Knorr (Ann., 94, 79, 188) has shown that 3and 5-methylpyrazols are identical.
Knorr, by the action of ammonia on aceto-acetic ester, obtained (3-imidobutyric ester, which with nitrous acid yields a-isonitroso-(3-imidobutyric ester, CH 3 C(:NH) C(:N OH) CO 2 C 2 H 5.
Knorr, Ber., 1889, 22, pp. 169, 2100).
Knorr (Ann., 1886, 238, p. 147), W.
Knorr (Ber., 36, p. 3067) obtained identical substances, viz.
Knorr and R.
Formulae have been proposed by Pschorr and Knorr explaining this and other decompositions (in Pschorr's formula the morphine ring system is a fusion of a phenanthrene and pyridine nucleus); another formula, containing a fusion of a phenanthrene with a pyrrol ring, was proposed by Bucherer in'1907.
The problem is discussed by Pschorr and Einbeck (Ber., 1907, 40, p. 1980), and by Knorr and Horlein (ibid.
Knorr, Ann., 1886, 236, p. 69) or from aniline, acetone, formaldehyde and hydrochloric acid (C. Beyer, Jour.
Knorr, Ann., 1886, 3 73).