1194
ANALYTICAL CHEMISTRY
isobutane (2-methylpropane), isobutene (2-methylpropene), 2butene, and butadiene] was found to cause no difficulty. This is indicated by the data in Table 111, which show an average deviation of 0.2 mg. and a standard deviation of 0.2 mg. The solvent action of the solution a t the low temperature ( - 15' to -20" C.) prevented the escape of the hydrocarbon gases. If lighter hydrocarbons were present, provision would have to be made to meter the exhaust gas for inclusion in the sample weight. The time required to conduct the complete determination is 30 to 40 minutes. This time does not include preliminary standardization of the reagent or drying of flasks and delivery tube. A note of caution should be added on two points. During the time that the sample is being collected, the flask must be kept cold because high results have been obtained occasionally when the solution became warm. This may have been the result of reaction between the hydrogen chloride and methanol (6). Because hydrogen chloride is such a hygroscopic material, every precaution should be used to exclude atmospheric moisture during the analysis. Although the samples of gas from petroleum refinery operations, for which this method was intended, will, in all probability, contain nothing but hydrogen chloride, small amounts of hydrocarbon gases, and minute amounts of water, a limited investigation of the effect of some sulfur compounds was made. As would be expected, there was no reaction with sulfur dioxide in the absence of water. However, hydrogen sulfide and methyl and ethyl mercaptans (methanethiol and ethanethiol) were oxidized in the absence of moisture. I t is well known that thp following equations H p S
2RSH
+ I p --+ S + 2HI
+ I p +RS - SR + 2HI
apply in the reaction of hydrogen sulfide and mercaptans with aqueous iodine solutions. As the data in Table IV show, the same stoichiometric relationship was observed when the mercaptan and hydrogen sulfide were oxidized with the Fischer reagent. As the exact composition of the Fischer reagent was not known in terms of available iodine, the amount consumed is expressed in
Table IV. Wt. of Sulfur Compound
Relationship of Ethyl Mercaptan and Hydrogen Sulfide with Fischer Reagent
Af ff .
Iodine Consumed %-iff.H20
72.7 629.7 615.0
10.28 84.5 83.1
Sulfur Compound Mole
1320 Mole
Molar Ratio S Compound/HnO
Ethyl Mercaptan 0.0006 0,0012 0.0101 0.0047 0,0099 0.0046
2/1,00
2/0,93 2/0.93
Hydrogen Sulfide 6.4 6.3 6.3
3.7 3.6 3.1
0.00019
0.00018 0.00018
0.00020
0.00020 0.00017
1/1,05 l/l,ll
1/0.95
terms of the equivalent amount of water. On this basis, each mole of mercaptan consumes an amount of Fischer reagent approximately equivalent to 0.5 mole of water, and each mole of hydrogen sulfide is approximately equivalent to 1 mole of water. On this basis it will be possible to apply a correction for the interference of these sulfur compounds when the amounts of hydrogen sulfide and mercaptan have been determined. LITERATURE CITED
Almy, E. G., Griffin, W.C., and Wilcox, C. S., ISD. E m . CHEM., AXAL.ED.,12,392 (1940). DiCaprio, B. R., AN.AL.CHEY.,19, 1010 (1947). Fischer, K., Angew. Chem., 48, 394 (1935).
Goff, W.H., Palmer. W.S.,and Huhndorff, R. F., ANAL.('HEM., 20, 344 (1948) McKinney, C . D., and Hall, R. T..ISD.EXG.CHEM., ANAL.ED., 15, 460 (1943). Mitchell, J . , J r . , and Smith, D. M . , "Aquametry," p. 239, Xew York, Interscience Publishers, 1948. Universal Oil Products Laboratory. "Test Methods for Petroleum a n d Its Products," Method A-166-43, 1913. Wernirnont, G., and Hopkinson, F. J., IXD.ESG. CHEM.,.INAL. ED.,15, 272 (1943). RECEIVED October 2, 1946. Presented before the Division of Analytical and hlicro Chemistry a t the 110th Meeting of the ANERICAK CHEMICAL SOCIETY, Chicago, Ill.
Determination of Unsaturation in Dehydrogenated Dichloroethylbenzene By Use of Mercuric Acetate ROLAND P. MARQUARDT AND E. N. LUCE, The Dow Chemical Company,Midland, Mich.
W
H E X dichlorostyrene was first considered for use in the rubber and plastic industry, no suitable analytical procedure was available for ascertaining the purity of this monomer. Owing to the presence of two chlorine atoms on the benzene ring, the addition of chemical reagents to the unsaturated side rhain proceeas with considerable difficulty. Thus, the usual methods of analysis for unsaturation \yere found to be inadequate. The popular bromate-bromide method (Koppeschaar, 5)and the bromination procedure using bronllne in cdi bon tetrachloride (RlcIlhiney, 4 ) did not give quantitative results. Low results were likewise obtained by the methods of Wijs (f4),using iodine chloride in acetic acid; Hanus (I),using iodine bromide in acetic acid; and Hub1 (21, using mercuric chloride and iodine in methanol.
