The oxidative reaction of hexamethylbenzene (HMB) with nitric acid was studied, and the hitherto unknown polymethylbenzenepolycarboxylic acids were isolated: tetramethylphthalic anhydride, tetramethylisophthalic acid, 1,3,5-, 1,2,4- and 1,2,3-trimethylbenzenetricarboxylic acids. When HMB was warmed with 50% nitric acid at about 80 C, tetramethylphthalic anhydride and tetramethylisophthalic acid were initially produced. The continued reaction led to the production of trimethylbenzenetricarboxylic acids, but only slight amounts of dimethylbenzenetetracarboxylic acids were detected in the reaction mixture. Whereas tetramethylphthalic anydride and tetramethylisophthalic acid were obtained, pentamethylbenzoic acid, a possible precursor of them, was scarcely produced. On the other hand, a yellow material extracted with ether from the initial reaction mixture contained bis-(nitromethyl)prehnitene (CH3)4C6(CH2NO2)2, which was easily converted into the phthalic anhydride

Chiba, K.

Mizuno, T.

Tomura, S.

English

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NASA TECHNICAL MEMORANDUM NASA TM-77945
S1UDIES ON THE OXIDATION OF HEXAMETHYLBENZENE, I;
O X I D A T I O N OF H E X A M E T H Y L B E N Z E N E W I T H N I T R I C A C I D
Koj i Chiba, Sh in 'ya Tomura , Toshiyuki Mizuno
Translation of "Hekisamechirubenzen no shosan-sanka, " Nippon Kagaku
Kaishi, No. 10, 1973, pp. 1959-1962
§f SIIOS or
HEXAflETHYLBEHZEKE WITH NITEIC flCIC iNational
10 P Unclas
CSCL 07D G3/25 05700
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON, D.C. 20546 FEBRUARY 1986
https://ntrs.nasa.gov/search.jsp?R=19860012157 2020-03-20T14:58:57+00:00Z
ORIGINAL PAGE, IS
OF POOR
STANDARD TITLE
1. R.pott N«.
NASA TM-77945
>. R«c!p<«nlVC«l«U0
<. TI.I. ~<« J-I..U.
 3TUDIES ON THE OXIDATION OF
HEXAMETHYLBENZENE, I: OXIDATION OF HEXAMETHYL-
BENZENE WITH NITRIC ACID
3. R.po.,0...
4. Pvforalng O'goni
7. >U,CSo.(.)
Koji CHIBA, Shin'ya TOMURA, Yoshiyuki MIZUNO
Yamagata University, Yonezawa, JAPAN
t. Pu
10. V.rV Unit H..
Leo Kanner Associates,
Redwood City, CA 94063
11.
Translation
National Aeronautics and Space Administration
D.C.- 20546
Translation of "Hekisamechirubenzen no shosan-sanka,"
Nippon Kagaku Kaishi, No.]0, 1973, pp. 1959-1962
1 6-
The oxidative reaction of hexamethylbenzene (HMB) with nitric acid was studied, and the
hitherto unknown polymethylbenzenepolycarboxylic acids were isolated : tetramethylphthalic
anhydride, tetramethylisophthalic acid, 1,3,5-, 1,2,4- and 1, 2, 3-trimethyIbenzenetrtcarboxylic
acids.
When HMB was warmed with 50% nitric acid at about 80CC, tetramethylphthalic anhydride
and tetramethylisophthalic acid were initially produced. The continued reaction led to the
production of trimethylbenzenetricarboxylic acids, but only slight amounts of dimethylbenzene-
tetracarboxylic acids were detected in the reaction mixture. Whereas tetramethylphthalic
anhydride and tetramethylisophthalic acid were obtained, pentamethylbenzoic acid, a possible
precursor of them, was scarcely produced. On the other 'hand, a yellow material extracted
with ether from the initial reaction mixture contained bis-(nitromethyl)prehnitene
(CH2NO2)2, which was easily converted into the phthalic anhydride.
r
17. K,r «e«i< (Sdccted Or Auinor(i)) II. Dl ildbvl.on S'oKomt
Unclassified - Unlimited
}<(«nir Cl»«.ll. (.1 <
Unclassified
JO.
