正溴丁烷 的制备 思考题（Preparation of n-bromobutane）

1、正溴丁烷 的制备 思考题（Preparation of n-bromobutane）tetrabromobutane1. What is the role of sulfuric acid in this experiment? The amount of sulfuric acid and the concentration is too large or too small what is not good?Answer: action is: reactant, catalyst. When too large, the reaction generates a large amount

2、 of HBr running out, and easy to oxidize bromine ion to bromine; After an hour, the reaction is incomplete.2. What impurities may be in the products after the reaction? What is the purpose of each step washing? Why do I need to use a dry separatory funnel when washing with concentrated sulfuric acid

3、?A: it may contain impurities: n-c4h9oh, (n-c2h5), HBrEach step of washing purposes: (1) water in addition to the six HBr, most of the n - C4H9OH (2) sulfuric acid wash (n - C4H9) 2 o, the rest of the n - C4H9OH (3) for most - H2SO4 (4) use NaHCO3 wash with water in addition to the rest of the - H2S

4、O4 (5) finally washed with water except NaHSO4 residues, such as excessive NaHCO3.With concentrated sulfuric acid washing, the purpose of using the dry separatory funnel is to prevent the concentration of sulfuric acid and influence the washing effect.If 1 - bromobutane containing n-butyl alcohol di

5、stillation will form before fractions (1 - bromobutane - n-butyl alcohol constant boiling point 98.6 , inclusive of our 13% n-butyl alcohol), and results in the decrease of refined production rate.3. The product is washed with a liquid funnel. The product is sometimes in the upper and lower layers.

6、What is the easiest way to judge?Answer: pour a little bit of superfluid from the split funnel or release a little bit of the lower level liquid in a water test tube to see if there is any oil bead appearing to judge.4. Why do you need to wash with water before washing with saturated sodium bicarbon

7、ate solution?Answer: first washed with water, can remove part of sulfuric acid, to prevent wash with sodium bicarbonate, sodium bicarbonate and sulfuric acid reaction to generate a large amount of carbon dioxide gas, make the stress in the separatory funnel, lead to the piston, then wash with satura

8、ted sodium bicarbonate solution can further remove the sulfuric acid. The washing vibration process should pay attention to the gas!5. Why should I release the product in time when I wash the product with a liquid funnel? How should I operate?A: during this process, the gas will be produced after sh

9、aking, making the pressure inside the funnel much larger than the atmosphere. If the air is not regularly released, the stopper may be opened and leaking. The operation is as follows: tilt the funnel upward, toward the unattended, unexposed fire, open the piston and release the gas in time.Supplemen

10、t:1. When adding material, if not according to the loading sequence in the experimental operation, first, the sodium bromide and the concentrated sulfuric acid are mixed, then the addition of normal butanol and water will occur.A: there will be Br2 generation2. When the crude product 1-bromobutane w

11、as isolated from the reaction mixture, why was the distillation separated, instead of directly separated by the separation funnel?Answer: after the reaction, except for the main product 1-bromobutane, it may also contain unreacted positive butanol and the side reaction of butyl ether. And inorganic

12、product sodium bisulfate, with usually liquid method is not easy to remove, finished in response to crude distillation, on the one hand, makes the generated 1 - bromobutane, on the other hand the crude distillation process can further make alcohol and hydrobromic acid reaction tend to be more fully.

13、3. What are the side effects of this experiment? What measures should be taken to suppress it?Side reaction: H2SO4 (thick) + ch3ch2ch2ch2ch2ch = CH2 + H2O- H2SO4 concentration) + 2 ch3ch2ch2ch2oh - CH3CH2CH2CH2OCH2CH2CH2CH + H2OControl the reaction temperature not too high4. What is the purpose of e

14、ach step washing in reprocessing? Why do you use sulfuric acid? Why do you want to wash it with water before washing it with saturated sodium bicarbonate solution?A: use the same volume of concentrated sulfuric acid to remove the raw material butanol or dissolved byproducts. The organic phase, in tu

15、rn, USES equal volume of water (except sulfuric acid), saturated sodium bicarbonate solution (neutralizing the undivided sulfuric acid) and water (except for the remaining base).5. What are the advantages of reflux in organic preparation? Why would you use a spherical condensation tube in a reflux d

16、evice?Answer: organic reactions in many cases are in solvents, boiling temperature or higher temperature of the raw material, in order to prevent solvent, raw materials, product or escape reaction system caused loss, bring pollution and unsafe factors, often need to adopt the reflux device. Because

17、spherical condensing tube condenses the area is big, the area that the area cuts is different, the condensate is easy to return to come down.6. What is the result of high concentration or too low concentration of sulfuric acid in the preparation of bromobutane?A: sulfuric acid concentration is too h

18、igh: (1) the NaBr is oxidized to Br2, and Br2 is not a nucleophile.2 NaBr + 3 H2SO4 (thick)(2) there may be a large number of HBr gases coming from the top of the condensing tube to form acid fog. The concentration of sulfuric acid is too low: the amount of HBr produced is insufficient to make the r

19、eaction difficult.7. What is the purpose of each step washing in the preparation of bromobutane?Answer: use sulfuric acid washing: remove unreacted n-butanol and by-products 1-butylene and n-butyl ether.First wash: remove some of the sulfuric acid and water-soluble impurities. Alkaline wash (Na2CO3)

20、 : neutralizing residual sulfuric acid.Second wash: remove residual alkali, sulfate and water-soluble impurities.In the synthesis of 1-bromobutane, the distillate of 1 - bromobutane is usually in the lower layer, but sometimes at the top. Why? How to deal with this phenomenon?A: if there is more pos

