A text-book of organic chemistry / by A.F. Holleman ; edited by A. Jamieson Walker ; assisted by Owen E. Mott ; with the co-operation of the author.

  • Arnold F. Holleman
Date:
1913
Catalogue details

Licence: In copyright

Credit: A text-book of organic chemistry / by A.F. Holleman ; edited by A. Jamieson Walker ; assisted by Owen E. Mott ; with the co-operation of the author. Source: Wellcome Collection.

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    § 398] PYR AZOLE. boxylate and ethyl diazoacetatc to form triethyl pyrazolelri- carboxylate: c,h5ooc-c ch.cooc2h5 C2H5OOC-C+ UN N Diethyl acetylene- dicarboxylate C0H5OOC • C—C • COOC2II5 II II C0H5OOC.C N \y NH Triethyl pyrazoletricarboxylate Pyrazole is formed in several reactions, one of them being the combination of hydrazine with propiolaldehydeacetal (142): CH C •Cir(0(,2H5)2 ~b H2N • NH2 — Propiolaldehydeacetal = CH — C • C H=N • N H 2 ■+ 2C2H50 H; Intermediate product (not isolated) C—CH )N nh2 Intermediate product CH—CH \v CH /* \NH Pyrazole or NH /‘\n. a 1 4 3 This synthesis proves that pyrazole has the formula indicated, so that it may be regarded as pyrrole in which one of the CH-groups has been replaced by N. It is crystalline, melts at 70°, and is very stable. It is only a weak base, for its aqueous solution has a neutral reaction. The identity of the 3-derivatives and the 6-derivatives of pyrazole is of theoretical interest, since the structural formula- given indicates that they should be dissimilar. On replacing the hydrogen atom of the imino-group by alkyl or phenyl, the deriv- atives with substituents at positions 3 and 5 are no longer identical. Since migration of the hydrogen atom from one nitrogen atom to the other, with a simultaneous migration of the double bonds, makes position 3 equivalent to position 5, it must be assumed that free pyrazole readily undergoes this type of tautomerization:
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