Chapter 209: 2 deep 1 shallow, 1 deep 2 shallow

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"School girl is coming soon, the reaction time is over." Xu Qiu started calling for help. Now time is very precious. Every minute of delay will cause the reaction to proceed in an irreversible direction.
"Come on, come on, right away." Han Jiaying was originally at the liquid nitrogen bottle and planned to pour some liquid nitrogen out to play. After hearing the call, she quickly put on her lab coat, gloves and mask, and ran over.
‘It’s pretty fast. 'Xu Qiu arranged a task for her, "You go to prepare the developing agent, according to the previous two ratios, petroleum ether: methylene chloride 1:1 and 1:2," he said, he did not forget to explain, " I checked the information before, and the polarity of the product after bromine substitution is usually similar to that of the raw material."
"Okay." Han Jiaying walked to the reagent cabinet.
Seeing that Chen Wanqing was also coming, Xu Qiu turned around and said hello:
"Senior sister, come to help?"
"How to help?"
Xu Qiu thought for a while and said, "Help me prepare the methylene chloride solution of three PDI raw materials. The raw materials are in my drawer. They are PDI-2, PDI-5 and PDI-6."
"2, 5, 6..." Chen Wanqing repeated, "I remembered, so what's the concentration."
"Look at it, I'll use it later." Xu Qiu replied casually. With the help of senior sisters and younger sisters, his pressure was much less.
He took a disposable dropper, then stretched it into the reaction vessel, sucked a little bit of the internal solution, and then transferred the taken solution to a disposable centrifuge tube, then added dichloromethane to dilute, and finally got three types The solution samples of the reaction products, labeled 1, 2, and 3 in turn, are placed on the centrifuge tube rack.
Afterwards, he took three more silica gel plates, numbered them as well, and then dipped the solutions of the three reaction products with a clean capillary, and placed four sample points in parallel on the underlined positions of the silica gel plates with the same number. There is a free space for two sample points next to it.
At this time, Chen Wanqing handed over three bullet-shaped centrifuge tubes, "Here you are, all three sets of solutions have been prepared for you."
"Thank you." Xu Qiu thanked him and put the three centrifuge tubes on the rack.
"You are welcome," Chen Wanqing smiled, "I need your help when I respond."
Xu Qiu also smiled and responded, and then dipped the solution of the three raw materials with a clean capillary, and clicked four points on the correspondingly numbered silica gel plate. Two of the points were in the blank area, and the other two points were the same as before. The points coincide.
After completion, there are six points on each silica gel plate, the arrangement is: product product product + raw material product + raw material raw material.
"Cross-point board, you are quite good at school." Chen Wanqing obviously saw the doorway.
"What is a cross-point board?" Han Jiaying suddenly appeared with an unfolding bottle filled with unfolding liquid.
Xu Qiu put the silicone plate into the unfolding bottle with tweezers, and explained:
"There are three sample points on this silica gel plate, one is a single raw material, one is a single product, and the other is a blend of raw materials and products. The last one is the so-called cross point.
Comparing the three with each other, according to the different climb heights of different sample points under the same developing agent, you can easily distinguish which sample point is, and then infer the product point.
Under normal circumstances, only one point for the raw material and one point for the product is needed, such as the reaction we used last time.
The point of intersection is mainly for insurance, because the product may be very mixed this time, and the polarity of the raw material and the product are not very different, and they may be close together during the climbing process. "
"That's it."
After the silica gel plate is put into the unfolding bottle, the unfolding agent is slowly climbing from the bottom to the top along the surface of the plate, moving up with the sample.
Suddenly Xu Qiu thought of something, and then ordered: "Sister, go and mix some saturated sodium thiosulfate solution."
"Sodium thiosulfate..." Han Jiaying muttered, and then suddenly said: "Used to treat liquid bromine?"
"Yes," Xu Qiu nodded, "I was so busy just now that I almost forgot about it."
"Okay." The school girl rushed to the reagent cabinet again and quickly ran back, standing next to them to make the solution.
Sodium thiosulfate is very safe, the common name is "soda", plus it is an aqueous solution, and there is no need to shrink it in a fume hood for experimentation.
After the spreading agent was moved to the top of the silicone plate, Xu Qiu took it out with tweezers, dried it, and then irradiated it under a UV lamp.
He talked to the people around him about the experimental phenomena he observed, "The product of sample No. 1 mainly has three points, two deep and one shallow, and some very shallow points, which are almost unclear." Then he began to analyze:
"The few sample points that are hardly visible are by-products with very little content. They may be tribromo, tetrabromo substituted products or dibromo substituted products substituted at different positions. Their climbing positions do not overlap with the main products. tube."
Han Jiaying stirred the solution in the beaker with a glass rod, didn't think much, and asked casually:
"What about two depths and one shallow?"
