DRUG AND CHEMICAL TOXICOLOGY, 1(3), 219-230 (1978)
ACUTE TOXICITY OF TETRAMETHYLBENZENES : DURENE, ISODURENE AND PREHNITENE
Dennis ;J. Lynch Vernon R. Perone Ronald L. Schuler William B. Ushry Trent rl. Lewis
3epartment of Bealth, Education, and Welfare Public Health Service Center for Disease Control National Institute for Occupational Safety and Health 4676 Columbia Parkway Cincinnati, Ohio 45226
ABSTRACT
Oral LD50 (rat), primary skin irritation (rabbit), cutaneous
sensitization (guinea pig) and eye irritation (rabbit) studies
For personal use only. were conducted on the three tetramethylbenzene isomers: durene,
isodurene and prehnitene. The order of oral toxicity was
isodurene > prehnitene > durene. Durene was not a skin irritant,
while isodurene and prehnitene each produced a mild positive skin
response (erythema). None of the tetramethylbenzenes were skin
sensitizers or eye irritants. qurene, isodurene and prehnitene
are only slightly toxic on an acute toxicologic basis and only
pose an acute health hazard when injested in excessive quantities. Drug and Chemical Toxicology Downloaded from informahealthcare.com by Hacettepe Univ. on 11/24/12
219
Copyright 0 1978 hy Marcel Dekker, InL All Rights Reserved Neither this work nor dny pdrt may be reproduced or transmitted in dny form or by any means, electronic or mechanicdl including photocopying, microfilming, and recording, or by any information storage and retrieval system without permission in writing from the publisher 220 LYNCH ET AL.
INTRODUCTION
Durene (1,2,4,5-tetramethylbenzene), isodurene (1,2,3,5-
tetramethylbenzene) and prehnitene (1,2,3,4-tetramethylbenzene)
are used as starting materials in the organic synthesis of
plastics and resins. At room temperature durene is a solid,
while the other isomers are liquids. Physical constants for the
tetramethylbenzenes are presented in Table 1.
TABLE 1
Physical Constants for Tetramethylbenzene Isomers 9
Durene Isodurene Prehnitene (1,2,4,5-tetra- (1,2,3,5-tetra- (1,2,3,4-tetra- methylbenzene) methylbenzene) methylbenzene)
Formula '10H14 '10H14 '10H14 Mol Wt 134.22 134.22 134.22
Physical State Solid Liquid Liquid For personal use only. (21OC)
Specific Gravity 0.838 0.890 0.905
Melting Point 79 -24 -6 ("C)
Boiling Point 196.8 198 205 ("C)
Flash Point 74 68 73 ("C)
Solubility Insolub-3 Insolu Insolu Le
Drug and Chemical Toxicology Downloaded from informahealthcare.com by Hacettepe Univ. on 11/24/12 (H20) Solubility - Organic Compounds Alcohol Very Soluble Very soluble Very soluble Ether Very soluble Very soluble Very soluble ACUTE TOXICITY OF TETRAMETHYLBENZENES 221
The tetramethylbenzenes are also important industrially
because they possess extremely high reactivity relative to
benzene and toluene, and they can form only one mono- and one di-
nuclear derivative. This enables high yields of high purity
products under relatively mild treatment conditions. 1 Durene is
important for its oxidation product, pyromellitic anhydride, used
in high molecular weight polymers, particularly in some
engineering plastics. Durene has also been employed experi-
mentally as a fungi~ide.~*~
In the course of production and utilization of tetramethyl-
benzenes in industry, the working environment and employees may
become contaminated. Data on the acute toxicity of the
tetramethylbenzenes are sparse.
Gerarde6 orally administered a homogenized suspension of
durene (in olive oil warmed to 4OoC) to fasted 250g rats and had
For personal use only. no deaths among the animals dosed. He determined that the oral
LD was greater than 5000 mg/kg body weight. The oral LD for 50 50 durene has been estimated at 6800 mg/kg.?
It is essential, therefore, to obtain additional data on the
acute toxicity of industrial compounds in order to ascertain what
health hazards, if any, are associated with their industrial
uses.
Drug and Chemical Toxicology Downloaded from informahealthcare.com by Hacettepe Univ. on 11/24/12 The present study describes the acute toxicity of durene,
isodurene, and prehnitene for three routes of industrial
exposure, i.e., oral, cutaneous and ocular. 222 LYNCH ET AL.
METHODS
The following compounds were studied: durene (1,2,4,5-
tetramethylbenzene), isodurene (1,2,3,5-tetramethylbenzene) and
prehnitene (1,2,3,4-tetramethylbenzene). The chemicals were
analyzed for purity by gas chromatography using a flame
ionization detector. The durene sample was better than 99+%
pure; isodurene had a purity of 98% (the major impurity appeared
to be prehnitene): and prehnitene was 96% pure (the major
impurity appeared to be isodurene). All the test materials were
administered undiluted, except for durene which was suspended in
corn oil for the oral LD studies. 50
Acute Oral LD50. In rat oral LD50 studies, each test material
was administered by gastric intubation as a single dose. The
experimental subjects were male, cesarean-derived, Sprague-Dawley
albino rats weighing 175-250g that were fasted overnight prior to For personal use only. dosing. Dose levels were seven to eight in number (durene 5200-
9800 mgfkg, prehnitene 4000-9000 mg/kg and isodurene 2000-8200
mg/kg). The number of rats employed per dose level was eight.
