US2775624A - Stabilized tetrachloroethylene - Google Patents

Description

r 2,775,624 Ice Patented DeQ'ZS, 1956 STABILIZED TETRACHLOROETHYLENE Maxwell J. Skeeters, Painesville, Ohio, and Norman L Beckers, Houston, Tex., assignors to Diamond Alkali Company, Cleveland, Ohio, a corporation of Delaware No Drawing. Application September 25, 1953, r Serial No. 382,484

6 Claims. (Cl. 260-6525) This invention relates to inhibiting the decomposition of tetrachloroethylene catalyzed by light, air, heat, moisture, and metal surfaces and more particularly relates to a composition of matter consisting essentially of tetrachloroethylene and stabilizing amounts of an acetylenic carbinol.

It has heretofore been known that tetrachloroethylene (perchloroethylene) of a high degree of purity and containing only minute amounts of saturated, or other unsaturated, lower aliphatic chloro-hydrocarbons is very inert to the action of air, light, heat, moisture, and metal surfaces with which it comes into contact during storage and commercial use. However, the obtaining of such high purity tetrachloroethylene in commercial production is not generally feasible and it has been found that the impure material normally encountered in commerce decomposes when in contact with the substances noted above. Hence, means other than purification for preventing or inhibiting the decomposition of tetrachloroethylene and the lower chlorinated aliphatic hydrocarbons generally associated therewith must be had.

It is generally believed that tetrachloroethylene exposed to air, light, heat, moisture, etc., decomposes, es pecially in the presence of moisture, principally by way of oxidative attack at the doublebond involving a series of steps in which the ultimate products include phosgene, trichloroacetic acid, and hydrogen chloride. It is also believed that the oxi-dative attack is catalyzed by light and by the products ofoxidation, as a result of which, oxida tive decomposition once initiated is self-catalyzing and self-sustaining. Other chloro-hydrocarbons generally associated with crude commercial tetrachloroethylene also are subject to oxidative attack and decompose to some of the same products as those formed by the oxidation of tetrachloroethylene, and at a somewhat accelerated rate, as compared to the oxidation of tetrachloroethylene. These products are then available to catalyze the decomposition of the tetrachloroethylene. For example, tetrachloroethylene obtained commercially from the crude products of chlorination and chlorinolysis of lower aliphatic hydrocarbons may contain small but appreciable amounts of saturated and unsaturated chlorinated hydrocarbons, such as dichloroethylene, trichloroethylene, trichloroethane, unsymmetrical tetrachloroethane, pentachloroethane, and the like. These lower chloro-hydrocarbons in themselves are relatively innocuous in solvent extraction processes in which the tetrachloroethylene is used, but the oxidation decomposition products thereof corrode metal surfaces with which a body of tetrachloroethylene containing them comes into contact. These less stable chloro-hydrocarbons are believed to be the principal initial source of chloro oxygen-containing impurities, such as phosgene, chloroacetic acid, trichloroacetic acid, and the like, in the tetrachloroethylene, which impurities catalyze decomposition of the tetrachloroethylene.

The problem, therefore, is principally one of inhibiting the initiation of the oxidation of the chloro-hydrocarbons commonly associated with commercial tetrachloroethyl- 2 ene, as well as inhibiting the oxidation of tetrachloro ethylene itself.

One of the objects of the present invention is to provide means for inhibiting oxidation of tetrachloroethylene and lower aliphatic chloro-hydrocarbons generally associated therewith during exposure to air, light, heat, moisture,

and metal surfaces.

Another object of the invention is to provide a procedure for treating'and purifying crude tetrachloroethylene in order to obtain maximum efliciency of the stabilizer in the purified product.

These and other objects will be apparent to those skilled in the art from the discussion hereinafter.

