921
V O L U M E 21, NO. 8, A U G U S T 1 9 4 9 Listed in Table I1 are the percentage limits of detection of the most common metallic elements. The sensitivities were determined under conditions similar to those under which the quantitative curves %-ereobtained; the criterion for the limit of detection was the disappearance of the persistent lines as the concentrations were gradually decreased. I n many cases the limits of detection could be increased by the use of such buffers as graphite or ammonium salts; however, this would be at some expense of uniformity of results. The limits could also be considerably improved for certain elements by using lines outside the working range of the spectrum analysis No. 1 film. The method of analysis as described is simple, rapid, and reproducihlr It is readily adaptable to routine analysis of silica
samples, and with proper instruction all operations could be performed by nontechnical laboratory personnel. LITERATURE CITED
(1) Ahtens, L. H., J . 8 . African Chem. Inst., 27, 28 (1944). (2) Gilard, P., Dubrul, L., and Jamar, F., J . SOC.Glass Technol., 20, 326 (1936). (3) Lester, H. M.,"Photo-Lab-Index," Vol. I, p. 5, New York, Morgan and Lester, 1941. (4) Pierce, W. c..and Nachtricb, rl'. H., IND.E N G .CHEM., AN4L. ED., 13, 774 (1941). ( 5 ) Srhlegel. H., Angew. Chem.,49, 411 (1936). ( 6 ) Slawn, &I.,Glass Ind , 22, 341 (1941). Analyst, 71, 368 (1946). (7) Smith, D. M., R E C E UE D October 28, 1048
Rapid Estimation of Ethylenes R . W. 3IARTIN General Electric Company, Pittsfield, Mass.
This paper describes a rapid procedure for the determination of styrene and The procedure is based on the recertain homologs with an accuracy of *0.5"& action of an excess of mercuric acetate in methanol solution with an ethylenic double bond. During the reaction one mole of acetic acid is liberated for each ethylenic bond. The acid liberated is, therefore, a measure of the unsaturation, and can be titrated directly with standard sodium hydroxide after the addition of an excess of sodium chloride. The applicability of the procedure to fifteen ethylenic cnmpounds has been indicated.
A
R.\PID and simple procedure for the estimation of ethylenic compounds has been developed in this laboratory and used successfully for over 3 years. A reaction similar to the one described in this paper was recently reported by Marquardt and Luce (2) for the determination of styrene and styrene derivatives. Earlier Tausz used a similar procedure in the analysis of petroleum oils ( 4 ) and turpentine (5). Connor and Wright have also used such a reaction for t,he determination of geometric isomers ( 1 ) . I n the procedure described by Marquardt and Luce, the styrene or styrene derivative is treated with an excess of aqueous mercuric acetate to form a hydroxy mercuric acetate addition product. The excess mercuric acet,ate in the reaction mixture is treated with sodium hydroxide to form mercuric oxide, which is reduced to metallic mercury by boiling with hydrogen peroxide. The mercury in the addition product is then titrated in an acid medium with standard ammonium thiocyanate as a measure of the unsaturation. I n the procedure described below styrene and its derivatives as well as fifteen other monomers used in the plastics or synthetic rubber industries reacted with an excess of mercuric acetate in methanol. 1-nder such treatment a number of the ethylenic compounds added the elements of methoxy mercuric acetate to. the double bond and liberated a mole of acetic acid for each mole of mercuric acetate reacting: R-CHrCH-R'
+ (CH,C00)2Hg + CH30H + R--CH-CH-R' + CHsCOOH 1
I
OCHI HgOOCCH3 The reaction in methanol is generally more rapid than the corresponding reaction in an aqueous medium. The addition of an excess of sodium chloride to the reaction mixture converts the excess mercuric acetate to mercuric chloride and permits one to make a direct titration with standard alkali of the acetic acid liberated iii the reaction mixture. Because one mole of acetic