A procedure previously disclosed by the authors (6) for the determination of the unsaturation in styrene and styrene derivatives by use of an aqueous l,.l-dioxane solution of mercuric acetate, in which the amount of mercury adding to the double bond is determined by direct titration with standard ammonium thiocyanate, gives low results with dichlorostyrene. However, it was found that mercuric acetate in methanol solution would, with moderate warming, add much more easily to carbon-carbon double bonds, and this led to the development of the following method for the quantitative estimation of the unsaturation in dichlorostyrene. It differs from the previous mercuric acetate method in that the acetic acid produced by the addition reaction is titrated instead of the mercury that chemically combines with the styrene derivative.
V O L U M E 21, NO. 10, O C T O B E R 1 9 4 9
1195
A new method for the determination of the terminal unsaturation in many olefinic compounds is described, in which use is made of the addition reaction of mercuric acetate to double bonds. One equivalent of acetic acid per double bond is produced and titrated. This method has proved satisfactory as an assay procedure for dichlorostyrene, styrene, and many other styrene derivatives. I t is often possible to make the determination in the presence o f other unsaturated or halogen-substituting compounds.
OUTLINE
Whitinore ( I 0 ) states that mercuric salts dissolved in methanol add the groups -HgX and -OCH, to the double bonds of olefinic compounds. A general equation for thiq reaction may be shown as:
hydrate to regenerate the acetone arid hydroxyl ions orginally taken by the excess mercuric acetate:
nCH(OCH,)CH,HgI
The atidition in general follons JIarkownikoff's rule, mercury going to the carbon having the most hydrogen atoms. Whitmore states also that nearly all of the compounds formed from unsaturated substances and mercuric salts are soluble and stable iri sodium hydroxide solution ( I 2 ) , but that they react readily with halogen acids to give back the original unsaturated compound ( I f ). I n 1919, Tausz and Peter (9) prepared a mercury compound of styrene by use of an aqueous mercuric acetate solution. Pllanchot ( 5 ) found that styrene reacts with aqueous mercuric acetate to give a mercury-containing product, which was perhaps a basic compound, in which the mercury was not firmly held. I n 1928, Priewe (8) reported that styrene reacts with mercuric acetate in acetic acid solution to form p-phenyl-p-acetoxymercuriethyl acetate. Wright ( I 6 ) obtained ol-acetoxyn~ercuri-p-niethoxy-/3-phenylethane when he treated styrene with a methanol solution of mercuric acetate. Other workers, by reaction of styrene with an aqueous solution of mercuric acetate, produced b-acetoxymercuria-hydroxyethylbenzene ( 7 ) . I n the procedure given below, a weighed sample of dehydrogenated dichloroethylbenzene reacts with an excess of mercuric acetatr in methanol.
HOHg('H---Hg-CHHgOH
I
\
CH3C(OH)-O-C(
OH)CH,
+
OKOH
12 KI
+ CHiCOOK
+ 3H& +
+ 3K2HgId + 2CII,CO('H,
A standard amount of dilute acetic acid is added to the solution to neutralize most of the hydroxyl ions:
(K
+ Sa)OH + (1 -
2) CHsCOOH + ( 1 - z)CH3COO(Ii K'a)
+
+ z (K + S a ) O H
The remaining alkalinity is finally titrated with standard hydrochloric acid :
z (K
+ S a ) O H + zHCl +z (K + Sa)CI + zHnO
The titration obtained by use of the reagents only, or the blank titration, should be equivalent to about 49 ml. of 0.1 N hydrochloric acid. The acetic acid produced by the addition reaction is equivalent to the difference between the blank titration and the titration obtained b y the analysis of the sample. Finally:
n
CH=CHB
CHIGOOH
==
)o(
c1
c1
REAGERTS
Q
CH(OCH,)CH*HgOOCCH,
c1
+ CH3COOH +
Hg(OOCCH3)a (excess -1)
c1
Acetone is added to the solution and the excess mercuric ion is then precipitated as mercuric oxide by the addition of a standard amount' of chloride-free aqueous sodium hydroxide: (CH3COO)ZHg
+ 2SaOH
(excess)
f
HgO
+ 2CH3COOSa + H20 + SaOH (excess -2)
The mercuric oxide reacts with the acetone to produce soluble trimercuric diacetone hydrate ( I S ) :
3HgO
+ 2CHaCOCHs-