It has now been found that where the crude tetrachloroethylene, particularly that obtained from commercial proc esses involving the chlorinolysis of lower hydrocarbons or hydrocarbon chlorides, or the chlorination and simultaneous dehydrochlorination of hydrocarbon chlorides, such as ethylene dichloride, or of unsaturated hydrocarbons, such as acctylene, ethylene, and the like, contains appreciable amounts of lower chlorinated aliphatic tially of tetrachloroethylene and stabilizing amounts of,

a monohydric alcohol characterized by the presence of a triple bond, the hydroxyl group being secured to a carbon atom substituted by three other substituents.

These compounds have been found particularly etfective in stabilizing tetrachloroethylene contaminated with minor amounts of other lower aliphatic chloro-hydrocar: bons, both in the liquid and in the vapor phase. For

the most part the stabilizing efiect has been found to be most pronounced and prolonged where pre-treatments which destroy the greater part of the chloro-acids and acid chlorides have been resorted to prior to the addition of the stabilizing acetylenic alcohol.

The initial treatment of the crude tetrachloroethylene may include adding an organic base of the amine type and having a boiling point higher than tetrachloroethylene, for example, aniline or morpholine, in an amount from approximately 0.2-2.0% by weight to the crude product,

and fractionally distilling the crude mass to recover sub stantially all of the tetrachloroethylene as an intermediate fraction in the distillation; additional treatments may include washing the tetrachloroethylene fraction with a solution of an inorganic base, such as an alkali metal or alkaline earth metal base, for example, sodium hydroxide, sodium carbonate, calcium hydroxide, magnesium bicarbonate, and the like, drying the washed product and distilling the dried product to recover a more highly refined tetrachloroethylene fraction. The purpose in using an amine, such as aniline, is to allow for the reaction of such amine with acid chloride products contained in the crude product, whereby an anilide or analogous com pound may form during distillation and the undesired impurity is retained in the distillation residue. The purpose of washing the effluent from the initial distillation with an alkali metal or alkaline earth metal base is to remove the more volatile of the acid chloride impurities, such as hydrogen chloride, phosgene, and the like, which may not have reacted with the amine.

The crude product may also be washed initially with a solution of an inorganic base, such as those noted above,

dried, and combined with an amine having a boiling point substantially higher than tetrachloroethylene, generally inan amount from 0.2-2.0% by weight, and the mixture thus obtained distilled as described above in order to recover the'purified tetrachloroethylene substantially free from chloro oxygen-containing impurities.

Where such impurities ashydrogen chloride, phosgene, chloro-acids, and the like, are known to be extremely low in the crude product, this material maybe combined with an amine, such as aniline, as noted hereinabove, and subjected to fractional distillation to recover the substantially pure tetrachloroethylene without the necessity of resorting to the treatment with a solution of an inorganic-base. Moreover, the dilute alkaline wash may be omitted even where the chloro oxygen-containing compounds are presentin appreciable quantities in the crude product, but it has been found that the amount of organic amine consumed and thevolume of distillation residue accumulated is excessive.

After any one of the above-described initial treatments, the recovered tetrachloroethylene may be combined with a stabilizing amount of an acetylenic carbinol as noted above, for example, in an amount from 0.0l-1.0% by weight of tetrachloroethylene, preferably, however, from 0.2-0.3% where the abovepre-treatrnents or their equivalent have been used. The extremes within the abovenoted broad range are preferred where the amount of chloro-hydrocarbon impurities associated with the tetrachloroethylene is unusually high or unusually low, while the amounts within the intermediate preferred range are generally sufllciently effective where the purified tetrachloroethylene contains not more than about l3% of the lower chlorinated aliphatic hydrocarbon impurities consisting essentially of trichloroethylene, the most common impurity obtained in commercial production.

The beneficial effects of the present invention may also be realized where tetrachloroethylene has been purified in a commercial operation and stabilized either with a high boiling point stabilizer, i. e., a stabilizer such as one of the amine or of the ether type having a higher boiling point than that of tetrachloroethylene, or with stabilizers which are more volatile than tetrachloroethylene, by removing such stabilizer as by chemical reaction, azeotropic distillation, or the like; the thus-treated mass is then fractionally distilled to recover the tetrachloroethylene fraction, which may be combined with an acetylenic carbinol, as described above, in an amount suflicient to effect stabi lization, whereby the tetrachloroethylene is rendered especially suitable, due to its stability, for degreasing or dry cleaning operations.

