GEORGIA INSTITUTE OF TECHNOLOGY Engineering Experiment Station Atlanta, Georgia
NOTICE This report was prepared as an account of work sponsored by the United States Government. Neither the United States nor the United States Atomic Energy Commission, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, com- pleteness or usefulness of any information, apparatus, product or process disclosed, or represents that its use PROGRESS REPORT would not infringe privately owned tights.
Project A-936-005
RADIATION CHEMISTRY OF MONO-SUBSTITUTED AROMATIC COMPOUNDS
by
J. A. KNIGHT, JR.
REPORT NO. ORO-3519-15
CONTRACT NO. AT-(40-1)-3519
15 JANUARY 1973 to 15 JANUARY 1974
Performed for UNITED STATES ATOMIC ENERGY COMMISSION OAK RIDGE OPERATIONS OAK RIDGE, TENNESSEE
DISTRIBUTION OF TH"..- 00:.! 15 UNUNITED TABLE OF CONTENTS
Page I. INTRODUCTION 1
II. EXPERIMENTAL 1
III. RESULTS AND SUMMARY 2
IV. PUBLICATION PLANS 2
A. Articles Published 2
B. Articles Submitted for Publication 2
C. Manuscripts to be Prepared 2
V. APPENDICES 3 I. INTRODUCTION
The broad objective of this research program is to investigate in reasonable detail the radiation chemistry of some substituted benzenes with both electron-releading and electron-attracting nonhydrocarbon substituents. The approach being used is that of detailed product analysis of irradiated pure samples of the aromatic compounds and of the compound plus additives.
12 3 The4 results from the Y-radiolysis of nitrobenzene * * and aniline have been published, A manuscript, "Radiolysis of Benzo- nitrile," has been submitted for publication (Appendix C), The radiation chemistry of benzonitrile with a number of additives is currently being investigated.
II. EXPERIMENTAL
Irradiation Samples
The irradiation tubes and glassware used in the preparation of pure samples of benzonitrile and of benzonitrile plus additives are baked at 300°C for at least twelve hours, and the glassware is then cooled in a vacuum desiccator. The samples are prepared in a dry nitrogen atmos- phere and then degassed immediately by the usual freeze, pump, and thaw technique. These procedures were found necessary to prepare samples which would yield reproducible results.
1. J. A. Knight, "Arylation of Nitrobenzene Induced by y-Radiation," Radiation Res.. 44, 50-58 (1970). 2. J. A. Knight, "Radiolysis of Nitrobenzene," Radiation Res.. 52, 17-24 (1972). 3. J. A. Knight, "Phenylation of Nitrobenzene by Y-Radiation," Radiation Res., 54, 207-211 (1973). 4. J. A. Knight, "Radiolysis of Aniline," Radiation Res. 51, 590-598 (1972).
1 Analytical Procedures
The radiolytic products were analyzed by gas chromatography, and the conditions are given in Appendix B and in the experimental section in Appendix C.
III. RESULTS AND SUMMARY
The results from the radiolysis study of pure benzonitrile have been submitted for publication (Appendix C). The effects of various additives on the radioiysis of benzonitrile are currently being investigated. Additives that are being used or will be used are biphenyl, naphthalene, anthracene and N,N,N*,N*-tetramethyl- paraphenylenediamine (TMPD). The results of this study will be submitted for publication as soon as sufficient data are obtained.
IV. PUBLICATION PLANS
A. Articles Published During the past twelve months, two articles, "Phenylation of Nitrobenzene by Y-Radiatinn" (Appendix A), and "Gas Chromatographic Conditions for the analysis of Y-irradiated benzonitrile for cyanoaromatic products" (Appendix B), were published.
B. Article Submitted for Publication
An article, "Radiolysis of Benzonitrile," (Appendix C) has been submitted for publication.
C. Manuscript Preparation
A manuscript will be prepared on the results of the Y-radiolysis of benzonitrile with additives as soon as sufficient data are obtained.