"The light-colored corresponding position is the unreacted PDI raw material, and the two dark-colored dots are the monobromo and dibromo." Xu Qiu added:
"As for the specific one, it is difficult to distinguish which is which, and it needs to be determined through subsequent analysis and characterization methods."
"Yeah." Han Jiaying nodded and stopped stirring. At this time, there were some sodium thiosulfate crystals remaining under the beaker.
"I have prepared the saturated solution, what should I do now, should I shut it down immediately?"
"No. 1's reaction can be stopped..." Xu Qiu paused, "Forget it, don't worry about it for a while, wait a minute for me to finish reading the remaining two silica gel plates before processing them together."
Xu Qiu picked up the silica gel plate of No. 2 sample again, inspected it carefully under the ultraviolet light, after a few seconds, said: "The main sample points are also two dark and one shallow. The lighter one is also the raw material. It should be the same as No. 1. It’s pretty much the same."
The practical results can be seen slightly by the naked eye. After all, the raw materials and products are all red, but the UV lamp is more accurate.
"Brother, look at it," Han Jiaying said suddenly: "The board of No. 3 seems to be different."
"Really," Xu Qiu put down No.2, picked up No.3, took a picture under the ultraviolet light, and said: "It's really different. One shade and two shades. One of the shallows is the raw material, and the other one is dark and the other is light. , But no matter what the situation is, the reaction can be stopped."
"Let's go." After speaking, he walked towards the fume hood.
"Um..." Han Jiaying carried the beaker, followed Xu Qiu, and analyzed to herself: "If the deep one is a monobromide, then the yield is very high and the reaction can be stopped. If the deep one is For dibromo compounds, it means that the reaction time is too long. Stop the reaction and stop the loss in time. How many monobromo products can be obtained."
"The analysis is good," Xu Qiu praised, and then said: "In fact, as long as the raw material is not the deepest, the reaction can stop."
Han Jiaying snorted and nodded: "I always feel that our synthesis this time is a bit of a look. What the synthesized product looks like is entirely based on luck, and even if you get the product, you can't be sure which one is what you want."
"Yes, because I chose a simple, one-step synthesis path, I naturally took the corresponding risks," Xu Qiu smiled, "How can there be such a good thing that is simple and easy."
"That's true." Han Jiaying nodded.
"In fact, these three reactions can have a yield of about 40%, which is already acceptable. After all, the synthesis of the raw materials in the previous step is not difficult. Now there are 4 grams of raw materials that can be used casually, but..." Xu Qiu said A turn, "This time I didn't have time to hit the board in the middle of the reaction, otherwise it might be more perfect."
"At least the ending is not bad." Han Jiaying comforted.
The two went to the fume hood.
"Is it enough to add saturated sodium thiosulfate solution directly with a dropper?" Han Jiaying asked.
"Yes, don't stop stirring, keep adding the solution until the traces of liquid bromine in the solution disappear."
After a while, under the action of sodium thiosulfate, the liquid bromine in the three reaction flasks was cleaned.
The liquid in the bottle turned bright red again. Due to the continuous stirring, there was no obvious layering phenomenon~EbookFREE.me~ The reaction to remove the liquid bromine would generate sulfuric acid, hydrobromic acid and sodium sulfate, but We didn't add much liquid bromine before, so just wash it with water several times later. "Xu Qiu stopped stirring, took out a separatory funnel, and said casually:
"I see in the literature there is a method of blowing air directly into the solution with an air blower. You can try it next time."
"We don't seem to have an inflator." Han Jiaying responded. She also took a separatory funnel and poured the processed reaction solution into it.
"You can make one yourself using the existing experimental conditions," Xu Qiu smiled and said:
"For example, if you modify the double row tube to make something similar to a nitrogen gun, you can directly pour nitrogen into the solution to achieve the same function."
"This method is good. It can eliminate the steps of washing and liquid separation and directly rotate and steam."
"Well, by the way, the response to your back-up vote is almost two hours away. You can click on the board and see first."
"Okay." Han Jiaying nodded.
...
The reaction of the subsequent supplementary dose, that is, the spotting result of sample No. 4, is similar to sample No. 3, with one dark and two shallows, one of which is the raw material.
After confirming the result, Han Jiaying used the same method to remove the excess liquid bromine in the reaction flask.
Then the two of them mixed the samples in the methylene chloride solution of the four reaction products by adding an appropriate amount of silica gel according to 0.5 g of the raw materials, and then rotating the steam to obtain a uniformly mixed silica gel powder.
The next step is to separate and purify the product through the column.
The two didn't start right away. After all, liquid chromatography is no better than others. Once the column is turned on, it can't stop.
There is another reason, the senior sister is about to start the experiment, calling Xu Qiu to help.
What kind of sparks will liquid nitrogen and n-butyl lithium collide with?