[organica]

Hello.
How I can do the esterification reaction if both of starting materials (carboxylic acid and alcohol) are solids?

It is for my last project.
Thank you so much for your questions.

[discodermolide]

Find a solvent in which they both dissolve.

[AntonioSillo]

Hi, i suppose you could carry out the reaction in solid phase, using appropriate systems, such as Microwaves. I reccomend you to find in literature if there are some examples. Bye

[discodermolide]

What good are microwaves going to be in this case. With no solvent you will surely just melt the mixture, but if it will react I doubt.

[AntonioSillo]

I take your point: Microwaves have thermal effects in order to increase the systems temperature. Besides, cause of their polarization effects, they may influence transition states of the reactions. So if you expect to have polar TS in your reaction, MW could stabilize it, thus decrease reaction activation energy. I strongly recommend you to look up in literature!

[discodermolide]

I have several times and I do not believe the polar TS stabilisation by microwaves.
I cannot see how microwaves lower the activation energy of a reaction, they are not catalysts, but a source of thermal energy.
You might as well say that by having polarised microwaves you can produce one enantiomer or the other.

[AntonioSillo]

Microwaves enhance reaction because influence directly on Arrhenius equation. MW cause an increment of collision between molecules, so an increment of probabilities of effective collision. MW influence the exponential factor of same equation: in particular the entropy, because the polarization change the order of fundamental and TS. If You don't trust me, you could find more and more else on the web;)

[discodermolide]

I did not say I didn't trust you, I was disagreeing with you. One example quoted from a 2001Tetrahedron Review by Lidström etal, Tetrahedron 2001, 57, 9225-9282 which states the following:
The rate of the reac- tion can be described by the Arrhenius, there are basically two ways to increase the rate of a chemical reaction. First, the pre-exponential factor A, which describes the molecular mobility and depends on the frequency of vibrations of the molecules at the reaction interface. We have described previously how microwaves induce an increase in molecular vibrations and it has been proposed that this factor, A, can be affected. Other authors, however, have proposed that microwave irradiation produces an alteration in the exponential factor by affecting the free energy of activation, DG.17
In most examples, the specific microwave effects claimed, can be attributed to thermal effects.

So I think the final answer is not known with any certainty.

[AntonioSillo]

..Or you can say that answers are both: microwaves affect pre exponential and exponential factor . So a microwave assisted reaction result enhanced regards his kinetics constant, because MW increase the probability of effective collisions, and because MW are able to affect the Free Gibs Energy Factor making it more negative or more positive, depending on the reaction you consider.

[curiouscat]

and because MW are able to affect the Free Gibs Energy Factor making it more negative or more positive, depending on the reaction you consider.

I still don't see how Microwaves can affect the barrier?  Pre-exponential, yes; but how do they lower the TS?

[curiouscat]

What good are microwaves going to be in this case. With no solvent you will surely just melt the mixture, but if it will react I doubt.

Aren't conventional Liq-Liq reactions essentially carried out in the "molten state"? Only that the MP is below Room Temp.

Why wouldn't two molten solids react? Is there reason to think they'd react slower on melting than on solvation?
Mass transfer effects?

[AntonioSillo]

we can define MW as a sort of polarizing electromagnetic radiations. So if you have a polar reaction, for example a reaction in which reagents are apolar, while product are polar, you'll expect a transition state more polar than the foundamental state of the reaction you considered. So MW can stabilize That TS, as a polar solvent would stabilize it. As a consequence, you'll have a lowering of energy band gap between fundamental and transition state, and an enhancement of activation energy.

[discodermolide]

As I said above:

In most examples, the specific microwave effects claimed, can be attributed to thermal effects.

I think the committee is still out on this one. Time will tell.

[AntonioSillo]

mmmmmmm!!!!!!!!. infact MW have 2 types of effects on reactions: specific effects (thermal effects such as superheating) and aspecific effects, as the ones i talk about previously, wich affect transition states. such effect contribuite all to influence in a good or in a bad way reactions
 transition states!!!!!!