CA2079195A1

CA2079195A1 - Method and additive for stabilizing degreasing compositions based on halogenated solvents

Info

Publication number: CA2079195A1
Application number: CA002079195A
Authority: CA
Inventors: Pascal Michaud; Jean-Jacques Martin
Original assignee: Individual
Current assignee: Arkema France SA
Priority date: 1991-09-27
Filing date: 1992-09-25
Publication date: 1993-03-28
Also published as: FI924318A0; JPH07196545A; KR930005950A; NO923715D0; EP0534829A1; FI924318A7; FI924318L; NO923715L

Abstract

A B S T R A C T

METHOD AND ADDITIVE FOR STABILIZING DEGREASING
COMPOSITIONS BASED ON HALOGENATED SOLVENTS

The invention provides a method for stabilizing compo-sitions based on halogenated solvents such as those used for degreasing metals, which consists in adding limonene epoxide in an amount of 0.01 to 5% by weight to said compositions, and the stabilized compositions thus obtained.

Description

~7~

METHOD AND ADDITIVE FOR STABILIZING DEGREASING
COMPOSITIONS BASED ON HALOGENATED SOLVENTS

BACKGROUND OF THE INVENTION
Field of the invention The present invention relates to a me-thod for stabiliæ-ing compositions based on halogenated solvents and to ad-ditives employed ~or this purpose. It also relates to the compositions thus obtained, that contain said additives, and to the use of said compositions in the degreasing and clean-ing of metal parts. The invention also xelates to a method for obtaining stabili~ed compo~itions of halogenated solvents of formula CnHzFpCly, in which 1 < n < 6, p > 0, y ~ 1, z ~
0, as well as to the additives employed for this purpose, the compositions that are thus obtained and containing said additives, and the abovesaid application of said compos-itions.
Halogenated solvents, for example, methylene chloride, trichloroethylene, perchloroethylene, 1,1,1-trichloroethane, are widely used in industry. 1,1,1 trichloroethane (or methyl-chloroform) in particular, is employed for ob-taining aerosols, for dry cleaning purposes and for degreasing and/or cleaning metal parts or components which have for example been wetted by cuttiny oils. The problem that the use of chlorinated and/or 1uorinated organic solvents, in particu-lar 1,1,1 trichloroethane, poses is their tendsncy to decom-pose in the presence of lightweight me-tals and alloys there-of. This particular problem hence limits their use as a degreasing and/or cleaning agent for metal parts in aluminum, magnesium or alloys thereof. It is known that 1,1,1-tri-chloroethane, in the presence of a scratched or rubbed , .

2 0 ~

aluminum surface is unstable and decomposes in a fairly shortperiod of time forming a black tar-like slurry the compos-ition of which is practically uncontrollable. A change in pH accompanies this decomposition, becoming basic or acid as a function of the cutting oil used, hydrochloric acid being formed in the lat-ter of -the two cases. Moreoverr whenever a chlorinated or fluorinated organic solvent in the form of a thin film is subjected to pressure between two sheets of aluminum, the pronounced tendency of the solvent to decompose is enhanced. D0composition in the vapor phase also takes place during hot degreasing operations. Numerous additives have hence been pu~ forward for the purpose of preventing or at least minimising decomposition of these solvents, leading to -their becoming colored, to the formation of undesirable by-products and to loss of their solvent properties.
The various additives proposed for stabilizing halogen-ated solvents can be nitro-alkanes, saturated or unsaturated alcohols, ethers, nitriles, esters, phenolic derivatives, epoxy derivatives and mixtures thereof. Epoxy derivatives are currently used, alone or mixed with other stabilizers known in the art. Butylene oxide is the stabilizer that is most frequently used at present, on account of its price.
Several compound have been proposed as a replacement for butylene oxide, including particular epoxy compounds.
Prior art EP-A-044 111 (Solvay) describes stabilizing composi-tions of halogenated solvents containing 2-methyl-2,3-epoxy-butane. Wacker Chemie has proposed several epoxy compounds suitable for replacing butylene oxide. These include, for example: cyclohexene oxide, 4-vinyl-cyclohexene, 7,8-epoxy-octene. Conventionally, the epoxy compounds employed are selected from: epoxypropane, epoxybutane, 2-methyl-epoxy-propanes, 2-methylepoxybutanes and epichlorhydrine.
No publication teaches nor sugges-ts the particular use of the epoxy compounds according to the invention, nor the 2 ~ g ~

