UBC Theses and Dissertations

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UBC Theses and Dissertations

An analysis of ethyl alcohol and ether mixtures Fraser, Duncan 1929

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CAT Lf^/S;. ) t ACC. THE ANALYSIS OF ETHYL ALCOHOL AND ETHER MIXTURES A THESIS PRESENTED BY: DUNCAN^ FRASER, B.A.Sc. FOR THE DEGREE OF MASTER OF APPLIED SCIENCE THE UNIVERSITY OF BRITISH COLUMBIA. 1929. ANALYSIS OF ALCOHOL, ETHER, WATER MIXTURES In a research conducted "by Mr. Graham-*- on the catalytic conversion of of ethyl alcohol to ether a large number of yields consisting of alcohol, ether and water were obtained. These mixtures also contained ethylene dissolved in them. The ethylene was present in small amounts and it could easily be got rid of by boiling under a long reflux condenser. The problem was to find a method of determining the amounts of ether and alcohol present. A survey of theavailable literature showed that very few methods had been developed. I. Masson and T McEwan^ give a method whereby the alcohol and ether are separted with paraffin. This method requires fairly large amounts of solution and it does not seem as if the method would give very accurate results owing to varation in temperature and to in-complete separation. L. D e s v e r g n e s S describes a method whereby the.amount of one of the constituents that has to be added to produce turbidity or homogeneity is determined. From this value the alcohol ether content of the mixture can be obtained form a graph. Only an abstract of the method was avail-able and it did not give complete details. g P. Szeberinyi gives an oxidation method. The unknown solution is treated with potassium dichromate solution under certain conditions to oxidize the alcohol. It is then oxidized under different conditions to determine the ether. He gives factors by which the number of cubic centimeters of dichromate used cane be converted to grams of alcohol or ether. In Szeberinyi's method, the factors are empirical and. a certain correction has to be made to allow for the potassium dichromate reduced "by the ether in the determination of the alcohol. His method was tried on known mixtures but satisfactory results were not obtained. However, the method seemed capable of development. If alcohol is oxidized to acetic acid by potassium dichromatq, the reaction that takes place is expressed by the following equation: SKgCRaO? + 8HgS0^ + SCHgCHgOH = SCHgCOOH 4 gK^sO^ 4 2C3^(S0^ ^ ^ ^ If ether is oxidized by potassium dichromate it should also give acetic acid in accordance with th following equation: 4K2CR2O7 + 16 H2SO4 + SCHgCHgOCHgCHg = 6CHgC00H 4 ^ S O ^ 4 4Crg(S0^)g ^ 19^0 P^he theory on which the method to be described is developed is, that it ought to be possible to find a potassium dichromate solution of such strength that it will oxidize the alcohol only and not act on the ether. Thep.,it should also be possible to prepare a solution of such strength that it will completely oxidize both the alcohol and the ether. From the amount of each solution used the amount of alcohol and ether present could be calculated. The* first procedure was to find out if potassium dichromate solution would act on acetic acid. Accordingly acetic acid was boiled with known amounts of .5 N potassium dichromate solution. There was no evidence that acetic acid reduced the chromate. It was discovered, however, that the sulphuric acid reduces a few cubic centimeters of the solution and a correction, obtained by making a blank test, has to be applied^ - 3 -In order to determine whether the reaction represented in the ahove equation took place quantitatively, weighed amounts of alcohol were treated with dichromate solutions of various strengths and under various conditions. The method is as follows: The alcohol is weighed in a small glass stoppered bottle and this bottle and contents are transferred to a 500 c.c. flask containing a known amount of standarized dichromate. Sulphuric acid is added and the mixture heated. The excess dichromate is titrated and the amount of alcohol present is calculated from the above equation. The alcohol used was the ordinary 95% commercial alcohol which had been carefully dried by digestion with lime. Table I give results from a few preliminary determinations. 