Procedure for Determination of the Bromine Number of 0Iefinic Hydrocarbons HERBERT L. JOHNSON AND RICHARD A. CLARK, Sun Oil Company Experimental Diuision, Norwood, Pa. A n improved method for the determination of bromine absorption by olefinic compounds in gasoline and similar products has been developed. All hydrocarbons tested have been found to give results very close to theoretical except a few highly branched or sterically hindered olefins and anthracene.
T
A bromine absorption method should be precise and rapid, and the amount of bromine reacted should correspond with the theoretical value for all molecules containing olefinic unsaturation. It is desirable that minor changes in temperatuTe, excess of reagent, or nature of the solvent should not appreciably affect the bromine number obtained. The difficulty in developing a satisfactory halogen titration procedure is increased by the fact that the rate of reaction of halogen with the various types of olefins differs widely. The tendency for halogen substitution to occur with saturated and aromatic hydrocarbons, as well as with olefins, is pronounced under certain conditions. The development of a satisfactory halogen titration procedure is in fact an attempt to find s procedure which will give satisfactory conditions for the reaction of halogen with all types of olefins and will in general avoid substitution or other side reactions. Many procedures have appeared in the literature for the determination of olefinic unsaturation by means of halogen titration.
H E procedure described in this paper for the determination of olefinic unsaturation was developed in 1941 but publication was held up because of wartime conditions. In 1942 it was submitted to the American Society for Testing Materials and formed the basis of the bromine number procedure incorporated in Method ES-45, Method ES-45a, and finally a tentative AS.T.M. standard (D-875-46T) for olefins and aromatics in petroleum distillates. The method as originally developed is applicable to ole& samples with high or low bromine absorptions. Data justifying the scope of this procedure are included in this paper.
CYCLOHEXENE7 s
r[
P
*
!i
l90b
/
z
The methods of Hub1 ( 7 ) Hanus ( 6 ) , and Wijs (15), which were among those first used, gave good results on some compounds while on others they gave high values because substitution occurs as well as addition. To correct this deficiency McIlhiney (11) developed a method whereby both addition and substitution could be measured. Johansen (8) compared the Hanue and McIlhiney methods and concluded that the latter after some minor modifications, gave satisfactory results. However, since negative numbers for the bromine addition were sometimes obtained, there has been some doubt whether or not the method correctly measures either addition or substitution. In an attempt to minimize the effect of a large excess of halogen, Francis ( 3 ) used an aqueous potassium bromide-bromate solution which liberates bromine in the presence of sulfuric acid. A number of modifications involving different acids and solvents have been used by other investigators (1, 2 ) .
e
W
tl50-
1 0
2 145140
I
I
I
I
1
I
----I
CYCLOHEXEN
IS5t
loot-
-
-=
CYCLOHEXENE 7
dl
e
I
a ~.
i
i
5z 155'
I I
150-
145' I40
I
15-
Figure 2.
I
eo. TEMPE RAT U R E *C.
I
25.
J
-
ISSO
SO
I
I
I
I
PO
40
60
0
I
100
TIME IN SEC.AFTER ADDITION OF I m l EXCESS
120
KBr-KBr Os SOLN.
Effect of Time after Addition of 1-M1. Excess Reagent on Bromine Number
Figure 3.
