Some Hydrocarbons of the Gas Phase of Cigarette Smoke ROGER J. PHILIPPE, HENRY MOORE, ROBERT G. HONEYCUTT, and JOHN M. RUTH Research Department, Liggetf and Myers Tobacco Co., Durham,
b Gas chromatographic analysis on alumina of the liquid air condensable fraction of cigarette smoke showed the presence of some 37 compounds, mainly hydrocarbonis, in this fraction. Twenty of these hydrocarbons have not been previoiisly reported in cigarette smoke. F!etention times on two different packing materials and infrared and mass spectrometric techniques were used as identification criteria. Semiquantitative analytical data, obtained b y gas chromatographic techniques, (are given for most of the identified compounds. Some discussion is given as to the preferential occurrence, in cigarette smoke gases, of some hydrocarbons over others in relation to their structural configurations.
A
RELATIVELY
LARGE
NUMBER
Of
N. C.
tionable compounds has recently spurred a renewed interest in the gas phase of that smoke. The purpose of this investigation is to estend our knowledge of the hydrocarbon composition of this gas phase. EXPERIMENTAL
Apparatus and Procedure. Regular length cigarettes (70 mm.) of a cased commercial blend of tobaccos were selected in a weight range of 1.04 to 1.06 grams and conditioned a t 74’ F. and 60% relative humidity. Groups of 10 cigarettes were smoked manually, one a t a time, using the smoking apparatus shown schematically in Figure 1. This smoking technique was used to collect quantitatively the condensable smoke gases. X nominal 40-ml. puff of 2 seconds’ duration was taken once a minute; the measured puff volume actually used in the calculations was 30 ml.; after 8
analyses have been performed on the gas phase of tobixco smoke during the first half of the 20th century ( 7 ) . The compounds reported were detected and estimated by conventional chemical methods. The avaiability and widespread use, after 19!50, of much more powerful techniques such as gas chromatography, infrared fipectrophotometry and mass spectrometry made it possible to extend the sesxch for other components of the gas phase. Among these compounds are those which are difficult to handle by purely (:hemica1 methods, as well as those present in relatively small or even trace ainounts (2, 4 , 6-8, 10-19). The selectike partial removal from cigarette smoke of some objec-
puffs, the average butt length was 28 mm. The apparatus consists (Figure 1) of a Cambridge filter (4)equipped with a latex rubber sleeve in which the cigarette is inserted, a critical flow orifice followed by a three-way stopcock leading either to a 40-ml. bulb or to a series of gas traps. The 40-ml. bulb is connected, through a stopcock, to a mercury-filled leveling bulb. By appropriate manipulation of stopcocks and leveling bulb, a puff was taken on the cigarette and the collected smoke gases were transferred to the previously evacuated and closed system of gas traps immersed in liquid air (Figure 1). This train of traps consisted of three 700-ml. plain gas traps similar to the Corning Glass Korks trap Cat. No. 96600 with an outer tube 150 mi. long and of 90-mm. o.d., and an inner tube of 20-mm. 0.d. Each trap was equipped with a pair of 28/15 ball and socket joints. After the tenth cigarette had been smoked and approximately one
t Y
e xE
m
TIME
WJRS
.
S
Figure 2. Gas chromatogram on alumina of the liquid air condensable fraction of the gas phase of cigarette smoke 1.
Air ( X 6 4 ) Ethane f nitrous oxide ( X 6 4 ) Ethene (ethylene) ( X 6 4 ) 4. Propane ( X 6 4 ) 5. Ethyne (acetylene) ( X 6 4 ) 6. Propene (propylene) ( X 6 4 ) 7. Propadiene (allene) ( X 1 ) 8. 2-Methylpropane (isobutane) ( X 2 ) methyl chloride ( X 3 2 ) 9. n-Butane 10. Butene-1 frans-butene-2 ( X 4 ) 1 1 . 2-Methylpropene (isobutylene) ( X 4 ) cis-Butene-2 ( X 4 ) propyne (methylacetylene) ( X 4 ) Butadiene-1,3 2-Methylbutane (isopentane) cyclopentane ( X 1) n-Pentane ( X 1) 3-Methylbutene-1 cyclopentene ( X 1) butene.3-yne-1 (vinylacetylene) ( X 1 ) Pentene-1 2-Methylbutene-1 trans-pentene-2 ( X 1) . 2-Methylbutene-2 -j- cis-pentene-2 ( X 1) 20. Pentadiene-1,4 ( X 1 ) cyclopentadiene ( X 1 ) 21. Butyne-1 (ethylacetylene) 22. 2-Methylbutadiene-l,3 (isoprene) ( X 4 ) 23. Furan 2-methylpentane 3-methylpentane ( X 1) pentadiene-1,3 (mixture of geometrical isomers) ( X 1) 24. n-Hexane 2. 3.
+ +
+
+
+
+ +
I.
Figure 1.
