AZEOTROPE-LIKE COMPOSITIONS OF 1,3-DICHLORO-1,1,2,2,3-PENTAFLUOROPROPANE AND 2-METHYL-2-PROPANOL

Description

[0001] This invention relates to azeotrope-like mixtures of 1,3-dichloro-1,1,2,2,3-pentafluoropropane and 2-methyl-2-propanol. These mixtures are useful in a variety of vapor degreasing, cold cleaning, and solvent cleaning applications including defluxing and dry cleaning.

[0002] Fluorocarbon based solvents have been used extensively for the degreasing and otherwise cleaning of solid surfaces, especially intricate parts and difficult to remove soils.

[0003] 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 the object free of residue. This is contrasted with liquid solvents which leave deposits on the object after rinsing.

[0004] A vapor degreaser is used 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. 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.

[0005] 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 sump, a water separator, and other ancillary equipment.

[0006] 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 cloths soaked in solvents and allowed to air dry.

[0007] Recently, nontoxic nonflammable fluorocarbon solvents like trichlorotrifluoroethane, have been used extensively 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 missile hardware and aluminum parts.

[0008] The art has looked towards azeotropic compositions having fluorocarbon components because the fluorocarbon components contribute additionally desired characteristics, like polar functionality, increased solvency power, and stabilizers. Azeotropic 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. Therefore, unless the solvent composition is essentially constant boiling, 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 an 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.

[0009] 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. Currently, fluorocarbon-based azeotrope-like mixtures are of particular interest because they are considered to be stratospherically safe substitutes for presently used fully halogenated chlorofluorocarbons. The latter have been implicated in causing environmental problems associated with the depletion of the earth's protective ozone layer. Mathematical models have substantiated that hydrochlorofluorocarbons, like dichloropentafluoropropane, have a much lower ozone depletion potential and global warming potential than the fully halogenated species. EP-A-347 924 to Asano discloses the use of hydrogen-containing chlorofluoropropanes as solvents. Dichloropentafluoropropane isomers HCFC-224ca, HCFC-225cb and HCFC-225cc are among the hydrogen-containing chlorofluoropropanes listed. The reference also provides that when the compounds of the invention are used as cleaning solvents, an organic solvent such as a hydrocarbon, an alcohol like methanol, ethanol, n-propyl alcohol, isopropyl alcohol and tert-butyl alcohol, a ketone, a chlorinated hydrocarbon, an ester or an aromatic compound or a surfactant may be incorporated to improve the cleaning effects of the solvent. The reference also provides, "When azeotropy or pseudozaeotropy exists with a composition obtained by the combination of the compound of the present invention with [an]other compound, it is preferred to use them under an azeotropic or pseudozaeotropic condition...". This reference does not, however, teach or suggest the instant binary or ternary compositions applicants are claiming. More importantly, there is no teaching or suggestion in reference that applicants' claimed combinations (or the combination of any other compound listed in the reference to the basic solvent compositions) will result in the formation of an azeotrope-like composition.

[0010] EP-A-0381216, which is believed to form a part of the state of the art only in accordance with Article 54(3) EPC, discloses a hydrochlorofluorocarbon azeotrope or azeotrope-like mixture comprising at least one member selected from the group consisting of hydrogen-containing fluoropropanes of the formula


wherein a + b + c = 3, x + y + z = 3, a + x≧1, b + y≧1, and 0≦a,b,c,x,y,z,≦3, and at least one member selected from the group of compounds II consisting of halogenated hydrocarbons having a boiling point of from 20 to 85°C other than said hydrochlorofluoropropanes, hydrocarbons having a boiling point of from 20 to 85°C and alcohols having from 1 to 4 carbon atoms.

[0011] It is an object of the present invention to provide novel environmentally acceptable azeotrope-like compositions which are useful in a variety of industrial cleaning applications.

[0012] It is another object of this invention to provide azeotrope-like compositions which are liquid at room temperature and which will not fractionate under conditions of use.

[0013] Other objects and advantages of the invention will become apparent from the following description.