869
Effect of Excess Reagent on Bromine Number
V O L U M E 19, NO. 1 1
870
5Iulliken and Wakeman (12) studied the original Francis method and found that it gave accurate results for all straight-chain olefins; for cyclic compounds the accuracy was not so good. Thomas, Block, and Hoekstra ( I S ) modified the procedure and found that cooling reduced the possibility of substitution. Lewis and Bradstreet (10) made further improvements which eliminated the necessity of cooling. Green (4)repeated a portion of the 1 1ork of Lewis and Bradstreet and concluded that the method was very reliable for straightchain olefins, obtained less than theoretical values for tri- and tetraisobutene. In 1938, Grosse-Oetringhaus ( 5 ) made a survey of a number of methods applicable to the measurement of unsaturation in pztroleum fractions and concluded that the Kaufmann (9) method, employing a solution of bromine and sodium bromide in methyl alcohol, gave reliable results. However, Uhrig and Levin (14) found that the bromine number obtained by this procedure was too high. ii method that is satisfactory for a number of olefins, which utilizes bromine in acetic acid as the reagent, has been described by the same authors. The bromine color end point used in this method cannot be used satisfactorily for colored samples. The Lewis and Bradstreet procedure is slow relative to that of Uhrig and Levin because it involves the use of a two-phase reaction mixture which requires vigorous agitation. However, the back-titration, using starch as the indicator, enables one to obtain precise results. I n the present procedure the authors have attempted t o incorporate the advantages of the other methods by using acetic acid as a solvent so the reaction is carried out rapidly in a single phase, using a bromide-bromate solution in slight excess as the reagent, and backtitrating with thiosulfate after all free bromine has been converted t o iodine after the addition of potassium iodide. Starch solution is used as the indicator. METHOD
Scope. This method is intended for use in determining the bromine number of olefins in petroleum products boiling below anthracene. If used for cracked products boiling sufficiently high to include anthracene and its derivatives, the results cannot be interpreted in terms of olefin content. I t is least qatisfactory for highly branched olefins.
Bromine Number. The bromine number is defined as the number of grams of bromine which will add t o 100 grams of sample. The reactions involved in this procedure are: 6 HAC
+ KBr03 + 5 KBr =
6KAc
H
H
R-C=C-R
+ 3 Bra + 3H20 H H
+
Br? = R-C-C-R Br Br Br2 2 K I = I2 2KBr I2 2 Sa,S203= Ka?SaOa 2 S a 1
+
+
+
+
Reigents. 0.5 N s t a n d a r d p o t a s s i u m bromide-bromate solution (49.6 grams of potassium bromide plus 13.9 grams of potassium bromate per liter). Standard sodium thiosulfate solution, 0.1 N , standardized with potassium dichromate. Glacial acetic ac'ld, C.P. Carbon tetrachloride, C.P. Potassium iodide solution, 1.5%. Starch solution, O..5y0
Table I.
Bromine Numbers of Hydrocarbons Purity by retica Synthesized Method Bro-
Compounds Which M a y Be Present in Gasoline Straight-Chain Olefins 233.4 P 9 S + c 228.0 141.5 P 9 8 + e 142.4 142.3 P 9 8 + e 142.4 P 9 7 f b 1 1 4 . 1 111.2 92.0 P 95+c 95.1
1-Pentene 1-Octene 2-Octene 1-Decene 1-Dodecene
4,4-Dimethyl-Z-pentene Diisobutene 2,4,4-Trimethyl-l-pentene 2,4,4-Trimethyl-Z-pentene 3,4,4-Trimethyl-Z-pentene 3-Methyl-2-isopropyl-1-butene 2-Ethyl-1-hexene Triisobutene
Branched-Chain Olefins S 98+e 1 6 2 . 8 142 4 P S 9 8 C e 142.4 S 98+e 1 4 2 . 4 S 9 8 + c 142.4 S 97+6 1 4 2 . 4 S 9 5 f C 142.4 94.8 P
...
Cyclic Olefins P 98fb
4-2.3 -0.6 -0.1 -2.0 -3.3
161.0 144.5 145.7 144.5 170.6 165.6 169.0 96.3
-1.1 f1.5 f2.3 f1.5 $19.7 $16.3 +18.6 +1.6
-0.7
194.8
193.4
Toluene Xylenes, mixed Tetralin (technical)
Aromatic Hydrocarbons P 99+b 0.0 P 98d 0.0 P ... 0.0
0.0 0.5 0.0
llethylcyclohexane Decalin
Naphthene Hydrocarbons P 98b 0.0 P ' *' 0.0
0.0 0.0
.... ....
