Azeotrope-like compositions comprising 1,1,2-trichloro-1,2,2-trifluoroethane, methanol, nitromethane, 1,2-dichloroethylene and 1-chloropropane are stable and have utility as degreasing agents and as solvents in a variety of industrial cleaning applications including the defluxing of printed circuit boards.

FIELD OF THE INVENTION 
This invention relates to azeotrope-like mixtures of 
1,1,2-trichloro-1,2,2-trifluoroethane, methanol, nitromethane, 
1,2-dichloroethylene and 1-chloropropane. These mixtures are useful in a 
variety of vapor degreasing applications and as solvents in a variety of 
industrial cleaning applications including defluxing of printed circuit 
boards. 
BACKGROUND OF THE INVENTION 
Vapor degreasing and solvent cleaning with fluorocarbon based solvents have 
found widespread use in industry for the degreasing and otherwise cleaning 
of solid surfaces, especially intricate parts and difficult to remove 
soils. 
In its simplest form, vapor degreasing or solvent cleaning consists of 
exposing a room-temperature object to be cleaned to the vapors of a 
boiling solvent. Vapors condensing on the object provide clean distilled 
solvent to wash away grease or other contamination. Final evaporation of 
solvent from the object leaves behind no residue as would be the case 
where the object is simply washed in liquid solvent. 
For difficult to remove soils where elevated temperature is necessary to 
improve the cleaning action of the solvent, or for large volume assembly 
line operations where the cleaning of metal parts and assemblies must be 
done efficiently and quickly, the conventional operation of a vapor 
degreaser consists of immersing the part to be cleaned in a sump of 
boiling solvent which removes the bulk of the soil, thereafter immersing 
the part in a sump containing freshly distilled solvent near room 
temperature, and finally exposing the part to solvent vapors over the 
boiling sump which condense on the cleaned part. In addition, the part can 
also be sprayed with distilled solvent before final rinsing. 
Vapor degreasers suitable in the above-described operations are well known 
in the art. For example, Sherliker et al. in U.S. Pat. No. 3,085,918 
disclose such suitable vapor degreasers comprising a boiling sump, a clean 
sump, a water separator, and other ancillary equipment. 
Fluorocarbon solvents, such as trichlorotrifluoroethane, have attained 
widespread use in recent years as effective, nontoxic, and nonflammable 
agents useful in degreasing applications and other solvent cleaning 
applications. Trichlorotrifluoroethane has been found to have satisfactory 
solvent power for greases, oils, waxes and the like. It has therefore 
found widespread use for cleaning electric motors, compressors, heavy 
metal parts, delicate precision metal parts, printed circuit boards, 
gyroscopes, guidance systems, aerospace and missile hardware, aluminum 
parts and the like. 
The art has looked towards azeotropic compositions including the desired 
fluorocarbon components such as trichlorotrifluoroethane which include 
components which contribute additionally desired characteristics, such as 
polar functionality, increased solvency power, and stabilizers. Azeotropic 
compositions are desired because they exhibit a minimum boiling point and 
do not fractionate upon boiling. This is desirable because in the 
previously described vapor degreasing equipment with which these solvents 
are employed, redistilled material is generated for final rinse-cleaning. 
Thus, the vapor degreasing system acts as a still. Unless the solvent 
composition exhibits a constant boiling point, i.e., is an azeotrope or is 
azeotrope-like, fractionation will occur and undesirable solvent 
distribution may act to upset the cleaning and safety of processing. 
Preferential evaporation of the more volatile components of the solvent 
mixtures, which would be the case if they were not azeotrope or 
azeotrope-like, would result in mixtures with changed compositions which 
may have less desirable properties, such as lower solvency towards soils, 
less inertness towards metal, plastic or elastomer components, and 
increased flammability and toxicity. 
A number of 1,1,2-trichloro-1,2,2-trifluoroethane based azeotrope 
compositions have been discovered which have been tested and in some cases 
employed as solvents for miscellaneous vapor degreasing and defluxing 
applications. For example, U.S. Pat. No. 3,573,213 discloses the azeotrope 
of 1,1,2-trichloro-1,2,2-trifluoroethane and nitromethane; U.S. Pat. No. 