[0014] The present invention provides azeotrope-like compositions consisting essentially of from 98 to 99.99 weight percent 1,3-dichloro-1,1,2,2,3-pentafluoro-propane and from 0.01 to 2 weight percent 2-methyl-2-propanol, and boiling at 55.7°C + 0.2°C at 99.87 KPa (749.1 mm Hg).

[0015] The present invention also provides a method of cleaning a solid surface comprising treating said surface with an azeotrope-like composition as defined above.

[0016] Dichloropentafluoropropane exists in nine isomeric forms: (1) 2,2-dichloro-1,1,1,3,3-pentafluoropropane (HCFC-225a); (2) 1,2-dichloro-1,2,3,3,3-pentafluoropropane (HCFC-225ba); (3) 1,2-dichloro-1,1,2,3,3-pentafluoropropane (HCFC-225bb); (4) 1,1-dichloro-2,2,3,3,3-pentafluoropropane (HCFC-225ca); (5) 1,3-dichloro-1,1,2,2,3-pentafluoropropane (HCFC-225cb); (6) 1,1-dichloro-1,2,2,3,3-pentafluoropropane (HCFC-225cc); (7) 1,2-dichloro-1,1,3,3,3-pentafluoropropane (HCFC-225d); (8) 1,3-dichloro-1,1,2,3,3-pentafluoropropane (HCFC-225ea); and (9) 1,1-dichloro-1,2,3,3,3-pentafluoropropane (HCFC-225eb). For purposes of this invention, 1,3-dichloro-1,1,2,2,3-pentafluoropropane (HCFC-225cb) is used.

[0017] The dichloropentafluoropropane component of the invention has good solvent properties. The 2-methyl-2-propanol component also has good solvent capabilities; dissolving polar organic materials and amine hydrochlorides. Thus, when these components are combined in effective amounts, an efficient azeotropic solvent results.

[0018] The precise or true azeotrope compositions have not been determined but have been ascertained to be within the indicated ranges. Regardless of where the true azeotropes lie, all compositions within the indicated ranges, as well as certain compositions outside the indicated ranges, are azeotrope-like, as defined more particularly below.

[0019] From fundamental principles, the thermodynamic state of a fluid is defined by four variables: pressure, temperature, liquid composition and vapor composition, 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 a stated P and T. In practice, this means that the components of a mixture cannot be separated during distillation, and therefore are useful in vapor phase solvent cleaning as described above.

[0020] For purposes 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 compositions 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 minimally. This is contrasted with non-azeotrope-like compositions in which the liquid composition changes substantially during boiling or evaporation.

[0021] Thus, one way to determine whether a candidate mixture is "azeotrope-like" within the meaning of this invention, is 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.

[0022] 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 different pressures, the composition of a given azeotrope will vary at least slightly as does the boiling point of the composition. Thus, an azeotrope of A and B represents a unique type of relationship but with a variable composition depending on temperature and/or pressure. As is readily understood by persons skilled in the art, the boiling point of the azeotrope will vary with the pressure.

[0023] In the process embodiment of the invention, the azeotrope-like compositions of the invention may be used to clean solid surfaces by treating said surfaces with said compositions in any manner well known in the art such as by dipping or spraying or use of conventional degreasing apparatus.

[0024] As stated above, the azeotrope-like compositions discussed herein are useful as solvents for a variety of cleaning applications including vapor degreasing, defluxing, cold cleaning, dry cleaning, dewatering, decontamination, spot cleaning, aerosol propelled rework, extraction, particle removal, and surfactant cleaning applications. These azeotrope-like compositions are also useful as blowing agents, Rankine cycle and absorption refrigerants, and power fluids.

[0025] The dichloropentafluoropropane and alkanol components of the invention are known materials. Preferably, they should be used in sufficiently high purity so as to avoid the introduction of adverse influences upon the solvent or constant boiling properties of the system.

[0026] Commercially available 2-methyl-2-propanol may be used in the present invention. Most dichloropentafluoropropane isomers, are not available in commercial quantities. Therefore until such time as it becomes commercially available, it may be prepared by following the organic synthesis disclosed herein.

Synthesis of 1,3-dichloro-1,1,2,2,3-pentafluoro- propane (225cb).

[0027] The synthesis of this compound involves four steps.