unexpected and surprising results that come about from their use.
SUMMARY OF THE INVENTION
- The invention hence provides an additive for stabiliz~
ing a halogenated solvent composition of formula CnHzFpCly, in which 1 < n < 6, p > 0. y ~ 1,z > 0. said additive contain-ing from O.0001 to 16.5% by weigh-t of limonene epoxide.
The expression 'llimonene epoxide" as employed in the present invention means the 1,2 epoxide of limonene, in other words this means that the epoxy function is carried by the double bond located on the cycle~
In one preferred embodiment, the additives includes one at least of the following co-stabilizers:
a) a C2 to C7 epoxy compound different from limonene epox-ide,b) a C1 to C7 saturated alcohol, c) a C3 to C6 unsaturated alcohol, d) a Cl to C4 nitro-alkane, e) mono- or poly-cyclic internal ether, ~0 f) a C3 to C10 aliphatic or an aromatic amine, g) a nitrogen-containing heterocyclic compound.
In a preferred embodiment, the components a), b), c), d), e), f) and g) are present in respective amounts of:
a) 0-~ to 16.50 ~ b) 0.001 to 16.50 ;~ c) 0.001 to 16.50 ` d) 0.001 to 10.00 e) O.OOl to 16.50 f) O to 3.33%
g) O to 3.33%
by weight based on the weight of said additive.
The invention also provides a method for stabilizing a composition based on halogenated solvents of formula CnHzFpCly, in which 1 < n < 6, p > 0. y > 1,z > 0 comprising the addition to said solvents of 0.01~ to 5~ by weight, based 2~79~ ~

on the weight o~ the solvents of limonene epoxide. The meth-od pre~erably consists in the addition to said solvents of an amount of 0.2~ to 3% by weight, based on the weight of said solvents, of limonen~ epoxide.
In a preferred embodiment, the composition addi-tionally contains at least one of the ~ollowing co-stabilizers:
a) a Cz to C7 epoxy compound different from limonene epox-ide, b) a C1 to C7 saturated alcohol, c) a C3 to C6 unsaturated alcohol, d) Cl to C4 nitro-alkane e) mono- or poly-cyclic internal ether, f) a C3 to C10 aliphatic or an aromatic amine, g) a nitrogen-containing heterocyclic compound.
The C2 to C7 epoxy compound dif~erent from limonene epoxide makes up 0 to 5~ and preferably ~rom 0% to 3% by weight, based on the weight of said composit~on and is seleot~
ed from the group comprising: epoxypropane, epoxybutane, 2-methyl-epoxypropanes, 2-methyl-epoxybutanes, epichlorhy-drine and mixtures thereo~.
The C1 to C7 saturated alcohols make up from 0.1 to 5~, preferably 0.5 to 3.5~ by weight o the composition. Examples o~ such saturated alcohols are: methanol, ethanol, propanol, isopropanol, butanol-l, butanol-2, tertiary butylic alcohol, pentanols such as tertiary amylic alcohol, methylcellosolve, ethylcellosolve, propylcellosolve, butylcellosolve, glycer-ine, ethyleneglycol, propyleneglycol, 2-hydroxy-2-methyl-3-butanone, 3,3-dimethoxy-2-methylbutanol-2 and 3-amino-2-methyl-butanol-2. Preferred saturated alcohols are: propanol, ter-tiary and secondary butanol and tertiary pentanol. Tertiarybutanol is the saturated alcohol that is particularly preferred.
The C3 to C6 unsaturated alcohols are added in an amount of 0.1 to 3~, preferably 0.3 to 3~ by weight, to said compo-sition based on the weight thereof. Preferred unsaturated alcohols are: allylic alcohol, 2-methyl-3-butene-2-ol and 2 ~