x a 0 ~ +HOHgCH-Hg-CHHgOH I
CH,C( OH )-0-C(
\
0H)CHs
Aqueous potassium iodide is then added, which reacts x i t h the c~-acetoxymercuri-p-methoxy-~-dichlorophenylethaneto form the a-iodomercuri compound, and with the trimercuric diacetone
Mercuric Acetate, approximately 0.24 S. Dissolve 38.0 grams of analytical reagent' grade mercuric acetate in approximately 900 ml. of methanol and 2.0 ml. of glacial acetic acid. Dilute to exactly 1 liter with methanol and filter. Acetone, good commercial grade. Sodium hydroxide, standard 0.1 S (chloridefree). Potassium Iodide Solution. Dissolve 300 grams of potassium iodide in water, add 1 ml. of 0.1 N sodium thiosulfate, and dilut,e to 1 liter. Check neutrality with phenolphthalein indicator, adjusting to a faint pink color if necessarv. *icetic Acid, approximately 0.65 1'. Dissolve 76.0 ml. of glacial acetic acid in water and dilute to exactly 2 liters. The normality of this acid may need to be adjusted slightly to make t,he titration of the blank about 49 ml. of 0.1 N hydrochloric acid. Hydrochloric acid, standard 0.1 S . Phenolphthalein indicator. APPARATUS
Constant-temperature bath maintained a t 50" C. Two-ounce screw-cap bottles. The caps should he lined with rubber to provide a tight seal. PROCEDUHE
Pipet 50.0 ml. of the mercuric acetate solution into a screw-cap bottle and add an accurately weighed sample that will have a net t,itration of less than 46 ml. of 0.1 S hydrochloric acid. Screv- the cap on tightly, mix well, and suspend the bottle in the constant,-
1196
ANALYTICAL CHEMISTRY
temperature bath for 1 hour. Then take the bottle out of the bath, unscrew the cap, and pour the contents of the bottle into a 250-ml. Erlenmeyer flask, washing the bottle with methanol. Add 10 ml. of acetone, pipet 20.00 ml. of 0.1 N sodium hydroxide into the flask, and swirl occasionally until all the mercuric oxide is dissolved. After adding 25 ml. of aqueous potassium iodide and mixing well, pipet 20.00 ml. of 0.65 N acetic acid into the flask while swirling to prevent any part of the solution from becoming acidic. Add 20 to 30 drops of phenolphthalein indicator and titrate with 0.1 1%’ hydrochloric acid, swirling while titrating. Finally, run a blank determination, for which the titration should be approximately 49 nil. of 0.1 N hydrochloric acid. The end point is reached when the last trace of pink color has vanished from the solution. CALCULATION
Calculate the unsaturation for dichlorostyrene as follows: (mol .wt .) 10,000
A - -- 100 - A
Wt. of sample where A = ml. 0.1
-
0*0173 loo = % unsaturation as wt. of sample % dichlorostvrene (by weight) I -
-V hydrochloric acid (blank) - ml. 0.1 -2’ hydrc-
Table IT. Known Number
Analysis of Known Solutions of Styrene in Eth j-lbenzene Styrene Calculated, Yo Styrene Found, %
99.60 by freezing point 75.71 50.87 20.57 1.05
1 2 3 4
99.46,99.74,99.38,99.50,99.51
75.52,75.44.75.50 50.63,50.80,50.76 20.52,20.52,20,51 1.06, 1.06, 1.05
Table 111. Analysis of Solutions of Ethylvinylbenzene, Divinylbenzene, and Diethylbenzene Known Number EVB DVB 1 2 3 4 5 6
EVB Added (Calculated)
168.22 90.44 41.95 11.86
3.07 0.99
DVB Total UnTotal Added saturation Unsaturation (Calculated) (Calculated) (Found) P e r Cent as Ethylvinylbenzene 98.79, 98.78, 98.74 201.0 , 2 0 0 . 6 ,200.7 16.02 184.2 184.0 , 184.1 , 184.0 42.92 133.3 133.4 , 133.0 , 132.5 39.57 81.52 81.39, 81.21, 81.11 10.64 22.50 22.54. 22.543 22.47 2.52 5.59 5.77, 5.78, 5.77 0.48 1.47 1.63, 1.66, 1.70
chloric acid (sample)
Table I. Known Number 1
2 3 4 5 6 7
Analysis of Known Solutions of 2,5-Dichlorostyrene in 2,5-Dichlorodiethylbenzene 2,5-Diohlorostyrene Calculated, % 99.81 by freezing point 80.25 60.71 40.87 20.40
10.15 5.14 1.09
2,5-Dichlorostyrene Found, 70 99.86,100.06,100.08,99.82,99.83 80.30, 80.31, 80.24 60.64, 60.74, 60.65 41.03, 40.98, 41.06 20.43, 20.41, 20.48 10.10, 10.22, 10.22 5.13, 5.18, 5.23 1.15, 1.14, 1.13