21、itive butanol in the reaction, or some hydrobromic acid is in constant boiling, the relative density of the liquid layer changes, and 1-bromobutane can be suspended or changed to the upper layer. This phenomenon can be diluted with water to allow the oil layer (1-bromobutane) to sink.9. What is the

22、reason that crude product 1-bromobutane has been washed with red brown? What should be done?A: if the oil layer is red and brown, it indicates free bromine. Use a small amount of sodium bisulfite water solution washing to remove free bromine. The reaction equation is Br2 + NaHSO3 + H2O10. With the p

23、reparation of sodium bromide, concentrated sulfuric acid and n-butane, concentrated sulfuric acid is diluted with the right amount of water.A: (1) reduce the oxidation of concentrated sulfuric acid and prevent the production of side reactions; (2) the generated brominated hydrogen gas is fully disso

24、lved in water, and it becomes hydrobromic acid and the positive butanol reaction.The reaction mechanism of 1-bromobutane was prepared with the reaction of n-butanol and hydrobromic acid. And what measures are used in the experiment to make the equilibrium of the reversible reaction move in the direc

25、tion of 1-bromobutane?A: the reaction is mainly based on the SN2 mechanism.The mechanism is as follows: in the experiment, the following measures are taken to make the equilibrium of reversible reaction move in the direction of 1-bromobutane.(1) excessive sulfuric acid was added. In this reaction, c

26、oncentrated sulfuric acid is used to generate hydrobromic acid in addition to NaBr, and excessive concentrated sulfuric acid can remove the by-product water as a water-absorbent agent. At the same time, as the source of the hydrogen ion to increase the concentration of protonitol, the non-moving hyd

27、roxyl group is transformed into a good leaving group H2O.(2) add an appropriate amount of NaBr. Excessive amounts of NaBr can produce an excess of hydrobromic acid in excess of sulfuric acid.(3) when the reaction is properly done, the side reaction is still distilled, and the product 1-bromobutane i

28、s removed.12. Why should a small amount of water be added to the reaction bottle in preparation of 1-bromobutane? How good is water? Why is that?Answer: add a small amount of water:(1) to prevent a large amount of foam during the reaction;(2) reduce the volatilization of HBr in the reaction;(3) redu

29、ce the generation of by-product ether and ene;(4) reducing HBr is oxidized to Br2 by concentrated sulfuric acid.The amount of water added should not be excessive. Because butyl alcohol reacts with hydrobromic acid 1-bromobutane is reversible, the byproduct is water, which increases the amount of wat

30、er, which is not conducive to the equilibrium of the reversible reaction to the formation of 1-bromobutane.When adding material, why add water and concentrated sulfuric acid to cool to room temperature, and add normal butanol and sodium bromide? Could you first mix the sodium bromide with the concen

31、trated sulfuric acid, and then add the normal butanol and the water? Why is that?A: because when they add water dilute sulfuric acid, a significant amount of heat if without cooling and n-butyl alcohol and sodium bromide, while charging, positive reaction and reverse reaction will happen immediately

32、, is not conducive to the operation, and even dangerous. If the sodium bromide is mixed with concentrated sulfuric acid first, then a large amount of hydrogen bromide will be produced, and a large number of bubbles will burst out, which will not be conducive to the operation and the reaction.14. Pre

33、paration of 1-bromobutane with n-butyl alcohol and hydrobromic acid, which side effects might occur? What impurities may be contained in the crude products distilled?Answer: possible side effects: crude products may contain impurities: n-butanol, n-butyl ether, water and a small amount of 2-bromobut

34、ane.?What are the impurities for washing products with concentrated sulfuric acid? What is the basis for impurities?Answer: the main thing is to eliminate n-butanol, n-butyl ether and water. Because alcohol, ether and water can form salt with concentrated sulfuric acid and dissolve in sulfuric acid

35、solution. The other concentrated sulfuric acid is hygroscopic.16. Do not use concentrated sulfuric acid to wash crude products, how does it affect the quality of the reaction products? Why is that?Answer: if there is no sulfuric acid washing coarse product, in the next step in the distillation, n-bu

36、tyl alcohol with 1 - bromobutane as can form azeotrope (b.p. 98.6 0 c, inclusive of our 13% n-butyl alcohol), it is difficult to eliminate, make our products still contains n-butyl alcohol impurities.17. How to determine whether bromobutane is steamed when the crude product is distilled?Answer: can

37、be judged from the following aspects:(1) whether the evaporating fluid is changed from turbidity to clarification;(2) whether the upper layer of the reaction bottle disappears;(3) take a test tube to collect a few drops of distillate, add the little water to vibrate, observe the presence of oil bead

38、s, and if nothing indicates that the organic matter has been steamed up.After heating, the contents of the reaction bottle often appear reddish brown. What is the reason? After steaming the rough products,Why do the residues pour out the reaction bottle?A: after heating, the contents of the reaction

39、 bottle often appear reddish brown, which is the reason why the hydrogen bromide is dissolved in the content in the process of the reaction. After the product is distilled, the residue is still hot to pour out the reaction bottle. Otherwise, the residues in the reaction bottle can be cooled with sod

40、ium bisulfite to cool down.19. After the crude products are washed with concentrated sulfuric acid, why not wash them with saturated sodium bicarbonate and then add saturated baking soda to wash them?A: thats because just using sulfuric acid washing product also contains a lot of concentrated sulfuric acid (including the funnel wall), if with saturated sodium bicarbonate neutralized directly, is due to the amount of acid is too much, acid and alkali neutralization, a significant amount of heat at the same time there is a