Nitrogen evolution

The rearrangement of the azide is complete when nitrogen evolution ceases. This is usually concluded in the time indicated, but occasionally takes longer. 

A total of 222 g of 3)5-acetoxy-5a-pregn-9(l l)-en-20-one-[17a,16a-c]-A -pyrazoline is added portionwise and with stirring during a period of 25 min to 880 ml of diethylene glycol held at 165°. When nitrogen evolution ceases the mixture is cooled to 100° and 3 liters of water is added. The crude product is crystallized from ethanol to yield 146 g (71%) of 3 -acetoxy-16-methyl-5a-pregna-9(ll),16-dien-20-one mp 139-142° [aj 53° (CHCI3) 249 mf.1 (e 8,600). 

An example is cholest-4-en-3-one (15a) which fails to react with diazomethane under normal conditions, but reacts rapidly with nitrogen evolution... 

A-Homo-cholest-4a-en-3-one (16a) A total of 200 ml of a cold 0.232 M solution of diazomethane in methylene dichloride is added dropwise to a stirred solution of cholestenone (15a 5.6 g) in anhydrous methylene dichloride (25 ml) containing freshly prepared fiuoroboric acid catalyst. Nitrogen evolution begins immediately, and after 5 min the colorless solution turns cloudy due to precipitated polymethylene. After the addition is complete, the mixture is stirred for 1 hr and filtered. The filtrate is diluted with ether, washed with saturated sodium bicarbonate solution followed by... 

During a study of azonitrones (70), Forrester and Thomson showed that reaction with toluene-p-sulfinic acid resulted in nitrogen evolution and formation of the hydroxamic acid (66) together with the pyrrolidone (71) and the amidine (72). These workers suggested the following reaction course. Although the yield of hydroxamic acid was high, the method is not likely to be of preparative value. 

The disulfide has a special interest as the catalyst in the carbon disulfide-catalyzed iodine-azide reaction. No perceptible nitrogen evolution will take place in a solution containing iodine and azide ions without the presence of a catalyst. Thiosulfates, sulfides, and many other sulfur compounds act as catalysts. In 1922 Browne et found that carbon disulfide is a powerful catalyst in this... 

Until recently, most of the evidence for the rate-determining formation of a nitrene intermediate came from experiments in which the nitrene was trapped or from the temperatures required to effect decomposition and the nature of the products formed. Horner and Christmann 5> observed that the rate of nitrogen evolution from /-toluenesulphonyl... 

To a solution of 1.84 g Na metal in 60 ml ethanol at 5-10° add, over Vi hour with vigorous stirring a mixture of 0.08 M ethyl azidoacetate and 0.02 M 2 (or 2,5 2,3 etc. but not 6) substituted benzaldehyde and continue stirring at 5-10° until nitrogen evolution ceases (about V2-I hour) then stop immediately and rapidly evaporate in vacuum Vi the ethanol (keep temperature below 30°). Basify the solution with solid NH CI, dilute with 500 ml water and extract 3 times with ether. Filter, wash with water to neutrality and dry, evaporate in vacuum the ether (or can dissolve the residue in petroleum ether, or 1 1 petroleum ether.benzene for methoxy compounds, and filter through silica gel) to get the ethyl-alpha-azidocinnamates (1) in about 50% yield. Store in freezer until used in next step. Dissolve 1 g (I) in 100 ml p-xylol and reflux 10 minutes. Evaporate in vacuum (or add 5 ml pentane, filter, evaporate in vacuum) to get about 90% yield of the 4 substituted-2-car-bethoxyindole which can be decarboxylated as described elsewhere here. 

Mechanistic details of this reaction are scarce, but Aratani (14) mentions that the catalyst needs to be activated by heating in the presence of the diazo compound at 75-80°C until nitrogen evolution is observed and the color of the complex changes from green to brown. Reduction of the cupric precatalyst with a substituted hydrazine results in a yellow cuprous complex capable of inducing an instantaneous decomposition of diazoacetate at ambient temperature. Aratani proposes that the active catalyst is tetrahedral Cu(I), 26 in Scheme 2. Reaction with the diazoester from the less hindered face forms the Cu carbenoid having one hemilabile ligand (al-... 

The reaction of ethyl azidoformate (93) with tetramethylallene yielded triazoline 94 and oxazoline 95 [88]. The triazoline 94 was formed by [3 + 2]-cycloaddition of azide 93 to the allene. The oxazoline 95 may result from [3 + 2]-cycloaddition of car-bethoxynitrene (96), which is formed from 93 by nitrogen evolution, to the allene or by the [2 +1] addition of the nitrene and subsequent rearrangement. 

Treatment of thiobenzophenone with 1 equivalent of diazoethane in CH2CI2 at — 78°C produced 5-methyl-2,2-diphenylthiadiazoline (143) which actually crystallized from a concentrated solution however, when the crystals were warmed to room temperature, they exploded. In a THE solution at — 45°C (143) decomposed with nitrogen evolution following first-order kinetics with a half-life of 18 minutes. The product was 2-methyl-1,1-diphenylthirane (144) which slowly lost sulfur to yield 1,1-diphenylpropene (145) <83H(20)2363>. 

