Stabilizers diphenylamine

Pyrocollodion and Pyrocellulose powders belong to the single-base type because they contain only NC and about 1% of a stabilizer, diphenylamine. Both are nearly completely sol in eth-alc mixts. According to microscopic observations conducted by Sapojnikoff (Ref 5), Pyrocollodion powder is much more uniform than the Fr Poudre B , both CPL and CP2 types... 

Test 7. Available Stabilizer (Diphenylamine or Ethyl Centralite). This is Method 217.2.1 of MIL-STD-286A (Kef 25). It was investi-... 

Available stabilizer (diphenylamine and/or ethyl centralite) in aged or stored propints 1 AS 16... 

Nitromannitol can be obtained by nitrating mannitol with a mixture of nitric acid and sulphuric acid. The method is inconvenient, however, since the reaction produces a thick crystalline mass and the nitration proceeds unevenly [8]. Generally therefore, mannitol is dissolved in a five-fold amount of nitric acid (d — 1.51) at a temperature below 0°C, which is maintained while a ten-fold quantity of sulphuric acid (d = 1.84) is added to the solution. Fine crystals of the product are precipitated which were separated on a vacuum filter. The product is slightly impure due to the presence of mannitol pentanitrate. The acid product is drowned quickly in cold water, filtered again, washed with cold water, neutralized by means of dilute sodium bicarbonate solution and once again washed with water. Nitromannitol is crystallized from alcohol, to which a stabilizer (diphenylamine) is added. 

Trojan Explosive. A Nitrostarch based expl used by the USA during WWI and to a limited extent in WWII in demolition charges. It contained Nitrostarch 40, Na nitrate 37.7, Ba nitrate 20, oil 0.8, and stabilizer (diphenylamine or Ca carbonate) 1.5% grey solid pressed in Vi and 1-lb... 

Available Stabilizer (Diphenylamine and/or Ethyl Centralite) in Aged or Stored Propellants is determined by Method 2l7.2(T) listed in specification MIL-STD-286... 

Test 7. Available Stabilizer (Diphenylamine or Ethyl Centralite), This is Method 217.2.1 of MIL-STD-286A (Ref 25). It was investigated by Apatoff Cohen of Frankford Arsenal and found to be "inadequate . They proposed to replace it. with a new method which they described in Ref 29. We have described their, method in Vol 2 of Encycl, pp C132 C133 Test 8, Determination of DPhA in Air,... 

The beater additive process starts with a very dilute aqueous slurry of fibrous nitrocellulose, kraft process woodpulp, and a stabilizer such as diphenylamine in a felting tank. A solution of resin such as poly(vinyl acetate) is added to the slurry of these components. The next step, felting, involves use of a fine metal screen in the shape of the inner dimensions of the final molded part. The screen is lowered into the slurry. A vacuum is appHed which causes the fibrous materials to be deposited on the form. The form is pulled out after a required thickness of felt is deposited, and the wet, low density felt removed from the form. The felt is then molded in a matched metal mold by the appHcation of heat and pressure which serves to remove moisture, set the resin, and press the fibers into near final shape (180—182). 

In explosives, diphenylamine stabilizes cellulose nitrate by reacting with nitrogen oxides (see Explosives and propellants). The products formed include /V-nitrosodiphenylamine and mono andpolynitro derivatives. 

Aromatic Amines. Antioxidants derived from -phenylenediarnine and diphenylamine are highly effective peroxy radical scavengers. They are more effective than phenoHc antioxidants for the stabilization of easily oxidized organic materials, such as unsaturated elastomers. Because of their intense staining effect, derivatives of -phenylenediamine are used primarily for elastomers containing carbon black (qv). 

Because nitrile rubber is an unsaturated copolymer it is sensitive to oxidative attack and addition of an antioxidant is necessary. The most common practice is to add an emulsion or dispersion of antioxidant or stabilizer to the latex before coagulation. This is sometimes done batchwise to the latex in the blend tank, and sometimes is added continuously to the latex as it is pumped toward further processing. PhenoHc, amine, and organic phosphite materials are used. Examples are di-Z fZ-butylcatechol, octylated diphenylamine, and tris(nonylphenyl) phosphite [26523-78-4]. All are meant to protect the product from oxidation during drying at elevated temperature and during storage until final use. Most mbber processors add additional antioxidant to their compounds when the NBR is mixed with fillers and curatives in order to extend the life of the final mbber part. 

Some other inhibitors from the patent literature include hydroquinone [129], ionoP [130], and quinone [131]. Other inhibitors used to stabilize MMA include butylated hydroxy toluene (BHT), phenothiazine, methylene blue, hydroxy-diphenylamine and di-/jc/<3-napthol [132]. Several good reviews of inhibition and inhibitors have been written [133-136]. The mechanisms of inhibition are subtle and complicated. For example, it has been reported that highly purified benzo-quinone acts as a retarder rather than an inhibitor [137]. It has been proposed... 

DuPont in the U.S. developed about 1909, a smokeless powder from cotton of relatively low nitrogen that was quite soluble in ether alcohol. A small amount of diphenylamine was used as a stabilizer. After forming the grains and removing the liquid, a coating of graphite was added to make the smokeless powder that was used in the U.S. Other double-base types contain about 25% nitroglycerin. Cotton lint for nitration has been replaced by purified wood cellulose. 

If the proplnt is double-base, it has been observed that even the most stable propints bleach methyl violet paper in much shorter periods than one year. Investigations conducted by P.F. Macy at Picatinny Arsenal (Ref 4) showed that diphenylamine-stabilized doublebase proplnts in service storage at about 30°, may be considered of satisfactory stability if they do not cause complete bleaching of 0.1 N methyl violet paper in one month or less. Such proplnts always show satisfactory stability when subjected to the 65.5° Surveillance Test. It was observed at the same time, that double-base proplnts which had deteriorated, but were not yet hazardous, took from 11 to 24 days to bleach methyl violet paper at 30°... 

