Phenyl isocyanate method

Table 3.1 compares hydroxyl values obtained by three methods. In every case the acid-catalysed acetylation method gives a higher result than that obtained by phthalation, the mean difference between the two methods being 2.5% of the determined value. Agreement between the p-toluene sulfonic acid method and the phenyl isocyanate method is good. 

The hydroxyl number can be deterrnined in a number of ways such as acetylation, phthalation, reaction with phenyl isocyanate, and ir and nmr methods. An imidazole-catalyzed phthalation has been used to measure the hydroxyl number for a number of commercial polyether polyols and compared (favorably) to ASTM D2849 (uncatalyzed phthalation) (99). The uncatalyzed method requires two hours at 98°C compared to 15 minutes at the same temperature. 

The acetyl content of cellulose acetate may be calculated by difference from the hydroxyl content, which is usually determined by carbanilation of the ester hydroxy groups in pyridine solvent with phenyl isocyanate [103-71-9J, followed by measurement of uv absorption of the combined carbanilate. Methods for determining cellulose ester hydroxyl content by near-infrared spectroscopy (111) and acid content by nmr spectroscopy (112) and pyrolysis gas chromatography (113) have been reported. 

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... 

A number of simple reactions are now known which form 2-oxo-tetrahydro-1,3-oxazine (18). Here, also, 3-aminopropanol and some of its derivatives are frequently used, Cyclizing reagents are carbonic acid esters in strongly basic medium, " ethyl chloropropionate, trichloracetic esters, or phenyl isocyanate. An example of the first of these methods is ... 

An interesting method of forming 2-oxo-3-phenyltetrahydro-l,3 oxazine (19) and its derivatives was recently given by Gulbins et at. It consists of heating a 2-oxo-l,3-dioxane with phenyl isocyanate ... 

The Mukaiyama-Hoshino reaction between a nitroalkane and phenyl isocyanate generates a nitrile oxide, and this method has been used in the synthesis of 1,2,4-oxadiazoles as discussed in CHEC-II(1996) <1996CHEC-II(4)179>. In a more recent advance, nitroethane undergoes ultrasound-mediated cycloaddition with trichloroacetonitrile to give the extremely useful (see Equation 11) 5-trichloromethyl-l,2,4-oxadiazole 228 (Equation 45) <1995TL4471>. 

The most widely used method for the dehydration of primary nitroalkanes involves their treatment with phenyl isocyanate and triethylamine, introduced in 1960 by Hoshino and Mukaiyama (7). A probable mechanism for the formation of the nitrile oxide is shown in Scheme 6.4. This method is known to be very effective for the preparation of aliphatic or aromatic nitrile oxides. In some cases, the separation of the byproduct A,A -diphenylurea from the reaction mixture may be troublesome. In order to circumvent this problem, 1,4-phenylene diisocyanate was introduced (82,83). The polymeric urea that is formed as a byproduct is largely insoluble in the reaction mixture and can easily be removed. 

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. 

Chemical methods used for the determination of hydroxyl groups or alcoholic constituents in polymers are based on acetylation [16-18], phthalation [18], and reaction with phenyl isocyanate [18,19] or, when two adjacent hydroxy groups are present in the polymers, by reaction with potassium periodate [9,17]. Alcoholic hydroxyl groups may be found in the following polymers (1) poly(ethylene terephthalate) (PET) [20], (2) poly(methyl acrylate), [21], (3) poly(methyl methacrylate) [21], and (4) polyhydric alcohols in hydrolysates of poly(ester) resins [22]. 

In the case of 3,4-dimethylmetalloles 58, which are stable in their monomeric form (see Section III.A.l), the method proposed was the thermolysis of iV-phcnylcarbamates 57, the decomposition of which is regioselective (equation 22). Intracyclic ft C—H elimination giving the metallole 58 is the main process (80-90%), and the transoid isomer 59 is always the minor product. Tertiary /V-phenylcarbamates 57 decompose at about 70 °C in common solvents. In carbon tetrachloride, one can follow easily the progress of the reaction by NMR spectroscopy. An interesting one-pot synthesis is possible with two equivalents of phenyl isocyanate, the side products are gaseous carbon dioxide and diphenylurea which precipitates (equation 23)14,22,67c. 

The dimerization of aryl isocyanates to l,3-diarylazetidin-2,4-diones is one of the classical methods for the synthesis of 1,3-diazetidinones. In 1993 trimerization of phenyl isocyanate catalyzed by a fluoride ion was also reported, and a small amount of l,3-diazetidin-2,4-dione was obtained at room temperature <1993JOC1932>. 

The functionality of hydroxy-telechelic polybutadiene and polyisoprene was determined by -NMR after modification with phenyl isocyanate or naphthyl isocyanate. Liquid telechelic polybutadiene and polyisoprene, prepared by choosing appropriate reaction conditions, showed Fn value of about 1.9, which agreed with the values determined by titration method [69]. 

The other method starts from nitroalkanes and is a dehydration. Inspect the two molecules and you will see that the nitro compound contains H2O more than the nitrile oxide. But howto remove the molecule of water The reagent usually chosen is phenyl isocyanate (Ph-N=C=0). which removes the molecule of water atom by atom to give aniline (PhNHa) and C02. This is probably the mechanism, though the last step might not be concerted as we have shown. 

An alternative common method of nitrile oxide synthesis, frequently referred to as the Mukaiyama method (60JA5339), involves dehydration of primary nitroalkanes using, for example, phenyl isocyanate in the presence of a catalytic amount of triethylamine (Scheme 5). Phosphorus oxychloride (730S59 90S817), chloroformate esters (86BCJ2827), aryl... 

Cyclization of A -[2-(dichloromethyl)phenyl]ureas 7, which are easily available from 2-(dichloro-methyl)phenyl isocyanates and ammonia, is a simple and efficient method for the synthesis of quinazolin-2(1 f/)-ones 8. The cyclization can be carried out under different experimental conditions, i.e. by heating the reagents above 120 C (Method A), in aqueous acids (Method B), in boiling lower alcohols (Method C), or with ammonia in dioxane (Method... 

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