Determination of Unsaturation Hydrogenation
by
Catalytic
MICHAEL SEDLAK Mobil Oil Corp., Research Department, Paulsboro Laboratory, Paulsboro, N. 1.
A study of several of the variables associated with analytical catalytic hydrogenation was made to extend the usefulness of the technique to petroleum products. In addition, an apparatus more suitable for routine use was developed. The apparatus may be used for the simultaneous reduction of two samples at room temperature and atmospheric pressure. A large number of different types of unsaturated compounds were examined and the results compared with those obtained by bromination. The hydrogenation method was generally reliable and in many cases superior to bromination. As little as 0.05 meq. of unsaturation per gram of sample can be determined.
U
NSATURATES IN PETROLEUM PRODUCTS are usually determined by
bromination. While this method is rapid it does not always give good results (21). The advantages of catalytic hydrogenation for determining unsaturation have been described (IS, 19, 20). However, catalytic hydrogenation has been used to only a limited extent in the petroleum industry because no detailed investigation of its possibilities had been made, and previously described apparatus (6, 12, 17, 18, 22) was not convenient for making the larger number of routine determinations required. This paper describes an improved apparatus and gives data obtained using various catalysts, solvents, and interfering materials with a variety of petroleum compounds. By using multiple units of this apparatus, unsaturates can be determined with only a little more operator time per sample than is required for the bromine number method
the same density. The use of this device eliminates the need for corrections due to fluctuations in temperature or barometric pressure. Cetane, tinted with a dye, is used instead of mercury. This increases the sensitivity of the unit and enables one to observe small changes in volume. Two catalyst scoops, constructed as shown in Figure 2, are used to dispense about 100 mg. of catalyst; a different scoop is used for each catalyst to prevent contamination. The low pressure regulators, VI and V 2 , with a range of 0 to 15 inches of water column are available from Matheson Co., East Rutherford, N. J., Catalog No. 70B. Rubber serum stoppers, size 11, 9 mm. X 5 mm.; and hypodermic syringes, assorted sizes 1 through 10 ml. and syringe needles, 5 / / ~ inch in length, 25 gauge are used. The hydrogenation unit is assembled as shown in Figure 1. All tubing carrying gases to the units should be metal or glass; short lengths of Tygon tubing may be used for connections. All joints and stopcocks are greased with Apiezon N.
Regulators V1 and V z should be adjusted to give pressures of approximately 11 inches of water. The regulators should be supplied with gas a t about 25 p.s.i. As a safety precaution, metal tubing leading from V1 should contain a 1-mm. orifice to restrict the flow of hydrogen. Restrictors R1 and Rz, constructed from approximately 0.5-mm. capillary tubing, should be selected to give flow rates of 250 to 350 ml. per minute and 400 to 600 ml. per minute, respectively. The gas inlet to the flask should be a t least 1-mm. i.d. throughout. The tip should be bent at least 45' from the vertical; this prevents blowing of a solid sample from the cup when flask S (Figure 2) is used. During purging operations gases are vented through stopcock D to a hood. The reaction flask is supported about inch above the magnetic stirrer by means of an aluminum plate. This prevents transfer of heat from the stirrer to the flask. Reagents. CATALYSTS. 5% Palladium on charcoal and 5% rhodium on charcoal were obtained from Engelm " 2
I'BALL JOINT
COMPENSATOR
45-50~~.0.R
EXPERIMENTAL
Apparatus. One unit of a multipleunit hydrogenation apparatus for the simultaneous reduction of a number of samples at room temperature and atmospheric pressure is shown in Figure 1. All units are connected to a single reservoir and compensator bulb. The compensator contains hydrogen, and when the level of liquid in the bulb is made equal to that in a buret, the gas in these two vessels has
LEVELING BULB 75 ML./ UNIT
H 3/16' I.D.
Figure 1.