0.0 -0.1 1
....
Cyclohexene
Paraffin Hydrocarbons P 99.7b S lOOb S 99.8b P 99 7b S 99.6b
n-Hentann
0.0 0.0 0.0 0 0 0.0
Cyclic Olefins P 95fC 98.lb S
Indene 1,4-DihydronaphthaIene
137.7 122.7
.... ....
+0.6
-0.5
Compounds Sormally S o t Present in Gasoline Branched-Chain Olefins P .., 71 3 71.9
Tetraisobutene
....
+o.
Deriation from Theory, % ' One Two double double bond bonds
f0.8
137.4 122 7
-0.2
.... ....
0 7
....
-2. -3.
0.0
i
Sonconjugated Cyclic Diolefins P 233 0 P ,, 235 0 P 233 0 P 98+6 295 5
Terpinolene &Limonene DiDentene 4-Vinyl-1-cyclohexene
.
....
.... ....
+l. '+O.
270 227 1 240.7 257 9
$14.9 f16.6 -0.5 4-11.9
-42.6 -41.7 -50.2 -45.0
Aromatics with Unsaturated Side Chains 152.6 98+6 153 4 P 88 4 13 7 93-95C P
-0.5 -89
.... ....
Conjugated P P S
Isoprene 2-Xf ethyl-l,3-pent adiene C yclopentadiene cis-Piperylene Styrene Stilbene
229 227 237 297
S
Diamylnaphthalene a-Methylnaphthalene &Methylnaphthalene Triisopropylnaphthalene Di-tert-butylnaphthalene Tetraisopropylcyclohexane
Diolefins 9 8 + e 470 389.3 95+e g j + e 483 o 470.0 96b
Saphthalene Hydrocarbons 0.0 P ... 97b 0.0 P 0.0 95+* P 0.0 S si+. 0 . 0 S
6
Naphthenes 99+e
5
5
0.0 1.1 0.4 1.8 0.3
..
..
....
... .
.. .... ,...
0.0
0.1
....
....
0.0 0.0
137.0 0.0
+51.3
.... ....
56.7
54.6
-3.7
....
Other Hydrocarbons Anthracene Triphenylmethane
P P
... ...
Organic Acids
P
Oleic acid a S synthesized P purchased. b Purity obtainkd from freezing point. Purity as stated b y supplier. d Purity estimated from R a m a n spectrum. C Purified b y careful fractionation.
...
'
871
NOVEMBER 1947
-
r
0
a
m 150
A
POLYMER GASOLINE BR112.2 Z-ETHYL-I-HEXENE 0 I-METHYL-2-ISOPROPIL-l-BUTENE 0 3,4,4-TRIMETHYL-Z-PENTENE @ POLYMER GASOLINE B P I 0 1 4
140 Om1
05ml
Iml
2 ml
3ml
EXCESS K B r - K B r O j S O L N
4 ml
Figure 4. Effect of Excess Reagent on Bromine Xumber
Standardization of Solutions. For standardization, exactly 5 ml. of potassium bromide-bromate solution are added from a pipet to 50 ml. of acetic acid and 5 ml. of carbon tetrachloride in a 500-ml. iodine number flask. The solution is shaken well and allowed to stand 5 minutes. Five milliliters of 157' potassium iodide solution are placed in the lip of the flask and allowed to flow into the flask by slowly removing the stopper before addition of 100 ml. of water and titration with standard thiosulfate. Starch is used as an indicator. Procedure. A sample of 1 to 5 grams is weighed or an equivalent quantity pipetted into a 50-ml. volumetric flask containing 25 ml. of technical carbon tetrachloride as a diluent. The flask is filled to the mark with additional carbon tetrachloride and properly mixed so that a 5-ml. aliquot 11-ill contain 0.1 to 0.5 gram of sample. (Viscous samples are xeighed, while fluid samples, whose densities are readily obtained, may be pipetted providing this can be done without an appreciable drainage error.) The size of the sample must be controlled to a certain extent in order to prevent the use of a large volume of bromide-bromate solution which will cause separation of a carbon tetrachloride phase. .For bromine values of 150 to 200 the sample size should be 0.1 to 0.2 gram; for values of 20 or less a 0.5-gram sample is preferable. A 5-ml. aliquot of the carbon tetrachloride-hydrocarbon solution a t the same temperature as that used in preparing the diluted sample is pipetted into a 500-ml. iodine number flask containing 50 ml. of C.P. glacial acetic acid. The bromide-bromate reagent is added a t the rate of 1 to 2 drops per second while the flask is shaken with a swirling motion until a distinct yellow color is obtained which does not, fade in 5 seconds. (A distinct yellow color means color equal to that obtained by adding 0.5 ml. of standard bromide-bromate solution to 50 ml. of acetic acid and 5 ml. of carbon tetrachloride in a 500-ml. iodine