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Stability of Chlorohydrocarbons 1 I. Triclriloror tti y lene 1'. J. CARLISLEANI) A. A. I , ~ v i n i &1'lre Koessler & Ifasslacher (:herrrical Co., Inc., Niagdra Falls, N. Y. S A p r e v i o u s article i ~ y the authors ( 1 ) the &a-
1
Trirhloroelhylene dues not decorripuse in durkI t i s riot deconiposed in light unless oxygen is present. The presence of truces of certain untiozidunls prevents thr decimposition in light. Trichloroethyleru: does riot decompose on heutirig up lo 130" C. It nu2y decompose on heulirzg in the presrnce of oxygen unless antioxidants arc present. Trichloroethylerle does riot hydrolyze. It i s oiily sligh.tly uffected by ferric chloride. The ordinary metals du riot cnla1y:e decornposiliori if trichloroethylene. Trichlororlhylene is no1 corrosire if antioxidurkls are present; even i n the uhence of these siihstunces its corrosive effect is smull. IWSS.
bility of methylene chloride Tho present article deals with the stabilit,y a n d t h e behavior of trichloroethyleric under v a r i o u s cmditions arid its corrosive effect toward certain metals. The iiicreased use of trichloroe t h y l e n e as a noninflninmablc low-boiling solvent for extracting nils, fats, waxes, and food products, for degcaeing nret,ds, and for d r y cleaning pnrposes, Itas g i v e n rise t o illquiries coricerrririg the behax-ior of this s o l v e n t under variuiir n,iiditions. Conflict.ingopinione as to its stability arid-corrosive elfect are Souiid in scieiitific literature. Sastry ( 7 ) and Crudes ( 2 ) maintain that the decomposition and conosivc effect of trichloroethylene are slight. Griesheiiri Electron A. G. ( 6 ) states that trichloroetl~ylcneis corrosive, basing this coiiclusion on its use in the extraction of vegetable oils. Elsner ( 3 ) , studying the splitting off of hydrochloric acids from tricliloroethylene, finds that i t is slight and that consequently this solvent is not corrosive. Formanek (4)finds that the effect of trichloroethylene on coppcr, brass, tin, and iron after exposure for 8 weeks is negligible. In a series of tests trichloroethylene was submitted t o more drastic treatment than it encounters iii actual use, in order to determine its behavior under most extreme conditions. was discussed.
foiiiig
For iiistaiice, trichloroethyieiic was h e a t e d w i t h water from 50" to 150°C. (1229 t o 302'"F.) u n d e r p r e s s u r e , to note the amount of hydrolysis a t t,hese temperatures. I'HYsICAl. f'Eol'lWrIES r . .
Iricliloroethyleiie is a iieitvy l o w - b o i l i n g , noninflamiiiable liquid with a pleasant ethereal odor. Tlie physical properties of highly piirified trichloroetliylene have iieen d e t e r m i n e d in this IaborsLory and t i m e values are given in Table I. V a p o r pressures were detcrrnined by the mctiivd of I l a m s a y a n d (") a i ~ :*re l given in Figurc I Ikmi~i,~.vr~ OPo sT ~ l i ~ . t r i , l , a o t .i .r1~. :~~ .
Tile trichloroethylene used in determiniiig the pl~yaiciil properties and for stability tests was purified by steam-distilling factory-grade trichloroetliyiene (i:oiling range of 0.3-0.6" C.) from 10 per cent of its o w i m i g h t of niilk of lime. Tile steam-distilled material was chilled to -30" to -50' C. (-22' to -58' F.),and the ice removed by filtration through a chamois skin filter. The dried product was fractionated at an absolute pressure of 252 mnr. in a vacuum batch still of 45 kg. capacity, equipped with a i . 6 X 259 cm. column packed with chains, with a 3 1 refliis:produet ratio. .411
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October, 1932
ISDUSTRI.4L
A S D ENGINEEKISG
parts of the still, except the receivers, were constructed of iron. The receivers were of Pyrex glass covered with black paper t o exclude light. T.JLBLE I.
PHYsIC.4L P R O P E R T I E S O F
TRICHLOROETHYLEXE
Formula hlolecular aeiglit Color Odor Specific gravity ( 0"/4'
CzHCL? 131.4 Water-,white Sweet, ethereal
1.4996 1.4762 1.4514 1.4777
C.) (15'/4' C.) (30°/4' C.)
