Phenylurethanes, from alcohols

Follow the procedure given later for preparing phenylurethanes from alcohols, but substitute a-naphthylisocyanate for phenylisocyanate. 

It forms a characteristic benzoic ester, Cj HjgO. CO. CgH, melting at 54°. This is a useful compound for identifying menthol and may be obtained by heating menthol with the theoretical amount of benzoic acid, in a sealed tube to 170° excess of acid is removed by shaking with a boiling solution of sodium carbonate, and the ester is crystallised from alcohol. Menthol forms a phenylurethane, melting at 111° to 112°. 

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]. 

Fenchyl alcohol yields a phenylurethane melting at 88° when prepared from the optically inactive alcohol, and at 82-5° when prepared from the optically active form. It yields fenchone on oxidation, which can be identified by its crystalline combinations (vide fenchone). 

A sesquiterpene alcohol, CjgHjgO, has been extracted by means of phthalic anhydride from oil of opoponax resin. It distils at 135° to 137° in vactu) (2 imm.), and yields a crystalline phenylurethane. But as, in spite of repeated crystallisations, it could not be obtained of constant melting-point, it is probable that the substance is a mixture of two or more alcohols. 

The final residue from the mother liquor is an oil which does not solidify in a freezing mixture, and appears to be a mixture of p- and w-tolylcarbinols. Only a trace of phthalic acid (phenolphthalein test) was obtained by oxidizing this oil with permanganate the portion of it which was more readily soluble in water yielded a phenylurethan which depressed the melting point of the phenylurethan of either />-tolylcarbinol or benzyl alcohol. 

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