lation of their enolate forms. Fivemembered lactones react like esters ( 7 ) ; lactones which undergo ring openings may not interfere provided they are not acetylated. Mechanism of Hydroxamation. The rate of hydroxamation of hindered acetates such as 4-heptyl acetate (Tables I1 and 111) is enhanced more by a n increase in hydroxide concentration t h a n by a similar increase in hydroxylamine concentration. To account for this, one may postulate mechanisms similar to mechanism A proposed by Bruice and Bruno (3) for aqueous hydroxamation of lactones : NHzOH
+ OH-;=” 0
CH,COR
i“
HZSO- H--NOH u H
+ Hz0
“20-
(1)
0
#I
+
CH,CSHOH SH20- (2) ROH
++
Khere hydroxylamine is present a t higher concentrations than sodium hydroxide (Table 111), most of the hydroxide is consumed by reaction 1 in the nearly nonaqueous medium ( 3 7 , water), and mechanism 2 predominates. This is probably the case for standard hydrovamation methods ( 7 , 8) where heat is used to increase the rate of the reaction, which is probably kinetically fourth order over-all and seconil order in hydrouylamine (3). In the procedure, h y d r o d e is present
in such substantial excess over hydrosylamine that the hydroxide consumed in reaction 1 becomes less important, yet the rate increases with increasing hydroxide concentration. I n this case, the more rapid mechanism 3 may compete with mechanism 2 and probably predominates :
LITERATURE CITED
(1) Aksnes, G., Acta Chem. Scand. 11,
710 (1957). (2) Banick, W.M., . ~ N A L . CHEM.34, 296 11962’1. (3j Bruice, T. C.,Bruno, J. J., J. Am. Cheni. SOC.83, 3494 (1961). (4) Critchfield, F. E.,Hutchinson, J. A., ANAL. CHEY.32, 863 (1960). (5) . , Davidson. D.. J . Chem. Ed. 17, 81 (1940). (6) Fritz, J. S., Schenk, G. H., ANAL. CHEM.31, 1808 (1959). ( 7 ) Goddu, R. F., LeBlanc, N. F., Wright, C.M.,Ibid., 27, 1251 (1955). (8) Goldenberg, V., Spoerri, P. E., Ibid., 30, 1327 (1958). (9) Hestrin. S..J . Biol. Chem. 180, 249 ( 1949). (10)Hill, U., Ind. Eng. Chein., 9naI. Ed. 18, 317 (1946). (11)Johnson, D. P.,Critchfield, F. E., AXAL. CHEW32, 865 (1960). 112) hleloan. C. D..Brandt. W.W., Zbzd., 33, 1’ (13’1hl I
CH,&oR ----+
i*
HO- H--NOH u H
I1 CH,CSH~H R O H + O H - (3)
+
k t very high hydroxide concentrations, this third order reaction n ill become pseudo second order (only first and is also thus more order in “,OH) rapid than the fourth order reaction in mechanism 2. This is then the actual nucleophilic attack of -”OH on the carbonyl group. I n the latter case or in mechanism 3, it should be understood that equilibrium forms of -“OH, XH20H,or the hydroxamic acid may be involved. ACKNOWLEDGMENT
The authors express their appreciation to Sorman A. LeBel for helpful discussion and to the Kyandotte Chemical Corporation for permission to publish a portion of their n-ork and for use of their research facilities for part of the research.
,
‘ (ig58). (16) Pilz, W.,Ibid., 166, 189 (1959). (17)Reuther, K. H., Bayer, E., Ber. 89, 2.541 - _- (1956). (18)5Schenk, G. H., AYAL. CHEM.33, 299 (1961). (19)Siggia, S., “Quantitative Organic Analysis via Functional Groups,” p, 28. Wilev. New York. 1954. (2O)’Tanakk,M.,Talanta 5, 162 (1960). RECEIVEDfor review April 27, 1962. Accepted July 16, 1962. JVork sup orted by Public Health Research Grant RE-7760 from the National Institutes of Health,
Public Health Service.
ChemicaI Qua Iitative a nd Qua nt it a t ive An a lysis of Some Epoxy Coating Materials M.
H. SWANN
and M. L. ADAMS
Coating and Chemical laboratory, Aberdeen Proving Ground, Md.
b Two related methods of analysis for epoxy resins of the bisphenolepichlorohydrin type are described that allow fast, dependable detection of epoxy resin in painted surfaces and a means of estimating the epoxy portion of most modifications including amine-, polyamide-, and phenol-catalyzed enamels, fatty acid esters, and simple mixtures.
