Sciencemadness Discussion Board

MAPP gas as a reagent?

Antwain - 3-11-2007 at 09:25

so MAPP gas is a mixture of methylacetylene and allene (presumably also able to be called 'propane something' and hence MAPP... but anyway. Some sources have claimed that these two compounds rapidly or at least easily interconvert, while other sources mention nothing about it. Unfortunately it also contains LPG but for mild reactions this may be able to be disregarded.

So, does anyone know if they interconvert and if so how rapidly at room temperature. For some reactions it wouldn't matter, for instance hydrobromination of either one should give the gem-dibromide (don't know if that terminology is still valid), but bromination would yield different products.

Alternatively I could try to form an acetylide (such as sodium, from the metal) and this would solve all problems, but I am hesitant to waste good sodium unnecessarily. Does anyone know whether allene is more reactive than acetylene (I would assume so, since apparently reaction with acetylenes is hard to stop because the alkene is more reactive, and I think allene is more reactive than alkenes). I have not found a great deal of information about allene(s)

I do not have a specific reaction in mind yet, though I have toyed with a few ideas. Basically I am curious as to whether or not it can even be used as a reagent.

Edit- Well I just looked at the bottle, and I swear this wasn't there before ;) , but it is 44% methlyacetylene/propadiene and 56% liquefied petroleum gas.

[Edited on 4-11-2007 by Antwain]

Eclectic - 3-11-2007 at 11:24

I also have noticed that as I get older, falling between alternate realities where suddenly something appears or disappears seems to be happening more frequently...;)

chemkid - 3-11-2007 at 12:51

Methyl acetylene and propadiene sound interesting. Allene appears to be an alternate name for propadiene or is it a class of chemical like alkyne, alkane, alkene etc? Is petroleum gas a methane/ethane mix? I have always been interested in MAPP gas, but have never purchased a cylinder because i am unsure if it can be burned in a propane torch. Anyone know if it can? Sorry to pose more questions about your question than actually answers.

Chemkid

Magpie - 3-11-2007 at 15:31

Quote:

I have always been interested in MAPP gas, but have never purchased a cylinder because i am unsure if it can be burned in a propane torch. Anyone know if it can?


Yes, MAPP gas can be used with a propane torch. I use it in my bunsen burner when propane will not provide a hot enough flame.

Antwain - 3-11-2007 at 15:42

Well, I just founds this on the wiki:
Quote:
Propyne is a convenient three-carbon building block for synthesis. When propyne is condensed and treated with n-Butyllithium, solid propynyllithium is formed. This nucleophilic reagent can then be added to a carbonyl, producing a secondary alcohol. While purified propyne is expensive, in this reaction it can be replaced with MAPP gas to cheaply generate large amounts of the reagent.


nbutyl is one of those things I need :( but not until I have a vacume pump.

chemrox - 3-11-2007 at 16:26

please be specific in your posts it will pay dividends to you in the form of useful comments and answers and it will make your contributions more interesting. As an example
Quote:
nbutyl is one of those things I need but not until I have a vacume pump


vacuum is how that is spelled by the way.. did you mean you need n-butyllithium? and what makes the vacuum pump a prerequisite? and would an aspirator suffice for your purpose? allene doesn't seem a very useful reagent unless one was going to build up to an aromatic acid, amine, alcohol, halide, ester, ketone or etc. from the most very basic building blocks. I'd still prefer allyl alcohol because that can be had nearly free from cooking oil by way of glycerol. MAPP burns just a bit hotter than propane but comes packaged to use with the same requipment. I like it for soldering but not so much for glass bending.

The_Davster - 4-11-2007 at 22:52

Well in another thread over in energetic materials, Axt made the silver salt of propyne easily from silver nitrate and the gas producing silver methylacetylide, which is only mildly energetic, it just burns.

However I wonder if this could be a starting material for sodium or lithium methylacetylides, which could be used as a reagent for whatever such a carbanionic type compound could normally be used for.

One could also perhaps react the methylacetylene with something like butyl magnesiumbromide, giving the grignard of propyne (butane gas would be released).

Could add the salts to ketones like acetone to make a tertiary alcohol for whatever reason.

Antwain - 5-11-2007 at 03:06

Quote:
Originally posted by chemrox
to use with the same requipment.


Lecturing me on spelling??? :P

Yes, I can't spell and I missed that one with the spell checker.

I wasn't asking for help with n-butyllithium and "n-butyl" is what we call it around the lab, anything else 'n-butyl' is called by its full name (I guess, but it has never come up because we have never used any other n-butyl compounds). It was fairly clear from the quote above what compound I was referring to, though.

The pyrophoric nature of n-butyllithium makes the vacuum pump a prerequisite. Flushing with gas is next to useless for displacing all of the air. But we have balloon gas (80%He, 20%N2) cylinders sitting around so a vacuum pump is all I need.

What if someone wanted 2,2dibromopropane? Allene seems useful then.

@ The_Davster- I believe you can make grignards from propyne. It certainly reacts with organolithium compounds.