2 V. APPENDICES Page .A. Phenylation of Nitrobenzene by Y-Radiation.
B. Gas Chromotographic Conditions for the Analysis of the Y-Irradiated Benzonitrile for Cyanoaroniatic Products. Journal of Chromatography, 79 (1973) 325-328
C. Radiolysis of Benzonitrile 13-29
Radiation Rkskarcii, Volume 54. No. 2 May l<>7,; Copyright © 1973 by Academic Press, Inc. Printed in US.. I.
3 APPENDIX C pp. 13-29 of Report
Radiolysis of Benzonitrile*
J. A. KNIGHT
Nuclear and Biological Sciences Division Engineering Experiment Station Georgia Institute of Technology Atlanta, Georgia 30332
1. Supported in part by the United States Atomic Energy Commission. This is AEC document number ORO-3519-16.
Number of copies submitted 3 Number of manuscript pages 17 Number of Tables 4 Running head:
Radiolysis of Benzonitrile
Proofs should be sent to:
Dr. James A. Knight Radioisotopes Laboratory Engineering Experiment Station Georgia Institute of Technology Atlanta, Georgia 30332
2 Radiolysis of Benzonitrile
Knight, J. A., Radiolysis of Benzonitrile
Radiation Res, , pp - 9 .
Abstract
Gamma irradiation of benzonitrile shows that most of the identified products are related structurally to the parent molecule. The gaseous products are hydrogen, acetylene, and hydrogen cyanide. Nitrogen and cyanogen vere not detected as products. Other than the gaseous products, benzene was the only product with a molecular weight less than benzoni- trile. The three isomeric dicyanobenzenes were identified, and the relative reactivity for radiation-induced cyanation of benzonitrile is approximately 1:1:1.7 for the ortho:meta:para positions. The three isomeric cyanobiphenyls were identified, and the relative reactivity for radiation-induced phenylation of benzonitrile is approximately
1.4:1:1.9 for the ortho:meta:para positions. The six isomeric dicyano- biphenyls (on«5 cyano group/phenyl ring) were identified, and the yields show that the radiation-induced cyanophenylation process is not random.
There are some unidentified products with each group of isomeric cyano aromatic products, and a group of products with molecular weight greater than the dicyanobiphenyls. The total yield of the unidentified products is approximately \2% of the total yield of the identified cyano aromatic products.
Key words: Radiolysis, benzonitrile.
3 RADIOLYSIS OF BENZONITRILE
J. A. Knight
INTRODUCTION
The radiolysis of monosubstituted benzenes with nonhydrocarbon substituents has not been investigated as extensively as aromatic hydrocarbons (1), Recently, we have reported on the radiolysis of nitrobenzene (2,3,4) and aniline (5). The nanosecond-pulse radiolysis of aniline has been studied in which two transient species were found
(6). Weiss has recently reported on the isomeric effects in radiolysis of a large number of substituted benzenes and toluences (7). The radiolysis of the halobenzenes has also been reported (8,9,10). The radiation chemistry of monosubstituted benzenes with nonhydrocarbon substituents is of interest because of effects of the electron-releasing and electron-attracting substituents on radiation stability, reaction mechanisms, and product distribution. Substituents such as NH3, OH,
CH3 and 0CH3 are ortho-para directing with activation toward electro- philic substitution of the aromatic nucleus; substituents such as CI, Br, and CH2C1 are ortho-para directing with deactivation; and substituents such as N0S, C00H, CHO, and CN are meta directing with deactivation 0.1).
EXPERIMENTAL
Materials
Benzonitrile, reagent grade, was fractionally distilled at reduced pressure to obtain a middle cut. The middle cuts were redistilled to obtain a highly purified middle cut which was used for irradiations.