2-methyl-3-butyne-2-ol.
The Cl to C4 nitro-alkanes are added in an amount of from 0.1 to 3%, preferably from 0.5 to 1.5~ hy weight of said composition. Preferred nitroalkanes are: nitromethane, nitro-ethane, nitropropane-l or -2 and mixtures thereof. Nitro methane and/or nitroethane are particularly preferred.
The internal ethers make up O.l to 5~- and preferably 0.5 to 2.5% by weight of said composition. Suitable internal ethers for use as co-stabilizers comprise: mono- or poly-cyclic ethers, optionally containing other hetero-atoms, containing ons or several saturated or unsaturated optionally substituted cycles having 5 or 6 carbon atoms such as 1,3-dioxanne, 1,4-dioxanne, 1,3,5-trioxanne, 1,3-dioxolanne, dio~ene, dioxadiene, thioxanne, oxazole, tetrahydrofuranne, or diphenyl oxide. The preferred ether is 1,3,5-trioxanne~
The C3 to C10 aliphatic or aromatic amines are, present in an amount of from 0 to 1~ by weight, preferably from 0.005 to 0.1% by weight, based on the weight of the composition.
Sui-table amines are those having 3 to lO substituted or un-substituted carbon atoms such as secondary and tertiary ali-phatic amines and aromatic amines such as aniline optionally substituted by C1 to C4 alkyl groups or chlorine atoms.
Preferred amines are triethylamine, diisopropylamine, amyl-amine, hexylamine. Diisopropylamine is particularly pre-ferred.
The nitrogen-containing heterocyclic compounds are present in an amount of from O to 1~, preferably 0.005 to 0.1% by weight based on the weight of the composition.
Suitable compounds are those having 4 to 12 carbon atoms and 1 to 2 nitrogen atoms in their molecule, such as pyridine, the plcolines, phenothiazine, morpholine, pyrrole and pyrrol-idine and derivatives thereof substituted by alkyl groups on the nitrogen atom. Preferred heterocyclic compounds are N-met~ylmorpholine, diisopropylamine, pyrrolidone and N-methylpyrrole. Particularly preferred heterocyclic compounds ' 2 ~ 7 ~

are N-methylmorpholine and N-methylpyrrole.
The compositions stabilized in accordance with the present invention are halogenated solvent compositions. They have the formula CnHzFpCly, in which 1 < n ~ 6, p > 0. y > 1, z > 0. The number z can be zero or non-zero, as a function of the degree of substitution or unsaturation of the carbon chain; z is thus adjusted so as to preserve the carbon's tetravalency. Examples of such solvents are: 1,1,1-trichloro-ethane, trichloroethylene, perchloroethylene, methylene chloride, and mixtures thereof. The preferred solvent is l,1,1-trichloroethane.
Compositions stabilized according to the present in-venti~n can also contain other conventional co-stabilizers such as esters, nitriles, ketones, phenolic compounds and olefinic compounds, and can be present in an amount o up to 5% by weight, based on the weight of the composition.
Esters that can be employed as co-stabilizers are sat~
urated or unsaturated mono~ and di-esters having 2 to 8 car-bon atoms, optionally substituted by halogens or hydroxyl ~roups, such as ethyl, propyl, isopropyl, butyl, sec-butyl, tert-butyl, amyl, hexyl and cyclohexyl formates; methyl, ethyl, propyl, isopropyl, butyl, amyl, ethynyl or propynyl acetates; methyl, ethyl, propyl, isopropyl, butyl, amyl and ethynyl propionates; methyl, ethyl, propyl, isopropyl and 2-propynyl butyrates; methyl, ethyl, propyl, isopropyl, butyl, sec-butyl and tert-butyl acrylates and methacrylates;
methyl and ethyl cro~onates and isocrotonates; ethyl and methyl sorbiates; ethyl diformate and ethyl diacetate.
Unsubstituted mono-esters having 4 to 6 carbon atoms give good results. Excellent results have been obtained with ethyl acetate, isobutyl acetate, n-propyl acetate, methyl methacrylate and n-butyl acetate. Methyl methacrylate, ~thyl acetate and n-propyl acetate have shown themselves to be particularly appropriate.
Nitriles that are suitable for use as co-stabilizers 20791g~

