1,3-diphenylurea

Dissolve 12 g. of aniline hydrochloride and 6 g. of urea in 50 ml. of warm water, and then filter the solution through a fluted filter to remove any suspended impurities which may have been introduced with the aniline hydrochloride. Transfer the clear filtrate to a 200 ml. conical flask, fit the latter with a reflux water-condenser, and boil the solution gently over a gauze for about hours. Crystals of diphenylurea usually start to separate after about 30-40 minutes boiling. Occasionally however, the solution becomes supersaturated with the diphenylurea and therefore remains clear in this case, if the solution is vigorously shaken after about 40 minutes heating, a sudden separation of the crystalline diphenyl compound will usually occur. The further deposition of the crystals during the re-... 

When the ij hours boiling is complete, preheat a Buchner funnel and flask by pouring some boiling water through the funnel with the filter-paper already in position, and then quickly filter the boiling solution. Transfer the filtrate to a beaker to cool, and then wash the insoluble residue of diphenylurea on the filter twice with hot water, and drain thoroughly. Cool the filtrate in ice-water the monophenylurea separates as colourless needles. Filter at the pump and drain well. Recrystallise the crude product from boiling water, as in the previous preparation. Yield of monophenylurea, 2 5-3 g. m.p. 147°. 

The insoluble residue of diphenylurea from the original filtration is chemically almost pure. It may be recrystallised from hot rectified spirit or ethanol, a process which will be necessary if the material contains fragments of porcelain. When using either of these solvents, however, the hot solution should be filtered at the pump using a small Buchner funnel and flask which again have been preheated by the filtration of some of the hot solvent, as the solution when cooled rapidly deposits the diphenylurea. iSym-Diphenylurea (or carbanilide) is thus obtained as fine colourless crystals, m.p. 237° yield, 1-1 5 S ... 

Example. Add a solution of 0 5 ml. of benzyl alcohol in 5 ml. of petroleum (b.p. 100-120 ) to a similar solution of 0 5 ml. of phenylisocyanate, and boil the mixture gently under reflux for 20 minutes. Filter hot if necessary from any insoluble diphenylurea, and cool. Filter off the crystalline urethane, and recrystallise from the petroleum colourless crystals, m.p. 76 . 

R NHa + C.HjNCO = RNH CO NHC,Hj Traces of water will contaminate the product with diphenylurea (p. 336) if the solution is boiled hence the need for anhydrous conditions. i-Naphthylisocyanate reacts more slowly with water, and the i-naphthyl-urea derivative can often be obtained using a cold aqueous solution of an aliphatic amine it is particularly necessary in such cases to purify the product by recrystallisation from, or extraction with, boiling petroleum, leaving behind any insoluble di i-naphthylurea. Note that the amine must also be free from alcohols (p. 335) and phenols (p. 337). 

If the alcohol is not anhydrous, reaction also occurs between the water and the reagent to produce diphenylurea (m.p. 242°) and di-a-naphthyl-urea (m.p. 284°) respectively, for example ... 

Somespnt.-diphenylurea is also formed and the quantity increases with continued refluxing ... 

Reductive carbonylation of nitro compounds is catalyzed by various Pd catalysts. Phenyl isocyanate (93) is produced by the PdCl2-catalyzed reductive carbonylation (deoxygenation) of nitrobenzene with CO, probably via nitrene formation. Extensive studies have been carried out to develop the phosgene-free commercial process for phenyl isocyanate production from nitroben-zene[76]. Effects of various additives such as phenanthroline have been stu-died[77-79]. The co-catalysts of montmorillonite-bipyridylpalladium acetate and Ru3(CO) 2 are used for the reductive carbonylation oLnitroarenes[80,81]. Extensive studies on the reaction in alcohol to form the A -phenylurethane 94 have also been carried out[82-87]. Reaction of nitrobenzene with CO in the presence of aniline affords diphenylurea (95)[88]. 

Ethoxy-6-methylpyrimidine 1-oxide (499) reacts with phenyl isocyanate to eliminate carbon dioxide and give a mixture of 4-ethoxy-6-methyl-N-phenylpyrimidin-2-amine (SOO) and (the derived) 7V-(4-ethoxy-6-methylpyrimidin-2-yl)-7V,7V -diphenylurea (SOI) phenyl isothiocyanate reacts quite differently (79CPB2642). 

The salt should not be boiled with water any longer than is necessary, as some decomposition occurs and diphenylurea, melting at about 235-240°, is produced. 

Phenylsemicarbazide has been obtained by the action of hydrazine hydrate on diphenylurea, phenylurethane,i phenyl isocyanate, or the potassium salt of dibenzohydroxamic acid. For its preparation, Curtius method of treating phenylurea with hydrazine liydratc is better Ilian either the older method of... 

Carbanilide ( 3fin-diphenylurea) [102-07-8] M 212.3, m 242 . Crystd from EtOH or a large volume (40mL/g) of hot water. 

A further class of stabilisers are the amines, such as diphenylurea and 2-phenylindole. These materials are effective with certain emulsion polymers but rather ineffective with many other polymers. 

Aliphatic nitro compounds 1035 with an a-hydrogen atom are readily O-silylated by N-trimethylsilyl-N,N -diphenylurea 23b to give a mixture of 1036 or 1037 [99]. This silylation works in particularly well if Ri and or R2 are activating nitro or car-... 

If it is heated alone at 160°, ammonia comes off rapidly, the aniline and phenylisocyanate may be detected by their odor but they combine in large part to form 5ym.-diphenyliu ea which crystallizes out from the hot liquid, and cyanic acid may be detected by means of silver nitrate in the water with which the apparatus is washed out after the experiment. When an aqueous solution of phenylurea is distilled, aniline may be detected in the distillate and 5ym.-diphenylurea crystallizes from the boiling liquid. By heating urea with the amine or with its hydrochloride at 160°, or by refluxing urea in aqueous solution with the amine or its hydrochloride, we have prepared sym.-6i-o- and />-tolyl, di-a- andjS-naphthyl, dimethyl, di-w-butyl, di-w- and i5 -amyl and dibenzylureas in satisfactory yield. 

When 5ym.-ethylphenylurea is heated alone at 160°, ethylamine escapes and the phenylisocyanate and aniline combine to form 5ym.-diphenylurea. The imea dearrangement then provides the true explanation of the apparently metathetical reaction in which the ethyl groups of 5ym.-diethylurea are successively replaced by phenyl. ... 

---