E
of the type formed by the condensation of epichlorohydrin with bisphenol (p,p’-isopropylidenediphenol) may be used in coatings in three important ways: as epoxy resin esters or styrenated epoxy esters; in combination with other resins such as urea, melamine, or phenolics; and in combination with eo-reactants or POXY RESINS
curing agents such as polyamine or polysulfide resins. I n the first case, the fatty acid esters, the epoxy content usually ranges around 50%; in the second, it may vary from very low to very high quantities; in the third case, the concentration usually runs from iOYGto loo%, either in the finished coating or as one part of a two-part system. Lesser amounts of other materials such as flow control agents-Le., silicone resin or ethyl cellulose-may be present but do not usually exceed 1% and are not an analytical problem; neither are such quantities sufficient to interfere seriously with other analyses. Sornially in analyzing polymeric materials, it is easier and more accurate to determine the quantities of the minor constituents present in the system, but in the great
variety of coating materials that may be encountered which are based on epoxy resins, all of the additives may not be identifiable and, in addition, analytical procedures may not be available. An analytical method for measuring the epoxy resin in various coating systems is particulsrly useful for specification control purposes. The two tests described here for qualitative and quantitative determination of epoxy resins in coatings are based on reaction of the resins with fuming nitric acid. K h e n the reaction product is diluted with water, a filterable yield of 165% is obtained with epoxy resins of all molecular weights that allows gravimetric measure of the epoxy portion of coating systems. The rapid qualitative technique is based on the red to violet color obtained by VOL. 34, NO. 10, SEPTEMBER 1962
1319
adding alkali to the nitrated resins under anhydrous conditions. QUALITATIVE CONSIDERATIONS
Several qualitative tests (1-3) have been described for the detection of epoxy resins in coating materials, and satisfactory results are obtainable with these tests. The new test described in this paper is more versatile and is especially suitable for testing painted articles. It is rapid, very simple, highly sensitive, specific, and uses common reagents. There are several coating materials that demonstrate complete resistance to the attack of the 90% fuming nitric acid used initially in this test, but the epoxy compositions are not among them. This test indicates reaction products of bisphenol and epichlorohydrin, the most commonly used type of epoxy resins. Pure bisphenol does not respond to the test and neither does bisphenol-formaldehyde. All of the common coating compoeitions have been tested and no interference from other materials has been found. Epoxy resins that have been reacted with amines, polyamides, nitrogen resins, other phenols, and phenolic resins are readily detected. Vehicles, resin solutions, pigmented enamels, and other liquid coating materials can also be tested, but must first be dried. Several advantages over the "spot" test (3') using sulfuric acid and formaldehyde can be listed. In the old test, dilution with sulfuric acid to a specified point was necessary to eliminate interference from such other reactive materials as fish oils, tung oil, drying oils treated with cyclopentadiene, rosin, and some phenolic resins. Because none of these materials tend to produce color under any conditions or concentrations, interference is impossible with the new test. The most widely used analytical technique for general resin identification is the preparation and comparison of infrared spectra. When painted surfaces are encountered, the examination is made on the pyrolyzates or distillates from thermal decomposition. The nitric acid test is much more rapid and sensitive than any of the infrared techniques. If alcoholic potassium hydroxide is maintained as a stock reagent, the test can be concluded in approximately 3 minutes. QUANTITATIVE CONSIDERATIONS
The only quantitative chemical method proposed for measuring the epoxy portion of coating materials (4) utilizes the blue color formed by dilution with water of the formaldehyde treated sample in concentrated sulfuric acid. This method is not generally applicable, is more time-consuming, and is less accurate with certain coatings than the gravimetric method described here. The colorimetric method could not be applied to epoxy resins mixed or reacted with phenolic or nitrogen resins and could only estimate the epoxy content of fatty acid esters or modified alkyds. These modifications are important 1320
ANALYTICAL CHEMISTRY
classes of coating materials and can be analyzed without difficulty by the gravimetric procedure. A special alternate procedure is supplied for use with samples containing polystyrene or styrenated oils. The only resins known to interfere, for which corrections cannot be applied, are the silicones and pentaerythritol alkyds. The silicones are not usually present in sufficient amounts to interfere, but if encountered, their presence is readily detected by the infrared spectrum and by the deep violet color that forms in the first step of the analysis, upon addition of fuming nitric acid. The product of nitration utilized in this gravimetric technique is insoluble in both water and alkali. Many potentially interfering resins form products that are also water insoluble but are washed from the filter crucible with alkali and their interference is thus eliminated. I n the case of polystyrene modifications, a correction is made by dissolving the nitrated epoxy from the crucible and reweighing to correct for the insoluble portion. PROCEDURE
Qualitative. Five drops of fuming nitric acid (90%) are placed on a horizontal portion of the surface to be tested. After one or two minutes, a small amount of the reaction product is transferred t o a test tube with a glass rod or dropping pipet. About 5 ml. of acetone are added followed by alcoholic potassium hydroxide (0.5N in 9 5 1 0 0 % ethyl alcohol), which is added slowly and with shaking until the sample is alkaline. A red to violet color indicates that the coating tested contains an epoxy resin of the bisphenolepichlorohydrin type. If preferred, the use of acetone and the test tube may be omitted by absorbing a drop of the nitric acid test solu-
Table I.