Hydrogenation apparatus
VOL 38, NO. 1 1 , OCTOBER 1966
1503
CATALYST SCOOP
I
- 5 MM
FLASK AND CUP FOR HYPROGENATION OF SOLIDS
ROD 9 BALL JOINT
160 MM,
2EML ERLENMEY
Fusn
propriate flask, Attach the flask containing 10 ml, of acetic acid, stirring bar of Teflon and about 100 mg. of catalyst to M . The palladium catalyst is used for olefinic unsaturation and rhodium catal st is used for total unsaturation. T e d n and glass retain catalyst; therefore, stirring bars and flasks which have been used for rhodium catalyst should not be used with palladium because the rhodium retained on the surface will catalyze reduction of aromatics. If the sample is insoluble in acetic acid, 10 ml. of 50 v./v. yo of acetic acid in isooctane or isooctane alone may be used. If a sample is a solid or nonvolatile liquid, weigh 2 to 3 meq. into a previously weighed sample cup (Figure 2). Lubricate the outer half of the ground surface of the samde CUD. Insert the cup into flask S. If the samde is a volatile liauid. fit a new serum stopper to side b m ’ of flask F . Equilibration of Apparatus. Turn stopcock B to purge flask with nitrogen for 1 minute a t about 300 ml. per minute through stopcock D. Turn stopcock B to purge with hydrogen for 1 minute at about 500 ml. per minute. Close stopcock D. Start stirrer. Continue to admit hydrogen for a t least 5 minutes. Close stopcock B; turn stopcock A to admit hydrogen from buret to flask. By adjusting the height of C and L, align the level in the compensator with the mark on the compensator and with the level in the buret. Repeat this alignment procedure whenever a reading is taken. Record buret reading. Continue stirring and recording buret readings at &minute intervals until successive readings agree to within 0.1 ml. Addition of Sample. (1) If flask S is used, introduce sample by inverting the cup. (2) If flask F is used, fill a hypodermic syringe with 2 to 3 meq. of sample. Discharge any gas bubbles and reinove any sample -adhering to the outer parts of the syringe; weigh the syringe. Stop stirrer. Pierce the Serum stopper and discharge the contents of the syringe into the flask. Align the buret and compensator, record the volume and start the stirrer. If the sample has a high vapor pressure or if hydrogen uptake is very rapid, it is preferable t o obtain the initial buret reading VOby adding the volume injected to the buret reading taken before the sample is added. If step 2 was followed, immediately reweigh the syringe. Follow the hydrogen uptake as follows: (a) If the initial rate of hydrogen uptake is greater than 1 ml. per minute, record buret readings every 15 minutes until successive readings agree within 0.2 ml. (b) If the initial rate of hydrogen uptake is 0.5 to 1 ml. per minute, record buret readings every 30 minutes until successive readings agree within 0.2 ml. (c) If the initial rate of hydrogen uptake is less than 0.5 ml. per minute, or if after 4 hours, successive readings A
3.5 MM;
- 7 MM. Figure 2.
Hydrogenation apparatus
hard Industries, Newark, N. J. Glacial acetic acid, reagent grade; isooctane, knock-test grade percolated through silica gel or spectro grade; oil-soluble dye; and cetane (n-hexadecane) were used. Add sufficient dye to make the meniscus observable. Filling and Calibrating the Apparatus. Attach a reaction flask to the unit and with the three-way stopcocks, A and B , closed (Figure l ) , and stopcock D open, fill the leveling bulb, L , with cetane. Lower the compensator, C, to a position below the buret. Turn stopcock A momentarily to connect the buret to the flask and half fill the buret with cetane. Tap the tubing connecting the compensator to the buret and allow the liquid to displace the air in the bulb. Occasionally, it may be necessary to vent the displaced air through the flask by turning stopcock A . During this operation it is necessary to have the leveling bulb raised to a position above the graduation marks on the buret. When all air in the compensator and tubing has been displaced, fill the buret with cetane to within l / 2 inch of stopcock A and then close stopcock A . Lower leveling bulb L and fill the buret with hydrogen by means of stopcock A . Displace the cetane in the compensator with hydrogen by closing stopcock A and raising the compensator after the buret has been inclined or inverted. Line up the level of liquid in the compensator with the liquid level in the buret by raising or lowering the leveling bulb L. Observe and record the barometric pressure and the room temperature. Observe and record the distance 1504
ANALYTICAL CHEMISTRY
between the liquid level in the compensator and that in the leveling bulb. Calculate the apparatus factor F by Equations 2 and 4.
