Chapter 207: Mostly the experiment failed, and I was so angry

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Zhang Jiang laboratory.
Han Jiaying turned on the liquid chromatograph to purify the product mixed yesterday, while Chen Wanqing went to the fume hood to deal with the reaction.
Xu Qiu also began to prepare for the next reaction-modification of PDI molecules.
Before receiving the JACS review, his idea was to synthesize a simple PDI molecule, and then directly make 3D-PDI, and quickly publish this idea.
Now that other people have put forward the concept of 3D-PDI, there is no need to rush.
He plans to proceed step by step, first by synthesizing several currently known high-performance PDI materials, mainly twisted and bridged PDI dimers.
Even if these materials are not used now, there will be opportunities to use them in the future. They can be stored to expand the breadth of materials in the laboratory and build a material library, including the samples that are sold by the optoelectronic company today, which are also used to enrich this material. Library.
After each new material is developed, it can be matched with the materials in the material library in the simulation laboratory II to construct dual or even multi-element battery devices and test its performance.
Moreover, this can be regarded as a re-traveling of the predecessors' synthesis road, which can further accumulate his synthesis experience.
PDI dimers, whether they are twisted or bridged, the main design idea is to dimerize to make a twist angle between the two PDI molecules, thereby inhibiting the crystallinity of the entire dimer molecule and improving spin coating After the film morphology.
The difference is that the twist type is to directly connect two PDI molecules, while the bridge type is to add an additional "bridge" between the two PDI molecules. The so-called bridge is a small conjugated structural unit, such as thiophene and vinyl. some type of.
However, it is not so easy to connect two PDI molecules obediently, and direct reaction is obviously impossible.
First, the PDI molecular structure needs to be modified. The common method is to replace a hydrogen atom on the molecule with a bromine atom to obtain a monosubstituted PDI-Br molecule.
Then the two PDI-Br molecules are directly reacted, or a bridge molecule is introduced to obtain a twisted or bridged dimer.
In theory, PDI+Br2→PDI-Br+HBr, in one step.
There will actually be problems.
A single PDI molecule has 8 hydrogen atoms. Because the molecule is symmetrical, there are two hydrogen atoms in different chemical environments, which are divided into in-situ and bay positions. There are 4 hydrogen atoms in the same chemical environment. The reactivity is equivalent.
Relatively speaking, the bay position, that is, the 4 hydrogen atoms near the center of the molecule, is more chemically active, and is easier to be replaced when the bromine substitution reaction occurs.
If the reaction conditions are well controlled, the hydrogen atoms in situ will hardly participate in the chemical reaction.
But it can only exclude 4 in situ.
There are 4 hydrogen atoms in the bay position. When the bromine substitution reaction occurs, it is possible to produce 0, 1, 2, 3, 4 substituted products.
Because there are related literature published, this question has an answer, the key lies in how Xu Qiu chooses.
One method is to directly synthesize according to "2PDI+Br2→2PDI-Br", and then use the column method to filter out PDI-Br.
The advantages of this method are obvious, simple and crude, one step is in place, and the shortcomings are also obvious. Post-processing may be painful and the yield is worrying. If it can reach 50%, it will burn high incense.
Another method is to introduce a nitro group at the bay position of PDI, and then reduce the nitro group to an amino group. This amino group can eat two hydrogen atoms on one side at the same time, and then connect to the nitrogen position of the amino group. One alkyl side chain, and finally bromine substitution reaction.
The shortcomings of this method are obvious, the reaction steps have increased by three steps...
The advantages are not very obvious, maybe the yield will be increased, maybe not, and there may be some hidden advantages.
After some trade-offs, Xu Qiu chose the first method.
In fact, it is not easy to react to the three or four substitution if it is so straightforward.
Because when the PDI molecule is replaced by bromine, the chemical environment of the hydrogen atoms in the other three bay positions are all changed. The position of the hydrogen atom that is most likely to react is changed to the opposite position or distance from the substitution position of bromine. The bay position with the farthest monobromine substitution position.
So the products obtained are mainly mono- and di-bromo substituted products and unreacted raw materials.
Moreover, dibromo-substituted PDI is not useless. For example, in the future, it can be still coupled with the di-substituted trimethyltin to synthesize PDI polymer materials.
...
Start preparing the reaction.
For the three reactions, the raw materials for the reaction are the PDI molecules purified yesterday and the elemental bromine, the solvent is dichloromethane, the reaction is performed at room temperature, and the target product is the monosubstituted PDI-Br molecule.
Xu Qiu carefully took out the brown bottle of liquid bromine from the medicine cabinet and transferred it to the fume hood.
Then, weigh about 500 milligrams of PDI molecules of PDI, put them into a 50 milliliter reaction flask, add 20 milliliters of dichloromethane as the reaction solvent, and put a PTFE spindle-shaped magnetic stirrer.
The last step is to add liquid bromine equivalent to the PDI molecule.
Liquid bromine is the only non-metal element that is liquid at room temperature. It is volatile, toxic, and corrosive, and can only be weighed quickly and roughly.
