CA1049567A - Inhibition of aromatic compound degradation of methylene chloride - Google Patents

Abstract

ABSTRACT
Diisopropylamine, N-methyl pyrolle, butylene oxide, propylene oxide, methyl acetate, acetone, tertiary amylenes and optionally methyl alcohol in admixture with methylene chloride have been found to prevent degradation of methylene chloride in the presence of metals, metal halides, combinations thereof, and aromatic compounds, which react with methylene chloride in the presence of said metals, metal halides and combinations thereof. A method for vapor degreasing metals by using the stabilized methylene chloride is described.

Description

~IL0495~7 BACKGROUND OF THE INVENTION
Methylene chloride is a highly versatile and useful solvent for various industrial applications at both normal and elevated temperatures. A particularly important industrial use is the vapor degreasing of metals. Methylene chloride is ,known to be more stable than other chlori,n~ted hydrocarbons solvents such as perchloroethylene, trichloroethylene and methyl chloroform when the solvents are used in unstabilized condition. For example, methylene chloride is more resistant to oxidation, hydrolysis and pyrolysis than other chlorinated solvents and does not substantially react with aluminum in '~
the aluminum scratch test commonly used to indicate unstabilized or minimally stabilized methyl chloroform. In addition, methylene chloride may be used to greater advantage in vapor degreasing of metals than other known degreasing solvents since it may be used effectively at lower temperatures due to its lower boiling point and excellent stability. MethyLene chloride is particularly desirable for such degreasing operations since it is substantially resistant to photochemical activity 20 and therefore does not contribute to air pollution by smog '-`
formation. However, methylene chloride when used in various metal cleaning functions, including vapor degreasing, suffers the disadvantage of being reactive with aromatic compounds in the presence of metals, metal halides and combinations thereof, including aluminum, zinc and iron, halides thereof, and com~
binations of said metals and halides which react with the methylene chloride to produce hydrochloric acid and objection- ' able high boiling tarry substances which render the methylene chloride unsuitable for further useO The entire reaction of methylene chloride in the presence of aromatic compounds is : -2-~4~567 not completely understood but is bel.ieved to be a condensation reaction catalyzed by metal, metal halides or combinations thereof~ Thus, the aromatic compound reaction wit.h methylene chloride is believed to be catalyzed, or inltiated and catalyzed by the presence of metals such as aluminum, zinc, iron and the like, halides of said metals and combinations ':
of said metals and halides. Such ,reactions are thought to be of the nature of a Fxiedel-Craft type reaction. Aromatic . ~
organic compounds of this nature and metals such as aluminum, .~ ' .' 10 iron and zinc, their halides and combinations are generally ~
introduced into the methylene chloride from various cutting ~: ' oils and Iubricants used in metal fabricating operations : -which are carried over into the methylene chloride solvent during vapor degreasing or other cleaning of the fabricated ~;
metal parts. Solvent manufacturing, handling and storage equipment is another source for introduction of such impuritiesO
To prevent degradation and other types of deterioration such as oxidation, hydrolysis and pyrolysis whi.ch may occur in some instances, it has been the practice to incorporate ~ 20 minor quantities of various organic compounds into methylene ;~ chloride, which compounds act as stabilizers to substantlally '.' , prevent such degradationO It is desirable to provide methylene chloride stabilized to effectively prevent degra-dation in various applications/ and the demand still exists for a low cost stabilized methylene chloride composition that can be easily prepared and which provides optimum stabiliza-tion under many different operating conditions~
. SUMM~RY OF THE INVENTI_ .
An object of this invention is to prevent deterloration 30 or degradation of methylene chloride in assocat.ion with metals, ~' :