Unclassified
II. H.. •( P.,..
8
77.
STUDIES ON THE OXIDATION OF HEXAMETHYLBENZENE, I;
O X I D A T I O N O F H E X A M E T H Y L B E N Z E N E W I T H N I T R I C A C I D
(received 17 March 1973)
Koji CHIBA, Shin'ya TOMURA, Toshiyuki MIZUNO*
The oxidation reaction of hexamethylbenzene (HMB) with nitric
acid was investigated, and previously unknown polymethylbenzene-
polycarboxylic acids were separated: tetramethylphthalic anhydride,
tetramethylisophthalic acid, and 1,3,5-, 1,2,4- and 1,2,3- trimethyl-
benzenetricarboxylic acids.
o
HMB was heated at approximately 80 C with 50% nitric acid, and
first tetramethylbenzene dicarboxylic acids were produced, and as time
passed trimethylbenzentricarboxyic acids were produced, but almost no
dimethylbenzentetrcarbonic acids were produced. Furthermore, penta-
methylbenzoic acid, thought to be the precursor of tetramethylbenzene-
dicarboxylic acid, was hardly detected at all, but bis-(nitromethyl)-
prenitene was detected in the initial reaction mixture.
1 Introduction
Currently the use of aromatic hydrocarbons is focused on
benzenes, toluenes and xylenes, and heavy aromatic hydrocarbons with
C and above are not sufficiently utilized.
9
The present research concerns the heavy aromatic hydrocarbon
hexamethylbenzene (abbreviated to "HMB" in the following), and
investigates the reactions products when this is oxidized by nitric
acid. Up to now there have been practically no examples of oxidation
of HMB with nitric acid, the only report has been of the tetramethyl-
2)
phthalic acid produced by Jacobsen by heat-processing for two or
three days in dilute nitric acid. However, repeated attempts by the
authors have not established the repeatability of even the
experimental results of Jacobsen
1) This report is referenced as "Research on Oxidation of
Hexamethylbenzene (Part 1)".
* Applied Chemistry Dept., Faculty of Engineering, Yamagata
University, Shio-minami, Komezawa-shi, 992
2) 0. Jacobsen, Ber., 22, 1215 (1889).
The present report involves oxidation of HMB with 50% nitric
acid, examination of the reaction products, and the separation of
several polymethylbenzenepolycarboxylic acids as new substances, as
well as several new observations.
2 The Experiment and Results
2.1 Raw Materials and Reagents
HMB was prepared using a method set forth in a separate reports),
and the substance synthesized by gas-phase contact reaction of phenol
and methanol in the present of an active alumina catalyst was
dissolved in petroleum ether, then purified by passing through a
column packed with active alumina. The solvent was removed, yielding
crystals, and these were then recrystallized from methanol and
used in the experiment (melting point 164-166 C). Diazomethane was
synthesized by the usual method from nitrosomethyl urea, dissolved in
an ether solvent, and for the other reagents, high-quality commerical
reagents were used. Bis-(nitromethyl)prenitene (CH ) C (CH NO ) was
4) 346 2 22
prepared as described in the literature for use as a gas-
chromatography identification sample, HMB and benzoilnitric acid were
combined, and the resulting colorless crystals in the shape of long
o
needles and a melting point of 138-139 C had IR and NMR spectra which
identify the structure. In the IR spectrum, absorption at the NO
-1 2
frequencies of 1548 and 1373 cm were noted, and in the NMR spectrum
(delta ppm, CHC1 ), absorption of the CH protons at 2.35 and 2.45,
«J «J
and absorption of the -CH - proton at 5.95 were noted, and integration
£*
rations of these were observed to be 3:3:2.
Retention time (mm)
Fig. 1 Gas chromatogram of e&tenfied products (Me-
esters)
Column : Silicone DC 550 (20^)/Cehtc 545 (60-80 mesh)
4 mm X 1m, Temp : 215*C, Carrier gas : N3 40 m//min
Detector : FID
10 20 30
3) Koji CHIBA, K. Endo, Japan Chem., 1973, 1152.
4) R. Willstaetter, H. Kubli, Ber., 42, 4151 (1909).