Schematic diagram of the smoking apparatus
(1) Cambridge filter; (2) critical flow orifice; (3) three-way stopcock; (4) 40-ml. bulb; ( 5 ) mercury leveling bulb; ( 6 ) plain gas traps; (7) stopcock equipped U-trap
+
+
+ +
VOL. 3 6 , NO, 4, APRIL 1964
0
859
Table 1.
Comparison of Retention Times on Alumina of Peaks from Smoke Gases and of Known Compounds
13 14 15 16
Smoke gases peak retention times, min. 18.7 1 h. 05 1 h. 20 1 h. 32 2 h. 00
17
2 h. 28
18
2 h. 45
19
3 h. 03
20 21 23
3 h. 15 3 h. 20 4 h. 19
24
5 h. 12
Peak No. 7
Compound name Propadiene Propyne Cyclopentane n-Pentane Cyclopentene 3-hlethylbutene-1 Butene-3-yne-1 Pen tene- 1 trans-Pentene-2 2-Methvlbutene-1 cis-~eniene-2 2-hlethylbutene-2 Pentadiene-1,4 Butyne-1 2-hlethylpentane 3-Methylpentane Pentadiene-l,3 (two isomers) %-Hexane
Table II. Retention Times on Alumina 3,3'-Oxydipropionitrile of Alumina Unresolved Components
+
+
Peak KO.
from +urnma column 13 14 16
17 19 20 21 23 24
Retention time on alumina 3,3'oxydiprop ionitrile colu,mn, min. 7.7 11.8 3.8 10.8 5 2 17 5 6 8 26 0
Compound name Butadiene-1,3 Propyne 2-Methylbutane CvcloDentane 3-"Met'hylbutene-1 Cy clopentene Pentene- 1 Butene-3-yne-1 czs-Pentene-2 2-Methylbutene-2 Pentadiene-l,4 Butyne-1 2-Methylpentane 3-hlethylpentane n-Hexane Pentadiene-l,3 (isomer I ) Pentadiene-l,3 (isomer 11)
8 0
8 8
11 5
18 5
Fi 8
6 8 7 0 21 7 25 7
hour had been allowed for complete condensation, the traps were evacuated, allowed to warm up to room temperature and all condensable materialq were collected, with the aid of liquid air, in the stopcock-equipped U-trap. These materials were then transferred to a conventional gas handling vacuum apparatus and treated with Ascarite and Drierite to remove carbon dioxide and water. The volume of the gaseouq materials remaining after these treatments was approximately 1 ml. per cigarette. The bame procedure was used for obtaining the smoke gases from 15 groups of 10 cigarettes each. One of the gas chromatographic apparatus used in this investigation is a laboratory built instrument. Its main 860
ANALYTICAL CHEMISTRY
Known compounds retention times, min. 18 . O 1 h. 03 1 h. 17 I h. 30 1 h. 51 1 h. 57
2 h. 23
2 h. 25
2 h. 33 2 h. 42 2 h. 55 2 h. 57 3 h. 10 3 h. 15 4 h. 20 4 h. 20 4 h. 51 5 h. 05
components are a Perkin-Elmer thermal conductivity detector equipped with thermistors (tppe used on the Vapor Fractometer Model No. 154), a control panel made of Perkin-Elmer parts, and a Varian Associates G-IO recorder with a 10-mv. span, a 1-second full-scale balancing time and two chart speeds of 1 inch/minute and 2 inches/hour. The thermal conductivity cell is kept in a Dewar flask, in air, the temperature of which is maintained a t about 35' C. and controlled within 0.1' C. The column, a '/,-inch diameter, 9-foot coiled copper tubing, is filled with Burrell activated alumina and kept in a Dewar flask, a t room temperature (about 24" C.), without thermostatic control. Besides a regular PerkinElmer injection block, a solenoidoperated injection system allows the introduction into the carrier gas stream of a known amount of an air-free sample contained in a calibrated capillary gas trap. After separation on the column, the individual components may be vented to the atmosphere or trapped by using a solenoid-operated recovery syqtem with three separate outlets. Helium was used as carrier gas a t a flow rate of 50 ml. per minute; to reduce the retention of the gas mixture components, the alumina was partially deactivated by passing the carrier gas over CuS0,.5H20. This technique has the added advantage of keeping the retention times constant over a period of several months. Some fractions eluted from the alumina column contained more than one component and nere further fractionated a t room temperature on a Perkin-Elmer Vapor Fractometer Model Yo. 154 using a 15foot column of Burrell activated alumina coated with 18.7% (wt./wt.) of 3,3'oxydipropionitrile ; the helium flow rate waq 40 ml. per minute. The infrared spectra were recorded on a Perkin-Elmer Model Yo. 21 spectrophotometer equipped with a NaCl prism and a n ordinate scale expander. The cell used was a Connec-
ticut Instrument Corp. M.G. microgas cell of 50-mm. path length, with Irtran-2 windows. The mass spectra were obtained on a Bendis time-of-flight mass spectrometer Model 14-101 equipped with a Tektronix Type 543 oscilloscope and an analog output. The spectra were recorded on a Sanborn recorder Model 152-100B with dual channel amplifier. RESULTS AND DISCUSSION