Refractive index. n12"* Viscoeity (25' C;), reentipoises (50; C.), centipoises (70 C.), centipoises Boiling p o i i t (760 mm.), C. Freezing point. O C. Coefficient of expansion Heat of vaporization, cal./gram ( B.t.u./lb.) Specific heat (liquid) Dielectric constant
0.550 0.446 0.371 86.7 -
ss
0 , 0 0 1193 58 (104.4) 0.233 3.42
Only the middle fraction of trichloroetliylene, amounting to about 40 per cent of the total, n-as saved for use in the
experimental work. The hoiling range of the middle fraction was within 0.2" C. and the acidity was less than one part in ten thousand; the moisture content was less than 0.005 per cent by weight. I n some of the experiments factory-grade trichloroethylene was used without any further purification. The boiling range of this material was within 0.6' C., and the acidity about fourteen parts in ten thousand. KO difference was detected in the stability of these two grades of material. In certain cases noted below, traces of antioxidants m-ere added. Small amounts of certain antioxidants are very effective in stabilizing trichloroethylene toward the accelerating effect of light. METHOD^
OF
AXALYSIS
T h e m e t h o d u s e d i n determining acidity in all the euperimental work c o n s i s t e d in adding 25 cc. of neutral d i s t i l l e d water to 25 cc. of trichloroethylene and t i t r a t i n g with 0.01 S sodium hydroxide, using phenolp h t h a l e i n a s i n d i v a t o r , until one drop of caustic gave a faint pink c o l o r , p e r m a n e n t for 30 s e c o n d s . One cubic centimeter 0 IC 2G 30 fo 50 60 70 g(l W of 0.01 S s o d i u m h y d r o x i d e TEFPEEATWE * C thus c o r r e s p o n d s to a n acidity FIGURE1. V ~ P O R PRESSURE OF TRICHLORO-of 0.001 p e r c e n t b y w e i g h t , E T H l LE\ F calculated as hydrochloric acid. The moisture content was found 1,y tletermining the temperature where trichloroethylene was saturated n-ith water (cloud point) and reading the per cent from a graph giving the relationship between cloud point :ind percentage moisture (Figure 2). STABILITY T E ~ T S
CHEJfISTRY
116.5
sulfuric acid, rinsed free from acid with distilled water, and dried. The stability tests where trichloroethylene was heated or exposed to light, when it was desired to exclude air, were carried out in 2 x 25 ern. glass t u b e s p r o v i d e d with a 1 x 10 em. constricted t u b e to facilit a t e s e a l i n g after trichloroethylene had been a d d e d . These t u b e s were carefully cleaned. and a i r w a s displaced w i t h n i t r o g e n . - Trichloroethylene was adg mitted through a longo o o o +*-----I _ _ stemmed dropping aoP,S I funnel in order not to A !
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introduce air, light be8Mli -_LAPA ing excluded in handling IO 2 t h e trichloroethylene. 7 f W P f R 8 7 L W' 6 These tubes were sealed, FICVRF2. SOLUBILITY OF W ~ T E R placed i n s i d e c a p p e d I \ TRICHLOROETHYLENE iron pipes, and heated in electrically controlled oil baths maintained to within 1O C. of the desired temperature.
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RESULTSOF TESTS STABILITY IS DARKXESSAT ORDIN.4RY TEMPERATURES. Pure trichloroethylene or factory-grade trichloroethylene coming directly from the stills does not decompose when stored in darkness in glass tubes, in glass-stoppered bottles, or in steel drums. In tests extending over one year, trichloroethylene has not developed any acidity. Since no decomposition has been noted in factory-grade or purified material, the presence of antioxidants has no apparent effect in darkness. STABILITY IS LIGHT. Trichloroethylene behaves like chloroform toward light and air. Schoorl (8) has found that chloroform decomposes in the presence of oxygen in light and that no decomposition occurs if either factor is excluded. I n the absence of oxygen trichloroethylene is not decomposed by direct or diffused sunlight. In a series of experiments trichloroethylene in a n atmosphere of nitrogen n.as exposed to direct light for 30 days, and the acidity n-as determined a t regular intervals and found to be from 6 to 10 cc. of 0.01 AT hydrochloric acid per 25 cc. of trichloroethylene (Table 11). The acidity noted is due to traces of oxygen. The fact that the acidity did not change or increase after the third day indicates that the last traces of oxygen had not been completely removed from the nitrogen. TABLE 11. DECOMPOSITIOS O F ~ ~ N S T A B I L I Z E DTRICHLOROETHYLEXE EXPOSED TO DIRECTSIXLIGHT (In cr. 0.01 ,V " 2 1 per 2 5 cc. C2HClsa) ~ D E C O J I P O S I TOI NO BEISG N EXPOSED:1 day 3 daye 11 days 17 days 140 178 155 118 In airb In nitrogenb 6 10 10 9 a Throughout this paper 1 cc. of 0.01 N HCI per 2 5 cc. of sample corresponds approximately t o 0.001% by weight of acidity calculated as HCI. b In sealed tube. CONDITIOXS OF EXPOSURE
The measurement of stability of trichloroethylene in light n a s carried out by placing 400 cc. of the material in clean
glass-stoppered bottles together n-ith iron strips and eyposing the bottles to diffused sunlight. The initial acidity and the acidity a t giren intervals n ere determined by titration. In the stability test in darkness trichloroethylene was stored in 2 x 1 3 inch ( 5 x 33 cm.) capped iron pipes. These pipes had been cleaned preriously by pickling in 20 per cent
In direct or diffuqed sunlight trichloroethylene develops acidity in the presence of oxygen. I n difiused sunlight the average amount of acidity after exposure for 3 days a t rooin temperature is about 20 cc. of 0.01 S hydrochloric acid per 25 cc. of trichloroethylene. After 7' days it amounts to about 50 cc. of 0.01 N hydrochloric acid. The acidity gradually increases so that after a month it may amount to over
Ilsal. 'l'rir:liioroetliSlti~~,heated in x d c d at,mosphcre of nitrogen ur i n an atrrrosjrliere i > I its WII vapors for 24 trows at, tempcr:it.ures belov; 130" C. (%Mi" F.), develops 110 acidity that can be ascribed to lieat ;dme The observed acidities as recorded in Tabit: 111, :iniinuiting to 10 cc. of 0.01 N Irydrocllloric acid l i e l m ~130" C., itre diir to traces of oxygen. At 150' C . ( 3 ( W F.: tlicrirral ,li.eoiril",sitiorr occurs uti exposure for 24 hours. Trichloroethylene vapor is sta.ble at terq)crature~Irelor\ %(iooC. ( 3 9 ! 2 O F,). In Table IV t.lx result of espoaiiig trii:trlorw&iylene vapor to the designated teniperaturw For 4 seeo~idsin coiltact with iron surfaces is surnniarized. At 2(10"
