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Vapour pressures of cis decahydronaphthalene Pilkington, William Thomas 1941

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ff7 /o Vapour Pressures of CIS DECAHYDRONAPHTHALENE .William T.Pilkingtom 0 O 0 A Thesis submitted i n P a r t i a l Fulfilment of The Requirements for the Degree of MASTER OP APPLIED SCIENCE i n the Department of CHEMISTRY 0 O 0 The University of B r i t i s h Columbia Table of Contents. Page Acknowledgment Purpose of the investigation 1 Method of raeasurment 1 Method of obtaining pure decalin 1 Diagram 3 Results of experiment 7 Consideration of results 8 Dynamic method attempted 11 Diagram 12 Suggested dynamic method 14 Consideration of pl o t of log P vs ^  16 Acknowledgment.. The author wishes to take t h i s oportunity to thank Dr.W.F.Seyer of the Department of Chemistry, under whose supervision t h i s work has "been carried out, for the many help f u l suggestions he has given throughout the investigation. Vapour Pressures of CIS DECAHYDRONAPHTHALENE. ,. Purpose of the Investigation. This investigation was carried out to confirm, i f possible, the experimental results obtained by H.Nemetz MASc i n 1937 at the University of B r i t i s h Columbia i n his work on the vapour pressures of c i s deeahydronaphthalene, or, f a i l i n g to confirm these, the values of t h i s investigation w i l l be tabulated. Method of measurement The method used was the same as i n previous va-pour pressure investigations of the vapour pressures of "de-c a l i n . " This was a s t a t i c method using a special type of mercury manometer f o r themeasurements. The description and operation of the apparatus has been described i n e a r l i e r works. This work does not warrant a lengthy description of the apparatus and the method of operation since i t was carried out merely to check e a r l i e r values. The author wishes, though, to describe i n d e t a i l the technique devel-oped to obtain pure decalin f or the vapour pressure measure-ments because when t h i s method i s carefu l l y followed i t was- • found possible to obtain reproducable results with diff e r e n t decalin samples* Method of obtaining pure decalin. The apparatus i s constructed as shown i n the -1-diagram.,, ,f>age 3. The tubing i s of 2 to 3 mm. inside diameter and heavy walled. The bulb (d) has approximately < twice the capacity of (e) and (c) twice the capacity of (d). A l l the glass must be carefully cleaned with some suitable cleansing agent, say, chromic acid; i t i s next washed w e l l , dried i n an oven and then cooled. While blowing the glass, a drying tube of ?2°5 s n o u l d ^ e used to prevent moisture from the breath from entering the apparatus. When the various parts are sealed together as shown, the apparatus i s evacuated and tested f o r leaks, and, i f there are no leaks then i t i s pumped off for several days. During the pumping Ufi;i't,V;:v!;.±.£ o f f the glass i s gently heated at i n t e r -vals to help expel the l a s t traces of a i r and water vapor. Pumping i s with a mercury d i f f u s i o n pump backed with a Cenco rotary o i l pump and such a pumping unit w i l l give a very low pressure and t h i s pressure should be checked occa-sion a l l y with the meLeod gauge to make sure the pumping i s progressing s a t i s f a c t o r i l y . When the pumping off has gone on f o r several days the mercury i n the manometer (k) i s frozen with "dry i c e " and a i r , dried by passing over: PgOgin (1), i s admitted to the part of the apparatus shown as the l e f t hand side i n the diagram. The bulb (c) i s f f i l l e d with pure c i s decalin, the mouth i s connected to a drying tube and the bulb i s immersed i n dry ice u n t i l the decalin i s frozen. Then the bulb i s sealed on as shown i n the diagram. The decalin i s kept -3-Diagram showing construction of" apparatus used to obtain pure.decalin. to pump f ^ stop-cock to pump • i : P2°5 - 1 stop-cock "^~thermpmeter -m MP Y h -mercury d g Ah decalin a frozen with dry ice and the apparatus pumped o f f for about an hour. After pumping has proceeded for an hour the dry ice i s taken away from the decalin bulb and the decalin allowed to melt slowly. Bubbles of entrained a i r w i l l be seen to r i s e through the l i q u i d . At t h i s time the trap (a) i s surrounded with dry ice to