number flask.) This titration should be made a t 2 5 " * 5' C. and the flask and contents should not be exposed to direct sunlight. An additional 1 ml. of reagent is then run in, the flask closed, and the shaking (qith a swirling motion) continued for 40 * 5 seconds. Five milliliters of 15% potassium iodide solution are immediately added to the flask by placing the solution in the lip of the flask and removing the stopper, thus preventing the possible loss of bromine vapor. One hundred milliliters of distilled water are added, the flask is shaken vigorously for one minute, the solution is promptly titrated Ivith 0.1 N sodium thiosulfate solution. Kear the end of the titration 1 nil. of 0.5$ starch solution is added as an indicator.. This back-titration should normally use about 5 nil. of thiosulfate solution. Calculations. The bromine values are expressed as grams of broniine per 100 grams of sample and are calculated as follows: Bromine value
=
(nil. of Br-Br03 X .V Br-Br03 solution) (1111. of Sa&Oa X LYSa&03 solution) X 7.992 grams of sample
DISCUSSION OF EXPERIIIER-TAL RESULTS
The importance of reaction temperature, time, and excess of reagent used has been mentioned by many investigators. In
working out this procedure a careful check was made using cyclohexene, diisobutene, 1-octene, and 2-octene as representative olefins. [Cyclohexene (xyhite label grade from the Eastman Kodak Co.) and 1-octene and 2-octene from the Connecticut Hard Rubber Company were further purified to at' least 98 mole 70 purity. Diisobutene (Eastman Kodak white label grade diisor butylene) was used as received and appeared to be of a comparable purity with respect to olefin content.] ' Figure 1 illustrates the change in bromine number over a temperature range of 10' t o 30 C. TThen other variables were const,ant. Diisobutene was the only one of the representative compounds that showed a detectable change in bromine absorption over this temperature range. In this inst,ance the variation was less than 3%. On the basis of these results there appears to be no justification for controlling the temperature closer .than mentioned above. The effect of time, after the 1-ml. excess reagent was added, on the bromine number is illustrated in Figure 2. The only compound among the representative olefins to be appreciably affected by longer reaction time TTas diisobutene. K i t h this compound, the effect,is large and if the time interval is not strictly adhered to, an appreciable error in the bromine number will result. Using the recommended time interval of 40 seconds, all the st'andard compounds gave adsorptions very close to theoretical. Figure 3 illustrates the effect of excess reagent on the bromine number of the same standard samples, using the standard reaction time of 40 seconds. Again, diisobutene is the only represent,ative olefin that shows an appreciable increase in absorption with excess reagent. Inasmuch as the data in Table I indicate that a number of highly branched olefins are sensitive to excess reagent, a short study was made of this effect in an attempt to utilize it for quantitatively determining the type of olefin present in olefin mixtures. Bromine numbers were determined on three pure hydrocarbons and two fractions of polymer gasoline by the regular procedure, using 0.5- and 4.0-ml. excess bromide-bromate reagent in addition to the recommended 1.0-ml. excess (Figures 3 and 4). The slopes of these curves are quite different; 3,4,4-trimethyl-2pentene, 3-methyl-2-isopropyl-l-butene, and 2-ethyl-1-hexene give very high values even though only a small excess of reagent was used, while diisobutene gives values close to theoretical. Therefore, it is impossible to analyze olefin mixtures quantitatively for branched-chain compounds in this way unless only one such hydrocarbon is present