1.2- Diamines, aromatic

Compounds containing two primary amino groups attached to a benzene ring can be prepared by the reduction of dinitro compounds and of nitroanilines, usually with tin or stannous chloride and hydrochloric acid or with iron and very dilute hydrochloric acid. Pam-diamines may also be obtained by the reduction of aromatic amino-azo compounds (e.g., p-aminodimethylaniline from methyl orange, see Section IV,78). p-Phenylenediamine may also be prepared from p-nitroacetanilide reduction with iron and acid yields p-amino-acetanilide, which may be hydrolysed to the diamine. 

Experimental details are given for o-phenylenediamlne, which is conveniently prepared by the reduction of o-nitroanUine in alcoholic sodium hydroxide solution wi zinc powder  

The first 2 single electron transfer steps were postulated to occur via the o-benzosemiquinonediimine (17) and the o-benzoquinonediimine (18) intermediates [37]. 

Free diimines cannot be observed as products owing to their reactivity toward oxidative dimerization and polymerization. In spite of that, the reaction is energetically favorable, as the semiquinone- and quinonediimine species formed can be stabilized by coordination to the metal ion used as catalyst. These complexes are sometimes the products of catalytic oxidations of aromatic diamines [35,36]. A case in point 

These complexes have been isolated as products of the reaction of 15 with 0 in the presence of Co(C10 )2. and L. The tetragonal 

In acetone and other ketones as solvents, under O, at room 

In the presence of copper(I) chloride in pyridine N-benzylidene-o-phenylenediamines 20 undergo catalytic oxidative dehydrogenation with 0 to afford 2-arylbenzimidazoles 21 or 2,2 -diaryl-1,1 - 

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Primary aromatic diamines cannot be diazotised (tetrazotised) and coupled normally. Thus o-])henylenediamiiie yields a triazole derivative and m-phenylenediamine gives an azo dye (Bismarck brown) by selfcoupling. 

The rate of the Nf -catalysed Diels-Alder reaction is barely sensitive to the presence of ligands. Apparently no significant effect due to -back donation is observed, in contrast to the effect of aromatic diamines on the metal-ion catalysed decarboxylation reaction of oxaloacetate (see Section 3.1.1). 

Heating Kemp s acid with appropriate aromatic diamines yields bis-imides with two convergently oriented carboxylic acid groups on the edges of a hydrophobic pocket. Dozens of interesting molecular complexes have been obtained from such compounds and can be traced in the Journal of the American Chemical Society under the authorship of J. Rebek, Jr., (1985 and later e.g. T. Tjivikua, 1990 B). 

Poly(amide-imide) is the condensation polymer of 1,2,4-benzenetricarboxylic anhydride and various aromatic diamines and has the general structure ... 

Synthesis and Properties. Several methods have been suggested to synthesize polyimides. The predominant one involves a two-step condensation reaction between aromatic diamines and aromatic dianhydrides in polar aprotic solvents (2,3). In the first step, a soluble, linear poly(amic acid) results, which in the second step undergoes cyclodehydration, leading to an insoluble and infusible PL Overall yields are generally only 70—80%. 

A series of cross-linkable copoly(amide—imides) is known to be possible from aromatic diamines and substituted isophthaloyl chlorides containing unsaturated imide rings as a pendent function (13). 

Aliphatic Isocyanates. Aflphatic diisocyanates have traditionally commanded a premium price because the aflphatic amine precursors ate mote expensive than aromatic diamines. They ate most commonly used in appHcafions which support the added cost or where the long-term performance of aromatic isocyanates is unacceptable. Monofuncfional aflphatic isocyanates, such as methyl and -butyl isocyanate, ate used as intermediates in the production of carbamate-based and urea-based insecticides and fungicides (see Fungicides, agricultural Insectcontroltechnology). 

Uses. Pyromellitic dianhydride imparts heat stabUity in applications where it is used. Its relatively high price limits its use to these applications. The principal commercial use is as a raw material for polyimide resins (see POLYIMIDES). These polypyromellitimides are condensation polymers of the dianhydride and aromatic diamines such as 4, -oxydianifine ... 

Other Preparative Reactions. Polyamidation has been an active area of research for many years, and numerous methods have been developed for polyamide formation. The synthesis of polyamides has been extensively reviewed (54). In addition, many of the methods used to prepare simple amides are appHcable to polyamides (55,56). Polyamides of aromatic diamines and aUphatic diacids can also be made by the reaction of the corresponding aromatic diisocyanate and diacids (57). 

This scheme eliminates the process of converting bis(etherimide)s to bis(ether anhydride)s. When polyetherimides are fusible the polymerization is performed in the melt, allowing the monamine to distill off. It is advantageous if the amino groups of diamines are more basic or nucleophilic than the by-product monoamine. Bisimides derived from heteroaromatic amines such as 2-arninopyridine are readily exchanged by common aromatic diamines (68,69). High molecular weight polyetherimides have been synthesized from various N,lSf -bis(heteroaryl)bis(etherimide)s. 

Almost all IDA derived chain extenders are made through ortho-alkylation. Diethyltoluenediamine (DE I DA) (C H gN2) (53), with a market of about 33,000 t, is the most common. Many uses for /-B I DA have been cited (1,12). Both DE I DA and /-B I DA are especially useful in RIM appHcations (49,53—55). Di(methylthio)-TDA, made by dithioalkylation of TDA, is used in cast urethanes and with other TDI prepolymers (56). Styrenic alkylation products of TDA are said to be useful, eg, as in the formation of novel polyurethane—polyurea polymers (57,58). Progress in understanding aromatic diamine stmcture—activity relationships for polyurethane chain extenders should allow progress in developing new materials (59). Chlorinated IDA is used in polyurethane—polyurea polymers of low hysteresis (48) and in reinforced polyurethane tires (60). The chloro-TDA is made by hydrolysis of chloro-TDI, derived from TDA (61). 

