AZEOTROPE-LIKE COMPOSITIONS OF 2-TRIFLUOROMETHYL-1,1,1,2-TETRAFLUOROBUTANE AND METHANOL, ETHANOL OR ISOPROPANOL

Abstract: Azeotrope-like compositions comprising 2-trifluoromethyl-1,1,1,2-tetrafluorobutane and methanol, ethanol or isopropanol and optionally nitromethane are stable and have utility as degreasing agents and as solvents in a variety of industrial cleaning applications including cold cleaning and defluxing of printed circuit boards and dry cleaning.

Description: AZEOTROPE-LIKE COMPOSITIONS OF 2-TRIFLUOROMETHYL-l.1,1.2-TETRAFLUOROBUTANE AND METHANOL. ETHANOL OR ISOPROPANOL FIELD OF THE INVENTION This invention relates to azeotrope-like mixtures of 2-trifluoromethyl-l,l,l,2-tetrafluorobutane. These mixtures are useful in a variety of vapor degreasing, cold cleaning and solvent cleaning applications including defluxing and dry cleaning. 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. Patent 3,085,918 disclose such suitable vapor degreasers comprising a boiling sump, a clean stomp, a water separator, and other ancillary equipment. Cold cleaning is another application where a number of solvents are used. In most cold cleaning applications, the soiled part is either immersed in the fluid or wiped with rags or similar objects soaked in solvents and allowed to air dry. 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. Azeotropic or azeotrope-like compositions are desired because they do not fractionate upon boiling. This behavior 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 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-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. The art has looked towards azeotrope or azeotrope-like 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. The art is continually seeking new fluorocarbon, hydrofluorocarbon, and hydrochlorofluorocarbon based azeotrope-like mixtures which offer alternatives for new and special applications for vapor degreasing and other cleaning applications. Currently, of particular interest, are fluorocarbon, hydrofluorocarbon, and hydrochlorofluorocarbon based azeotrope-like mixtures with minimal or no chlorine which are considered to be stratospherically safe substitutes for presently used chlorofluorocarbons (CFCs) . The latter are suspected of causing environmental problems in connection with the earth's protective ozone layer. Mathematical models have substantiated that hydrofluorocarbons, such as 2-trifluoromethyl-l,l,l,2-tetrafluorobutane (known in the art as HFC-467) , will not adversely affect atmospheric chemistry, being negligible contributors to ozone depletion and to green-house global warming in comparison to chlorofluorocarbons such as 1,1,2- trichloro-1,2,2-trifluoroethane (CFC-113) . European Publication 431,458 published June 12, 1991 teaches a mixture of 1,1,2,3,4,4-hexafluorobutane and ethanol. U.S. Patent 5,023,010 teaches an azeotropic mixture of 1,1,1,2,3,3-hexafluoro-3- methoxypropane and methanol. U.S. Patent 5,035,830 teaches an azeotropic mixture of hexafluoropropylene/ethylene cyclic dimer and methanol or ethanol. U.S. Patent 5,064,559 teaches an azeotropic mixture of 1,1,1,2,3,4,4,5,5,5- decafluoropentane and methanol or ethanol. U.S. Patent 5,073,291 teaches an azeotrope-type mixture of 1,4- dihydroperfluorobutane and methanol. U.S. Patents 5,073,288 and 5,073,290 teach binary azeotrope-like compositions of 1,1,1,2,2,3,5,5,5- nonafluoro-4-trifluoromethylpentane or 1,1,1,2,2,5,5,5- octafluoro-4-trifluoromethylpentane and methanol or ethanol. U.S. Patent 4,842,764 discloses azeotrope-like compositions of 1,1-dichloro-l-fluoroethane and methanol. U.S. Patent 4,970,013 discloses azeotropic mixtures of 2,3-dichloro-l,l,l,3,3-pentafluoropropane and methanol. U.S. Patent 4,986,928 discloses azeotropic mixtures of l-chloro-1,2,2- trifluorocyclobutane and methanol. Commonly assigned U.S. Patent 4,988,455 discloses azeotrope-like compositions of l,l-dichloro-l,2,2-trifluoropropane and methanol. U.S. Patent 5,023,010 discloses azeotropic mixtures of l,l,l,2,3,3-hexafluoro-3-methoxypropane and methanol. Kokai Patent Publication 98,699 published April 17, 1989 discloses azeotropic compositions of l,l-dichloro-2,2,2-trifluoroethane and methanol. Kokai Patent Publication 304,194 published December 7, 1989 discloses azeotropic mixtures of l-chloro-2,2,3,3- tetrafluoropropane and methanol. DETAILED DESCRIPTION OF THE INVENTION Our solution to the need in the art for substitutes for chlorofluorocarbon solvents is mixtures comprising 2-trifluoromethyl-1,1,1,2-tetrafluorobutane and methanol, ethanol or isopropanol and optionally nitromethane. Also, novel azeotrope-like or constant-boiling compositions have been discovered comprising 2-trifluoromethy1-1,1,1,2-tetrafluorobutane and methanol, ethanol or isopropanol and optionally nitromethane. Preferably, the