CRUDE DISTILLATE Table 11. Gas Chromatographic Analysis of Separated Fractions of the Naphtha Distillate Reported as Weight Per Cent
c9 ClO c 1 1
Cn Cia Ci4
41
42
0.0 0.0 0.0
0.0 0.0
1.5 23.8 16.9 28.3
Cia+
2.6 18.2 45.8 46.4 61 . O
Fraction number 43 44 45 & 46 0.0 0.0 0.4 0.7 4.3 7.4 20.2 34.6 24.3 35.8 25.4 26.0 28.7 19.0 24.3 27.3 11.1 12.5 3.5 4.2 3.5
A cursory look was taken at extending the separation into a higher molecular weight range. For this, the branched 47-49 0.3
1.3 13.9 35.2 26.4 14.1 7.3
cycloparaffins are primarily noncondensed; whereas, the composite of fractions 47, 48, and 49 contained 27.4z condensed cycloparaffins. A separation of the condensed cycloparaffins according to the number of rings is also shown in Table I. In fraction 44, the condensed cycloparaffins contain only two-ring compounds; whereas, in the composite of fractions 47, 48, and 49 both two-ring and three-ring condensed cycloparaffins appear. This type of separation was obtained with n-butylcyclohexane and decahydronaphthalene in the model compound studies. The carbon number distribution data, as obtained by gas chromatography, are presented in Table 11. A gel filtration type of separation is clearly shown in fractions 41, 42, and 43-i.e., as the elution volume increases, the average carbon number of the isoparaffins decreases. With the elution of the cycloparaffins,the trend is reversed.
paraffin and cycloparaffin fraction from a Cl&ze+ crude distillate was used. The mass spectrometric analysis of this paraffin fraction showed 93.1 cycloparaffins and 6.9 branched paraffins with the cycloparaffins consisting of 54.8 noncondensed and 34.3 condensed. The mass spectrometric results of the separated fractions showed that the initial fractions contained only tetrahydrofuran. The distillate appeared in six fractions. The first two were combined before analysis. The separations obtained were similar to, but not as complete as, those found for the naphtha using the longer column. The first three fractions contained both branched and cycloparaffins, but the last three contained only cycloparaffins. A separation of noncondensed from condensed cycloparaffins is again indicated. A discrepancy was noted in the combined fractions 1 and 2 but as the elution continued through fractions 3, 4, 5, and 6, the percentage of noncondensed cycloparaffins decreased and that of condensed cycloparaffins increased. A separation of the condensed cycloparaffins according to the number of rings is also shown. Except for the composite fraction 1-2, the ring content increased with elution volume.
z z
z
z
ACKNOWLEDGMENT
The authors express their gratitude to H. T. Best, P. W. Mazak and R. E. Swab for their efforts in obtaining the mass spectrometric and gas chromatography data. RECEIVED for review July 27. 1968. Accepted September 3, 1968.
Quantitative Determination of Qrganic Halides in Dimethylsulfoxide Joe A. Vinsonl and James S. Fritz Institute f o r Atomic Research and Department of Chemistry, Iowa State Unioersity, Ames, Iowa 50010 NUMEROUS methods have been proposed for the determination of organic halides. The Carius, Pregl, and Schoniger methods make use of various oxidants to convert the organic halide to carbon dioxide, water, and halide ion, which is then determined titrimetrically or gravimetrically. These methods have been reviewed by Schoniger (1). Reduction methods include the use of potassium fusion ( 2 ) and sodium biphenyl (3). These are general methods for organic halides. Hydrolysis methods offer the possibility for the selective determination of certain halides in the presence of others. Rates of hydrolysis of organic halides in basic solution vary considerably, depending on the structure of the compound. In many instances it should be possible to find conditions such that one halide would react quantitatively while another would not react perceptively. With water and alcoholic solvents, 1 Present address, Department of Chemistry, Washington & Jefferson College, Washington, Pa. 15301
(1) W. SchiSniger in “Advances in Analytical Chemistry and Instrumentation,” Vol. 2, C. N. Reilley, Ed., Interscience, New York, N. Y., 1960. (2) G. Kainz, Mikroclzeinie Der. Mikrochim. Acta, 39, 1 (1952). (3) L. M. Liggett, ANAL.CHEM., 26,748 (1954). 2194
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ANALYTICAL CHEMISTRY
however, the time and temperature required for quantitative reaction of many types of organic halides is excessive. It has been shown that rates for the reaction of base with organic halides are greatly accelerated in dimethylsulfoxide (DMSO) ( 4 ) . For example, the rate of reaction of methyl iodide with hydroxide ions is 5 x 106 faster in DMSO than in water. This may be explained by the decreased solvation of hydroxide ions in DMSO compared with protic solvents. Other aprotic solvents such as dimethyl formamide or dimethyl acetamide also possess large rate enhancing characteristics (5). However, these are not as stable as dimethylsulfoxide toward base and tend to hydrolyze. Therefore, dimethylsulfoxide appears to be the solvent of choice. The procedures described below make use of the hydrolysis reaction with dimethylsulfoxide as the solvent and potassium hydroxide as the base. The reaction may be either or both of the following : R-X
+ OH-+
R-OH
f X-
(1)
(4) E. Tommila and L. Hamalainen, Acta Chern. Scand.. 17, 1985 (1963). (5) A. J. Parker, Quart. Rev. (London), 16, 163 (1962).
