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Ernest Pohl Doetsch.

On the rearrangement of the tautomeric salts of 1,4,-diphenyl -5-thionurazole and 1,4,-diphenyl -5-thiolurazole .. online

. (page 1 of 2)
Online LibraryErnest Pohl DoetschOn the rearrangement of the tautomeric salts of 1,4,-diphenyl -5-thionurazole and 1,4,-diphenyl -5-thiolurazole .. → online text (page 1 of 2)
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L"^



^i^i-



%t methyl enol

ester and sodium iodide.

fc) Sodium keto salt and methyl iodide ^ methyl keto

ester and sodium iodide.

These would he represented by the differential equations:



tt^



^4 . /r^^^^. -^?-sy ^^-^^-^.-^;

In these equations K is the velocity constant for the



change of the ^keto salt Into the enol salt, K-j^ the constant
for the reverse rearrangement. Kg that for the formation of
the keto ester, and K^ that for the formation of the enol es-
ter. The question whether the rearrangement and alkylatlon
reactions of the two tautomeric compounds is molecular or ionic,
or hoth m<
equations.

The possihlllty that the rearraneiement is due to the
union of ions in the solution with the molecular forms of the
salt or to other complex reactions must also he considered.
This work and that previously undertaken by Nirdlinger and
Acres



salt is a reversible monomolecular reaction. These workers
have suggested how evidence on the question of abnormal hy-
drolysis in concentrated solution could be obtained by a
study of the slow attainment of equilibrium between the two
forms of this weakly acid tautomeric substance.

While working on the various reactions of the thio-
ls)
semicarbazia^s, Markwald subjected these substances to the

action of phosgene and found that the resulting compounds pos-
sessed a certain similarity to the semlcarbazidl^ and seemed
to be tautomeric. He therefore assiemed the following formu-
lae to these compounds. which clearly show their relationship:



From the method of synthesis he was led to believe that the
only other possibility would be expressed by the fornrala

This substance however would show basic properties,
while in reality the cne found had acid properties. If the
substance represented by formula I were alkylated it should
give a sulphur ester, while that represented by formula II
should certainly give a nitrogen ester provided no rear-
rangement took place during the alkylation.

In 1906 Busch and Relnhardt took up the study of

these compounds and arrived at the concluslot that both
the sodium l,4-dlphenyl-5-thionurazole, and 1,4-diphenyl-
-5-thiolurazole reacted with methyl iodide at 100° to form
the l,4-diphenyl-5-thiolmethyl ester. This substance when
saponified with potassium hydroxide yielded the potassium
salt of the 1.4-diphenylurazole and methyl mercaptan. The
course of the reaction according to Busch is:



G-) ^^ > ^y



as fast as the sodium l,4-diphenyl-5-thiomirazole under the
same cocditlons. Busch^ who Gondticted his work idMliw,quall-
tative methods; affirmed the correctness of the view held
by Mrdlinger and Acree regarding the structure of the tauto-
meric compounds and the esters obtained.

In determining the ratio of l,4-dlphenyl-5-thlonura2ole
to 1 ,4-dlphenyl-5-thlolurazole in a mixture, the salts were
alkylated and the ratio of esters was used to express the
amount of each form present in the original mixture. Since
the rearrangement of one salt into the other is slow, in
comparison with the rate of alkylatlon in a neutral solution,
this is permlssible.lt was found by Markwald and Eusch and
also by ITlrdllnger and Acree that in slightly acid alcohol-
ic solutions the 1 ,4-dlphenyl-5-thionurazole rapidly rear-
ranged to form the l,4-diphenyl-5-thiolura20le. Since the
alkylations were effected by equlmolecular amounts of sodium
hydroxide and l,4-dlphenyl-5-thionura2ole to form the soditim
salt of l,4-dlphenyl-5-thlonurazole, the solution at the be-
ginning of the reaction was neutral. During the alkylatlon^
however^ the hydrlodlc acid formed from the hydrolysis of the
methyl iodide reacted with the sodium l,4-dlphenyl-5-thion-
urazole to form l,4-dlphenyl-5-thlonurazole and sodium iodide.
In the alcoholic solution the l,4-diphenyl-6-thionurazole
rearranged into l,4-dlphenyl-5-thlolurazole. The 1,4-diphenyl-






5-thlolurazole, beiEg the stronger acid, formed the sodium
salt of 1 ,4-dipheiiyl-5-thiolurazole, at the same time lib-
erating l,4-diphenyl-5-thiontirazole which then rearranged.
The results obtained from alkylations conducted by means of
methyl iodide in alcoholic solution on the sodium 1,4-di-
phenyl-5-thionurazole must necessarily show a higher per
cent of sodium l,4-diphenyl-5-thiolurazole, if the ratio of
esters is used to determine the ratio of sodium 1,4-diphenyl-
5-thionurazole and sodium l,4-diphenyl-5-thiolurazole in the
original compound. The following reactions will help to
this clear:



^g'^



/'^!'a-'^^^^'t'e^l^^^c^^'S.c.t^ Co o^ £)t3x.c^f_



^ U Lo i~ ^ Jr —^ ^ It 'do



^2



TLC' Kr



10






7L^^\ '



/
5


1

Online LibraryErnest Pohl DoetschOn the rearrangement of the tautomeric salts of 1,4,-diphenyl -5-thionurazole and 1,4,-diphenyl -5-thiolurazole .. → online text (page 1 of 2)