novel azeotrope-like compositions comprise effective amounts of 2-trifluoromethyl- 1,1,1,2-tetrafluorobutane and methanol, ethanol or isopropanol and optionally nitromethane. The term "effective amounts" as used herein means the amount of each component which upon combination with the other component, results in the formation of the present azeotrope-like compositions. The azeotrope-like compositions comprise from about 64 to about 99.5 weight percent of 2- trifluoromethyl-1,1,1,2-tetrafluorobutane and from about 0.5 to about 36 of ethanol or isopropanol and from 0 to about l weight percent nitromethane. When methanol is present the novel azeotrope-like compositions comprise from about 70 to about 99.5 weight percent of 2-trifluoromethyl-1,l,l,2- tetrafluorobutane and from about 0.5 to about 30 weight percent of methanol. The present azeotrope-like compositions are advantageous for the following reasons. The 2- trifluoromethy1-1,1,1,2-tetrafluorobutane is a negligible contributor to ozone depletion and has a boiling point of 37°C. The methanol, ethanol and isopropanol components have good solvent properties. Thus, when these components are combined in effective amounts, an efficient azeotrope-like solvent results. The preferred methanol based azeotrope-like compositions are in Table I below where 2-trifluoro- methyl-1,1,1,2-tetrafluorobutane is abbreviated as HFC- 467: TABLE I The preferred ethanol based azeotrope-like compositions are in Table II below where 2- trifluoromethyl-1,1,1,2-tetrafluorobutane is abbreviated as HFC-467: TABLE II The preferred isopropanol based azeotrope-like compositions are in Table III below where 2- trifluoromethyl-1,1,1,2-tetrafluorobutane is abbreviated as HFC-467: TABLE All compositions within the indicated ranges, as well as certain compositions outside the indicated ranges, are azeotrope-like, as defined more particularly below. The precise azeotrope compositions have not been determined but have been ascertained to be within the above ranges. Regardless of where the true azeotropes lie, all compositions with the indicated ranges, as well as certain compositions outside the indicated ranges, are azeotrope-like, as defined more particularly below. The term "azeotrope-like composition" as used herein is intended to mean that the composition behaves like an azeotrope, i.e. has constant-boiling characteristics or a tendency not to fractionate upon boiling or evaporation. 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. As is readily understood by persons skilled in the art, the boiling point of the azeotrope-like composition will vary with the pressure. The azeotrope-like compositions of the invention are useful as solvents in a variety of vapor degreasing, cold cleaning and solvent cleaning applications including defluxing and dry cleaning. In one process embodiment of the invention, the azeotrope-like compositions of the invention may be used to dissolve contaminants or remove contaminants from the surface of a substrate by treating the surfaces with the compositions in any manner well known to the art such as by dipping or spraying or use of conventional degreasing apparatus wherein the contaminants are substantially removed or dissolved. The 2-trifluoromethyl-1,1,1,2-tetrafluorobutane of the present azeotrope-like compositions may be prepared by reacting commercially available 4-iodo-2- trifluoromethyl-1,1,1,2-tetrafluorobutane with zinc and hydrogen chloride. The methanol; ethanol; isopropanol; and nitromethane components of the novel solvent azeotrope-like compositions of the invention are known materials and are commercially available. The present invention is more fully illustrated by the following non-limiting Examples. EXAMPLE 1 This Example is directed to the preparation of 2-trifluoromethyl-1,1,1,2-tetrafluorobutane. A 500 milliliter flask fitted with a mechanical stirrer, distillation column, and take-off head was charged with 15 grams (0.046 mole) of commercially available 4-iodo-2-trifluoromethyl- 1,1,1,2-tetrafluorobutane, 28.5 grams (0.45 mole) zinc dust, and 230 milliliters of 10% hydrogen chloride. The mixture was stirred and heated to 50°C and 7.4 grams (80% yield) of distillate (boiling point 37°C-39 β C) was collected. 