The Saturation of 2 Pentene with Hydrogen Bromide Citation Moyse, Hollis Weaver (1924) The Saturation of 2 Pentene with Hydrogen Bromide. Bachelor's thesis, California Institute of Technology. doi:10.7907/ABQD-8M14. https://resolver.caltech.edu/CaltechETD:etd-06162004-133650 Abstract No Abstract. Item Type: Thesis (Bachelor's thesis) Subject Keywords: Chemical Engineering Degree Grantor: California Institute of Technology Division: Chemistry and Chemical Engineering Major Option: Chemical Engineering Thesis Availability: Public (worldwide access) Research Advisor(s): Unknown, Unknown Thesis Committee: None, None Defense Date: 1 January 1924 Record Number: CaltechETD:etd-06162004-133650 Persistent URL: https://resolver.caltech.edu/CaltechETD:etd-06162004-133650 DOI: 10.7907/ABQD-8M14 Default Usage Policy: No commercial reproduction, distribution, display or performance rights in this work are provided. ID Code: 2616 Collection: CaltechTHESIS Deposited By: Imported from ETD-db Deposited On: 17 Jun 2004 Last Modified: 31 Jul 2020 20:51 Thesis Files Preview PDF (Moyse_hw_1924.pdf) - Final Version See Usage Policy. 883kB Repository Staff Only: item control page

THE SATURATION of 2@ PENTENE WITH ’ HYDROGEN BROMIDE. THESIS by Hollis W. Moyse. In partial fulfillment of the requiremeuts for the degree of Bachelor of Science in Chemical Engineering. CALIFORNIA INSTITUTE OF TECHNOLOGY. Pasadena California. 1924 THE SATURATION OF 2 PENTENE WITH HYDROGEN BROMIDE. INTRODUCTION. The purpose of this investigation was to de- termine whether 2 pentene upon saturation with hy- drogen bromide, gave 2 brom pentene or 3 brom pen- tane or, in case some of both compounds was formed, to determine the relative proportion of the two compounds existing in the product. _ There are two theories existent by which the position to which the entering hydrogen and brimine atoms will go, can be predicted. | 1. The first of these two theories is the alter- nate polarity theory which states that the carbon atoms in a chain are alternately positive and nega- tive. This theory as avplied to the structure of 2 pentene will appear as follows: -C- +04 - ¢ =tO+ - ¢- 1 2 3 4 5 The first carbon atom has four negative charges, three of which are neutralized by the positive charges of the three hydrogen atoms joined to it. ‘The second carbon atom has two negative charges neutralized by hydrogen and two positive charges neutralized by the two negative charges of adjoining carbon atoms, etc. Page 2 Prom a study of the relation between the third and fourth ~ garbon atoms, it is evident that the third carbon atom is much more negative than is the fourth carbon atom. Hence, in the addition of H* Br’to this compound, the prediction of the al- ; ternate polarity theory is that the KBydrogen atom being posi- . tive would be attracted to the more negative of the two carbon atoms, and therefore, would go to the third carbon atom. On the other hand, the bromine being negative would go to the fourth carbon atom. Thus we may see that in the saturation of 2 pentene with hydrogen bromide, the alternete polarity theory would predict that the compound formed would be 2 brom pentane. CH. CH, CH, CH BF OH, The second of the two theories is known as the electron displacement theory and its theory as to the relation existing between carbon atoms in a chain, appears graphically as follows - only the electrons participating in the displacement will be illustrated: Cs: GC: C:: €: C The above represents the relative position of the electron without any displacement. After the displacement of the elec- trons we have the following relationship. Page 3 2 C 3: Cc ;: The reason for this shift may be stated as follows: The carbon atoms 1 and 2 constitute an ethyl group, which is more C positive in its effect than is the single carbon atom 5. AS a result the, two electrons between carbon atoms 2 and 8 are displaced toward carbon atom 3. This causes a shift of the four electrons between carbon atoms 2 and 4 toward carbon - atom 4. This may be explained by Saying that each carbon atom has a constant potential and, because of this, when the potential is increased on the one side by a displacement of the electrons toward a carbon atom, there must be a corres- ponding shifting away of tne electrons oi the other side of the atom. From a consideration of carbon atoms 3 and 4, it is seen that carbon atom 4 is much more negative than is carbon atom 3, because of the displacement of the four electrous constituting the so-called double bond toward the fourth carbon atom. Hence, in the addition of E* Br; the vromine being neg- ative, will be attracted to the more positive of the two car- bon atoms, which is the third carbon atom. The hydrogen atom, similarly, since it ig positive, will be attracted to the fourth carbon atom which is the more negative of the two. . _ Page 4 The prediction of the electron displacement theory then > is that upon the addition of hydrogen bromide to 2 pentene, 3 brom pentane, CH, CH, CH Br CH, CH,, will be formed. 