acid is formed for each equivalent of ethylenic group reacting, the amount of sodium hydroxide consumed in the titration is a direct measure of the unsaturation. Only part of the ethylenic compounds investigated reacted as outlined in the equation above. Tausz ( 5 ) loosely classified the reactions of mercuric acetate with ethylenes into four groups: ( I ) those that add the elements of methoxy mercuric acetate to the ethylenic group, (11)those that are oxidized by the reagent, (111) those that react by substitution (usually only at elevated temperatures), and (IV) those that form no mercuric addition compound and are not oxidized by the reagent, This paper describes a procedure for the estimation of those compounds in Group I where the reaction proceeds a t a reasonable rate and is essentially complete under the evperimental conditions chosen. REAGENTS
Mercuric Acetate, Merck's C.P. reagent grade. Must be low in free acetic acid content. Svnthetic Methanol. The reagent should be substantially free of acids or aldehydes. Sodium Chloride. Commercial grades of sodium chloride are satisfactorv. The aaueous salt solution should be saturated with sodium chloride, thkn filtered and made neutral to phenolphthalein. Sodium Hydroxide, 0.1 S solution. I t was carbonate-free and standardized against Baker's C.P. reagent grade benzoic acid. Vinyl Monomers. The unsaturated compounds were obtained from various sources. Where their purity was not indicated by the supplier, they mere carefully redistilled and only a very narrow middle cut was used. I n most cases the purified materials boiled over a 1' C. range, and never over more than LL 3" C. range. Sodium Nitrate, C.P. reagent grade, is used as a saturated solution in methanol. ANALYSIS
Accuratcly weigh approximately 4 milliequivalents of the ethylenic compound in a weighing bottle and transfer the weighing
ANALYTICAL CHEMISTRY
922 Table 1.
Analysis of Styrene and Styrene Derivatives 7 ' ., Found,
Compound Dow styrene Monsanto styrene Styrene solution
% Purity
Determined by 99.8 Supplier 99.8 Melting point 2.02 Dilution of 99.8% styrene Styrene solution 1.45 Dilutionof 99.8% styrene Divinyl- and ethylvinyl142.2 Method of l f a r q u a r d t benzene and Luce a Calculated as ethylvinylbenzene.
This Method 99.85,99.75 99.80,99.66 2.06 1.50
142.3.142 . g a
Table 11. Factors Affecting Reaction Ethylene: T:mp., IIg(OAc)2 C. 1:l 25 1:l 45 1:1.25 25 1:1.50 25 1:l 25 1:l 25 1:l 25 Methyl methacry- 1:2 25 late 25 1:2 25 1:2 25 Allyl alcohol 1:l 25 1:l.S 25 2-Vinylpyridine 1:l 25 1:2 25 1:3 25 1:2 25 1:2 25 1:3 Compound Styrene
Time, Min. 10 10 10
10 120 240 15 10
Catalyst
0 0 0 0 0 0
NaKOa
0
420 10 10 15 30 30 30 30 960 1200
X
Reaction 95.4,95.6 97.0 99.8 99.9, 100.6 99.1,99.8 100.1 99.7,100.5 1.3 6.8 4.0 98.1 98.7 19.8 36.1 47.4 51.8 97.0 97.3
bottle and contents to a X - 11. Erlenmeyer flask containing 20 to 25 ml. of carbon tetrachlc di. Empty the contents of the \\eighing bottle into the solvent. Add 4.00 grams of mercuric acetate and 30 ml. of methanol. If the ethylenic compound reacts slowly with the reagents, the use of 30 ml. of a saturated solution of sodium nitrate in methanol in place of the pure methanol will increase the rate of reaction. Stopper the flask, swirl the contents, and warm slightly, if necessary, to dissolve the mercuric acetate. Allow the reaction to proceed 10 to 15 minutes and then add 75 ml. of neutral saturated sodium chloride solution and 50 to 100 ml. of water. Add 20 drops of phenolphthalein solution and titrate to the first pink end point with standard 0.1 S sodium hydroxide. Shake the reaction mixture vigorously during the titration, so as to ensure complete removal of the acrtic acid from the carbon tetrachloride layer.
