I Have a Research Support System

"School girl, come quickly, the reaction time is over." Xu Qiu began to call for helpers. Time is very precious now, and every minute of delay will cause the reaction to proceed in an irreversible direction.

"Come on, come on, right away." Han Jiaying was at the liquid nitrogen bottle, planning to pour some liquid nitrogen out to play, but after hearing the call, she hurriedly put on her lab coat, gloves and mask, and trotted over.

'It came pretty fast. Xu Qiu arranged a task for her, "You go to prepare the developing agent, according to the previous two ratios, petroleum ether: dichloromethane 1:1 and 1:2." After finishing speaking, 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 starting material.”

"Okay." Han Jiaying walked towards the reagent cabinet.

Seeing that Chen Wanqing had also followed, Xu Qiu turned around and said hello:

"Sister, help me?"

"What kind of help?"

Xu Qiu thought for a while and said, "Help me prepare three dichloromethane solutions of PDI raw materials. The raw materials are in my drawer, namely PDI-2, PDI-5 and PDI-6."

"2, 5, 6..." Chen Wanqing repeated, "I remember, what about the concentration."

"You see, come here, I'll order some board later." Xu Qiu replied casually, with the help of his seniors and juniors, his pressure was much less.

He took a disposable dropper, then inserted it into the reaction vessel, sucked up a little bit of the solution inside, then transferred the taken solution to a disposable centrifuge tube, and added dichloromethane to dilute, and finally got three kinds of The solution samples of the reaction products are marked as No. 1, No. 2 and No. 3 in turn, and placed on the centrifuge tube rack.

Afterwards, he took three more silica gel plates, numbered them as well, dipped a clean capillary tube into the solutions of the three reaction products respectively, and placed four sample points in parallel on the underline of the same numbered silica gel plate, and Leave free space for two sample points on the side.

At this time, Chen Wanqing handed over three bullet-shaped centrifuge tubes, "Here you are, the three sets of solutions have been prepared for you."

"Thank you." Xu Qiu thanked, and put the three centrifuge tubes on the rack.

"You're welcome," Chen Wanqing smiled, "I still need your help when I submit a response later."

Xu Qiu also responded with a smile, then dipped a clean capillary tube into the solutions of the three raw materials respectively, and dotted four more dots on the corresponding numbered silica gel plate, two of which were in the blank, and the other two dots were the same as before. points coincide.

After completion, there are six points on each silica gel plate, and the arrangement is: product/product/product+raw material/product+raw material/raw material/raw material.

"Intersection board, you know how to do it, junior." Chen Wanqing obviously saw the way.

"What is a cross-point board?" Han Jiaying suddenly appeared with a developing bottle filled with developing fluid.

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 blended sample point of raw material and product, and the last one is the so-called intersection point.

Comparing the three with each other, according to the different climbing heights of different sample points under the same developing agent, it is easy to 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 required, such as the reaction we submitted last time.

The point of intersection is mainly for insurance, because the product may be very complicated this time, and the polarity difference between the raw material and the product is not large, and they may be very close during the climbing process. "

"I see."

After the silica gel plate is put into the developing bottle, the developing agent is climbing slowly from bottom to top along the surface of the plate, moving upward together with the sample.

Xu Qiu suddenly thought of something, and ordered: "Sister, go and make some saturated sodium thiosulfate solution."

"Sodium thiosulfate..." Han Jiaying muttered something, and then suddenly asked, "Is it used to deal with liquid bromine?"

"That's right," Xu Qiu nodded, "I almost forgot about it when I got busy just now."

"Okay." The junior girl ran to the reagent cabinet again in a hurry, and quickly ran back, standing next to them to prepare the solution.

Sodium thiosulfate is very safe, the common name is "big soda", and it is an aqueous solution, so there is no need to shrink in a fume hood for experiments.

After the developer moved to the upper line on the silica gel plate, Xu Qiu took it out with tweezers, dried it, and then irradiated it under a UV lamp.

He told the people around him about the experimental phenomenon he observed, "This No. 1 sample, the product mainly has three spots, two deep and one shallow, and some very shallow spots, which can hardly be seen clearly." Then began to analyze:

"Several sample points that are barely visible are by-products with a small content. They may be tribromine, tetrabromine substitution products or dibromine substitution products substituted at different positions. Their climbing positions do not coincide with the main products. They are not used for the time being. Tube."

Han Jiaying stirred the solution in the beaker with a glass rod, without much thought, she asked casually:

"What about two deep and one shallow?"

"The corresponding position of the light-colored one is the unreacted PDI raw material, and the two dark-colored dots are mono-brominated and di-brominated compounds." Xu Qiu added:

"As for which one is which, it is difficult to distinguish, and it needs to be determined through subsequent analysis and characterization methods."

"Yeah." Han Jiaying nodded and stopped stirring. At this time, there were still some crystals of sodium thiosulfate under the beaker.

"I have prepared a saturated solution, what should I do now for the reaction, should I shut it down immediately?"

"Number 1's reaction can be stopped..." Xu Qiu paused and said, "Forget it, there's no rush, wait for me to finish reading the remaining two silicone plates in a minute and then deal with them together."

Xu Qiu picked up the silicone plate of No. 2 sample again, checked it carefully under the ultraviolet light, and after a few seconds, said: "The main sample points are also two deep and one shallow. The shallow one is also the raw material. It should be the same as No. 1. Pretty much the same situation."

In fact, the results can be seen a little with the naked eye. After all, the raw materials and products are red, but the detection with ultraviolet light is more accurate.

"Senior brother, look quickly," Han Jiaying said suddenly, "The board on No. 3 seems to be different."

"That's right," Xu Qiu put down No. 2, picked up No. 3, took a photo under the ultraviolet light, and said: "It's really different, one dark and two shallow, one of which is the raw material, and the other is dark and the other shallow, it's hard to distinguish , but no matter what the situation is, the reaction can be stopped."

"Let's go." With that, he walked towards the fume hood.

"Hmm..." Han Jiaying followed Xu Qiu with a beaker, and analyzed to herself: "If the dark one is monobromide, the yield is very high, and the reaction can be stopped. If the deep one is monobromide, the reaction can be stopped. The dibrominated product means that the reaction time is too long, so the reaction must be stopped, and the loss should be stopped in time, and how much monobrominated product can be taken.”

"The analysis is good," Xu Qiu praised, and then said: "Actually, as long as the raw material point is not the deepest one, the reaction can be stopped."

Han Jiaying hummed, nodded and said: "I always feel that our synthesis this time is a bit tricky. What the synthesized product looks like depends entirely on luck, and even if you get the product, you can't be sure which one you want."

"That's right, because I chose the simple, one-step synthesis route back then, I naturally had to bear the corresponding risks," Xu Qiu smiled, "How can there be such a good thing, it's simple and easy."

"That's right." Han Jiaying nodded.

"In fact, these three reactions can all 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 still 4 grams of raw materials that can be used casually, but..." Xu Qiu remarked Turn around, "This time I didn't have time to click in the middle of the reaction, otherwise it might be more perfect."

"At least the ending is not bad." Han Jiaying comforted.

The two walked to the fume hood.

"Just add saturated sodium thiosulfate solution with a dropper, is that enough?" Han Jiaying asked.

"Yes, don't stop stirring, keep adding the solution until the trace of liquid bromine in the solution disappears."

After a while, under the action of sodium thiosulfate, the liquid bromine in the three reaction bottles was all cleaned up.

The liquid in the bottle turned bright red again, and due to continuous stirring, there was no obvious stratification.

"The reaction to remove the liquid bromine will produce sulfuric acid, hydrobromic acid and sodium sulfate, but we didn't add much liquid bromine before, just wash it with water a few times later." Xu Qiu stopped stirring and took Come to a separatory funnel, and casually mentioned:

"I see that there is also a method of blowing air directly into the solution with an air blower in the literature. You can try it next time."

"We don't seem to have an air blower." Han Jiaying responded, and she also took a separatory funnel and poured the processed reaction solution into it.

"You can use the existing experimental conditions to make one yourself," Xu Qiu said with a smile:

"For example, modify the double-row tube to make something similar to a nitrogen gun, and directly inject nitrogen into the solution to achieve the same function."

"This method is good. It can save the steps of washing and liquid separation, and directly rotate and evaporate."

"Well, by the way, it's been more than two hours since your reaction to the make-up vote later, you can click on the board later to see."

"Okay." Han Jiaying nodded.

...

The subsequent re-investment response, that is, the spotting result of sample No. 4, is similar to that of sample No. 3, one deep and two shallow, one of which is the raw material.

After confirming the results, Han Jiaying used the same method to remove excess liquid bromine in the reaction flask.

Then the two people added an appropriate amount of silica gel according to 0.5 grams of raw materials to the dichloromethane solution of the four reaction products to mix the sample, and then rotary steamed to obtain a raw material that was uniformly mixed with silica gel powder.

The next step is to separate and purify the product through a column.

The two didn't start immediately. After all, liquid chromatography is no better than others. Once the column is opened, it can't be stopped.

There is another reason, the senior sister is about to start the experiment, so she called Xu Qiu to help.

What kind of sparks will liquid nitrogen and n-butyl lithium collide with?