1H NMR (CDC1 3 ) : 2.1 (m, 2H) , 1.2 (t, 3 H) ppm. EXAMPLE 2 A microebulliometer which consisted of a 15 milliliter round bottom double neck flask containing a magnetic stirbar and heated with an electrical heating mantel was used. Three illiliters of 2- trifluoromethyl-1,1,1,2-tetrafluorobutane was charged into the icroebulliometer and methanol was added in small measured increments by an automated syringe capable of a injecting microliters. The temperature was measured using a platinum resistance thermometer and barometric pressure was measured. An approximate correction to the boiling point was done to obtain the boiling point at 760 mm Hg. The following Table IV shows the boiling point measurements, corrected to 760 mm Hg (lOlkPa) , for various mixtures of 2-trifluoromethyl-1,1,1,2-tetra- fluorobutane and methanol. From about 6.5 to about 25 weight percent methanol as shown in Table IV, the boiling point of the composition changed by only 1°C. Therefore, the composition behaves as a constant- boiling composition over this range. TABLE IV Liquid Mixture Parts by weight% Parts by Weight % Boiling Point (CFC) 2CFCH2CH3 Methanol @760mmHσ(101kPa) 100.00 0 37.0 97.28 2 .72 36.3 95.72 4 . 28 35.1 94.70 5 . 30 34.6 93.71 6. 29 34.1 92.00 8 . 00 33.0 90.00 10. 00 32.8 86.70 13 . 30 32.6 75.40 24 . 60 32.8 EXAMPLE 3 This example shows that a minimum in the boiling point versus composition curve occurs in the region of 88.7 weight percent 2-trifluoromethyl-l,1,1,2- tetrafluorobutane (hereinafter HFC-467) and 11.3 weight percent ethanol indicating that an azeotrope forms in the neighborhood of this composition. A microebulliometer which consisted of a 15 milliliter round bottom double neck flask containing a magnetic stirbar and heated with an electrical heating mantel was used. Approximately 2.5 milliliters of the lower boiling material, HFC-467, was charged into the microebulliometer and ethanol was added in small measured increments by an automated syringe capable of injecting microliters. The temperature was measured using a platinum resistance thermometer and barometric pressure was measured. An approximate correction to the boiling point was done to obtain the boiling point at 760 mm Hg. The boiling point was measured and corrected to 760 M Hg (101 kPa) for various mixtures of HFC-467 and ethanol. Interpolation of the data shows that a minimum boiling point occurs in the region of about 1.5 to about 18 weight percent ethanol. The best estimate of the position of the minimum is 11.3 weight percent ethanol, although the mixtures are constant-boiling, to within 0.3°C, in the region of 0.5 to 35 weight percent ethanol. A minimum boiling azeotrope is thus shown to exist in this composition range. From the above example, 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 outer limits of the composition ranges which are constant-boiling. Anyone skilled in the art can readily ascertain other constant-boiling or essentially constant-boiling mixtures containing the same components. EXAMPLE 4 Example 3 was repeated except that isopropanol (purity 90%) was used instead of ethanol. Approximately 2.8 milliliters of the lower boiling material, HFC-467, were initially charged into the microebulliometer and isopropanol was added in small measured increments by an automated syringe capable of injecting microliters. The boiling point was measured and corrected to 760 mm Hg (101 kPa) , for various mixtures of HFC-467 and isopropanol. Interpolation of these data shows that a minimum boiling point occurs in the region of about 1.4 to about 1.7.7 weight percent isopropanol. The best estimate of the position of the minimum is 8 weight percent isopropanol, although the mixtures are constant-boiling, to within 0.3°C, in the region of 0.5 to 27.5 weight percent isopropanol. A minimum boiling azeotrope is thus shown to exist in this composition range. Inhibitors may be added to the present azeotrope-like compositions to inhibit decomposition of the compositions; react with undesirable decomposition products of the compositions; and/or prevent corrosion of metal surfaces. Any or all of the following classes of inhibitors may be employed in the invention: alkanols having 4 to 7 carbon atoms, nitroalkanes having 2 to 3 carbon atoms, 1,2-epoxyalkanes having 2 to 7 carbon atoms, phosphite esters having 12 to 30 carbon atoms, ethers having 3 or 4 carbon atoms, unsaturated compounds having 4 to 6 carbon atoms, acetals having 4 to 7 carbon atoms, ketones having 3 to 5 carbon atoms, and amines having 6 to 8 carbon atoms. Other suitable inhibitors will readily occur to those skilled in the art. The inhibitors may be used alone or in mixtures thereof in any proportions. Typically, up to about 2 percent based on the total weight of the azeotrope-like composition of inhibitor might be used. When the present azeotrope-like compositions are used to clean solid surfaces by spraying the surfaces with the compositions, preferably, the azeotrope-like compositions are sprayed onto the surfaces by using a propellant. Preferably, the propellant is selected from the group consisting of hydrocarbons, chlorofluorocarbons, hydrochlorofluorocarbon, hydrofluorocarbon, dimethyl ether, carbon dioxide, nitrogen, nitrous oxide, methylene oxide, air, and mixtures thereof. Having described the invention in detail and by reference to preferred embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims.