4 The dicyanobenzenes and 4-cyanobiphenyl were commercially available
and were purified by recrystallization. The 2- and 3-cyanobiphenyl
and the six isomeric dicyanobiphenyls were prepared from the corres- ponding nitro or dinitro compounds by reduction to the amino compounds*
The amino compounds were converted to the cyano compounds by the
Sandmeyer reaction.
Irradiations
The irradiation tubes and glassware used in the preparation of the
samples were baked at 300°C for at least twelve hours, and the glassware was then cooled in a vacuum desiccator. The samples were prepared
in a dry nitrogen atmosphere and then degassed immediately by the usual freeze, pump, and thaw technique. The benzonitrile, just prior
to transfer to the irradiation tubes, was given a final drying using
silica gel which had been baked for at least twelve hours at 300°C.
These precautions were found necessary to prepare samples which would yield reproducible results. The dose rate which was determined by
the Fricke dosimeter and corrected for electron density was 19 5.9? x 10 eV/g-hr. The irradiation source has been described (5).
Analytical Procedure
The radiolytic products were analyzed by gas chromatography. The
gas chromatographic conditions for the analysis of the dicyanobenzenes,
the cyanobiphenyls, and the dicyanobiphenyls have been reported (12).
Hydrogen was analyzed on a 20 ft. 1/4 in. alumina column with argon .
carrier gas utilizing a thermal conductivity detector. Acetylene was
analyzed on a 10 ft. 1/8 in. column of 80/100 mesh Chromosorb 104 at
5 25°C with a flame ionization detector. Hydrogen cyanide and cyanogen were analyzed on a 12 ft. 1/8 in. stainless steel column of 80/100 mesh Porapak Q at 100°C with a flame ionization detector. Benzene was analyzed on a 10 ft. 1/8 in. column of 107. Versamid 900 on 80/100 mesh Chromosorb P, AW-DMCS, at 80°G. Radiolytic products of molecular weight greater than the dicyanobiphenyls were analyzed on a 5 ft. 1/8 in.
column of 3% Poly A103 on 100/120 mesh Chromosorb W, AW-DMCS, at 260°C.
RESULTS
The identified radiolytic products with G-values from pure
benzonitrile are given in Table I. The unidentified radiolytic products with approximate G-values are given in Table II and are divided into four
groups. The unidentified radiolytic products in group I are those that
appear with the dicyanobenzenes in the gas chromatographic analysis;
group II, with the cyanobiphenyls; and group III, with the dicyanobi-
phcnyls. The unidentified products in group IV are those with G.C.
retention times that are greater than the dicyanobiphenyls and, hence,
have larger molecular weights than the dicyanobiphenyls. The sample for
analysis of the group IV products was obtained by distilling off the
benzonitrile under vacuum from a known weight of the irradiated benzo-
nitrile. The residual material from the distillation was dissolved in
a known weight of acetone, and this solution was used for G.C. analysis.
The gas chromatograms of this sample showed at least 20 products with
retention times greater than the dicyanobiphenyls, and there was consid-
erable overlap of the peaks in the chromatogram. The total approximate
G-value for these 20 products was 0.0091, which is one-tenth of the total
G-value for the 6 isomeric dicyanobiphenyls.
6 TABLE I
Radiolytic Products from Benzonitrile
2 Product G x 10
Hydrogen 0.96 Acetylene 0.55 Hydrogen cyanide 1.3 Benzene 0.36 1.2-Dicyanobenzene 0.59 1.3-Dicyanobenzene 0.58 1.4-Dicyanobenzene 0»48 2-Cyanobiphenyl 0.70 3-Cyanobiphenyl 0.49 4-Cyanobiphenyl 0.47 2,2'-Dicyanobiphenyl 0.7 2,3'-Dicyanobiphenyl 3.46 2,4'-Dicyanobiphenyl 1.73 3,3'-Dicyanobiphenyl 0.9x 3,4'-Dicyanobiphenyl 1.34 4,4'-Dicyanobiphenyl 0.53
7 TABLE II
Approximately G-Values of Unidentified Radiolytic Products 2 Unknown Products G x 10 Group Ia
1 0.02B
2 0.016
3 0.01B 4 0.04s £ 0.10 Group IIb 1 0.05!