A blank should be run immediately after mixing the reagents, omitting only the unsaturated compound. If the blank is allowed to stand too long, its titer has a tendency to increase slowly. Each milliequivalent of sodium hydroxide consumed in the titration, after subtraction of the blank, represents one milliequivalent of ethylenic group. The analyses reported in Tables I and I11 were obtained using the above procedure; the analyses reported in Table I1 viere obtained by modifying the procedure as indicated. F A C T O R S I N F L U E N C I N G REACTION
When the elements of methoxy mercuric acetate add to an ethylenic double bond, a number of factors influence the rate and extent of the reaction. The effect of some of these factors can be seen from an inspection of the data in Table I1 where variations in the regular procedure were employed. Increasing the temperature and adding sodium nitrate (6) accelerate the reaction. An excess of mercuric acetate not only increases the rate of reaction but also serves to force the reaction to completion, the excess necessary depending on the particular ethylenic compound. I n practice 1 gram of mercuric acetate was used for approximately 1 milliequivalent of ethylenic compound. If this amount of mercuric acetate was not sufficient to give complete reaction in 15 minutes, the method was considered impractical so far as that particular compound is concerned. As indicated in Table 11, longer reaction periods give more complete reaction, but may result in some inaccuracies due t o an increase in the blank. The structure of the compound is the ultimate factor in deter-
mining the extent, rate, and type of reaction occurring when an ethylenic compound is treated with mercuric acetate in methanol. Although this paper deals primarily with the analysis of styrene and styrene derivatives, Table I11 shows the results of one or two determinations on fifteen other ethylenic compounds. These exploratory results indicate that the procedure will give satisfactory results with allyl and crotyl alcohol, certain allyl ethers and esters, certain vinyl ethers, and vinylcarbazole. Unsatisfactory results were obtained with acrylate, methacrylate, itaconate, and maleate esters as well as with acrylonitrile and vinylpyridine. Vinyl acetate and vinyl benzoate gave results approximately ttyice that expected. Of major importance in the use of this procedure is the quality of the mercuric acetate, This reagent should not only be low in free acid but the entire supply should be thoroughly blended, so that each portion used for an analysis has the same acid content. If this is not the case, checks d be poor. If the mercuric acetate contains appreciable amounts of acid, it is often advisable to place it in a vacuum desiccator for 2 or 3 hours and then blend carefully before use. The bottle containing this reagent should be tightly stoppered except when in use. Some difficulty was experienced in detecting the end point. However, after a few titrations and the addition of somewhat more than the usual amount of phenolphthalein the end point gave little trouble. The procedure described has been in use for over 3 years in this laboratory for the rapid routine estimation of styrene and divinyl and ethylvinylbenzene samples. I t has been entirely satisfactory and in general gave results checking within a few tenths of 1%. Typical data on styrene and ethylvinyl and divinylbenzene appear in Table I.
Table 111. Compound hf ethyl methacrylate Diallsl phthalate Diethyl itaconate hfethyl acrylate Vinyl acetate Vinyl benzoate Diethyl maleate Acrylonitrile Allyl alcohol Crotyl alcohol &Chloroallvl alcohol K-F'inylcarhazole
Analysis of Unsaturated Compounds
70Purity 99u
...
Purification Redistillation Redistillation Redistillation
98" 99"
... ... ...
3O lo 1' '1
.... C. boiling range C. boiling range C. boiling range C. boiling range
1' C. boiling range
2' C.boiling range 1' C. melting point range
92.8b 2-Vinylpyridine 1 0 C. boiling range Diallyl ether ... Anesthetic grade 96.Sa Vivinyl ether a As given by commercial supplier. b Determined b y acid titration using Fe(OH13 indicator.
% Found, This Method 1.3 94.5 Trace 43.5 201 187 4.0 3.4 99.48,98.71 101.5 15 99.4,99.7 39.8 99.9 96.8
CONCLUSION
A known reaction has been applied to the estimation of styrene and styrene derivatives. The procedure is rapid and simple, requires no special equipment or reagents, and in general gives results within =+=0.5%of theory or better. Substitution, which often occurs when halogens are added to ethylenes, is avoided. .4n indication of the range of applicability of the procedure to a number of vinyl monomers, commonly used in the plastics and synthetic rubber industries, is indicated. LITERATURE C I T E D
(1) Connor, T., and Wright, G. F., J . Am. Chem. SOC.,68, 256-8 (1946). (2) Marquardt, R. P., and Luce, E. N., - 4 ~ a t .CHEM.,20, 751-3 (1948). (3) Tauss, J.. Chem. Ztg., 42, 349-51 (1918). (4) Tausz, J., Petroleum, 13, 649-54 (1918). (5) Tauss, J., 2 . angew. Chem., 32, I, 233 (1919). (6) Wright, G . F., J . Am. Chem. SOC.,57, 1994 (1935). RECEIVEDSovemher 19, 1948.