prevent any decalin being carried through the apparatus because, i f i t i s , then i t i s impossible to pump down to the desired low value. Vi/hen a l l the entrained a i r has ' escaped the decalin i s again frozen and pumping off i s contin-uedfor about 1-^- hours. During t h i s time the tubing i s gently heated to aid i n expelling the a i r . A tedious but necessary procedure of slow d i s t i l l a t i o n of decalin follows next. The dry ice i s taken away from bulb (c) and i s placed around (b) and dry ice packs are placed on the tubing at (h) and ( f ) , The pumps can be l e f t on to the end of the d i s t i l l a t i o n s provided the trap (a)' i s properly surrounded'with the dry i c e . The decalin should not be heated yet but should warm slowly. Some of i t w i l l be d i s t i l l e d from the bulb as i t warms and w i l l condense and be frozen to form constrictions or plugs at (h) and ( f ) . Not u n t i l these two places are completely stoppedwitri frozen decalin should d i s t i l l a t i o n be started else the operator w i l l have decalin i n any bulb but the one he wants. When the plugs are frozen i n place the tubes "; w i l l be blocked at (h) and (f) and then the decalin bulb (c) may be surrounded with a water bath and the temperature raised to about 80°G. This causes decalin to d i s t i l l into the reject "bulb (b).' "When of the t o t a l decalin has been d i s t i l l e d into, .(b) the water :.bath i s removed and ( c ) i s surrounded with dry, ice to prevent, further d i s t i l l a t i o n to prevent further d i s t i l l a t i o n into (b). and also to prevent the d i s t i l l a t i o n being so rapid that the positions of the plugs cannot be changed. These plugs at (f) and (h) are melted and new ones are formed at (g) and ( i ) . Then the procedure i s repeated^ i . e . the dry ice i s removed from bulb (c) and d i s t i l l a t i o n allowed to proceed slowly u n t i l the two new plugs have been formed at (g) and ( i ) . Bulb (d) i s surrounded with dry ice and (c) with a water bath at about 80°C. D i s t i l l a t i o n i s maintained from .(c)••to (d) u n t i l approximately \ of the o r i g i n a l volume of decalin remains. At t h i s point the water bath i s removed and replaced with, dry ice for a few minutes. The neck of (c) i s constricted and the bulb containing \ of the o r i g i n a l volume of decalin as reject i s drawn o f f , Now,I with bulbs (b) and (d) frozen and also the trap (a), the plugs at (g) and ( i ) are melted and as much as possible are driven into either (a) or (b). The dry ice i s taken from the trap and the trap i s inspected to make sure that i t i s not constricted with decalin frozen i n the i n l e t tube. I f i t i s , then t h i s w i l l melt i n a few minutes and w i l l f a l l to the bottom of the trap and so allow pumping o f f of the whole apparatus. Then the dry ice i s replaced and the apparatus pumped o f f f o r an hour, i f possible, or at leas t f o r a h a l f hour. After t h i s pumping the whole procedure i s repeated i n d i s t i l l i n g from (d)to (e). D i s t i l l a t i o n , from (d) to (e) i s done by placing plugs at ( i ) and (f) and allowing \ of the decalin i n (d) to d i s t i l l into (b). The plugs (1) and (f) are removed and new ones are placed at (h) and ( j ) . Decalin i s d i s t i l l e d into (e) u n t i l i t i s approximately f u l l . The bulb (d) i s surrounded with ice and i s sealed o f f as was (c). The ice i s taken from (e), (b) i s surrounded with ice and the plugs are removed at (h) and (j) and a new one formed at ( f ) . Then (e) i s gently warmed and decalin d i s t i l l s into (b) u n t i l the required amount i s l e f t - say, to •§ f u l l . Then (e) i s surrounded with ice and frozen, plug (f) i s removed by d i s t i l l a - t i o n into the trap and the trap i s inspected to see that i t i s not stopped and i s clear f or pumping. When i t i s cleared pumping i s continued for at least an hour longer. The glass tubing i s gently warmed to malee sure that no decalin i s condensed on i t especially at the section where the tubing i s to be sealed f i n a l l y because; any decalin here would be decomposed by the hot tubing andgive high results (as shown later).When pumping i s complete the f i n a l sealing o f f i s at (n) ~ as close to the decalin bulb:,as possible. I f t h i s procedure i s carefully-carried'out the results obtained have been shown to be reproducible by t h i s investigation. The results obtained i n the investigation are shown on the next page; also calculations of log P and where T i s i n absolute degrees. Table 1 shows the results at one temperature obtained with three different samples. Table 2 shows the pressures obtained with t h i s sample 3. -7-Results of experiment. Table 1 .  