3? Since the alternate polarity ‘theory predicts the form- ation of 2 brom penta née and the clectron displacement theory ndicates that 3 brom pentane will be formed, the correctness ot the ‘two theories can be ascertained through the saturation + Oot 2 pentene with hydrogen bromide In the attempt to test the correctness of the alternate polarity and electron displacement theories, it.was decided ‘that the Saturation of 2 pentene with hydrogen bromide would be used as a test reaction, because of the fact that the al- ternate polarity theory predicted that the oromine would be added to the second carbon atom of the chain, while the elec- tron displacement theory predicted its addition to the third carbon atom. s fi In order to carry out the above reaction it w. t or ? ae] necessary to synthesize & pentens involving the following steps, in the order mentioned: (1) Preparation of ethyl formate from sodium formate snd ethyl alcohol. Page 5 (2) Preparation of diethyl carbinol by use of Grignard's Re- action. (3) Preparation of 3 brom pentane from diethyl carbinol. {4) Unsaturation of 3 brom pentane to give 2 pentene. “The 2 pentene was then saturated with hydrogen bromide, form- ing brom pentane. | | Since the boiling points of the 2 brom and 3 brom pen- tane are 113°C anda 118°C respectively, it seemed advisable to have a method of analysis for the two comrounds which was in- ‘dependent of the boiling points because of the small temper- ature difference existing between them. | Since no chemical method of analysis could be found to “use in distinguishing between the two compounds, it was de- cided to ascertain whether there existed any appreciable dif- ference in the refractive indices of the two compounds. Upon preparation of the two compounds a reading at 20°C for the 3 brom pentane of 1.4443 was obtained with an Abbe refractometer, while the reading of the 2 brom pentane was 1.4322 at 20°C. However, because of the difficulty of obtaining pure 2 pentanol the figure given for the index of 2 brom pentane may be slight- ly in error. The large difference that was found to exist between the indices of refraction of the two compounds justified the use Page 6 of the indices as a metrod of analysis and the results of the : promination of 2 peutene were interpreted by the use of this method of analysis in conjunction with that of the difference .of the boiling points. The first bromination of the 2 pentene was carried out at 60°C, in’ a pressure bottle containing glacial acetic acid gaturated with an excess of hydrogen bromide and gave a brom pentane which, after washing and drying, was distilled using a fractionating colwmi. The first drop of distillate came over at 117.2°C, but practically the whole of the distillate. came over between the temperatures of 118° and 118.2%. ‘The reading for the refractive index of the product of this run was 1.4430 at 20°. The second oromination was carried out in the cold without the use of pressure by placing the pentene in an Erlenmeyer Flask containing glacial acetic acid saturated with an excess of hydrogen bromide. In the distillation of the washed and-well dried product the first drop of the distillate came over at 117.4°and, as in the virst run, the temperature immediately rose to 118° and stayed constant there for the remainder of tne run. | Page 7 The: refractive index for the brom pentane obtained in this run was l. 4431 at 20° agreeing very closely with the value of 1.4430 from the first run. DISCUSSION OF EXPERIMENTS.» In the preparation of some-of the comrounds involved in the synthesis of 2 pentene, the literature on the subject was. found to be either unsatisfactory or totally lacking and for this reason original methods of preparation were used which may be of interest. | A new method of preparing ethyl formate was developed in which ethyl sulphuric acid (1 mol of ethyl alcohol+1.15 mols of sulphuric acid, sp. G. 1.84) was added to 1 mol of OP. Sodium formate and allowed to stand over night. Upon distillation the following day, water white ethyl formate was obtained. The whole of tke ethyl formate upon redistill- ation came over within a temperature range of .4°. The yields using this method were very satisfactory varying from 87% to practically theoretical. 