2 0.023 3 0.017 4 0.01
5 0.018
6 0.018 7 0.008 8 0.03b Z 0.18 Group IIIC 1 0.4s 2 0.01a 3 0.02s 4 O.O81 5 O.O64
6 0.028 7 0.02a Z 0.27s
20 Products 2 0.91
a- Unknown products that appear with the dicyanobenzenes in the gas chromatographic analysis. Unknown products that appear with the cyanobiphenyls in the gas chromatographic analysis. c- Unknown products that appear with the dicyanobiphenyls in the gas chromatographic analysis. d- Unknown products that have retention times greater than the dicyano- biphenyls. Individual G-values were not determined for each unknown. The range of G-values was from 0.00002e to 0.0023.
8 Nitrogen and cyanogen, which were considered as possible radiolytic products, were not detected by gas chromatographic techniques• Nitrogen would have been detected if it had had a G-value greater than approxi- .5 mately 4 x 10 , and cyanogen would have been detected if it had had a -4 G-value greater than approximately 2 x 10 . Nitrogen was reported as a radiolytic product in the radiolysis of o-, m-, and p-tolunitrile (7),
In the first phase of this study of benzonitrile, it was not possible to obtain reproducible results, particularly with the dicyanobiphenyls.
This difficulty was eventually discovered to be due to traces of water in the benzonitrile used for irradiation. The removal of the last traces of water from benzonitrile is difficult, and hence, every precaution was
taken to prepare samples free of moisture. Therefore, in the ptr¶tion of irradiation samples, all glassware and irradiation tubes were baked at
300°C for at least 12 hours and then cooled in a vacuum desiccator. The benzonitrile was dried, just prior to use, with silica gel which had been
activated at 300**C for at least 12 hours. The transfer of the dried benzonitrile to the irradiation tubes was carried out in an atmosphere of
dry nitrogen in a dry box. The samples were degassed immediately by the usual freeze, pump, and thaw technique. In this way, samples were
obtained which yielded reproducible results.
DISCUSSION
The Y~radiolysis of monosubstituted benzenes yields a variety of
products which can be related structurally to the parent molecule.
The gaseous products are hydrogen, acetylene, and hydrogen cyanide.
The hydrogen yield, G = 0.0096 is ~ 22% of G^ • 0.044 for benzene (13).
9 The G-value of 0,0055 for acetylene from benzonitrile is also less Chan the G • 0,0073 for acetylene from benzene (13), The formation of acety- lene shows that carbon-carbon bond scission occurs during radiolysifl.
The Gg^ - 0,013 is much less than the G-values of 0.25 for HCi and 0.43 for RBr reported for chlorobenzene and bromobsnzene, respectively (8).
Cyanogen and nitrogen were considered as possible radiolytic products, and cyanogen would have been detected if its G-value had been greater than 2 x 10"\ In the radiolysis of chloro-, bromo-, and iodobenzenes, each of the frefe halogens— G^ • 0.006; G^ • 0.20; G^ « 0.79— were formed (8), In the radiolysis of o-, and p-tolunitrile, nitrogen was reported as a radiolytic product with G-value of 0.U01, 0.17, and
0,007, respectively (7), Nitrogen from irradiated benzonitrile would have been detected if it had had a G-value greater than 4 x The presence of the methyl group in the isomeric tolunitriles evidently contributes in some way to the nitrogen formation.
Benzene was the only radiolytic liquid product with molecular weight less than benzonitrile that was detected by the gas chromatographic analysis. The irradiated samples were analyzed for products that would appear on the gas chromatogram before benzene and between benzene and benzonitrile. Produts in this region of the gas chromatogram would -5 have been detected if G-values were greater than approximately 3 x 10 .
