Патент USA US2108390код для вставки
2,108,390 Patented Feb. 15, 1938 UNITED STATES PATENT orrlca 2,108,390 STABILIZING CHLggggATED HYDROCAR Whit?eld Price, Charleston, W. Va, assignor, by assignments, to ‘Westvaco Chlorine Products Corporation, New York, N. Y., a cor mesne poration of Delaware No Drawing. Application July 20, 1936, Serial No. 91,620 14 Claims. (Ci. 23-250) . ternal changes by dissolving a modicum of an al are particularly effective stabilizers for chlorin ated hydrocarbons. The reason for this is not obvious, but the fact is as stated. For practical reasons, alkyl thiocyanates are employed, these kyl thiocyanate, most advantageously methyl all being volatile materials. The isothiocyanates thiocyanate, therein; a similar method being ap plicable to other chlorinated. hydrocarbons; and it also comprises a chlorinated hydrocarbon show ing on test the presence of a volatile thiocyanate 10 ester; all as more fully hereinafter set forth and are serviceable, albeit not better than the thic cyanates. In these compounds, there is a char acteristic nucleus. They contain a single hydro carbon group connected by a single bond to the This invention relates to stabilizing chlorinated hydrocarbons; and it comprises a method of sta bilizing trichlorethylene against deteriorative in 5 as claimed. Chlorinated hydrocarbons'are in large commer group SCN and the latter group in turn has the 10 carbon atom thereof attached to a single nitrogen atom by at least two bonds; in the isothiocy cial use because of their unin?ammability, con anates the carbon and nitrogen are linked by a venient boiling points and good properties as solvents for grease, resins, rubber, etc. Trichlor ethylene in particular ?nds much favor. It. is a substance of convenient boiling point, around double bond and in the thiocyanates by a triple bond. The best of these alkyl thiocyanates is 15 87° 0. Most of these chlorinated hydrocarbons are bodies of good stability, insofar as attack by reagents is concerned. They are quite inert chemically. All, however, have some tendency to undergo internal changes in time, this being particularly marked in the case of trichlorethyl ene. The nature of these changes, that is, the 25 chemical mechanism involved, is not quite de? nitely known, but in all cases there is ‘a develop ment of acidity. Exposure to both light and air favor these changes; neither singly having as much e?ect as the two together. The particular susceptibility of trichlorethylene may be due .to its unsaturated character. Various additions to these chlorinated hydro the methyl ester, CH3._SCN. Methyl thiocyanate has the lowest boiling point of these alkyl esters having a boiling point between 130 and 131° C. I have found it most advantageous for my pur poses, partly because of this fact and partly be 20 cause it seems to have a characteristic stabiliz ing effect greater than that of the other alkyl thiocyanates. Among these other thiocyanates ' which I have used and found desirable are ethyl thiocyanate, isopropyl thiocyanate, butyl thio cyanate, methyl isothi cyanate, ethyl isothiocy— anate, and allyl isothidgyanate. _ In degreasing with trichlorethylene, all these esters stabilize the boiling liquid and stabiliza tion is not impaired by accumulating impurities. When the trichlorethylene is recovered by distil lation the thiocyanate can also be distilled over. vWhile the ‘stabilizing e?ect of these thiocy carbons have been proposed in enhancing their stability and inhibiting internal changes. To anates is most marked with trichlorethylene, they 85 some extent, these are e?‘ectiv‘e, but the difficulty are also advantageous with carbon tetrachloride, arises that any inhibitor in the chlorinated hy drocarbons must itself withstand trying ‘condi tions; it must itself be stable. In many of the commercial uses of these chlorinated hydrocar bons, the ‘same portion of solvent may be kept , at a boiling temperature inde?nitely in the pres-l ence of various, impurities. For example, in a current method of degreasing metal and other articles, the article is passed through a body of 45 vapor of trichlorethylene overlying a body of boil ing liquid. ‘Condensed solvent trickles off the article, carrying grease with it, and the solvent is revaporized to serve anew. In this operation, a limited amount of trichlorethylene at its boil 50 ing temperature is continually passing back and forth between the liquid and the vapor states and the stabilizer must persist over an inde?nitely long time. I have found that various thiocyanate esters, or sulfocyanides, containing the radical .SCN, chloroform, ethylene dichloride, the tetrachlor ethanes and even with chlorinated aromatics. Ordinary unstabilized trichlorethylene. in a loosely stoppered bottle exposed to diffused day light in a few hours becomes heavily acid on test; an aqueous extract made with neutral water ex hibits enough acidity to titrate. Phenolphthalein is a suitable indicator for this purpose. With a loose stopper, a little» access of air occurs, but there is not much-evaporation. On the other hand, a similar test'made with the same tri-. chlorethylene containing a trace of methyl thio cyanate does not develop appreciable acidity after long standing. In accelerated tests of similar character but under more drastic conditions as regards illumi-_v nation and access of air, trlchlorethylene contain ing a little methyl thiocyanate does not develop‘ substantial acidity over long periods of .time. Some of these tests simulate in a few days what 25 2 2,108,390 would happen in years of normal storage at the are in constant contact with the metals. In the In one test a quantity of the liquid is placed in the ?ask of a Soxhlet apparatus. The compart case of trichlorethylene, experience has shown that with a little dissolved methyl thiocyanate, the trichlorethylene becomes stable inde?nitely long in the degreaser, whatever the character of ordinary temperature. Cl ment of the Soxhlet which acts as a receiver for condensate, and which is equipped to siphon back into the ?ask at intervals, contains a piece of copper. A second piece of copper is placed in the ?ask itself and is of such dimensions that part 10 of its surface is below the liquid and part in the vapor space above. Corrosion of the copper is evidence of decomposition of the solvent. In this particular accelerated test conditions are like those occurring in a degreaser system. 