The condensable smoke gases of 10 cigarettes, after removal of carbon dioxide and water, were gas chromatographed on alumina. Figure 2 shows such a chromatogram recorded for a period of 51/2hours, after which the recording was discontinued. For illustrative purposes the recording was made using the recorder's low speed chart drive of 2 inches/hour. All calculations were, however, made on chromatograms obtained with the chart-speed of 1 inch/minute up to and including peak No. 13. Further analysis of the 24 peaks shown in Figure 2 revealed the presence of some 37 compounds, mainly hydrocarbons, in that smoke fraction. Figure 2 also gives a list of the peak numbers, in order of elution, and the compounds which were identified in the fractions collected from the corresponding peaks of the chromatogram. The compounds have been named according to the Geneva System of Nomenclature, with the more familiar names in parentheses; these more common names will be used in the text. Kumbers in parentheses are the recorder's attenuation factors. The insert of Figure 2 shows part of a chromatogram made on a fraction collected from the smoke gases of 50 cigarettes; peaks No. 20 and 21, although still small, are clearly indicated. The only nonhydrocarbons identified in the smoke fraction studied in this investigation are nitious oxide, methyl chloride, and furan, and have been reported already (4, ?',1 0 , I I ) . As for the 34 hydrocarbons identified, 20 had not been previously reported as present in cigarette smoke gases. These hydrocarbons are, in order of elutinn from alumina : allene, methylacetylene, cyclopentane, isopentane, n-pentane, cyclopentene, 3-methylbutene-I, penvinylacetylene, 2-methyltene-1 , butene-1, trans-pentene-2, %methylbutene-2, cis-pentene-2, pentadiene-l,4, ethylacetylene, 2 - methylpentane, 3methylpentane, n-heuane, and pentadiene-1,3 (the two geometrical isomers). The retention times of these compounds on alumina are presented in Table I and compared with the retention times of the corresponding authentic samples. Table I1 shows some retention times on the alumina + 3,3'-osydipropionitrile column which was used to separate compounds unresolved by alumina; these retention times were identical to those of corresponding known samples.
I n addition to retenliion times on these two different packing materials, the criteria on which identification was based were infrared and mass spectra. These criteria will be reviewed, discussed, and evaluated for each newly identified hydrocarbcn. Allene. This compound, eluted from alumina as fraction No. 7, was well characterized by its infrared band a t 1960 cm.+, typical of the asymmetrical stretching ~ i b r a t i o nof its two adjacent double bonds, and the complex C=C=C deformation vibration band centered a t about 850 cm.-' The mass spectrum of fraction No. 7 also showed the characteristic features of allene: parent peak a t mass 40 and the sequence of mass peaks 19, 19.5, and 20, doubly charged ions corresponding to the mass peaks sequence 38,39, and 40. Methylacetylene. The infrared spectrum of methylacetylene isolated from fraction No. 13 showed characteristic bands a t 1250 cm.-l, an overtone of the C z C - C bending vibration, a t 2150 and 3333 cm.-', respectively, the C 4 and =C-H stretching vibrations. Being structural tautomers, allene and methylacetylene have very similar mass spectra; both showed similar sequences of mass peaks 36 to 40 and the doubly charged ions peaks 19, 19.5, and 20. Isopentane, n-Pentane, and Cyclopentane. The infrared spectra of fractions of No. 14 and 15 showed only bands characteristic of saturated hydrocarbons. The mass spectra of isopentane, after its separation from peak No. 14, and of peak No. 15 (n-pentane) were in good agreement with the corresponding mass spectra of authentic samples. No infrared spectrum of cyclopentane could be obtained, the amount of sample collected being insufficient. The identification of this hydrocarbon was based on its mass spectrum after coirection for butadiene-1,2, tentatively detected in fraction No. 14. 3-Methylbutene-1 and Cyclopentene. The infrared spectrum of the fraction correspondir g to peak No. 16 had bands characteristic of the vinyl group at 995,911 cm.-' with its overtone a t 1830 cm.-'; sweral other bands confirmed the presence of 3-methylbutene-1. The small band which appesred a t 1045 cm.-' is the &-branch of a strong cyclopentene absorption band. The mass spectra of 3-methylbutene-1 and of cyclopentene, after their separation from fraction KO.16, compared reasonably with those of known samples. Pentene-1 and Vinylacetylene. The fraction corresponding t o peak No. 17 had a n infrared spectrum showing t h e main features of both pentene-1 a n d vinylacetylene. The vinyl group of pentene-1 was characterized by the
