Preparation from Ethyl Allophanate

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. 

The reaction mixture is chilled to obtain 0.32 g. of a by-product, biurea (m.p. 244 to 246° with decomposition). The filtrate is concentrated to one-half its volume and chilled to give 4.34 g. of crystals (m.p. 188 to 190°). Further concentration of the filtrate to one-half its volume gives 3.55 g. of crystals (m.p. 194 to 195°). An excess of ethanol is added to the filtrate to produce an additional 1.41 g. of white crystals (m.p. 193 to 194°). The over-all yield of crude hydrazine urazolate is 9.30 g. (70%). Conversion to urazole is accomplished as described in procedure A. 

Urazole is a white, crystalline, nonhygroscopic compound which melts at 249 to 250° with decomposition. It does not decompose when heated at 110° for 48 hours.1 The compound is soluble in water to the extent of 2.83 g./lOO g. at 0° and 23.7 g./lOO g. at 65°. An aqueous solution is acidic to litmus, the pH of a saturated aqueous solution being 3.15 at 25°. Urazole is a weak acid,9 Kk = 1.6 X 10 6, and forms stable alkali metal, ammonium, and amine salts. 

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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... 

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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