comprise saturated or unsaturated optionally subs-titu-ted aliphatic or aromatic compounds having 2 to 7 carbon atoms such as acatonitrile, propionitrile, acrylonitrile, butyro-nitrile, methacrylonitrile, malonitrile, benzonitrile, di-methylaminoacetonitrile, methylaminopropionitrile, dimethyl-aminopropionitrils, diethylaminoacetonitrile, methylethyl-aminoacetonitrile, thiodipropionitrile, tetrac~anoethylene, tetracyanoquinodimethane, tetracyanodithiine, 1,2-dicyano-1,2-bis(trifluoromethyl)ethylene, cyanobenzaldehyde, nitro-benzonitrile, cyanopyridine. O~ the above, acetonitrile,propionitrile and acrylonitrile are the preferred nitriles.
Ketones suitable for use as co-stabilizers comprise substituted or unsubstituted ketones having 3 to 7 carbon atoms, such as for example acetone, methylethyl ketone, di-ethyl ketone, methylpropyl ketone, methylisopropyl ketone,1-(2-furyl)propanone, 3-hydro~y-2,5-hexane-dione, ~-methyl-2-hydroxy-4-pentanone, etc.
Phenolic compounds conventionally employed as co-stabilizers can carry one or several hydroxyl groups bound to a benzenic ring which can already be optionally substituted by alkyl groups. Preferred compounds are phenol and alkyl derivatives thereof such as thymol, cresols, paramethoxy-phenyl, methyl-di-tert-butylphenols and dimethyl-tert-butyl-phenols. Phenol, ~hymol and p-methoxyphenol are particularly preferred.
Olefinic compounds that can be used as co-stabilizers are in general compounds having one or several double bonds in the molecule and 4 to lO carbon atoms. Of these, tertiary amylene and diisobutylene are the preferred compounds.
Other compounds and notably alkoxyalcanes such as al-koxyethanes, nitrates such as alkyl nitrates having 1 to 5 carbon atoms in the alkyl moeity, quinones such as hydro-qulnone, anthraquinones, hydrazines such as dimethyl-hydrazine, and aromatic compounds such as toluene, can also be employed as co-stabilizers.

l g 5 The following examples are provided by way of illus-tration of the present invention and should in no case be considered as limiting the scope thereof.
Example 1 A l,1,1-trichloroethane composition that included the following stabilizers was prepared:
by weight . limonene epo~ide......... ~................. 0.91 . tertiary butylic alcohol ........... 2.2 10 . methyl-2-butyne~3-ol-2 ............. ~. 0.86 . nitromethane .............................. 0.51 . nitroethane ............................... 0.81 . N-methylmorpholins ........................ 0.005 The resulting composition was subjected to successive distillations which consisted in distilling it 4 times in succession and only collecting the first 90~ by volume that passed over at each distillation. A scratch test in ac-cordance with ASTM D 2943-71 T was carried out on aluminum plates using each one of the 4 distillates.
The aim of this scratch test was to determine the abil-ity of the association of stabiliæers in the l,1,1-trichloro-ethane to prevent deterioration of the chlorinated solvent in the presence of aluminum and of alloys thereof. It consisted of taking a piece of grade AA 1100 (ASTM standard) cleaned and degreased metal, immersing it in 50 cm3 of stabilized l,1,1-trichloroethane, at ambient temperature, and scratching it using a mild steel rod. After a sufficient period of time had elapsed (1 hour) to allow any potential reaction to take place, the presence or absence of bubbles, the color of the solvent and the possible presence of dark resinous matter was noted. The 1,1,1-trichloroethane was properly stabil-ized and no reaction was observed.
The above composition passed this test without any trace of reaction being observed on the aluminum plates.
In order to test the compositlon's ability to trap ., ~