bands at 997 and 916 cm.-' with its The vinyl overtone at 1835 cm.-' group of vinylacetylene, strongly affected by its conjugation with a triple bond, had bands a t 973 and 924 cm.-l, with its overtone a t 1852 cm.-l The mass spectra of pentene-1 which is characteristic among the pentenes' mass spectra, and of vinylacetylene aftei being resolved from fraction No. 17, were in good agreement with the corresponding spectra of known samples. 2-Methylbutene-1 and trans-Pentene-2. These two compounds were not separated on either chromatographic column used in this investigation; they were eluted together from alumina as fraction No. 18. The infrared spectrum of this fraction had a strong band a t 889 cm.-* which, with its overtone a t 1780 crn.-', is characteristic of the hydrogen out of plane vibration of an asymmetric disubstituted ethylene and belongs to 2methylbutene-1. Several other bands confirmed the presence of this compound. The only two bands characteristic of trans-pentene-2 occurred a t 1300 and 960 cm.-', the last band being typical of a trans-disubstituted ethylene structure. With the exception of pentene-l, all pentenes have similar mass spectra which are therefore of no value as identification criteria. The mass spectrum of fraction No. 18 showed, however, that it is a pentene fraction, 2-Methylbutene-2 and cis-Pentene2. These two hydrocarbons were not separated on alumina and were eluted together as peak No. 19. Their retention times on alumina coated with 3,3'-oxydipropionitrile are, however, slightly different (about 0.8 min.); although not enough to allow for the collection in separate fractions, this retention time difference indicated the presence of both compounds in peak No. 19. The infrared band observed a t 800 ern.-' is typical of the hydrogen out of plane vibration of a trisubstituted ethylene and belongs to 2-methylbutene-2; several other bands were also attributed to 2-methylbutene-2. The only band which could be assigned to cis-pentene-2 appeared a t 935 cm.-' That fraction No. 19 is a pentene fraction was confirmed by its mass spectrum, Pentadiene-1,4. No infrared spectrum of fraction No. 20 could be recorded, the amount of sample collected being too small. Tentative identification of pentadiene-1,4 was however obtained by mass spectrometry. T h e parent peak of pentadiene-1,4 a t mass 68, as well as the parent peak minus one mass unit at mass 67, were clearly indicated. The lower intensities of peaks 53, 67, and 68 relative to peaks 27 and 39, as compared to their relative intensities in the known pentadiene-1,4 spectrum,
were attributed to a rapid drop of the sample's pressure in the spectrometer ionization chamber. Ethylacetylene and Cyclopentadiene. These two compounds were tentatively detected in peak No. 21. Only traces of these two hydrocarbons were collected and no infrared spectra could be obtained. The only evidence of t h e presence of cyclopentadiene in this fraction was given by the appearance in its mass spectrum of small peaks at masses 65 and 66, the last being the parent peak. Positive identification cannot be claimed on such tenuous grounds. We think, however, t h a t cyclopentadiene is present in this fraction for the following reasons: the retention time on alumina was correct (3 hours, 20 minutes) ; cyclopentadiene has been tentatively identified by infrared techniques in cigarette smoke (11) and in tobacco pyrolysates (9); it is known to be a thermal decomposition product of coal and of paraffin oils ( 5 ) . Ethylacetylene was identified by its mass spectrum. The higher intensities of peaks 15, 25, 26, 27, 37, 38, and 39 in relation to peaks 53 and 54, the parent peak of ethylacetylenr, were attributed to a pressure drop in the mass spectrometer ionization chamber. 2-Methylpentane and 3-Methylpentane. These two hydrocarbons were eluted with furan from our alumina column. An infrared spectrum of fraction S o . 23 showed numerous bands characteristic of furan. However, bands a t 2959 and 2870 em.-* are typical of the stretching vibrations of a methyl group and belong to the spectrum of 2- and 3-methylpentanes. The same conclusion was obtained from the mass spectrum of fraction No. 23. After removal of furan, the mass spectrum of the remaining portion of fraction KO.23 showed that mass 6s peak had disappeared and that mass 39 peak had been drastically reduced, whereas mass peaks 86, 71, 57, 56, 55, 43, 42, 41, 29, and 27 had emerged very clearly. These m a s peaks are characteristic of a hexane spectrum and belong to 2- and 3-metbylpentanes. n-Hexane and Pentadiene-1,3 (two geometrical isomers). These three hydrocarbons were eluted together from alumina as peak KO. 24. An infrared spectrum of this fraction had characteristic bands of pentadiene-l,3 (both isomers). However, the high intensities of the bands at 2959 and 2870 cm.-l, as well as the bands a t 1460 and 1380 cm.-', indicated the presence of a saturated aliphatic hydrocarbon which was identified as n-hexane. The presence of n-hexane and of both isomers of pentadiene-1,3 was confirmed by mass spectrometry. The n-hexane fraction showed a sizable mass 84 peak. Cyclohexane and methylcyclopentane were ruled out by retention time consideraVOL. 36, NO. 4, APRIL 1964
861
tions. The compound or compounds responsible for this mass 84 peak is or are p r o h b l y one or several hexenes; the lowest boiling tiexene, 3,3-dimethylbutene-1, has retention times compatible with its presence in the hexane frwtion (about 4 hours, 50 minutes on alumina and 6.8 minutes on alumina
+
Table 111.