Claims: What is claimed is: 1. Azeotrope-like compositions comprising from about 64 to about 99.5 weight percent of 2- trifluoromethyl-1,1,1,2-tetrafluorobutane and from about 0.5 to about 36 of ethanol or isopropanol and from 0 to about 1 weight percent nitromethane. 2. The azeotrope-like compositions of claim 1 wherein said compositions boil at about 36.5°C at 760 mm Hg. 3. The azeotrope-like compositions of claim 1 consisting essentially of from about 79.5 to about 99.5 weight percent said 2-trifluoromethyl-1,1,1,2- tetrafluorobutane and from about 1 to about 20.5 weight percent said ethanol and from about 0 to about 0.5 weight percent said nitromethane wherein said compositions boil at about 36.5°C at 760 mm Hg. 4. The azeotrope-like compositions of claim 1 consisting essentially of from about 71.5 to about 99.5 weight percent said 2-trifluoromethyl-l,l,1,2- tetrafluorobutane and from about 0.5 to about 28.5 weight percent said isopropanol and from about 0 to about 1 weight percent said nitromethane wherein said compositions boil at about 38.1°C at 760 mm Hg. 5. The azeotrope-like compositions of claim 1 consisting essentially of from about 82.9 to about 98.6 weight percent said 2-trifϊuoromethyl-l,l,1,2- tetrafluorobutane and from about 1.4 to about 17.1 weight percent said isopropanol and from about 0 to about 0.4 weight percent said nitromethane wherein said compositions boil at about 38.1°C at 760 mm Hg. 6. Azeotrope-like compositions comprising from about 70 to about 99.5 weight percent of 2- trifluoromethyl-1-1-1,2-tetrafluorobutane and from about 0.5 to about 30 weight percent of methanol. 7. The azeotrope-like compositions of claim 1 which boil at about 33.5 β C± about 1.0'C at 760 mm Hg. 8. The azeotrope-like compositions of claim 2 comprising from about 75 to about 97 weight percent said 2-trifluoromethyl-1,1,1,2-tetrafluorobutane and from about 3 to about 25 weight percent said methanol. 9. The azeotrope-like compositions of claim 1 through 8 wherein said compositions additionally contain an inhibitor selected from the group consisting of alkanols having 4 to 7 ςarbon atoms, nitroalkanes having 2 to 3 carbon atoms, 1,2-epoxyalkanes having 2 to 7 carbon atoms, phosphite esters having 12 to 30 carbon atoms, ethers having 3 or 4 carbon atoms, unsaturated compounds having 4 to 6 carbon atoms, acetals having 4 to 7 carbon atoms, ketones having 3 to 5 carbon atoms, and amines having 6 to 8 carbon atoms. 10. A method of dissolving contaminants or removing contaminants from the surface of a substrate which comprises the step of: using said azeotrope-like composition of claims 1 through 8 as solvent.

Inventors: BASU RAJAT SUBHRA, HOLLISTER RICHARD MERVIL, SWAN ELLEN LOUISE, VAN DER PUY MICHAEL, BASU, RAJAT, SUBHRA, HOLLISTER, RICHARD, MERVIL, SWAN, ELLEN, LOUISE, VAN DER PUY, MICHAEL
Applicants: ALLIED SIGNAL INC, ALLIED-SIGNAL INC.
Application year: 1992
Main classification: C11D7
IPC codes: C11D7, C23G5, D06L1, H05K3