2 ~

hydrochloric acid, the composition was subjected to the Acid Acceptance Test in accordance with ASTM D 2942. Acid ac-ceptance measured in NaOH weight equivalent was 0.240.
The composition was subjected to the co~called BAM
test, this being a test for which the conditlons applied to chlorinated compounds are drastic. No exothermicity was observed, and the composition fully sa-tisfied the B~M test (6 batches). The composition is hence particularly stable.
Example 2 A composition based on 1,1,1-trichloroethane containing the following was tested:
b~ weight . limonene epoxide ......................... 0.74 . butylene oxide............................ 0.1 . methyl-2-butyne-3-ol-2 ...... ~............. 0.86 . nitromethane ............................. 0.51 . nitroethane ................. ~. 0.81 . N-meth~lmorpholine ....................... 0.0085 This composition passed all the above tests. The mea-sured acid acceptance was 0.24.
Example 3 A trichloroeth~lene-based composition was prepared which contained the following additives:
~ b~ weight . limonene epoxide ......................... 0.84 . triethylamine ............................ ~.0075 . N-methylpyrrole .... n ~ O~ 030 . isopropyl acetate ........................ 0.28 . Di-isobutylene ........................... 0.28 This composition was tested on aluminum using the fol-lowing procedure: lOOml of composition, lOOml of toluene, 18g of aluminum and 0.7g aluminum chloride were introduced into a flask refrigerated at its upper end and subjected to reflux boiling for 9 hours, left to stand for 15 hours and again sub;ected to reflux conditions for 9 hours. No reaction 20~:l95 exotharmicity was observed and the composition was hence perfectly stable.
Example 4 A composition based on l,1,1-trichloroethane and con-taining the following additives was prepared and tested:
by weight . limonene epoxide .......................... 0.91 . tertiary butylic alcohol .................. 2.2 . methyl-2-butyne-3-d-2 ..................... 0.86 . 1,3-dioxolanne ............................ 1.42 . N-methylmorpholine .... ~................... 0.005 The measured acid acceptance value was 0.24. There was no reaction from thP scratch test when this composition was used; it is hence stable.
Example 5 (comparative tast) :
The composition used in ~xample 1 was tested again, but this time replaaing the O.91g of limonene epoxide by 0.45g of butylene oxide. The molar contents of both were hence sub-stantially the same, equal to 0.0064 and 0.0063 respectively.
Both compositions were then subjected to a hydrolysis test at equal molar contents. The comparative test was aarried out as follows: 50ml of composition and 50ml of water were intro-duced into a flask and boiled with reflux being ensured by a refrigerant. A 5 ml sample was taken in order to determine the acid acceptance using the me~hod described in ASTM D
2g42. The results are given in the table below:

- i ¦ TIME (h) ¦ 0 ¦ 2 ¦ 3 ¦ 4 30 1 - _ Composition as per example 1 1 0~215 1 0.203 1 0.170 1 0.144 ¦ Composition with l l l l l 35 ¦ butylene oxide ¦ 0.218 ¦ 0.138 ¦ 0.077 ¦ 0.014 ¦

11 2~91 ~

The results given in the table clearly show that the composition based on limonene epoxide is more stable than the composition based on butylene oxide.
The invention is obviously not limited to the case of the examples provided above by way of illustration of the invention, but should be considered to include all variations thereof available to those skilled in the art.

2n

Claims

1.- An additive for stabilizing a halogenated solvent composition of formula CnHzFpCly, in which 1 ? n ? 6, p ? 0.
y ? 1,z ? 0. said additive containing from 0.0001 to 16.5% by weight of limonene epoxide.

2.- An additive according to claim 1, wherein it additionally contains one of the the following co-stabilizers:
a) a C2 to C7 epoxy compound different from limonene epoxide, b) a C1 to C7 saturated alcohol, c) a C3 to C6 unsaturated alcohol, d) a C1 to C4 nitro-alkane e) a mono- or poly-cyclic internal ether, f) a C3 to C10 aliphatic or an aromatic amine, g) a nitrogen-containing heterocyclic compound.

3.- An additive according to claim 1, wherein compon-ents a), b), c), d), e), f) and g) are present in respective amounts of:
a) 0% to 16.50%
b) 0.001 to 16.50%
c) 0.001 to 16.50%
d) 0.001 to 10.00%
e) 0.001 to 16.50%
f) 0 to 3.33%
g) 0 to 3.33%
by weight based on the weight of said additive.

4.- A method for stabilizing a composition based on halogenated solvents of formula CnHzFpCly, in which 1 ? n ?
6, p ? 0. y ? 1,z ? 0 comprising the addition to said sol-vents of 0.01% to 5% by weight, based on the weight of said solvents of limonene epoxide.

5.- A method for composition stabilization according to claim 4, comprising the addition to said solvents of an amount of 0.2% to 3% by weight, based on the weight of said solvents of limonene epoxide.

6.- A method for composition stabilization according to claim 4, wherein it includes the addition to said composition of at least one of the the following co-stabilizers:
a) a C2 to C7 epoxy compound different from limonene epoxide, b) a C1 to C7 saturated alcohol, c) a C3 to C6 unsaturated alcohol, d) a C1 to C4 nitro-alkane, e) a mono- or poly-cyclic internal ether, f) a C3 to C10 aromatic or aliphatic amine, g) a nitrogen-containing heterocyclic compound.