15 Heat is applied to the ?ask at such a rate that mild re?uxing occurs, so that over a period of time, such as an hour or two, the siphon com partment ?lls up and discharges back into the ?ask, Precautions are taken that the equip ment stands in di?used light rather than direct sunlight. Acidity determinations are made at intervals on the liquid at a time when the siphon compartment is empty. One‘of the features of this test is the fact that liquid is distilled out of the ?ask and condensed, and is exposed to the the metal used in making the apparatus or treated for degreasing. - While I have spoken of the stabilizing effect of methyl thiocyanate and the other thiocyanates ' used with pure liquid: chlorinated hydrocar 10 bons, the same stabilizing e?ect is secured in admixtures; either of chlorinated hydrocarbons with each other or with other compounding materials. In chlorinated materials containing the thio ll cyanates of the present invention its presence can be recognized by e?’ecting saponi?cation of a sample of the chlorinated hydrocarbon with caustic soda, thereby making a thiocyanate. This can be identi?ed by the usual ferric iron test. What I claim is: 1. 'I‘richlorethylene stabilized by the presence of a small amount of an alkyl thiocyanate. 2. The composition of claim 1 in which the alkyl thiocyanate is methyl thiocyanate. 3. A chlorinated hydrocarbon stabilized by the action of light and oxygen away from the main body. It is assumed that certain stabilizers will . presence therein of a fraction of a per cent of follow the vapor and condense with it so as to stabilize the liquid in the siphon chamber, while 30 others of lower vapor pressure will remain in the ?ask while unstabilized vapor passes into the siphon compartment. Using this accelerated test, a sample of tri chlorethylene containing 0.004 per cent methyl thiocyanate developed no substantial acidity in_ a period of 72 days, whereas unstabilized trichlor ethylene in the same test will show high acidity in a very short time. . In another accelerated test, a sample of tri 40 chlorethylene without stabilizer in 2 days devel oped an acidity requiring 550 drops of hundredth normal NaOH for neutralization, per 10 cc. of the sample. The sample was extracted with neu tral water and the water titrated. On the other 45 hand, the same trichlorethylene with an addi tion of 0.01 per cent methyl thiocyanate, after 4 days’ exposure, had an acidity requiring only 7 drops per 10 cc., while trichlorethylene contain ing 0.05 per cent isopropyl thiocyanate, after 3 50 days’ exposure developed only an acidity of the same order of magnitude, requiring 8 drops per 10 cc. for neutralization in lieu of '7 drops. Similar results are given by other chlori nated hydrocarbons, such as, perchlorethylene (CClzICClz). Ethylene dichloride is a solvent much in use and it shows some tendency to de an alkyl thiocyanate. ‘ . 4. The composition of claim 3 wherein the chlorinated hydrocarbon is ethylene dichloride. 39 5. The composition of claim 3 'wherein the chlorinated hydrocarbon is trichlorethylene. 6. The composition oi.’ ‘claim 3‘ wherein the chlorinated hydrocarbon is perchlorethylene. '7. In the stabilization of chlorinated hydro carbons against deteriorative internal changes, the process which comprises dissolving therein an alkyl thiocyanate in an amount correspond ing to a fraction of a per cent by weight. 8. The process of claim 'I‘wherein the alkyl 40 thiocyanate is methyl thiocyanate. 9. The process of claim 7 wherein the addition of thiocyanates is in amounts between 0.001 per cent and 1.00 per cent. 10. The process of claim 7 wherein the alkyl 45 thiocyanate is methyl thiocyanate. 11. The composition of claim 1 wherein the alkyl thiocyanate is the normal thiocyanate. 12. The composition of claim 1 wherein the alkyl thiocyanate is an iso-cyanate. 13. As a composition of matter, a substan 50 tially neutral, stable liquid comprising a vola tile liquid chlorinated hydrocarbon containing dissolved therein between 0.001 to 1.000 per cent by weight of a thiocyanate having the follow 55 ing structure: composition under drastic industrial conditions. - R—S-C EN A sample of a particular ethylene dichloride of wherein R is an alkyl group, the amount of the . high commercial grade subjected to an acceler 60 ated test for 10 days developed in 10 cc. an acid , said thiocyanate being su?lcient to stabilize the ity requiring 260 drops of the hundredth normal said chlorinated hydrocarbon against deteriora caustic soda, for neutralization while the same tive internal changes. ethylene dichloride with an addition of 0.02 per 14. As a composition of matter, a substan cent methyl thiocyanate, after 10 days’ exposure. tially neutral, stable liquid comprisingv a volatile 65 developed an acidity requiring only 10 drops per liquid chlorinated hydrocarbon containing dis solved thereln between 0.001 to‘ 1.000 per cent by 65 10 cc. for neutralization. ' 'As stated, the chlorinated hydrocarbons are weight of a thiocyanate having the following bodies of tolerably inert character. In aapure structure: R-N=C=S neutral anhydrous state, they do not affect, nor 70 are they affected by, the common metals. But wherein R isan alkyl group, the amount of the with any .development of acidity, the situation said thiocyanate being su?icient to stabilize the 70 alters. It is, 01' course, of enormous practical importance to maintain the inert character of these solvents, this being especially true with the solvents used in degreasing metals, where they said chlorinated‘hydrocarbon against deteriora tive internal changes. WHITFmD PRICE.