50 c.c. of .5 N potassium dichromate, diluted with 100 to 125 c.c. of water, was used. TABLE 1. Weight of Alcohol Weight Determined Percent Determined. .2256 .204 46 .3218 .237 73.7 .1740 .1692 97.2 .2060 .196 95 .2228 .207 94 .2936 .251 86 .1740 .1725 99.3 .1615 .1745 108 .1832 .1893 103.3 .1989 .216 108.6 From the above table we see that the results are very erratic. However, it seems to indicate that the reaction goes according to the equation given above. Owing to the strength of the solutions used, a small error in reading the burette, or measuring the solution will make quite a large error in the calculated value for the alcohol. To decrease - 4 -this error .IN solution was prepared and 100 c.c. of this was used far about l/lO of a gram of alcohol. Table 11 give results obtained by boiling the alcohol with 100 c.c. of .1 N potassium dichromate and 25 c.c. sulphuric acid (1:1) for fifteen minutes. TABLE 11. Weight of Alcohol Weight Determined Percent Determined. .0899 .0974 .0509 .1018 .0828 .0997 .1111 .0928 .0985 .0497 .0928 .0779 .0903 .1065 103.3 101 97.6 91 94 90.5 96 The above results are better than the previous ones, but show that something is wrong since the error varies greatly. It was suspected that the alcohol used, might contain impurities. Mallindrocht's absolute alcohol was then obtained and dried over lime. This alcohol was used in all the following determinates. Table 111 gives results obtained with the pure alcohol. The conditions were the same as in Table 11 except that 20 c.c. of concentrated sulphuric acid was used instead of 25 c.c. of 1:1 acid. TABLE III. Weight of Alcohol Weight Determined Percent Determined. .1108 .107 96.8 .0956 .0945 98.8 .0978 .0970 99.3 The above results are better but all are low. This was accounted for by assuming that on boiling, the alcohol was vaporized and remained above the solution. Accordingly a new procedure was adopted. The oxidizing mixture consisted of 100 c.c. of .1 N KgCrgOy and 25 c.c. of HgSO^. 1:1. The weighed amount of alcohol was added to this solution and the mixture heated on a water bath at a temperature kept between 75 and 80. Table IV shows some results. Weight of Alcohol TABLE IV. Weight Determined Percent Determined .0877 .0875 99.7 .0829 .0791 95.5 .0726 .0724 99.7 .0808 .0806 99.7 .0693 .069 99.5 .0804 .0803 99.9 .0880 .0893 101.5 .0817 .082 100.3 From the above table we see that the oxidation gives practi-cally exact results. However, when ether was added it was found that the results always came too high and a blank test with ether alone showed that from 3 to 6 c.c. of the chromate were reduced. Various mixtures were then tried, to which water was added to reduce the concentration. However, it was found that when the concentration went below .08 N the reaction went very slowly. Reference to Beilstein showed that Kurilau^ had used dich-romate for determining ethyl acetate by hydrolysis and oxidation of the alcohol. He found that 100% oxidation could be obtained at 100 C with .1 N chromate solution and 80 c.c. 6f dilute sulphuric acid. Accordingly the following procedure was tried. A weighed amount of alcohol was added to a mixture of 100 c.c. of .08 N KgCrgQy and 80 c.c. of HgSO^ (1:1) . This solution was heated for two hours at 100 C on a water "bath and then the excess dichromate titrated. Very satisfactory results were obtained as shown in Table V. Weight of Alcohol .0961 .0957 .0871 .0794 .0871 TABLE V. Weight Determined .0967 .0965 .0885 .0791 .0865 Percent Determined 100.6 100.5 101.6 99.5 99.2 This table contradicts Table II where low results were ob-tained by heating to 100 C. The only explanation that can be offered is that in the previous case the solution was not accurately standardized. Next, about .2 c.c. of ether was added along with a weighed amount of alcohol and the mixture treated exactly as in Table V. Table VI gives the results: TABLE VI. Weight of Alcohol Weight Determined Percent Determined. .0905 .0822 .0910 .0848 .0901 .0825 .0921 .0846 99.5 100.2 101.1 99.8 Several determinations were also made using the same solution as above and pure ether alone. In no case was it found that the ether reduced any of the chrornate. It was therefore assumed that in any mixture of ether and alcohol, only the alcohol would be oxidized under the above conditions. - 7 -The Oxidation of ether with .5 N potassium dichromate was next investigated. Several determinations were made using a hot solution, and in all cases it was found that the ether determined was imich less than the amount put in. This was probably due to the fact that ether is very volatile and is practically insoluble in water. The oxidation of ether in the cold was next tried. The method was to weigh out about .1 gram of ether and put it in a small flask with 20 c,c. of .5 N dichromate solution and 10 c.c. of concentrated sulphuric acid. This mixture was allowed to stand from twelve to eighteen hours and then the excess dichromate was titrated. The ether was completely oxidized to acetic acid in that time as Table VII shows: TABLE VII. Weight of Ether Weight Determined Percent Determined .0757 .0754 99.5 .0745 .0756 101.5 .0742 .0745 100.3 .0836 .0830 99.2 .0789 .0791 100.4 A few determinations were made with alcohol alone under the above conditions to see if it were oxidized completely. The results of two determinations are shown in Table VIII. TABLE VIII. Weight of Alcohol Weight Determined Percent Determined .0821 .0854 .0824 .0850 100.3 99.6 Mixtures of alcohol and ether were then prepared containing known amounts of each. These were treated as above so that both alcohol and ether were oxidized. The excess of dichromate was then titrated. The number of cubic centimeters of chromate used by the alcohol was calcu-lated from the weight and subtracted from the total number of cubic centi-meters used. This gave the amount of chromate used by the ether. In this case all the error is thrown on the ether determination since the alcohol is assumed to react exactly quantitatively. Some results are shown in Table IX. TABLE IX. Weight of Ether Weight of Alcohol Ether Determined % Detmd. .0564 .0895 .0573 98.8 .0895 .0806 .0901 100.8 .0506 .0632 .0511 100.1 A mixture of alcohol, water and ether was prepared containing 43.7% alcohol and 26.0% ether. Analysis by the above method gave: Alcohol 43.8% Ether 25.8% The analysis of one mixture is really not sufficient proof of the accuracy of the method and more analysis will have to be done before the method can be relied on. The detailed procedure for analyzing a mixture is as follows: Analysis for Alcohol: A mixture consisting of 100 c.c. of potassium dichromate solution (.08 to .09 N) and 80 c.c. of sulphuric acid (1:6) is prepared. About ' - - W - 9-About .15 grams of the unknown alcohol solution is added, to the above in a 500 c.c. flask. This mixture is heated, on a water bath at 100 C under a reflux condenser for two and a quarter hours. At the end of that time the solution is cooled and diluted to about 500 c.c. 25 c.c. of a 10% potassium iodide solution is next added and the liberated iodine is titrated with sodium thiosulphate using starch as an indicator. This gives the amount of chromate not acted on by the alcohol. From this, the amount of chromate used and the weight of alcohol can be calculated. Using the equation, the calculation works out to the following formula: C x N x .01152 = Wa C 2 number of c.c. of chromate used. N - Normality of chroma,te solution. Weight of Alcohol. Determination of Ether. 50 c.c. .5 N potassium dichromate is mixed with 25 c.c. of con-centrated sulphuric acid in a 60 c.c. flask. The mixture is cooled and to it is added a weighed amount of the alcohol solution. This mixture is allowed to stand for 12 to 18 hours at room temperature. It is then diluted to 400 c.c. 25 c.c. of a ten percent potassium iodide solution is added and the liberated iodine is titrated with sodium thiosulphate as before. The bich-romate used by the alcohol is calculated, and hence the amount used by the ether can be found. The formula for the calculation is: N x C x .00926 = Wg Wg = Weight of ether. The above reaction for ether should be carried out in a small flask since it is necessary to keep the ether in as close contact with the solution as possible. - 10 -REFERENCES: 1. Graduate Theis - University of British Columbia. 2. Transactions of the Society of Chemical Industry, Vol.40, 1921, p.29 T. 3. Moniteur Scientifique due Docteur Quesneville. 11, 145 - 150, 1921. 4. Zeitschrift fur Analytische Chemie. 1915, 54: 409 - 4 1 1 . 5. Berichte der Deutschen Chemischen Gesellschaft. 7.341. 


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