Phenyl azides

In order to convert it into phenyl azide ( diazobenzeneimide ) the perbromide is added in three or four portions to about 10 c.c. of well-cooled concentrated ammonia solution. A vigorous reaction takes place, resulting in the formation of the pungent smelling phenyl azide, which is purified by steam distillation. It can also be distilled in a vacuum without decomposition. Since it explodes when rapidly heated it must be handled cautiously. 

The bromides of organic bases form with bromine insoluble per-bromides, in the present case the addition compound C6H5.N=N. 

The mechanism of the reaction with ammonia is as follows. The perbromide bromine is converted into hypobromite and at the same time the diazonium salt undergoes rearrangement to syre-diazohydroxide, which immediately couples with NHS to give phenyltriazene ( diazo-benzeneamide ). The latter is then dehydrogenated by the hypobromite yielding phenyl azide (Dimroth)  

By very careful hydrogenation (with stannous chloride in ethereal hydrogen chloride) phenyl azide has been converted into the exceedingly sensitive phenyltriazene (Dimroth), which, as has been shown, can be reconverted into the former by dehydrogenation. As in the case of the aliphatic diazo-compounds, an open chain structural formula has lately also been assigned to hydrazoic acid and its esters, so that the changes just mentioned may be formulated as follows  

The aryl azides are very reactive compounds. By the action of acids, for example, they lose the two terminal N-atoms as N2 the residual C8H5N combines with water to form aryl hydroxylamine, but this at once undergoes rearrangement and becomes an aminophenol. 

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Addition on to the exocyclic C—C double bond of an alkylideneaziridine also occurs when this compound is allowed to react with organic azides (75JOC2045). The initially formed spirotriazolines (332) are converted into four-membered ring amidines (334) with extrusion of molecular nitrogen. In the case of phenyl azide, the amidine (334) is obtained alongside the triazoline (333). 

Benzenediazonium fluoroborate, 2-carboxy-xanthone synthesis from, 3, 838 Benzenediazonium ions phenyl azide formation from, 5, 839 Benzenediazonium salts, o-(imidazol-l-yl)-intramolecular diazo coupling, 5, 404 Benzene-1,2-disulfonimides N-substituted reactions, 6, 930 Benzene episulfide formation, 7, 577 Benzeneimine... 

Qf-receptor blocking agent, 1, 176 Phenylalanine hydroxylase in tyrosine synthesis from phenylalanine, 1, 261 L-Phenylalanine hydroxylase mechanism, 1, 261 Phenyl azide formation... 

The additions of phenyl azide and phenylnitrile oxide to pentafluorophenyl-acetylene are also regiospecific [75, 7S] (equation 12). Interestingly, in the latter reaction, phenylacetylene gives regiochemistry that is opposite to that observed for pentafluorophenylacetylene [75]... 

Perfluoro-2-butyne is, as expected, even more reactive in its reaction with phenyl azide [75]. Its reaction with 7V-phenylsydnone is also reported [79] (equation 13). 

Perfluorotetramethylthiadiphosphanorbornadiene and bis(trifluoromethyl) thiadiphosphole can be prepared by thermolysis of an adduct of methanol and hexakis(trifluoromethyl)-l,4-diphosphabarrelene with sulfur [113] (equation 23) Pyrolysis of the adduct of hexafluorinated Dewar benzene and phenyl azide results in ring expansion giving azepine, which photochemically yields an intramolecular 2-1-2 adduct, a good dienophile for the Diels-Alder reaction [114, //5] (equation 24) Thermolysis of fluonnated derivatives of 1,5-diazabicyclo-... 

Azides can use enamines as dipolarophiles for ],3 cycloadditions to form triazolines. These azides can be formate ester azides (186), phenyl azides (187-195), arylsulfony] azides (191-193,196), or benzoylazides (197,198). For example, the reaction between phenyl azide (138) and the piperidine enamine of propionaldehyde (139) gives 1 -phenyl-4-methy l-5-( 1 -piperidino)-4,5-dihydro-l,2,3-triazole (140), exclusively, in a 53% yield (190). None of the isomeric l-phenyl-5-methyl product was formed. This indicates that the... 