[0028] Part A - Synthesis of 2,2,3,3-tetrafluoropropyl-p-toluenesulfonate. 406 gm (3.08 mol) 2,2,3,3-tetrafluoropropanol, 613 gm (3.22 mol) tosylchloride, and 1200 ml water were heated to 50°C with mechanical stirring. Sodium hydroxide (139.7 gm, 3.5 mol) in 560 ml water was added at a rate such that the temperature remained less than 65°C. After the addition was completed, the mixture was stirred at 50°C until the pH of the aqueous phase was 6. The mixture was cooled and extracted with 1.5 liters methylene chloride. The organic layer was washed twice with 200 ml aqueous ammonia, 350 ml water, dried with magnesium sulfate, and distilled to give 697.2 gm (79%) viscous oil.

[0029] Part B - Synthesis of 1,1,2,2,3-pentafluoropropane. A 500 ml flask was equipped with a mechanical stirrer and a Vigreaux distillation column, which in turn was connected to a dry-ice trap, and maintained under a nitrogen atmosphere. The flask was charged with 400 ml N-methylpyrrolidone, 145 gm (0.507 mol) 2,2,3,3-tetrafluoropropyl-p-toluenesulfonate (produced in Part A above), and 87 gm (1.5 mol) spray-dried KF. The mixture was then heated to 190-200°C for 3.25 hours during which time 61 gm volatile product distilled into the cold trap (90% crude yield). Upon distillation, the fraction boiling at 25-28°C was collected.

[0030] Part C - Synthesis of 1,1,3-trichloro-1,2,2,3,3-pentafluoropropane. A 22 liter flask was evacuated and charged with 20.7 gm (0.154 mol) 1,1,2,2,3-pentafluoro-propane (produced in Part B above) and 0.6 mol chlorine. It was irradiated 100 minutes with a 450 W Hanovia Hg lamp at a distance of about 7.6 cm. The flask was then cooled in an ice bath, nitrogen being added as necessary to maintain 1 atm (101 kPa). Liquid in the flask was removed via syringe. The flask was connected to a dry-ice trap and evacuated slowly (15-30 minutes). The contents of the dry-ice trap and the initial liquid phase totaled 31.2 g (85%), the GC purity being 99.7%. The product from several runs was combined and distilled to provide a material having b.p. 73.5-74°C.

[0031] Part D - Synthesis of 1,3-dichloro-1,1,2,2,3-pentafluoropropane. 106.6 gm (0.45 mol) of 1,1,3-trichloro-1,2,2,3,3-pentafluoropropane (produced in Part C above) and 300 gm (5 mol) isopropanol were stirred under an inert atmosphere and irradiated 4.5 hours with a 450 W Hanovia Hg lamp at a distance of 5-7.6 cm. The acidic reaction mixture was then poured into 1.5 liters ice water. The organic layer was separated, washed twice with 50 ml water, dried with calcium sulfate, and distilled to give 50.5 gm C1CF₂CF₂CHC1F, bp 54.5-56°C (55%). ¹H NMR (CDC1₃): ddd centered at 6.43 ppm. J H-C-F = 47 Hz, J H-C-C-Fa = 12 Hz, J H-C-C-Fb = 2 Hz.

[0032] It should be understood that the present compositions may include additional components which form new azeotrope-like compositions. Any such compositions are considered to be within the scope of the present invention as long as the compositions are constant-boiling or essentially constant-boiling and contain all of the essential components described herein.

[0033] 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: epoxy compounds such as propylene oxide; nitroalkanes such as nitromethane; ethers such as 1-4-dioxane; unsaturated compounds such as 1,4-butyne diol; acetals or ketals such as dipropoxy methane; ketones such as methyl ethyl ketone; alcohols such as tertiary amyl alcohol; esters such as triphenyl phosphite; and amines such as triethyl amine. Other suitable inhibitors will readily occur to those skilled in the art.

[0034] 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.

[0035] The present invention is more fully illustrated by the following non-limiting Examples.