Semiquantitative Results Obtained from Gas Chromatograms
Compound name Mole yo X lo2 Alkanes and cycloalkanes 0.11 f 0.03 n-Pentane 0.08 2-Methylbutane 0.012 Cyclopentane 0.024 n-Hexane 0.012 2-Methylpentane 0.008 3-Methylpentane Alkenes and cycloalkenes 0.12 Pentene-1 2-Methylbutene-1 tram-pentene-2 0.22 f 0.03 0.08 3-Methvlbutene-1 2-MethGlbutene-2 cis-pentene-2 0.34 f 0.05 0.04 Cyclopentene Alkadienes and cycloalkadienes 0.08 f 0.01 Propadiene (allene) trace Pentadiene-1,4 0.034 Pentadiene-1,3 (one isomer) Pentadiene-1,3 (other isomer) 0.024 trace Cyclopentadiene Alkynes Propyne (methylacetylene) 0.12 Butyne-1 (ethylacetylene) trace Butene-3-yne-1 (vinylacetylene) 0.06
C no. c 5
C5
+ +
c 3 c 5
C3 C4
Table IV.
+
+
+
0
pg./puff 1.2 f 0 . 3 0.84 0.12 0.32 0.16 0.11 1.3 2.4 f0.3 0.8 3 . 8 f 0.4
0.4
0.52 f 0.05 trace 0.36 0.26 trace 0.8
trace 0.5
Comparison of Analytical Results from Several Authors
Compound name Ethane Propane n-Butane 2-Methylpropane n-Pentane 2-Methylbutane Cyclopentane n-Hexane 2-Methylpentane 3-Methylpentane Ethylene Propylene 2-Methylpropene trans-Butene-2 Butene-1 transbutene-2 cas-Butene-2 Pentene-1 2-Methylbutene-1 trans-pentene-2 2-Methylbutene-2 cis-pentene-2 3-Methylbutene-1 Propadiene Butadiene-1,3 Isoprene Acetylene Methylacetylene Methyl chloride
862
3,3-oxydipropionitrile). Subtraction of the known n-hexane mass spectrum from a mass spectrum of a n-hexane smoke fraction suggested the presence of 3,3dimethylbutene-1. Table I11 gives semiquantitative analytical results derived from the gas chromatograms. The hydrocarbons not
Mole % X lo2 of total gas phase Carugno and GiovanHobbs nozai- Norman. Fishel Patton et al., -Ser- Newsome, and Av. of manni and and Haskins Touey (7) and (Type C) Keith (8)
(8)
(11)
(2)
(6)
...
20 6 0.6
11.4 8.9 0.5 ...
27.3 8.6 3.7 ... .., ...
9.5 3.0 0.67 0.23 0.16 0.15
... I
.
.
0.1
...
I
... ...
... .
.
I
...
...
...
...
ANALYTICAL CHEMISTRY
... ... ...
13.6 1.6
,.. ... ...
... ...
0.4 ...
...
...
1
... ...
...
0.012
0.06s 0.03~ 0.00;
4.6 3.3
0.64
0.08
0.012 0.02, 0.012 6.3 & 0.5 3 . 3 f 0.1 0.98 f 0.12
0.29
...
0.90 0.4 0.15
0.61 f 0.05 0.28 f 0.02 0.12
...
0.25
0.22 f 0.03
,..
0.56
0.34 f 0.05 0.08 0.08 f 0.01
1.4
0.4
9.6
0.55 0.10
0.79 f C 0.12
7:s
2.3
2.6
...
Table V. Hydrocarbons Distribution in C5 and Ca Saturates of Cracked Gasoline ( 7 ) and of Cigarette Smoke
Hydrocarbon
0 .oo.
1.5
...
1 t0'2
.
6.8 5.3 0.6
10
7
...
... ...
.