The mechanism of the cycloaddition of phenyl azide to norbornene has been shown to involve a concerted mechanism with a charge imbalance in the transition state (199). In a similar manner the cycloaddition of phenyl azide to enamines apparently proceeds by a concerted mechanism (194, 194a). This is shown by a rather large negative entropy of activation (—36 entropy units for l-(N-morpholino)cyclopentene in benzene solvent at 25°C), indicative of a highly ordered transition state. Varying solvents from those of small dielectric constants to those of large dielectric constants has... 

The Reaction between Azide and Benzenediazonium-lP-N ] Ions a. The Distribution of the N -Lahel in the End Products. Clusius and Hiirzeler observed that phenyl azide-[a-A ] (16) and unlabeled nitrogen are formed by the union of unlabeled azide and isotopically unrearranged benzenediazonium-[a-A ] ions (15). They concluded... 

The addition of phenyl azide to diacetylene in benzene at 20-70°C has been performed (79KGS849). Depending on the amount of phenyl azide, 1-phenyl-4(5)-ethynyl-1,2,3-triazoles (96) and 4,4 -di(l-phenyl-1,2,3-triazoles) (97) were obtained in 64 and 55.5% yield, respectively. 

Friesner and coworkers investigated the 1,3-dipolar addition of phenyl azide 60 to carbon-carbon double bonds forming l-phenyl-4,5-dihydro-l//-l,2,3-triazoles (61 and 62) (Scheme 39) [99JPC(A)1276]. 

Stickstoffwasserstoffsaure, /. hydrazoic acid, hydronitric acid, -phenylester, m. phenyl azide (or hydrazoate). azidobenzene. 

The C —C double bonds of 3-benzothiepins do not react with bromine (vide supra), nor with phenyl azide or diazoacetate however, one or two equivalents of diazomethane do add to 3-benzothiepins, e.g. 4, to yield crystals which melt with quantitative loss of nitrogen.65... 

Poly-1,2-1//-azepines, produced by gas-phase photopolymerization of aryl azides yield, after oxidation, electrically conducting films.103 By photolyzing 4-(pcntyloxy)phenyl azide in the gas phase, a flexible polyazepine is produced which can be deposited directly as a thin polymer film onto a suitable surface. 

Generation of phenylnitrcne by thermal decomposition of phenyl azide in the same solvent mixture, or by deoxygenation of nitrosobenzene with triethyl phosphite in the absence of the trifluoroethanol, fails to yield the 1//-azepine. The role of the alcohol in promoting l//-azepine formation is not understood. 

The thermal, and more importantly, the photolytic decomposition of aryl azides in the presence of nucleophiles, generally amines or alcohols, is the commonest method for preparing 3H-azepines. In fact, jV-phenyl-3//-azepin-2-amine (32, R = Ph), the first example of a 3//-azepine, was prepared by thermal decomposition of phenyl azide in aniline.32... 

Pioneering studies have shown that the yield of iV-phenyl-3//-azepin-2-amine (32, R = Ph) from the thermolysis of phenyl azide in aniline increases as the ratio of azide to aniline decreases, and in dilute solution with an azide to aniline ratio of 1 200 a 54% yield of the 3//-azepine can be achieved.34 The reaction is successful with other arylamines, but the procedure is of limited preparative value as large volumes of amine are required and only moderate yields of 3H-azepines are obtained. 

Likewise, thermolysis of 4-azidophenyl methyl ketone in methanol yields 5-acetyl-2-methoxy-3//-azepine (60%), compared to only an 8% yield from the photolytic reaction.78 119 The thermolysis of phenyl azide in refluxing cyclohexanol yields no 3H-azepine, only diphenyl-diazene (10%) and aniline (30%).74 In contrast, thermolysis of methyl 2-azidobenzoate in cyclohexanol furnishes a mixture of methyl 2-(cyclohexyloxy)-3//-azepine-3-carboxylate (20 % bp 127°C/0.1 Torr) and methyl 2-aminobenzoate (60%). Thermolysis of the azido ester in methanol under nitrogen in an autoclave at 150 C yields a 7 10 mixture (by 1HNMR spectroscopy) of the amino ester and methyl 2-methoxy-3//-azepine-3-carboxylate, which proved to be difficult to separate, and much tar.74 The acidic medium179 is probably responsible for the failure of methyl 2-azidoberjzoate to yield a 3//-azepine when thermolyzed in 3-methoxyphenol aniline (40%) is the major product.74... 

Interestingly, photolysis of phenyl azide in liquid ammonia yields 3//-azepin-2-amine (39)35 (see experimental procedure in Houben-Weyl, Vol.4/5b, pi268). 