Alkyl-5-alkyliminothiatriazolines (50) decompose slowly around 40-60 "C and rapidly at 125°C with formation of sulfur, nitrogen, and carbodiimide (51) (Equation (4)). However, the carbo-diimides (51) formed react with undecomposed thiatriazoline (50), which in part explains the low yields of isolable carbodiimide. It has not been possible by trapping experiments to decide whether the decomposition involves an intermediate as addition of electron-rich alkenes or heterocumulenes induces immediate nitrogen evolution in a bimolecular reaction (see Section 4.19.5.2) <78JCS(P1)1440>. 

In contrast to 4-alkyl-5-sulfonylimino-A -l,2,3,4-thiatriazolines (58) (Section 4.19.5.1.2), 4-alkyl-5-alkylimino-A -l,2,3,4-thiatriazolines (50) react with immediate nitrogen evolution when added to electron-rich alkenes or to heterocumulenes such as enamines, carbodiimides, isocyanates, isothiocyanates, or styrene. Reaction kinetics for certain of this type of system show that they undergo bimolecular processes as described below. 

Addition of electron-poor alkenes such as /ran -stilbene, diethyl fumarate and maleate, and fumaronitrile to (50) do not cause nitrogen evolution. Even on heating cycloaddition products were not isolated, although decomposition was induced. Addition of bases such as benzylamine had no influence on the decomposition rate <78JCS(P1)1440>. 

Methyl-5-phenylimino-l,2,3,4-thiatriazoline (70) reacts with phenyl isothiocyanate at RT under nitrogen evolution to give compound (71) (R = Ph) as the main product (Equation (7)) <77JOCi 159>. 

Peseke treated the 1,3-dithietane (desaurin) (162) with sodium azide in aqueous ethanol and obtained a product believed to be a thiatriazolinylidenecyanoacetate <81ZC102>. Attempts to isolate the free acid were unsuccessful as upon acidification of the solution of the salt, nitrogen evolution took place and the hitherto unknown 2/7,5//-l,4-dithia-2,5-diazine (164) was formed (Scheme 34). According to L abbe et al. the 1,3-dithietane reaction product is best formulated with a negatively... 

In this paper the rate expressions have all been corrected for nitrogen evolution from the azo initiator, oxygen absorption by initiator radicals, and oxygen evolution in termination. It is assumed that the initiator which decomposes without starting oxidation chains does not react with oxygen (21). This correction involves the addition of (l-e)Ri/2e to the measured rate, where e is the efficiency of chain initiation, found to be 0.5 at 30 °C. and 0.6 at 56 °C. The rate constant for Reaction 7 has been written as 4ktCT in order that the three termination constants may be comparable (26, footnote 27).]... 

A correction to the observed rate (—d02/dt) is made by subtracting the term (2e — l)ki[AIBN], which allows for"oxygen absorption and nitrogen evolution by AIBN. 

The conversion of 3-amino-4-oxo-l,jc-naphthyridines (117) into the corresponding 3-diazo-4-oxo compounds (118) followed by photolysis results in the formation of azaindoles (119) via nitrogen evolution and ring contraction (56LA(599)233, 60JCS1794). 

Most carbenes are relatively easily generated by photolysis of nitrogeneous precursors such as diazo compoundsor diazirines. The reaction is clean, as nitrogen is the only byproduct and it is also very efficient as nitrogen evolution is a highly exothermic reaction. Therefore carbenes can be easily generated even under very inert conditions, such as in a noble gas matrix at very low temperatures. 

A minor transient feature was also manifested when ammonia was admitted to the reactor (t — 0 s) the NO outlet concentration immediately decreased, went through a weak minimum near 150 s and finally slightly increased, reaching steady state in correspondence of the end of the ammonia feed phase (tx 2,800 s). Again, the nitrogen evolution was symmetrical to that of NO. The same ammonia inhibition effect invoked to explain the enhancement in the deNOx conversion at ammonia shutdown can explain this transient behavior, too. In fact both features suggest the existence of an optimal ammonia surface concentration, which is lower than the coverage established at steady state. 

Analogous methyl azidoformate forms with norbornene a thermal unstable triazoline.251 The decomposition products are 40% aziridine and 55% imide. Furthermore it has been observed that the rate of nitrogen evolution of the triazoline from methyl azidoformate increases threefold when triglyme and 20-fold when dimethyl sulfoxide are substituted for 1,1-diphenylethane as solvents. This fact supports a betaine intermediate in the thermal decomposition reaction. The triazoline from 2,4-dinitrophenyl azide and norbornene could just be isolated, but from picryl azide only the aziridine was obtained.252-254 Nevertheless, the high negative value of the activation entropy (—33.4 eu) indicates a similar cyclic transition state for both reactions. 

Olefinic azides (60) containing unsaturation at least three carbon atoms away from the azide group decompose in hydrocarbon solution into cyclic imines (62) and l-azabicyclo[3.1.0]-hexanes (63).158 The reaction proceeds through an intermediate triazoline (61) which is formed in quantitative yield when the azide is heated at 50° or allowed to stand at 25° for 2 months. Here, too, a dipolar intermediate is formed during the decomposition of triazoline 61 because the rate of nitrogen evolution increases about 10-fold when nitromethane and 20-fold when aqueous diglyme are substituted for toluene as solvents. 

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