[HP]

Hello
Now i am wondering what kind of H-bonds could be formed if between an aliphatic aldehyde (acetaldehyde for example) with neat formic acid. I am wondering because the formic acid itsself have two protons HCOOH and which of the will form H-bonds with the aldehyde R-CHO Is possible forming 2 H-bonds of the CO-carbonyl athom and two molecules HCOOH?
Thanks
HP

[Albert]

In my opinion, there is only one bond you can properly call Hbond between an aldehyde and formic acid.

[HP]

I mean that:

[Albert]

Is possible forming 2 H-bonds of the CO-carbonyl athom and two molecules HCOOH?

Yes, of course.

[HP]

Yes these are the intra H-bond formic acid. Do you think possible H-bond between the two CHO groups from the aldehyde and aldehyde-acid ?

[Albert]

No, not at all, not even once in a blue moon!

As I said in my first post, they can't be called h-bonds, although they may be capable of extremely weak interactions (weaker than h-bonds).

[HP]

Hehe you right CHO-CHO onteraction weaker than COOH-COOH and OH-OH i know because acetaldehyde have lower b.p than acetic acid and ethanol...
My question was induced by one my experiment when tried to make acetal from acetaldehyde and ethanol. When i put some acetaldehyde in mixture ethanol-85% formic acid - no reaction occurs for very long period. But when add some water to this mixture the formation of diethylacetal quickly occurs. How can i explain that result Could formic acid supress the reaction forming acetal when water only 15% in mixture and how?
Ths again

[Albert]

Here is a key step for your reaction. As you can see water has a paramount importance: without it, the reactions cannot go on. If I have understood your question.

[HP]

Thank you very much for the comprehensive explanation. Intuitively i tought the water content in reaction micture is from great an importance for acetal forming and your suggested reaction mechanism is very right. Although when i used comercial 85% formic acid, reaction of acetaldehyde and ethanol occur to some extend but after 24h "induction" period. May be the exist 15% H2O play some role that Do you think 85%formic acid may cause esterification of ethanol at room temperature?

[Albert]

Do you think 85%formic acid may cause esterification of ethanol at room temperature?

Mmm, I don't think so. In my opinion, you always need a stronger acid (in small quantity, but you need it) and a higher temperature.

[HP]

Aha good discussion...Formic acid the simples but still interesting one  

[davidzhangsh]

pardon me to get in a word.
i want to know how long the H-bone is?
it is usually 0.1nm,right?!

[HP]

I know usually H-bond lenght from 1.5 to 3.5A. It;s different with different donor-aceptor pairs...

[moussa]

i think 2 h bond will occur
polimerization would be taken in account .
don't you read that it must be tored carefully on such chemiscals' containers?

[HP]

You mean 2 possible H-bonds from HCOOH - H from carboxyl moestry (COOH) and/or CHO moestry formic acid? Polymerization of acetaldehyde very possible in aqueous solution but i still cant find what happens in my case acetaldehyde in 85% HCOOH. Anyway thers no solid product(polymer as polyacethal or cyclic polyacethals are insoluble in water and i dont know if soluble in formic acith though its very possible:)
Continue thinking...