Sample Vap. press. cm.Hg. at 3 7 O C . 1 0,246 2 0.246 3 0,252 Temperature Table 2 Vap. press. log.P i x 10 °c °A Cm. Hg. -20.0 253.0 0.017 -1.7700 . 3.953 -10.0 263.0 0.030 -1.5229 ..3,802 0,0 .273.0 0,051 -1.2924 3.663. 24.1 297.1 0.160 -0.8239 3,365 29.0 302.0 -0.7670 3.311 30.0 303.0 0.185 -0.7328 3.300 37,0 310.0 0.252 . -0.5986 . 3.226 46.0 319.0 0.334 -0.4763 3.135 52.0 325.0 0.433 -0.3635 3.077 59.0 332.0 0.644 -0.1911 3.012 68.0 341.0 1,100 0.0414 2.933 30.0 353.0 1.886 0,2755 2,833 102.0 375.0 4.857 0.6864 2,667 109.0 115:0 125.0 140.0 157.0 167.0 177.0 382.0 388,0 398.0 413.0 430.0 440.0 450,0 6.256 7; 953 11.439 18,210 30.101 40.02 53.01 0.7963 0.9005 1.0584 1.2603 1.4786 1,6023 1,7244 2.618 2.577 2.513 2.421 2.326 2.273 2.222 Consideration of Results. The results shown i n table 1 are for three different samples of pure c i s decalin which were obtained using the method described e a r l i e r . The temperature 37°C was chosen to check the values because i t lends i t s e l f quite easily to accurate temperature control and also because the vapour pressure was appreciable and so the r e l a t i v e error i n reading was less than i f a lower temperature such as 0°C was chosen. The results show that there was quite a good check i n the values f o r the three samples. These results should have considerable significance as may w e l l be pointed out here. With t h i s method of measuring vapour pressure there i s always danger of the presence of a i r or water vapour i n the bulb with the decalin along with the danger of having decomposit-ion products present, these being formed by contact of decalin vapour or l i q u i d being i n contact with the hot glass during •' the f i n a l sealing-off of the apparatus. These errors would a l l give high r e s u l t s , Now, with the s t a t i c method, i t i s f a i r l y obvious that, provided the evacuated side of the manometer i s kept at a very low pressure, then the smaller the value observed the more closely the sample i s to being pure and giving only the vapour pressure of the decalin at the temperature considered,Numerous samples were tested during the course of the work and i t i s very s i g n i f i c a n t to point out that.no sample gave a vapour pressure lower than ,246 cm. at 37°C. Now three independant samples gave vapour -9-pressures l^ w^ -tl^ aa^ -fe^ fefei©. value. Further,the apparatus was so constructed that the evacuated side of the manometer could be pumped o f f at any time and t h i s was done a number of. times during the test because the only factor wMch could give low values would be leakage on t h i s side. Since the samples gave f a i r l y reproducable r e s u l t s , the true value of the vapour pressure at 37°C must be close to t h i s value -- i t may be found to be a l i t t l e lower but could never be higher. Therefore, with any sample used i n the future, t h i s temperature could be used as a means of checking the sample and i f the new sample were higher than those shown, then i t should be discarded as of l i t t l e use i n vapour pressure determination. The results of table 2 show the highest value obtained with the sample under test was 177°C. In attempting to go to a higher temperature of 188°C, the temperature of the.tube connecting the decalin and the manometer was set at 216°C as read by the.thermometer (m). The temperature of the bath was held at 188°C but the column of mercury had to be continuously and slowly increased u n t i l i t was obvious that the vapour pressure was abnormally high. The bath was cooled to room temperature and the vapour pressure decreased as was expected but when at room temperature i t was found that there was s t i l l a pressure of some 20 cm of mercury above the . decalin. This pressure neither increased nor decreased on standing. This pressure must be attributed to decomposition of the decalin i n the tube connecting the decalin bulb with the mercury : manometer when the temperature registered on the- • thermometer was 216°C because there was no evidence of leak-age i n the system and because the increasing pressure stopped when the temperature of the tube was decreased. This fact i s very s i g n i f i c a n t because i t may account for- the higher values obtained with some of the e a r l i e r samples i f the f i n a l sealing was attempted before the decalin had been completely removed from the inside of the tube. Even i f a l l the decalin i n the: system i s frozen, there w i l l s t i l l be a very small amount of vapour l e f t corresponding to the pressure i n equilibrium with the frozen decalin and t h i s vapour w i l l be subject to decomposition thus leading to error which i s inherent i n the apparatus. However, t h i s pressure .must be very small provided i t i s the pressure i n equilibrium with the frozen decalin so that: the error introduced may be negiigable or nearly so. The f a c t that i t may be negiigable could possibly be drawn from the reproducability of the results as shown i n table 1. For low temperature work, say from 0°C down, considerable d i f f i c u l t y was encountered because the pressures found were too small to be measured with any desired accuracy with the cathetometer. I t was seen that some other method was desirablef® for these low temperatures and a dynamic method was chosen because i t not nnly gave a very desirable means of obtaining these pressures but also gave a means of checking the values being obtained with the s t a t i c method.Such a method - 1 1 - , , was attempted "by the author but was not successful. The method used w i l l be described together with another method which should prove successful. This new method was developed with the aid of experience gained through the older dynamic method. Dynamic method attempted. 'The apparatus used was as shown i n diagram l, page 1 2 . Nitrogen, dried by passing over P 2 O 5 , was bubbled very slowly through f i v e bulbs as shown and these bulbs were immersed i n a constant temperature bath. The tube connecting the decalin bulbs and the absorbing unit was wound with nichrome wire so that the tube could be heated when working above room temp-erature otherwise there would be condensation i n t h i s tube and lead to low res u l t s . The decalin was to be absorbed out of the nitrogen by passing the decalin laden nitrogen through a series of tubes containing activated charcoal and immersed i n dry ice thus giving double assurance that the decalin had been removed - i.e. freezing i t out and also absorbing i t out with the charcoal. The amount of decalin absorbed was found by weighing the absorbing bulbs before the t e s t and aft e r and talcing the difference. Then the nitrogen was passed to a large f l a s k so that i t s volume could be measured. A P 2 O 5 tube i s used between the fla s k and the absorbing unit because the volume of nitrogen was measured over water and some water vapour might be absorbed with the charcoal and so give high r e s u l t s . At the beginning of the t e s t , water i s introduced from the bottom of the f l a s k to displace the a i r -12-gjagram 1^ , Showing arrangment.of apparatus f o r dynamic method. through the stop-cock at the top of the fla s k until- i t came to .the mark scratched on the top of the flask. The pressure of the a i r above the water was made equal to atmospheric by opening the stop-cock and the manometer was leveled. During the test t h i s water was. run out of the flask at the same rate that the nitrogen entered u n t i l i t reached the lower mark. The rate could be observed by watching the manometer. The volume of gas collected must be known and t h i s i s best found • by ca l i b r a t i n g the fla s k between the two marks. The calibar-t i o n can best be done be weighing the amount of water contained between the marks. The vapour pressure of the decalin at the temperature of test can be calculated from:-v.p,, of decalin _ volume of vapour t o t a l pressure ~ t o t a l volume In order to determine whether or not the nitrogen was saturated as i t l e f t the decalin, decalin was introduced into only three of the f i v e bulbs and a test run. The results shown below indicate that only p a r t i a l saturation was obtained. Then the f i v e bulbs were f i l l e d and another test made. The re s