Phenylurea decomposition

Hydroxyphenylpyruvic acid plays an important role in the biogenesis of compounds with a phenylpropane skeleton, and it has been used as substrate in several enzyme studies. Published procedures for its preparation are unsatisfactory in many ways. The alkaline hydrolysis of the azlactone of a-bcnzoylamino- -acetoxycinnamic acid 7 makes necessary a tedious separation of the resulting benzoic acid, and the yield is only 34% based on -hydroxybenzaldehyde. The hydrolysis of 5- ( -hydroxybenzal)-3-phenylhydantoin 9 requires a separation of phenylurea. Finally, the two-step cleavage of the azlactone of a-acetamino- -acetoxycinnamic acid 8 does not proceed easily, and impure products are obtained. In applying this procedure to the synthesis of a carboxyl-labeled -hydroxyphenylpyruvic acid, the overall yield was only 9%.u It must be kept in mind that any prolonged isolation procedure will cause some decomposition of this sensitive compound. 

Of the various published methods of preparing phenylurea, such as treatment of aniline salts with potassium cyanate in water solution,1 heating aniline with urea,2 with cyanic acid,3 or with cyanogen chloride,4 and the interaction of phenyl isocyanate or phenylcarbamine chloride with ammonia,5 the only ones to be considered as practical methods for preparation are the first two. The first suffers from the disadvantage that potassium cyanate is not easily prepared in the laboratory and rapidly undergoes spontaneous decomposition in storage while by the action of urea on aniline alone, carbanilide is formed in rather larger proportion than phenylurea. 

It was reported that the recoveries of 17 PAHs from six certified reference marine sediments and soils [77] increased from 70 to 75% when the temperature was increased from 50° C to 115°C, and remained at 75% from 115 to 145°C. In the extraction of OCPs from sediments, recovery was unchanged from 100 to 120°C [74]. In the extraction of phenylurea herbicides from soils, the recovery peaked in the range 60 to 80°C and decreased at lower or higher temperatures [75]. In the extraction of sulfonylurea herbicides from soils, recovery dropped from 70 to 80% to 1 to 30%. due to decomposition when temperature increased from 70°C to 115°C [79]. The recovery of oligomers from poly(ethyleneterephthalate) increased as temperature rose... 

Gas chromatography of phenylurea herbicides is difficult because of their ease of thermal decomposition. Procedures have been reported in which careful control of conditions allows these compounds to be gas chromatographed intact [177,178], Alternatively, the phenylurea herbicides can be hydrolysed to the corresponding substituted anilines (see below) which are then determined either by gas chromatography directly [179], or as derivatives [180], or colorimetrically after coupling with a suitable chromophore [181], For example, monolinuron is converted to /j-chloroanilinc, formation of the bromide derivative produces the following ... 

Gas chromatography of phenylurea herbicides is difficult because of their ease of thermal decomposition. Procedures have been reported in which careful control of conditions allows these compoimds to be gas... 

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