2
2.2 Laboratory Tests on Reaction Products
10.0 gm of HMB and 30 ml of 50% nitric acid were heated for 19
o
hours at approximately 80 C over a bath. After cooling, 0.6 gm of the
colorless needle-shaped crystals (Precipitate 1) were brought to pH
4.2 by adding a 50% sodium hydroxide solution, then the yellow
substance produced (Precipitate 2) was separated by filtering. The
filtered liquid brought to pH 8, and 40.0 g of silver nitrate
dissolved in a small amount of water was added and heated for 30
o
minutes at approximately 80 C. The precipitate produced was removed
by filtering, then after vacuum-drying suspended in 100 ml of benzene,
and this was circulated for 6 hours with 15 ml of methyl iodide,
yielding 4.1 gm of oily methylester. The results of analyzing this by
gas chromatography are shown in Fig.l, and the main peaks 1, 2 and 3
were found. This methylester mixture was cooled in icewater, then the
crystals extracted were removed by filtering and recrystallized from
methanol, yielding colorless plate-shaped crystals [1] with a melting
o
point of 128-129 C. This substance matches Peak 3 of the preceding
chromatogram. In the IR spectrum (cm ), absorption at the C=0
frequency of 1732, and absorption at the C-O-C frequencies of 1218 and
1166 were noted. The results of elemental analysis agreed with the
calculated values for trimethyl trimethylbenzenetricarboxylic acid.
Analytical values: C 61.83%, H 6.32%
Calculated values for C H 0 : C 61.22%, H 6.16%
15 18 6
Substance [1] was heat-processed for several hours over a bath
with a solution of 2N sodium hydroxide, then oxidized with
concentrated hydrochloric acid, and then vacuum-dried. This was mixed
well with about the same quantity of calcium hydroxide, heated to 300-
o
350 C in a circulating nitrogen, and the vapors produced were
collected with ice-cooled ether. This results of analyzing this ether
solution by gas chromatography (Hitachi Gaulet column: DDP-15 0.24 mm
o
x 15m, column temperature: 60 C, carrier gas: 2 ml/min N ) revealed a
^peak matching 1,2,3-trimethylbenzene. From the preceding facts, it
was concluded that substance [1] was trimethyl 1,2,3-trimethylbenzene-
tricarboxylic acid. This is also supported by the fact that the NMR
spectrum (delta ppm, CD) revealed the absorption of CH proton
66 3
nucleus substitutions at 1.60 and 2.01, and absorption of -OCH
3
protons at 3.50 and 3.61 (integration ratios 1:2:1:2). After removal
by filtering from the methylester mixture, a small quantity of ethanol
was added to the mother liquor, and this was cooled by a cooling agent
(ice, table salt), and by repeating recrystallization from methanol of
the cyrstals extracted, colorless needle-shaped crystals with a
o
melting point of 76-77 C were separated. This substance corresponds to
Peak 2 of the gas chromatogram in Fig.l. In the IR spectrum (cm
absorption was noted at the C=0 frequency of 1726 and at the C-O-C
frequencies of 1241 and 1157, and in the NMR sptectrum (delta ppm,
CHC1 ) exhibited clear triple lines with an integration of 1:1 at
3
2.2-2.4 (CH proton nucleus substitution) and 3.9-4.0 (-OCH proton),
3 3
which indicates that [2] is trimethyl 1,2,4-trimethylbenzene-
tricarboxylic acid. Peak 1 matches trimethyl 1,3,5-trimethylbenzene-
5)
tricarboxylic acid, which is reported in a subsequent report. The
previous Precipitate 1 was recrystallized from benzene, yielding a
o
colorless needle-shaped crystal having a melting point of 238-239 C,
of which the IR spectrum (cm exhibited absorption at the C=0
frequencies of 1836, 1768, and absorption at the C-0 frequencies of
1200, 910, suggesting the structure of an acid anhydride, and the
results of elemental analysis agreed with the calculated value of
tetramethyl-phthalate anhydride.
Analytical values: C 70.70%, H 5.81%
Calculated values for C H 0 : C 70.61%, H 5.93%
12 12 3
The NMR spectrum (delta ppm, CHC1 ) also exhibited absorption of
3
CH proton nucleus substitution at 2.30 and 2.62 (integration ratio
3
1:1), supporting the structure of a tetramethylphthalate anhydride.
