Note: Descriptions are shown in the official language in which they were submitted.
1124~33
Background of the Invention
Oxirane compounds such as ep~chlorohydrin, cyclohexene oxide,
glycidol, glycidyl ethers, and the like, usually in combination with
other compounds such as alkoxynitriles, amines, amides, alcohols, and
esters, are commonly used to stabilize chlorinated solvents, such as
perchloroethylene, against metal induced decompvsition.
Of the oxirane compounds, epichlorohydrin is perhaps most
commonly used due to its proven effectiveness and ready availability.
However, since epichlorohydrin hàs been shown by the Ames Test to exhibit
mutagenic activity, its continued permissible use in chlorinated solvent
stabilization systems is questionable for reasons of health and safety.
Cyclohexene oxide has been demonstrated to be an acceptable
non~mutagenic substitute for epichlorohydrin in chlorinated solvent
stabilization systems; however, cyclohexene oxide suffers from the disad-
vantage that it, itself, is unstable and develops acidity upon storage,especially when exposed to air.
It is believed that cyclohexene oxide autoperoxidizes to form a
tecomposition product which is believed to be cyclopentane carboxylic
acid, which decomposition product causes severe pitting and corrosion of
metals, particularly aluminum. Consequently, before cyclohexene oxide
.y . .. , ~ .
llZ4733
can be effectively used to stabilize chlorinated solvents against metal
induced decomposition, the cyclohexene oxide itself must be stabilized
against peroxidative decomposition.
Cyclohexene oxide is usually stabilized against decomposition
by the inclusion of a stabili~ing amount of butylated hydroxytoluene
(BHT). However, it has been found that BHT stabiliæed cyclohexene oxide is
not very effective in stabilizing unsaturated cblorinated solvents, for
example, perchloroethylene, a~ainst metal, particularly aluminum, induced
decomposition, especially when the solvent is used in degreasing operations.
It i9 desirable, therefore, to devise means of stabilizing
cyclohexene oxide against decomposition, which stabilized cyclohexene
oxide would be particularly effective in stabilizing unsaturated chlorinated
solvents against metal induced decomposition in addition to having the
capacity to neutralize any hydrochloric acid decomposition product.
Description of the Invention
In accordance with this invention, it has been found that
cyclohexene oxide is stabilized against peroxidative decomposition by
the inclusion therein of a stabilizing amount of di-n-butyl sulfoxide.
A~though di-n-butyl sulfoxide has been found to be particularly
effèctive in stabilizing cyclohexene oxide against peroxidative decomposition,
it is contemplated that other dialkyl sulfoxides would be suitable for use
in the invention. Such other dialkyl sulfoxides may be represented by the
general formula, R2S = 0, wherein R is a C2 to C8, preferably C2 to C4,
aliphatic radical that must contain at least one hydrogen atom on a beta-carbon
atom. Some other aliphatic radicals of which R is representative include,
for example, ethyl, n-propyl, isopropyl, t-butyl, sec-butyl, isobutyl,
hexyl, cyclohexyl, 2-ethylhexyl, 2-phenoxyetbyl, and the like. The quantity
~Z4733
of dialkyl sulfoxide used to stabilize cyclohexene oxide may vary over a
range of from about 0.3 percent to 20 percent by weight, preferably from
about 0.5 percent to 5.0 percent by weight, and most preferably from about
0.9 percent to 2.0 percent by weight based on the weight of cyclohexene
oxide.
The dialkyl sulfoxide stabilized cyclohexene oxide is particularly
effective in stabilizing chlorinated solvents such as perchloroethylene
against aluminum induced decomposition. When used to stabilize chlorinated
solvents, the dialkyl sulfoxide stabilized cyclohexene oxide is employed in
typical stabilizing amount, usually rom about 0.01 to 0.5 percent, prefer-
ably from about 0.1 to 0.3 percent by weight of cyclohexene oxide based on
the weight of solvent, although as much as 5.0 percent by weight may be
used.
The cyclohexene oxide may be stabilized with dialkyl sulfoxide
~15 prior to stabilizing the solvent or unstabilized cyclohexene oxide anddialkyl sulfoxide may be added separately to the solvent thus stabilizing
the cyclohexene oxide in situ.
The stabilization afforded cyclohexene oxide by dialkyl sulfoxide
is not appreciably affected by the presence of stabilizing amounts of other
commonly used chlorinated solvent stabilizing components such as, for
example, phenols, alcohols, esters, amines, amides, nitriles, and the
like.
The invention is further illustrated but is not intended to be
limited by the following examples.
