groups that are present in the molecule attached to the residue. The anomalous behavior of the 1-methyl-, 2-methyl-, and 3-methylcarbazoles, in which the methyl group is lost with the nitrogen atom, has been confirmed b y repeated hydrogenations of samples from several sources. Furthermore, the hydrogenation of a methyl diphenyl yields the expected methyldicyclohexyl, implying that the loss of the methyl group in the denitrogenation of a methyl carbazole does not occur after the formation of a methyl biphenyl. Thus, the nitrogen and alkyl-chain elimination must occur virtually simultaneously. Differences
in time, temperature, or character of catalysts might result in the removal of the nitrogen atom in these compounds without loss of methyl groups, but this possibility has not been investigated. The anomaly described rvill limit, to some extent, identification studies in mixtures containing carbazole and its methyl homologs. LITERATURE CITED
(1) Sabatier, Paul, Senderens, J. B., Compt. rend. 132, 1254-7 (1901). (2) Thompson, C. J., Coleman, H. J.,
Hopkins, R. L., Ward, C. C., Rall,
H. T., A N A L . CHEM.32, 1762-5 (1960). (3) Thompson, C. J., Coleman, H. J., Ward, C. C., Rall, H. T., Zbid., 32, 42430 (1960).
RECEIVED for review July 19, 1961. Accepted October 16, 1961. 16th Southwest Regional Meeting, ACS, December 1-3, 1960, Oklahoma City, Okla. Investigation performed as part of the work of American Petroleum Institute Research Project 48A on "Production, Isolation, and Purification of Sulfur Compounds and Measurement of Their Properties," which the Bureau of Mines conducts at Bartlesville, Okla., and Laramie, Wyo. Reference t o specific makes is made to facilitate understanding and does not imply endorsement of such brands by the Bureau of Mines.
Identification of Halogen Compounds by Catalytic Dehalogenation C. J. THOMPSON, H. J. COLEMAN, C. C. WARD, and
H. T. RALL
Bartlesville Petroleum Research Center, Bureau o f Mines, U . S. Depurtment o f the Interior, Bartlesville, Okla.
b A microhydrogenation technique, developed for and employed in sulfur compound identification studies, now has been successfully applied to halogen compounds. By means of catalytic hydrogenation this technique quantitatively removes the halogen atom or atoms from the molecule, leaving a paraffin or cycloparaffin. The identification of the hydrocarbon will characterize or aid in the characterization of the halogen precursor, the identification of which would otherwise b e difficult or impossible because of the limited catalog of pure halogen compounds. and of reference spectra. The method is rapid and quantitative, and will handle samples as small as 0.0002 ml.
'LUOROBENZENE 9 CYCLOHEXANE
..
~
'
T
HE Federal Bureau of Mines previously has reported the removal of the sulfur ( 2 ) , oxygen ( I ) , and nitrogen (3) atoms from organic molecules by microhydrogenation. The process now has been applied to halogens with equal success. Thus hexyl, phenyl, tolyl, benzyl, cyclohexyl, and naphthyl fluorides, chlorides, bromides, and iodides have been successfully dehalogenated. Limited experimental data from polychlorinated hydrocarbons suggest that no difficulty should be experienced in dehalogenating any chloro, bromo, or iodo compounds; the only compound that has defied dehalogenation is perfluoroheptane, C7Fl6. The technique is of potential usefulness in the preparation of unavailable
154
0
ANALYTICAL CHEMISTRY
-
. .
L..
HYDR05ENiT13N PRcCUCTs
HYDROGEhA+ION OF ChLORO3ENZEhC
H Y C R O G E h A T l O N OF BROMOBEhZENE
-. N O T E A B S E N C E OFICDOBENZEhE ~~
~
__~-_
73
72
66
Figure 1.