Analysis of Some Epoxy Coating Materials
Epoxide equivalent.of epoxy reem (approx.)
Coating material Curing agent (adduct) Curing agent (adduct) Coal tar coating Enamel, hot spray=
180 485 255 950
tion from the painted surface onto a glass fiber filter paper disk held in tweezers. The disk is placed on a flat glass surface and most of the acid is allowed to evaporate (10 to 15 minutes), then an excess of the alcoholic alkali is added from a dropper. A positive test is indicated by violet or blue colors. Quantitative. A sample of the vehicle or resin solution approximating 1 gram or less is weighed accurately and dissolved in a low-boilin solvent such as acetone or mixe! lacquer solvents or a 1:1 mixture of benzene-ethanol and diluted to a convenient volume such as 50 ml. or 100 ml. in a volumetric flask. An aliquot is withdrawn that is estimated to contain not more than 50 mg. of epoxy resin and is transferred to a glass-stoppered Erlenmeyer flask of 125- or 250-ml. capacity. The solvents are evaporated with a gentle current of air by placing the flask in a water bath a t 60" C. so that the sample dries in a uniform thin film on the bottom of the flask. About 3 ml. of acetone are added and the sample is redried. Five milliliters of 90% fuming nitric acid are added and the flask is stoppered and swirled frequently until most of the sample appears digested. The stopper is then vented and the flask placed in a water bath either a t room temperature or not over 40" C., and the bath temperature is gradually increased to 75' C. After 90 minutes a t 75", the flask is cooled to room temperature, and 100 ml. of water is added rapidly from a graduate. The flask is stoppered and the sample swirled for a full minute. If, upon settling of the precipitate, the supernatant liquid appears very cloudy, the sample should be agitated repeatedly until maximum clarity is obtained. It is then filtered through B large (50-ml.) fritted glass crucible of medium porosity and washed thoroughly with water. The collected precipitate is then washed
Other component of nonvolatile vehicle Diethylene triamine Phenol niethylene triamine
Coal tar pitch Urea-formaldehyde Melamine-formaldehyde Alkyd Primer, red lead 485 (50%) Urea-formaldehyde 2250 (SOTG) Primer,mixedwith 485 Grea-f ormaldehyde curing agent Polyamide resin, amine terminated Fatty acid ester 950 Soya fatty acids Dimer acids Not a commercial item; specially compounded in the ference.
EPO.XY resm Amount prqsent other m Epqxy com- sample resin ponent, aliquot, found, 3' 6 mg. mg. 52 2 26
2 7 . 3 27.0; 2 7 . 4 2 2 . 6 22.4; 2 2 . 9
60 3 3 40 5.5
33.3 33.7;33.6 42.2 41.7;42.1
5.4 29.5
23.6 22.6;22.8
46 8
29.8 30.6; 3 0 . 9 '
26.5 26.0;26.6
laboratory to teat for inter-
alternately with 25-ml. portions of Jiqueous alkali and with water in the following manner: The first two washings nith alkali should be with 0.1N sodium hvdrovide and the last two with 1.OA; sodium hydroxide. Finally the sample is washed thoroughly with water to remove all traces of alkali. ‘I’he rrucible is t h d r i e d in an oven a t 60” C. for several hours, cooled in a desiccator, and weighed. If there is any chancp of styrene’s being present in the original ssmple, the dried crucible is next mashed under vacuum with acetone until all acetone-soluble matter is removed and then redried and weighed for correction, the soluble portion being calculated 3 s epoxy resin. Epoxy = -_Weight-of precipitate X 0.606 X 100 Weight of aliquot sample x nonvolatile fraction DISCUSSION
The exact composition of the reaction product has not been determined. I t contains both nitro and nitrate groups, along with carboxyl groups that probably resulted from oxidation. The treated resins retain their poly-
meric structure and the melting points of the reaction products are higher than the corresponding resins but in the same relative order. The fuming nitric acid used should be full strength 90% HiYOs. Bottles that have been opened, partly used, and stored for any length of time may have lost some of their concentration, Most of the adduct curing agents containing free amines must be dissolved in a mixture of alcohol and benzene t o facilitate aliquot sampling. The qualitative test may be applied, if desired, to the collected precipitates in the quantitative procedure after weighing] by adding a drop or two of alcoholic alkali. A way of preventing interference from silicone resins has not been found; they yield a product that resembles the epoxy resin product in its water and alkali insolubility and ketone solubility so that a method of separation or correction has not been developed. Some results of analyzing a variety of products are shown in Table I. Among the coating materials tested were a mixture of epoxy resin with tar,
