Difluorourea Solutions

Acidification of the aqueous difluorourea solution with a nonoxidizing mineral acid results in the smooth liberation of difluoroamine as well as carbon dioxide. 

A solution of 30 g. of urea in 350 ml. of water is placed in a 1-1., three-necked, creased Pyrex flask and cooled to 0°C. with an ice bath. A gas inlet tube made of 2-mm., heavy-wall, glass tubing is attached to the end of the fluorine supply line by means of a Tygon sleeve in such a manner that no Tygon is exposed. It is fitted into one of the necks of the flask so that the tip is under the surface of the solution. A thermometer and a gas outlet are attached to the other two necks. It is convenient to use a bubbler on the gas outlet containing urea, potassium iodide, and a little acid. This not only will remove the excess fluorine but will serve to indicate when the fluorination is complete. 

The equipment for handling tank fluorine has been described in Volume XI of this series.10 The fluorine tank is opened, 

The solution may then be removed from the reactor and stored in capped polyethylene bottles at —20 to — 80°C. Caution. Concentrated difluorourea solutions decompose above —%0°C. and commonly reek of ietraftuorohydrazine and difluoroamine. Therefore storage facilities should be well vented. 

The solution may be conveniently analyzed by the addition of excess potassium iodide followed by an iodimetric titration. The stoichiometry of the reaction is  

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DIFLUOROUREA SOLUTIONS AND DIFLUORO-AMINE—EXTRA-HAZARDOUS MATERIALS... 

In the case of the solution prepared above, it was found to be 1.21 M in difluorourea. The checker obtained a solution which was 0.99 M. Yields of 80-90% are generally obtained. For disposal, concentrated difluorourea solutions should be heavily diluted with water before being neutralized with sodium hydroxide. 

Concentrated aqueous solutions of difluorourea decompose above —20°C with evolution of tetrafluorohydrazine and difluoramine, both explosive gases. 

A particularly valuable synthesis of HNF2 involves the acid hydrolysis of N,N-difluorourea, A 2 1 N2/F2 mixture is passed into an aqueous urea solution at 0-5°C until the theoretical amount of fluorine has been absorbed. The product is then hydrolyzed by adding concentrated H2S04 and heating to 90°C, the yield of HNF2 being quantitative (9, 230). 

When concentrated aqueous KOH is added to an aqueous solution of lV,lV-difluorourea at — 10°C, a 40% yield of a 3 1 mixture of the trans and cis isomers is obtained (162). A further convenient preparative reaction is that between the N,lV-difluorocarbamate (NF2C02-i-C3H7) and potassium t-butoxide in a nonaqueous solvent (C2H2C14). A 3 1 trans cis mixture results (174). 

The preparation of N2F2 in solution by basic hydrolysis of N,N-difluorourea [1] or from N,N-difluoroisopropyl carbamate and potassium t-butoxide [2] (see also p. 387) presumably occurs by dimerization of intermediate NF. 

A concentrated KOH solution is added dropwise to aqueous difluorourea cooled to about -10 C. The products are passed through a KOH scrubber and condensed in a liquid-nitrogen cold trap. Water is removed in a C02-acetone cold trap. A 3 1 mixture of trans- and cis-N2F2 is obtained with a maximum yield of 42%. The use of dilute base at 25°C or above only yields traces of N2F2 [8]. The procedure is reported to work under nonaqueous conditions as well [9]. 

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