Chlorination of 1-(8-hydroxyethy1)-2-nitriminoimidazolidi gives a mixture of I-@-chloroethyl)-2-nitriminoimidazolidine and l-nitro-2,3,5,6-tetrahpdro-l(H)-irnidaz(l,2-a)i1~1i-dazole hydrochloride. The other products, 1-(,9-aminoethyl)-3-nitro-2-imidazolidone hydrochloride and 1-(8-nitraminoethy1)-2-irnidazolidone, isolated during the original study of the chlorination of 1-(8-hydroxyethyl)-2-nitrin1inoi111idazolidie are formed by the action of ethanol on 1-nitro-2,3,5,6-tetrahyclro-1 (H)-imidaz(l,2-a)imidazole hydrochloride. Amines add to 1-nitro-2,3,5,6-tetrahydro-l(H)-imidaz(l,2-a)imidazole nitrate to give the correspor~ding 1-(~-nitraminoethyl)-2-substit~1ted amino-2-i~l~idazoline nitrates. These reactio~ls and the aminolysis of 1-(8-chloroethy1)-2-imidazolidone are described in detail.
INTRODUCTIONThe present work was directed to a comparisoil of the chemical properties of 1-(Pchloroethy1)-2-nitroguanidine (I) with 1-(P-chloroethy1)-2-nitriminoimidazolidine (2) and to an attempt to find an explanation for the origin of the products isolated from the reaction of thionyl chloride with 1-(P-hydroxyethy1)-2-nitriminoimidazolidine (2).The cyclization of 1-(P-chloroethy1)-2-nitroguanidine to 1-nitro-2-iminoimidazolidine hydrochloride (or its tautomer, 1-nitro-2-amino-2-imidazoliniuin chloride) was described first in 1950 (1). This cyclizatiorl occurred a t the melting point of the compound or it could be effected by heating the compourld with an inert solvent. A carbonium ion mechallisin was suggested (3, 4) for this cyclization reaction but it was noted that this suggestion was premature owing to the absence of kinetic data. Later the lcinetic data were supplied by the work of Boyars, Sager, and Sltolnik (5). They found that the relative rates of cyclization of the 1-P-substituted-2-nitroguanidines were 1-p-bromoethyl-> 1-0-chloroethyl-> 1-P-nitroxyethyl-. These relative rates of reaction are in agl-eement with the bond energies for C-Br, C-C1, C-0 covalent links which would be expected in a carbonium ion mechanism. However, since the rate of cyclization of I-(@-nitroxyethyl)-2-nitrog~1a11idii1e was greater than the cyclization rate of 1-(0-nitroxypropy1)-2-nitrog~ianidine, an internal Sn2 mechanism rather than a carbonium ion mechanism was favored. Further evidence for the interilal Sn2 mechanism was established by a demoilstration (6) of the lack of salt effect on the cyclization rate. Thus the cyclization of 1-(0-chloroethy1)-2-nitroguanidine is considered to occur by a backside approach of the nitrimino group to the substituted side chain as follows:lMa7zuscript received M a y 14, 1958.