F , meq./ml. = @ / e ) (273.1/T) (PJ760) (0.03204) (Pi) F= T
(1)
where d
0.08989 mg. per ml., the density of hydrogen at S.T.P. e = 1.008, the weight in milligrams of 1 meq. of hydrogen T = observed temperature in O K. Pt = total pressure in the buret in millimeters of mercury. It is calculated as follows: =
Pt = Pa
+ (h) ( j l m ) =
+ (h) (0.770/13.6) Pt = P, + (h) (0.0566) P.
(3) (4)
where
P,
observed atmospheric pressure in millimeters of mercury h = height of millimeters that the liquid level in the leveling bulb is above that in the compensator j = density of cetane m = density of mercury =
Procedure. Lower bulb L. Turn stopcock A t o admit hydrogen to the buret. Fill the buret to below the 45-ml. mark. Lubricate the outer half of the ground surface of the ap-
still differ by more than 0.2 ml., it is advisable to plot buret readings us. time on log x log paper and estimate the end point from the graph. Lengthen the time interval between successive readings as the reaction proceeds SO that the points are about equally spaced on the log X log graph. Close stopcock A during the period between readings and if a large sample is used or if the reaction time is greater than 6 hours, i t is preferable to run a blank and apply the appropriate corrections. When the determination is complete, open stopcock D , turn A to connect the buret to the flask, raise L until the buret is filled with cetane, and then close A . Turn stopcock B to purge flask with nitrogen for 1 minute through stopcock D. Stop stirrer.
Calculation. The olefinic or total unsaturation in terms of milliequivalents of hydrogen per gram of sample is calculated as follows. Unsaturates] meq./gram
=
where
vo = initial buret reading, ml. Vf =
final buret reading, ml. F = apparatus calibration factor, meq./ml. = weight of sample, grams
w
RESULTS AND DISCUSSION
Generally, in the petroleum industry it is desired to determine the olefin content of mixtures that contain olefins and aromatics. This requires a catalyst that selectively hydrogenates olefins in the presence of aromatics. A number of catalysts have been reported to be selective (14, 25); we have found palladium on charcoal to be a more selective catalyst than platinum oxide or platinum on charcoal. The latter catalysts slowly reduced some aromatics (Figure 3). As shown in the tables below, palladium on charcoal did not reduce any of the aromatics investigated. The results of hydrogenating various types of commercially available unsaturates] using palladium on charcoal in glacial acetic acid, are presented in Table I. The samples were used as received unless otherwise stated. Data obtained by t,he bromine number method (1) are also given. From the table it can be seen that the hydrogenation procedure gives more reliable and accurate results with a greater variety of compounds than does the bromine number. The majority of olefins were completely hydrogenated in 30 minutes although a few, such as propylene polymers, required several hours. However, this is not considered a serious disadvantage because with a multiple unit several
samples can be reduced concurrently. It should be noted that the yo theory quoted in Table I for anethole] indene, and dibenzal acetone is for the reduction of the olefinic portion of the molecule only. The aromatic rings did not appear to be reduced. The selectivity was further demonstrated by hydrogenating n-hexadecene in the presence of three times its weight of benzene; no hydrcgen was consumed by the benzene. Cyclohexene was the only compound in Table I that did not give acceptable results in the initial experiments. Therefore] additional work was done with this olefin, hydrogenating it in solutions of acetic acid containing either isooctane or toluene. Results in these solutions were considerably better, particularly in the presence of toluene. Low results were obtained only when no other hydrocarbon was present. When cyclohexene was reduced in solvents containing hydrocarbons, acceptable results were obtained (Table 11). However] even in mixtures] low results were obtained with dipentene, a terpene olefin. However, this type of compound is not a p t to be present in a p preciable amounts in petroleum products. The higher results with cyclohexene in Table I1 were not caused by the reduction of toluene because the results were independent of the amount of toluene present and the contact time. The anomalous reaction of cyclohexene in the presence of palladium is believed to be caused by one or two competing reactions] viz., addition of acetic acid to the multiple bond and/or disproportionation of the olefin to cyclohexane and benzene (4, 8, 14). The formation of ester would, of course, remove an olefinic bond and cause low results. When ethanol is used instead of acetic acid, the hydrogenation is slower but the amount of olefin hydro-
Table II.
