Ethyl allophanate, preparation

Ethyl allophanate, preparation of, for synthesis of allophanyl hydrazide and urazole, 6 48,... 

C2H4N2O3, NH2CONHCOOH. Unknown in the free state as it breaks down immediately to urea and COi- The NH4, Ba, Ca, K and Na salts are known and are prepared by treating ethyl allophanate with the appropriate hydroxide. The esters with alcohols and phenols are crystalline solids, sparingly soluble in water and alcohol. They are formed by passing cyanic acid into alcohols or a solution of an alcohol or phenol in benzene. The amide of allophanic acid is biuret. Alcohols are sometimes isolated and identified by means of their allophanates. 

Allophanyl hydrazide has been prepared previously as the hydrochloride by the zinc-hydrochloric acid reduction of 1-nitrobiuret.1 The new procedure2,3 outlined here entails the hydrazinolysis of allophanic esters in alcoholic solution. Excellent yields (80 to 84%) of allophanyl hydrazide are obtainable with a minimum of difficulty using readily available starting materials. The methyl and ethyl allophanates are prepared from urea and the corresponding chlorocarbonic esters.4... 

Preparation from Ethyl Allophanate. Thirteen and two-tenths grams of ethyl allophanate (0.1 mol), 15 ml. of 100% hydrazine hydrate (0.3 mol), and 100 ml. of water are placed in a 200-ml. three-necked flask equipped as in procedure A. The reaction mixture is heated for 3%. hours, during which the pot temperature rises from 25 to 101° and the still-head temperature rises from 25 to 99°. Fifteen milliliters of distillate is collected. 

Diaryl allophantes as indicated by the above equation have been prepared with R = H, 0-CH3, p-Cl, p-CH R = H, p-CHs, m-OCHa R" = CjHs, CeHs. The allophanate formation fails to occur if the carbanil-ate or the aryl isocyanate is replaced by ethyl carbamate or by ethyl isocyanate, respectively. 

The distribution of aluminum between tetrapedral and octahedral sites may not be controlled solely by the Si/Al ratio, as indicated by Fripiat [1965], but also by other factors in the chemical environment, such as the pH. Yamada and Kimura [1962] and Ossaka [1963] synthesized allophanes with the same Si/Al ratio which behaved differently on heat treatment. The first-mentioned authors prepared an allophane from silicon ethyl ester and aluminum ethyl ester, which yielded a spinel on heating, before transforming to mullite. The last-mentioned author prepared allophane from sodium silicate and aluminum sulphate, which transformed directly to mullite on heating. This may indicate that one allophane had a chain structure, while the other is chainlike. Udagawa and Nakada [1969] then proposed a sheetlike structure for allophane, which took these facts into account, and which differed from Wada s [1967] chainlike model. 

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