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~49567 metaL halides and combinatl.ons inclu,ding aluminum, iron and zinc, halides oE sai.d metals and combinations and an aromatic compound capable of reacting w.ith methylene chlo:ride in the presence of said metals, metal halides and combinations.
A further object of this invention is to provide a stabilized methylene chlo:ride composition in which the stabilizers are low in cost. and capable of being incorporated with ease into ~he methylene chlorideO
A still further object of this invention is to provide a process for the degreasing of metals b,y contacting the metals with methylene chloride stabilized to prevent degrada-tion of the methylene chlor.ide in the presence of metals, metal halides and combinations thereof including aluminum, iron and zinc r halides of said metals and combinations and aromatic compounds which react w.ith the meth,ylene chloride in the presence of said metalsl metal halides and combinations thereof.
Still another object of this inven.tion ,is to provide a process for the degreasing of metals by contacting the metals 20 with methylene chlo.ride stabilized to prevent deg.radation ; ::-of the methylene chloride in the presence of impurities such as reactive aromatic compounds and metals including aluminum, : ' iron, zinc and the like~ halides of said metals and comb.ina~
tions of the individual metals and salts thereof. ~ ~
These and additional objects of the present invention - :-will become apparent to those skilled in the art from the ,~,'. ,~
description and claims which follows~
DESCRIPTIO_ OF THE PREFER~ED EMBODIMÆNTS .
The objects set fo.rth above have been found to be attained by provid.ing a compositlon consisting essentialLy . .~ .

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:~L049567 of methylene chloride containing stabilizing amount of from about 0.001 to about 2.0 percent by weight of tne methylene chloride of each of diisopropylamine, N-metnyl pyrolle, butylene oxide, propylene oxide, methyl acetate, acetone, tertiary amylenes and optionally methyl alcohol. ;~
The quantity of the stabilizing agents useful in the practice of this invention will vary depending upon the con-ditions of use, the identity and ~uantity of other stabilizers incorporated into the methylene chloride and other practical ;
operating considerations. ~ach stabilizing agent or compound may generally be used within the range of from about .001 to about 2.0 percent and preferably from about 0.002 to about 1.0 percent by weight of the methylene chloride. Although higher concentrations may be used, if desired, no additional benefit is obtained and the cost is unnecessarily increased.
While the above composition containing stabilizing agents provides optimum prevention of degradation of the methylene chloride under a variety of operating conditions it is also possible to stabilize methylene chloride by deleting the propylene oxide depending on the stabilization required for the particular operating conditions.
Tne stabilized composition may be used for the degreasing ` of metals by contacting the metals with the stabilized composition. Thus, the process for vapor degreasing metals comprises contacting the metals to be degreased with the above described stabilized methylene chloride compositions i wherein the methylene chloride contains an admixture of `li stabilizing amounts of diisopropylamine, N-methyl pyrolle, butylene oxide, propylene oxide,methyl acetate, acetone, tertiary amylenes and optionally methyl alcohol. In degreasing `~ metals with the above described preferred stabilized methylene _5_ ~ . , ` '": " , 10495~7 chloride in the presence of an aromatic compound which reacts with methylene chloride in the presence of metals, metal halides and combinations thereof including aluminum, iron, zinc, halides of said metals and combinations, there exists upon contact of the metal with the stabilized methy-lene chloride a composition comprising methylene chloride, a stabilizing amount of from about 0.001 to about 2.0 weight percent of the methylene chloride of each of diisopropylamine, N-methyl pyrolle, butylene oxide, propylene oxide, methyl acetate, acetone, tertiary amylenes, optionally methyl alcohol, and an organic compound which reacts with methylene chloride in the presence of said metals, metal halides and combinationsO The metals, metal halides and combinations may be present from any source such as chloride formed by drilling -.
or other machining of aluminum or aluminum-containing materials with various working fluids such as cutting oils, lubricants : -and the like, or aluminum chloride may be present from the reaction of methylene chloride with aluminumO The reactive aromatic compounds include toluene, mesitylene, napthalene, and the like~
In order that those skilled in the art may readily understand the present invention and certain specific embodi- .. -ments by which it may be carried into effect the following ~ :
illustrative examples are presented. .
In Examples 1 and 2, respectively, of Table I, 15 ml.
of substantially water free methylene chloride and methylene .;
chloride stabilized with the specified quantities of diiso-propylamine, N-methyl pyrolle~ propylene oxide, butylene . oxide, methyl acetate, acetone, tertiary amylenes and methyl ; 30 alcohol were placed in glass vials containing a 1 cm2 aluminum ~.
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. : . . ,, ! , 9St;'7 coupon 1~64" thick. The vials were tightly capped and allowed to stand at ambient conditionsO After 16 hours no changes had taken place in the appearance of the solvent, the pH or the aluminum in each vial. Toluene in an amount of 5~ by volume and about 0.04 grams of anhydrous aluminum chloride were then added to each vial, the contents stirred, changes in the contents recorded, and the vials loosely capped and allowed to stand. After four hours and after twenty-two hours changes in the appaarance of the aluminum coupons and the solvents, and relative pH values of the solvents, were recorded. The procedure of Examples 1 and 2 was followed in Examples 3 to 7 of Table I. In the latter Examples various compounds reported in ths prior literature to be useful in stabilizing chlorinated solvents were evaluated for their ability to stabilize methylene chlorideO In Examples 3 to 7 after the tightly capped vials had been standing for 16 hours no changes had occurred in the appearance of the solvent, the pH or the aluminum coupons. The results of the tests of Examples 1 to 7 are set forth in Table Io " ' '~
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~049567 From Table I it will be readily observed that after four hours the methylene chloride without the stabilizing composition of this invention had undergone a degradation reaction resulting in a dark orange coloration, evolvement of hydrogen chloride gas and complete loss of utility of the solvent.
Examples 3 to 7 inclusive of Table I show that various com-pounds frequently used as solvent stabilizers are not as effective as the stabilizing composition of this invention in :
inhibiting degradation of methylene chloride by reaction of aromatic compounds with methylene chloride in the presence of ~ ,: . -: -metals, metal salts and combinations thexeof.