Presentwork 8.4 f 0 . 6 2.4 f0.2 0.51 0.19 f 0.01 0.11 f 0.03
previously reported in cigarette smoke are classified in four sections: alkanes and cycloalkanes, alkenes and cycloalkenes, alkadienes and cycloalkadienes, and alkynes. Calibration curves were determined for each compound. The results are expressed in mole yo X IO2 of the total gas phase and in pg./puff. For calculation purposes, all compounds were assumed to be ideal gases. For the compounds eluted individually from alumina, the standard deviation was calculated from the results of analyses on 15 groups of 10 cigarettes each. Whenever composite fractions eluted from alumina could be resolved on alumina coated with 3,3'-oxydipropionitrile, the data were determined for each individual compound. These results have been corrected for losses occurring during collection and transfer of these fractions. Too few data in these cases prevented the evaluation of meaningful standard deviation values. I n two instances, 2-methylbutene-1 and trans-pentene-2, 2-methylbutene-2, and cis-pentene-2, no adequate resolution could be obtained on either column. The analytical results are expressed as the sum of both compounds in each case. Since the hydrocarbons in each pair are chemically very much alike, their calibration curves are almost identical; the calibration curve of the major component in each fraction-Le., 2-methylbutene-I and 2-methylbutene-2-were used in the calculations. Taking into account all compounds identified in the smoke fraction investigated (Tables I11 and IV) and with a value of 0.3 X lo-* mole % for furan (11), the calculated gas volume accounted for was 0.98 ml. per cigarette as compared to a measured average volume of 1.0 ml. per cigarette, before injection into the gas chromatograph. Distribution of the
n-Pen tane 2-Methylbutane 2,2-Dimethylpropane Cyclopentane
Cracked Cigarette gasoline smoke yo by volume of the Cs saturates Cata- Therlytic mal 11.3 60.6 55.0 87.2 35.1 40.0
0.2 0.0 4.1 5.0 yoby volume of the C6 aliphatic saturates Cata- Therlytic mal n-Hexane 8 . 4 53.7 54.5 2-Methylpentane 46.9 25.0 27.3 3-Methylpentane 29.8 18 .O 18.2 2,3-Dimethyl14.5 2.6 0.0 butane 2,2-Dimethyl0 . 7 0 .0 0 . 3 butane ,..
1.5
Structures of Some Hydrocarbons Identified and Not Yet Identified in Cigarette Smoke
Table VI.
No. of C 1 2
3 4
5
Name Methane Ethane
Compounds identified Carbon skeleton Alkanes and cycloalkanes C
Propane n-Butane 2-Met hylpropane n-Pentane 2-Met hylbutane
Name
Compounds not identified Carbon skeleton’
e-c
c-c-e c-c-c-c c-c-c
c---c c-c I 1 c-c
Cyclopropane Cyclobutane
I
C C-C-C~C--C
c-c-c-c I
2,2-Dimethylpropane (neopentane)
C Cyclopentane
cI-e
C
1 I
c-c-c C
I
C 6
n-Hexane 2-Met hylpentane 3-Methylpentane
I I
c-c-c-c-c-c c-c-c-c-c 1
2,2-Dimethylbutane (neohexane)
c-c-c-c
c-c-c-e-c
2,3-Dimethylbutane
c-c-c-c cI cI
C
I
C
C
Cyclohexane C
A d \C/
Methylcyclopentme
c-e-c I I c c 1
1
C ’‘
Alkenes and cycloalkenes 2
Ethene
c=c
3
Propene Butene-1
c4-c c=c-c-c
2-Methylpropene
c=c-c
4
Cyclopropene Cyclobutene
/C\ c-c c=c I ! c-c
I
C
5
cis-Bul,ene-2 trans-Elutene-2 Pentene-1 2-Methylbutene-1
c-c=c-c c-c=c-c c=c-c-e4 c=c-c-c I
C 3-Methylbutene-1
c=c-c-c I
C 2-Methylbutene-2
c-c=c-c I
C cis-Pen tene-2 trans-Pentene-2 Cyclop?ntene
c-c=c-c-c c-c=c-c-c c-=c I
I
C\,/C C
6
3,3-Diniethylbutene-l (neohexene)
c=c- b-c I
C (Continued on page 864)
VOL. 36, NO. 4, APRIL 1964
863
Table VI. No. of
Structures of Some Hydrocarbons Identified and
C
Name
3
Propadiene Butadiene-1,3 Butadiene-1,2
c=c=c c=c-c=c c=c=c-c
Pentadiene-1,3
c=c-c=c-c
4
5
Not Yet Identified in Cigarette Smoke [continued)
Compounds identified Carbon skeleton Alkadiene8 and cycloalkadienes
Compounds not identified Name Carbon skeleton
Cyclobutadiene Pentadiene-l,2 Pentadiene-2,3 3-Methylbutadiene-l,2
c-c II It c-c c=c=c-c-c c-c=c=c-c c=c=c-c I
C Pentadiene-1,4 2-Methylbutadiene-l,3
c=c-c-c=c c=c-c=c I
C Cy clopentadiene
C-I-C
2
Ethyne
crc
3
Propyne
CSC-c
4
Butyne-1 Butene-3-yne-1
CEC-c-c CrC-C=C
E,c,d
Alkynes
compounds with respect to class was as follows: saturates 37.6%, alkenes 39.2%, dienes 11.1%, alkynes 3.1%, methyl chloride S.O%, and furan, using the value quoted earlier, 1%. Table I V gives the analytical results obtained by various authors, whenever comparison is possible. Although serious discrepancies are evident for several components, most analytical data are essentially of the same ordei of magnitude. Different tobacco types and blends as well as different analytical techniques may account for some of the discrepancies. In Table Y a comparison is made between the C5 and Cg saturated hydrocarbon composition of cigarette smoke and of thermally and catalytically cracked gasolines (1). Although tobacco, consisting mainly of a carbohydrate substrate with a host of minor constituents characteristic of the vegetable kingdom, is a quite different charging stock than crude oil, comparison of the cracking reaction products may lead to some interesting conclusions. The conditions under which cracking reactions take place are also different in the two cases. Thermally cracked gasolines are generally produced a t relatively low temperatures (450' to 5OOOC.) and at pressures of the order of 500 p.s.i., whereas cigarette smoke is produced at atmospheric pressure and temperatures as high as 800' to 900" C. The lower temperature and higher pressure of the gasoline cracking reactions may ac-