and its identity is known. Since the method has thus far had widest, use in connection with the analysis of gasolines, the compounds in Table I have been divided into two sections; the first including compounds boiling within the gasoline boiling range and believed to be present in gasolines in certain cases, and the second, those boiling above gasoline. The difficulty of obtaining pure hydrocarbons has been a serious handicap in work of this kind. $11 samples used in t'his study were of relatively high purity. However, in a number of cases the uncertainty of the bromine number method is less than the uncertaint,y of the purity of the hydrocarbon. K i t h few exceptions the method is accurate to 3% and the number of compounds giving positive and negative deviations are about equal in number. There is a slight, tendency for the straight-chain olefins to yield bromine numbers lower than theoretical while branchedchain olefins yield results slightly higher. The only compounds in the gasoline boiling range that exceed the limits mentioned above are some of the branched olefins prepared by olefin polymerization. Cyclic olefins such as cyclohexene, indene, and 1,4-dihydronaphthalene yield results very close to theoretical. Sonconjugated diolefins such as I-vinylcyclohexene and &limonene also give good results.
872
V O L U M E 19, NO. 1 1
The authors have been unable to find any aromatic, naphthene, or paraffin hydrocarbon in the gasoline or kerosene boiling range that reacts with bromine under the conditions of the procedure. In the higher boiling range anthracene reacts and it is expected that some of the anthracene derivatives will behave in a similar manner. Stilbene and related olefins add bromine slowly because of steric effects. Fortunately, compounds of this type do not appear to be present in petroleum products. Conjugated diolefinsyield low results for two double bonds and high results for one double bond. Cyclopentadiene gives close to the theoretical value for one double bond. Inasmuch as this procedure was intended primarily for mono-olefins, no attempt was made to work out a procedure that would yield accurate results for $his type of olefin. The method if used for cracked products boiling sufficiently high to include anthracene and its derivatives cannot be interpretedin terms of olefin content, Since satisfactory results have been obtained on practically all types of olefins, it is believed that the procedure as written is adequate for use on the olefins present in gasoline, kerosene, and gas oil samples. I t is least satisfactory for highly branched olefins.
ACKNOWLEDGMENT
Acknowledgment is hereby given to S. S. Kurtz, Jr., and to J. H. Bruun for helpful suggestions, to A. P. Stuart for the preparation of some of the compounds used, t o A. E. Hirschler and W. B. ill. Faulconer for freezing point purities, to W. T. Harvey, A. H. Heyn, and M. R. Lipkin for helpful discussion, and to Evan Street for assistance in a portion of the experimental work. LITERATURE CITED
Bacon; I n d . Eng. Chem., 20,970 (1928). (2) Cortese, Rec. trav. chim., 48,564 (1929). (3) Francis, Ind. Eng. Chem., 18,821 (1926). (4) Green, J . Inst. Petroleum, 27,66 (1941). (5) Grosse-Oetringhaus, Brennstof-Chm., 19, 417 (1938). (6) Hanus, 2. Untersuch. Nahr- u. Genussm., 4,913 (1901). (7) Hubl, Dinglers Polytech. J., 253,281 (1884). (8) Johansen, J . I n d . Eng. Chem., 19,288 (1922). (9) Kaufmann and Kornmann, 2. Untersuch. Lebensm., 51, 3 (1926). (IO) Lewis and Bradstreet, IXD.ENG.CHEM.,ANAL. ED., 12, 387 (1940). (11) McIlhiney, J. A m . Chem. Soc., 21, 1084 (1899). (12) Mulliken and Wakeman, IND.ENG.CHFX, ANAL. ED., 7, 59 (1935). (13) Thomas, Block, and Hoekstra, Ibid., 10, 153 (1938) (14) Uhrig and Levin, Zbid., 13,90 (1941). (15) wijs, Ber., 31,750 (1898). (1)
I
RECEIVEDMarch 19, 1947.