R-X
+ OH-
+ Olefin
+ X- + HzO
(2)
In DMSO primary halides undergo reaction 1; secondary and tertiary halides undergo primarily reaction 2. EXPERIMENTAL
Apparatus and Reagents. Dimethylsulfoxide and nitrobenzene were reagent grade. Potassium hydroxide was a 40z water solution. Potassium hydroxide, l M , was standardized against potassium acid phthalate with phenolphthalein as an indicator. Hydrochloric acid, 0.2M, was standardized against potassium hydroxide. Potassium thiocyanate, 0.4M, was a primary standard. Silver nitrate, 0.2M, was standardized against potassium thiocyanate. Ferric nitrate was a 10 % solution in water. Nitric acid was reagent grade. Organic halides were reagent grade of 98-100 % purity. Borosilicate culture tubes, 25 x 200 mm drawn in ampoules, or 50-ml Erlenmeyer flasks were used as reaction vessels. Determination of Alkyl Iodides or Bromides. PROCEDURE 1. Weigh accurately approximately 2 meq of the sample into a weighing bottle. Transfer the sample to an ampoule with DMSO or to a flask if the sample is not volatile at 100 "C. Add 5 ml of 1M potassium hydroxide from a pipet and enough DMSO for a total volume of 30 ml. Seal the ampoule or cork the flask and place in a steam bath. After reaction is complete, remove the flask, cool, transfer the contents into a 125-ml flask with 50 ml of distilled water and acidify with nitric acid. Pipet 10 ml of standard 0.4M silver nitrate. Shake with 10 ml of nitrobenzene if chloride is being determined. Add 2 ml of 10% ferric nitrate and titrate with standard 0.2M potassium thiocyanate to a light orange end point. PROCEDURE 2. The above procedure is used for the reaction. Titrate the excess phenolphthalein base after the reaction to the phenolphthalein end point with standard 0.2M hydrochloric acid. This procedure requires that both base and acid be standardized. A blank should be run under the same conditions as the sample. The blank titer is usually within 0.1 ml of 0.2M HC1 of the normal acid-base titer. The acid-base titration can also be done potentiometrically. This is especially necessary for nitroaromatic halides which give colored solutions with base and DMSO thus prohibiting visual indicators. Determination of Chlorides and Other Slow-Reacting Halides. PROCEDURE 3. A large excess, 5 ml of 40% potassium hydroxide, is mixed with 2 meq of halide and 25 ml of DMSO producing a two phase mixture. After reaction at 100 "C, the halide ion is determined as in Procedure 1 with the Volhard procedure. Rate Determinations. Mix 4 meq of halide and 10 ml of 1N potassium hydroxide in a 50-ml volumetric flask and dilute to the mark with DMSO. Take 5-ml aliquots and seal in an ampoule. Place the tubes in a constant temperature bath at 55.5 "C. Determine the halide ion by the Volhard procedure after cooling the ampoule and acidifying the water solution. RESULTS -4ND DISCUSSION
Aliphatic halides and polyhalides are generally determined in 30 minutes or less in DMSO at 100" C. Nitroaromatic halides require an hour or less. The results are summarized in Table I. As a comparison Abdulla-Zade (6) used ethanolic potassium hydroxide at 125 "Cfor 2 hours to determine dichloro-
(6) G. A. Abdulla-Zade, Azerb. Med. Zh., 10,74 (1956).
