OTC preparation of oxalyl chloride: a idea worth trying
Here's a little bit of fluff that's been tickling the back of my neck for some time now...finally I got around to typing it up and bringing it around to you, the HIVE at LARGE, to beat, bash, and abuse at your leisure. With a little luck, this idea may even work.
Rationale:
You know why you want oxalyl chloride, or you wouldn't bee reading this.
Basic Idea:
Dry ethylene glycol is exhaustively chlorinated to yield oxalyl chloride. The reaction proceeds in two steps:
(CH2OH)2 + 2 Cl2 --> (CH=O)2 + 4 HCl
(CH=O)2 + 2 Cl2 --> (COCl)2 + 2 HCl
With no water available to hydrate the formed glyoxal intermediate or react with the product oxalyl chloride, what the reaction amounts to is the use of chlorine to carry all the hydrogens away. And therein lies the beauty of it all -- in most reactions of this type, oxidation and chlorination are competing with each other, making yield not so good. But this glycol is the perfect substrate--no alpha hydrogens to be preserved, no unsaturated bonds to screw up, nothing. Just chlorinate the hell out of it, and whatever sequence the reactions happen in, at the end, you will have oxalyl chloride.
I think the use of chlorine to oxidized alcohols to aldehydes is pretty well known since ye olde days, when the only chemists spoke german. So I won't go looking for refs on that unless requested. I probably couldn't get them even if I found them--they'd all bee back in the 1800s, in Chemische Berichte and Liebig's Annalen. So just trust ole' ning on this one, chlorine will oxidize alcohols to aldehydes, and no further without water present.
The second step needs more documentation. Luckily, I'm in a typing mood today, so here is a prime source--a patent that does just what we need:
US patent 5,872,290 : Preparation of acid chlorides
Abstract:
Disclosed is a method of making an acid chloride having the general formula R3C.COCl, where R is saturated aliphatic or aryl. A solution is formed in an inert solvent of an aldehyde having the general formula R3C.CHO and chlorine gas is sparged into said solution. The reaction between the aldehyde and the chlorine gas to produce the acid chloride is performed in the absence of a catalyst, an initiator, and UV light.
...
In the first step of the process of this invention, the aldehyde is reacted with chlorine gas to produce the corresponding acid chloride: R3.COCl
To avoid the production of unwanted byproducts such as the t-alkyl chloride, an inert solvent is used in this first reaction. The aldehyde is dissolved in the solvent and chlorine gas is sparged into the resulting solution. The solvent should be a liquid between about 80 C and about 250 C. In general, the choice of a solvent depends on the boiling point of the acyl chloride to be prepared, the solvent being selected so that it can easily be separated from the acyl chloride by distillation. Chlorinated benzenes, such as mono, di, and trichlorobenzenes, and particularly o-dichlorobenzene are the preferred solvents. Other aromatic solvents that lack active hydrogens and also lack ether linkages can also be used.
No initiator, catalyst, or UV light is used in this reaction as they not only add to the cost of the reaction, but also reduce the yield and selectivity. Since the reaction proceeds in the absence of light, the process can be carried out industrially in glass-lined steel reactors.
The reaction is complete when chlorine breakthrough is observed. The reaction can be followed by GC.
...
In the following experiments an aldehyde was reacted with chlorine gas in a three-necked flask under various conditions in the absence of an initiator or a catalyst, with and without ambient light. The following table gives the conditions and a GC analysis of the product mixture.
Aldehyde PA wt% / solvent initiator temp (C) RHCO RCOCl RCl other Light
PA 20 % o-PhCl2 426 ppm 65-70 15 50 12 22 ambient
PA 20 % o-PhCl2 426 ppm 30-35 12 68 5 14 ambient
PA 20 % o-PhCl2 none 30-35 <1 85 2 10 ambient
PA 100 % none none 35-45 5 25 44 24 ambient
CPA 20 % o-PhCl2 none 40-50 <1 94 0 5 ambient
PA 20 % o-PhCl2 none 30-40 1 60 2 38 none
The experiments show that the presence of the initiator reduced the yield of acid chloride product, that the yield was higher at lower reaction temperature, and that the solvent significantly enhanced the yield. The last run shows the reaction proceeds even in the dark.
See also US patent 2,490,386 : Production of unsaturated acid halides, for more information on this, as well as Organic Syntheses CV 1, 155 (
http://www.orgsyn.org/orgsyn/prep.asp?prep=cv1p0155
): o-benzoyl chloride.
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So, to make oxalyl chloride from antifreeze, you would dry it, probably with CaCl2 or MgSO4, then put it in a big flask on a scale with a stirbar and a stink-pipe going to a water tank to absorb the generated HCl gas. Chlorine would then bee passed through a wash-bottle of H2SO4 or a CaCl2 drying tube and into the flask until a certain amount of weight gain had occurred, indicating complete conversion. One would have to see whether a dilutive solvent was needed or if the reaction could bee run neat.
The chlorine could bee generated by electrolyzing concentrated HCl, probably the most convenient way to make several moles of it.
Unfortunately, most of our favorite solid chlorinating agents like NaOCl and Ca(OCl)2 will not work as replacements for the chlorine gas, due to the reactivity of the formed oxalyl chloride. However, it may bee possible that the chloramines (NBS, DCDMH, TCCA) will not react with the formed oxalyl chloride. If this bee the case, the whole synth would beecome a great deal easier. However, I would await the word of a real hive chemist, and not a mere wannabee like myself before getting my hopes up.
Chemists: Will (COCl)2 react with (RCO)2.NH? Or is it too deactivated?
Well, whatcha think?