Transfer nitration preparation

We also found N-nitropyridinium salts such as C5HjN N02BF4 as convenient transfer nitrating reagents in selective, clean reaetions. Transfer nitrations are equally applicable to C- as well as to 0-nitra-tions, allowing, for example, safe, acid-free preparation of alkyl nitrates and polynitrates from alcohols (including nitroglycerine). 

It has been mentioned ( 4.4.2) that nitronium tetraffuoroborate reaets with pyridine to give i-nitropyridinium tetraffuoroborate. This compound and several of its derivatives have been used to effect what is called the transfer nitration ofbenzeneandtoluene. i-Nitropyridinium tetraffuoroborate is only sparingly soluble in acetonitrile, but its homologues are quite soluble and ean be used without isolation from the solution in which they are prepared. i-Nitropyridinium tetra-fluoroborate did nitrate toluene in boiling aeetonitrile slowly, but not at 25 In eontrast, i-nitro-2-pieolinium tetraffuoroborate readily... 

As useful as tetranitromethane is as a charge-transfer nitrating agent, it is generally too unreactive to effect the comparable electrophilic nitration of most aromatic donors, except the most electron-rich ones. Thus in order to make the direct comparison between the photochemical and thermal nitration of the same ArH, we now turn to the A-nitropyridinium acceptor (PyNOj) as the alternative nitrating agent (Olah et al., 1965, 1980). For example, PyNO can be readily prepared as a colourless crystalline salt, free of any adventitious nitrosonium impurity, and used under essentially neutral conditions. Most importantly, the electrophilic reactivity of this... 

Olah and co-workers ° conducted a comprehensive study into the use of N-nitropyridinium salts for nitration. Such salts are easily prepared from the slow addition of the appropriate heterocyclic base to an equimolar suspension of nitronium tetrafluoroborate in acetonitrile. Olah studied the effect on nitration of changing both the structure of the heterocyclic base and the counter ion. Three of these salts (20, 21, 22) illustrated above have been synthesized and used for the 0-nitration of alcohols with success. Transfer nitrations with Al-nitropyridinium salts are particularly useful for the preparation of nitrate esters from acid-sensitive alcohols and polyols because conditions are essentially neutral. 

The efficient At-nitration of secondary amines has been achieved by transfer nitration with 4-chloro-5-methoxy-2-nitropyridazin-3-one, a reagent prepared from the nitration of the parent 4-chloro-5-methoxypyridazin-3-one with copper nitrate trihydrate in acetic anhydride. Reactions have been conducted in methylene chloride, ethyl acetate, acetonitrile and diethyl ether where yields of secondary nitramine are generally high. Homopiperazine is selectively nitrated to At-nitrohomopiperazine or At, At -dinitrohomopiperazine depending on the reaction stoichiometry. At-Nitration of primary amines or aromatic secondary amines is not achievable with this reagent. 

Olah and co-workers [42] suggested a convenient and safe method for the preparation of alkyl nitrates (particularly polynitrates) via transfer nitration of... 

Alkyl nitrates must be prepared and stored with care, as particularly in the presence of even traces of adds they can become explosive [15]. They should not be stored over prolonged periods of times. This is particularly the case for nitrates of polyols. The simplest and effective means of their preparation involves reaction of alcohols with nitronium salts in the presence of an acid-binding agent. Transfer nitrations with. -nitropyridinium salts are particularly suited for their acid-free preparation [16],... 

Alcohols undergo transfer nitration with N-nitrocollidinium tetra-fluoroborate under essentially neutral conditions. Yields were found to be close to quantitative. Separation of alkyl nitrates by distillation or crystallization gave good-to-excellent preparative yields (Table XXVII),... 

Salts containing the nitronium ion can be prepared, and they are reactive nitrating agents. The tetrafluoroborate has been used most frequently," but the trifluoromethanesulfonate can also be prepared readily. Pyridine and quinoline form iV-nitro salts on reaction with N02Bp4. These N-nitro heterocycles in turn can act as nitrating reagents. This is called transfer nitration. ... 

Heat Treatment and Heat-Transfer Salts. Mixtures of sodium nitrite, sodium nitrate, and potassium nitrate are used to prepare molten salt baths and heat-transfer media. One of the most widely used eutectic mixtures uses 40% NaN02, 7% NaNO, and 53% KNO [7757-79-1] to give a... 

Cyclic and acyclic silyl enol ethers can be nitrated with tetranitromethane to give ct-nitro ketones in 64-96% yield fEqs. 2.42 and 2.43. " The mechanism involves the electron transfer from the silyl enol ether to tetranitromethane. A fast homolydc conphng of the resultant cadon radical of silyl enol ether with NO leads tn ct-nitro ketones. Tetranitromethane is a neutral reagent it is commercially available or readdy prepared. " ... 

Hanus recommends that )S-naphthyl hydrazine hydrochloride should be added to the solution of vanillin in such pioportion that from two to three parts are present for each part of vanillin. After standing for five hours the precipitate is transferred to a tared filter, washed with hot water until the washings no longer precipitate silver nitrate, dried at 90° and weighed. The weight of the hydrazine formed, divided by 1-92 gives that of the vanillin present. This method is avaUable in all cases where an aqueous solution of the vanillin can be prepared. 

Method B. Prepare the solution and transfer 25 mL of it to a 250 mL conical flask as detailed under Method A. Add two to three drops of diphenylcarbazide indicator and titrate with standard 0.1M silver nitrate solution until a permanent violet colour is just produced. 

Preparation of 2-nitro-2-methyl-1 -propanol-nitrate. 50g of the 2-nitro-2-methyl-1-propanol purified as above were sifted into a mixt of 58.5g of 90.5% nitric acid.and 241,5g of 103.1% sulfuric acid (oleum) while the well-agitated mixt was maintained close to 15°. Stirring was continued for 1 hour and the mixt allowed to stand for hour. No separation of the nitration product occurred and the mixt was poured over cracked ice. An oily layer separated. The mixt was transferred to a separatory funnel, washed with water, Na bicarbonate, and twice with water to neutrality. The separated diluted spent acid together with the washings were thoroughly extracted with ether, the ether extract washed to neutrality and added to the main product. 

Standard preparation Dissolve an accurately weighed quantity of USP Miconazole Nitrate RS in methanol to obtain a solution having a known concentration of about 500 pg/mL. Transfer 10 mL of this solution to a test tube, and evaporate on a steam bath with the aid of a current of filtered air to dryness. Dissolve the residue in 2 mL of the Internal standard solution. This Standard preparation has a concentration of about 2500 pg/mL. 

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