Compound 2-Octene 1-Decene 1-Hexadecene 1-Tetradecene &Methyl-2 pentine 2,3-Dimethyl-2pentene Triisobut ylene Diisobutylene Anethole Indene Cyclohexene IsoDrene 2,3~Dimethyl-1,3butadiene 2,5-Dimethyl-2,4hexadiene 1,sPentadiene Dibenzal acetone 1-Ethynylcyclohexanol 5-Methyl-lhexyne
Brcmine no.
110.5
100.4
111.1
111.2 123.5
Hydrogenation 99.4 97.3, 97.3 99.7, 98.2, 100.1 100.1 102.2
99.8 100.1 97.7 105.0 116.2 99.8 99.0 65.5 47.8 74.4
102.4 100.9]101.0 101.6 97.7 77.0 100.0 99.5 98,4
94.7 0 103.0 0 . 8 94.6, 95.4
49.0 0.2
98.6
genated is increased. This suggests that in acetic acid there are two side reactions while in ethanol there is only one-disproportionation of the olefin to cyclohexane and benzene. The aromatic compound is not reduced in the presence of palladium but is reduced in the presence of rhodium. Although cyclohexene could be reduced in mixed solvents with palladium] dipentene could not. This may be due to the fact that dipentene is a diolefin which can undergo facile disproportionation to l-isopropyl-4-methylcyclohexane and p-cymene in the presence of palladium. However, the compound can be reduced in acetic acid in the presence of rhodium.
Determination of Cyclic Olefins Using Pd/C Catalyst in Various Solvents
Compound Cyclohexene"
Theory1 % I 77.0, 82.0, 85.5 94.0 102.6 103.0 102.0 101.5
Dipentene*
a
Table I. Olefinic Unsaturation Using Pd/C Catalyst Theory, %, by
100.4 86.7 94.5 96.0 91.7 95.6 97.6 99.6 87.9 99.7, 100.7 34.9 49.7 48.8
Solvent 100% Acetic acid 99% Acetic acid in toluene 80% Acetic acid in toluene 50y0 Acetic acid in toluene 20% Acetic acid in toluene 10% Acetic acid in toluene l'$&Acetic acid in toluene 80% Acetic acid in isooctane 607, Acetic acid in isooctane 50y0 Acetic acid in isooctane 40% Acetic acid in isooctane 20% Acetic acid in isooctane 10% Acetic acid in isooctane 1% Acetic acid in isooctane 95% Ethanol 2Y0 Piperidine in ethanol 100% Acetic acid 10% Acetic acid in toluene lYGAcetic acid in toluene
Distillation Products Industries, chromatographed on silica gel. Industries, redistilled.
* Distillation Products
VOL 38, NO. 11, OCTOBER 1966
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1505
The behavior of other cyclic olefins Auch as alkylcyclohexenes and cyclopentenes was not investigated. However, the cyclohexenes qualitatively would be expected to behave in much the same fashion as cyclohexene. On the other hand, the cyclopentenes would not be expected to undergo disproportionation, only addition of acid to the double bond. Although perhaps as much as 20 to 30% of cyclohexenes and cyclopentenes can be present in a cracked naphtha, the use of acetic acid as a solvent is still recommended since the addition and disproportionation reactions would give an absolute error of only about 4 to 5 per cent. Catalysts. Various catalysts were examined for their ability to catalyze selectively the reduction of olefins in the presence of aromatics. Indene was chosen as the standard olefin because it contains an olefinic bond in conjugation with an aromatic ring. T h e catalysts examined were: platinum oxide (Adams' catalyst), and 5% each of palladium, platinum, and rhodium on charcoal. All are commercially available. It waa observed earlier that palladium on charcoal in acetic acid catalyzed hydrogenation of only the olefinic bonds in indene, anethole, and dihenzal acetone (Table I). Rhodium catalyzed reduction of both the olefinic and aromatic bonds of
Table 111.