~1247~3
Example 1
A series of stabilized perchloroethylene samples was prepared
using the following stabilization systems. The stabilizing materials are
expressed as percent by weight based on the weight of perchloroethylene:
Sample No. 1 2 3 4 5
CH0 0.27 0.27 0.27 0.27 0.27
HQMME 0.01 0.01 0.01 0.01 0.01
NMM 0.005 0.005 0.005 0.005 0.005
EPN 0.06 0.06 0.06 0.06 0.06
BHT 0.00135(a) ~
DNBS ~~ - O.OOl(b) 0.0025(c) 0.005(d)
(a) 0.5 weight percent BHT based on weight of CH0
(b) 0.37 weight percent DNBS based on weight of CH0
(c) 0.93 weight percent DNBS based on weight of CH0
(d) 1.86 weight percent DNBS based on weight of CH0
Le8end: CH0 - cyclohexene oxide
MQMNE - hydroquinone monomethyl ether
NMM - N-methylmorpholine
EPN - beta-ethoxypropionitrile
BHT - butylated hydroxytoluene
DNBS - di-n-butyl sulfoxide
4~:~3
100 milliliters of each of the above stabilized solvents were
placed in individual 250 milliliter Erlenmeyer flasks. A 2024 aluminum
coupon measuring 112 inch x 4 inches x 1/32 inch was placed in each flask.
Each coupon was polished with a crocus cloth and cleaned with acetone
immediately prior to its being placed in its respective flask. Each flask
was provided with a reflux condenser and heated to refluxing temperature.
The flask contents were refluxed until visible signs of corrosion, i.e.,
black spots, appeared on the coupons. Under the microscope, these spots
appeared as small craters covered with a reddish-brown powder.
The results of the reflux tests are as follows: -
Days Until Days Until
SampleCorrosion Observed Test Terminated
1 5 5
2 6 6
3 10 10
4 None 35
None 35
Example 2
A simulated glass degreaser was constructed from a three-
liter capacity, one-neck, round bottom flask, a two-liter capacity flask,
and a water-cooled condenser.
The condenser outlet was connected by rubber tubing to a safety trap
and a silver nitrate trap connected in series. The two-liter flask
was modified by inserting and fusing a piece of glass tubing with a
24/40 T male joint through the bottom of the flask. One end of the
tube extended about halfway into the flask such that about one liter
- 5 -
l~lZ~33
of solvent could be collected before overflowing back into the bottom
three-liter flask ~simulated boiling sump). Before starting the test,
about 60 grams each of 2024 and 7075 aluminum turnings, 200 milliliters
of Limex #78 oil and two liters of perchloroethylene were added to the
boiling sump. The modified two-liter flask (simulated rinse tank) was
fitted to the three-liter flask and 500 milliliters of perchloroethylene
were added to the two-liter flask. The assembly was heated to and maintained
at reflux temperature by means of a Variac controlled heating mantle.
Solvent decomposition was indicated by the appearance of a white silver
chloride precipitate in the silver nitrate trap.
One test was run using perchloroethylene that was stabilized by
the addition thereto of 0.27 weight percent cyclohexene oxide, 0.005 weight
percent di-n-butyl sulfoxide, 0.01 weight percent hydroquinone monomethyl
ether, 0.06 weight percent beta-ethoxyproprionitrile and o.oa5 weight
percent N-methylmorpholine (solvent A).
Another test was run using perchloroethylene stabilized as
above except that no di-n-butyl sulfoxide was added ~solvent B).
Samples of perchloroethylene were taken from the boiling sump at
periodic intervals and analyzed acid acceptance. The results of these
tests are summQrized as follows: -
Solvent A Solvent B
Days Acid Acid
Reflux pH Acceptance,%pHAcceptance,%
0 8.60 0.10l 8.350.1043
1 - -- 8.400.0859
6 8.35 0.089 --
11 8.41 0.0818 7.550.0276
~ ~ra4~ ~1aY~ .
-- 6 --
~lZ~733
Solvent A Solvent B
Days Acid Acid
Reflux pHAcceptance,% pHAcceptance,%
13 8.43 0.0818
14 -- 5.15-0.0356
18 8.36 0.0815 --
8.33 0.0807 - --
As seen from the above, perchloroethylene stabilized with
unstabilized cyclohexene oxide ~solvent B) de~elops acidity quite rapidly
under simulated degreasing conditions as compared with perchloroethylene
stabilized with di-n-butyl sulfoxide stabilized cyclohexene oxide (solvent
A). Moreover, examination of the aluminum turnings showed no attack from
solvent A whereas the aluminum turnings were severely pitted from solvent B.
The acid acceptance of the solvent is a measure of the capa-
city of the solvent to neutralize hydrochloric acid ant is expressed in
percent by weight of equivalent sodium hydroxide. The acid acceptance
is determined as follows. To an Erlenmeyer flask is added 25 milli-
liters of 0.1 N hydrochloric acid in isopropyl alcohol, 10 milliliters
of solvent, and 25 milliliters of isopropyl alcohol. The contents of
the flask are thoroughly mixed, the flask is stoppered and allowed to
stand for 10 minutes at room temperature. Three drops of bromophenol
blùe indicator are added and the flask contents are titrated with 0.1 N
sodium hydroxide to the blue-green end point.