864
ANALYTICAL CHEMISTRY
Butyne-2
count for the higher percentage of saturated hydrocarbons (from 55 to 65% as compared to some 38% in cigarette smoke), for the insignificant amounts of dienes (as compared to 11% in cigarette smoke), and for the absence of alkynes (as compared to 3% in cigarette smoke). Comparison of the yields of olefins in both cases is somewhat difficult and does not lead to any definite conclusion. On the other hand the distribution of the saturated hydrocarbons in cigarette smoke, at least in the C5and Cs fractions, closely parallels the distribution of these hydrocarbons in thermally as opposed to catalytically cracked gasoline as shown in Table V. The predominance of straight-chain or slightly branched aliphatic hydrocarbons in thermally as compared to catalytically cracked gasoline is attributed to the reluctance of the thermal reaction free radicals to isomerize their carbon skeleton; the carbonium ions which act as intermediates in the acid catalyzed cracking reactions have, on the other hand, a high tendency to assume branched-chain configurations. It seems therefore logical to conclude that a t least the production of some saturated hydrocarbons in cigarette smoke might, to a large extent, be governed by cracking chain reactions initiated and propagated by free radicals. Table VI is a list of hydrocarbons which have been identified, some of them tentatively, in the gas phase of cigarette smoke, Some hydrocarbons
c-Ckc-c
which might be present but which have not been identified as yet are also tabulated. I n the saturated hydrocarbons group, both of open-chain and cyclic structures, the unlikely presence of highly branched structures such as neopentane, neohexane, etc., a t least in detectable amounts, has already been discussed. The relative ease with which both cyclopropane and cyclobutane are converted to the corresponding openchain alkenes a t high temperatures is probably responsible for their absence in cigarette smoke. A4sfor cyclohexane and methylcyclopentane, indications are at the present time that one of these hydrocarbons or both are present in cigarette smoke. In the alkene and cycloalkene series, it is not surprising that relatively unstable structures such as cyclopropene and cyclobutene were not detected. Preliminary investigations seem to indicate the presence of 3,3-dimethylbutene-1 (neohexene). If this tentative identification is confirmed, from the low relative abundance of 3methylbutene-1 in the pentene series as well as from the failure to detect any neoalkane-type hydrocarbon, there is every reason to expect the presence of the 16 other isomeric hexenes in cigarette smoke. Experimental results as well as theoretical considerations indicate a higher stability for the conjugated 1,&derivatives in the diene series. The allene type structure has a tendency to isomerize to the corresponding more stable acetylenic compound, and dienes
with nonconjugated double bonds do not benefit from the resonance energy stabilization of the 1.3-derivatives. This trend is confirmed by the results given in Tables I11 and IV; it must be pointed out, howevcr, that the relatively high amount of 2-methylbutadiene-l,3 (isoprene) is due to its direct formation from thermal degradation of polyisoprenoid compounds present in tobacco. Preliminar:r. results seem to indicate the presence of butadiene-1,2; moreover there is no reason why the allene-type structure hydrocarbons of the Cr series could not be espected to be present in cigarette smoke. Cyclobutadiene is apparently a very unstable substance which has not yet been prepared; cyclopentadiene was tentatively found in small amoLnts. The acetylenic hydrocarbons are usually indicative of a fairly high thermal degradation temperature and are found in relatively
small concentration in cigarette smoke. The conjugated nature of vinylacetylene probably accounts for its presence in a higher concentration than ethylacetylene. The higher boiling temperature and longer retention time of dimethylacetylene, as compared to its isomer ethylacetylene, accounts probably for the lack of identification of this hydrocarbon in the smoke fraction studied in this investigation. LITERATURE CITED
(1) Brooks, B. T., Stewart, S. K., Jr., Boord, C. E., Schmerling, I,., “The Chemistry of Petroleum ‘Hydrocarbons,” 1‘01. 11, p. 63, Reinhold, New York, 1955. (2) Carugno, N., Giovannozzi-Sermanni, G., Proceedings of the 2nd Inter-
national Scientific Tobacco Congress, p. 501, Brussels, June 1958. (3) Fishel, J. B., Haskins, J. F., Znd. Eng. Chem. 41, 1374 (1949).
