The mystery of Ott's product is probably (almost) solved.
Way upthread I posted about a reaction described by E.Ott in Chem Ztg. and cited by Sartori in The War Gases, in which ethyl oxamate was treated with
phthaloyl chloride. Ott, and Sartori believed the product to be Cl-C(=O)-CN, cyanoformyl chloride, a hybrid molecule between phosgene and the oddity
carbonyl cyanide.
However, the bp of this oily liquid was given by Ott as 126-128 C/750 mm which is quite high for that molecular weight and structure. Phosgene boils
near 0 C, and carbonyl cyanide, a little above ambient. One would expect cyanoformyl chloryde to boil somewhere between these two.
Moreover in recent years German investigators prepared cyanoformyl chloride by unambiguous direct means (from phosgene and HCN) and found the bp to be
right where one would expect, almost 100 C lower than that of Ott's product. And cyanoformyl chloride is unstable; even at low temperatures it slowly
disproportionates into the symmetrical phosgene and carbonyl cyanide.
So, I have been asking myself, what did Ott actually make?
In the course of other work I have been planning to prepare phthaloyl chloride.
Ethyl oxamate is ready obtained by treating diethyl oxalate with the calculated amount of ammonia in ethanol. It is beautifully crystalline.
However, I did not yet get around to trying this reaction. But the question kept nagging at me, so a little more paper chasing turned up two reactions
of ethyl oxamate with the closely related chlorinating reagents PCl5, and oxalyl chloride.
In both cases reported in the contemporary literature, ethyl oxamate gave not cyanoformyl chloride, but (with oxalyl chloride) EtO-C(=O)-C(=O)-N=C=O
the acyl isocyanate, or (with PCl5) 2,2-dichloro-2-ethoxyacetamide, that is, the product of addition of two chlorine atoms to the carbonyl carbon
adjacent to the ester moiety. In this case by product is POCl3.
Ott clearly believed that phthaloyl chloride would dehydrtae the amide side of ethyl oxamate to nitrile and chlorinate the ester side. This clearly
did not happen.
This isocyanate is reported as boiling at 136-138 C and to exhibit a very characteristic IR maxima of 2225 so now we have a very serious suspect
compound.
EtO-C(=O)-C(=O)-N=C=O is said to be a liquid with an unpleasant odor similar to human sweat. It is very moisture-labile. bp 136-138 C.
Dichloroethoxyacetamide is thermally stable and only slowly hydrolyzed by water.
Whether phthaloyl chloride yields the isocyanate or the dichloroethoxyacetamide remains to be seen. I suppose it could produce some completely
different product such as EtO-C(=O)-CN. We will see just what Ott actually made.
References:
Ethyl oxamate and PCl5:
Kiranov, Russian Chemical Bulletin 3, 551 (1954)
A brilliant dissection and excoriation of Wallach's mechanism for the dehydration of carboxylic acid amides to nitriles.
Ethyl oxamate and oxalyl chloride:
Berree, Michelot and Le Corre, Tet.Lett 39 8275 (1998)
[Edited on 8-11-2007 by Sauron]
[Edited on 8-11-2007 by Sauron]
Sic gorgeamus a los subjectatus nunc.
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