Precipitate 1 was dissolved in a hot alkaline solution, silver nitrate
was added and the silver salts produced processed with methyl iodide
yielding a methylester which had the IR and NMR spectra and melting
6)
point matching observations reported for dimethyltetramethylphthalic
acid. It is considered unusual for acid anhydrides to be produced in
the presence of excess water, but the anhydrous ring of anhydrous
tetramethylphthalate is extremely stable, and it has been confirmed
that even when boiled with water for long periods it still does not
release.
5) Koji CHIBA, Yoshiyuki MIZUNO, Japan Chem.. 1973. No.11 Noti
6) Koji CHIBA, Hideji SATA, Japan Chem., 1973, 1249 ces
Next, 10.0 gm of HMB and 300 ml of 50% HMB were heated together
o
for 15 minutes at approximately 80 C, and the liquid reaction mixture
obtained was buffered with a 50% sodium hydroxide solution, after
which an oily substance was ether-extracted. 30.0 gm of calcium
chloride (CaCl H 0) was added to the yellow aqueous solution and
2 2
precipitation occured. After washing with hydrated methanol, the
o
excess was placed in a 102. sodium carbonate solution at 80 C for 30
minutes. The calcium carbonate produced as a white precipitate was
removed by filtering, and the filtered liquid was oxidized with conc-
entrated hydrochloric acid, yielding 0.1 gm of light-yellow precipi-
tate. This was esterified with diazomethane, and then recrystalliza-
tion from ether yielded needle-shaped crystals [3] with a melting
o -1
point of 123-123 C. The IR spectrum (cm ) exhibited absorption at
the C=0 frequency of 1724 and absorption at the C-O-C frequencies of
1233 and 1162. The NMR spectrum (delta ppm, C D ) exhibited
6 6
absorption of the proton CH nucleus substitution at 1.80, 2.02, and
3
2.15, and absorption of the -OCH proton at 3.55 (integration ratio
3
1:2:1:2). The results of elemental analysis are as follows, matching
the calculated values of dimethyl tetramethylisophthalic acid.
Analytical value: C 66.70%, H 7.04%
Calculated value for C H 0 : C 67.10%, H 7.25%
14 18 4
The preceding facts indicate that [3] is dimethyltetramethyl-
isophthalic acid.
On the other hand, the ether extract (9.6 gm) obtained above was
subjected to gas chromatography under the following conditions, and
unreacted HMB (approximately 10% of the extract), anhydrous tetra-
methylphthalate (approximately 10%) and and bis-(nitromethyl)prenitene
(approximately 40%) were identified, and several other peaks were
noted, but it was not clear whether mononitro compounds were produced.
Column: Silicone SE-30 (10%)/Celite 545 (80-100 mesh) 4 mm x 1 m,
o
Column temperature: 150 C, Carrier gas: 20 ml/min N .
2
2.3 Reaction Time and Reaction Products
2.0 gm of HMB and was dissolved in 30 ml of 50% nitric acid and
o
heated to approximately 80 C over a bath. After 1-2 hours the
reaction mixture liquid had turned brown and produced bubbles, and a
yellow oily substance was floating in it. After a specific reaction
time, this was buffered with a 50% sodium hydroxide solution and
ether-extraction was performed. 7.0 gm of silver nitrate dissolved in
a small quantity of water was added to the water layer, and held at
o
80 C for 30 minutes with occasional mixing. The precipitated silver
chloride was removed by filtering, and after vacuum-drying, processed
with methyl iodide and esterified. The methylesterified substance
obtained in this way was subjected to gas chromatography in nearly the
same conditions as described in the preceding paragraph, yielding the
experimental results shown in Table 1. The amounts of each of the
components was determined as the mixture ratios by weight from the
peak area ratios, and it was ensured beforehand that the repeatability
of the experimental results would be satisfactory. Reaction mixtures
for which reaction times were greater than one hour were preceded by
ether extaction, and the needle-shaped crystals floating in the liquid
were removed by filtration and estimated as anhydrous ethylphthalic
acid, and substances for which the reaction time was within 30 minutes
were ether-extracted with approximately 10 ml, concentrated, cooled,
and the extracted crystals were removed by filtering and became
Table 1 Reaction p:oducts
HMB 2 Og, 50j£ HX03 30m/, React ion temp • 8(TC
Tetramethyl-
React,
time
5(min)
,. 10
"". 15
30
l (hr)
2
5
9
16
19
a ) mol^£
phthal ic isophthalic
anhydride acid
—
6 0
9 9
„.