1 One method for the preparation of ethyl formate which was found in the literature, involved the mixing of ethyl alcohol and glacial formic acid with a subseouent satura- tion with dary hydrochloric acid gas. It can easily be seen that the first mentioned method rossesses several iy J. Gheme Soon Vol 63. P 1508, Page 8 “ gdvanteges, in that it does away with the necessity of obtain- ing glacial formic acid and also does not call for the satura- tion of the solution with hydrochloric acid gas. In preparing this ester it is desirable to have all re- agents as water-free as possible and because of the tendency -of formic acid to form a constant boiling mixture containing about 30% water, it is advantageous to do away with the use of formic acid in the reaction. The preparation of diethyl carbinol from ethyl formate was carried out by means of Grignard's reaction and conformed very closely with the methods mentioned in the viterature, with the exception perhans of the relative auantities of material used and in minor points of technique, as for instance the dissolving of the solid matter in the bottom of the resctio. flask with dilute sulphuric acid in order to form two layers of liquids in the flask, one of which, the ether layer, contained practically the whole of the product desired. An extremely satisfactory method for brominating alcohol and unsaturated hydrocarbons was made use of in the experi- mental work of this research. Use was made of pressure bottles in all cases reouiring bromination. The alcohol to be 1. Compt. Rend 152, 336, 1901 Je Chem Soc, 1901, 1,250 Je Chem Soe, 1901, 1,679 Je. Chem Soc, 1900, 382 Page 9 " prominated is placed in the pressure bottle, preferably fill- ing it about one-half full. The alcohol is next saturated “with hydrogen bromide formed by dropping liquid bromine upon _ hapthalene and removing bromine vapor by use of a drying tube filled with napthalene. An excess of hydrogen bromide is dissolved, generally around 25%, The bottle is next closed, placed in a pressure frame and heated in a water bath. The heating serves not only to increase the rate of reaction by raising the temper- ature but also greatly increases the rnressure of the hydrogen bromide gas in the bottle. A few hours of heating usually suffices to complete the reaction, whereuron the contents of the bottle are poured in- to water, the hydrobhomric acid going over to the aqueous layer while the brominated alcohol forms a layer of its own. Any of the original alcohol remaining in the brominated layer may be removed by washing with corceintrated sulphuric acid. The ungaturating of brom pentane was carried out by dropping the brom pentane slowly into boiling alcoholic po-’ tassium hydroxide solution. A reflax condenser was placed above the reaction flesk and was xept at 40°, at which temper- ature the vaporized alcohol would be condeised and returned to the flask, while the rentene was allowed to pass through the condenser. 7 - ' Page 10 ‘The addition of hydrogen bromide to the & pen- tene was accomplished in much the same manner aS was the bromination of the alcohol. The pentene was placed in glacial acetic acid and saturated with an ex- cess of hydrogen bromide. In one case the reaction was carried out in a pressure bottle at about 50°, while in the second case, the abromination was allowed to take place in the cold. The addition proceeds very quickly even at low temperatures. The reaction was carried out at a low temperature in the second run to do @way with any possibility of any 2 brom pentane “changing over to 3 brom rentane upon heating. In both cases, however, the products were identical in all respects and varied by only 0.0001 in their indices of refraction at 20 C. CONCLUSION. | From a consideration of the fact that in both eases where 2 peutene was saturated with hydrogen bro- mide, to give brom pentane, the product upon careful distillation with an efficient fractionating column, pave absolutely no distillate at 112°- 113°, or the boiling point of 2 brom pentane, but rose to practic- ally 118°, the boiling point of 3 brom pentane before any distillate appeared and then continued to distill over at 118° till the whole of the charge ; Page 11 “had been distilled, we can conclude that little or no. 2 brom pentane was present in the product formed by the saturation of the pentene,. This conclusion is further strengthened by the fact that the index of refraction of the brom pentane — made by saturating 2 pentene with hydrogen bromide check~ ed very closely the index of refraction of some 3 brom pentane made by brominating diethyl carbinol, 1.4430 as compared with 1.4443, while it varied by a very large amount from the index of refraction of 2 brom pentane whose index was 1.4322. SIGNIFICANCE OF EXPERIMENTAL RESULTS. * As was stated earlier in this paper, the prediction of the alternate polarity theory was that, in the case of this reaction, the product formed would be 2 brom pentane, while, according to the electron displacement theory, the compound resulting from the saturation of 2 _ pentene with hydrogen bromide should be 5 brom pentane. The experimental work connected with this investi- gation has shown, in the case of the reaction in question, that the product formed was 3 brom pentane. Hence, the following two conclusions may be made: (1) That the alternate polarity theory is incorrect and does not give a satisfactory explanation of the relations between the carbon atom in a chain compound. Page 12 (R) That the predictions of the electron displacement theory are thoroughly in agreement with what has been found to take place in the case of this reaction and while this work does not serve as a finel proof, it at least furnishes a partial substantiation for the electron displacement theory. ‘BXPERIMSNTAL. 