Table 2. Structure and Properties of Aromatic Diamines and Acid Anhydrides Used in Epoxy-Matrix Resins...

Bismaleimides are best defined as low molecular weight, at least diftinctional monomers or prepolymers, or mixtures thereof, that carry maleimide terminations (Eig. 3). Such maleimide end groups can undergo homopolymerization and a wide range of copolymerizations to form a highly cross-linked network. These cure reactions can be effected by the appHcation of heat and, if required, ia the presence of a suitable catalyst. The first patent for cross-linked resias obtained through the homopolymerization or copolymerization of BMI was granted to Rhc ne Poulenc, Erance, ia 1968 (13). Shordy after, a series of patents was issued on poly(amino bismaleimides) (14), which are synthesized from bismaleimide and aromatic diamines. 

Micha.elAdditions. The reaction of a bismaleimide with a functional nucleophile (diamine, bisthiol, etc) via the Michael addition reaction converts a BMI building block into a polymer. The non stoichiometric reaction of an aromatic diamine with a bismaleimide was used by Rhc )ne Poulenc to synthesize polyaminobismaleimides as shown in Figure 6 (31). 

Fig. 7. Acetylene-terminated aspartimides. (a) Reaction of aromatic diamine with A/-(3-ethynylphenyl)maleimide [105280-01-17 ia a 1 2 molar ratio yields a prepolymer of this general formula, (b) Bismaleimide reacts with 3-ethynylaniline [54060-30-9] ia a 1 2 molar ratio to yield a prepolymer of this general...

Aromatic polyimides are generally produced by the reaction of aromatic dianhydrides with aromatic diamines to yield a material with the general stmcture... 

Polyamide Imides. Polyamide imides (PAIs) are formed from the condensation of trimellitic anhydride and aromatic diamines (33). The polymer is called amide—imide because the polymer chain comprises amide linkages alternating with imide linkages, with the general chemical stmcture ... 

Nonthermoprocessible Condensation Polyimides. These are obtained from condensation of aromatic dianhydrides with aromatic diamines. They are linear noncross-linked resins but their rigid chain stmcture and strongly hydrogen-bonded character leads to systems which do not melt or soften before decomposition. 

In addition to electrical uses, epoxy casting resins are utilized in the manufacture of tools, ie, contact and match molds, stretch blocks, vacuum-forrning tools, and foundry patterns, as weU as bench tops and kitchen sinks. Systems consist of a gel-coat formulation designed to form a thin coating over the pattern which provides a perfect reproduction of the pattern detail. This is backed by a heavily filled epoxy system which also incorporates fiber reinforcements to give the tool its strength. For moderate temperature service, a Hquid bisphenol A epoxy resin with an aHphatic amine is used. For higher temperature service, a modified system based on an epoxy phenol novolak and an aromatic diamine hardener may be used. 

A considerable number of non-cross-linked aromatic and heterocyclic polymers has been produced. These include polyaromatic ketones, aromatic and heterocyclic polyanhydrides, polythiazoles, polypyrazoles, polytriazoles, poly-quinoxalines, polyketoquinolines, polybenzimidazoles, polyhydantoins, and polyimides. Of these the last two have achieved some technical significance, and have already been considered in Chapters 21 and 18 respectively. The most important polyimides are obtained by reacting pyromellitic dianhydride with an aromatic diamine to give a product of general structure (Figure 29.17). 

Phosphorus containing poly(maleimide-amines) were synthesized from N,N -bisdichloromaleimido-3,3 -diphenyl alkylphosphine oxides and aromatic diamines or piperazine [144]. The polymers prepared from piperazine are soluble in DMF, DM AC, DMSO, etc., but have poor thermal stability and flame retardancy. 

Phenothiophosphine ring-containing polyamides and polyesters were also prepared by the polycondensation of 2,8-bischloroformyl-lO-phenylphenothiophos-phine 5,5, 10-trioxide with aromatic diamines such as 4,4 -diaminodiphenyl ether and 4,4 -diaminodiphenyl-methane, and bisphenols such as 4,4 -dihydroxybiphe-nyl and 4,4 -dihydroxydiphenylmethane, respectively [159]. These polymers are soluble in polar aprotic solvents and also exhibit good heat and fire resistance. Phosphorus containing high performance polymers are shown in Table 6. 

The polymerization of aromatic diamines with acid chlorides in solution works well.7 914 35 The basicity of the aromatic diamine is low and acid binding can be achieved with several compounds and even solvents such as TV-methylpyrrolidonc (NMP) and dimethylacetamide (DMAc). The all-para aromatic amide poly(p-phenyleneterephthalamide) can be synthesized in DM Ac.7,9,14 To prevent precipitation of the polymer, a salt such as calcium chloride or lithium chloride can be added. It is also possible to react the acid chloride with a silylated diamine ... 

The partially aromatic PAs are exclusively made of die diamine-diacid type and not die amine-acid type. The aromatic diamines, similar to phenylene diamines, color easily and dieir polymers are conjugated, having a golden brown color. The aromatic diacids used in the formation of partially aromatic PAs are mainly terephthalic and isophthalic acids. Starting with the diacids, the PA salt is made first and with this the salt prepolymers are prepared. The prepolymerization is usually carried out in an autoclave to prevent die sublimation of the reactants. In a laboratory synthesis it would be preferable to avoid this autoclave step as one is not always available. It is possible to start with the more reactive esters, such as diphenyl isophtiialate, or with the acid chlorides starting with the reactive isocyanates is, in principle, also possible. The terephthalic and isophthalic acids are also used to modify PA-6,6 and PA-4,6 to more dimensionally stable copolymers.6,18... 

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