Secondary aryl amines

Antioxidants markedly retard the rate of autoxidation throughout the useful life of the polymer. Chain-terminating antioxidants have a reactive —NH or —OH functional group and include compounds such as secondary aryl amines or hindered phenols. They function by transfer of hydrogen to free radicals, principally to peroxy radicals. Butylated hydroxytoluene is a widely used example. 

With primary and secondary aryl amines a reaction at the amino nitrogen can occur, leading to formation of an aryl triazene 5 ... 

The secondary aryl amine 24 is far less basic than primary or secondary alkyl amines, and does not form the carbamic acid to any detectable extent in the presence of scC02 [31]. Therefore, 24 is extracted readily from the catalyst-containing IL phase, which can be recycled without noticeable loss of activity and selectivity [13]. In fact, it transpires that the active species is more stable towards oxygen in the IL than in organic solvents. Furthermore, the choice of anion of the IL largely controls the performance of the active cationic species, allowing even the use of an otherwise inactive iridium chloride precursor [ Ir(cod)Cl 2] to form in-situ catalysts... 

Hinsberg oxindolc synthesis. Formation of oxindoles from secondary aryl amines and sodium bisulfite addition compound of glyoxal primary aryl amines give glycine or glycinamide derivatives. 

A related synthesis produces indolones by a different Friedel-Crafts route. The Stolle synthesis reacts with a secondary aryl amine such as diphenylamine with an a-chloro acid chloride or an a-bromo acid bromide to give an a-bromoamide (such as 315) or an a-chloroamide. An early version of the reaction used oxalyl chloride, but a more typical example is the reaction of 2-bromopropanoyl bromide with 314 to give 315. Friedel-Crafts cyclization (with AICI3) led to the indolone 316.1 ... 

Aromatic amines are usually polybrominated on treatment with bromine. Several mild brominating agents have been introduced in attempts to achieve partial bromination without the necessity of protecting the amino group and subsequent hydrolysis, but these give variable results when applied to a large variety of amines. Dioxane dibromide monobrominates tertiary aromatic amines, but gives poor yields with primary and secondary aryl amines. The use of A-bromo-succinimide (l-bromo-2,5-pyrrolidinedione) leads to monobrominated compounds that are frequently contaminated with decomposition products. 

Due to poor reactivity, aryl amines normally require higher reaction temperatures than aliphatic amines to ensure good conversion. In early studies, phenathroline and its Cu(I)-complex were used in the arylation of aryl amine [10, 11], but they were only applicable to the synthesis of triarylamine from secondary aryl amines. L-Proline (LI) promoted Cul-catalyzed arylation of primary aryl amines took place at 90°C (Table 9.1, entry 1) [3]. However, only electron-rich anilines gave complete conversion, while electron-deficient anilines provided low yields. Fu found that this drawback could be overcome by heating at 110°C and using pipecolinic acid (L5) as a ligand (entry 2) [12]. Similar studies were reported by Liu and coworkers in which DMEDA (Lll) was found to be a better ligand (entry 3) [13], Recently, Buchwald reported that pyrrole-2-carboxylic acid (L6) [14] is an efficient promoter for the synthesis of diarylamines (entry 4) (Table 9.3). 

There are two major classes of antioxidants and they are differentiated based on their mechanism of inhibition of polymer oxidation chain-terminating or primary antioxidants and hydroperoxide-decomposing secondary antioxidants [5]. Primary or free-radical scavenging antioxidants inhibit oxidation via very rapid chain-terminating reactions. The majority of primary antioxidants are hindered phenols or secondary aryl amines. Generally, hindered phenols are nonstaining, nondiscoloring, and are available in a wide... 

As this reaction has not been extensively studied and not much mechanistic information is available, a tentative mechanism is outlined here. It is possible that the primary aryl amine has less steric hindrance than the secondary aryl amine during the substitution, hence substituted glycine is produced as the product. 

Stabilisers Primary antioxidants (sterically hindered phenols, secondary aryl amines) Hydroperoxide decomposers (organophosphites, thioesters) Acid absorbers (lead salts, Ca/Ba-Ba/Cd-Ba/Sn salts, organotins, epoxidised oils)... 

Antioxidants function by preferentially reacting with the radical intermediates, thereby protecting the polymer and extending its usage life. There are two types of antioxidants that are typically used in commercial polymer stabilization primary and secondary. The majority of primary antioxidants are either hindered phenolics or secondary aryl-amines. Both hindered phenolics and aryl-amines have one or more reactive OH and NH groups. The hydrogen atoms which are liberated from the alcohol or amine groups readily react with free radicals to form stable species. Secondary antioxidants are usually phosphites or thioesters. 

Keywords degradation, hindered phenolics, secondary aryl-amines, extraction, solvents, HPLC, GC/MS, supercritical fluids, thermal analysis, OIT test, FT-IR, near infrared spectroscopy (NIR), XRF. 

Hindered phenols and secondary aryl amines act as primary antioxidants by donating their reactive hydrogen (N-H, O-H) to free radicals, particularly peroxy radicals as shown here ... 

Secondary aryl amines function by hydrogen donation, similar to the phenols however, at higher temperatures they are also capable of decomposing peroxides. This single feature, which will be discussed later in this chapter, eliminates, most... 

Almost at the same time, Liu and Che published a cascade intermolecular hydroamination/asymmetric reduction sequence, which included achiral Au complex-catalyzed hydroamination of aryl amines and chiral phosphoric acid-promoted Hantzsch ester reduction to afford secondary aryl amines [70], More recently, the same group reported a tandem one-pot assembly of functionalized tetrahydroquino-lines from amino aldehyde and alkynes by combining Au and chiral phosphoric acid catalysis [71], The reaction was initiated by Au-promotedquinololine 210 generation, followed by an enantioselective HEH-incorporated transfer hydrogenation process (Scheme 9.67). 

This is also a pathway taken in the metabolic transformation of primary and secondary aryl amines to toxic intermediates that can sometimes initiate tumor... 

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