2 (1) Preparation of Ethyl formate (H COO C, H,) ( Na OOCH+H, SO, = HOOCH +Ne HSO, ( HOOCH+C,H,WOH = HCOOC,H,+H,0 Materials used: -NaQOCH -100 gms C.P. C, H,OH 89 c.c. -95% H, 80, 81 c.c. SP.G. 1.84 Method: 100 gems, of C. P. sodium formate were placed in a 1.5 litre flask to which was added ethyl sulphuric acid (89 c.c. ethyl alcohol#81 c.c. Sulphuric acid), while still warm from mixing. The mixture was allowed to stand over night and then distilled from a water bath, using a Hempel column and coil condenser in series and catching the liquid in an ice colled flask. The distillate was then washed with Page 13 - godium carbonate solution three times using a separatory funnel for separating the product from the aqueous layer. Phosphoric an hydrid was then added until no further hissing was heard on further addition. The solution was then cleared of the sludge by decantation and filtration and finally redistilled. Practically the whole of the liquid distilled over within a temperature range of 0.4°. The yield obtained using the above method were extremely good, varying from 87% to practically theore- tical. Prepsration of Di - Ethyl Carbinol. yA) yy) Mg HC-OC, H,+C, H,Mg Br = HC- Sale YS Me Olle Br HOC, H, + C,H,Mg Br HO>C,H So, ; H, “OLHS Mg Br _—OH per ac (C,H) +H, = HC-(C,H,), Me<OH Materials used. C, H, Br 294 ¢ C Co, He OOCH 16Zcx M, 96 cite (C,H, 0. 416 cc Method: The first step was to cover 96 gms of Magnesium ribbon with 416 c c's of absolute ethyl ether, using a 3 litre Page 14 flask. 294 ¢ c. of ethyl bromide were then added thru a refleaxing column, care being taken to keep the re- action flask well cooled. Following the addition of the ethyl bromide, 162 ¢ c of ethyl formate were added to the ethyl magnesium bromide. Upon completion of the reaction sufficient dilute sulphuric acid was added to dissolve up the magnesium bromide and form magnesium . sulfate. There were two layers in the flask at this point, one being the aqueous layer and the other the ether layer containing the diethyl carbinol. The layers were Separated by use of a separatory funnel. The ether solution was then distilled, the ether passing off quick- ly, leaving the diethyl carbinol, which later aistilled over. The diethyl carbinol was then well washed, dried over calcium chlorid and redistilled over a range of 117® - 119°. (Cor.) | | (Mathod of Prepartion) A yield of approximately 75% was obtained. Preparation of 3 Brom Pentane from Diethyl Carbinol. The bromination of diethyl carbirol was carried out by placing the carbinol in a pressure bottle, saturating the alcohol with hydrogen bromide gas and then subject- ing to pressure by putting the bottle into a pressure ° bottle frame and heating by immersing in water at 60. Page 15 This process of saturation and compression was repeated until the relative size of leyers in the pressure bottle underwent no change upon further treatment, requiring about ten hours in ell. | The product was then poured into a separatory funnel and washed four times with water to remove any hydro- bromic acid thet might be present in excess. The next Washing was aone with cold, concentrated sulphuric acid and served to remove any alcohol remaining. This was followed with twq washings ’with water and two with sodium carbonate solution. The product was then dried over calcium chloride and distilled. The ‘distillate came over entirely between 117.5 and 119°. (cor.) Preparation of 2 Pentene from 3 Brom Pentane and Bromination of 2 Pentene. | In the first run the 3 brom penténe was unsaturated by using boiling alcoholic potassium hydroxide solution and the @ pentene wes caught in e pressure bottle con- taining glacial acetic acid saturated with hydrogen bromide. | The second run was changed in a few details. The vapors from the reaction flask were caught in xylene cooled with a salt and ice cooling beth. The pentene was distill- e . ed from the xylene into a flask containing glscial acetic Page 16 | acid saturated with hyarogen bromide. The hydrogen bromide and pentene Were allowed to react in the cold. In the first run the pressure bottle was used and the reaction carried on under pressure. Run #1. . CH, CH, CHBr CH, CH, + KOH (alc) —> CH, CH, CH=CH - CH, +KBr + #0. CH, CH, CH = CH CH +HBr ~> CH, CH,- CH Br CH, CH, or CH, CH, CH, CH Br CH. | | Materials. (C,H,), CH Br 60 gms. KOH 60 gms. C,H,O 90 gms. Method. 