2,999,816 discloses an azeotropic composition of 
1,1,2-trichloro-1,2,2-trifluoroethane and methyl alcohol; U.S. Pat. No. 
3,960,746 discloses azeotrope-like compositions of 
1,1,2-trichloro-1,2,2-trifluoroethane, methanol and nitromethane. U.S. 
Pat. No. 3,455,835 discloses azeotrope-like compositions of 
1,1,2-trichloro-1,2,2-trifluoroethane and and trans-1,2-dichloroethylene. 
U.S. Pat. No. 4,767,561 discloses azeotrope-like compositions containing 
1,1,2-trichloro-1,2,2-trifluoroethane, methanol and 
trans-1,2-dichloroethylene. 
The art is continually seeking new fluorocarbon based azeotropic mixtures 
or azeotrope-like mixtures which offer alternatives for new and special 
applications for vapor degreasing and other cleaning applications. 
It is accordingly an object of this invention to provide novel 
azeotrope-like compositions based on 1,1,2-trichloro-1,2,2-trifluoroethane 
which have good solvency power and other desirable properties for vapor 
degreasing and other solvent cleaning applications. 
Another object of the invention is to provide novel constant boiling or 
essentially constant boiling solvents which are liquid at room 
temperature, will not fractionate under conditions of use and also have 
the foregoing advantages. 
A further object is to provide azeotrope-like compositions which are 
nonflammable both in the liquid phase and the vapor phase. These and other 
objects and features of the invention will become more evident from the 
description which follows. 
DESCRIPTION OF THE INVENTION 
In accordance with the invention, novel azeotrope-like compositions have 
been discovered comprising 1,1,2-trichloro-1,2,2-trifluoroethane, 
methanol, nitromethane, 1,2-dichloroethylene and 1-chloropropane. 
1,2-Dichloroethylene exists in two isomeric forms, the 
trans-1,2-dichloroethylene and the cis-1,2-dichloroethylene. Each isomer 
forms azeotrope-like mixtures with 1,1,2-trichloro-1,2,2-trifluoroethane, 
methanol and nitromethane in accordance with the invention, as well as do 
mixtures of the trans- and cis-isomers. For example, 
trans-1,2-dichloroethylene is often provided as a mixture with up to about 
5 weight percent cis-1,2-dichloroethylene. 
The trans-isomer is the preferred 1,2-dichloroethylene isomer in accordance 
with the invention. 
With respect to the preferred trans-1,2-dichloroethylene embodiment of the 
invention, the azeotrope-like compositions comprise from about 51.9 to 
about 62.8 weight percent of 1,1,2-trichloro-1,2,2-trifluoroethane, from 
about 5.7 to about 6.2 weight percent of methanol, from about 0.05 to 
about 0.3 weight percent of nitromethane, from about 10.0 to about 19.5 
weight percent of 1-chloropropane and from about 16.3 to about 24.3 weight 
percent of trans-1,2-dichloroethylene. 
Still preferably, such azeotrope-like compositions containing the 
trans-isomer of 1,2-dichloroethylene comprise from about 58.4 to about 
62.8 weight percent of 1,1,2-trichloro-1,2,2-trifluoroethane, from about 
6.0 to about 6.2 weight percent of methanol, from about 0.05 to about 0.3 
weight percent of nitromethane, from about 15.5 to about 10.5 weight 
percent of 1-chloropropane and from about 17.3 to about 19.8 weight 
percent trans-1,2-dichloroethylene. 
The most preferred azeotrope-like composition containing the trans-isomer 
of 1,2-dichloroethylene consists essentially of about 64.7 weight percent 
of 1,1,2-trichloro-1,2,2-trifluoroethane, about 6.1 weight percent of 
methanol, about 0.2 weight percent of nitromethane, about 13.6 weight 
percent of 1-chloropropane and about 17.9 weight percent 
trans-1,2-dichloroethylene. This composition boils at about 38.degree. C. 
at 760 mm Hg. 