Example 1

[0036] The azeotropic properties of 1,3-dichloro-1,1,2,2,3-pentafluoropropane (225cb) and 2-methyl-2-propanol were studied. This was accomplished by charging the dichloropentafluoropropane isomer into an ebulliometer, bringing it to a boil, adding measured amounts of 2-methyl-2-propanol and finally recording the temperature of the ensuing boiling mixture. The range over which the compositions are constant boiling is

225cb :

98 - 99.99 wt%.

2-methyl-2-propanol:

0.01 - 2 wt.%

Constant boiling temperature:

55.7 ± 0.2°C at 99.86 KPa (749 mm Hg).

Examples 2-3

[0037] The azeotropic properties of the dichloropentafluoropropane isomers listed below with 2-methyl- 2-propanol are studied by repeating the experiment outlined in Example 1 above. In each case a minimum in the boiling point versus composition curve occurs indicating that a constant boiling composition forms between each dichloropentafluoropropane component and 2-methyl-2-propanol.

Ex. 2

[0038] 1,1-dichloro-2,2,3,3,3-pentafluoropropane/(mixture of 1,3-dichloro-1,1,2,2,3-pentafluoropropane (225ca/cb)

Ex 3

[0039] 1,1-dichloro-1,2,3,3,3-pentafluoropropane/(mixture of 1,3-dichloro-1,1,2,2,3-pentafluoropropane (225eb/cb)

Claims

1. Azeotrope-like compositions consisting essentially of from 98 to 99.99 weight percent 1,3-dichloro-1,1,2,2,3-pentafluoro-propane and from 0.01 to 2 weight percent 2-methyl-2-propanol, and boiling at 55.7°C ± 0.2°C at 99.87 KPa (749.1 mm Hg).

2. An azeotrope-like composition according to Claim 1 characterised in that an effective amount of an inhibitor is present in said composition.

3. An azeotrope-like composition according to Claim 2 characterised in that said inhibitor is selected from epoxy compounds, nitroalkanes, ethers, acetals, ketals, ketones, alcohols, esters, and amines.

4. A method of cleaning a solid surface comprising treating said surface with an azeotrope-like composition according to any one of Claims 1 to 3.

Ansprüche

1. Azeotrop-ähnliche Zusammensetzung, welche im wesentlichen aus 98-99,99 Gewichtsprozent 1,3-dichloro-1,1,2,2,3-Pentafluoropropan und 0,01-2 Gewichtsprozent 2-Methyl-2-Propanol besteht, und deren Siedepunkt bei 99,87 KPa (749,1 mm Hg) bei 55,7°C ± 0,2°C liegt.

2. Azetrop-ähnliche Zusammensetzung nach Anspruch 1, dadurch gekennzeichnet, dass eine wirkungsvolle Menge eines Inhibators in dieser Zusammensetzung vorhanden ist.

3. Azetrop-ähnliche Zusammensetzung nach Anspruch 2, dadurch gekennzeichnet, dass dieser Inhibitor unter Epoxyverbindungen, Nitroalkanen, Ether, Azetalen, Ketalen, Ketonen, Alkoholen, Estern une Aminen ausgewählt ist.

4. Verfahren zum Reinigen einer Feststoffoberfläche durch Behandlung dieser Oberfläche mit einer Azetrop-ähnlichen Zusammensetzung nach irgendeinem der Ansprüche 1 bis 3.

Revendications

1. Composition de type azéotrope se composant essentiellement de 98 à 99,99 % en poids de 1,3-dichloro-1,1,2,2,3-pentafluoro-propane et de 0,01 à 2 % en poids de 2-méthyl-2-propanol, et bouillant à 55,7 ± 0,2 °C à 99,87 KPa (749,1 mm Hg).

2. Composition de type azéotrope selon la revendication 1, caractérisée en ce qu'une quantité efficace d'un inhibiteur est présente dans ladite composition.

3. Composition de type azéotrope selon la revendication 2, caractérisée en ce que ledit inhibiteur est choisi parmis les composés époxys, les nitroalcanes, les éthers, les acétals, les cétals, les cétones, les alcools, les esters, et les amines.

4. Méthode de nettoyage d'une surface solide comprenant le traitement de ladite surface avec une composition de type azéotrope selon l'une quelconque des revendications 1 à 3.