In Examples 8 to 12 of Table II, below, aluminum reflux ~ :
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stability tests were carried out by placing 200 ml of methylene chloride in a 300 ml flask, adding about 1.0 grams of 20 mesh granular aluminum and suspending a bright aluminum coupon about 2 x 7 cmO in a condenser fitted to the flaskD Methylene chloride and the solvent containing 5~ by volume of Mesitylene, 5% by volume of Mesitylene with the stabilizing composition ~
of this invention and 5% by volume of Durene were refluxed for :: .
varying time periods. In the tests the pH and acid content, as HCl, were determined and visual observations of the aluminum condenser coupon were made at the completion of the test~ The .
results of these tests are set forth in Table II below.
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The tests in Table II were conducted by venting the condenser to room air and without the addition of water.
Also in Table II the pH determinations were made with a portion of the water layer obtained by extraction of the solvent with water equal to the volume of the solvent system.
Table II illustrates the prevention of degradation of methylene chloride by the stabilizing components of this ' ~ -invention in the presence of aluminum and the aromatic com-pound Mesitylene in Example lOo Examples 9 and 11 to 12 show degradation of methylene chloride in the presence of the aromatic compounds Mesitylene and Durene (tetramethyl benzene) when refluxed with aluminum in the absence of the stabilizing composition of this invention.
In Table III hydrolytic stability tests were made by placing 150 ml. of methylene chloride in Example 13 and 150 ml.
of methylene chloride containing the stabilizing composition specified in Example 14 into a 300 ml. boiling flask. The flask was fitted with a Soxhlet extractor equipped with a syphon break and a condenser vented to room air. Fifty milli-liters of the solvent of each Example were first introducedinto the Soxhlet and 50 ml. of water was then added. One gram of 20 mesh granular aluminum, about one gram of 30 mesh -~
granular zinc and about 0.1 g of iron powder were placed in the flask. A 2 x 7 cm. zinc coupon of known weight was positioned in the Soxhlet and a 2 x 7 cm. weighed steel coupon was mounted in the condenser. The contents of the flask were refluxed for the period of time specified by heating the boiling flask with an electric heater. At the end of the reflux period the pH and alkalinity, as NaOH, of the solvent contents of the So~hlet and of the flask were determined from a portion of the aqueous phase obtained by extraction of the solvent with an equal volume of neutral distilled water after the solvent system had been refluxed for the time specified~
The zinc and iron coupons were cleaned of any accumulated corrosion products, weighed and the difference in initial and f.inal weight recorded as weight loss, The results are shown below in Table III.