The 14-day oral LD50 values and their 95% confidence limits were
calculated by the exact probit analysis of Finney.8 When the
data were nonlinear on log-probit graph paper, the moving average
method of Thompson was employed .g Drug and Chemical Toxicology Downloaded from informahealthcare.com by Hacettepe Univ. on 11/24/12
Primary Skin Irritation. In the primary skin irritation studies,
the three test materials and a negative control (distilled ACUTE TOXICITY OF TETRAMETHYLBENZENES 223
water), were tested on six rabbits, each rabbit receiving the
three tetramethylbenzenes plus the distilled water control. For
each test and control material, two skin sites were used, one
abraded and one intact. A 0.1 ml volume or 100 mg (durene) of
each undiluted test compound, and 0.1 ml of the control compound
(distilled water) was applied to each 20 mm2 test site. The
durene test sites were moistened with 1-2 ml of distilled water
immediately prior to application of the test compound. The test
sites were covered with a gauze patch. Each animal was provided
with a leather harness to prevent the animal from disturbing the
test site." Following a 24-hr exposure the harness and patches
were removed and the skin reactions evaluated. A second
evaluation was performed 48 hr after administration of the
compounds. The method employed for determining the degree of
primary skin irritation was a modification of the Draize
For personal use only. technique." The reactions were evaluated on the basis of the
designated values in the following table:
React ion Intact Skin Abraded Skin
No irritation 0 (Nonirritant) 0 (Nontoxic)
Erythema (regard- 1 (Mild irritant) 1 (Xild cellular less of degree) toxicant)
Erythema and edema 2 (Irritant) 2 (Cellular toxi- confined to test cant) area Drug and Chemical Toxicology Downloaded from informahealthcare.com by Hacettepe Univ. on 11/24/12
Erythema and edema 3 (Strong irritant) 3 (Strong cellular extending beyond toxicant) test area
Eschar 4 (Corrosive) 4 (Corrosive) 224 LYNCH ET AL.
Skin Sensitization. Fifteen male albiqo guinea pigs, weighing
300-400g, were employed for each test material in the repeated
insult test for cutaneous sensitization. Five animals were
assigned to the control group. The testing method was similar to
that described by Landsteiner and Jacobs.13 A 0.1 ml volume or
100 mg (durene) of undiluted test compound was applied topically
to separate abraded skin sites on the animals three times weekly
for a total of nine treatments. Each durene test site was
moistened with distilled water. Following a two week rest period
for an immune response to develop, during which time no further
treatments were made, a challenge dose of a test compound was
administered to both test and control animals in the same dosage
and by the same method used during the initial treatment period.
Skin reactions were examined and recorded at 24, 48 and 72
hr following the challenge dose. For personal use only. Eye Irritation. Yale albino rabbits, weighing 2 to 3 kg, were
used in the eye irritation studies. A 0.1 ml volume or 100 mg
(durene) of each undiluted test material was placed in one eye of
each animal by pulling the lower lid of the eye to form a cup
into which the compound under investigation was instilled. The
eyelids were held together for approximately one second and the
animal was then released. The rabbit eye was exposed to the test Drug and Chemical Toxicology Downloaded from informahealthcare.com by Hacettepe Univ. on 11/24/12 compound for either 5 min or 24 hr before washing the eye with
approximately 300 ml of distilled water over a 2 min period. The
eyes were examined at 1, 24, 48 and 72 hr, and again at 7 days; ACUTE TOXICITY OF TETRAMETHYLBENZENES 225
if any injury persisted, the eyes were re-examined at 14 and 21
days. The nontreated eye served as a control. Grading of the
severity of the eye irritation was performed according to the
United States Food and Drug Administration method13 based upon
the presence and degree of ulceration or opacity of the cornea
and iris and erythema, chemosis and ulceration or necrosis of the
conjuctival mucosa.
RESULTS
Acute Oral LD The oral LD values and their 95% confidence 50' 50 limits for the three test compounds are presented in Table 2.