TIME, MINUTES
Figure 3.
indene in 50 minutes. Platinum oxide and platinum on charcoal also catalyzed reduction of both types of bonds but required a longer time. Thus, of the four catalysts examined, only palladium was truly selective (Figure 3). Results on samples containing highly substituted aromatics are sometimes low because the rate of reaction a t ambient conditions is too slow for practical purposes. The literature states that the rate of hydrogenation decreases exponentially with increase in the number of methyl groups (2, 11). However, naphthalene itself was reduced successfully using rhodium. I n Table I11 are summarized the results of the hydrogenation of unsaturates in the presence of rhodium on charcoal catalyst. Solvents. Ethanol, a solvent frequently recommended in the literature, was not so effective as acetic acid. Reductions in ethanol did not proceed as rapidly as in acetic acid and the end point was not as sharp because
Total Unsaturation Using Rh/C Catalyst
Sample Theory, % Dipentene 105.7 Cyclohexene" 102.3 Octene-2 in xylene 101.0 44% 4Methyl-2-pentene in 2,5dimethyl-2,4 hexadiene 101.0 45% 4-Methyl-2-pentene in cyclohexene 106.4 46% &Methyl-Zpentene in hexadecene-1 99.4 46y0 Hexadecene-1 in triisobutylene 100.2 100.2 Indene sec-Butyl benzene 104.7 Naphthalene 101.9,102.5 Distillation Products Industries, chromatographed on silica gel. 5
Table IV.
Olefinic Unsaturation Using Pd/C Catalyst in Ethanol and Tetrahydrofuran
Compound Isoprene
2,5-Dimethyl-2,4-hexadiene Styrene derivative As Styrene derivative Bo
Styrene derivative C4 ZOctene 1-Hexadecene a Prepared in these laboratories.
1506
Hydrogenation of indene and propylene polymer
ANALYTICAL CHEMISTRY
Theory, % 91.2 97.7 100.2 98.6
102
95.0 99.0
Solvent Ethanol Ethanol Tetrahydrofuran Tetrahydrofuran Tetrahydrofuran Ethanol Ethanol
the reaction slowed down when almost all of the olefin had been reduced. Results in ethanol also were somewhat lower than in acetic acid. Hydrogenation of hindered olefins in 1 or 10% acetic acid solutions in toluene were not as rapid as in loo% acid. A few compounds, soluble only in tetrahydrofuran, were quantitatively reduced in this solvent with palladium. I n general, it has been observed that hydrogenations proceed most rapidly in loo% acetic acid. Therefore, this is the preferred solvent. If the sample is insoluble in acetic acid, a 50% solution of acetic acid in isooctane or isooctane alone can be used. However, the rate of hydrogenation in isooctane alone is much slower than in the other solvents. Results obtained on hydrogenation of unsaturates in ethanol and in tetrahydrofuran are given in Table IV. Differentiation of Olefins. An interesting feature of the hydrogenation is t h a t , generally when hydrogen adsorption is plotted us. time on log x log paper, a straight line is produced with a sharp discontinuity. I n favorable cases the olefins in a mixture appear to be reduced consecutively rather thanconcurrently. If, for such a mixture, hydrogen absorpt,ion is plotted us. time, the straight line will eshibit several discontinuities. These discontinuities enable one to estimate the minimum number of different olefins present (different with respect to the amount of aubstitution about the carbon-carbon double bond) and to make a semiquantitative determination of their relative amounts.
