Hello sir, very good explanation, I wanted to know few things. 1. Is hydrogen balloon with needle needs to be dip inside the solution or just above in the free space of RB is fine. 2. Can we simply discard celite with Pd after filtration or any treatment is needed before throwing it in the waste. 3. I often see, you letting the hydrogen leak at the end in the hood, is it safe to do so? 4. Is purging necessary and safe as we let the hydrogen gas go into the air?
I'm glad you liked it. 1. Just into the head space is fine. 2. We usually just discard the celite into the trash, especially some the amount of Pd used is so small. If concerned, it could go into a solid waste container for disposal with hazardous water. 3. Yes, this is safe as long as kept away from any ignition sources. 4. Yes, this is safe and also probably a good idea since without the purge your head space may remain largely air (since hydrogen is lighter than air) and the reaction may be slow. One final note: the rate of the reaction may depend on how active your palladium source is. You may need to extend the reaction time if full conversation is not observed during the regularly allotted time.
This is a good question. In this case, the Pd catalyst remains on the carbon support which was collected on the Celite. Theoretically, it could be recycled and reused. I haven't tried that since we normally just throw the celite away, but I don't see any reason why you couldn't.
great video. how do you know when the rotavap has finished? both the solvent and the product are liquid and they are under vacuum, won't some of the product evaporate? isn't it better to use distillation? thx.
Good question. It is true that if your product is low boiling that it is quite possible to lose some (or all) of it on the rotovap. However, in many cases, the boiling point of the product is much higher than that of the solvent and so it is not difficult to remove the solvent without losing much product. In this case, our product actually ought to be a solid, but if you check the NMR you will see there is still some solvent remaining. I should have left it on the rotovap for a bit longer. Solids will often solidify on the sides of the flask as the solvent is removed, but if it is a bit of an oily solid (or low melting, etc.) then it might only solidify after you remove it from the rotovap. I hope this helps!
Good question! It is a 3mL plastic syringe that has been cut in half. The balloon is then slid over the cut end and sealed with parafilm or electrical tape. The appropriate size of syringe will vary depending on the size of the balloon.
Very well presented and informative, doc! Just curious if it is mandatory for the hydrogen balloon needle to be immersed into the Pd/C/ethanol suspension, or is the hydrogenation still facile by simply filling up the headspace above the suspension? Thanks!
Good question! It is not mandatory to have the needle immersed. Most of the time I just have a needle into the headspace and the stirring action helps being it into solution.
I do not understand why you are not taking more care to ensure the hydrogen does not come into contact with air....? maybe the way i was taught? Also no purging or nitro back fill of reaction flask? just straight hydrogen into it? no glove boxy for adding p/c inertly or h2 inert.... im so confused? please help me understand what is going on
13:30, he is purging the reaction flask. Maybe there's no nitrogen because the hydrogenation of ethyl cinnamate is fairly insensitive to contaminants, but idk... Or do you think that there's a risk for a hydrogen explosion by not purging?
Good question! This specific substrate is chosen mostly because of the ease of the reaction and the short time required, rather than the particular value of the resulting product. However, cinnamates and hydrocinnamates (the class of products resulting from this hydrogenation) have uses in the flavor and perfume industries. I hope this helps.
