Preparation of 3(5)-methylpyrazoles

Details Preparation of 3(5)-methylpyrazoles Preparation of 3(5)-methylpyrazoles

1994-05-06

1996-01-16

Ramsuer, Robert W.

Organic compounds -- part of the class 532-570 series

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

5483771, C07D23112

Patent

active

054849411

DESCRIPTION:

BRIEF SUMMARY
This application is a 371 Pct/Ep 92/02514 filed Nov. 3, 1992.
The present invention relates to a process for the preparation of 3(5)-methlpyrazoles from diacetylene and hydrazine.
3-Methylpyrazole and its derivatives are important nitrification inhibitors for ammoniacal fertilizers (cf U.S. Pat. No. 4,975.107 and DE 2,745,633 A1, for example).
N-Substituted pyrazoles are of industrial significance as components of numerous biologically active agents (cf, e.g., EP 286,969-A; EP 320,750; EP 234,045-B1; EP 0,269,806-B1).
Methods of synthesizing 3(5)-methylpyrazole from diacetylene and hydrazine on a laboratory scale are known (Schroth et al, Z. Chem. 9, (1969), 110; Paudler et al, J. Org. Chem., 34, (1969), 999).
Disclosures in the literature indicate that diacetylene is extremely difficult to handle in large-scale operations (cf, e.g., DE-AS 1,222,910), for which reason this compound is virtually only used for small-scale syntheses in the laboratory (EP 274,600 A1).
Zh. Prik. Khim. 44 (1971), 1921 also discloses the reaction of diacetylene with hydrazine hydrate. This reference recommends the purification of pyrolysis gases (cracked gas) by means of this reaction, and this gives rise to the following problems: The cracked gas generally has a content of unsaturated hydrocarbons having three or more carbon atoms of only 0.5% or less. This makes the cracked gas hardly suitable as a source of diacetylene for synthesis reactions due to the fact that the low concentration of diacetylene would necessitate the reaction of very large quantities of gas. Moreover, the cracked gas, not having undergone any purification and thus containing higher acetylenes in undue proportions, would yield numerous by-products.
DE-OS 2,157,537 proposes a way of avoiding such problems by the employment of a method of safely handling low molecular-weight acetylenes which consists of adsorbing such acetylenes on to activated charcoal and subjecting them to subsequent processing operations in this form. This method is extremely complicated, and a continuous process poses engineering problems on account of the adsorptive agent.
EP 274,600 reveals a process for the reaction of diacetylene with alcohols, which is reportedly capable of being carried out on an industrial scale by the addition of certain higher hydrocarbons.
It is an object of the present invention to provide a process for the preparation of 3(5)-methylpyrazoles of the formulae Ia and Ib ##STR1## in which R denotes hydrogen, a C.sub.1 -C.sub.6 alkyl radical or an optionally substituted phenyl radical, without incurring engineering problems.
We have now found that this object can be achieved by the cracked gas resulting from the acetylene synthesis,
Surprisingly, the partial gas stream containing the higher acetylenes as obtained in the normal industrial process for working up cracked gas can be directly reacted with hydrazine to give very good yields of 3(5)-methylpyrazoles without the need for physical or chemical pretreatment of said gas stream. The yields are, unexpectedly, much higher than those stated in the literature for reactions with pure diacetylene (cf Paudler and Schroth loc. cit., 73% and 80% respectively).
The reaction can be illustrated by the following scheme: ##STR2## where R denotes hydrogen, C.sub.1 -C.sub.6 alkyl or an optionally substituted phenyl radical. The compounds of the formulae Ia and Ib are together referred to as 3(5)-methylpyrazoles.
The various industrial processes used for the production and purification of the cracked gas used in the process of the invention are well known (cf Ullmanns Encyclopedia of Industrial Chemistry, 5th Edition, A1, 1985, 97 et seq, 111, FIG. 13), for which reason they are only briefly outlined here:
Hydrocarbons (e.g. natural gas or, possibly, higher-boiling fractions) are cracked at the high temperatures required for the production of acetylene, and the resulting gases are rapidly cooled by injected quench water or quench oil immediately on leaving the reaction zone. The composition of the cracked gas depends on the mat

REFERENCES:
patent: 2900044 (1959-08-01), Scofield
patent: 2941020 (1960-06-01), Dunn
patent: 3235557 (1967-06-01), Scharein et al.
patent: 3706181 (1972-12-01), Walker et al.
Journal of Organic Chemistry, Bd. 34, No. 4, Apr. 1969.
Chem. Abstracts, vol. 94, 1981, Abst. No. 174287e.

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