Thus, the absorption curve for propyTable V. Hydrogenation of n-Hexadecene in Presence of Nonhydrocarbons lene polymer 671-D-1 in Figure 3 (Theory 8.91 meq./g.) indicates the presence of at least two and possibly more different types of Wt. % Found, olefins. I n this example the slopes are Impurity hetereatom. meq./g. Theory, % less than for the reduction of the C-5 Pynd,ine 0.633N 11.700 131.0 Pipendine 0.734 N 95.9 8.57 ring in indene, probably indicating Phenol 0.6850 9.13 102.2 that the carbon atoms connected by 0.930 S Thiophenol 0.23 2.6 double bonds are more highly subThiophenol 0.108s 100.7 9.00 stituted. This differentation of olefins &Butyl mercaptan 0.855S 1.15 12.9 0.084 s &Butyl merca tan 8.93 100,2 by determining the rate of hydrogena0.835 S n-Propyl sulfite 8.26 92.7 tion has been observed earlier and used 0.705S Phenyl sulfide 6.27 70.3 with limited success by Lebedev and 0.073 S Phenyl sulfide 9.11 102.0 other workers (6, 9, 10, 16, 16). 0.724S n-Propyl disulfide 0.66 7.4 n-Propyl disulfide 0.097S 8.96 100.4 Interferences. NITROGEN, OXYPhenyl disulfide 0.919s 0.49 5.5 QEN, A N D SULFURCOMPOUNDS.TO 0.098s Phenyl disulfide 8.86 99.4 check further the activity of the pal0.922S Thiophene 6.9gb 78.4 ladium catalyst, a typical olefin, 0.920S Thiophene 8.24bc 92.4 n-hexadecene, was reduced in the Pyridine also reduced. presence of the compounds listed in b Result after 30 minutes; reaction continued slowly, apparently reducing thiophene. Increased catalyst concentration. Table V. A suspension of palladium catalyst in acetic acid was saturated with hydrogen and then the nonhydrocarbon compound was introduced. hydrogen chloride, in agreement with The errors discussed above can be A known amount of n-hexadecene was the literature. partially or completely eliminated by added and the rate of hydrogen absorp Sources of Error. HYDROGENATION means of suitable blanks. I n general, tion was determined. The possible OF STOPCOCK GREASE. A source of this is necessary only for large samples interferences included saturated and positive error is excessive use of stopor for samples which require a reaction unsaturated nitrogen compounds, cock grease on the reaction flask. time greater than 6 hours. Generally, phenol, aliphatic and aromatic sulfides, Experiments with Apiezon N added no blank corrections are necessary and disulfides, and thiols. Results are to t h e flask indicated t h a t this error none have been applied to the data in summarized in Table V. would be negligible when the recomthis paper. Thiols and unsaturated sulfur commended procedure was used. VAPOR PRESSUREOF SAMPLE. A pounds had a deleterious effect on the SOLUBILITY OF HYDROGEN IN SAMPLE. highly volatile sample, such as isoprene, catalyst and decreased the rate of reI t was thought that the solubility of when injected may vaporize and disaction. However, if more catalyst was hydrogen in samples would produce a place several milliliters of hydrogen. added or if the sulfur content was repositive error if a large sample was used. This error can be avoided by reading duced to less than O . l % , hydrogenation T o check this, 5 ml. of isooctane was the buret before the sample is injected of hexadecene was complete in 30 injected into acetic acid in the absence and correcting for the volume injected. minutes. Hexadecene was reduced If the vapor pressure of the hydroof catalyst. The hydrogen uptake was slowly in the presence of thiophene; less than 0.1 ml. indicating the error due genated sample is high, it will displace however, the reaction did not stop when to solubility of hydrogen would be hydrogen and a negative error will the stoichiometric amount of hydrogen negligible even for a 5 m l . sample. result. Because the sample is diluted necessary for reduction of the olefin SOLUBILITYOF OXYGENIN SAMPLE. with acetic acid, this error will be a p had been added. Hydrogen absorp T o check the possibility that oxygen in preciable only if a sample more volatile tion continued and apparently the samples would produce a positive error than isoprene is analyzed. thiophene also was reduced (3). RAPIDREACTION.Some olefins may if a large sample was used, 5 ml. of airPyridine alsr, was reduced in the saturated isooctane was injected into a take up hydrogen before the buret can presence of palladium. The