A blank determination is made by titrating 25 milliliters of
0.1 N hydrochloric acid in isopropyl alcohol and 25 milliliters of iso-
propyl alcohol with 0.1 N sodium hydroxide to the blue-green bromophenol
blue end point.
~33
Acid acceptance in weight percent equivalent sodium hydroxide
is calculated as follows:
Acid Acceptance = (K-S)N x 0.04 x 100
W
wherein:
K = milliliters of NaOH solution required for the
blank titration;
S = milliliters of NaOH solution required for the
sample titration;
N = normality of the NaOH solution; and
W = grams of sample (volume in milliliters x specific
gravity).
Example 3
The perchloroethylene solvents A and B prepared as described
in Example 2 were tested in a Baron-Blakeslee model ~VW-125 vapor-Ypray
degreaser.
After 814 hours of operation, a sample of solvent A taken
from the boiling sump had a pH of 7. 91 and an acid acceptance of 0.112
percent. No sign of corrosion was observed on a 2024 aluminum test panel
that had been immersed in the solvent in the boiling sump throughout the
test period.
After 574 hours of operation, a ~ample of solvent B taken
from the boiling ~ump had a pH of 7. 7 and an acid acceptance
of 0.094 percent. A 2024 aluminum test panel that had been immersed
-- 8 --
i~33
in the boiling sump throughout the test period was severely corroded
and pitted.
Although the invention has been described with specific ref-
erences and specific details of embodiments thereof, it is to be understood
that It is not intended to be so limited since changes and alterations
therein may be made by those skilled in the art which are within the full
intended scope of this invention as defined by the appended claims.
~247~3
SUPPLEr~lENTARY DISCLOSURE
The principal disclosure of this application specifies the dialkyl
sulfoxide used to stabilize cyclohexene oxide according to the invention as
being of the formula R2S=O wherein R is an aliphatic radical containing 2 to
8 carbon atoms having at least one hydrogen atom on a beta-carbon atom. The
definition of the R groups was specified in that manner to clearly exclude
dimethyl sulfoxide. It has now been found, however, that dimethyl sulfoxide
is an effective stabilizer for cyclohexene oxide against peroxidative
decomposition and in fact is one of the most preferred dialkyl sulfoxides for
this purpose, the other most preferred being di-n-butyl sulfoxide as set out
in the principal disclosure.
FurtheL-more~ in the general formula representing the dialkyl
sulfoxides which can be used according to the present invention, the alkyl
groups need not be the same but can be different.
Thus, according to the present invention cyclohexene oxide is
stabilized against peroxidative decomposition by the inclusion therein of a
stabilizing amount of dialkyl sulfoxide o~ formula
R
~=0
Rll
wherein R and R are the same or different and represent alkyl radicals of 1
to 8 carbon atoms, preferably 1 to 4 carbon atoms.
The amounts of dialkyl sulfoxide according to the aforementioned
formula which may be used are those set out in the principal disclosure for
the dialkyl sulfoxides disclosed therein as stabilizers and the other
- 9a -
conditions and considerations of the principal disclosure apply here also.
The following examples further illustrate the invention but are not
to be taken as limiting thereto.
Example 4
Perchloroethylene solvent stabilized by the addition thereto of 0.27
weight percent cyclohexene oxide, 0.0035 weight percent dimethylsulfoxide,
0.01 weight percent hydroquinone monomethyl ether, 0.06 weight percent
beta-ethoxyproprionitrile and 0.005 weight percent N-methylmorpholine was
tested in the Baron-Blakeslee MVW vapor-spray degreaser referred to in Example
L0 3 of the principal disclosure.
The stabilized perchloroethylene had an initial p~/titer of
8.27/1.2. After 744 hours of operation, a sample of solvent taken from the
boiling sump had a pH/titer of 7.83/0.5. No si~n of corrosion was observed on
a 2024 aluminum test panel that had been immersed in the solvent in the
boiling sump throughout the test period.
Example 5
Perchloroethylene was stabilized by the addition thereto of 0.27
weight percent of cyclohexene oxide, 0.01 weight percent of hydroquinone
monomethyl ether, 0.005 weight percent of N-methylmorpholine, 0.06 weight
percent of beta-ethoxypropionitrile and 0.0035 weight percent of dimethyl
sulfoxide. To a 250milliliter Erlenmeyer flask was added 100 ~illiliters of
the stabilized p~rchloroethylene. One strip each ~measuring 0.5 x 2~5 inches~
of polished type 3003 aluminum, pure copper and type 1010 mild steel were
placed in the flask such that each strip was partly immersed in the liquid and
partly exposed to the vapor phase. The flask was heated to reflux and
maintained at reflux for 168 hours. At the end of the reflux period, the
metal strips were inspected and showed no visible signs of discoloration or
corrosion.
~1^"'`
- 9b -
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