Acetylenic alcohols which may be used in accordance with this invention comprise those having a hydroxyl group secured to a carbon atom substituted by three other substituents. Of this class both straight and branched chain compounds may be employed and within the limitation expressed in the previous sentence, the relative position of the triple bond and the hydroxyl group is not pertinent. Of the straight chain mono-hydric compounds, there maybe mentioned propargyl alcohol, propargyl carbinol, methyl acetylenyl carbinol, ethyl acetylenyl carbinol, Z-butyne-I-ol, and higher homologues of this series, including the octyl and nonyl substituted compounds,-as well as aryl substituted compounds. Of the branched chain mono-hydric compounds may be mentioned dimethyl acetylenyl carbinol and higher homologues, such as diethyl, dibutyl, diamyl and similar substituted compounds, including those having two different substituents, such as methyl, ethyl acetylenyl carbinol, and the like. Of especial use in this group are methyl butynol and methyl pentynol, and of particular interest of the isomers of these compounds are respectively 2- methyl-3-butyne-2-0l and 3-methyl-1-pentyne-3-ol.

Thus it will be appreciated from the foregoing description of compounds embodying the present invention that 4 these materials may be characterized by the structural formula:

OH R] wherein R1 and R2 are selected from the group consisting of hydrogen and lower alkyl radicals.

Those skilled in the art will appreciate that while all of the above class of compounds, and particularly the specifically mentioned members thereof, will be useful in the practice of the present invention, those materials which have boiling points in the same general range as that of tetrachloroethylene (B. P. 119122 C.) will be especially desirable as they may be expected to have the property of going into the vaporphase with the solvent and returning with it to the liquid phase. This is especially significant in vapor phase metal degreasing operations, as well as in the dry cleaning industry where solvents commonly are recovered by distillation and reused. It will be recognized that 3-rnethyl-l-pentyne-3-ol (B. P. 121-l22 C.) is outstanding in this property, while 2- methyl-3-butyne-2-ol (B. P. l04-105 C.), methyl acetylenyl carbinol (B. P. 107-l09 C.), propargyl alcohol (B. P. ll41l5 C.), ethyl acetylenylcarbinol (B. P. 125 C.), dimethyl acetylenyl carbinol (B. P. l02-l03 C.), methyl, ethyl acetylenyl carbinol (B. P. l20l2l C.), and ethyl pentynol (B. P. l37 C.) are also Well within a desirable range.

In order that those skilled in the art may better understand the present invention and in what manner the same may be carried into effect, the following specific examples are offered: I

In all examples, stability is tested in accordance with the following procedure:

One hundred mls. of the tetrachloroethylene to be tested for stability are placed in a 300-ml. flask equipped with a ground glass joint. A copper strip 2.0 X 7.5 x 0.005 cm., which has been washed with concentrated hydrochloric acid, water, dried and Weighed, is placed in the flask. Next, 0.2 ml. of water is added. The flask is attached to a small Soxhlet extractor equipped with a bottom ground glass joint and a top ground glass joint. A bulb type condenser with a bottom ground glass joint is attached to the Soxhlet. An acid washed, weighed copper strip (2.0 x 7.5 x 0.005 cm.) is placed in the Soxhlet, and another acid washed and weighed copper strip of the same size is placed in the bottom part of the condenser, so that the condensing tetrachloroethylene condenses on the strip. The water scrubber (containing -200 mls. H20) absorbs any HCl that does not react with the copper during the stability run. To prevent the sucking back of water, two filter flasks, so arranged that water is pushed from one flask to the other with changes in pressure, are

employed. The flask containing the tetrachloroethylene is heated on a heater controlled to adjust the boiling rate so that the Soxhlet extractor empties every 8-10 minutes. A IOU-watt bulb is placed one inch from the vapor line of the Soxhlet extractor to furnish light for the photochemical oxidation. The stability test is run for 72 hours.