The formation of the three isomeric dicyanobenzenes shows that radia- tion-induced cyanation of the benzonitrile occurred at ail three ring positions and that the relative reactivity for the radiation-induced cyanation is approximately 1:1:1.7 for the ortho:meta:para positions.
Radiation-induced nitration of nitrobenzene occurred also with a relative
10 reactivity of 2:1:2 for the ortho:meta:para positions (3). In the
radiolysis of aniline, there was no evidence for radiation-induced
amination as the diaminobenzenes were not detected as radiolytic
products (5)*
Each of the iromeric cyanobiphenyls were formed showing that
radiation-induced phenyl atio.i of the benzonitrile occurred at all
positions. Radiation-induced phenylation has been reported for some
other monosubstituted benzenes—nitrobenzene (4), aniline (5),
chlorobenzene (8,10,14), bromobenzene (9), and toluene in benzene (15).
Free radical phenylation of aromatic compounds, in which the free
radicals are generated chemically, has been investigated extensively
(16), and the results of these studies have shown that in general,
all positions are attacked and that ortho-para substitution is favored
ov^r meta substitution, including those compounds which have meta
directing groups, such as CN and NQa. The relative reactivities at
the ortho, meta, and para positions, based on the yields of the isomeric
monosubstituted biphenyls, are given in Table III for both radiolytic
and radical phenylation of a number of monosubstituted benzenes.
The data show that radiation-induced phenylation of substituted
benzenes agrees in general with free radical phenylation in that all
positions are attacked and that ortho-para substitution is favored over
meta substitution. In the radiolytic phenylation, however, ortho-para
substitution is generally less than in radical phenylation. This is
particularly pronounced with benzonitrile and nitrobenzene. Closer
agreement between radiolytic and radical phenylation is found with chloro- benzene and bromobenzene. The results indicate that in the radiolytic
11 phenylation one or more of the radiolytic reactive species are less ortho-para selective than the chemically generated phenyl radicals.
TABLE III
Relative Reactivities for the Phenylation of
Monosubstituted Benzenes
Radiolytic Ref. Radical* Ref. Compound Orthc Meta Para Ortho Met a Para
Benzonitrile 1.4 1 1.9 6 1 6 (16)
Nitrobenzene 2.8 1 4.3 (4) 6.4 1 5.7 (16)
Aniline 6.5 1 4 (5)
Chlorobenzene 1.1 1 1.3 (10) 1.6 1 1.6 (16)
Chlorobenzeneb 1 1 2 (14)
Bromobenzene 1.3 1 1 (9) 1.5 1 1 (16)
Toluene 1.3 1 1.3 (15) 3.5 1 1.5 (16)
^Phenyl radicals generated from benzoyl peroxide at 80°C.
^Pulsed radiolysis.
The six isomeric dicyanobiphenyls (one cyano group per phenyl ring) were each identified as radiolytic products. The six isomeric disubsti- tutedbiphenyls have also been reported as radiolytic products from nitro- benzene (2), toluene (17), and biphenyl (18). The chemical processes leading to the formation of the disubstitutedbiphenyls have been discuss- ed (2), The iromer ratios of the radiolytic dimers from the substituted benzenes along with the values which are expected for a statistical fragmentation followed by a statistical substitution are given in
Table IV.
12 TABLE IV
Isomer Ratios of the Radiolytic Dimers from
Monosubstituted Benzenes
% Isomer Ref. Compound Radiation 2,2'- 2,3'- 2,4'- 3,3'- 3,4'- 4,4'-
Benzonitrile V 8.1 39.9 20.0 10.5 15.5 6.1
Nitrobenzene Y 21.6 22.6 19.5 7.6 12.0 16.7 (2)
Toluene Y 9 31 18 17 18 5.7 (17)
** Biphenyl e 12.5 24 22 11 22.5 8 (18)
Calculated Statistical Value 16 32 16 16 16 4
From the yield data of the isomers, it is evident that the processes
leading to the radiolytic dimers are not statistical in the monosubstituted
benzenes. In an electron irradiation study of biphenyl (18), a mathe- matical model was developed from which the relative reactivities of the
ortho, meta, and para reactive species were obtained. The model also
provided the relative reactivities of the ortho, meta, and para positions
of biphenyl in the substitution of biphenyl by the radiolytically generated
free radicals. Attempts to use the model to obtain the relative reacti-
vities of the positions of benzonitrile in the generation of reactive
species and in subsequent substitution of benzonitrile were unsuccessful.