literature suspension of catalyst in acetic acid. states that in the presence of noblebe read. This will cause a negative The hydrogen uptake was 0.7 ml., error. However, this can be corrected metal catalysts a pyridine ring is recorresponding to an error of 0.14 ml. per by reading the buret before the sample is duced in preference to an aromatic milliliter of sample. ring. For example, quinoline is reduced injected and correcting for the volume DIFFUSIONOF SOLVENT VAPORS. A to 1,2,3,4-tetrahydroquinolinein the injected. negative error can occur if the stopcock presence of palladium, but in the presTEMPERATURE. I n using the combetween the flask and buret is left open ence of platinum both rings are reduced pensator to correct for temperature and during hydrogenation of a very slowly (7). pressure changes, it is assumed that the reduced compound. This error is The data in Table V indicate that the temperature of the apparatus is unicaused by vapors of solvent diffusing catalyst can tolerate moderate amounts form. Generally, a difference of '1 C. into the buret and increasing the of nitrogen, oxygen, and sulfur without between the temperature of the buret apparent volume of the hydrogen. impairing its efficiency to catalyze reand the compensator will produce an Acetic acid and isooctane were placed duction of an olefin. The amount of error of about 1%. I n practice, the in separate flasks and stirred. No sulfur and nitrogen compounds added flask is at a slightly higher temperature. catalyst was added and the stopcock in these experiments was greater than This error due to the temperature was left open. For acetic acid the that normally found in commercial gradient cancels when the stirrer is buret reading increased overnight from gasolines. operated continuously. 31.8 ml. to 32.1 ml. (lye change) and H A L O G E N A T EH DY D R O C A R B O N S . Stability of Compensator. The for isooctane, after 3 days stirring, These compounds normally are not compensator was calibrated occathe buret reading increased from 44.5 present in appreciable amounts in sionally t o determine diffusion of hyml. to 45.2 ml. (1.5y0 change). This petroleum products. Some limited drogen through the cetane. T h e error is negligible when the stopcock is work indicates that they do undergo change over a 75-day period was less closed during slow hydrogen uptake. hydrogenolysis to form an alkane and 0
0
VOL 38, NO. 1 1 , OCTOBER 1966
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than 0.5%. Therefore, t h e compensator need be calibrated only monthly. Repeatability. A number of Samples were run in duplicate t o determine the repeatability of the method. Results are listed in Table VI. ~~~
Table VI. Repeatability of Hydrogenation of Unsaturates (Palladium Catalyst)
Sample Meq./g. Butene polymer A 4.31 4.24 Butene polymer B 9.31 8.96 Butene polymer C 6.23 6.28 Butene polymer D 5.17 5.05 Butene polymer E 19.96 19.94 Butene polymer F 2.31 2.35 Hexadecene-la 8.91 8.96 Decene polymer 1.01 0.97 Mixed-olefin polymer 1.61 1.65 42% Octene-2 in xylene 7.01 7.02 Hydrog. cat. poly gasoline 0.05 0.06 Hydrog. cat. poly ~gasoiine 0.24 0.22 Diisobutylene 17.95 18.00 Decenel 13.90 13.90 1-Ethynylcyclohexanol 30.50 30.75 sec-Butyl benzene“ 47.07 46.92 Naphthalene” 79.52 80.00 Standard deviation = 0.12 Chromatographed. Rhodium catalyst used. 0
Time Requirements. The elapaed time per determination will vary with the sample. Pure olefins can be reduced in about 20 minutes, gasoline fractions require 2 to 4 hours, and lowmolecular-weight polymers (about 800) may require 8 to 10 hours. The man-hours per determination will vary with the time required for the hydrogenation and with the number of units operated concurrently. With a dual unit about 1man-hour is required per sample. This could probably be improved by the use of more than two units. ACKNOWLEDGMENT
The author thanks J. R. Glass for valuable assistance in designing the apparatus and for helpful suggestions in the development of the method. LITERATURE CITED
(1) Am. SOC.Testing Materials, D115957T, p. 589, 1957. (2) Balandin, A. A., Khidekel, M. L., Dokl. Akad. Nauk SSSR 123,83 (1958). (3) Bateman, L., Shipley, F. W., J. Chem. SOC.1958, 2888. A., et al., Zbid., 1954, p. (4) Braude, “C“0
%.
0010.
( 5 ) Colson, A. F., Analyst 79, 298 (1954).