Table I. Quantitative Hydrolysis of Organic Halides Reaction time, ProCompound min cedure Found, %" n-Butyl chloride 20 3 9 8 . 7 f : 0.1 10 2 9 9 . 2 5 ~0.2 n-Butyl bromide 5 1 98.6& 0.2 n-Butyl iodide Cyclohexyl chloride 60 3 9 9 . 4 3 ~0.6 10 1 100.5 3Z 0.5 Benzyl chloride Isopropyl bromide 10 1 99.2 f 0.2 1 98~55C0.5 tert-Butyl bromide 5 1,3-Dibromopropane 10 1 98.7 =I= 0.2h Bromoform 15 1 9 9 . 0 r t 0.3b Methylene dibromide 15 1 99.2 =I= 0.2b 3 lOl.O& 0.5b 1,2-Dichloroethane 30 2,4-Dinitrochlorobenzene instantaneous 2 99.5 & 0 . 5 p-Fluoronitrobenzene 60 2 9 9 , 0 & 1.0 p-Chloronitrobenzene 45 2 9 8 . 0 P 1.0 o-Chloronitrobenzene 60 2 9 9 . 0 2 ~0.3 Q
b
Average of two or more determinations. Based on all halogen atoms in the molecule.
Table 11. Second Order Rate Constants for the Reaction of Base with n-Butyl Halides in DMSO at 55.5 "C k (1 m-1 . sec-l) Relative rate Compound n-Butyl chloride 1.68 X 1 n-Butyl bromide 1.44 x 10-4 38.4 n-Butyl iodide 3.94 x 10-3 235 +
Table 111. Analysis of Binary Mixtures Reaction conditions Compounds and procedure Found, 2 Chlorobenzene and 45 min at 100 "C, 9 9 . 2 of nitro p-chloronitrobenzene procedure 3 100.7 5C 0. la 1 min at 25 "C, p-Chloronitrobenzene and 2,4-dinitrochlorobenzene procedure 2 of dinitro I-Bromoethylbenzene and 1 min at 0 "C, 98.2 5C 0 . 5 ~ 2-bromoethylbenzene procedure 1 of 1-bromo a
Average of two determinations.
ethane. The present method requires 30 minutes at 100 "C. Unsubstituted aromatic halides such as chlorobenzene, bromobenzene, and iodobenzene were found to be completely unreactive toward 40 % potassium hydroxide in DMSO after an hour at 100 "C. Substituted nitroaromatic halides reacted to produce a dark color (usually deep red) which did not completely disappear even after acidifying in water. This color is caused by the formation of a Meisenheimer adduct (7). In order to demonstrate the selectivity of the method, rates for the reaction of base with n-butyl halides were run. The results are shown in Table 11. It should be possible to determine binary mixtures of the compounds shown in Table I1 by using differential rate methods. Crude rate runs demonstrated the feasibility of completely analyzing the following scheme: halobenzene
HNOa
HIiOa
mononitrohalobenzene dinitrohalobenzene
(7) J. Meisenheimer, Ann. Chim., 323, 205 (1902). VOL. 40, NO, 14, DECEMBER 1968
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2195
Synthetic binary mixtures were made from 1 meq of each halide and the results recorded in Table 111. Any functional group that reacts rapidly with base in DMSO at 100 “cwill interfere in procedure 2 in which the excess base is back titrated. Esters, aldehydes, or ketones with alphahydrogens, anhydrides, and acidic compounds such as
carboxylic acids would interfere. However, if the Volhard method is used (procedures 1 and 4), there will be no interferences except with mixtures of halides. RECEIVED for review August 5, 1968, Accepted August 26, 1968. Work performed in the Ames Laboratory of the U. S. Atomic Energy Commission.