The composite propints are not the only ones subject to degradation processes which affect shelf-life, although they are relative newcomers to propint history. In NC-based pro pints, NC decomposes slowly to release NOa which reacts catalytically to hasten the degradation in physical and ballistic properties. To slow the process, stabilizing agents such1 as diphenylamine or 2-... 

Although these are no longer used as explosives, they are formed from diphenylamine that is used as a stabilizer for nitrocellulose explosives. The metabolism of nitrodiphenylamines has been examined under anaerobic conditions, and phenazine and 4-aminoacridine that are cyclization products of the initially formed 2-aminodiphenylamine have been identified (Drzyzga et al. 1996). 

Acid-treated clay catalyst Engelhard F-24 was found to be very effective for the alkylation of diphenylamine (DPA) with an olefin such as a-methyl styrene (AMS) to obtain a mixture of mono and dialkylated diphenylamines (Chitnis and Sharma, 1995). For example, alkylation of DPA with AMS produced a mixture of 4-(a,a-dimethyl benzyl) diphenylamine, i.e. monocumyl-diphenylamine (MCDPA) and 4,4 -bis(a,a-dimethylbenzyl) diphenylamine, i.e. dicumyldiphenylamine (DCDPA) (Eqn.(l 1)). The dialkylated diphenylamine, i.e. DCDPA, is indu.strially important as an antioxidant and heat stabilizer. DCDPA is reported to be an ideal antioxidant for many materials like polyethylene, polypropylene, polyether polyol, polyacetals, nylon 6, synthetic lubricants, hot melt adhesives, etc. 

Studies of the hydrogenation of aromatic nitroso compounds have rarely been published. One of the earliest studies is the Pd/C catalyzed hydrogenation of p-nitrosothymol to its corresponding amine (100%) in ethanol at 1 atm hydrogen.289 Useful antioxidants and gasoline stabilizers are made from diamines, which can be produced by hydrogenating their relatively easily formed nitroso derivatives.290 As a result, the hydrogenation of 4-nitroso-diphenylamine has been studied more heavily than others.291-293... 

Many methods have been proposed and are used to study the thermal stability of propellants and to ensure the absence of possible autocatalysed decompositions during storage. None are sufficiently reliable to merit individual description. In practice, stabilisers are added, the usual being diphenylamine for nitrocellulose powders and symmetrical diethyl diphenyl urea (carbamate or centralite) for double base propellants. Provided a reasonable proportion of stabiliser remains, the propellant can be assumed to be free from the possibility of autocatalytic decomposition. The best test of stability is therefore a chemical determination of the stabiliser present. 

The original catalyst for this reaction is Pd(PPh3)4. Heterogenization of this catalyst was attempted by grafting it onto functionalized polystyrene or modified silica gels,185 which increased significantly the selectivity for the reaction of 3-acetoxy-5-carbomethoxy-l-cyclohexene with diphenylamine. Data concerning the stability of these solids are, however, not reported. 

Although diselenonium-, ditelluronium- and mixed sulfonium-selenonium dications can exhibit either oxidative or electrophilic properties in reactions with nucleophiles, substitution at the onium chalcogen atom is more typical.96 Owing to the increased stability of heavier dichalcogenium-dications, they react only with highly activated substrates such as aniline and tV,A-dimethylaniline, while no reaction is observed with phenol and diphenylamine.113 Reactions of ditelluronium dications with activated aromatics are also not known (Scheme 44).114... 

Potassium dichromate exhibits much greater stability in aqueous solution in comparison to potassium permanganate. Potassium dichromate possesses an inherent oranage colour that is not intense enough to serve its own end-point signal, specifically in the presence of the green Cr3+ ion, which is supposed to be present at the end-point. Hence, redox indicators are usually employed to locate the exact end-point e.g., barium diphenylamine sulphonate. 

As we move to A-methylaniline, we see only a modest change in pK ,. This is undoubtedly due to the electron-donating effect of the methyl group, and this would be expected to stabilized the conjugate acid, increasing observed basicity. There is a modest increase in basicity, but it is apparent that the resonance effect, as in aniline, is also paramount here, and this compound is also a weak base. However, diphenylamine (A-phenylaniline) is an extremely weak base this can be ascribed to the resonance effect allowing electron delocalization into two rings. 

Adoption in 1906 by the French Navy of propint with 8% amyl alcohol stabilizer did not prevent the disastrous expin in 1907 of battleship Iena. As a result of this, previously tested DPhA (diphenylamine) was approved as stabilizer of Naval cannon proplnt, which became known as poudre B(Bo) (Ref 44, p 249) (See also Vol 1 of Encycl, p A395-L)... 

Propellants were especially susceptible to spontaneous ignition before it was learned how to stabilize the NC. This was done by including substances called stabilizers in the propellant formulations. These substances, such as diphenylamine, centralite etc absorb the nitrogen oxides as they are formed, thus removing them from the sphere of reaction. This prevents further decomposition and the rise in temperature which decomposition produces. 

The presence of N02 and other nitrogen oxides and/or acids in explosives (especially in smokeless powders and dynamites)is very undesirable because they act as catalyzers and promote further, more rapid decomposition. Most of the stabilizers used in smokeless powder, such as diphenylamine, centralites, urethanes etc are really inhibitors because they react with N02 and other nitrogen oxides to form nitroso- and nitrocompounds. 

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