Interesting document - A challenge to a claim of the synthesis of 4-nitroimino-perhydro-1,3,5-oxadiazine as an intermediate or byproduct in a related reaction. The experimental procedure is given on p. 11:
"Example 5 specifically states that: A mixture consisting of nitroguanidine (10 g), methoxyamine hydrochloride (9.6 g), 75% paraformaldehyde (11.5 g), toluene (80 ml) and a catalytic amount of concentrated hydrochloric acid was subjected to heating under reflux for three hours, while the water was removed therefrom.[2] Under reduced pressure, the solvent contained in the mixture was distilled off to obtain white crystals of the hydrochloride of 5-methoxy-2-nitroimino-hexahydro-1,3,5-triazine (16.2 g) having a melting point from 160° to 170°C."
The reaction forming 4-nitroimino-perhydro-1,3,5-oxadiazine is given on p. 42.
It was claimed that:
"A person of ordinary skill in the art of heterocyclic chemistry in the 1988-90 time frame knew that production of 1,3,5-oxadiazines could occur without any external nucleophile like water. Only the formaldehyde, a guanidine, and an acidic environment are needed. 1,3,5-oxadiazines have been synthesized under non-aqueous conditions (from a urea, paraformaldehyde with an acid catalyst in chloroform) by Seidel et al. SX 2052."
But this claim was challenged:
"Example 5 makes no mention as to the coproduction of a 1,3,5-oxadiazine intermediate compound. ..."
This case was heard by the Board of Patent Appeals in 2001. It looks like, up to that time, there was not an actual published procedure using "only the formaldehyde, a guanidine, and an acidic environment" to prepare the oxadiazine, or it would have been referred to specifically.
Steve
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