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~L~49567 The superiority of the stabilizing composition of this invention is evident ~rom a comparison of the results of Example 14, the composition of the present invention, and Example 13, a stabilizing composition of known good stabilizing characteristics formulated by the applicant hereinO Much less corrosion of the zinc coupon in the Soxhlet and the iron coupon located in the condenser occurred in the use of the composition of this invention during the 15 day reflux period.
In Examples 15 and 16 of Table IV reflux stability tests were conducted by following Federal Specification O-T-236b modified by the use of 200 ml. of the solvent system in place of 100 ml. and by positioning a 6-watt ultra-violet lamp about one inch from the vapor tube of the Soxhlet extractor. A 300 ml. boiling flash was fitted with a Soxhlet extractor, a condenser connnected to the extractor, about 1.0 gram of granular zinc and about 0.5 ml. of water was added . ~-to the flask and a 2 x 7 cm~ zinc coupon was inserted in the extractor and the condenser. The condenser was vented to a water scrubber.
The results of the tests are presented in Table IV

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~o~5~;7 Storage stability tests of stabilized methylene , chloride carried out in Examples 17 ko 19 of Table 5O About 250 ml each of three stabilized methylene chloride composition~
specified in the Examples was placed in a pint bottle contain-ing three lJ16" diameter x 5" rusty steel rods and two 1/2" x 6" x 0,003" gauge rusty steel coupons. About lo 32 ml ~0~4 WtD%~
of distilled water was added and the entire contents of the bottle thoroughly agitated at the start of the test period.
In Example 17 an additional 0. 4 wto % was added to the bottle after one day~ The capped bottles were permitted to stand for five days after which visual observations of the steel coupons, the solvent and the surface of the solvent were made and recordedO The bottles were then uncapped and any detectable objectionable odor noted.
The results of the tests are included in Table V.

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, 1~4956t7 The superiority of the compos.it.ion of this i.nvention in stabilizing methylene chloride on exposure to water and rusty steel storage conditions is evidenced by the .result.s of Example 19 as compared to the results of the tests in Examples 17 and 18 in which two different stabllizing compo-sitions known in the axt were usedO In Example 19 no uncharac teristic odor was detected but both Examples 17 and 18 had an objectionable putrid odor.
- Although the present invention has been described with .
detailed reference to specific embodiments thereofl it is not intended to be so limited since modiflcations and alter-ations may be made therein which are wit.hin the complete intended scope of this invention as defined by the appended claims.

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Claims (10)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A methylene chloride composition inhibited against degradation, containing from about 0.001 to about 2.0 percent by weight of the methylene chloride of each of diisopropylamine, N-methyl pyrolle, butylene oxide, propylene oxide, methyl acetate, acetone and tertiary amylene.

2. The composition of claim 1 wherein methyl alcohol is also present.

3. The composition of claim 1 wherein diisopropylamine, N-methyl pyrolle, butylene oxide, propylene oxide, methyl acetate, acetone, tertiary amylene and optionally methyl alcohol are each present in from about 0.002 to about 1.0 percent by weight of the methylene chloride.

4. The composition of claim 3 wherein methyl alcohol is present.

5. A method for preventing the degradation of methylene chloride in contact with metals, metal halides or combinations thereof and an aromatic compound capable of reacting with methylene chloride in the presence of said metals, halides and combinations comprising maintaining in intimate admixture with said methylene chloride while in contact with said metals, halides and combinations and said aromatic compound from about 0.001 to about 2.0 percent by weight of the methylene chloride of each of diisopropylamine, N-methyl pyrolle, butylene oxide, propylene oxide, methyl acetate, acetone and tertiary amylene.

6. The method of claim 5 wherein methyl alcohol is also present.

7. The method of claim 5 wherein the admixture contains from about 0.002 to about 1.0 percent by weight of the methylene chloride of each of diisopropylamine, N-methyl pyrolle, butylene oxide, propylene oxide, methyl acetate, acetone, tertiary amylene and optionally methyl alcohol.

8. The composition of claim 7 wherein methyl alcohol is present.

9. A process for degreasing metals which comprises contacting said metals with a methylene chloride composition stabilized against degradation by metal in the presence of aromatic compounds with stabilizing amounts of from about 0.001 to about 2.0 percent by weight of the methylene chloride of each of diisopropylamine, N-methyl pyrolle, butylene oxide, propylene oxide, methyl acetate, acetone and tertiary amylene.

10. The process of claim 9 wherein methyl alcohol is also present.