R. M., Jr., Harlow, E. S., Tobacco Sci. 3, 52 (1959). ( 5 ) Karrer, P., ‘‘Organic Chemistry,” 3rd English Ed., p. 638, Elsevier, Ameterdam, 1947. (6) Norman, V., Newsome, J. R., Keith, C. H., The 17th Tobacco Chemists’ Research Conference, September 22-25, 1963, Montreal, P. Q., Canada. ( 7 ) Osborne, J. S., Adamek, S., Hobbs, M. E., ANAL.CHEM.28, 211 (1956). (8) Patton, H. W., Touey, G. P., Zbid., 28, 1685 (1956). (9) Philippe, R. J., Unpublished data Research Department, Liggett and Myers Tobacco Co., Durham, N. C.,
(4) Irby,
1957. (IO) Philippe, R. J., Hackney, E. J., Tobacco Sci. 3, 139 (1959). (11) Philippe, R. J., Hohbs, M. E., ANAL.CHEM. 28,2002 (1956).
(12) PhiliDDe. R. J.. Moore. Henry, ‘ Tobucco’Sci: 5, 131 (1961). RECEIVED for review October 31, 1963. Accepted January 7, 1964. Seventeenth Tobacco Chemists’ Research Conference, September 22-25, 1963, Montreal, P. Q., Canada.
Spectrophotometric Determination of Ammonia as Rubazoic: Acid with Bispyrazolone Reagent LIDMILA PROCHAZKOVA Hydrobiological I aboratory, Czechoslovak Academy of Science, Prague, Czechoslovakia
b Ammonia reacts with bispyrazolone, 3,3’ dimethyl 53’ dioxo 1,l ’-
-
-
-
- -
-
-
diphenyl-(4,4’-bi-2-pyrazoline), in the presence of Chloramine T at p H 6.0 to produce rubazoic acid, 3-methyl4-(3 methyl 5 oxo 1 phenylpyrazonyliden-4-amino)-!i-oxo- 1 -phenyl2-pyrazoline. This compound, pinkviolet in aqueous !;elution, can b e extracted after acidification into trichloroethylene as the yellow undissociated acid. The absorbance of the extract at 450 mp is a linear function of ammonia in the range 1 to 500 pg. of NH4-N per liter with a The standard deviation of 0.9%. influence of reagents and reaction variables has been studied and a procedure based on the results. The product has been identified by its spectral characteristics and by isolation and comparison with the authentic compound. A reaction mechanism is described.
I
- -
1947 Epstein (E?)first reported the use of pyrazolone( [) in combination with pyridine and bisDyrazolone(I1) to determine cyanide ion. I n 1953 Kruse and Mellon ( 8 ) ,who had observed a strong interference o f ammonia in this method, worked out a procedure for the determination of ammonia based on the N
fact that ammonia reacted in the presence of Chloramine T a t pH 3.7 with a mixture of pyrazolone and a pyridine solution of bispyrazolone to produce a pink-violet color which was proportional to the concentration of ammonia and could be extracted into cc14 as a yellow product. Strickland and Austin subsequently modified the method and used i t for the determination of ammonium ion in sea water (16). Unemoto et al. ( I 7) used pyridine-bispyrazolone reagent for the determination of ammonia in relatively high concentrations in small volumes. This method is not applicable to very dilute solutions of ammonia. Kruse and Mellon assumed that the reaction was of the Koenig type ( 6 ) , with the pyridine ring opening to form the glutaconic aldehyde, which then reacted with the active methylene group of the pyrazolone. The function of the T, individual reactants-Chloramine pyridine, and pyrazolone-was not explained. In a subsequent study, Lear and Mellon (9) offered several schemes to explain the mechanism of the reaction, but could neither explain the experimental facts nor completely define the mechanism. These workers had substituted a number of other primary and secondary amines for pyridine, only to find that the color was no longer
proportional to the concentration of ammonia. When pyrazolone was replaced by various ketones and aldehydes-benzophenone, acetophenone, salicylaldehyde, and the like-the mixtures gave no color. The authors concluded that the reaction was not created by the active methylene group of the pyrazolone nor by a Koenig-type ring opening. The chemical properties of the principal component, pyrazolone, are of interest in connection with this reaction. Pyrazolone is soluble in acids, bases, and ethanol. It is an amphoteric substance existing in tautomeric equilibrium between the keto and enol forms, I a and Ib. The presence of the enol form was confirmed by the reaction of
Ib
oH
diazomethane to produce the methyl enol ether and by acylation to form the corresponding enol ester (4, 16). Mild oxidation-e.g., refluxing with phenylhydrazine-gives bispyrazolone, a small amount of which is added to the pyrazolone reagent used by Kruse and Mellon. Stronger oxidants convert the bispyrazolone to Pyrazolone Blue (6). VOL. 36, NO. 4, APRIL 1964
865