time vias limited to 5 minutes at room temperature. The results obtained are shown in Table 111. Other styrene derivatives that have been successfully analyzed by this method are vinyltoluene, vinylxylene, and ethovystyrene ( 5 minutes’ reaction time at room temperature), and monochlorostyrene and vinylchlorotoluene (15 minutes’ reaction time at room temperature). Evperience seems to indicate that the method gives somewhat low results with a-methylstyrene, because perhaps the addition compound is not completely stable in basic solution in the presence of potassium iodide. DISCUSSION
ADAPTABILITY OF METHOD TO STYRENE AND OTHER STYRENE DERIVATIVES
This method has been found very reliable for determining the unsaturat,ion in styrene and in nearly all the other styrene derivatives. Accurate results are obtained because the addition reaction is quantitative and there is no possibility of substitution as in the methods involving the use of halogen. Furthermore, as styrenes in general, except those having two or more halogens on the henzene ring, react easily with mercuric acetate, it is not necessary to heat to 50” C. l o complete the reaction; often 5 minutes’ reaction time a t room temperature will give quantitative results. Thus the mercuric aceta& solution and the weighed sample may be placed directly in the 250-nil. Erlenmeyer flask. ANALYTICAL DATA
A sample of 2,5-dichlorostyrene, 99.81% pure as determined by the freezing point method, was prepared and mixed with 23dichlorodiethylbenzene in known proportions. Result,s obtained by aiialysis of these solutions with the described procedure are shown in Table I. The results obtained on knonm solutions of styrene in ethglbenzene are shown in Table 11. The mercuric acet,ate solution and the weighed samples were placed directly in 250-ml. Erlenmeyer flasks and t,he reaction time was limited to 5 minutes a t room temperature to show that a longer time was not necessary. It was shown in a previous paper (6) that, mercuric acetate adds quantitatively t,o the vinyl groups in divinylbenzene and ethylvinyl benzene. To show the consistency of results on these two compounds over a wide range of percentages, the unsaturations in samples of ethylvinylbenzene and divinylbenzene were determined by this analytical method. Knolvn solutions of these samples were then made with diethylbenzene and t,he unsaturations found by analysis were compared with the calculated values. The mercuric acetate solution and the weighed known solutions were placed directly in 250-ml. Erlenmeyer flasks and the reaction
Because mercuric acetate dissolved in methanol adds easily and quantitatively to the vinyl group at,tached to the benzene ring, the analytical procedure described is generally well suited to the analysis of the unsaturation in styrene and styrene derivatives. There is no danger of subst,itut,ion to cause high results. In general, mercuric acetate in methanolic solution adds readily and quantitatively to compounds containing terminal unsaturat,ion, such as allylbenzene, hut slo~vlyand not quantitatively to compounds containing nonterminal unsaturation, such as propenylbenxene, thus limiting the method to the analysis of the double bonds in styrene, styrene derivatives, and many endof-chain unsaturated compounds. This selective feature has been used, with proper limit,ations of reaction time and temperat,ure,to det,ermine directly t,he unsaturation of compounds containing terminal double bonds in the presence of other unsaturated conipounds that react, with halogen but not with mercuric acetate under the conditions of the analytical procedure. LITERATURE CITED Hanus, J., Chem. Zentr., 2, 1217 (1901). Hubl, Baron, Dinglers Polytech. J., 253, 281 (1884). Koppeschaar, W.F., Z . anal. Chem., 15, 233-245 (1876). J . Am .Chem. SOC..16, 275-8 (1894). McIlhiney, P. C.. M a n c h o t , IT., Ann., 421, 316 (1920); Ber., 53, 986 (1920). M a r q u a r d t , R. P., a n d Luce, E. K., AXAL.CHEM.,20, 751-3 (1948). Nesineyanov, -1.X , , and Freidlina, R. Ch., Chem. Zentr., 1, 103 (1939). Priewe, H., I b i d . , 4 , 1615 (1928); Friedl&nder, 16,2571 (1931). Tauss, J., a n d Peter, W , , Chem. Zenfr., 2, 125 (1919). Whitmore, F. C., “Organic Compounds of Mercury,” p. 31, New York, Chemical Catalog Co., 1921. Ibid., p. 46. I b i d . , p. 48. Ibid., p. 157. ITijs, J. J. A , , Ber., 31, 750 (1898). Wright, G. F., J . Am. Chem. Soc., 57, 1997 (1935)
RECEIVEDFebruary 7, 1949.