60 gms. of 3 brom pentane were added, drop by drop, to a boiling solution of 60 gems. of potassium hydroxide in 90 gms. of ethyl alcohol. Connected to the flask was a reflax condenser kept at 40°which allowed the pentene to pass but refluxed the alcohol. From the reflux condenser the vapor passed to a bottle of water at 4c? through which it bubbled. This bottle served to catch any elcohol that might have passed over. The vapor next passed through a. calcium chloride drying tube, also at 40°, and finally was condensed in a pressure bottle cod@led by a salt and ice cooling mixture. The pressure bottle contained approxi- mately 60 gms. of glacial acetic acid to which 40 gms. of Page . hydrogen browide were added by bubbling the gas through the acetic acid. The pressure bottle was then removed, closed and placed in the pressure frame where it was allowed to remain three hours at 50°. The contents of the bottle were then poured into water and the brom pentane layer separeted by use of & separatory funnel. This layer was washed twice with water, once with sodium carbonate solution, three times with cold, concentrated sulphuric acid, once with water and twice with sodium carbonate solution,in the order named. The product was then ariedi.over night using calcium chloride. Upon distillation, using a fractionating column, the first of the distillate came over at 117.2°(cor.) but raised immediately to 118° (cor.) where it remsined constant until only e very small quantity of liquid remained in the flask. The final product weighed 28.2 ems., a yield of 46.7% from the 3 brom pentane and had a refractive index of 1.4430 at 20°. , Run #2 The generation:of the pentene was carried out exactly as in the first run. The vapor was caught in an ice-cooled flask of ®ylene from which it was later distilled, the pen- tene coming over at 36° - 37. The pentene distilled was caught in a cooled Erlenmeyer flask containing 60 gms. of glacial acetic acid saturated with 43.2 gms. of hydrogen bromide. Page 18 The yield of pentene from 57.5:ems. of 3 brom pentane was 20.8 pems., corresponding to a yield of 78.2%. The reaction mixture of pentene and hydrogen bromide in acetic acid was kept for two hours at O° to 5 and then allowed to stand over night in an ice box at a temperature of 10°to 15. The following day it was worked up as des- _cribed in the first run, the final distillation giving a Gistillate whose first drop came over at 117.4° (cor.). The temperature rose quickly to 118’(cor.) where it remained for practically the whole of the distillation. The last part of the distillation. peve a gradual temperature rise up to 118.8 (cor.). The weight of brom pentane was 33.3 ems, a yield of 74.3% from the pentene and 57.9% from 3 brom pentane. The refractive index at 20°was 1.4431,Indices of Refrac- tion of 3 Brom Pentane et Various Temperatures. The S$ brom pentane which was used in obteining the following readings was the fraction which distilled over a range of 118° - 118.2%(cor.). The 3 brom pentane used for the refractometer reading was some that had bean made by brominating diethyl cerbinol. The fraction boiling at 118° - 118.2°(cor.) was considered the purest because it Was at this temperature that the lergest portion of the Gistillate came over. This fraction gave the following refractive indices as measured with an Abbe refractometer Page 19 using white light. d 20 = 25 = | os | 1.4443 1.4427 Preparation of An effort 2 pentanol put = 1.4351 » = 1.4322. 2 Brom Pentane. was made to prepare 2 brom pentane from out by the Standard 011 Company. The procedure was the same in all respects as was the brom- ination of diethyl carbinol, 3 pentanol. 2 brom pentane boils at 113°but upon distilletion of the brominated alcohol no satistactory results Were obtained in that the boiling point rose gradually from about 110° to 125 with no period where it seemed as though @ pure product were coming over. The fraction boiling from 112° - 114°(cor.) had the tollowing refractive indices: J20 1.4405 1.4382 1.4354 1.4297 1.4269 Because of the fact that there is only a lor 2° difference in the boiling points of 2 pentanol and oo Page 20 ‘pentanol, there is no surety in the correctness of the above resdings.e There is a distinct possibility that the brominated product was a mixture of 2 and 3 brom pentene. A second attempt was made to obtain 2 brom pentane by first carefully fractionating the alcohol. Following the pro- cedure mentioned before in this paper, the product was prepared and gave a refractive index reading of 1.4522. at 20°. This value is probably much closer to the correct value than are the reaaings for 2 brom pentane made from the 2 pentanol not fractionated. Summary , Ethyl formate was produced by a new method which, from the standpoint of yields and purity of product, was exceptionally good. | Diethyl carbinol was synthesizea from ethyl formate. by use of Grignard's resction with minor changes. 5 brom pentane was made from diethyl carbinol by use of & pressure bottle containing diethyl cerbinol’ saturated with en excess of hydrogen bromide. 2 pentene wes obtained from 3 brom pentane by adding the 3 brom pentane to a boiling solution of alcoholic potessium hydroxide. Brom pentane was made from 2 pentene by allowing the 2 pentene to react with hydrogen bromide. Page 21 Boiling points and refractive indices indicated that the brom pentane mentioned above was 3 brom pentane. This fact serves to disprove the correctness of the pre- dictions of the alternate polarity theory and also serves to substantiate the election displacement theory.