60
--
54
-
48 42 36 TIME M I N U T E S
3 C - 2 4 - - 7 2 6 0
Hydrogenation of halobenzenes
hydrocarbons from available sulfur, oxygen, nitrogen, or halogen compounds as well as in the study of desulfurization, denitrogenation, deoxygenation, and dehalogenation reactions. APPARATUS A N D PROCEDURE
The apparatus and procedure used have been described. The catalyst was a commercial 0.5% palladium-on-alumina catalyst sold under the trade name Deoxo catalyst. The reaction was con-
ducted a t 200' C., and the products from the hydrogenation reactor were trapped in special dry ice-cooled traps. Other catalysts of the type used might be equally as successful in this reaction. A Perkin-Elmer Model 154-D gas chromatograph equipped with a thermistor detector was used in this work. Several 1/4-inch columns of various lengths and packing were employed t o achieve the separations desired. It is necessary to use a solvent to recover the material from the trap in which the dehalogenated products are
condensed. This solvent appears in the chromatograms as a large, unattenuated peak that is extraneous to the dehalo-
genation reaction. I n the chromatograms of the pure compounds that serve to identify the products of de-
halogenation the solvent peak been omitted in some instances.
has
DISCUSSION
I CHLOROCYCLOHEXANE a
Table I lists some of the halogen compounds, typical of five common classes of organic halides, that were investigated in this study. Figure 1 shows gas-liquid chromatograms of each of the four monohalobenzenes, plus the hydrocarbon product expected from their dehalogenation; and the actual product from the dehalogenation of the halobenzenes. I n each instance it is evident that the emergence time of the product agrees with the emergence time of the expected hydrocarbon (cyclohexane in all four instances). The hydrocarbon also has been identified by means other than emergence time. It is evident that the reaction is complete, as no
I
CYCLOHEXANE
PRODUCTS OF HYDROGENATION OF I - CHLOROHEXANE
PRODUCTS OF H Y D R O G E N A T I ~ N ' O F CHLOROCYCLOHEXANE
NOTE ABSENCE OF
NOTE ABSENCE OF
I
I 28
24
16
20
12
8
4
I I I l 28 24
0
I 1 20
1
1
16
1 12
l
I 8
I
I
I
I
I
I
4
0
Q - C H L O R O T O L U E N E 8 METHYLCYCLOHEXANE
z
2
c W LL
W
n W (r
PRODUCTS OF HYDROGENATION OF a-CHLOROTOLUENE
n K
0 W
a
7
'
a-CHLOROTOLUENE
l
:
I
I
I
1
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
-?u 9
PRODUCTS
OF
HYDROGEH4TlON
OF 2 - ETUYLHEXYLCHL3RIDE
I -CHLORONAPHTHALENE, TETRAHYORONAPHTHALENE AND a trons-DECAHYDRONAPHTHAL
-
c 4 - c - cI
c2
L
t
I
I
I
I
1
1'1
I
1
I
I
I
I
I
1
I
1
I
I
I
I
I
I
I
I
I
I
I
1I-,
1
PRODUCTS OF HYDROGENATION O F I-CHLORONAPHTHALENE
1 l
.
1
1
1
1
1
/
1
/
1
1
1
1
1
1
l
1
1
l
1
~
~
/
/
~
l
I 2~
N O T E A B S E N C E OF
I
~
10~
I
I
I
I
~ 8
6
4
2
TIME
,
-i 0
MINUTES
Figure 3. Hydrogenation of 2-ethyl hexyl chloride VOL. 34, NO. 1, JANUARY 1962
155
Table
I.
Hydrogenation Studies
of Certain Classes of Halogen Compounds
Compound Dehalogenated
Product GLC retentions time, min.
Formula
Name 1-Chlorohexane 1-Bromohexane 1-Iodohexane Chlorocyclohexane
Formula
c,-Cl CrBr
c,-1
C>-Cl e
Bromocyclohexane
r
cT)-I
Iodocyclohexane
74.2)
Fluorobenzene
4.8)
Chlorobenzene Bromobenzene 64.8
Iodobenzene
0 0
GLC retention” time, min. 2.2 2.2 2.2 3.9 3.9 3.9 4.0 4.0 4.0 3.9+
CY-C hlorotoluene
5.6
a-Bromotoluene
5.6
a-Iodotoluene
5.6
1-Fluoronaphthalene
20.2
1-Chloronaphthalene
55.5
1-Bromonaphthalene
89.3
...