With respect to the cis-1,2-dichloroethylene embodiment of the invention, 
the azeotrope-like compositions comprise from about 70.4 to about 72.0 
weight percent of 1,1,2-trichloro-1,2,2-trifluoroethane, from about 5.8 to 
about 6.3 weight percent of methanol, from about 0.03 to about 0.5 weight 
percent of nitromethane, from about 20.0 to about 22.0 weight percent of 
1-chloropropane and from about 2.0 to about 0.4 weight percent of 
cis-1,2-dichloroethylene. 
Still preferably, such azeotrope-like compositions comprise from about 70.4 
to about 71.3 weight percent of 1,1,2-trichloro-1,2,2-trifluoroethane, 
from about 6.1 to about 6.3 weight percent of methanol, from about 0.03 to 
about 0.2 weight percent of nitromethane, from about 21.2 to about 21.6 
weight percent of 1-chloropropane and from about 2.0 to about 0.8 weight 
percent of cis-1,2-dichloroethylene. 
The most preferred azeotrope-like composition containing the cis-isomer of 
1,2-dichloroethylene consists essentially of about 71.3 weight percent of 
1,1,2-trichloro-1,2,2-trifluoroethane, about 6.3 weight percent of 
methanol, about 0.2 weight percent of nitromethane, about 21.6 weight 
percent of 1-chloropropane and about 0.8 weight percent 
cis-1,2-dichloroethylene. This composition boils at about 38.5.degree. C. 
at 760 mm Hg. 
With respect to the embodiment of the invention containing a mixture of the 
cis and trans isomers of 1,2-dichloroethylene, the azeotrope-like 
compositions comprise from about 51.9 to about 65.5 weight percent of 
1,1,2-trichloro-1,2,2-trifluoroethane, from about 5.7 to about 6.3 weight 
percent of methanol, from about 0.02 to about 0.5 weight percent of 
nitromethane, from about 10.0 to about 22.0 weight percent of 
1-chloropropane, from about 16.3 to about 24.3 weight percent of 
trans-1,2-dichloroethylene and from about 2.0 to about 0.4 weight percent 
of cis-1,2-dichloroethylene. 
Still preferably, such azeotrope-like compositions comprise from about 58.4 
to about 65.5 weight percent of 1,1,2-trichloro-1,2,2-trifluoroethane, 
from about 6.0 to about 6.3 weight percent of methanol, from about 0.02 to 
about 0.2 weight percent of nitromethane, from about 15.5 to about 10.5 
weight percent of 1-chloropropane, from about 16.0 to about 18.0 weight 
percent of trans-1,2-dichloroethylene and from about 2.0 to about 0.5 
weight percent of cis-1,2-dichloroethylene. 
The most preferred azeotrope-like composition containing the cis- and 
trans-isomers of 1,2-dichloroethylene consists essentially of about 65.5 
weight percent of 1,1,2-trichloro-1,2,2-trifluoroethane, about 6.1 weight 
percent of methanol, about 0.2 weight percent of nitromethane, about 10.8 
weight percent of 1-chloropropane, about 16.8 weight percent of 
trans-1,2-dichloroethylene and about 0.7 weight percent of 
cis-1,2-dichloroethylene. This composition boils at about 39.2.degree. C. 
at 760 mm Hg. 
The precise azeotrope compositions in accordance with the invention have 
not been determined but have been ascertained to be within the above 
ranges. Regardless of where the true azeotrope lie, all compositions 
within the indicated ranges, as well as certain compositions outside the 
indicated ranges, are azeotrope-like, as defined more particularly below. 
It has been found that these azeotrope-like compositions are stable, safe 
to use and that the preferred compositions of the invention are 
nonflammable (exhibit no flash point when tested by the Tag Open Cup test 
method--ASTM D 1310-86) and exhibit excellent solvency power. These 
compositions have been found to be particularly effective when employed in 
conventional degreasing units for the dissolution of rosin fluxes and the 
cleaning of such fluxes from printed circuit boards. 
