Sciencemadness Discussion Board

preparation of CH3AlCl2

whupharm_xu - 29-9-2004 at 17:01

who will give certain literature or some details about the reaction?!

Mephisto - 29-9-2004 at 17:15

You started already two threads about very similar compounds. Learning chemistry means also to learn to research. As student you should be able to research by yourself and not let do others the work. Your university has the Chemical Abstracts for sure in its library. Check also Beilstein and Houben-Weyl. Ask for access to an internet-database like CASREACT (via SciFinder or BeilsteinCrossfire), since searching goes faster there, as in the book-version of CAS.

true_alchemy - 29-9-2004 at 18:54

If you can't readily obtain literature why don' t you just try it? I think I once accidently made a propylaluminum bromide by simply reacting aluminum with PrBr in THF. MeCl will stay in the reaction mixture even with light reflux at THF temps. I think it is because of the vapor density. Be careful I think alkyl aluminums are pyrophoric. That's why I said "accidently" :D

JohnWW - 29-9-2004 at 20:48

If organic-substituted Al halides can be made so easily, I wonder if anyone has thought of the possibility that such compounds could be used as a substitute for Grignard reagents? I have not been able to find anything definite on Google about this.

John W.

tokat - 29-9-2004 at 23:20

Johnww whats the general jest of Grignard reagents?

BromicAcid - 30-9-2004 at 07:16

Went to the library, spent 5 minutes looking up methylaluminum dichloride on Beilstein. Got several references to its production including a few along the lines of your reaction. Printed them out (free) went to the second floor in the reference section, looked some up and found a good reference and photocopied it ($0.10). Here goes:

From J. Amer. Chem. Soc.; 60; 1938; 2276
The desired amount of aluminum metal, preferably in an alloy such as Aluminum Company of America Alloy 12 (8% Copper), is cut in clean, dry shavings or chips. These are placed in a glass or steel reaction vessel equipted with: halide inlet and product discharge line, temperature and pressure gauges, provision for heating and cooling, and a safety blow-out. The catalyst, about 0.1% of anhydrous aluminum chloride (or iodine, or the product of a previous preparation) is placed in on spot on top of the aluminum and the reaction vessel closed. Air is pumped or flushed out, and methly chloride gas introduced to a pressure of one atmosphere (or more, depending on the equiptment used). If the reaction fails to start in one hour at room temperature, the charge is heated to 100C. Once started, the reaction is autocatalytic and highly exothermic. More methyl chloride is added, and cooling is applied to maintain a suitable rate of reaction and to keep the temperature of the charge below 75C. At higher temperatures, the side reaction may occur with the formation of gas.

When no more methyl chloride is absorbed, the reaction is completed. The reaction of the aluminum is quantitative, while any iron or copper in the alloy remains unattacked. Side reactions are negligable. In a typical preparation, about 60 milimoles of aluminum in the form of alloy took up 88.9 milimoles of methyl chloride with the formation of only 0.9 milimole of methane; the non-volitile residue contained no aluminum and 0.4 miliatom of chlorine; no iron or copper was detected in the distilled product.

The water-white, oily liquid is decanted or vacuum distilled, from the reamining metallic sludge into a suitable closed container.


The product of the methyl chloride reaction is almost exactly an equimolecular mixture of dimethylaluminum chloride and methylaluminum dichloride. No evidence of either trimethylaluminum or aluminum chloride is obtained on fractional distillation.


When the individual compounds are desired, they may be separated from their mixture by fractional vacuum distillation, or the dimethylaluminum chloride may be obtained in pure form by heating the mixture with an excess sodium chloride and distilling the dimethyl compound from the monomethyl addition compound.

That is plenty of information for you to lean about this reaction. You can thank me later. :D

mick - 30-9-2004 at 09:26

If organic-substituted Al halides can be made so easily, I wonder if anyone has thought of the possibility that such compounds could be used as a substitute for Grignard reagents? I have not been able to find anything definite on Google about this.

This is what I generally think
Grignard reagents are similar organolithium reagents, they are nucleophiles, act as bases with out any water there, make a - , how to extend the idea of acid + base + water to things where there is no any water.
Organoaluminium reagents are electrophiles , they make a +, they are called Lewis acids.
If you want to do a cyclo-addition reaction in organic chemistry, which needs a plus some where. AlCl3 is a standard catalyst (personal experience, if you are doing a 25 gal reaction and your Boss tells you to use powdered AlCl3 in stead of the usual granular stuff do not listen or be ready to run when every thing starts getting hot and you have got what is called a run away reaction).
What I have found, from the literature, is that the alkylaluminium chlorides also act as a base towards water. If you have any water in the standard AlCl3 catalized reaction, the water catalizes a polimerization reaction.
With the alkylaluminium chlorides, the alkyl group acts as a base towards water and takes all the residue out, ending up as ethane or methane.
So you have got a Lewis acid and a Bronsted base in the same compound.
Who ever worked that out, I would like to shake thieir hand.
If neat, I think they are pyrrophoric, but the solutions seem to be OK.
Could be wrong


Edit was because I missed a bit

[Edited on 30-9-2004 by mick]

true_alchemy - 30-9-2004 at 09:49

Yes there is literature on the reactions of alkyl aluminum reagents. Ethyl Corp. has not only advertised sale of alkyl aluminums but I beleive they had a brochure on their reactions and uses.
I was looking at one of their items some time ago and if I remember correctly it acted as a RMgX but gave highly branched products but this may have just been from a trialkyl. I don't remember.
Calcium forms alkylcalcium compounds as grignard reagents also. I've been wanting to look at both of these.
Man, this is good stuff, I love it!