Determination of Benzoyl Peroxide in Organic Media SIDNEY SIGGIA, Central Research Laboratory, General Aniline & Film Corporation, Easton, P a .
A volumetric procedure has been developed which makes possible the determination of benzoyl peroxide in unsaturated compounds (monomers) and in solvents where iodometric methods cannot be used. It can also be applied to determine benzoyl peroxide in polymers. The procedure is precise and can determine 0.01 gram of active oxygen to *0.5%.
N
EED often arises for the hetermination of benzoyl peroxide
in media where methods involving the liberation of iodine from potassium iodide cannot be used. Kokatnur and Jelling ( 1 ) showed that the only common organic media in which iodometric methods will work efficiently for peroxides are 2-propanol and ethyl alcohol. In the case of benzoyl peroxide in unsaturated organic compounds, as in polymerization work, the iodometric methods present difficulties of addition and substitution and cannot be used. In the suggested method, arsenious oxide is used to reduce the peroxide. This procedure works in many of the common organic solvents and can be used to determine benzoyl peroxide in monomers and polymers. Reichert and eo-workers ( 2 ) used arsenious oxide to determine various inorganic peroxides.
creasethe rate of evaporation. Water is added until the volume is about 40 ml. This procedure is continued until practically all the monomer, alcohol, or other organic solvents are replaced with water. The solutih is made just acid with 1 N sulfuric acid and then 0.5 gram of sodium bicarbonate is added. The solution is chilled, and the excess arsenious oxide is titrated with standard 0.05 to 0.1 AViodine until the yellow iodine color appears. Large amounts of organic solvent in the water slow the final end point. The end point is very sharp if most of the organic solvents are removed.
Table I .
Determination of Benzoyl Peroxidea Active Oxygen Observed Calcd. Gram Gram
I n methanol
EXPERIMENTAL
A standard 0.1 N arsenious oxide solution (25 ml.), containing 25 grams of sodium bicarbonate per liter, is introduced into a 125-ml. Erlenmeyer flask, and to it is added a sufficient amount of peroxide-containing solution to yield about 0.005 to 0,010 gram of active oxygen. If the sample solution is immiscible with water, ethanol is added until the two layers disappear and a homogeneous solution is obtained. If the sample is in the solid state, it is dissolved in ethanol. In the case of polymers, the polymer is dissolved in benzene, and ethanol is added a s before. Precipitation of the polymer does not affect results noticeably. However, if the benzoyl peroxide content of the polymer is greater than 5y0,it is best t o pour off the liquid from the precipitated polymer, redissolve the polymer, and reprecipitate it with ethanol. Then the extracts are combined and analyzed. Boiling chips are added and the sample solution is boiled down to about 25 ml. with a stream of air flowing over the liquid to in-
I n acetone I n benzene I n styrene I n isobutyl vinyl ether I n methyl methacrylate I n polystyrene a
'
0.00387 0,00398 0.01304 0.01315 0.01303
0.00393
0,00400
0.00394
0.00397 0.00582 0.00581 0.00584 0.01322 0.01308 0.01332 0.01335 0.00579 0,00581
Benzoyl peroxide samples recrystallized from acetone.
0.01320
0.00581 0.01323 0.01323 0.00581
