For each of the following reactions, suggest which solvent(s) ...

Question

For each of the following reactions, suggest which solvent(s) would be compatible with the acids and bases involved. (We will ignore any other possible reactions for now.) Your choices of solvents are pentane, diethyl ether, ethanol, water, and ammonia. Refer to Appendix 4 for any needed values of pK_a, or estimate them.
c.
d.

c. Chemical reaction diagram showing the interaction of a nitrogen-containing compound with a sulfonium ion, producing a new compound.

d. Chemical reaction showing sodium amide and tert-butanol producing ammonia and sodium tert-butoxide.

Accepted Answer

All right. Hello everyone. So this question is asking us to choose the appropriate solvents for the following reactions. Considering that each involves acids and bases, ignore the other possible reactions that can occur. The choices of solvents are hexane, water, methyl, amine, diethyl ether and methanol. So before we talk about these separate reactions here labeled one and two, let's talk a little bit about the importance of a solvent in an acid base reaction because we're going to focus on assets and bases our, our main topic of discussion for this video is going to be PK. Now, when it comes to any given organic reaction, we want to avoid as many side products as possible, right? Which means that we also want to avoid the possibility of the solvent reacting with the acid or base that you are trying to react or rather that you are trying to use. So because of this, the acid or base that you're using must not be stronger than the solvent that you're trying to use for that reaction. So here the acid or the base must be weaker, meaning it must have a higher PK value or actually let me correct myself. The solvent must have relatively equal acid strength as the reactant because that means they can coexist in the reaction mixture. If the acid in the reaction mixture is stronger than the acidic forms of a solvent, it's going to react with the solvent and that causes unwanted side products. So let's consider the solvents that we're given before we go ahead and discuss each specific reaction starting off with hexane. Recall that hexane is a standard hydrocarbon with a six carbon parent chain. Under normal conditions. Hydrocarbons do not react as acids or bases because their PK value is approximately 50. So they're not very acidic at all in normal conditions because of this hexane is a solvent that can coexist with acids and bases in solution because it's relatively inert, right? It's not really going to react much. So because of this hexane is very much an appropriate solvent or acid base reaction. So hexane is going to be an answer for parts one and two. But now let's talk about the rest starting off with water, which is of course H2O recall that water is known as an amphoteric species. It can behave as an acid or a base. Now, the PK of H2O, the PK of water is approximately 15.7 and the PK of the conjugate acid which forms after water behaves as a base is negative 1.7. So assets and bases that have PK values within the range of the PK values for water can use water as a solvent because at that point, they can coexist in solution. So now let's move on to a methyl of meat. The PK of methyl amine, which is available in most textbooks and literature in general is about 40 and the PK of the conjugate acid is 10.64. So again, assets and bases that have PK values within this range can use meth amine as a solvent. Then we have die ethel Ethan. Now, diethyl ether notably is not an acid. It is not going to behave as an acid because the oxygen in diethyl ether does not have any protons to donate. So di o ether can only react as a base. And so therefore, the PK that I am discussing here is the PK A of the conjugate acid which is approximately 3.6. So this PK value of negative 3.6 is for the conjugate acid or C A for short. Now, because this very low number, it can be used as a solvent for very strong bases. But acids must have a PK greater than negative 3.6 last but not least we have methanol. Now, the PK of methanol is 15.5 and the PK of the conjugate acid is negative 2.5. So once again, acids and bases that have PK values within this range can use methanol as a solid. So now lets consider the first reaction here. For part one, we have pyrimidine reacting with methyl sium to produce pyrimidine one em and methane style. Now, our acid has a PK of negative 6.8 and our conjugate acid has a PK of 1.0. Now, as discussed previously, we know for a fact that hexane can behave as a solvent in any acid base reaction because he hexane does not behave as an acid or base. So if we consider the PK values for the remaining four possible solvents, the PK A of our given acid is actually less than all of the ranges provided for these possible solvents. This means that the acid can react with water, methyl amine, diethyl ether and methanol to form a weaker acid product. Recall that in acid base reactions equilibrium favors the formation of the weaker acid. So this reaction is going to go forwards and that produces unwanted side products. So the only solvent that can be used for reaction one is hexane and now we move on to part two. For part two, we have sodium methyl amide reacting with two methyl propane to all to produce methane amine and sodium two methyl propane two ate. So here our acid has a PK of 18 and our conjugate acid has a PK of 40. Now, for part two, once again, hexane is going to be an appropriate solvent. However, notably, our product or our conjugate acid product is methyl amine, which means that we can use precisely that as a solvent as well. However, the PK of our acid which is 18 is outside of the ranges for both methanol and water. So we cannot use either of them as a solvent. However, recall that the conjugate acid of diethyl ether has a PK of negative 3.6. This means that the conjugate acid of diethyl ether is much stronger then are given acid considering it has a much lower PK value. Because of this, we can also use diho ether as a solvent for reaction to and there you have it. So for part one, it, the only solvent we could use was hexane. And for part two, we could use hexane, Meho amine and diho ether. So with that being said, thank you so very much for watching and I hope you found this hopeful.

Key Concepts

Solvent Polarity

Acid-Base Chemistry

Solvent Compatibility

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