This indicates that events in addition to those proposed for the model
are taking place in irradiated benzonitrile to yield the dicyanobiphenyls.
A large number of unidentified radiolytic products appeared in the gas chromatographic analyses of the irradiated benzonitrile. In Table II,
13 the approximate G-values are given for these unidentified products.
The Group I products are those that appear with the dicyanobenzenes, and their total yield is about 6% of the tot*l yield of the dicyano- benzenes. The Group II products are those that appear with the cyanobiphenyls, and their total yield is about 11% of the total yield of the cyanobiphenyls. The Group III unknown products appear with the dicyanobiphenyls, and their yield is about 3% of the total yield of the dicyanobiphenyls. The Group IV unknowns, which have retention times greater than the dicyanobiphenyls, contain at least 20 products, and the G-values range from 0.00002b to 0.0023. These products are most likely cyano derivatives of the terphenyls and quaterphenyls.
The Group IV unknowns represent about 7.5% of total yields of all of the identified cyano radiolytic products. The processes leading to the formation of the number of unidentified products are evidently minor processes, but their formation points out the complexity of the overall radiolytic processes.
The absorption of high-energy radiation by any monosubstituted benzene would produce ionization and excitation to yield (X represents any substituent):
CbHbX —Vv\A-» CsHsX* + e" (1)
C6H5X —VVVW C6HBX* (2)
A fraction of the electrons from reaction 1 would undergo geminate recombination to produce the excited monosubstituted benzene, reaction
3, and the remainder would react to yield the anion, as in reaction 4:
+ C6H5X + e" > C6HSX* (3)
C6H5X + e" > C6HSX" (4)
14 Subsequent reactions of the reactive species from reactions 1-4 would
lead to stable radiolytic products. In a study of the yields of ions
and excited states produced in the radiolysis o£ polar organic liquids,
Hayon reported that for benzonitrile, the yield of electrons, G was
1.40 and the yield of triplets, was 1.C7 (19). An approximate G- value of 0.27 for the disappearance of benzonitrile can be obtained
by summing the G-values for the radiolytic products, taking into
account the number of benzonitrile molecules required to yield each
product and making some reasonable assumptions about the molecular
species in each group of unknowns. It is evident that a large propor-
tion of the ionic and excited species do not undergo reactions that lead
to radiolytic products. Work is continuing on the radiolysis of benzo-
nitrile with a number of additives in an attempt to determine the roles
that the reactive intermediates play in the formation of the stable
products.
SUMMARY
The Y-irradiation of benzonitrile yields a variety of products which
can be related structurally to the parent molecule with the dicyano-
biphenyls being the most important group of products. The gaseous
products are hydrogen cyanide, hydrogen, and acetylene. Nitrogen and
cyanogen were not detected as radiolytic products. The results show
that cyanation, phenylation, and cyanophenylation occurred at all
possible positions during radiolysis. A relative large number of
unidentified products were obtained with small G-values. The total
yield of the unidentified products is approximately 12% of the total
yield of the identified cyano aromatic products.
15 REFERENCES
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3. J. A. Knight, Radiolysis of nitrobenzene. Radiat. Res 52, 17-24
(1972).
4. J. A. Knight, Phenylation of nitrobenzene. Radiat. Res. 54, 207-211
(1973).
5. J. A. Knight, Radiolysis of aniline. Radiat. Res. 51, 590-598 (1972).
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17