u l t s of these are shown next. Test 1 using three bulbs Vap. press. = .113 cm. Eg. at 37°C. Test 2 using f i v e bulbs Vap. press. = .193 cm. Hg. at 37°C. . From the above results i t w i l l be seen that saturation was not nearly complete considering the fact that the rate at which saturation would be approached would be an Exponential. -14-Also, considering the values obtained by s t a t i c means, the vapour pressure indicated i s about-0,25 cm Eg., so the nitrogen'must have been f a r from being saturated. In test 2 using f i v e bulbs, the rate at which the nitrogen was passed through was made as slow as possible being 6^ hours to pass something over 5 1, of nitrogen. The absorbing unit was considered to be quite satisfactory; p r a c t i c a l l y a l l of the-decalin was removed by the f i r s t bulb. The results of test 2 show the increase i n weight of the charcoal bulbs ass-Increase i n 1st bulb 0,0677 gm« decalin Increase i n 2nd bulb 0,0017 .gm, decalin From the results of these tests i t i s indicated that the absorbing unit was quite satisfactory but that the method of saturation was poor. Suggested dynamic method. The method to be suggested i s designed to remove, .so f a r 'as possible, the d i f f i c u l t i e s encountered i n saturating the nitrogen with decalin. Apart from t h i s change the method i s the same as described above; i . e . dry nitrogen i s used as the carrying agent, charcoal cooled with dry ice i s the absorbant, and the same flask i s used to measure the volume of gas. The saturating unit i s to replace the f i v e bulbs used e a r l i e r . The method w i l l be to p a r t i a l l y saturate the nitrogen at a temperature somewhat higher than that at which -15-the vapour pressure i s desired, cool the gas to the desired temperature, and then absorbe the decalin. The p a r t i a l satur-ation at- the- higher temperature must he complete enough that ,.; the nitrogen i s saturated at the lower temperature. More complete saturation can he obtained by either r a i s i n g the temperature of p a r t i a l saturation or by having the nitrogen pass a greater S§pth; of l i q u i d . In order to make absolutely sure that the gas i s saturated i t i s better to have i t more than saturated at the lower temperature so that some conden-sation occurs. I f condensation i s to occur, then a l l - entrain-ed l i q u i d must be removed or the results w i l l be high. The saturation and also the-removal o f entrained l i q u i d w i l l be ; easier i f the bulbs for p a r t i a l saturaturation and the tube i n the constant temperature bath are f i l l e d with some type of packing, say with glass wool, to give greater surface. Some experimental work w i l l have to be done with the apparatus to make sure, f i r s t , that the nitrogen w i l l be saturated at the temperature of test and, secondly, that the glass wool i s s u f f i c i e n t to take out the excess decalin. An apparatus of the type described i s shown i n diagram 2,page 12. Apparatus of t h i s type can conveniently be used for temperatures below room temperature and also might be adopted f o r temperatures considerably above room temperature to include the c r i t i c a l regions i n the v i c i n i t y of 38° and 52°C. This method w i l l remove the d i f f i c u l t i e s encountered with the previous apparatus for dynamic determinations and w i l l also avoid the d i f f i c u l t i e s encountered i n obtaining satisfactory results -16-•with the s t a t i c method at low temperatures. Consideration of plot log P vs T With a normal pure l i q u i d , a pl o t of log P against jj* usually gives a straight l i n e . In the case of pure c i s &e decalin the l i n e i s not continuously straight but i s interupted with several discontinuities. When the results of t h i s work are plotted no dffinate conclusions can be drawn. This i s c h i e f l y because the values cannot be found with s u f f i c i e n t accuracy i n the temperature region up to, say, 100°C. I f the vapour pressures i n t h i s temperature region could be found with s u f f i c i e n t accuracy, then some definate conclusions could possibly be drawn. This was one of the reasons the dynamic method was t r i e d ; i t i s hoped that the dynamic method w i l l give precise values i n t h i s region e 


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