(6) Davia, H, S., et al., J . Am, Chem. floc. 54,2340 (1932). (7) Eisch, J., Gilman, H,, C h . Reu. 57 525 (1957). (8) kachinaai, H. E., Bergmann, E. D., J. Am. C h . SOC.72 5651 (1950). (9) Farmer, E. H., Gahey, R. A. E., J. Chem. SOC.1933 (IO) Farmer, E. iTiley, R. A. E., Nature 131, 60 (1953). (11) Gilman, G., Cohn, G., Aduan. Calalysia 9, 733 (1957). (12) Joshell, L. M., IND.ENQ.CHEM., ANAL.ED. 15, 590 (1943). (13) Judd, S. H., Nicksic, S. W., Division of Petroleum Chemistry, 135th Meeting, ACS, Boston, Mass., April 1959. (14) Knight, H. B., et al., J. Am. Chem. Soc. 75, 6212 (1953). (15) Lebedev, S. V., et al., J. Chem. SOC. 1925, p. 417. (16) Zbid., 1930, p. 321. (17) Ogg, C. L., Cooper, F. J., ANAL. CHEM.21, 1400 (1949). (18) Savacool, R. V., Ullyot, G. E., Zbid., 24, 714 (1952). (19) Swan Tiong, S., Waterman, H. I., Chzm. Znd. (Paria) 81 (2), 204 (1959). (20) Zbid., 81 (31, 357 (1959). (21) Unger, E. H., ANAL. CHEM. 30, 375 (1958). (22) Vandenheuvel, F. A., Ibid., 24, 847 (1952). (23) Waterman. H. I.. et al.. J . Znat. Petrol. 42,349 (1956). ’ RECEIVEDfor review April 28, 1966. Accepted July 25,1966. Presented at the First Middle Atlantic Regional Meeting, ACS, Philadelphia, Pa., February 1966.
e
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Behavior of 2,4-Dinitrobenzenesulfonic Acid as an Acid Catalyst in Acetylation Reactions DONALD J. PIETRZYK and JON BELISLE Deparfment o f Chemistry, University of Iowa, Iowa City, Iowa
b The catalytic behavior of 2,4dinitrobenzenesulfonic acid (DNBS) i s examined in acid-catalyzed acetylation reactions and compared to HCI04 and p-toluenesulfonic acid (PTS). It is observed that DNBS and HC104 are superior catalysts to PTS. Perchloric acid appears to be better than DNBS only when the acetic anhydride concentration or when the acid catalyst concentration is very low. This trend follows the acidic strength exhibited by the three acids. Quantitative results for the acetylation of a variety of amines, alcohols, sugars, and polymers using DNBS as catalyst are reported. In addition to being strongly acidic, DNBS has other advantages which suggest its use over HC104. DNBS is a solid, readily available and purified, it appears to be safe and stable when heated in organic mixtures, and does not result in a highly colored acetylating mixture. Its notable disadvantage is a side reaction that occurs when aniline derivatives 1508
ANALYTICAL CHEMISTRY
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are acetylated in the presence of DNBS is superior to PTS heat. (HCIO4 cannot be used) for analysis of polymers of certain structures.
T
HE ACETYLATION and related re-
actions have been used for a long time for the analysis of hydroxyl and amine functional groups. A major advance in this area in recent years has been the use of acid catalysis with emphasis on HC1O4 (4). This method which proceeds more rapidly than the previous ones and is carried out at room temperature has been used for alcohols (4), phenols, thiols, and amines (a, ketoximes and vic-dioximes (Q),alkoxysilanes (?), mercaptosilanes (I), and micro analysis of hydroxyl group (IO). The principal disadvantages of the HClO4-acetic anhydride method are its inability to be used at elevated temperatures, potential hazard if carelessly used, and color formation with time. Experiments in our laboratory (8) on
the acidity of aromatic sulfonic acids in nonaqueous media indicated that several of the nitro substituted acids are close in acid strength to HClO,. It was then of interest to examine 2,4dinitrobenzene sulfonic acid (DNBS) as an acid catalyst in the acetylation reaction. The sulfonic acid previously used, p-toluenesulfonic acid (PTS) (4, IS), is a weaker acid than HC104. This resulted in a milder acetylating reagent which required a longer reaction time or heat to keep the reaction time short. I n addition to being strongly acidic, DNBS has the advantages of being a solid, readily available, readily purified if needed, and appears stable to heat. The latter property along with its strongly acidic nature suggests that DNBS would be very suitable &s a general acid catalyst. I n this report, data are presented which show that DNBS can be used LU a replacement for HC1O4 in acidcatalyzed acetylations. The experiments also serve as further evidence for