some enamels modified with nitrogen resins, curing agents prepared by reacting a solid and a liquid epoxy resin with a large excess of amine t o form polyfunctional adducts, a fatty acid ester, and a mixed product ready for application in which the curing agent has been added to the base component. The second column in Table I showing “epoxide equivalent” is included only t o show the extent of the variety of epoxy resins tested. ACKNOWLEDGMENT
The advisory assistance of C. F. Pickett, director of the laboratory. is acknowledged and appreciated. LITERATURE CITED
(1) Foucry, M. J., Peintures, Pigments, Vernit 30, 925 (1984). (2) Lewin, G., Paint Jianuf. 24, 434 (1954). (3) Swann, hl. H., Ofic. Dig. Federation Paint Varnish Prod. Clubs 30, 1277 (1958). (4) Swann, M. H., Esposito, G. G., ANAL. CHEM. 28, 1006 (1956).
RECEIVEDFebruary 21, 1962. Accepted
July 2, 19G2.
Determination of Isomeric Nitrobenzenediazonium Salts DALE W. BOWINS, RICHARD C. DeGEISO, and L. GUY DONARUMA Experimental Station laboratory, Explosives Department, E. 1. du Pont de Nemours & Co., Inc., Wilmington, Del.
b A procedure for the direct diazotization of nitrobenzene with nitric oxide was investigated and three of the diazonium salts produced were identified by the preparation of 2naphthol derivatives. A method was developed for the quantitative determination of 0 - , m-, and p-nitrobenzenediazonium salts in mixtures of azo coupling products. The diazonium salts were reacted with 2naphthol and chromatographed on an alumina column. The ortho isomer was separated from the meta and para isomers and directly determined by spectrophotometry. Failure to resolve the meta and para isomers necessitated collecting them together and determining them by differential spectrophotometry a t two different wavelengths. Each individual isomer could b e determined with an accuracy to 2 to 5%.
J
(3) discovered that nitrophenylazo compounds produced blue-purple colors when treated with alcoholic potassium hydroxide. Porter ( 4 ) studied this reaction for various nitro compounds and proposed a mechANOVSKY
anism involving the nitro group in the color-forming reaction. English ( 2 ) extended this observation to the quantitative determination of dinitro aromatics in the presence of the corresponding mononitro compounds. However, he noticed a change in color in the presence of isomers, and standards had to be prepared to correspond to the approximate isomer content. During an investigation of the reaction between nitric oxide and nitrobenzene to produce diazonium salts, it was suspected that the 0-, m-, and p-nitrobenzenediazonium salts were produced. No known analytical techniques were available to identify and analyze these suspected reaction products. Diazonium salts are not stable enough t o permit facile direct separation; hence i t was desirable to convert the salts to stable 2-naphthol derivatives. The 2-naphthol derivatives gave intense purple colors when treated with alcoholic potassium hydroxide. However, the spectra of all three isomers were not resolved sufficiently to determine them simultaneously. A chromatographic technique was used t o separate these isomers before analysis.
However, the meta and para isomers could be separated only with difficulty. Therefore] the ortho isomer was separated from the other two. The meta and para isomers were collected together, treated with alcoholic potassium hydroxide, and determined simultaneously by measuring the absorbance a t 460 and 550 mp. APPARATUS
The chromatographic column consisted of a glass tube 100 cm. long and 30 mm. in diameter. One end terminated in a Teflon stopcock and the other end was open. Elution curves were prepared by collecting fractions with a fraction collector, Model 1205-A (Research Specialties, Inc., Richmond, Calif.), These fractions were analyzed by spectrophotometry with a PerkinElmer Model 4000 A spectrophotometer using a 1.0-cm. cell. REAGENTS AND SOLUTIONS
The isomeric nitrophenylazo-2-naphthols were made by diazotizing the corresponding nitroanilines and coupling with 2-naphthol according t o classical VOL 34, NO. 10, SEPTEMBER 1962
1321
