Question

Working on the questions at the end of this lab report (see above). I need help answering questions 2, 3, and 4 completely and thoroughly. Thank you!

s, until the I hexano 1 clean disti CYCLOHEXENE from CYCLOHEXANOL be dehydrated with solfuric acid to yield cyclohexene and waterf Add a 0°C (record ct and cal H,SO + H20 ainer. s in purification of any crude product are (a) the preliminary separation of the product from the reaction mixture by distillation or some other method, either physical or (c) final purification. exact process must be designed for the synthesis at hand. To devise a method for complete removatl of every possible contaminant is perhaps a laudable end, but such a e electivechemical, (b) the elimination of certain impurities from the separated product by extraction, and The method would require an excessive amount of time and would consume most of the product in handling wastage. Obviously some compromise is needed between the absolutely pure product (which is virtually unattainable) and the crude product of the reaction mixture. The degree of purity desired is governed by the use to which the product will be put. For precision measurements on the physical or chemical properties of the compound, it will be necessary to go to extremes in purification. If the product is to be used as an intermediate in the synthesis of another compound, only the most superficial purification may suffice. Occasionally a crude product can be used without any purification at all zed? o design a purification scheme, first decide what must be removed. There is obviously no concern for a compound that could not possibly be present. How can we determine what impurities likely to be present in a given synthetic product? These can be placed in three categories: (a starting materials which 「not. T eat completely, (b) products of the reaction other than the principal product (for instance, water in the synthesis of cyclohexene), and (c) products of competing reactions involving the starting materials (cyclohexanol and sulfuric acid give not only cyclohexene but also some dicyclohexyl ether). The impurities in the last group are the most difficult to determine, and their presence is usually anticipated through experience with the same or similar reactions or by knowledge of the mechanism of the reaction. From the mechanism, the most probable alternative modes of reaction of the intermediates can sometimes be predicted, and the purification scheme can be designed to accommodate these by-products. In the synthesis of cyclohexene, a probable mechanism (Equations 2,3,4) involves the formation of an intermediate carbocation ion: H2 он + HSO4 (2) + H2SO4 47 rated in a sep dilg calcit moved by f also removes som t there remain as and some dicycloh eparatio of the eyclohe this + H H30. ne puwelohexene it rification boiling n ur experiments, after d yields. Remember tha In yo Notice that the equations are reversible and the reverse process involves reaction fa ion with water, a Lewis base. If we generalize, and consider that this intermediate ion Equations 5,6), for cyclohexanol is a Lewis base present in large quantity Concentr with any other Lewis base present, it is easy to rationalize the formation ofoud Safety addition t Re Procedure: ALL WOR Cautiously add 6 mLo flask and mix the visc condenser for simple 0 collection of the distill chups, and equip the fla H2O Heat the flask careful remains below 98 deg because a large quant until 40 mL of mater Below are listced the most likcly impurities in the syntheti properties that determine the best means of purificatio gether with per Compound Cyclohexanol Water Sulfuric acid Solubility in Water bumping. 100 275 very high insoluble soluble soluble insoluble soluble insoluble Place the entire disti obtained. Wash onc with 20 mL of wat washing). Transfer anhydrous calcium occasional swirling Dicyclohexyl ether Sulfurous acid Tars In the reaction, the crude product is distilled as it is formed. This is principally an azeotrop: for distillation. T clohexene and water, but some higher boiling materials will be carried over either mechanivd material collecting or as ana trope. The distillate is first washed with water Filter the contents then with sodium carbonate solution to remove the last traces of acidic material (including S0 sodium sulfite), and finally with water to remove the sodium carbonate. In all of these wash water and the organic materials are immiscible, and the layers of aqueous and organic liquid plis move most of the sulfuric a material distill i s, it dry it a prod Weigh your 48 iThis combines with water to form solid calcium chloride hydrate, separatory fumnel. The wnter-washed cyclohexene is then treated with y scimoved f the cyclohexanol by formation of iltration to leave dry (free from + H2o this nd some dicycloh hordcetion of the cyelohexe ether, ssl fo ntaminants small amounts of cycl o ere because of the wide difference in bpints ote,however xy ether. It is evident that distillation represents a reasonable means tion Pit had been produced. itents, er that the boiling-point range shouid be given, not s hercybcause of the wide difference in boiling points. Note, however ould not have removed any neutral, water-insoluble compound + H3O In your expertiments, after i and yie after isolation of the synthetic prod uct, give experimental physical constants d sulfuric acid is corrosive and dangerous. Use an apron in ould be given, not simply a boiling point es reaction ofthe c intermediate,on couldhul mation of dicylohexyle antity ddition to gloves and goggles. Ref: Sec Zubrick, 7th ed., Chapter 10,11,15,17,18,19,20,30,34 re WORK NEEDS TO BE COMPLETED IN THE FUME HOOD! ALL of concentrated sulfuric acid to 50 g of cyclohexanol in a 250 ml distlling aduie viscous liquids thoroughly to produce one homogeneous layer. Add 10 boiling liquilla lask with a distilling adaptcr, a 270 degree thermometer and a water tad the f lsk and oix the imple d cooled I3o collection of the distillatc earefully with a heating mantle at such a ratc that the temperature of the distillate ees. It is important that a minimum of cyclohexanol appear in the distillate, of it would interfere with subsequent reactions. Continue the distillation wi Heat the lask ooge n of material is colleted. Further heating of the cocrated cid may cau her with pertinel because a large quantity of it would inte e ollected. Further heating of the concentrated acid may cause a violent bumping. ter entire distillate (both phases) in a small separatory funnel. Record the amount of water Place the obtained. Wash o with 20 mL of washing). Transfer the organie phase to a 125 m water and finally with 20 mL of brine (discard the aqueous phase after each l. Erlenmever flask and add a small amount of er the Hask and allow it to stand for about 15 minutes with rccasional swirling. The liquid should become transparent. Os g Eller the contents of the flask directly into a small distijhing flask, add a boiling chip, and arrange cipaly an azeotrope of for distillation. The receiver should be a pre-weighed|125 mL Erlenmeyer flask. Distill the wll most likely appear bottle. ver either mechanically material collecting only the portion boiling through e range 80-85 degrees (if high-boiling of the sulfuric acid material distills, it will interfere with subsequent reactions). The product sity of your ost dela. y,so dry it again with more calcium chloride and filter it into apre-weighed allofthese washings d organic liquid phase bo be Weigh your product and determine the % yield. Masure the refracti 49 alcohol is s ester. Refluxin product and o and on an IR spectrum. Ensure the lid is on tightly, scal it with Durase Store it safcly in your drawer for use in next week's experiment, room t discardingdpa lean-up: Afler allowing the pot residue from your first distilation to cool to room with 20 mL of a saturated to a separatory funnel and separate the la d Nresultta the boiling solu 50 mL of water. Transter layer. Wash once more with 20 ml. of water and then on. Discard only the organic layer in the non-halogenated recovery container duc from the second distillation should also be placed in the non-halogenated container. Report I. Calculate the theoretical amount of water that could be obtained from this reaction yield of water did you obtain? How does this compare with the experimental Concern el safetyadditior (a) Explain why the synthetic process used here permits us to carry the reaction essential. Place a maz of watert 3. Where and how, is each of the following contaminants removed from the cyclohexene?needed laterh cyclohe Wha cyelohexene? Explain. re tw 2. The reactions shown in Equations 2, 3, and 4, which illustrate the mechanis dehydration process, are all shown as reversible processes. completion. (b) Suggest how you might alter conditions so that the reverse process of hydration Slowly add 19 mL of c has cooled to room te cyclohexene would predominate. cyclohexanol, (b) dicyclohexyl ether, (c) sulfuric acid and sulfurous acid, (d) water 10 mL of the cyclohe minutes add the rema minutes at which poi homogeneous. After minutes to assure hon everything should be the mixture for 20 mi condensed and return the ice bath again in product should be a c 4. Although the sulfuric and sulfurous acids are soluble in water, they are washed out with aquen carbonate solution. Why is this preferred to the simpler washing with water? Adapted from "Selected Experiments in Organic Chemistry" by Helmkamp& Johnson. Pour the cold reaction organic layer larger a prevent foaming of m portions of water, a l finally a 20 mL porti into a clean, dry 125 intermittently for 10 small disttting flas Purify your product your distillation set refractive indey 50