9 0
—
7.9
—
—
2.4
based on HMS
J ) The reaction mixture
0.4
3.1
8 3
10. 5
9 0
6.2
3 3
1.9
0 8
1 0
added
1,3,5-
—
0.2
0 3
0 6
1.3
2.8
4.0
4.4
3.9
1.9
was neutralized with
(mol^)"'
1,2,4-
0.1
0.6
0 5
0 8
1 2
4.2
4.8
6.3
5.8
6.5
NaOH, and
1,2,3-
0 1
0.3
0 3
0 1
0 6
2.7
3.6
4 1
4 2
6.2
extracted
txtracts"
1.8
1.8
1.9
1 8
1.5
0.7
0.5
0.3
0 3
—
with ether.
tetramethylphthalic anhydrides. These exhibited nearly a single peak in
all gas chromatographs, and the retention time matched tetramethyl-
phthalic anhydride.
When the reaction time was comparatively short, tetramethyl-
isophthalic acid and tetramethylisophthalic anhydride were preferen-
tially produced, and next trimethylbenzenetricarboxylic acids were
produced. There was a slight difference among the production rates of
isomers of trimethylbenzenetricarboxylic acid, and it was found that
somewhat more of the two isomers other than 1,2,4-trimethylbenzenetri-
carboxylic acid were produced. However, even when the reaction con-
tinued for 19 hours, hardly any benzenetetracarboxylic acids were
produced. Furthermore, pentamethylbenzoic acid, which is thought to
be the precursor of tetramethylisophthalic acid and anhydrous tetra-
methylphthalic acid, was not detected at all. When the reaction
continued for 1 or 2 hours and the methylesterified substances simi-
larly obtained from the reaction mixture were subjected to gas chroma-
tography, a very small amount of methylpentamethylbenzoic acid was
detected and no more. Furthermore, since there is some doubt as to
whether the pentamethylbenzoic acid was ether-extracted, a similar
laboratory analysis was conducted using the ether-extracton for diazo-
methane, but methylpentamethylbenzoic acid was not detected.
3 Conclusions
HMB and 50% nitric acid wre heated over a bath, and trimethyl
benzenetricarboxylic acids were produced with relative ease, while no
dimethylbenzenetetracarboxylic acids were produced. There was a
slight variation in the yield rates among the isomers of the
trimethylbenzenetricarboxylic acids, and slightly more of the two
isomers other than the 1,2,4-form were produced, and this may be
because they have structures which are easily synthesized through
either tetramethylisophthalic acid or tetramethylphthalic anhydride.
As for tetramethylbenzenedicarboxylic acids, tetramethylisophthalic
acid and tetramethylphthalic anhydride were detected, but pentamethyl-
benzoic acid, which is assumed to be its precursor, was hardly
detected at all. On the other hand, after the inital reaction mixture
liquid was buffered in alkali, the yellow substance obtained
by ether-extraction was found to contain unreacted HMB along with
small quantities of bis-(nitromethyl)prenitene. It was already known
that bis-(nitromethyl)prenitene readily produces tetramethylphthalic
6)
anhydride by hydrolysis . From the preceding it was clear that the
preceding dicarboxylic acids were not produced by acidification of the
pentamethylbenzoic acids, and they are thought to be synthesized
through various compounds produced in the reaction between HMB and
nitric acid, but this is not clear from the scope of the present
report.
Finally, we wish to express our gratitude for the valuable advice
of Prof. Shunroku KANNO, and Asst. Prof. Yoshio IMAI of our Macro-
molecular Chemistry Dept., and the support provided in elemental
analysis by Haneyama Laboratories.
(Presented at the Tohoku Regional Session of
the Japan Chemical Association, (Part One), October 1972)
8


Studies on the oxidation of hexamethylbenzene 1: Oxidation of hexamethylbenzene with nitric acid

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