From fundamental principles, the thermodynamic state of a system (pure 
fluid or mixture) is defined by four variables: pressure, temperature, 
liquid compositions and vapor compositions, or P-T-X-Y, respectively. An 
azeotrope is a unique characteristic of a system of two or more components 
where X and Y are equal at the stated P and T. In practice, this means 
that the components of a mixture cannot be separated during distillation 
or in vapor phase solvent cleaning when that distillation is carried out 
at a fixed T (the boiling point of the mixture) and a fixed P (atmospheric 
pressure). 
For the purpose of this discussion, by azeotrope-like composition is 
intended to mean that the composition behaves like a true azeotrope in 
terms of its constant boiling characteristics or tendency not to 
fractionate upon boiling or evaporation. Such composition may or may not 
be a true azeotrope. Thus, in such compositions, the composition of the 
vapor formed during boiling or evaporation is identical or substantially 
identical to the original liquid composition. Hence, during boiling or 
evaporation, the liquid composition, if it changes at all, changes only to 
a minimal or negligible extent. This is to be contrasted with 
non-azeotrope-like compositions in which during boiling or evaporation, 
the liquid composition changes to a substantial degree. 
Thus, in order to determine whether a candidate mixture is "azeotrope-like" 
within the meaning of this invention, one only has to distill a sample 
thereof under conditions (i.e. resolution--number of plates) which would 
be expected to separate the mixture into its separate components. If the 
mixture is non-azeotropic or non-azeotrope-like, the mixture will 
fractionate, i.e. separate into its various components with the lowest 
boiling component distilling off first, and so on. If the mixture is 
azeotrope-like, some finite amount of a first distillation cut will be 
obtained which contains all of the mixture components and which is 
constant boiling or behaves as a single substance. This phenomenon cannot 
occur if the mixture is not azeotrope-like i.e., it is not part of an 
azeotropic system. If the degree of fractionation of the candidate mixture 
is unduly great, then a composition closer to the true azeotrope must be 
selected to minimize fractionation. Of course, upon distillation of an 
azeotrope-like composition such as in a vapor degreaser, the true 
azeotrope will form and tend to concentrate. 
It follows from the above that another characteristic of azeotrope-like 
compositions is that there is a range of compositions containing the same 
components in varying proportions which are azeotrope-like. All such 
compositions are intended to be covered by the term azeotrope-like as used 
herein. As an example, it is well known that at differing pressures, the 
composition of a given azeotrope will vary at least slightly and changes 
in distillation pressures also change, at least slightly, the distillation 
temperatures. Thus, an azeotrope of A and B represents a unique type of 
relationship but with a variable composition depending on temperature 
and/or pressure. Accordingly, another way of defining azeotrope-like 
within the meaning of this invention is to state that such mixtures boil 
within .+-.1.degree. C. of the boiling point of the most preferred 
compositions disclosed herein (i.e. within .+-.1.degree. C. of the 
38.0.degree. C./760 mm Hg boiling point of the azeotrope-like compositions 
containing at least 16.3 weight percent trans-1,2-dichloroethylene; within 
.+-.1.degree. C. of the 38.5.degree. C./760 mm Hg. boiling point of the 
azeotrope-like compositions containing at least 0.4 weight percent 
cis-1,2-dichloroethylene isomer and within .+-.1.degree. C. of the 
39.2.degree. C./760 mm Hg boiling point of the azeotrope-like compositions 
containing a mixture of at least 16.3 weight percent trans- and at least 
0.4 weight percent cis-1,2-dichloroethylene). 
The 1,1,2-trichloro-1,2,2-trifluoroethane, methanol, nitromethane, 
1,2-dichloroethylene and 1-chloropropane components of the novel solvent 
azeotrope-like compositions of the invention are all commercially 
available. Preferably they should be used in sufficiently high purity so 
as to avoid the introduction of adverse influences upon the solvency 
properties or constant boiling properties of the system. A suitable grade 
of 1,1,2-trichloro-1,2,2-trifluoroethane, for example, is sold by 
Allied-Signal Inc. under the trademark GENESOLV.RTM. D.