Answer 1

2a) The dehydration of cyclohexanol with concentrated sulfuric acid is a reversible reaction, i.e, both the forward as well as the backward reactions are favored at equilibrium. However, the reaction, as depicted in the synthetic scheme, essentially proceeds to completion, i.e, the reaction is favored in the forward reaction. This is due to the fact that the reaction employs a 1:1 molar ratio of cyclohexanol and sulfuric acid. However, the reaction uses an excess of cyclohexanol so that the reaction essentially behaves as an irreversible reaction and proceeds to completion.

2b) The dehydration of cyclohexanol to cyclohexene is a reversible reaction. However, reactions conditions can be designed as such that the reaction is essentially irreversible in the reverse direction, i.e, the hydration of cyclohexanol to cyclohexene can be the major reaction if a large excess of cyclohexene or water (products of the forward reaction) is added to the equilibrium system.

3a) Cyclohexanol is removed from the products of the reaction (cyclohexene and water) during the first distillation cycle. The reaction is carried out in a distillation flask so that advantage can be taken of the differences in boiling points of cyclohexanol and cyclohexene so as to remove the excess cyclohexanol by distillation.

3b) The boiling points of cyclohexene and dicyclohexyl ether are about 83ºC and 242ºC. Dicyclohexyl ether is removed from the product cyclohexene during the second distillation when only the fraction boiling at 80-85ºC is collected.

3c) The first distillate (azeotrope of cyclohexene and water) are transferred to a separatory funnel and extracted with water and 10% sodium carbonate solution followed by washing with water and saturated brine solution. The addition of water and 10% sodium carbonate solution removes sulfuric and sulfurous acids from the product.

3d) Water is removed from the product during the solvent extraction of the azeotrope obtained from distillation. Water is removed from the mixture by extraction with saturated brine solution. Traces of water in the product are removed by adding anhydrous calcium chloride to the organic product.