eterrnination of Trace Copper in Petroleum Middle DistiIIates C. E. Lambdin and W. V. Taylor Research and Technical Department, Texaco, Inc., P. 0. Box 1608, Port Arthur, Texas 77640
THE VERY LOW CONCENTRATIONS of copper usually present in refined petroleum middle distillates necessitate sensitive analytical methods. The amount of soluble copper in aviation turbine fuels is of considerable interest to the air transportation industry. Copper in the range of 150 ppb adversely influences the thermal stability of hydrocarbon fuels ( I ) as measured by the CFR fuel coker test (2). The sources of soluble copper in middle distillates can be traced to carry-over from primary distillation of crude and other refining processes including amounts picked up from brass valves, fittings, and heat exchanger tubes, for example. The use of cuprizone (biscyclohexanone oxaldihydrazone) as a spectrophotometric ligand for inorganic Cu(I1) was first described by Nilsson (3). Wetlesen and Gran ( 4 ) applied cuprizone to the determination of copper in pulp and paper. The high sensitivity of cuprizone was reported by Peterson and Bollier (5). High selectivity was reported by Rohde (6) who employed cuprizone for determination of copper in a variety of nonferrous metals and alloys. These publications describe formation of the cuprizone-copper complex in aqueous solutions after chemical treatment of the sample matrix to obtain inorganic Cu(I1) ions. Both inorganic and organic Cu(1I) can be successfully extracted and determined from petroleum middle distillates and other hydrocarbon solvents by complexing with solutions of cuprizone. The extraction with cuprizone is effected using methanol or other selected polar solvents. When E 00 grams of sample are extracted, copper in the range of 0.02 to 2 pg per ml can be determined. The method is applicable to a wide variety of hydrocarbon fuels and solvents. Heavier stocks can be extracted after they are diluted in a suitable light solvent. EXPERIMENTAL
Apparatus. Absorbance values were measured with a Bausch and Lomb Spectronic 20 using 1-cm cells. Reagents. Cuprizone (biscyclohexanone oxaldihydrazone) solution, 0.2z prepared in anhydrous methanol. Warm gently to effect solution. (1) “Thermal Stability of Hydrocarbon Fuels,” Progress Rept. No. 4, Air Force Contract AF-33, (616) 7241, Jan 1962, p 5. (2) “ASTM Standards,” ASTM Designation: D 1660-67, Part 17,
American Society for Testing and Materials, Philadelphia, Pa., January 1968, p 610. (3) G. Nilsson, Acta. Chem. Scand., 4, 205 (1950). (4) C. U. Wetlesen and G. Gran, Suensk Papperstidr., 55, 212 (1952).
( 5 ) R. E. Peterson and M. E. Rollier, ANAL.Cnmi., 27, 7 (1955). (6) R.K. Rohde, ibid., 38, 7 (1966).
2196
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ANALYTICAL CHEMISTRY
0.6
-
0.5
-
0.4
n
/ \
/
O , I l ,
400
, 460
\
/A\ 500
550
600
WAVE LENGTH,
650
7GQ
7%
my
Figure 1. Absorption spectra of the copper-cuprizone complex in methanol 1. Copper, 1.0 p g per ml cs. reagent blank 2. Copper, 0.46 p g per ml us. reagent blank 3. Copper, 0.24 p g per ml cs. reagent blank Ammonium acetate buffer solution, 1 molar, is prepared in water and adjusted to pW 9.0 by addition of ammonium hydroxide before being diluted to volume. Standard copper solution, 100 ppm in methanol, may be prepared from either inorganic or organo copper(1H) certified reagents. Equivalent calibration curves were obtained from either class of copper reagent. Cupric acetate is recommended because of its solubility in methanol. Procedure. Samples containing 0.1 to 2.0 pg of copper are weighed into a 250-ml glass-stoppered separatory flask. Usually 100-gram samples of middle distillate are transferred into the flask, followed by addition of 8 ml of 0.2% cuprizone solution and 2 ml of ammonium acetate buffer. The flask is shaken vigorously for 1 minute with venting to relieve pressure during the first half minute. Allow 15 minutes settling time. The settling time can be shortened by centrifuging. Withdraw the aqueous methanol phase into a 25-ml volumetric flask. Repeat the extraction with another 10 ml of cuprizone-buffer solution mixture. After making the second extraction, dilute to mark with methanol. Measure absorbance of the blue solution at 606 mp against a reference solution of cuprizone reagent. Copper content is read from a straight line calibration curve. Beer’s law is obeyed for the range 0 to 2 pg of copper per ml. Sampling middle distillates for copper determination presents several difficulties. Nonreproducible analyses will often result from samples containing appreciable amounts of water. Copper-rich components have a strong tendency to