Isodurene was more toxic than prehnitene which was more
toxic than durene. Lethal doses of the tetramethylbenzenes
(durene > 6000 mgfkg, prehnitene and isodurene > 4400 mgfkg)
induced stomach and intestinal hemorrhage, labored breathing,
lacrimation, bladder distention and adhesions of abdominal organs
For personal use only. (stomach, pancreas, spleen, liver and small intestines). Death
was related to the degree of blockage of the gastrointestind
tract from the resultant adhesions and/or leakage of bloody
TABLE 2
Acute Oral LD50 Values in Rats
Number of Animals Number Estimated LD50 95% Confidence
Drug and Chemical Toxicology Downloaded from informahealthcare.com by Hacettepe Univ. on 11/24/12 Compound per Dose of Doses (mglkg) Limits
Isodur ene a 7 5157 4 53 2- 570 1
Prehnitene a a 6408 5488-7688
Durene 8 7 6989 5948-7892 226 LYNCH ET AL.
exudate into the peritoneal cavity. Behavioral effects noted for
survivors of the LDjO study were initial hyperexcitability,
followed by apathy and weakness, which persisted for several
hours to several days, depending upon the dosage administered.
The signs and symptoms observed were essentially identical for
the three compounds tested. All deaths occurred within three
days, except for one rat which received isodurene and died on day
six.
Primary Skin Irritation. Results of the skin irritation studies
with rabbits revealed that isodurene and prehnitene produced a
mild positive response (erythema) which did not persist beyond 48
hr. Durene did not produce a positive response and was
considered to be a nonirritant to skin. Primary irritation
scores for each compound (average rating, intact vs abraded
skin) and the interpretation of the scores are presented in Table For personal use only. 3. The tetramethylbenzenes were not irritating to intact or
abraded skin.
TABLE 3
Primary Skin Irritation Scores in Rabbits
Average Ratinga Interpretation Intact Abraded Intact Abraded Compound Skin Skin Skin Skin
Drug and Chemical Toxicology Downloaded from informahealthcare.com by Hacettepe Univ. on 11/24/12 Durene 0 0 Nonirritant Nontoxic
Isodurene 0.7 0.9 Nonirritant Nontoxic
Prehnitene 0.4 0.9 Nonirritant Nontoxic
a Average score of six rabbits ACUTE TOXICITY OF TETRAMETHYLBENZENES 227
Skin Sensitization. There was minor irritation of the test sites
after each of the nine sensitizing cutaneous applications, with
the challenge dose eliciting an identical response. These
results indicate that the tetramethylbenzenes tested have little
or no potential for inducing cutaneous sensitization in man.
Eye Irritation. Isodurene, prehnitene and durene are nonirritants,
since no ocular reactions were induced by the substances beyond the
one-hour observation period.
DISCUSSION
The results of these studies provide a basis for evaluating
the absolute and relative acute toxicity of durene, isodurene and
prehnitene. There are no prior studies in the literature in
which these compounds were assessed simultaneously for their oral For personal use only. toxicity, primary skin irritation, cutaneous sensitization and
eye irritation responses. The oral LD50 results obtained in this
study for durene are supported quantitatively by the studies of
Gerarde6 and Uzhdavini, et al.? Gerarde estimated the LD50 to be
in excess of 5000 mglkg, and Uzhdavini reported the LD50 to be
6800 mg/kg, which is in agreement with the 6989 mglkg value
obtained in this study. The relatively low oral toxicity of the Drug and Chemical Toxicology Downloaded from informahealthcare.com by Hacettepe Univ. on 11/24/12 tetramethylbenzenes can be explained in terms of their biotrans-
formation products, carboxylic acids and alcohols, which have
a very low order of t0~icity.l~The necropsy findings are similar
to those reported in rats dosed orally with alkyl derivatives
of benzene. 6 228 LYNCH ET AL.
Gerarde4 reported that his unpublished data indicated that
guinea pigs did not develop a sensitivity to durene injected
intradermally. This finding is in agreement with the current
study in which topically applied durene failed to elicit a
sensitization response. Uzhdavini, et a1.15 reported that
durene had a lower local irritating effect than pseudocumene
(1,2,4-trimethylbenzene), 2-isopropylnaphthalene and
dodecylbenzene.
Brattsten and Wilkinsonl6 working with the southern armyworm
and Fabacher and Hodgsonl7 working with mice, have both demon-
strated that durene is an enzyme inducer. The other tetra-
methylbenzenes have not been tested for enzyme induction
activity. These facts should be considered in terms of
xenobiotic metabolism in workers exposed to tetramethylbenzene
isomers in the workplace.
For personal use only. The data from this study and other laboratories suggest that
durene, isodurene and prehnitene should not present acute
toxicological hazards to workers as long as standard good hygiene
practices are employed when handling these tetramethylbenzene
compounds.
ACKNOWLEDGMENTS
The authors wish to express their gratitude to Dr. Jeanne Drug and Chemical Toxicology Downloaded from informahealthcare.com by Hacettepe Univ. on 11/24/12 Burg for her help with statistics; to Ms. Ardith Grote for the
gas chromatographic analyses of purity; to Mr. Paul Wright and
Mr. Clinton Gray for their care of the animals; and to Els. Evelyn
Munro for typing this manuscript. ACUTE TOXICITY OF TETRAMETHYLBENZENES 229
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