1-Iodonaphthalene
03 03 plus
trans
and cis
8 . 8 11.1 17.0 8 . 8 11.1 17.0
extraneous fragments or products. I n dehalogenating halonaphthalenes, three hydrocarbons can result, as was indicated in Table I: tetrahydronaphthalene and cis- and trans-decahydronaphthalene. All of these compounds were identified in the reaction products from 1-chloronaphthalene, as illustrated in the bottom panel of Figure 2. Table I1 lists additional halo compounds, including mono-, di-, and trihalo varieties that also were SUCcessfully dehalogenated, and lists the products obtained. I n all instances, these were the products to be expected. Of particular interest is item 4, 2-ethyl hexyl chloride. It was found in the deoxygenation of the related compound 2-ethyl-1-hexanol ( I ) , a branched structure containing a side chain in which a carbon-carbon bond exists adjacent to a carbon-oxygen bond, that the carbon-carbon bond is weak and breaks preferentially to the carbon-oxygen bond. Thus the deoxygenation reaction resulted in two products, the expected one in minor yield. This anomaly apparently does not exist in the analogous halides, such as 2-ethyl hexyl chloride (item 4, Table 11), for here only the expected product, 3methylheptane, is obtained. This situation is more clearly indicated b y t h e following equations:
8.8 11.2 17.1 OH
8 . 8 11.1 17.0
I I
c4-c-c2
C C4-C-C2
+ H2
(10%)
+
In 6.3-mm. O.D. by 2-meter column, 25y0 D.C. Silicone 550 on 30- 60-mesh Chromo8orb, 100” C., 60 ml./min. helium flow. Temperature 158’ C. for bicyclic compounds. a
Table II.
I
C
Miscellaneous Compounds Dehalogenated
Compound Name
Retention time, min.
Formula
Product Name
Formula
c1\ 1. I-Bromo-3-chlorobenzene
eBr , 1 /
/
13’2
Br
Cyclohexane
0
I 46.8 J
2. 1-Bromo-2-iodobenzene 13 a-o-Dichlorotoluene
9
The pertinent chromatograms are shown in Figure 3, indicating that Equation 2 accurately describes the situation. Perfluoroheptane, C?Fle, under the conditions of time, temperature, and catalyst employed, was found t o be completely resistant to hydrogenation.
hle thylcyclohexane LITERATURE CITED
4. 2-Ethyl hexyl chloride
‘Cl C,-C-C-Cl
6.4
3-Methylheptane
I
cz 5. Benzotrifluoride
O
C
ANALYTICAL CHEMISTRY
I
C2 F
trace of the original halogen is found in the products of the reaction. In addition, no fragmentation products are produced, as shown by the absence of extraneous peaks in the chromatograms of the products of the dehalogenation.
156
Cr-C-C
,
31.6
hlethylcyclohexane
Figure 2 shows chromatograms from a similar series of experiments on the dehalogenation of some additional monochlorinated hydrocarbons. As was true for the halobenzenes, the reactions again were complete, resulted in the expected products, and did not produce
(1) Thompson, C. J., Coleman, H. J.,
Hopkins, R. L., Ward, C. C., Rall, H. T., ANAL.CHEM.32, 1762-5 (1960). (2) Thompson, C. J., Coleman, H. J., Ward, C. C., Rall, H. T., Ibid., 32, 424-30 (1960). (3) Ibid., 34, 151 (1962). RECEIVED for review July 27, 1961. Accepted October 16, 1961. Investigation performed as part of the work of American Petroleum Institute Research Project 48A on “Production, Isolation, and Purification of Sulfur Compounds and Measurement of Their Properties,” which the Bureau of Mines conducts a t Bartlesville, Okla., and Laramie, Wyo.
