Aniline formaldehyde

Aniline—formaldehyde resins were once quite important because of their excellent electrical properties, but their markets have been taken over by newer thermoplastic materials. Nevertheless, some aniline resins are stiU. used as modifiers for other resins. Acrylamide (qv) occupies a unique position in the amino resins field since it not only contains a formaldehyde reactive site, but also a polymerizable double bond. Thus it forms a bridge between the formaldehyde condensation polymers and the versatile vinyl polymers and copolymers. 

Isocyanates. The commodity isocyanates TDI and PMDI ate most widely used in the manufacture of urethane polymers (see also Isocyanates, organic). The former is an 80 20 mixture of 2,4- and 2,6-isomers, respectively the latter a polymeric isocyanate obtained by phosgenation of aniline—formaldehyde-derived polyamines. A coproduct in the manufacture of PMDI is 4,4 -methylenebis(phenyHsocyanate) (MDI). A 65 35 mixture of 2,4- and 2,6-TDI, pure 2,4-TDI and MDI enriched in the 2,4 -isomer are also available. The manufacture of TDI involves the dinitration of toluene, catalytic hydrogenation to the diamines, and phosgenation. Separation of the undesired 2,3-isomer is necessary because its presence interferes with polymerization (13). 

This was the process used by BASF and Floechst for about 30 years. Later, a variation of the original Fleumann process was made aniline, formaldehyde, and hydrogen cyanide react to form phenylglycinonitrile (40) which is hydrolyzed to phenylglycine. This is the most widely used process for manufacturing indigotin. 

The term aminoplastics has been coined to cover a range of resinous polymers produced by interaction of amines or amides with aldehydes. Of the various polymers of this type that have been produced there are two of current commercial importance in the field of plastics, the urea-formaldehyde and the melamine-formaldehyde resins. There has in the past also been some commercial interest in aniline-formaldehyde resins and in systems containing thiourea but today these are of little or no importance. Melamine-phenol-formaldehyde resins have also been introduced for use in moulding powders, and benzoguanamine-based resins are used for surface coating applications. 

Although occasionally in demand because of their good electrical insulation properties, aniline-formaldehyde resins are today only rarely encountered. They may be employed in two ways, either as an unfilled moulding material or in the manufacture of laminates. 

Because of the lack of solubility in the usual solvents, aniline-formaldehyde laminates are made by a pre-mix method. In this process the aniline hydrochloride-formaldehyde product is run into a bath of paper pulp rather than of caustic soda. Soda is then added to precipitate the resin on to the paper fibres. The pulp is then passed through a paper-making machine to give a paper with a 50% resin content. 

Aniline-formaldehyde resin has very poor flow properties and may be moulded only with difficulty, and mouldings are confined to simple shapes. The resin is essentially thermoplastic and does not cross-link with the evolution of volatiles during pressing. Long pressing times, about 90 minutes for a 5 in thick sheet, are required to achieve a suitable product. 

As with the other aminoplastics, the chemistry of resin formation is incompletely understood. It is, however, believed that under acid conditions at aniline-formaldehyde ratios of about 1 1.2, which are similar to those used in practice, the reaction proceeds via p-aminobenzyl alcohol with subsequent condensation between amino and hydroxyl groups (Figure 24.10). 

Some typical properties of aniline-formaldehyde mouldings are given in Table 24.2. 

Kadutskii AP, Kozlov NG (2006) A novel three-component reaction of anilines, formaldehyde and beta-diketones simple synthesis of 3-spirosubstituted 1,2,3,4-tetrahydroqumo-lines. Synlett 3349-3351... 

The two key isocyanates that are used in the greatest volumes for polyurethane polymers are toluene diisocyanate (TDl) and methylene diphenyl diisocyanate (MDl). Both isocyanates are produced first by nitration of aromatics (toluene and benzene, respectively), followed by hydrogenation of the nitro aromatics to provide aromatic amines. In the case of MDl, the aniline intermediate is then condensed with formaldehyde to produce methylene dianiline (MDA), which is a mixture of monomeric MDA and an oligomeric form that is typical of aniline/formaldehyde condensation products [2]. The subsequent reaction of phosgene with the aromatic amines provides the isocyanate products. Isocyanates can also be prepared by the reaction of aromatic amines with dimethylcarbonate [3, 4]. This technology has been tested at the industrial pilot scale, but is not believed to be practiced commercially at this time. 

Rastogi and Bisht (Ref 3a) made combustion studies on hybrid propints consisting of o-s m-and p-toluidine nitTates with aniline-formaldehyde polymer as solid fuels, and red fuming nitric acid as oxidizer. They found that the results fitted a burning rate equation of the type, = a (G)v, where a and v are constants and G is the mass velocity. The authors conclude that the heterogeneous combustion reaction is diffusion controlled, and its rate is dependent on particle size... 

A thermohardening composition for glass fiber reinforced plastics consists of PPO, BPA/DC and a bismaleimide [45]. Still higher heat resistance is achieved, if the poly-functional maleimide, based on aniline-formaldehyde condensation products (Scheme 11), is used [46]. 

Aniline was converted into its novolak analogue by reacting with formaldehyde and hydrochloric acid in the presence of divalent metal cations such as Ca and Fe. The ratio of aniline/formaldehyde/hydrochloric acid was 7.5 1.0 0.3, respectively, using 0.00025 wt% metal ions. These oligomeric products are designed to be further modified to isocyanates by reacting with phosgene. 

Methylenedianiline was previously prepared by Klein [1] using an aniline/ formaldehyde ratio of 9 1, respectively, in the absence of a metallic salt at 60°C. Scale-up production for methylenedianiline using an aniline/formal-dehyde ratio>2 and hydrochloric acid/aniline ratio of 0.05 is described by Steinbrenner [2]. 

Hagen [3] prepared diphenylmethane and poly amines in the absence of metallic ions using an aniline/formaldehyde ratio of 4 1, respectively, at 80°C. 

Among promising oligomeric foams one should also mention 2-pyranyl foams for a discussion of the chemistry, technology and properties of these materials see Finally, several works concerned with the preparation of foams from cumaron-indene and aniline-formaldehyde oligomers have been reported ... 

The only economic process for PMDI is the reaction via aniline-formaldehyde and subsequent phosgenation. 

The pyrazolone can be incorporated directly in the polymer by utilizing a polymer-forming derivative such as a 1 -(amino or hydroxy -phenyl)pyrazolone in a phenol (or aniline)-formaldehyde polymerization. Alternatively, the pyrazolone nucleus can be combined with a synthetic or natural polymer by reaction of a functional group in the pyrazolone with the polymer. Thus, a 1-formylphenyl type is used to form a polyvinyl acetal. A compilation of such reactions is given in Part 1, Chapter II, Section 14, pp. 108-110. 

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