EXAMPLES 1-4 
The azeotrope-like compositions of the invention were determined through 
the use of distillation techniques designed to provide higher 
rectification of the distillate than found in most vapor degreaser 
systems. For this purpose a five theoretical plate Oldershaw distillation 
column was used with a cold water condensed, automatic liquid dividing 
head. Typically, approximately 350 grams of liquid were charged to the 
distillation pot. The liquid was a mixture comprised of various 
combinations of 1,1,2-trichloro-1,2,2-trifluoroethane, methanol, 
nitromethane, 1-chloropropane, cis-1,2-dichloroethylene and 
trans-1,2-dichloroethylene. The mixtures were heated at total reflux for 
about one hour to ensure equilibration. For most of the runs, the 
distillate was obtained using a 3:1 reflux ratio at a boil-up rate of 
250-300 grams per hour. Approximately 150 grams of product were distilled 
and 4 approximately equivalent sized overhead cuts were collected. The 
vapor temperature (of the distillate), pot temperature, and barometric 
pressure were monitored. A constant boiling fraction was collected and 
analyzed by gas chromatography to determine the weight percentages of its 
components. 
To normalize observed boiling points during different days to 760 mm of 
mercury pressure, the approximate normal boiling points of 
1,1,2-trichloro-1,2,2-trifluoroethane rich mixtures were estimated by 
applying a barometric correction factor of about 26 mm Hg/.degree.C., to 
the observed values. However, it is to be noted that this corrected 
boiling point is generally accurate up to .+-.0.4.degree. C. and serves 
only as a rough comparison of boiling points determined on different days. 
By the above-described method, it was discovered that constant boiling 
mixtures were formed as indicated in the following Table. Supporting 
distillation data for the mixtures studied are shown in the Table. 
TABLE 
______________________________________ 
Starting Material (wt. %) 
Example 
(Distil- 
lation) 
FC-113 MeOH TDCE 1-CP NM CDCE 
______________________________________ 
1 51.9 5.7 24.3 18.0 0.3 -- 
2 59.0 5.8 20.0 15.0 0.2 -- 
3 70.4 6.1 -- 21.2 0.2 2.0 
4 62.5 6.2 18.0 11.1 0.2 2.0 
______________________________________ 
Distillate (wt. %) 
Example 
(Distil 
lation) 
FC-113 MeOH TDCE 1-CP NM CDCE 
______________________________________ 
1 58.4 6.2 19.8 15.5 0.06 -- 
2 62.8 6.2 17.3 13.6 0.02 -- 
3 71.3 6.3 -- 21.6 0.03 0.7 
4 65.5 6.1 16.8 10.8 0.03 0.7 
______________________________________ 
Boiling Point 
(Distil- 
Boiling Barometric Corrected to 
lation) Point (.degree.C.) 
Pressure (mm Hg) 
760 mm Hg 
______________________________________ 
1 37.8 748.0 38.1 
2 36.9 734.0 37.9 
Mean 38.0.degree. C. .+-. 0.1 
3 37.5 735.0 38.5 
4 38.2 735.0 39.2 
______________________________________ 
FC-113 = 1,1,2trichloro-1,2,2-trifluoroethane 
MeOH = methanol 
TDCE = trans1,2-dichloroethylene 
1-CP = 1chloropropane 
NM = nitromethane 
CDCE = cis1,2-dichloroethylene 
From the above examples, it is readily apparent that additional constant 
boiling or essentially constant boiling mixtures of the same components 
can readily be identified by anyone of ordinary skill in this art by the 
method described. No attempt was made to fully characterize and define the 
true azeotrope in the systems described above, nor the outer limits of the 
compositional ranges which are constant boiling. Anyone skilled in the art 
can readily ascertain other constant boiling or essentially constant 
boiling mixtures.