In addition, its density is greater than that of water, so when storing it, add water and liquid seal above the liquid bromine. The liquid bromine will be divided into three layers. The bottom layer is liquid bromine and the middle layer is bromine water, which also contains hypobromous acid and bromination. Hydrogen, the upper layer is water.
Xu Qiu pulled the glass of the fume hood to the bottom, reached in, carefully unscrew the cap of the liquid bromine reagent bottle, and inserted the disposable dropper into the bottom of the reagent bottle to absorb the red and black liquid bromine, and then quickly transferred to the reaction Inside the bottle.
After the red-black liquid came into contact with the bright red liquid under the reaction flask, it quickly smeared, and the flask was filled with dark red-brown bromine vapor.
Xu Qiu quickly plugged the reaction flask with a glass stopper. There are carbon-carbon double bonds in the rubber, which will react with bromine, so the rubber stopper cannot be used.
Subsequently, he added liquid bromine to the other two reaction vessels in turn, then capped the liquid bromine reagent bottle, disposed of the experimental garbage with liquid bromine, and started stirring.
‘The reaction is getting more and more dangerous. With a secret sigh, Xu Qiu pressed the stopwatch to start timing. This reaction time should not be too long, and the reaction should be stopped on time after 2 hours.
‘I used 10% of the product to test the water at a time. I hope I don’t fail. ’
...
Xu Qiu looked around. Chen Wanqing was not in the laboratory. She should have returned to the office. There was no reaction in her fume hood.
Han Jiaying is on the other side of the fume hood, while passing the column while simultaneously rotating and steaming.
Xu Qiu walked to the school girl, "I'm quite capable, and I'm still doing dual purposes."
"Hey," Han Jiaying turned around and said, "Brother, you are here, how's your reaction?"
"I have voted for the bromine substitution reactions of those three products. You can vote for this product yourself." Xu Qiu stood beside her.
"Okay," Han Jiaying pointed to the rotary steaming instrument, "Come and help me, it is very stressful to operate two devices at the same time."
"Okay, let me help you watch Xuan steaming." Xu Qiu nodded.
"Hoo... Saved." She walked back to the liquid chromatograph quickly.
The PE cup over there was almost full. She pressed Pause, quickly changed to a new PE cup, and continued to receive the fluid.
‘Very skilled. Xu Qiu thought for a while and asked: "By the way, do you know what happened to Senior Sister Chen Wanqing, I think her reaction stopped, I was busy responding just now and didn't pay attention to her situation."
"I don't know the specific situation. She just came over and ordered two boards, and then ran away without saying a word." Han Jiaying tilted her head, and then she smiled unkindly, "But I guess, Most of her experiments failed and she was so angry that she was autistic."
"That's it, I'll take a look." Xu Qiu glanced at the rotary steaming apparatus. At present, there is not much solution in the eggplant-shaped bottle, and it runs smoothly and is relatively safe, so he walked towards the experimental platform.
This experimental platform is specially used for spot board inspection, and there are two silica gel plates on it, which should be the ones that Chen Wanqing ordered before.
A handheld UV lamp is connected to the socket next to it, which is in standby mode.
Xu Qiu picked up the UV lamp, turned on the switch, and took photos of the two silica gel plates.
The sample points above are densely packed. One of them has at least seven or eight points, and some of them overlap each other. If you draw a line vertically, it looks like a candied haws; the other one is slightly better, but there are five or six points. .
"I guess you guessed it~EbookFREE.me~ She clicked the result and couldn't bear to look straight." Xu Qiu put down the UV lamp and returned to the rotary steaming machine.
"Are there many sample points?" Han Jiaying paused, "Three, four?"
"Not only, at least five or six," Xu Qiu sighed. "This product is difficult to separate even with liquid chromatography, and even if it is separated, it is difficult to determine which sample is the desired substance. Jane In other words, the immortal is difficult to save, either because of her operational errors, or there is a problem with her experimental design."
"At that time, didn't all the reaction steps have been shown to you and Teacher Wei, there are still problems?" The school girl curiously asked.
"Ms. Wei and I are not from the background of orthodox organic synthesis. They both crossed the river by feeling the stones. Moreover, for things like synthetic experiments, many times what we expect is one thing, but it is another thing to make it. Cooperate with various analytical instruments to push back."
"Then what to do, the senior sister, like us, has been busy for two days."
"Then it depends on how much material she put in at the beginning, and whether there is any stock of the reaction product from the previous step. Just like we synthesized 5 grams of product at one time, 500 mg of bromine substitution was used this time. Even if the reaction is unsuccessful, There are many opportunities to try."
"Um... I hope there is stock."
...
After more than an hour, the two completed the separation and purification of the last PDI product.
This time the output was slightly lower, and only 4.2 grams of product was obtained, but from the point of view of the results, the purity was not bad.
Xu Qiu copied it into the simulation laboratory and arranged for simulation experimenters to do basic characterization and device optimization.
Later, Han Jiaying took 500 mg of the product and added a liquid bromine substitution reaction.
With Xu Qiu looking after him, there was no problem.