The aggregate loss in weight of the copper strips is a measure of the stability of the tetrachloroethylene tested.

In general, material which shows a 45 mg. aggregate loss in weight in the 3 copper strips over the period of the test is acceptable for dry cleaning purposes. (National Institute of Cleaning and Dyeing, Perchlorethylene (Drycleaning), Tentative Standard 3-50.) 18 mg. loss is closer L0 industry standards, however, but naturally the more stable the material, the better.

Example I jected to fractional distillation. The fraction boiling between 119 and 122 C. is taken for a stability test. Two IOO-ml. samples of the tetrachloroethylene are chosen for testing, and to one of these samples there is added 0.25 by Weight of 3-methyl-1-pentyne-3-ol. On the conclusion of the test, the results are as follows:

Sample Total Loss in Weight of 3 Cu Strips Containing 3-methyl-1-pentyne-3-ol 5.2 mg.

Control (U nstabilized) More Than 100 mg.

Example 11 A similarly prepared sample is placed under test with 0.25% of 2-methyl-3-butyne-2-ol. Loss is 5.7 mg.

Example 111 A sample containing 0.25 of dimethyl hexynol (3,5- dimethyl-l-hexyne-B-ol) is tested and loses 9.4 mg.

Example IV A sample containing 0.25% of propargyl alcohol results, after test, in a loss of 12.5 mg.

Example V A sample containing 0.25 of dimethyl hexynediol (2,5-dimethyl-3-hexyne-2,5-diol) loses 4.6 mg.

Example VI Results commensurate with Example V are obtained on testing material containing 0.25% of dimethyl octynediol (3,6-dimethyl-4-octyne-3 ,6-diol) Example VII Commercial sample Mg. loss A 17.8 B 13.5 C 22.6 D 17.8 E 17.5 Average 17.8v

In addition to outstanding ability to withstand the vigorous dry cleaners test, the acetylenic alcohol-stabilized tetrachloroethylene of the present invention has been found to surpass all commercially available materials of its class, both in metal degreasing, where corrosion of the work and breakdown of the solvent are measures of stability, and in wood dehydration, where corrosion of equipment is especially to be avoided.

While there have been described various embodiments of the invention, the products described are not intended to be understood as limiting the scope of the invention as it is realized that changes therewithin are possible and it is further intended that each element recited in any of the following claims is to be understood as referring to all equivalent elements for accomplishing substantially the same results in substantially the same or equivalent manner, it being intended to cover the invention broadly in whatever form its principle may be utilized.

What is claimed is:

1. A composition of matter consisting essentially of tetrachloroethylene and a stabilizing amount of a compound of the structure:

wherein R1 and R2 are selected from the group consisting of hydrogen and lower alkyl radicals.

2. A composition of matter consisting essentially of tetrachloroethylene and a stabilizing amount of methyl butynol.

3. A composition of matter consisting essentially of tetrachloroethylene and a stabilizing amount of Z-methyl- 3-butyne-2-ol.

4. A composition of matter consisting essentially of tetrachloroethylene and a stabilizing amount of methyl pentynol.

5. A composition of matter consisting essentially of tetrachloroethylene and a stabilizing amount of 3-methyl 1-pentyne-3-o1.

6. A composition of matter consisting essentially of tetrachloroethylene and a stabilizing amount of propargyl alcohol.

References Cited in the file of this patent UNITED STATES PATENTS 1,097,145 Snelling et a1. May 19, 1914 2,371,644 Petering et al Mar. 20, 1945 2,593,267 Church et al Apr. 15, 1952 2,603,622 Berger et al July 15, 1952

Claims (1)

1. A COMPOSITION OF MATTER CONSISTING ESSENTIALLY OF TETRACHLOROETHYLENE AND A STABILIZING AMOUNT OF A COMPOUND OF THE STRUCTURE: