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What is the result of boiling the impure product with too much solvent and then cooling on ice?

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Topics for exams | Английский язык в школе и не только | ВКонтакте

Topics for exams | Английский язык в школе и не только | ВКонтакте – Too much cola is bad for your health. Ice-cream is full of sugar and fat. You will need to take Of flour dishes the most popular is zacirka. Pieces of specially prepared dough are boiled in water and then Everybody knows we are what we eat. It is very important to include various products into your menu…Background Information: The melting range of a pure solid organic is the temperature range at which the solid is in equilibrium with its liquid. As heat is added to a solid, the solid eventually changes to a liquid.Small Crystals Are Produced O Crystals With Impurities Remaining Within Them Are Produced. Small crystals are produced O Crystals with impurities remaining within them are produced.

PDF Ch 227 – Bivouacked in the middle of the Filchner-Ronne Ice Shelf—a five-hour flight from the nearest Antarctic station—nothing comes easy. Even though it was the southern summer, geologist James Smith of the British Antarctic Survey endured nearly three months of freezing temperatures, sleeping in a tent, and…Adding impurities to a solution, in most cases, increases the boiling point of the solution. Once this occurs, it takes a greater amount of heat to cause the same amount of impure solution to vaporize It is important to realize however, that impurities do not always increase boiling point, and, in certain…Recrystallize the final compound with same solvent with its boiling temperature then filter and evaporate at room temperature up to to As suggested by someone else too….TLC or HPLC is the best way to check the purity a new compound. Soluble product is possibly free of reactant impurity.

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Solved: What Is The Result Of Boiling The Impure Product W… – Saltwater is boiled, then the steam is cooled and condensed as fresh water, leaving the salt crystals behind in the heated vessel. More modern methods, according to Stanford University, "make use of various techniques such as low-pressure vessels to reduce the boiling temperature of the water and…19. The results of the experiment were carefully being checked up all the day yesterday. 20. These digits are easily multiplied. 21. The results of computations were recorded in the form of tables.It is known that when we tend to dilute an impure product with too much of solvent then it will lead to dissolution of the solute. As a result, the chances of formation of crystal reduces. And, when we increase the temperature then there will occur increase in the number of collisions between the solute…

Solved: What Is The Result Of Boiling The Impure Product W ...

Make p-Toluenesulfonic Acid – Warning: Toluene is flammable.
Sulfuric acid is corrosive. Wear gloves when handling them and fire safety protocols must be in place. Greetings fellow nerds. In this video I'm going to make p-Toluenesulfonic acid. So first an introduction, what is it and why do we want it. P-toluenesulfonic acid is basically a toluene molecule where we've attached on a sulfonate group. Sulfonates are pretty much a piece of sulfuric acid and in fact behave similarly. They are acidic and will form salts upon reaction with bases. Although a single sulfonate group will only have one acidic proton unlike sulfuric acid's two protons. So why use p-toluenesulfonic acid as opposed to sulfuric acid. The answer is that most of the time you won't actually. If you just need an acid then sulfuric acid and hydrochloric acid are preferred. I've been working on my youtube channel for ten years and never bothered with p-toluenesulfonic acid. That being said it does have some useful properties. First the toluene attached to it makes this acid somewhat more soluble in organic solvents. It dissolves very well in not just water, but alcohols, ketones, ethers, esters and so on. You'll get much less phase separation or even avoid it entirely. The resulting salts are also more soluble and that can aide separation if you plan your synthesis correctly. P-toluenesulfonic acid is also much less oxidizing than sulfuric acid. You saw in one of my videos of making hydrobromic acid that sulfuric acid is slightly oxidizing and will react to create undesirable side products like bromine. If you have sensitive chemistry and can't use something like hydrochloric acid then p-toluenesulfonic acid might be a good choice. Now i'll be honest though, for the amateur, there is not much need for it. Most reactions can still be done with more common and cheaper acids. But if you just want to have some it's pretty straightforward to make with the right equipment. It's one of the classic demonstration experiments to use with a dean stark apparatus. And all you really need to do it in terms of chemicals is sulfuric acid and toluene. So let's give it a try. First we get a 500mL flask and start with 200mL of toluene. I got mine from the hardware store as paint thinner. Then we add in 54mL of concentrated sulfuric acid, which corresponds to about 1 mole. I'm using low quality sulfuric acid from drain cleaner. Now on top of the flask we affix a dean stark apparatus and on top of that we install a condenser. Technically i'm using a clevenger apparatus but since i'm using it in light return mode it's the same as a dean stark apparatus. Now we turn on heating and stirring and raise the temperature until the mixture begins refluxing. What's happening is the sulfuric acid is reacting with the toluene to form p-toluenesulfonic acid. There is actually an explanation of why we get mostly the para-substituted product and not the ortho and meta versions. But it's pretty complicated so i'll skip over that. If you want to know why anyway then i've added it to the end of the video. Moving on, this reaction produces water which forms an azeotrope with the excess toluene we added earlier. This azeotrope boils out and phase separates in the dean-stark apparatus. Water on the bottom and toluene on the top. The lighter toluene then flows back and the reaction continues. Periodically we remove water from the trap so it doesn't also flow back into the reaction. Now, by removing the water from the right side of this reaction we drive it forward. You can actually convert p-toluenesulfonic acid back into sulfuric acid and toluene by refluxing it with excess water and an acid like hydrochloric acid. But that's an experiment for another time. Right now, just keep refluxing and collecting water until it stops accumulating. This took me about 12 hours. Then turn off the heating and let it cool. Now empty the trap of water, and then of toluene. Add the toluene back in to the reaction mixture so we can get more volume to filter. Now the p-toluenesulfonic acid is actually dissolved in the toluene. While anhydrous it's soluble but if we convert to the hydrate form it'll be insoluble. So to separate it out we actually add in 20mL of water to form the monohydrate. Give it a stir and… whoaů That was a lot more dramatic than i was expecting. Looks like it's formed a suspension with the toluene. I tried manually breaking it up but it was too thick. So instead i added even more toluene, 200mL worth and finally it was stirrable and the particles of p-toluenesulfonic acid hydrate were visible. Now we filter it to recover the product. And there is our impure p-toluenesulfonic acid. For some amateur purposes this is good enough but it contains large amounts of toluene still soaked into the particles and whatever impurities from the drain cleaner and paint thinner sources as well as any side products like ortho-toluenesulfonic acid. To purify further i'm going to try to recrystalize it. First to get rid off the insoluble impurities. P-toluenesulfonic acid is highly soluble in water so we first add in 350mL of water to dissolve it with stirring. Whatever doesn't dissolve cannot be our product. Filtering it out we can see we have quite a lot of this insoluble white material. I'm not exactly sure what it is. Some of it is toluene and impurities from the drain cleaner, but there is far too much to be just that. Anyway no matter, what we really want is the filtrate containing our product. And here it is, still impure but at least it doesn't have the insoluble impurities from earlier. Now we boil it down to try and recover our p-toluenesulfonic acid product. This is a little complicated by the fact that there are two common forms of p-toluenesulfonic acid. An anhydrous form that is just the product. And a monohydrate form where it crystalizes with a equal stoichiometry of water. The anhydrous form has a lower melting point than the monohydrate and is much more hygroscopic. So it's actually the monohydrate form that's preferred. Now boiling down to the monohydrate form is a bit of a hit or miss as you can overshoot if you boil for too long. So we'll have to go through an iterative drying process. We start by boiling down to where we expect the monohydrate volume to be, about 150mL, and let it cool. Unfortunately it does not seem to be crystalling so we'll have to boil off more water. I wish I had some easy method of knowing how much to boil off but without sophisticated apparatus like a karl-fischer titrator we'll just have to eyeball it. I boiled off another 30% of the volume or about 50mL before stopping and allowing it to cool. And it looks like we have our p-toluenesulfonic acid monohydrate. Okay it's probably not exactly the monohydrate so you'll need to store it a dessicator to fully dry it. For the most part this is pure enough for amateur purposes. But I want to purify it further by recrystallization from ethanol. So i took my entire stock and added it to 50mL of ethanol. Looking back I should have dried the excess water as much possible in a desiccator before doing this recrystallization step. Anyway, I heated the ethanol until it all dissolved and then cooled the mixture to hopefully crystalize out the product. Unfortunately nothing happened so I boiled off some ethanol, about 20mL, and then let it cool again. Finally i had crystals coming out. When it was completely cooled i broke up the mass and then filtered it to obtain purified product. Okay it's not quite pure but still much better than earlier. I recommend storing it a desiccator until completely dry before transferring to air tight containers. Anyway, total yield is 57g or about 30%. I think most of the loss was because i used low-quality drain cleaner acid which has a lot of water and impurities. The rest is probably in the ethanol filtrate. It can probably be recovered for better yield but i'm not going to bother. The fortunate thing about p-toluenesulfonic acid is that it's really cheap in terms of both labor and chemicals. Anyway i have no immediate use for it but I wanted to have some in my library of chemicals. Maybe to make aromatic esters where the sulfuric acid normally used would react with the aromatic groups to create undesirable side products. We'll see what happens. Thanks for watching. Special thank you to all of my supporters on patreon for making these science videos possible with their donations and their direction. If you are not currently a patron, but like to support the continued production of science videos like this one, then check out my patreon page here or in the video description. I really appreciate any and all support. Now a quick chemistry lesson for those that are wondering about why our predominant product is para-toluenesulfonic acid and not the other possible products like ortho or meta-toluenesulfonic acid. It has to do with how electrons move around the aromatic ring. Let's take a look at benzene for a second. Benzene has three double bonds but without moving the atoms we can move the double bonds over by hoping the electrons. This structure is essentially equivalent but with the double bonds in a new place. This is known as a resonance structure. Because there is no real energy change or barrier to this movement, it happens all the time and happens very quickly. In fact if you measured the bond distance between the carbon atoms on benzene, you'd find they were all the same. The hopping happens so fast, and the structures shift between resonance forms so quickly that we observe what is essentially an average of all structures. The electrons floating around the ring in a cloud. This makes the aromatic ring have special properties in chemistry. Let's look at phenol and i'm going to abstract the acidic proton to get a phenoxide ion. Now the electron doesn't always need to sit on the oxygen. It's connected directly to a sp2 hybridized carbon which means we can move the electron into the ring by moving the double bonds in the opposite direction. So now we have a sort of ketone benzene molecule and the electron is inside the ring. The double bonds can still move so we can draw more resonance forms moving the electron around as well. This happens extremely quickly so overall we get an average of all three forms. Now i want you to pay attention to where the electrons are. The extra electron is only on every other carbon, it cannot move to adjacent carbons. So overall we get higher negative charge at only these positions. These are known as the ortho and para positions. The meta positions are avoided. Now when we perform an electrophilic aromatic substitution, only the most negatively charged positions perform the attack. So that's why we get predominantly ortho and para products. Now you might be wondering, wait a minute, we're not reacting phenol, we're reacting toluene. How can this directing effect still occur? You're absolutely right, it seems odd that a methyl group, without a free negative charge, can still direct where the substitution occurs. It can do this because the methyl group is still somewhat electron rich compared to just hydrogen so it contributes more electron density. At the quantum mechanical level you don't need a formal electron to have an effect, just the cloud of electrons in the methyl group can push a bit of electron density into the cloud of the aromatic ring and thus make the aromatic ortho and para positions more attractive for a reaction. One way of visualizing is through the model of hyperconjugation. We know the methyl donates electron density so we visualize it as actually deprotonating itself and then drawing the consequent resonance structures with this restriction. At this point i want to make clear this is just a way of visualizing and rationalizing the results. This is not formally happening. We are not making zwitterionic toluene and your toluene is not going to spontaneously isomerize into methylidenecyclohexadiene. It's just not happening, as awesome as that would be. But we are pushing electron density from the methyl group and influencing where the electron density ends up. In the end, we still get the same ortho and para directing effect just like phenol. Granted the overall effect is indeed weaker for methyl as opposed to oxygen so you will get a different distribution of products with a bit more meta substitution. Okay so that covers why we get ortho and para products. But that doesn't explain why in our experiment we're getting predominantly para substitution. If all these sites are reactive, just by random chance we should be getting 2/3rds ortho products and 1/3rd para products. Indeed this has happened before. You can recall way, way, WAY, back during my pyrimethamine synthesis i was halogenating my toluene with chlorine. And in that case I actually had predominantly ortho products, it was actually a massive problem and I had to devise a complicated separation step to remove them. Why is this experiment different? Well it's because we're substituting with sulfuric acid. The sulfonate molecule is big, much bigger than chlorine. It actually bumps up against the methyl group. This physical effect is what we call a steric effect and substituents will try and stay away from each other to minimize such effects. One way to think of it is two guys going into a washroom with a row of urinals. All else being equal they will not use urinals next to each other if it can be avoided. So on this aromatic ring the sulfonate ortho-product is the minor product due to how large sulfonate is and how close it would be to the methyl. Its formation is unfavourable. So our majority product will be p-toluenesulfonic acid. I hope that explains it. .

Separation of chlorotoluene isomers (para and ortho) 2nd step in making Pyrimethamine – Warning: This experiment uses highly corrosive
sulfuric acid and chlorinated solvents.
Wear gloves when handling them. This experiment also generates sulfur dioxide. Work outside or in a fume hood. Greetings fellow nerds. In a previous video I made chlorotoluene by
reacting toluene and a chlorine source like chlorine gas or
trichloroisocyanuric acid. While this worked very well and gave better
than eighty percent yield, the resulting chlorotoluene consisted of a
mixture of para and ortho isomers. Since different experiments require different
isomers we'll need a way to separate them. Now ortho and para chlorotoluene have slightly
different boiling points and so they can be separated industrially
by fractional distillation. Unfortunately the overlap of their vapors
is so great that you need a huge column of 200 theoretical
plates or more. One of the patents i read called for a column
13 meters long. Yeah my puny little vigreux column is not
going to cut it. We're going to have to use a chemical approach
rather than physical. So here is our mixture of chlorotoluene isomers.
About 450 grams worth. Now chlorotoluene is clear but my sample is
a cloudy due to tiny amounts of water. This is not a problem though. Now add in about 65 mL of concentrated sulfuric
acid. This corresponds to a one third molar equivalent. My acid is red because it's low grade drain
cleaner acid. High quality acid will work better but isn't
strictly necessary. Now set up a dean stark apparatus around the
flask operating in heavy return mode. I've shown how to make these in a previous
video. A traditional apparatus cannot be used because
it only returns the lighter fraction but we want to return the heavy fraction. Now chlorotoluene boils at around 160 degrees
celsius. To minimize heat loss and makes this reaction
go faster i'm insulating the hot portions of the dean stark apparatus with foil. Normally I'd insulate more of this but i'm
leaving some parts open so you can see the progress of the reaction. Now turn on the heating to three hundred degrees
celsius and let it boil. What we're doing is sulfonating the chlorotoluene
and releasing water. By turning up the heat high enough to boil
the mixture, the water boils out along with chlorotoluene. The dean-stark trap allows us to conveniently
separate and return the chlorotoluene and keep just
the water. By removing the water from the reaction we
drive it forward. Now an interesting thing happens with the
isomers of chlorotoluene. Ortho-chlorotoluene reacts faster and is more
stable than para-chlorotoluene. This is because the sulfonate group is quite
bulky and thus is more stable on positions far away
from any other substituent. On ortho-chlorotoluene this is easy since
there are two positions it can react with that aren't beside another
substituent. But on para-chlorotoluene wherever it goes
it will bump against another substituent. So para chlorotoluene sulfonation is less
favored than ortho-chlorotoluene. This effect of the physical crowding affecting
reactivity is called the steric effect and allows us to fine-tune a lot of chemical
reactions that way. In this case we're using it to resolve ortho
and para chlorotoluene. Now even though some of the para chlorotoluene
is reacting, this isn't a problem because the reaction
is reversible. So the sulfuric acid regenerated can go to
react with the ortho isomer. If we use equal or less sulfuric acid than
the ortho isomer we can get almost exclusive ortho sulfonation. Unfortunately this is rather slow. So keep running the reaction until the water
content in the dean-stark trap stops increasing and then run an extra hour to ensure an equilibrium
is reached. Now you're probably wondering if i know this
mixture has 60% ortho-chlorotoluenes which i want to remove, why did i only about one third equivalent
of sulfuric acid which is not enough to remove it all. Well I did try adding a stoichiometric equivalent but i then notice a large amount of decomposition
happening. The chlorotoluene sulfonic acid decomposes
at high temperatures and concentrations to chlorocresols and sulfur
dioxide. By limiting the sulfuric acid to less one
third we limit the concentration of chlorotoluene sulfonic acids and thus limit decomposition. The drawback is that we'll have to repeat
the process to convert more of the o-chlorotoluene. Okay looks like we're done. Now turn off the heating and let it cool. So here we are. Now while some of our chlorotoluenes is in
the dean stark trap. Most of it is here as a mixture of chlorotoluenes,
chlorotoluene sulfonic acid and decomposition products. Now if you look very closely there is a small
amount of separation of the components. But there is still a lot of contamination and it's very difficult to get clean recovery
of just the chlorotoluenes this way. So we're going to use steam distillation. To the mixture add an equal amount of water. Since i have about 500 mL total i'm going
to add another 500 mL of water. Stir it up until thoroughly mixed. Now assemble the dean stark apparatus around
it and set it up for light return mode. You'll also notice that rather than a graduated
cylinder for our trap we're using a much larger 500 mL flask. This is because we're going to collect all
our chlorotoluenes there. Now simply heat up the mixture until boiling
and start collecting the heavier components. What we're doing is taking advantage of the
fact that water and chlorotoluenes form a low boiling azeotrope. This carries our chlorotoluenes out of the
mixture and separates them from our chlorotoluene
sulfonates and decomposition products. This is much cleaner than trying to decant
the mixture from earlier. The dean-stark apparatus lets us remove the
water and return it to the mixture to continuously
carry out the chlorotoluenes. Now you might be wondering if we originally
made the chlorotoluene sulfonate by sulfonation and removing water, wouldn't adding the water back in hydrolyze
it and thus reverse process destroying our progress. You're absolutely right and this would happen
at higher temperatures. But since we added so much water the mixture
is boiling and thus maintaining a lower temperature at
about the boiling point of water. At this lower temperature we can take advantage
of azeotropic distillation without worrying about the reverse reaction. This is also why we didn't directly distill
the mixture. As said before, chlorotoluenes boil at about
160 celsius which is hot enough to begin decomposing the chlorotoluene sulfonates. Okay, looks like the level of chlorotoluene
is no longer increasing, we can turn off the heating and let it cool. Here is our chlorotoluenes and I've decanted
most of the water. This mixture is enriched in para-chlorotoluene
isomers and depleted in ortho-chlorotoluenes. The residue back here contains our ortho-chlorotoluene
sulfonate and some water. Now we can convert this into pure ortho-chlorotoluene but first i'm going to set it aside and focus
on further purifying the para-chlorotoluene. Now this mixture has an unknown ratio of para
and ortho-chlorotoluenes. We know it's been para-chlorotoluene enriched,
we just don't know if it's pure. We could use nuclear magnetic resonance spectroscopy. But if you had access to that you wouldn't
be trying to make para-chlorotoluene in your basement and would just buy it directly from a chemical
supply company. Fortunately there is a simple test we can
perform. Ortho-chlorotolene has a much lower freezing
point than para-chlorotoluene so we can roughly figure out our purity based
on that. This is because para-chlorotoluene has a melting
point of 7 celsius while ortho-chlorotoluene has a melting point of -35 celsius. Take a small sample of your chlorotoluene
mixture and put it in the freezer. If it doesn't freeze at all then it has too
much ortho-chlorotoluene. If it freezes then make a mixture of ice water
and place the sample vial in that. If it melts again then it's richer in para-chlorotoluene
but not quite pure enough. If it stays frozen then it's highly pure para-chlorotoluene. Now we didn't simply drop our sample into
ice water because chlorotoluenes have a strong tendency to supercool so starting from a liquid state and lowering
the temperature to find the freezing point is terribly inaccurate. It's much more accurate to start from a solid
state and warm upward to find the melting point. Anyway, in our first run back here the melting
point test showed it remained liquid even in the freezer, so we still have a lot of ortho-chlorotoluene
that we need to separate. So we'll need to do our sulfonation again. Make a note of how much chlorotoluene you
have now and calculate how much sulfuric acid you'll
need to equal a one third mole equivalent. I have about 300 mL of chlorotoluenes and
this corresponds to about 40 mL of sulfuric acid. There is some water in my chlorotoluenes from
earlier. But i'm not bothering to remove it since we'll
be running the dean-stark trap in heavy return mode and removing the water anyway. So run the sulfonation as before and then
perform the azeotropic separation. Then run the freezing and melting point test
to see how pure the chlorotoluenes are. Keep saving the ortho-chlorotoluene sulfonates if the freezing and melting point test shows
the chlorotoluenes to be impure. If however the test shows the chlorotoluenes
to be pure para-chlorotoluene, do not save the ortho-chlorotoluene sulfonates
from that run. This is because that particular run was when
the sulfonation reaction finally exhausted all the ortho-chlorotoluene and is now consuming para-chlorotoluene. The sulfonates from that run now contain a
mixture of chlorotoluene sulfonates rather than pure ortho-chlorotoluene sulfonate. Anyway. Here is the purified para-chlorotoluene.
It took a lot of work. And from 450 mL of mixed chlorotoluenes we
only recovered about 70 mL of para-chlorotoluenes. Most of the loss was from the fact the para-chlorotoluene
was only present in about 40%, and the rest of the loss was from handling
losses since this is such a complicated and laborious process. Nonetheless by amatuer means we have produced
essentially a pure para-chlorotoluene isomer. To be absolutely sure i sent off a sample
for NMR analysis. As you can see the clean spectrum shows we
have indeed produced pure para-chlorotoluene. Now for storage i recommend adding some molecular
sieves to remove the cloudiness that comes from suspended water droplets. As for the ortho-chlototoluene sulfonates,
we can now convert it back into ortho-chlorotoluene. The process is actually quite simple. Just gradually heat the mixture and distill
off the water and ortho-chlorotoluene. The water from the original separation of
chlorotoluenes should still be there so we don't have to add more. What's happening is that at first the excess
water boils off at lower temperatures. As the temperature rises the water remaining
reacts with the ortho-chlototoluene sulfonates to produce sulfuric acid and ortho-chlorotoluene. The ortho-chlototoluene boils off and distills
over. Unfortunately there is also a large amount
of decomposition at these temperatures to chloro cresols and sulfur dioxide so our yield is severely
affected. Try and maintain a temperature of about 175
to 180 celsius in the mixture to reduce decomposition. Now if you don't actually need ortho-chlorotoluene
for anything then i say don't bother and just dispose of sulfonates. This hydrolysis is prone to boiling over and
ruining your reaction. Even worse is that once the hot sulfonates
get stuck in your condenser they solidify and it takes hours of cleaning to get them
out again. Anyway. After many aggravating days of work
i eventually got some ortho-chlorotoluene. I was actually expecting a lot more than this but a lot of the ortho-chlorotoluene sulfonates
decomposed and thus reduced our yield. I think the fact that i used drain cleaner
grade sulfuric acid with whatever impurities are in it may have accelerated decomposition. Oh well. NMR analysis shows i have reasonably pure
ortho-chlorotoluene so at least this wasn't a total loss. Anyway, that is how you use steric effects
and sulfonation to separate ortho and para chlorotoluene isomers. This is another step in our synthesis of the
antiprotozoal drug pyrimethamine. Thanks for watching. If you would like to support the continued
production of science videos like this one. Please support the channel on patreon. Links are in the video description. .

The Recrystallization of NaOH – .