An attempt to improve the yield of the azepin-2-amine by the addition of sodium amide to the photolysate failed, as a rapid nonphotolytic reduction of the phenyl azide to aniline took place. 

Photolysis of aryl azides in amine solution, with a tertiary amine as cosolvent to promote stabilization of the singlet nitrene, has met with some success. For example, the yield of 2-piperidino-3 W-azepme. obtained by the photolysis of phenyl azide in piperidine, is increased from 35 to 58% in the presence of A A /V. /V -tetramethylethylenediamine (TMLDA).180 Also, an improved yield (36 to 60 %) of A,(V-diethyl-3W-azepin-2-amine (38, R = Et) can be obtained by irradiating phenyl azide in triethylamine, rather than in dicthylaminc, solution.181 Photolysis (or thermolysis) of phenyl azide in TMEDA produces, in each case, 38 (R = Et) in 40% yield.181 In contrast, irradiation of phenyl azide in aniline with trimethylamine as cosolvent furnishes jV-phenyl-377-azepin-2-amine (32, R = Ph) in only low yield (2%).35... 

Photolysis of 2-(cu-phenylalkyl)phenyl azides 42 (n = 1-4) in diethylamine, followed by heating with methanol, furnishes 7V,Ar-diethyl-3-(a>-phenylalkyl)-3//-azepin-2-amines 43, albeit in low yields.295... 

Photolyses of 3-substituted phenyl azides 53 in hot diethylamine containing pyrene, a singlet sensitizer, furnish mixtures of the 4- and 6-substituted 3ff-azepines 54 and 55. The isomers, however, were not separated and the yields were based on quantitative GC analysis of the reaction mixtures.176 Of mechanistic significance is that the ratios of the isomeric azepines obtained compare favorably with those observed in the deoxygenation of 3-nitroarenes with trivalent phosphorus compounds. 

An in-depth study of the photolysis of a series of fluoro-substituted phenyl azides, e.g. 58, shows clearly that, in general, 3-substituted phenyl azides yield mixtures of the 4,5- and 5,6-disubstitutcd 3//-azepines, e.g. 59 and 60.188 Tri- and tetrafluoro-substituted azidoben-zoates yield NH-insertion products rather than 3//-azepines. 

Base-catalyzed loss of hydrogen fluoride from the initially formed //../V-diethylG-ltrifluoro-methyl)-3//-azepin-2-amine (66) to give iV,ALdiethyl-3-(difluoromethylene)-3//-azepin-2-amine (67) occurs on photolysis of 2-(trifluoromethyl)phenyl azide (65) in diethylamine.10... 

Early efforts to effect the photoinduced ring expansion of aryl azides to 3H-azepines in the presence of other nucleophiles met with only limited success. For example, irradiation of phenyl azide in hydrogen sulfide-diethyl ether, or in methanol, gave 17/-azepine-2(3//)-thione35 (5% mp 106—107 " O and 2-methoxy-3//-azepine (11 %),2 3 respectively. Later workers194 failed to reproduce this latter result, but found that in strongly basic media (3 M potassium hydroxide in methanol/dioxane) and in the presence of 18-crown-6, 17/-azepin-2(3//)-one was produced in 48% yield. In the absence of the crown ether the yield of azepinone falls to 35%. 

Attempts to effect ring expansion of methyl 2-azidobenzoate in the presence of other nucleophiles have failed. Thus, photolysis in tetrahydrofuran solution saturated with hydrogen sulfide, or with ammonia, produced methyl 2-aminobenzoate in 54 and 37 % yield, respectively, as the sole identifiable product.197 Photolysis of phenyl azide in ethanolic phenol gave 2-phenoxy-3//-azepine in poor yield (8 %).203,204 2-Mesityl-3//-azepine (10 %) is the surprising, and only tentatively explained, product from the photolysis of phenyl azide in mcsitylene in the presence of trifluoroacetic acid.179... 

The pyridines which are formed as minor products (1-8%) during the photolysis of 2-substituted phenyl azides in diethylamine are thought to be products of the aerial oxidation of nonisolable l//-azepine intermediates.11... 

Griess (1866 b) found that benzenediazonium tribromide (QHsN Br ) in the presence of ammonia is converted into phenyl azide in high yield. The reaction probably proceeds through phenyltriazene, as an intermediate which is subsequently oxidized to the azide by the tribromide ion (Scheme 6-14). 

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