longer d-spacings of the higher amides the film was placed at a greater distance, 10 cm., from the sample and was held in a flat cassette camera. The intensity of the spacings in the flat cassette films was estimated visually by comparison with the cylindrical films, The strongest lines appearing on the flat cassette films of the amides, C, t o C14, are listed in Table 11. The x-ray powder diffraction data for the amides of the aliphatic acids, C1 to C14, are presented in Table 111. The intensities are recorded relative to the intensity of the strongest line in each pattern, as measured by a Leeds & Northrup recording microphotometer. The three strongest lines of each pattern are listed in Table IF'. A marked similarity is apparent by visual observation among the members of the even series Cs to C,C,showing a similarity of structure. The odd members of the series above Cs also exhibit this isostructuralism. These findings are in accord nith those of Matthew and Michell (4)in their study on the anilides and also those of Slagle and Ott ( 5 )in their study of the fatty acids. In Figure 1, the largest d values of the saturated aliphatic acid amides are plotted against the number of carbon atombq. Unlike
A N A L Y T I C A L CHEMISTRY
1448 the aliphatic anilides, the amides do not show any evidence of 11 zigzag structure when the longest spacings are plotted against the number of carbon atoms. LITERATURE CITED 1
I)
Francis, F., Collins, F. J. E., and Piper, S.H., Proc. Roy. SOC. London, 158A,691 (1937).
(2) E’uaoii, 11. C., and Snyder, H. It.. “Organic Chemistry,” Nea York, John Wiley &- Sons, 1942. (3) Kamm, o., saQualitative Organir .irlalysis,vv New York. &‘iley & Sons, 1932. (4) Matthews, F. W.. and Michell, J . H.. IND.ENG.CHEM..A N A L ED., 18, 662 (1946). ( 5 ) Slagle, F. G., and Ott, E., J . Am. Chem. Soc.. 55, 4396 (1933) (6) Velick, S.F., Ibid., 69, 2317 (1947).
RECEIVEDMarch 24, 1949.
Determination of Dibasic Acids in Alkyd Resins Quantitative Methods of Analysis f o r Phthalic, Sebacic, Fumaric, Maleic, Succinic, and Adipic Acids MELVIN H. S W A ” Paint and Chemical Laboratory, Aberdeen Proving Ground, M d .
No specific methods of quantitatively determining individual acids in a mixture of dibasic acids in alkyd resins have been previously reported. New methods of analysis, accurate to 0.2% and specific for phthalic, fumaric, maleic, and sebacic acids in alkyd resins, are now available. Under certain conditions, succinic and adipic acids can also be determined by newly developed procedures. A new technique for accurately determining the nonvolatile content of resins, needed for calculating the dibasic acid content, is included.
0
F T H E synthetic resins, the alkyds probably possess the
widest range of applicability, especially for automotive equipment. They are unusually tough and durable and possess excellent solubility, compatibility, adhesion, and gloss-retention properties. Their use, on a volume basis, probably exceeds any other synthetic resin. The properties of the alkyds can be varied by the addition of various constituents to produce modified alkyd resins-the class most frequently encountered in commercial analysis. Originally, alkyd resins were composed entirely of phthalic anhydride, glycerol, and an oil constituent, dissolved in solvent. Among the addition constituents used to vary properties are such other acids as fumaric, maleic, succinic, sebacic, and adipic. The composition of modified alkyds is becoming more and more diverse as constantly increasing new materials are being put to use. Several methods of determining phthalic anhydride in the unmodified class of alkyds have been proposed and used (3). They were designed for use on alkyds that were known to be unmodified and dissolved in solvents that were known not to interfere in the determination. These methods and their many modifications have proved very useful for approximately 15 years, in accomplishing the limited purpose for which they were intended. The best of these methods based their calculations on the weight of the insoluble products of saponification, assumed to be dipotassium phthalate monoethanolate. They are actually a measure of the total insoluble products of saponification including other dibasic acid salts, and frequently contaminated with pigments, metallic hydroxides, potassium carbonate, phenolic condensates, cellulosic materials, etc. During the saponification process small quantities of chlorinated hydrocarbon solvents yield formates that would be weighed and calculated as phthalic anhydride and that resemble dipotassium phthalate in appearance and solubility properties. In addition, results have never been highly reproducible even under controlled conditions and variations of 3% on known samples in the hands of different analysts are common. There is extensive need for a more specific method of analysis for phthalic anhydride as well as the other dibasic acids. The uses and methods of application of alkyd resins require
varied dilutions, so that any quaiititative analysis of the dibaric acids present must be based on the nonvolatile content. Surveye have shown that there is even greater variation in the results of determining the solids content of resins of known composition than in the phthalic content, Thus the need for a method of accurately determining the nonvolatile content assumes importance comparable to that for the dibasic acids. The methods of analysis, detailed herein, enable qualitative identification of phthalic, fumaric, maleic, sebacic, and succinic acids in alkyd resins and are quantitatively accurate to 0.2% for phthalic, fumaric, maleic, and sebacic acids. The nonvolatile determinations are equally accurate. These methods are simple to conduct with standard laboratory equipment and reagents, and are readily adapted to a routine testing procedure. Although complete analysis of some resins may require 3 days, the total man-hours applied are comparatively few. After saponification by means of a modified Kappelmeier technique, the dibasic acids are separated from the reaction mixture as insoluble potassium salts. The salts are then converted to the acids and purified. REAGENTS
Alcoholic P o t w i u m H droxide, 0.5 N , 32.8 rams of C.P. reagent grade potassium $droxide, assay 8 5 . 6 d per liter of absolute ethyl alcohol, This reagent can be prepared rapidly b refluxing 30 minutes, cooling, and filtering through a fritteg glass filter funnel. A fresh supply should be used. Bromine in Sodium Bromide. Exactly 0.75% solution of liquid bromine in aqueous 50% sodium bromide, c.P., prepared in the following manner: A quantity of aqueous 50% sodium bromide solution is prepared, using C.P. salt and freshly boiled distilled water. This solution is filtered if not perfectly clear and kept in a glassstoppered container. When used, the stopper and neck of the flask should be wiped dry to prevent freezing of the stopper. A 125-ml. glass-stoppered flask containing ap roximately 25 ml. of the 50% sodium bromide solution is weighecfand approximately 1 ml. of bromine is added. The exact amount of bromine added is determined by reweighing the flask. It is then transferred to a glass-stoppered graduate and diIuted with 50% sodium bromide solution to a volume, calculated from the weight of the bromine