7.- A method for composition stabilization according to claim 6, wherein components a), b), c), d), e), f) and g) are added in respective amounts of:
a) 0% to 5%
b) 0.1 to 5%
c) 0.1 to 5%
d) 0.1 to 3%
e) 0.1 to 5%
f) 0.001 to 1%
g) 0 to 1%
based on the weight of said composition.

8.- A method for composition stabilization according to claim 6, wherein component a) constitutes from 0% to 3% by weight of said composition and is selected from the group comprising: epoxypropane, epoxybutane, 2-methyl-epoxypropane, 2-methyl-epoxybutanes, epichlorhydrine and mixtures thereof.

9.- A method for composition stabilization according to claim 6, wherein component b) makes up from 0.5 to 3.5% by weight of said composition and is selected from the group comprising: methanol, ethanol, propanol, isopropanol, butanol-1, butanol-2, tertiary butylic alcohol, pentanols such as tertiary amylic alcohol, methylcellosolve, ethyl-cellosolve, propylcellosolve, butylcellosolve, glycerine, ethyleneglycol, propyleneglycol, 2-hydroxy-2-methyl-3-butanone, 3,3-dimethoxy-2-methylbutanol-2 and 3-amino-2-methylbutanol-2.

10.- A method for composition stabilization according to claim 9, wherein component b) is selected from the group comprising propanol, tertiary and secondary butanol and ter-tiary pentanol and mixtures thereof.

11.- A method for composition stabilization according to claim 6, wherein component c) is added in an amount of 0.3 to 3% by weight to said composition and is selected from the group comprising: allylic alcohol, 2-methyl-3-butene-2-ol, 2-methyl-3-butyne-2-ol and mixtures thereof.

12.- A method for composition stabilization according to claim 6, wherein component d) is added in an amount of from 0.5 to 1.5% by weight of said composition and is selected from the group comprising: nitromethane, nitroethane, nitro-propane-1, nitropropane-2 and mixtures thereof.

13.- A method for composition stabilization according to claim 6, wherein component e) is added in an amount of from 0.5 to 2.5% by weight of said composition and is selected from the group comprising: mono- or poly-cyclic ethers, op-tionally containing other heteroatoms, containing one or several saturated or unsaturated optionally substituted cycles having 5 or 6 carbon atoms and preferably comprising 1,3-dioxanne, 1,4-dioxanne, 1;3,5-trioxanne, 1,3-dioxolanne, dioxene, dioxadiene, thioxanne, oxazole, tetrahydrofuranne, or diphenyl oxide.

14.- A method for composition stabilization according to claim 6, wherein component f) is added in an amount of from 0.005 to 0.1% by weight based on the weight of said composi-tion and is selected from the group comprising the secondary and tertiary aliphatic amines and aromatic amines such as aniline optionally substituted by C1 to C4 alkyl groups or chlorine atoms.

15.- A method for composition stabilization according to claim 14, wherein said amine is selected from the group com-prising: triethylamine, diisopropylamine, amylamine, hexyl-amine.

16.- A method for composition stabilization according to claim 6, wherein component g) is added in an amount of from 0.005 to 0.1% by weight based on the weight of said composi-tion and is selected from the group of heterocyclic compounds having 4 to 12 carbon atoms and 1 to 2 nitrogen atoms in

17 their molecule, such as pyridine, the picolines, phenothiaz-ine, morpholine, pyrrole and pyrrolidine and derivatives thereof substituted by alkyl groups on the nitrogen atom.
17.- A method for composition stabilization according to claim 4, wherein it includes the addition to said solvents of at least one other conventional co-stabilizer selected from the group comprising esters, nitriles, ketones, phenolic compounds and olefinic compounds, in an amount of up to 5% by weight, based on the weight of said composition.

18.- A method for composition stabilization according to claim 17, wherein said conventional co-stabilizers comprise isopropyl acetate and/or di-isobutylene.

19.- A stabilized halogenated solvent composition of formula CnHzFpCly, in which 1 ? n ? 6, p ? 0. y ? 1, z ? 0, obtained using the method according to any one of claims 4 to 18.

20.- A stabilized composition in accordance with claim 19, wherein said solvent is selected from the group compris-ing: 1,1,1-trichloroethane, trichloroethylene, perchloro-ethylene, methylene chloride, and mixtures thereof.

21.- Use of a stabilized composition in accordance with claim 19 or 20 for degreasing and/or cleaning metal parts.